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Potential Environmental Impacts of Dust Suppressants:
“Avoiding Another Times Beach”
An Expert Panel Summary Las Vegas, Nevada
May 30-31, 2002
Edited by
Thomas Piechota, Ph.D., P.E.1 Jeff van Ee2
Jacimaria Batista, Ph.D. 1 Krystyna Stave, Ph.D. 1 David James, Ph.D., P.E. 1
1University of Nevada, Las Vegas
2U.S. Environmental Protection Agency
Sponsored by
U.S. Environmental Protection Agency
Organized by University of Nevada, Las Vegas
U.S. Environmental Protection Agency
107CMB04.RPT v 03/30/2004
The information in this document has been funded by the United States Environmental Protection Agency under EPA Assistance Agreement #CR829526-01-0 to the University of Nevada, Las Vegas. It has been subjected to the Agency’s peer and administrative review and has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation by EPA for use.
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In the past decade, there has been an increased use of chemical dust suppressants such as water, salts, asphalt emulsion, vegetable oils, molasses, synthetic polymers, mulches, and lignin products. Dust suppressants abate dust by changing the physical properties of the soil surface and are typically used on construction sites, unpaved roads, and mining activities. The use of chemical dust suppressants has increased dramatically due to rapid population growth and increased emphasis on the need to control particulates in the interest of air quality. In the United States, there are over 2,500,000 km of public unpaved roads, of which 25% (625,000 km) are treated with chemical dust suppressants. A critical problem in the arid southwestern U.S. is dust suppression on land disturbed for residential construction.
Recognizing that it is important to achieve and maintain clean air, the concern that prompted this report is that application of dust suppressants to improve air quality could potentially have other adverse environmental impacts. Times Beach, Missouri is a classic example where the resolution of dust emissions from unpaved roads leads to the creation of a Superfund site. In 1972 and 1973 waste oil contaminated dioxin was sprayed on unpaved roads and vacant lots for dust control in Times Beach. After realizing the adverse situation that had occurred, the costs to relocate the residents and clean up the site was over $80 million. Much more stringent regulations are now in place to avoid another Times Beach; however, there is still concern over the use of dust suppressants since most products used as dust suppressants are by-products and their exact composition is unknown.
The purpose of this report is to summarize the current state of knowledge on the potential environmental impacts of chemical dust suppressants. Furthermore, the report summarizes the views of an Expert Panel that was convened on May 30-31, 2002 at the University of Nevada, Las Vegas to probe into the potential environmental issues associated with the use of dust suppressants.
There are several major categories of dust suppressants: hygroscopic salts, organic petroleum- based, organic nonpetroleum-based, synthetic polymer emulsions, electrochemical products, mulches of wood fiber or recycled newspaper, and blends that combine components from the major categories. Dust suppressants are frequently formulated with waste products recycled from other industries.
Most of the research on dust suppressants has been conducted by industry and has focused on the effectiveness (or performance) of dust suppressants, that is, the ability to abate dust. Little information is available on the potential environmental and health impacts of these compounds. Potential environmental impacts include: surface and groundwater quality deterioration; soil contamination; toxicity to soil and water biota; toxicity to humans during and after application; air pollution from volatile dust suppressant components; accumulation in soils; changes in hydrologic characteristics of the soils; and impacts on native flora and fauna populations.
The major known effects of salts in the environment relate to their capacity to move easily with water through soils. Water quality impacts include possible elevated chloride concentrations in
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streams downstream of application areas and shallow groundwater contamination. In the area near the application of salts, there could be negative impacts to plant growth. For organic non- petroleum based dust suppressants, ligninsulfonate has been shown to reduce biological activity and retard fish growth. Organic petroleum-based dust suppressants have been shown to be toxic to avian eggs; however, the leachate concentrations in other studies were low in comparison to health-based standards. There is also concern with the use of recycled oil waste that may have heavy metals and PCBs.
The expert panel was not able to identify specific concerns on the use of dust suppressants due to the high amount of variability associated with site conditions, dust suppressant composition, and application techniques. The experts did agree more attention should be paid to dust suppressant composition and management. The determination of whether a problem might exist in any given case, however, must be based on the assessment of site-specific conditions.
The potential impact of dust suppressants on soils and plants includes changes in surface permeability, uptake by plant roots that could affect growth, and biotransformation of the dust suppressants in the soil into benign or toxic compounds depending on the environmental conditions and associated microbiota. Vegetation adjacent to the area where dust suppressants are applied could be impacted by airborne dust suppressants. This includes browning of trees along roadways and stunted growth. These effects will vary since different plants have different tolerances.
The potential impact of dust suppressants to water quality and aquatic ecosystems include contaminated ground and surface waters, and changes in fish health. Dust suppressants that are water-soluble can be transported into surface waters and materials that are water-soluble but do not bind tenaciously to soil can enter the groundwater. Fish may be affected by direct ingestion of toxic constituents and also by changes in water quality (e.g., BOD, DO, salinity).
There are no federal regulations controlling the application of dust suppressants; however, some states have developed guidelines for the use of dust suppressants. These include the
U.S. Environmental Protection Agency (EPA) Environmental Technology Verification (ETV) program, three state programs in California, Michigan, and Pennsylvania, and a county-level program in Clark County, Nevada. In Canada, there is the Canada ETV national program.
Although there are no specific regulations in place to control dust suppressant application, it is noteworthy that existing regulations promulgated under the Resource Conservation Recovery Act (RCRA), Comprehensive Environmental Response Compensation and Liability Act (CERCLA), Superfund Amendments and Reauthorization Act (SARA), Clean Water Act (CWA) and TOSCA restrict the introduction of harmful substances into the environment. Regardless, there is concern that since no one program addresses the use of dust suppressants, the enforcement of what is used as dust suppressants could “slip through the regulatory cracks.”
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The expert panel and organizing committee identified several important issues related to scientific research and information about dust suppressant, and regulations on the use of the products. Below is a summary of the major issues and recommendations for each of these categories:
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The purpose of this report is to summarize the current state of knowledge of dust suppressants and potential environmental consequences. The material presented here is based on knowledge gained from scientific literature, industry reports, conversations with industry representatives and regulators, and an expert panel hosted by the University of Nevada – Las Vegas (UNLV) and the U.S. Environmental Protection Agency (EPA). The expert panel on the “Potential Environmental Effects of Dust Suppressant Use: Avoiding Another Times Beach” met on the University of Nevada, Las Vegas, campus on May 30-31, 2002 to consider whether or not dust suppressants pose risks to the environment or human health and how they should be used and managed.
Support for the expert panel and preparation of this report was provided by EPA Region 9 who encouraged the EPA’s Office of Research and Development in Las Vegas to consider the use of dust suppressants and their potential environmental and human health impacts.
The expert panel considered the potential for unintended consequences from dust suppressants and also if guidelines or regulations on the use of dust suppressants might prevent future problems. Twenty-six (26) experts from varying disciplines were invited to participate in the panel. They represented hydrologists, soil scientists, microbiologists, industry, applicators, and regulators. Several participants had specific knowledge about dust suppressants, but the majority was selected because of their expertise in a specific discipline. They were asked to participate in the panel and use their expertise for discussing the current and future use of dust suppressants in a variety of settings. The specific objectives for this expert panel were to: (1) review, and add to, industrial and scientific knowledge on the composition of dust suppressants;
(2) interpret the body of knowledge, and identify physical, chemical, biological, and regulatory issues related to the environmental impacts of dust suppressants; (3) begin to develop a strategy to assist federal, state, and local agencies in regulating the use of dust suppressants; and (4) contribute to a report describing the expert interpretations and a strategy for permitting the use of dust suppressants.
The panel and additional reviewers were asked to review this final report as to whether it fairly reflects the current knowledge of dust suppressants and their applications, potential problems, and a path forward to further resolve those problems and other issues. The report reflects a combination of views of the Expert Panel Organizing Committee and the Expert Panel, and information from the scientific literature and industry. There were many views presented by the group of experts and some of them differed. The statements and/or views of individual members or several members of the Expert Panel are referenced as (Expert Panel 2002), and scientific literature references use a standard reference form (e.g., Bolander, 1999).
The report is written for several audiences. It is intended to be a guidance document for regulators at federal, state, and local levels, scientific researchers, and the environmental community. It serves as a primer to give readers general background information on what dust suppressants are, how they are used, and what potential regulatory issues arise from their use. It provides the local-level employee, who has been given the task of learning about dust suppressants and assessing whether her or his organization should develop regulations, a basic understanding of the issues and kinds of questions that need to be asked about a particular dust suppressant application. It also provides information that could ultimately be used to determine the need for federal regulation of dust suppressants.
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Section 1 of the report provides an introduction and frames the potential problems associated with the use of dust suppressants. Section 2 provides an overview of dust suppressants, the various uses, and the current regulations/guidelines. Section 3 summarizes the current state of knowledge on environmental impacts of dust suppressants from the scientific literature and the Expert Panel. Section 4 outlines a framework for assessing the potential environmental impacts of dust suppressants. Finally, Section 5 lists the scientific and regulatory issues that are not resolved at this time and should be considered if guidelines are to be developed for dust suppressant use.
