EPA/600/R-20/811 March 2020 | www.epa.gov
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United States
Environmental Protection
Agency
Final Report:
Evaluation of the
Potential Toxicity
of Dust Palliatives
Used in Alaska
U.S. EPA Region 10 Air and Radiation
Division Tribal Air Program
and
U.S. EPA Office of Research and
Development
Center for Environmental Measurement
& Modeling
Watershed & Ecosystem
Characterization Division
Multimedia Methods Branch
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Final Report: Evaluation of the Potential
Toxicity of Dust Palliatives Used in
Alaska
EPA Contract: EP-C-17-017
Task Order: 68HERC19F0094
September 3, 2019
Submitted to:
U.S. EPA Region 10
Air and Radiation Division
Tribal Air Program
and
U.S. EPA
Office of Research and Development
Center for Environmental Measurement & Modeling
Watershed & Ecosystem Characterization Division
Multimedia Methods Branch
ine umtea urates tnvironmeniai protection Agency (u.b. lfa). tnrougn its uttice ot Kcsearcn ana Development
(ORD), funded and managed the research described here in under contract EP-C-17-017 to Eastern Research Group. This
document has been reviewed by the U.S. EPA, ORD, and approved for publication. Mention of trade names and
commercial products does not constitute endorsement or recommendation for use.
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Section 1-Summery
Table of Contents
1. Introduction 1-1
2. Background 2-1
2.1. Overview of Issues 2-1
2.2. Research Goal of Project 2-1
2.3. Project Objectives 2-2
2.4. Research Questions 2-2
3. Targeted Literature Review 3-3
3.1. Approach 3-3
3.1.1. Primary Documentation Search 3-6
3.1.2. Consultation with Palliative Manufacturers and a Subject Matter Expert 3-9
3.2. Findings 3-9
3.2.1. Palliative Toxicity 3-9
3.2.2. Chemical Make-up of Palliatives 3-11
3.2.3. Newer Regulations or Advisories Applicable to Palliative Use and Exposure 3-11
3.2.4. Frequency of Specific Palliative Use in Alaska 3-11
3.3. Data Gaps/Research Needs 3-11
4. Selection of Three Palliatives for the Computational Evaluation of Toxicity 4-12
4.1. Approach 4-12
4.1.1. Products with the Least Available Toxicity Data 4-12
4.1.2. Products with the Most Available Toxicity Data 4-12
4.1.3. Frequency of Palliative Use in Alaska 4-12
4.1.4. Input from Subject Matter Experts 4-13
4.2. Findings 4-13
4.3. Data Gaps 4-14
5. Computational Evaluation of Potential Palliative Toxicity 5-15
5.1. Approach 5-15
5.2. Findings 5-16
5.2.1. Step 1: Compare Ecological Toxicity Using Available Data 5-16
5.2.2. Step 2: Compare Ecological Toxicity of Palliatives (LC50s) to Familiar Household Products 5-20
5.2.3. Step 3: Extrapolate Ecological Toxicity Data (LC50s) to Mammalian Toxicity (LD50s) 5-20
5.2.4. Step 4: Compare Mammalian Toxicity Data (LD50s) to Common Household Products 5-24
5.2.5. Step 5: Extrapolate Mammalian Toxicity (LD50s) to HEDs 5-25
5.2.6. Step 6: Present the Toxicity of Palliatives Using Established Toxicity Scales 5-25
5.2.7. Computational Evaluation Conclusions 5-26
5.3. Data Gaps/Research Needs 5-28
6. References 6-30
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Section 1-Summery
Report Figures and Tables
Figure 1. Process to Collect and Document Information on Palliatives Used in Alaska 3-7
Figure 2. Main Objectives for the Computational Evaluation of Potential Toxicity 5-15
Figure 3. Comparison of Palliative Ecotoxicity to EPA's Ecotoxicity Scale for Aquatic Organisms 5-19
Figure 4. Regression Based on Data from Zolotarev et al. (2017) 5-22
Figure 5. Regression Based on Data from Hodson (1985) 5-23
Figure 6. Hodge and Sterner Toxicity Scale: LD50s (in mg/kg) for Palliatives and Household Products 5-27
Table 1. Palliatives Used in Alaska and Included in the 2015 Literature Review: Product Names, Manufacturers,
Types, and Chemical Compositions 3-4
Table 2. Steps for Primary Documentation Search Using Online Data Sources 3-8
Table 3. Available Toxicity Data for the Subject Palliatives 3-10
Table 4. Toxicity of Durasoil, EK-35, and EnviroKleen 5-17
Table 5. Common Toxicity Measures for Durasoil, EK-35, and EnviroKleen 5-19
Table 6. LC50 Rainbow Trout Toxicity of Household Items 5-20
Table 7. Regressions for Fish LC50s and Rat LD50s 5-21
Table 8. Predicted Rat LD50s in mg/kg for the Three Palliatives 5-23
Table 9. Oral Rat LD50 Toxicity of Household Items 5-25
Table 10. Human Equivalent Doses in mg/kg 5-25
Table 11. Toxicity Classes of Predicted Palliative LD50s (mg/Kg), Using the Hodge and Sterner Scale 5-26
iii
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Section 1-Summery
1. Introduction
Eastern Research Groups, Inc. (ERG), a contractor to the U.S. Environmental Protection Agency (EPA), helped
EPA evaluate the potential toxicity of dust palliatives used in Alaska. This is a follow-on task to a research effort
that ERG assisted the Agency conduct in 2015 (see EPA, 2016 for more information). This current effort in 2019
involved a three-pronged approach, which included (1) performing a targeted literature review to obtain relevant
information published since the 2015 literature review effort related to this topic, (2) evaluating literature review
findings to identify three palliatives for a computational evaluation, and (3) conducting a computational evaluation
to assess the potential toxicity of the three selected palliatives.