A draft version of this report was submitted to all of the 26 Expert Panelists and 10 outside individuals from government agencies, universities, and industry. A total of 19 individuals provided comments to the Organizing Committee. All comments were considered, and revisions were made to strengthen the report. Following is a list of the external reviewers.
| Amy, Penny, Ph.D. | University of Nevada, Las Vegas |
| Bassett, Scott, Ph.D. | Desert Research Institute, Reno |
| Bolander, Peter | U.S. Department of Agriculture, Forest Service |
| Colbert, Woodrow | Pennsylvania State Conservation Commission |
| Detloff, Cheryl | Midwest Industrial Supply, Inc. |
| Franke, Deborah | Research Triangle Institute |
| Johnson, Jolaine, P.E. | Nevada Division of Environmental Protection |
| Knight, Gaye | City of Phoenix, Office of Environmental Programs |
| Langston, Rodney | Clark County Department of Air Quality |
| Lee, G. Fred, Ph.D., P.E. | G. Fred Lee Associates |
| Letey, John, Ph.D. | University of California, Riverside |
| Pickrell, John, Ph.D. | Kansas State University |
| Sanders, Thomas, Ph.D. | Colorado State University |
| Scheetz, Barry, Ph.D. | Pennsylvania State University |
| Spear, Terry, Ph.D. | Montana Tech of the University of Montana |
| Starkweather, Peter, Ph.D. | University of Nevada, Las Vegas |
| Tyler, Scott, Ph.D. | University of Nevada, Reno |
| Wells, Jason | ILS, Inc., ESAT Contractor for U.S. EPA Region 4 |
| Wierenga, Peter, Ph.D. | The University of Arizona |
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Notice…………………………………………………………………………. iii
Executive Summary……………………………………………………… v
Foreword…………………………………………………………………….. ix
Acronyms………………………………………………………………….. xv
Section 1 Introduction…………………………………………………. 1
Section 2 Background………………………………………………… 3
Section 3 What is Known About Potential Environmental Effects……………………………………………………………………….. 13
Section 4 Framework for Assessing Potential Environmental Effects……………………………………………….. 19
Section 5 Path Forward – Issues and Potential Solutions………………………………………………………………………………….. 23
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References………………………………………………………………… 39
Appendix A – Literature Review…………………………………. 43
Appendix B – Fact Sheets for Verification Programs and Guidelines…………………………………………………………………. 59
Appendix C – Expert Panel Agenda…………………………….. 71
Appendix D – Organizing Committee and Expert Panel.. 73
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Table 2-1: Most commonly used dust suppressants (modified from Bolander, 1999a) 4
Table 2-2: Typical dust suppressant use rates for unpaved roads and vacant lands based
on industry data…………………………………………………………………. 9
Table 5-1: Relevant EPA and Standard test to be considered in assessing impacts of dust suppressants 27
Table 5-2: Blank Worksheet A – Estimation of soil mass fraction from suppressant constituent concentration……………………………………………………………….. 28
Table 5-3: Example calculation using Worksheet A 29
Table 5-4: Blank Worksheet B – Estimation of maximum allowable dust suppressant constituent concentration from risk-based limit in soil 30
Table 5-5: Example calculation of maximum allowable suppressant concentration based on RCRA 100 ppm action level for Total Petroleum Hydrocarbons (TPH) in soil as determined using EPA Method 8015………………… 31
Table 5-6: Example calculation of maximum allowable suppressant concentration based on CERCLA 1 ppb action level for TCDD……………… 32
Figure 2-1: Conceptual model of the various uses of dust suppressants and the potential environmental consequences……………………………………………………………….. 6
Figure 2-2: Topical application of a dust suppressant using a spray hose……………………………………………………………………………………. 7
Figure 2-3: Topical application of a dust suppressant using a spray bar……………………………………………………………………………………. 8
Figure 2-4: Topical application of a dust suppressant using a spray gun……………………………………………………………………………………. 8
Figure 4-1: Framework for assessing the potential environmental impacts of dust suppressants……………………………………………………………… 19
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APG Application Practice Guidelines
ASTM American Society of Testing and Materials
BOD Biological oxygen demand
CalCert California Environmental Technology Certification program
CCCP Clark County Comprehensive Planning
CERCLA Comprehensive Environmental Response Compensation and Liability Act
COD Chemical oxygen demand
CWA Clean Water Act
DO Dissolved oxygen
Eco-SSL Ecological Soil Screening Level guidance
ETV Environmental Technology Verification program
FIFRA Federal Insecticide, Fungicide and Rodenticide Act
MDEQ Michigan Department of Environmental Quality
MSDS Material Safety Data Sheet
PM Particulate matter
PSCDGRS Pennsylvania Conservation Commission Dirt and Gravel Roads Maintenance Program
RBCA Risk Based Corrective Action
RCRA Resource Conservation Recovery Act
RO Reverse Osmosis
RTAC Road and Transportation Association of Canada
SARA Superfund Amendments and Reauthorization Act
SIPs State Implementation Plans
TCDD Tetrachlorodibenzodioxin
TCLP Toxicity characteristic leaching procedure
TDS Total Dissolved Solids
TOC Total organic carbon
TOSCA Toxic Substance Control Act
TPH Total petroleum hydrocarbons
TSCA Toxic Substance Control Act
TPH Total petroleum hydrocarbons
TS Total solids
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| TSS | Total suspended solids |
| TVS | Total volatile solids |
| USDA | U.S. Department of Agriculture |
| USEPA | U.S. Environmental Protection Agency |
| USDOT | U.S. Department of Transportation |
| UNLV | University of Nevada, Las Vegas |
| VOC | Volatile organic compounds |
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The use of chemical dust suppressants in the United States is increasing, due to high rates of population growth in arid regions, the need to reduce airborne particulate matter to meet air quality standards, and increased recognition of the value of re- ducing erosion and maintenance costs on unpaved roads. Dust suppressants are used to control erosion and maintenance costs on unpaved roads, and to abate fugitive dust in mining, on construction sites, agricultural fields, livestock facilities, disturbed vacant land, landfills, and in steel mills. Materials used as dust suppressants include water, salts, asphalt emulsion, vegetable oils, molasses, synthetic polymers, mulches, and lignin products. Dust suppressants abate dust by changing the physical properties of the soil surface. The mechanisms by which suppressants abate dust vary with product type; some form crusts or protective surfaces on the soil, others act as binding agents causing particles to agglomerate together, and some attract moisture to the soil particles.
Across the United States, over 625,000 kilometers of public, unpaved roads are treated with chemical dust suppressants (Midwest Industrial Supply, Inc., personal communication). In Las Vegas, Nevada, and Phoenix, Arizona, degraded air quality from disturbed land and unpaved roads in the extremely arid environment has led to the potential for widespread use of dust suppressants. In spite of the growing use of dust suppressants, there are no agreed upon definitions, standards of performance and almost no regulation of dust suppressant contents, application rates, or management practices. Understanding of direct and indirect effects of dust suppressants on human health and the environment is limited. Frameworks for making meaningful cost benefit analysis of either benefits or risks are not yet developed.
There is concern that the unexamined use of dust suppressants might create future environmental and health liabilities similar to the problems resulting from dust suppres- sant use in Times Beach, Missouri in the 1970’s. In 1972 and 1973 waste oil contain- ing dioxin was sprayed on unpaved roads for dust control in Times Beach (EPA, 1983). A subsequent flood raised fears that dioxin had contaminated homes and yards. In 1983, the 2,800 people of Times Beach were permanently relocated at a cost of approximately $30 million (EPA, 1988) and the town was closed. Costs to excavate and incinerate the contaminated soils were estimated to be an additional $50 million (EPA, 1988). To avoid similar contamination and cost from current uses of dust suppres- sants, it is important to take an early, comprehensive look at dust suppressants and their application and to develop policies, guidelines, and recommendations for their use.
Although some programs have been developed to evaluate dust suppressant effectiveness and safety, most programs are voluntary; so most dust suppressant use is unregulated. Waste products or industrial by- products are often used as suppressants, with little examination of the product’s hazardous constituents. Application prac- tices are also not regulated. The method and frequency of application and amount of material applied varies. While risks to human health and the environment may be taken into consideration, the primary consideration driving the decision to use a particular suppressant is its initial cost. Frequently reliable performance data does not exist to determine true cost-effectiveness.
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Several states (California, Michigan, Penn- sylvania) and counties (Clark County, Nevada) are developing guidelines for the use of dust suppressants: where, when and which suppressant to use for a given environment. The guidelines (See Section 2.7) developed by the above agencies are based on limited information and are not sufficient for developing standard protocol in determining whether a dust suppressant should be used. These guidelines were developed out of a need to prevent adverse environmental impacts. An extensive testing
program would be needed to develop standard protocol for dust suppressant use.
Other agencies are interested in developing regulations for dust suppressant use, but feel there is little guidance available. Thus, the overall goal of this report is to summarize the current state of knowledge on dust suppressants. The material in the following sections focuses on the current state of knowledge about dust suppressants, areas where information is missing, and proposes an assessment framework for making decisions on the use of dust suppressants.
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There is no standard definition of a dust suppressant. Dust suppressants are materials used to control particulate matter emissions from land surfaces. They can include physical covers (such as vegetation, aggregate, mulches, or paving) and chemical compounds. This report focuses on chemical dust suppressants and one physical cover (fiber mulch). Chemical products used for dust suppression fall into eight main cate- gories, listed in Table 2-1. They include water, products manufactured specifically as dust suppressants, natural or synthetic compounds, and waste or by-products from other uses and manufacturing processes. In 1991, 75-80% of all dust suppressants used were chloride salts and salt brine products, 5-10% were ligninsulfonates, and 10-15% were petroleum-based products (Travnik, 1991). The products are usually provided as a concentrate. Dilution for application varies from 1:1 to 1:20 (1 part concentrate to 20 parts water) depending on the specific dust suppressant, application type, and site conditions. Since many of the products are mixed with water, non-aqueous phase liquids are not commonly used in dust suppressant formulation (Expert Panel, 2002).
The control of dust emission is closely related to erosion control, but differs slightly. In both cases, the goal is to restrict the movement of soil particles. Dust sup- pressants are used to prevent soil particles from becoming airborne. Erosion control technologies aim to minimize soil movement on and off a given site. Since erosion control agents counteract the forces of both wind and water, they may have different pro- perties than dust suppressants, which are used primarily to prevent wind erosion. The minor differences in the definition and classification of these materials may become important as decision makers and regulators begin to focus on unintended, negative consequences of these products.
Water alone can be a dust suppressant. It is commonly used on construction sites and unpaved roads where the surfaces are dis- turbed only for short time periods. Water is probably the most cost effective short-term solution for dust control (Gebhart et al., 1999); however, the cost will vary depending on climatic conditions influencing water avail- ability. The application rate is important since a heavy application may turn the road into mud destroying the soil’s structure and damage its ability to perform as the sub- grade. In some areas, reclaimed water is used for dust control. In these cases, the quality needs to be considered as well as the potential for human exposure to reclaimed water and environmental and wildlife impacts.
Salts and Brines are the most common type of dust suppressant used (Travnik, 1991). Calcium chloride (CaCl2) and magnesium chloride (MgCl2) are the major products in this category (Sanders and Addo, 1993). Calcium chloride is a byproduct of the ammonia soda (Solvay) process and a joint product from natural salt brines. Magnesium chloride is derived from seawater eva- poration or from industrial byproducts. These products stabilize the soil surface by absorbing moisture from the atmosphere, so it is critical to have sufficient humidity levels of 20-80% when applying these products (Bolander, 1999a).
Organic Non-petroleum Products include ligninsulfonate, tall (pine) oil, vegetable derivatives, and molasses. Ligninsulfonate is derived from the sulfite pulping process in
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the paper industry where sulfuric acid is used to break down wood fiber. Tall oil is a by-product of the wood pulp industry recovered from pinewood in the sulfate Kraft paper process. Vegetable oils are extracts from the seeds, fruit or nuts of plants and are generally a mixture of glycerides. Molasses is the thick liquid left after sucrose has been removed from the mother liquor in sugar manufacturing. It contains approximately 20% sucrose, 20% reducing sugar, 10% ash, 20% organic non-sugar, and 20% water
(Lewis, 1993).
Synthetic Polymer Products comprise many different compounds that promote the bind- ing of soil particles. The exact composition of these products is usually not provided in the Material Safety Data Sheets (MSDS) since the makeup of the product is confidential information of manufacturers.
Organic Petroleum Products are derived from petroleum and include used oils, sol- vents, cutback solvents, asphalt emulsions, dust oils, and tars. Petroleum-based pro- ducts are not water-soluble or prone to evaporation, and generally resist being washed away (Travnik, 1991).
Electrochemical dust suppressants are typi- cally derived from sulphonated petroleum and highly ionic products. This group of products includes sulphonated oils, enzymes, and ammonium chloride. A disad- vantage of these products is that their effectiveness depends on the clay miner- alogy of the site and may only work with certain types of soils.
Clay Additives are composed of silica oxide tetrahedra (SiO4) and alumina hydroxide octahedra (Al(OH)6) (Scholen, 1995). Clay additives provide some tensile strength in warm dry climates, however, their tensile strength decreases as moisture in the soil increases (Bolander, 1999b).
Mulch and Fiber Mixtures are formulated from waste wood fibers or recycled newspapers, a binding agent (for example, plaster of paris) and a carrier solvent (usually water). They generally work by forming a protective layer or crust over the soil surface instead of by binding soil particulates together.
Table 2-1: Most commonly used dust suppressants (modified from Bolander, 1999a).
| Suppressant Type | Products |
| Water | Fresh and seawater |
| Salts and brines | Calcium chloride, magnesium chloride |
| Petroleum-based organics | Asphalt emulsion, cutback solvents, dust oils, modified asphalt emulsions |
| Non-petroleum based organics | Vegetable oil, molasses, animal fats, ligninsulfonate, tall oil emulsions |
| Synthetic polymers | Polyvinyl acetate, vinyl acrylic |
| Electrochemical products | Enzymes, ionic products (e.g. ammonium chloride), sulfonated oils |
| Clay additives | Bentonite, montmorillonite |
| Mulch and fiber mixtures | Paper mulch with gypsum binder, wood fiber mulch mixed with brome seed |
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Dust suppressants are used on unpaved roads, road shoulders, construction sites, landfills, mining operations, military sites, animal enclosures, vacant lands and agricultural fields (Expert Panel, 2002). Figure 2-1 presents a conceptual model of major dust suppressant uses. The use of dust suppressants is largely driven by air quality regulations, but other concerns can also motivate their use (Expert Panel, 2002). For instance, transportation agencies may use dust suppressants to reduce the maintenance on unpaved roads. Private property owners may use dust suppressants to reduce nuisance dust.
The selection of a dust suppressant varies for the different uses. For example, magnesium chloride and petroleum-based products would not be suitable for agricultural use because they could affect crops grown on the fields after application. A fiber mulch might be more appropriate for use in agriculture areas. For an unpaved road, the dust suppressant needs to be more durable and a fiber mulch would not be appropriate to use. Instead, a petroleum-based product may hold up better under traffic conditions.
There is significant regional variation in the use of dust suppressants (Expert Panel, 2002). In Pennsylvania, the major use is on unpaved roads. In other parts of the eastern United States, dust suppressants are used on landfills, coal fields, steel mills, and mines. They are also used as temporary covers on lands that are disturbed for short periods, such as slopes exposed during road construction that are eventually revegetated. In Texas, dust suppressants are used largely on construction sites with disturbed lands and haul roads. In Clark County, Nevada, and other parts of the southwest, 90% of the use is on disturbed vacant land – land that has been cleared for residential or commer- cial development but on which construction has not yet begun. In some cases, disturbed land can remain vacant for several years. In
eastern Oregon and Washington, dust suppressants are used on fallow agriculture fields. The United States Department of Agri- culture (USDA) Forest Service also uses dust suppressants on unpaved roads.
An important consideration is the current magnitude of chemical dust suppressant usage. An unpublished 2001 analysis by the dust suppressant manufacturer, Midwest Industrial Supply, Inc., summarized existing and potential markets for chemical dust suppressants. Some of the study’s key findings are noted below.
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Potential Environmental Consequences of Dust Suppressants
U.S. Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Environmental Sciences Division Characterization and Monitoring Branch
A
Example Uses
Figure 2-1: Conceptual model of the various uses of dust suppressants and the potential environmental consequences.
It is also important to note the potential uses at a regional scale. Pennsylvania, for example, has over 33,000 km of public unpaved roads that could potentially be treated with dust suppressants (Expert Panel, 2002). In Maricopa County, Arizona, the Department of Transportation applies ligninsulfonate to
92 miles of road shoulders three times a year (Arizona Department of Transportation, personal communication). Clark County, Ne- vada, has 100-200 km of unpaved roads and approximately 150,000 acres (60,000 hectares) of vacant land in the urban core of the Las Vegas Valley (James et al., 1999). Of these 150,000 acres, 10-20% (15,000-
30,000 acres, or 6,000-12,000 hectares) are estimated to have a high potential to emit PM-10 (particulate matter less than 10 µm), and could be stabilized through physical cover (vegetation, aggregate) or via application of chemical dust suppressants. Clark County has decided to pave high-use public roads instead of treating them with chemical dust suppressants (CCCP, 2001). It was reported in Pennsylvania that long term environmental and maintenance costs are set in motion by public pressure to pave roads before a proper road base and drainage system is in place. Paved road failures in even the first year have occurred. However, haul roads at construction and mining sites are often treated with chemical dust suppressants.
Dust suppressants abate dust by changing the physical properties of the soil surface. When a dust suppressant is applied the soil particles become coated and bound together, making them heavier. Some products form a crust on the surface and others penetrate through the surface. Water and petroleum-based products form a crust by agglomerating the soil particles. The formation of a crust with adequate thickness with petroleum-based products reduces the amount of immediate maintenance that is required on unpaved roads, however, in the long term, when failures such as potholes occur, there is no way to repair them using normal low cost techniques, such as grading. Unless these roads are milled to return them
to unsealed status, the structural failures get paved over, again setting in motion the long- term maintenance and environmental costs referenced earlier (Expert Panel, 2002). Many of the synthetic organic materials are derived from petroleum products and are mixed with a binding agent that glues the particles together (Expert Panel, 2002). Salts absorb moisture from the air and retain it by resisting evaporation (Foley et al., 1996). Organic non-petroleum and synthetic polymer products act as a weak cement by binding the soil particles together or weighing down and agglomerating particles. The electro- chemical stabilizers work by expelling adsorbed water from the soil, which de- creases air voids and increases compaction (Foley et al., 1996).
Dust suppressants are applied either topical- ly or mixed into the top layer of the soil. Topical application is with a spray bar on the back of a truck or through a large hose with a nozzle on the end (See Figures 2-2 and 2-3). On vacant lands, dust suppressants are applied topically. On small plots, application is by hand-directed hoses (Figure 2-2). On larger properties, application is by truck- mounted spray bars (Figure 2-3) and modified water cannons (Figure 2-4). A less common type of application is when the dry products (flakes) are spread on the surface and the product is mixed into the soil (Expert Panel, 2002).
Figure 2-2: Topical application of a dust suppressant using a spray hose.
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Figure 2-3: Topical application of a dust suppressant using a spray bar.
Figure 2-4: Topical application of a dust suppressant using a spray gun.
Another application method is to mix the dust suppressant into the travel surface by a sequence of steps comprising, 1) grading the road surface to remove a windrow of earth from the travel lane, 2) application of dust suppressant, 3) grading the earth windrow back onto the travel lane and compaction to maximum density, and 4) a second topical application on top of the graded earth. Mixing the dust suppressant into the soil is more difficult, but it tends to last longer since the product is exposed to more soil particles.
Some dust suppressant vendors have soft- ware available to make recommendations to customers based on traffic conditions, vehicle speed, and other site conditions. However, a major factor that impacts the application rate for many situations is the
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amount of funding available for dust sup- pression. For instance, a heavier application often increases the durability of the dust suppressant and reduces the need for repeated applications (Expert Panel, 2002). Seldom are analysis made of the soil types, which may change numerous times on one road in some geographic areas.
Typical liquid application rates vary from 0.3 to 1.0 gallons per sq yard (1.4 to 4.5 liter/m2) and will depend on site-specific conditions (e.g., soil type, land use, weather during application, and weather after application). For liquid emulsions, dust suppressant concentrates are mixed with diluent (usually water) to give the correct mass application rate of solids for the desired application. For example, solids application rates for acrylic polymer emulsions are usually 0.20 to 1.00 pounds per square yard (0.11 – 0.54 kg/m2) at liquid application rates of 0.50 to 1.00 gallons per square yard (2.26-4.53 liter/m2). It is generally better to apply multiple light applications rather than a single heavy application, as the light applications generally allow for better penetration into the surface soil and also reduce the fraction of dust suppressant that may run off the target area.
The performance of a dust suppressant is determined by the mass of applied solids per unit volume of treated soil. Mass of applied solids per unit volume of soil will be the product of the mass application rate, and the penetration depth of solids into the soil. The mass application rate of a dust suppressant is computed as the liquid application rate times the mass concentration of bulk suppressant in applied liquid.
For example, if the liquid application rate is
0.50 gallon/yd2 (2.26 liter/m2) and the solids concentration is 1.00 lb / gallon (0.120 kg/ liter), then the mass application rate of the dust suppressant is 0.50 gallon / yd2 x 1.00 lb/gallon = 0.50 lb/ yd2 (0.271 kg/m2). If the penetration of the suppressant material was uniform to a depth of 2 inches (0.05 meters), then the bulk concentration of the suppressant in the surface layer of soil would be ~1,560 kg/m3), so the suppressant solids are
0.50 lb/yd2 / (9 ft2/yd2) / 0.167 ft = 0.336 lb/ft3 present in the soil at a mass fraction of about (or, 2.71 kg/m2 / 0.05 meters = 5.40 kg/m3). 1/300. Mass and liquid rate data for typical This bulk concentration is about 1/300 the application rates of dust suppressants are mass density of typical soils (~100 lb/ft3 or shown in Table 2-2 (James et al., 1999).