1. The main focus of the literature review was to fill toxicity data and information gaps for 17 different
palliatives used in Alaska. The targeted literature review involved contacting subject matter experts and
palliative manufacturers, as well as researching published literature to find the following information on
palliatives: chemical make-up, relevant toxicity values, newer regulations or advisories, and frequency of
use in Alaska.
2. EPA conducted a detailed evaluation of information collected during the literature review process to
identify 3 of the 17 palliatives to investigate in the next step: the computational evaluation.
3. The computational evaluation of potential palliative toxicity focused on the three palliatives identified by
EPA. This part of the project involved a six-step process that aimed to put the limited available palliative
toxicity data into perspective for potential human exposures by comparing predicted mammalian toxicity of
the palliatives to common household products and established toxicity scales.
This report provides details on activities performed during the targeted literature review, the selection of three
palliatives for the toxicity evaluation, and the computational evaluation; summarized findings from each component
of the effort; and identified data gaps/research needs. This information is organized into five main sections:
"Background," "Targeted Literature Review," "Selection of Three Palliatives for the Computational Evaluation of
Toxicity," "Computational Evaluation of Potential Palliative Toxicity," and "References."
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Section 2-Background
2. Background
Unpaved road surfaces are commonplace in Alaska, where more than 50 percent of state-owned roads and the
majority of local and private roads are unpaved (UAF/AUTC, 2013). Various sources can cause releases of fugitive
dust, such as vehicles (e.g., all-terrain vehicles [ATVs]) traveling on unpaved road surfaces (e.g., dirt roads, gravel
roads, unpaved runways), and wind blowing across these surfaces and gravel pits (ADEC and EPA, 2018). Much of
the fugitive dust in Alaska comprises particulate matter that is less than 10 microns in size (PMio), which can lead to
adverse health effects in some exposed individuals (Withycombe and Dulla, 2006). Fugitive dust has other potential
negative impacts, such as impairing driver safety by reducing visibility and requiring costly and frequent road and
runway maintenance (UAF/AUTC, 2013).
Dust palliatives are products used worldwide to suppress fugitive dust. For several decades in the state of Alaska,
tribal, state, urban, and rural city governments have been applying palliatives to control and suppress dust on
unpaved road surfaces. Palliative use dates back to the 1960s with the application of salt-based palliatives, such as
calcium chloride and magnesium chloride (Connor, 2015). Due to availability, effectiveness, and cost, common
palliatives used in Alaska include water, salt-based palliatives, synthetic fluids, and polymers (Milne, 2015).
EPA (2016) documents all of the different types of palliatives used in Alaska as reported by the State of Alaska
Department of Transportation & Public Facilities (Alaska DOT&PF), locations in the state where application is
generally known to occur, and typical application methods (see Section 4.1 in EPA, 2016 for more information). In
2015, ERG assisted EPA by performing an extensive literature review to investigate dust palliatives used on road
surfaces in the state of Alaska, the fate and transport of these palliatives in the environment, the documented effects
to human health and the environment, and the applicable regulations associated with palliative use in Alaska. The
findings of that report are documented in EPA, 2016. The purpose of this report is to summarize the follow-on effort
performed in 2019.
2.1. Overview of Issues
The use of palliatives in the state of Alaska has raised various concerns, including the potential impacts on
traditional subsistence resources, possible effects on the environment, and unknown human health risks from
exposure.
Several rural communities have expressed concerns about palliatives through Alaska Department of Environmental
Conservation (ADEC) Rural Alaska Road Dust Surveys, which have been conducted periodically since 2007. Using
findings from these surveys, ADEC concluded that out of 142 participating communities, 90% reported that dust is a
problem in their communities. Approximately one-third (about 47) of the communities surveyed reported at least
some use of dust suppressants. In addition, over half of the responding communities (>71) were willing to try
chemical-based dust palliatives, but they expressed various concerns such as about their potential toxicity, effects on
human health, impacts on the environment, and possible effects on subsistence resources (ADEC and EPA, 2018).