Table 2-2: Typical dust suppressant use rates for unpaved roads and vacant lands based on industry data. English and (SI units).
| Unpaved Roads | ||||
| Low Rate | High Rate | |||
| Liquid application rate | 0.50 gallon/yd2 | (2.26 l/m2) | 1.00 gallon/yd2 | (4.53 l/m2) |
| Solids concentration | 0.40 lb/gallon | (0.05 kg/l) | 1.00 lb/gallon | (0.12 kg/l) |
| Solids application rate | 0.20 lb/yd2 | (0.11 kg/m2) | 1.00 lb/yd2 | (0.54 kg/m2) |
| 10 foot (3.05 m)-wide travel lane: | ||||
| Topical 1 layer (solids) | 1,173 lb/lane-mile | (330 kg/lane-km) | 5,867 lb/lane-mile | (1,653 kg/lane-km) |
| Topical 1 layer (liquid) | 2,933 gal/lane-mile | (6,898 l/lane-km) | 5,867 gal/lane-mile | (13,799 l/lane-km) |
| Graded 2 layer (solids) | 2,347 lb/lane-mile | (661 kg/lane-km) | 11,733 lb/lane-mile | (3,306 kg/lane-km) |
| Graded 2 layer (liquid) | 5,867 gal/lane-mile | (13,799 l/lane-km) | 11,733 gal/lane-mile | (27,596 l/lane-km) |
| Vacant Lands | ||||
| Low Rate | High Rate | |||
| Liquid application rate | 0.50 gallon/yd2 | (2.26 l/m2) | 1.00 gallon/yd2 | (4.52 l/m2) |
| Solids concentration | 0.40 lb/gallon | (0.05 kg/l) | 1.00 lb/gallon | (0.12 kg/l) |
| Solids application rate | 0.20 lb/yd2 | (0.11 kg/m2) | 1.00 lb/yd2 | (0.54 kg/m2) |
| Application rate: | ||||
| per 100 ft2 (solids) | 2.2 lb/100 ft2 | (10.7 kg/100m2) | 11.1 lb/100 ft2 | (54.2 kg/100 m2) |
| per 100 ft2 (liquid) | 5.6 gal/100 ft2 | (228.1 l/100m2) | 11.1 gal/100 ft2 | (452.1 l/100 m2) |
| per acre (solids) | 968 lb/acre | (1,085 kg/ha) | 4,840 lb/acre | (5,426 kg/ha) |
| per acre (liquid) | 2,420 gal/acre | (22,637 l/ha) | 4,840 gal/acre | (45,273 l/ha) |
The majority of research on dust suppressants has been on the effectiveness of the products, where “effectiveness” reflects the ability of the product to keep soil particles on the soil surface when subjected to some erosive force, such as wind. Effectiveness varies with type of use, site condition, and climate. Water has been found to be be- tween 40% and 85% effective in suppressing the suspension of soil particles for short time periods, but not effective over longer time periods (Thompson, 1990; Travnik, 1991; Foley et al., 1996; Kestner, 1989; Cowherd et al. 1989). Salts are more
effective than water in controlling dust if sufficient moisture is available (Bolander, 1999a). Ligninsulfonates remain effective during long, dry periods with low humidity. They also tend to remain plastic, allowing reshaping and traffic compaction when applied to soils with high amounts of clay. The effectiveness of ligninsulfonates may be reduced or completely destroyed in the presence of heavy rain because of the solubility of these products in water (Bolander, 1999a). Synthetic polymer emulsions in- crease the tensile strength of clays on typical roads and trails up to ten times. Tests have shown that synthetic polymers applied in wet climates tend to break down if
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exposed to moisture or freezing for an increased time (Bolander, 1999a). Petroleum-based products generally resist being washed away, but oil is not held tightly by most soils and can be leached away by rain. Under the right conditions, these products can remain 90% effective after a year (Gilles et al., 1997).
The length of time that a dust suppressant is effective varies according to variables such as the type of product, soils, weather, application rate, and traffic conditions. How- ever, many manufacturers advertise that the products will be effective from 6-12 months. Some products will last up to 24 months under certain conditions.
At least six programs in the United States and one in Canada are directly or indirectly developing, or have developed, guidelines for dust suppressant use. Appendix B includes fact sheets for the programs and following is a summary of the key program elements. In the United States, there is the Environmental Protection Agency (EPA) Environmental Technology Verification (ETV) program, three states programs in California (CalCert), Michigan, and Pennsylvania, and a county level program in Clark County, Nevada. In Canada, there is the Canada ETV national program. The Canada ETV, CalCert, and EPA ETV programs are voluntary and available to any developer/vendor of environmental technol- ogy, including dust suppressants. All three verification programs (ETV, CalCert, and Canada ETV) were created by partnerships between regulatory environmental agencies and either the private sector or non-profit organizations, with an emphasis on the performance claims and some environmental tests of the products. Other programs that are ancillary to dust suppressants are those that provide specifications for the use of snow and ice control products such as the Pacific Northwest Snowfighters (www.wsdot.wa.gov/partners/pns/default.htm).
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The testing program in Pennsylvania was developed by joint efforts of conservation interests, academia and industry and, is used, for all materials, including suppressants, for projects funded by the Dirt and Gravel Roads Maintenance Program under the State of Pennsylvania Conservation Commission (PSCDGRS, 2003). The stringent specifications require product testing by a certified lab and manufacturer guaran- teed product uniformity, delivery, application and cure. Results in the program have been so positive, and reception by industry so strong, it has been used voluntarily by others. The Michigan Department of Environmental Quality created specific regulations for the application of oil field brine as a dust suppressant (MDEQ, 2000). Clark County, Nevada has issued detailed interim guidelines for the use of dust suppressants on disturbed lands (CCCP, 2001). The guidelines were drafted by a working group composed of air and water quality professionals from state and local agencies, as directed by the Clark County Commissioners.
In all three voluntary certification programs and in the Pennsylvania Dirt and Gravel Road regulations, it is the responsibility of the technology vendor/developer to provide sufficient performance data and documentation to support the claims of the technology under consideration. While the other pro- grams do not specify what data should be provided to support the technology claim, the Environmental Protection Agency (EPA) ETV and the Pennsylvania programs note specific tests that have to be performed to evaluate the environmental impacts of the products under consideration. In the EPA ETV, ETV Canada, and CalCert voluntary programs, scientists and engineers from regulatory agencies, universities, research laboratories, and the private sector examine the supporting documentation for product verification. However, ETV Canada maintains a list of approved expert entities (e.g. universities, private consultants) to be used to conduct tests to support the verification. An agreement is reached with the vendor/ developer regarding the expert entity to be used in the technology verification process.
In the case of Pennsylvania, the data sup- porting the claim, issued by EPA certified labs, are evaluated by the State Conservation Commission for authenticity. All three voluntary verification programs, as well as Pennsylvania’s, issue a report or certificate as proof of verification. Only the Canada ETV and the California CalCert programs require renewal of the verification after three years.
Michigan’s regulations for brine application as a dust suppressant do not specify any specific test methods. Instead, it establishes acceptable application rates and methods, and types of areas where it can and cannot be applied. It also requires the property owner or contractor to maintain detailed record keeping of the specific locations, amount, and source of brine applied. Clark County, Nevada guidelines specify types of areas where the application of specific dust suppressants are discouraged. In addition, they contain recommendations on the types of suppressants, dilution, and application rates to be used in different types of dust control areas (e.g. roads, construction sites). In general, the Clark County guide- lines discourage the application of products known to potentially contain specific pollutants near lakes, streams, channels, and flood control channels.
The EPA ETV program requires acute and chronic toxicity tests (EPA/600/4-90/027F and EPA/600/4-91/002), and analyses of biological oxygen demand (BOD), chemical oxygen demand (COD), volatile organic compounds (VOC), toxicity characteristic leaching procedure (TCLP) [EPA Method 1311], inorganics/metals (EPA 6010B), semi-volatile organics (EPA 8270D), volatile organics (EPA 8260B), pesticides/herbicides (EPA 8270D), and PAHs. The Pennsylvania program requires bulk analysis of products using EPA SW-846 tests (originally designed for testing RCRA wastes), leach analysis by EPA Method 1312 (includes metals, volatiles, and semi- volatiles), 7-day survival and growth test for rainbow trout and Ceriodaphinia dubia, BOD, and COD.
In addition to the programs noted above, the United States Department of Agriculture (USDA) Forest Service is developing the “Forest Service Specifications for the Construction of Roads and Bridges” that will have new requirements for dust suppressants. These requirements will include a certificate that states that the dust suppressant meets the chemical requirements of the Pacific Northwest Snowfighters, that a toxicity test (ASTM E 729) be submitted, and that the pH of the product be on the certificate as well.
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What is Known About Potential Environmental Effects
The majority of research on dust suppressants has been by industry and has focused on the effectiveness (or performance) of dust suppressants to abate dust, however, little information is available on the potential environmental and health impacts of these compounds. The numerous pathways of exposure to dust suppressants for humans, flora, and fauna and how suppressants may migrate through the environment to potentially sensitive recaptors are shown in Figure 2-1. Impacts will depend upon their composition, application rates, and interactions with other environmental components. Potential environmental impacts include: sur- face and groundwater quality deterioration; soil contamination; toxicity to soil and water biota; toxicity to humans during and after application; air pollution; accumulation in soils; changes in hydrologic characteristics of the soils; and impacts on native flora and fauna populations.
This conceptual model and all of the potential pathways and receptors of concern were presented to the expert panel for their consideration. Following is a brief summary of the literature on known potential effects of dust suppressants. A complete description of the studies is provided in the literature re- view presented in Appendix A. The views of the Expert Panel on potential environmental effects of dust suppressants are then presented Section 3.2.
Although there are several noteworthy studies on the effects of dust suppressants to water quality, plants, and fish, the majority of the studies have focused on salts and brines, ligninsulfonates, and a few organic petroleum-based products.
The major known effects of salt in the environment relate to its capacity of moving easily with water through soils. Water quality impacts include possible elevated chloride concentrations in streams downstream of application areas (Demers and Sage, 1990) and shallow groundwater contamination (Heffner, 1997). In the area near the application of salts, there have been negative impacts to the growth of fruit trees (RTAC, 1987), pine, poplar, and spruce (Foley et al., 1996, Hanes et al., 1976, and Hanes et al., 1970), and alterations in the plant nutrition due to increases in the osmotic pressure of soils (Sanders and Addo, 1993). Chloride concentrations as low as 40 ppm have been found to be toxic to trout, and concentrations up to 10,000 mg/L have been found to be toxic to other fish species (Foley et al., 1996, Golden, 1991). Salt concentrations greater than 1,800 mg/L have been found to kill daphnia and crustaceans (Sanders and Addo, 1993), and 920 mg/L of calcium chloride has been found to be toxic to daphnia (Anderson, 1984).
The majority of research in this category has focused on the impacts of ligninsulfonate. The toxicity of ligninsulfonates to rainbow trout and other biota has been investigated (Heffner, 1997). The 48-hour LC50 (concentration of ligninsulfonates which would be lethal to 50 percent of the tested population within 48 hours) value for ligninsulfonates was found to be 7,300 mg/L (Roald, 1977a and 1977b). A mortality of 50% was achieved for rainbow trout exposed to 2,500 mg/L ligninsulfonate for 275 hours. For concentrations equal to or higher than 2,500
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mg/L, rainbow trout showed loss of reaction to unexpected movements, rapid and irregular breathing, and finally loss of co- ordination before death. It has been found that calcium and sodium ligninsulfonate negatively affect the colon of guinea pigs causing weight gain and producing ulceration in those animals (Watt and Marcus, 1976).
High levels of ligninsulfonate in water bodies have high coloring effects, increase bio- chemical oxygen demand, reduce biological activity, and retard growth in fish (Raabe, 1968, Heffner, 1997, RTAC, 1987, Bolander, 1999a, Singer et al., 1982). However, lignin- sulfonate compounds do not impact seed germination in the areas where applied (Singer et al., 1982).
Potential environmental impacts are highest from organic petroleum products. The chemical characteristics of the oil deposit from which the petroleum product originated, results in varied impacts with the potential for high levels of heavy metals from specific oil deposits. Several studies have shown that waste oils may contain known toxic and carcinogenic compounds (e.g. PCBs); therefore EPA prohibits the use of these materials (RTAC, 1987; Metzler, 1985, and USEPA,
1983).
The accidental introduction of a petroleum- based dust suppressant (Coherex) into a stream in Southern Pennsylvania affected fish and benthic macroinvertebrate com- munities and killed a large number of fish (Ettinger, 1987). Organic petroleum-based products have also been found to be toxic to avian mallard eggs. When the eggs were exposed to a concentration of 0.5 µL/egg, 60% mortality was observed by 18 days of development (Hoffman and Eastin, 1981).
A recent UNLV study, funded by several local agencies in the Las Vegas Valley,
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generated preliminary data highlighting the potential of the major dust suppressant categories. The research focused on the quality of urban runoff and on the changes in the chemical composition of soils where suppressants were applied (Piechota et al., 2002 and Singh et al., 2003). Rainfall events were simulated on the dust-suppressant treated plots and the changes in soil com- position and the quality of the runoff emanating from the plots were examined.
In the study, a site was graded and divided into several individual plots. Each plot was
2.4 meters x 2.4 meters. Six categories of dust suppressant (11 individual products) were topically applied to the plots by local dust suppressant applicators. The dust suppressants applied included acrylic polymer emulsion, ligninsulfonate, petroleum-based organic, non-petroleum based organic, fiber mulch, and magnesium chlor- ide salt. Rainfall was simulated using water treated by a reverse osmosis (RO) system. The water supply characteristics were designed to be similar to those of the rainfall in the Las Vegas Valley. An approximate rainfall of 20 mm was generated for a 1-hour period. The first five gallons of runoff emanating from the plots were combined to form a composite sample that was divided into aliquots, preserved, and analyzed for chosen parameters. In addition, the top two- inches of soil from each plot were sampled after the rainfall events to determine remaining levels of different compounds. The soil samples were leached using the EPA Synthetic Precipitation Leaching Procedure (Method 1312). Parameters evaluated in the runoff and soil leachate include 67 toxic volatile and 76 semi-volatile organic com- pounds, organic pesticides, PCBs, 11 metals, nutrients, biochemical oxygen de- mand (BOD), total solids (TS), total volatile solids (TVS), total suspended solids (TSS), total dissolved solids (TDS), turbidity, total organic carbon (TOC), pH, alkalinity, chem- ical oxygen demand (COD), hardness, nitrate, ammonia, phosphate, sulfide, sulfate, cyanide, chloride, and coliform bacteria.
The results show that petroleum-based products had a higher number of potentially
toxic contaminants with concentrations greater than the control plot, followed by acrylic polymers and ligninsulfonate. Magnesium chloride presented the lowest number of contaminants with concentrations greater than the control. The majority of the dust suppressants created a surface that is more impermeable than the natural soil surface. This increased the runoff volume similar to that emanating from a developed land surface.
Although several compounds that affect water quality have been detected in the runoff of plots to which dust suppressants were applied, this information alone should not be used to evaluate the impacts of dust suppressants to water quality. The data generated in this study and others should be combined with information on dust suppressant effectiveness, the frequency of application, proximity to water bodies, and cost to thoroughly evaluate the feasibility of using these compounds when water quality is a concern.
This section summarizes the expert panel views on potential environmental impacts of dust suppressants, presented during the panel discussions. It is problematic to attribute specific views to a specific expert; therefore, the major points of consensus are noted below and collectively these represent the views of the experts as captured in the Expert Panel and through their review of the document.
On-site and off-site environmental effects of dust suppressant application depend on many factors including the physical characteristics of the suppressant, its chemical composition, concentration, the form it takes when it migrates, soil composition, and the climate conditions during and after application. From all the aforementioned factors, the lack of knowledge on the chemical com- position of the suppressants is of critical importance to the evaluation of the environ- mental impacts of these compounds.
There is a need to improve information about the chemical composition of suppressants. Although Material Safety Data Sheets (MSDS’s) for suppressants include the major components of the dust suppressants, they do not always include adequate details on toxic compounds that may be present and are of environmental concern. Because the vast majority of compounds used as dust suppressants are waste products from the manufacturing industry, their chemical com- position is often unknown and complex and may vary widely for each batch. Organic suppressants sometimes contain surfactants or foaming agents that can cause environ- mental effects. One applicator cited an instance in which they unexpectedly found benzene, a carcinogenic hydrocarbon, in an off-spec water-based paint product sold as a dust suppressant. The compound was detected in tests performed on the dust suppressant prior to application. However, testing of the dust suppressants prior to application is expensive and not a common practice.
Dust suppressants can potentially affect the environment beyond the application site. Overspray during application affects land, plants and fauna adjacent to the site. In addition, dust suppressants can be trans- ported onto adjacent lands by surface flow or air. Material can be spilled from application trucks during transport to or from the application site, and commonly during off- loading from tankers to distributor trucks. It is a concern that trucks applying suppressants to roads have been observed to continue spraying when they cross bridges, resulting in dust suppressants being sprayed directly into streams below.
After the application of the dust suppressants it must be borne in mind that suppressants attached to soil particles covered with dust suppressants can be transported due to wind or erosion to off-site
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areas. In Pennsylvania it has been observed that a farmer’s machinery kept under an open-sided shelter was completely rusted from salts carried on the dust from a nearby brine application demonstration.
Humans who are on the site during application (e.g., applicators) or after application could also come in direct contact with the dust suppressant. Road applications bear the additional exposure of suppressant product becoming embedded under the skin of errant runners or cyclers. In addition, there is the potential for deleterious effects of pumping water from remote streams to construction sites for dust control. One instance was reported in Pennsylvania where the contractor pumped a stream dry.
Dust suppressants may cause undesired dissolution of some soil constituents. In the simplest case, even water used as a suppressant may cause chemical dissolution of compounds bound to soil particles. In soils from arid regions, which have high salt con- tent, water used as a suppressant can mobilize the salts, increasing the salt concentration in nearby waterbodies or groundwater. In more complex scenarios, the chemical constituents of the suppressant can react with and leach toxic components out of the soils at the application site. The issue of leaching is particularly relevant where dust suppressants are used on coal- fields, landfills, and mine tailings piles, which may contain hazardous material.
The constituents of the suppressants may be taken up by plant roots and systemically affect plants. In addition, soil microorganisms may biotransform the suppressants into benign or more toxic compounds depending on the environmental conditions on the site of application.
The application of dust suppressants will have secondary effects on the characteristics of soils to which suppressants are applied including a decrease of surface permeability. Depending on precipitation, the change in surface permeability can lead to
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increased runoff from the site to adjacent sites and decreased soil moisture. Changes in surface flow can then change patterns of erosion on and off the application site.
Dust suppressant use can affect air quality characteristics in a number of ways. In arid areas, for example, the use of water may add moisture to air fostering the proliferation of microorganisms. Dust suppressants that adhere to soil particles can be re-entrained into the air with strong winds, potentially adding contaminants to the air in addition to particulate matter. It is noteworthy that dust suppressants have little efficacy at suppressing small respirable dust that have the potential to be inhaled directly into lung parenchyma and cause lung disease (Reilly et al., 2003). Dust suppressants are generally used to comply with PM10 regulations and improve visibility; but could be potentially harmful since smaller dust particles (less than 10 µm) can be inhaled. Lastly, some dust suppressants may have volatile organic compounds in the products that may be dispersed into the air when the product is applied. This is a particular concern in the formation of ozone.
Dust suppressant application is not limited to the soils on the site. Since dust suppressants are generally applied over the surface, any vegetation or fauna on the site, including soil microorganisms, may also come into direct contact with the suppressant. Application of dust suppressants, especially magnesium chloride, has been associated with the browning of trees along roadways and stunted vegetation growth in forestlands. Effects vary, because different plants have different tolerances.
Aquatic ecosystems are affected by direct contamination from spills or runoff from off- site applications of dust suppressants. Fish may be affected by direct ingestion of toxic constituents or their degradation products. They are also sensitive to increased salinity resulting from salts and brine applications.
Dust suppressants that result in an increase in biochemical oxygen demand (BOD) can result in decreased DO concentrations in nearby streams, which may affect fish health and survival. Dust suppressants that affect macroinvertebrates could cause a decrease in food supplies for fish. Dust suppressants that result in increased suspended solids concentration, either directly or indirectly, via erosion, can potentially degrade aquatic habitat. At the micro level, suppressants can potentially be toxic to soil and water micro- organisms.
There is a chance that reproductive effects for fauna could also be found in these areas. An example of adverse impact of dust suppressants in animals relates to using finely chopped asphalt in feedlots to suppress dust. With time, the animals started having convulsions and high levels of lead were found in their blood. When the animals were moved to another feedlot, the symptoms were reduced.
Dust suppressant use can potentially affect both surface and groundwater. Spills directly affect surface water and can impact ground- water depending on site characteristics. Dust suppressants that are water-soluble can be transported into surface waters and materials that are water-soluble but do not bind tenaciously to soil can enter the ground- water. If the soil surface is not bound together well (i.e., chlorides, lignin) or if the rain event is extreme, dust suppressant treated soil particles can be carried by over- land flow into streams, rivers, and ditches. Sedimentation and uptake of soil particles could adversely affect aquatic or marine life, if sufficient numbers of treated particles have significant and mobile concentrations of hazardous compounds. Settled particles can also change the composition of the ecological community and the dominant species (Sanders et al., 2003).
To further engage the experts and to work through the scientific and policy issues associated with dust suppressant use, the experts were posed the above question and asked to respond individually. Following is a compilation of the responses.
Primarily, materials that fail existing regulatory thresholds for toxicity and those containing FIFRA (Federal Insecticide, Fungicide, and Rodenticide Act), TSCA (Toxic Substance Control Act), and RCRA (Resource Conservation and Recovery act) regulated compounds should not be used as dust suppressants. Chlorinated compounds and materials containing any paints should be carefully evaluated if used in a dust suppressant. Food products (e.g. soy oil, molasses) could be used, when possible, for they are likely to contain less toxic com- pounds than the industrial materials and waste products currently used as dust suppressants. Natural products are likely to biodegrade in the environment and therefore toxic effects are expected to be minimal. However, the make up of these products needs to be considered since some bio- degradable products can be toxic before degradation occurs.
Application of all types of chemical dust suppressants should not be ruled out or permitted under all conditions. Instead, guidelines should be drafted to indicate where specific dust suppressants should be applied. Application of chemical dust suppressants should be avoided near sensitive environments, near water bodies and fractur- ed rock, in areas with a shallow groundwater table, and other areas where water could quickly reach the saturated zone. Site- specific characteristics should be considered when approving the use of dust suppressants. All of these recommendations would require the screening of suppressants via a certification program, and a proper monitoring program of product make up over time. This would eliminate suppressants that do not meet expected standards. Alternatively, the number of dust suppressants to be
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applied could be limited to specific types; that would facilitate regulation and monitoring of the environmental impacts.
The public perception of toxicity may be an important component of the acceptance of dust suppressants as a dust abatement technology notwithstanding the actual threat the suppressant may pose. Factors such as the smell and the visual impact of dust suppressants should be considered. Finally, information on environmental impacts and effectiveness of dust suppressants should be used together when determining the type of suppressant to be used. If only environ- mental concerns are used as guidance to select dust suppressants, one could end-up with the most environmentally friendly suppressants instead of the best suppressant for the application with the least potential environmental risks. Before adopting new regulations, the advantages (e.g., improved air quality) and disadvantages (e.g., contaminated soils) associated with dust suppressant should be considered in risk management analysis.
The Expert Panel was also presented with the above question on what would constitute a concern for them. The following items would cause the experts to limit the use of dust suppressants:
To further probe into the current practices used for dust suppressant selections, several agencies and dust suppressant applicators were asked what characteristics in a dust suppressant they felt were important when deciding on the use for a particular situation, and what other factors influence their decisions. The main considerations include:
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Framework for Assessing Potential Environmental Effects
To make decisions about dust suppressant use, managers must evaluate the potential level of concern that use will generate. The level of concern about a given dust suppressant depends on a number of site-, use-, and composition-specific factors. These factors are highly variable and information about many of them is uncertain. The diagram shown in Figure 4-1 presents a framework for assessing the level of concern about the use of a particular dust suppressant. This is not meant to be a comprehensive decision-tree model. Instead, it outlines it identifies the type of information
Figure 4-1: Framework for assessing the potential environmental impacts of dust suppressants.
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To determine the level of concern about a given use, both the effects of exposure of the suppressant on a range of ecosystem com- ponents and the significance of those effects must be considered. If a suppressant applied to a given site were carried off the site and into an adjacent stream, for example, the level of concern would depend on the effect of that suppressant on the aquatic ecosystem – an algal bloom caused by an input of phosphorus, for example – and the significance of that effect. The same effect could be critical in one system and insignificant in another. An algal bloom might be unacceptable in a water body used for swimming but unremarkable in a wastewater treatment plant outfall. The significance of the effect might also be determined by comparing the effect of use with the effect of not using the suppressant. Any decision to use or not use a suppressant should be based on an assessment of benefits and risks (Expert Panel, 2002).
The effects of dust suppressant exposure on and off the application site are a function of the site characteristics, amount of exposure the different ecosystem components receive, and climatic conditions at the site. Site characteristics such as topography, soil texture and chemistry, groundwater flow path, vegetation and wildlife types, and distribution set the parameters for environ- mental responses to dust suppressant exposure. A basic set of ecosystem com- ponents whose response to the dust suppressant should be evaluated, include air, soil, water, soil microbes, aquatic organisms, vegetation, fauna, and people (Expert Panel, 2002). Different categories might be more or less important at different sites. One site may contain species sensitive to a particular compound while another may not. Site characteristics can also affect the ecosystem response to a suppressant. Alkaline soils may buffer acidic constituents of a suppressant. Dense vegetation may take up excess nutrients in organic suppressants. Soil microbes may break down potentially toxic suppressant constituents. Climatic conditions at the site, including the precipitation regime, wind exposure, and temperature, also affect the
20
response of ecosystem components to the suppressants. Dust suppressant constituents might react differently under different moisture and temperature conditions, for example. The degradation rates of some constituents of dust suppressants may vary with exposure to ultraviolet radiation. The ecosystem response also depends on the amount of exposure to a given suppressant constituent received by the ecosystem component. The response of any given eco- system component may be non-linear, or involve thresholds.
The amount of exposure received by a given ecosystem component to a given suppressant constituent depends on the rate at which it is applied to the site (loading rate) and the transport of constituents to each ecosystem component. The constituent loading rate depends on the rate at which the suppressant is applied, the type of constituents in the suppressant, and their concentration. Once the suppressant is applied to the site, its constituents may migrate within the site, from the soil surface to the sub-surface, for example, or to the groundwater or into the air. The pathways and rate at which any given constituent moves within the site or off the site are a function of the site characteristics, climatic conditions, and the characteristics of the constituents. The amount of precipitation a site receives affects the transport of water- soluble constituents, as do its topography, soil, and geologic characteristics. Some constituents are more mobile than others. They may be more soluble, or more likely to be volatilized. Depending on soil chemistry, some may be adsorbed to soil particles. Constituents may be transformed after application, reacting chemically with each other or with components at the site, or being degraded.
The rate of suppressant application depends on the purpose and method of application. The purpose of application – to stabilize disturbed vacant land or agricultural land or to reduce the dust generated from travel over unpaved roads, for example – together with specific site characteristics and climatic conditions, determine the amount and frequency at which the suppressant is applied. The purpose and site characteristics also influence the method of application. If the surface to be stabilized is not expected to be disturbed, the suppressant may be applied topically. If the surface must withstand vehicle traffic, the suppressant may be mixed into the soil by grading.
The type and concentration of constituents in the suppressant are a function of the type and source of the suppressant. Dust suppressants can be water, brines, lignin- sulfonates, petroleum-based products, or
other types, as discussed in Section 2.1. Dust suppressants may contain components other than the primary suppressant, depending on the source of the suppressant (Expert Panel, 2002). Most suppressants are derived from waste materials from manufacturing processes. Even the source water (e.g., reclaimed water, groundwater) may contain additional constituents. The com- position of the suppressant, together with the rate of application determines the amount (mass) of each constituent applied to the site.
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Path Forward – Issues and Potential Solutions
There are a significant number of “data gaps” that need to be filled to more adequately address environmental and regulatory issues (Expert Panel, 2002). Research questions range from “What is the national scale of the problem?”; “How much is being applied and where?”; “What tests should one run to determine the chemicals leached into soil and the biological impacts of dust suppressants after they are applied?” These types of questions must be answered before a decision can be made about whether or not more federal regulation is needed. This section focuses on the scientific and regulatory issues, and then provides suggestions for a path forward.
As noted earlier, there is no standard definition of a dust suppressant. Current usage of the term “dust suppressant” implies that it can be any chemical formulation applied to the ground to control emission of dust. Furthermore, the term “effective” dust suppressant is not well defined. Currently, the definition of an effective dust suppressant focuses on the ability (efficiency) of the product to suppress particulate matter from becoming air borne over a period of time (Expert Panel, 2002). To support this, Indus- try has developed data on the performance of dust suppressants on various types of land surfaces (see Literature Review in Appendix A).
A more comprehensive definition of an effective dust suppressant is needed to consider the overall impacts of using the products. A comprehensive definition of an
“effective” dust suppressant might consider the following (Expert Panel, 2002):
In making the determination of what dust suppressant to use, it is also important to select the proper dust suppressant based on soil characteristics. Soil characterization tests are not always performed on sites when selecting a dust suppressant; however, several experts were asked what tests they would recommend. Recommendations in- cluded gradation tests (AASHTO T-11 and T-27), plasticity tests (AASHTO T-89 and T- 90), pH tests of the soil, tests for the ability of soil to attract of bind a particular dust suppressant, particle size distribution, moisture content, and a visual survey of the site (Expert Panel, 2002). A thorough description of soils tests necessary to determine the optimum product performance has been prepared by the US EPA ETV Generic Verification Protocol for Dust Suppression and Soil Stabilization Products.
To properly evaluate the impacts of dust suppressants one must understand the characteristics of dust. One key factor is the size of the particle matter. Airborne particle size fractions are classified as either Particulate Matter (PM) 2.5 or PM10, based on their aerodynamic diameter, when they are regulated under the Clean Air Act. Airborne fugitive dust entrained from road surfaces
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and wind-eroded from construction sites, agricultural fields and vacant lands span a physical size range from less than 1 micron to about 100 microns; this range includes (and exceeds, on the large end) the PM2.5 and PM10 size fractions. There is a need for proper characterization of particle size distribution and mineralogy related to variables such as vehicle tire loading and speeds on unpaved roads in different regions (Expert Panel, 2002). As noted earlier, the smaller PM2.5 particles may be more harmful from a human health perspective if inhaled.
The soil surface chemistry, moisture content, and shapes of dust particles can affect the ability of different suppressant formulations to adhere to the particles. The particle size, shape, surface chemistry, and soil moisture content are seldom used to assist in the selection of an appropriate suppressant. In some cases, the soil silt content (given as percent passing a #200 screen) and moisture content may be obtained prior to dust suppressant application. Many of the standard soil characterization tests are time- consuming and not well suited to the daily exigencies of field operations. Development of simple, robust field apparatus and rapid methods for characterization of relevant soil properties could assist in the selection of the right type of suppressant and the appropriate application rate for a particular region.
The fundamental mechanisms of how the dust suppressants work, break down, de- grade, and move in the environment are not well understood at this time. “Degradation” includes effects of solar radiation, abiotic oxidation, biological transformations, dissolution, and physical weathering. In addition, the soils characteristics will influence how the suppressants are degraded (Expert Panel, 2002). Mechanisms of how dust suppressants work are well established and based on research and industry development. However, it is not known what happens to the products after they are applied and weathering occurs. What daughter
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products are produced as dust suppressants break down? Are they benign or toxic, mobile or immobile? Answers to these questions can only be obtained from long-term testing of dust suppressants under field conditions.
Preliminary data was provided in Section 2.3 on the current and potential uses of dust suppressants; however, this issue should be further explored. If national regulations/ guidelines are considered for the use of dust suppressants, then there needs to be a better understanding of the scale of current and potential usage of dust suppressants. Answers to the following questions are needed:
A major concern is the current lack of information on the chemical composition of dust suppressants. Material Safety Data Sheets (MSDS’s) are commonly provided for dust suppressant products; however, since proprietary information may be involved, MSDS’s do not necessarily provide information about all the chemicals present in the products. Major manufacturers (e.g., Mid- west Industrial Supply and Pennzoil Products) will provide results of environ- mental tests if the customer asks for the information, or post the information on the Internet (Expert Panel, 2002). Manufacturers’ environmental testing data, while
valuable, is currently not standardized. As an example, several vendors provide reports containing bioassay data, but it is sometimes difficult to compare results among different products because different test species (e.g. fathead minnows or water fleas) and different test protocols may be used.
Chemical properties, particularly toxic contaminants, can vary significantly depending on the product. Constituents can also vary from batch to batch (Expert Panel, 2002). The environmental impacts of dust suppressants cannot be adequately identified until concentration ranges for major and trace chemical constituents are known for the most common products. Most experts in soil science, ecology, and biology can estimate potential environmental impacts in their field of expertise if they know the chemical com- position of the product and the site-specific conditions (Expert Panel, 2002). However, that information is not fully available.
There is also a concern regarding the sources of the products used in the dust suppressants. Although some manufacturers formulate suppressants from virgin materials, a majority of commercial products are reformulated by-products or brines from industries that would otherwise dispose of these materials as wastes. Several examples of waste products reformulated as dust suppressants include lignin sulfonates and magnesium chloride brines. In effect, un- paved roads have become disposal system for these by-products that are reformulated and used as dust suppressants. The chemical composition of broad categories of by- products, such as lignin sulfonates, oils, and brines will depend on the original source of the by-products and also on the chemical processes that generated them. For example, the waste oils originating from California crude oils may contain more metals than waste oils originating from Pennsylvania crudes (Expert Panel, 2002). Used oils and solvents may have even higher toxic concentrations.
It is also noteworthy that the use of toxic by- products in dust suppressants is a recycling process. The recycling of non-hazardous
waste products into dust suppressants reduces the cost of the dust suppressant and eliminates the need for disposal in landfills. Depending on the by-product, recycling and reuse into dust suppressants may be the best way to dispose of some non-hazardous wastes (Expert Panel, 2002). For example, some mulch-type suppressants are formulated with non-hazardous wood fiber or paper pulp, and large volume use of mulch- type suppressants can significantly reduce the volume of waste pulp that must either be landfilled or incinerated.
The sources of the water used for dust suppressants should also be considered in assessing the potential impacts. The majority of suppressants require dilution and typically applicators will use the water that is most readily available. Tap water, untreated surface or ground water or reclaimed municipal or industrial wastewater could all be used. Reclaimed wastewater may have higher levels of nutrients and pathogens than ordinary tap water or some surface or groundwaters. In some areas, contaminated groundwater could inadvertently be used for mixing of the dust suppressants (Expert Panel, 2002). Minimum quality standards for water used directly as a dust suppressant or as a dilution product should be established to prevent inadvertent contamination of lands treated with dust suppressants.
There is a need for more information about the chemicals and formulations used in dust suppressants (Expert Panel, 2002). Regulators, applicators, and the public don’t have easy access to information that would help them to decide which dust suppressant types are safe and effective for specific applications. An easily-accessible information center, a “clearinghouse”, could help applicators, regulators, and the public acquire the information needed to make good dust control decisions. The recommended form of this clearinghouse is as a World Wide Web site. EPA maintains several web sites that could serve as models for a dust suppressant clearinghouse. An example is the
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CHIEF bulletin board that serves the needs of state and local air quality regulators. The clearinghouse could be maintained by EPA or by another public agency or university. Content categories for this clearinghouse could include (Expert Panel, 2002):
Complete disclosure by dust suppressant manufacturers, formulators, and vendors would be needed in order to address all the items shown above. Some manufacturers, formulators, and vendors might be reluctant to release exact formulation information, since they could consider the information to be proprietary. The model for disclosure of pesticide formulations, where only “active” ingredients are specifically listed, might prove useful. However, in the case of dust suppressants the definition of an “active” ingredient should include both those constituents that control dust and any other trace constituent, which when applied to the land surface at the intended application rate, has the potential for environmental impact. How- ever, the lack of complete cooperation from vendors should not delay the creation of the clearinghouse.
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When making the determination on which dust suppressant should be used, a robust risk assessment framework is needed along with the identification of which test should be performed. In Section 4, a framework was provided that outlines the considerations that one might use to make an assessment. There are several detailed risk assessment frameworks available to the industry that could be used as models.
Unfortunately, these frameworks for risk assessment were developed for cases where contamination had already occurred. One proprietary general guideline exists for evaluating potential environmental impacts of release of chemicals to the environment (see Rohm and Haas Consumer and Industrial Specialties’ Risk Assessment Flow Chart for Safe Product Use, available at http://www.rohmhaas.com/rhcis/environmen- tal/safeproduct.html).
There are no relevant guidelines available for minimizing environmental and human health risk from intentional application of dust suppressants to roads construction sites, agricultural fields, and vacant lands. Guidelines do exist for:
However, in both of these cases, the active ingredients are well known and impacts have been fairly well studied. The situation with dust suppressants is much more ambiguous, as in many cases, data about their chemical composition and biological impacts are lacking.
It is recommended that tests performed, as part of a risk assessment for dust suppressants should focus on the constituents in the dust suppressant concentrate, in runoff, and
in the soil after application. It is very likely that no dust suppressants will be free of every potential harmful chemical; however, it is important that guidance documents and initial recommended threshold levels be developed to reduce risk. Relevant EPA methods, compiled from both Expert Panel recommendations and from the literature review, are summarized in Table 5-1. These tests could be applied to the raw product, the collected runoff, and/or the soils.
Table 5-1: Relevant EPA and Standard test to be considered in assessing impacts of dust suppressants.
| Analytical Method | EPA/ASTM Number | |
| Organic | Volatile organic compounds | 8260B |
| Semi-volatile organic compounds | 8270D | |
| Pesticides and herbicides | 8270D | |
| Chlorinated hydrocarbons | 8121 | |
| Petroleum hydrocarbons | 8440 | |
| PAHs | Tentatively identified compounds (TIC) | |
| Inorganics/Metals | Inductively Coupled Plasma-Atomic Emission Spectrometry | 6010B |
| Toxicity | Terrestrial bird toxicity | 850.2200 |
| Insect toxicity | 850.3020 | |
| Vegetation toxicity | 850.4000 | |
| Algal Toxicity | 850.4400 | |
| Acute to fishes and microinvertebrates | ASTM E-1192-88 | |
| Marine and Estuary organisms | EPA/600/4-85-013 and EPA 600/4-87-028 | |
| Chronic to fishes and microinvertebrates | EPA/600/4-89-001 | |
| Dredge material chemical and biological evaluation | U.S. Corps. Engr. Rep-D90 | |
| Bioconcentration | ASTM E-1022-84 | |
| Biodegradability | Soluble Chemical Oxygen Demand | 410.4 |
| Biochemical Oxygen Demand | 405.1 |
As part of an initial risk assessment for this report, a proposed standardized methodology for estimating soil mass fractions of dust suppressant constituents is shown below in Tables 5-2 and 5-3. The worksheets use known information about a dust suppressant constituent concentration, the application
rate, the soil penetration, and soil density to estimate a dust suppressant constituent concentration in soil. Table 5-2 is provided as a blank worksheet for vendors, applicators, regulators, and investigators to use in their risk assessments. Table 5-3 shows an example calculation for a constituent present at a 50 mg/L in a dust suppressant concentrate.
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Table 5-2: Blank Worksheet A – Estimation of soil mass fraction from suppressant constituent concentration.
Blank Worksheet A: Calculation of constituent concentration in soil
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Table 5-3: Example calculation using Worksheet A. Soil mass fraction resulting from application of dust suppressant with constituent concentration of 50 mg/L. Assumes 1,600 kg/m3 soil bulk density, 0.45 inch (1.14 cm) suppressant penetration into soil, 2 suppressant applications at 0.50 gallon/yd2, no runoff of liquid suppressant, and mixing of 1 volume of suppressant concentrate with 1 volume of water.
Worksheet A Example 1: Estimation of constituent soil mass fraction based on constituent concentration in suppressant as supplied (concentrate)
Environmental regulations establish action levels for contaminants or contaminant classes in soils. Remediation is usually required if values above these levels are recorded for
a contaminated site. Tables 5-4, 5-5, and 5-6 show a proposed calculation methodology for using an action level in soil to estimate the maximum allowable constituent concen-
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tration in a formulated dust suppressant concentrate. Table 5-4 is provided as a blank worksheet for interested parties to use in risk assessments involving suppressants. Table 5-5 shows a sample calculation for a RCRA-based action level of 100 ppm for total petroleum hydrocarbons (TPH). Table 5-6 shows a sample calculation for a CERCLA-based action level of 1 ppb for tetrachloro-dibenzodioxin (TCDD). The final result computed at the bottom of Tables 5-5 and 5-6 should not be considered as a fixed “not to exceed” value for TPH or TCDD, as teh numerical result depends on dust suppressant liquid application rate, penetration depth into the soil, fraction suppressant retained on the target surface, suppressant dilution, and soil bulk density. However, the results are instructive, and the accompanying blank worksheet (Table 5-4) could be used with site-specific data to compute maximum allowable constituent (or contaminant) concentrations for other combinations of site conditions, suppressant dilutions, and application rates.
Table 5-4: Blank Worksheet B – Estimation of maximum allowable dust suppressant constituent concentration from risk-based limit in soil.
Blank Worksheet B: Calculation of maximum suppressant contaminant concentration based on maximum allowed soil contaminant mass fraction
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Table 5-5: Example calculation of maximum allowable suppressant concentration based on RCRA 100 ppm action level for Total Petroleum Hydrocarbons (TPH) in soil as determined using EPA Method 8015. Assumes 1,600 kg/m3 soil bulk density, 0.45 inch (1.14 cm) suppressant penetration into soil, 2 suppressant applications at
0.50 gallon/yd2, no runoff of liquid suppressant, and mixing of 1 volume of suppressant concentrate with 1 volume of water.
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Table 5-6: Example calculation of maximum allowable suppressant concentration based on CERCLA 1 ppb action level for TCDD. Assumes 1,600 kg/m3 soil bulk density, 0.45 inch (1.14 cm) suppressant penetration into soil, 2 suppressant applications at
0.50 gallon/yd2, no runoff of liquid suppressant, and application of undiluted suppressant to land surface.
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At present, few specific regulations for dust suppressants exist. Decision-makers currently rely on emerging voluntary certification programs (Section 2.7), and a limited number of state and local guidelines to screen the different types of dust suppressants for a variety of application scenarios. Current state, local, and national guidelines are not uniform. While current voluntary certification programs have merit, they need to be expanded to incorporate a majority of dust suppressants in commerce. Dust suppressants should be evaluated not only for their effectiveness in suppressing dust but also for their potential toxicological and environmental effects.
Regulations to support existing environ- mental laws (e.g., RCRA, CERCLA/SARA guidelines, as were used to clean up the Superfund site at Times Beach) may apply at some point after a dust suppressant has been applied. However, existing regulations are not applicable to the production and application of dust suppressant. RCRA rules were not written with dust suppressants in mind. Although they allow for waste ex- changes and other waste reprocessing steps, their principal intent is to regulate the treatment, storage, and disposal of municipal and hazardous wastes. CERCLA/SARA rules are intended to finance and guide the clean up of contaminated sites. In contrast, the major regulatory need for dust suppressants is to develop guidelines that will prevent the creation of hazardous waste sites from the inappropriate use of dust suppressants. The Toxic Substance Control Act (TOSCA) is intended to regulate hazardous substances prior to them becoming hazardous waste.
Is the current regulatory environment for dust suppressants adequate to ensure that the risks have been considered and their use is acceptable? It was the opinion of the Expert
Panel that it is not adequate. The Expert Panel generally agreed that more research is needed to answer questions about the potential environmental impacts of dust suppressants, but also agreed that development of regulations should not wait for all the science to be completed (Expert Panel, 2002).
A complication in developing new regulations is that the composition of dust suppressants may not be adequately known and com- ponents or byproducts of the suppressants may have potentially harmful environmental impacts. Although existing regulations are not intended to regulate the flows of Indus- trial wastes into the formulation of dust suppressants and thence to the environment, the existing regulations do contain limits on contaminant concentrations in soil that could be used as a starting point for regulations and guidelines for dust suppressants. For instance, a similar approach may be considered as that for the land application sludges. The regulations currently in place for the land application of sewage sludge and wastewater on agricultural fields limits the loading rate of metals based on land use.
The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), Resource Conservation Recovery Act (RCRA), Comprehensive Environmental Response Compensation and Liability Act (CERCLA), Superfund Amendments and Reauthorization Act (SARA), Ecological Soil Screening Level (Eco-SSL) guidance with supporting regulations and guidelines collectively restrict the environ- mental concentrations of hundreds or thousands of chemicals. Many of these programs are good models for identifying potential problems; however, they need to be followed up with site-specific studies. It is recommended that:
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products in water should be compared against action levels used in the Clean Water Act and Safe Drinking Water Act since dust suppressants could eventually be transported into surface and ground waters. Any dust suppressant compound that could reasonably be expected to exceed existing regulatory-based action levels or thresholds would need to be examined in detail to determine whether additional regulatory controls were need- ed to prevent unreasonable risks to human health and the environment.
Regarding regulating dust suppressant application practices, some guidance might be found in U.S. Department of Agriculture (USDA) regulations that control the application of chemical fertilizers and also in regulations that control the application of pesticides under FIFRA. As noted earlier, there are also state programs being developed. These state programs may be the most appropriate since they can better address regional issues related to dust suppressant use than a “one size fits all” federal program.
New regulations must be developed to deal with the variety of compounds, application scenarios, and potential receptors that are involved with the growing use of dust suppressants. A variety of potential regulatory approaches specifically focused on dust suppressants exist, ranging from extending the current patchwork approach of local and state regulations to development of a com- prehensive national program enforcement of which would likely be delegated to the states. An alternative to a comprehensive national program might be a basic national program that specifically makes dust suppressant products subject to other existing regulatory thresholds for toxicity and requires some type of testing and/or certification to validate that these limits are met. States could be encouraged to develop a more comprehensive regulatory program for dust suppressant products and their use based on regional topography, hydrology, soil types, ecosystems, and material availability.
The range of regulatory topics could include:
An effort to limit and specify which dust suppressants could be applied for dust control would be challenging because of the broad variety of products used as dust suppressants, their complex chemistry, and the increasing number of products and industrial by-products regularly introduced to the market. However, limiting the types of dust suppressants allowed for use would make enforcement of environmental regulations much simpler (Expert Panel, 2002). A regulatory-derived list of acceptable dust suppressants would bar access of several vendors to the market and would not be well received. In addition, there was concern that such an approach would discourage the development of more effective and more environmentally benign suppressants (Ex- pert Panel, 2002).
Regulating dust suppressant application lo- cations and application practices, rather than the types and number of suppressants, would allow for the varying sensitivities of different ecosystems to different dust suppressant formulations (See framework proposed in Section 4). For example, a dust suppressant with relatively insignificant im- pacts in one area (an arid flatland system with no perennial surface water flows and deep groundwater) might have significant impacts in another area (a humid mountainous system with significant perennial surface water flows and shallow ground- water). In the flat arid land case, the suppressant is likely to stay put in the soil for a long time, with minimal aquatic impacts. In the mountainous humid case, significant portions of the suppressant may rapidly reach surface and ground waters and could have significant aquatic impact.
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Also, application rates and practices are important since dust suppressants with seemingly benign characteristics when applied at a rate of 1,000 mg/kg soil might produce significant impacts on the environment or human health if it is applied at 10 times the rate (10,000 mg/kg soil) or if the surrounding environment and individuals are particularly sensitive. High soil mass fractions could inadvertently develop if there is significant overspray onto previously treated surfaces during application.
The effectiveness of a suppressant should be considered in any evaluation of the application and potential impacts of dust suppressants. A short-lived, easily wea- thered dust suppressant requiring frequent re-application could have more significant environmental impacts than a long-lived, weather-resistant suppressant, when both contain the same concentration of a mobile trace contaminant. Frequent reapplication of the easily weathered suppressant would produce higher soil and aquatic concen- trations of the trace contaminant than infrequent applications of the weather- resistant suppressant. If effectiveness is not considered, decision-makers might choose the “most environmentally friendly suppres- sant” rather than select a more effective dust suppressant that is just as environmentally benign for one application and more benign over the long term (Expert Panel, 2002).
The evaluation and/or certification of specific dust suppressants should not be a one-time process, but should instead be subject to periodic renewal. Waste products that are recycled into dust suppressants can vary in composition through time, and this variability must be considered in any comparison of a dust suppressant batch to a fixed set of environmental criteria. Out-of-specification products should not be considered bad, but they should be scrutinized (Expert Panel, 2002).
If additional regulations are developed for dust suppressants, certain criteria should be met (Expert Panel, 2002):
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Among the questions that applicators and regulators would need answered in order to establish a list of prohibited categories of dust suppressants are (Expert Panel, 2002):
Additional Recommendations by the Expert Panel included the following:
environmental impacts of suppressants. Manufacturers should transparently and completely report the chemical compo- sitions of their dust suppressant formulations. (Expert Panel, 2002). Re- gulations requiring more information on an MSDS should be considered.
While current certification and testing proto- cols focus on evaluating the effectiveness of a dust suppressant, more needs to be done to assess potential adverse impacts from dust suppressants and to estimate risks. Regulatory efforts should be focused first on those compounds and applications that pose the greatest risks to human health and the environment.
A risk assessment model combined with a transport and fate model is required to eval- uate potential exposures and adverse risks. For the decision-maker or regulator, a decision-making model or expert system to assist in making site-specific decisions would be of value. Without these models or tools, a decision-maker could either make decisions or develop regulations that are very conser- vative in the use of dust suppressants. Excessively conservative regulation may not maximize the benefits to be gained from
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using dust suppressant products and could be challenged in the courts. Conversely, the decision-maker could allow widespread use of dust suppressants with the potential for unintended consequences. Sufficient infor- mation already exists to make a start at preventing either of the above two scenarios. After 25 years of environmental remediation efforts, risk-based concentration limits have been established for a number of com- pounds and compound classes. Additionally, risk assessment frameworks, such as ATSM’s RBCA guidelines, may prove instructive.
An example of this approach would be a risk- benefit analysis to determine how much PM10, and PM2.5 dust is suppressed with each suppressant. Information that would be needed include the potential environmental impacts, the costs associated with the using or not using dust suppressants, the potential environmental benefits associated using dust suppressants. There also needs to be a consideration that many regions are rapidly moving toward a PM2.5 standard and away from a PM10 standard. This is due to the emerging cancer issues and cardiopul- monary disease. However, tighter standards will raise the quality of the environment and the cost associated with that environment.
The additional environmental regulations that have been developed since the 1970’s when the Times Beach situation occurred have reduced the chances that dioxin-contamin- ated waste oil be used as dust suppressants. However, dust suppressants are not speci- fically regulated under any major federal legislation and there is still significant poten- tial for other environmentally hazardous materials to be used.
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Fact Sheets for Verification Programs and Guidelines
Organizing Committee and Expert Panel
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