Many data gaps and research needs were acknowledged during the last effort (EPA, 2016), such as no
documentation about specific impacts to humans or subsistence foods exposed to palliatives. While this previous
research did not locate documented information on possible impacts to subsistence resources, subject matter experts
referenced anecdotal information from local residents concerned about salt-based palliative components. For
instance, residents were concerned about calcium chloride negatively affecting the taste of subsistence berries and
fish (Connor, 2015b) and chloride salts without moisture breaking down into dust, becoming airborne, and then
landing on berries and fish left outside to dry (Hickman, 2015a).
Based on data gaps identified during the previous effort, EPA initiated this follow-on task in 2019, seeking to
determine the potential toxicity of palliatives commonly used in Alaska, which is of great concern to the Alaska
Native population.
2.2. Research Goal of Project
This follow-on project, similar to the previous 2015 effort, was created in direct response to questions received from
a number of Alaskan tribes and communities about the safety of dust suppressant products. The overarching goal is
2-1
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Section 2-Background
to evaluate existing knowledge and data gaps on the potential toxicity of palliatives used in Alaska as they relate to
possible exposures among the Alaska Native population. Evidence compiled for this project is intended to assist
EPA in communicating the relative toxicity of palliatives used in the state, particularly in the context of impacts on
subsistence resources and the potential risk to Alaska Natives. To achieve this overarching project goal, the data
compilation process focused on addressing the individual objectives stated in Section 2.3
2.3. Project Objectives
The defined objectives of this project include the following:
Conduct a targeted literature search to obtain relevant documentation published since the completion of the
2015 report and help populate toxicity data/information gaps for the 17 palliatives included in EPA's initial
Excel table.
Use data collected for the targeted literature search to identify three of some of the most common
palliatives used in Alaska for the computational evaluation.
Perform a computational evaluation of the potential toxicity and impacts on human health and the
environment associated with the three palliatives selected by EPA.
2.4. Research Questions
The overarching question EPA sought to answer was: What is the relative toxicity of some of the most commonly
used palliatives in Alaska? This project seeks to address the following specific questions:
What is the relative toxicity of palliatives for potentially exposed humans?
What are the potential health risks from exposure to palliatives?
Are existing regulations and advisories for all categories of palliatives adequate to protect Alaska Native
communities from harmful exposures?
Are existing regulations and advisories adequate to protect the environment (particularly subsistence
resources) and people exposed to these compounds daily?
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Section 3-Targeted Literature Review
3. Targeted Literature Review
This section will detail the approach, findings, and data gaps/research needs for the targeted literature review
conducted for this project.
3.1. Approach
The primary purpose of the targeted literature review was to obtain information on the chemical make-up, relevant
toxicity values (fish, mammal, plant, invertebrate), and frequency of use for the 17 palliatives identified in the
previous project (EPA, 2016) and presented in Table 1. In addition, any documentation was sought related to newer
regulations or advisories applicable to palliative use and exposure initiated since the 2015 literature search. This
initial toxicity information was used to help inform EPA's selection of the three palliatives to focus on in the
computational evaluation of toxicity (Section 5).
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Section 3-Targeted Literature Review
Table 1. Palliatives Used in Alaska and Included in the 2015 Literature Review: Product Names, Manufacturers, Types, and Chemical
Compositions
Product Name
Manufacturer
Type
Chemical Composition / CASRN
Alastac
Apun, LLC
Organic
nonpetroleum-based
(tall oil)
Lignosulfonate (CASRN 8062-15-5) (no percentage provided)
AlastaSeal
Apun, LLC
Organic
nonpetroleum-based
(tall oil)
Water (34.5-64.5%)
Proprietary pitch/rosin blend (30-60%, CASRN 8016-81-7)
Additives (5.5%)
DirtGlue
GeoCHEM
Polymer
Water (<52%)
Aqueous acrylate polymer (>45%, non-hazardous)
Additive (<3%, proprietary)
Aqueous ammonia (<1%)
Dowflake
Occidental Chemical
Corporation
Salt-based
Calcium chloride (83-87%, CASRN 10043-52-4)
Water (8-14%)
Potassium chloride (2-3%, CASRN 7447-40-7)
Sodium chloride (1-2%, CASRN 7647-14-5)
Durasoil
Soilworks
Synthetic liquid
Non-petroleum synthetic alkane fluid
A complex mixture of synthetic linear, branched and cyclic alkanes; "proprietary" component
% composition is a trade secret
Dustaway
Soilworks
Liquid
No hazardous ingredients at or above 1%
No applicable CASRN(s)
Dust-Off
Cargill
Salt-based
Water (63-70%)
Magnesium chloride (29-33%, CASRN 7786-30-3)
Magnesium sulfate (1-3.8%, CASRN 7487-88-9)
Proprietary corrosion inhibitor (0.02%)
Earth Armour
Midwest Industrial
Supply
Petroleum-based /
synthetic liquid
Severely hydrotreated paraffinic liquids (100% proprietary mixture)
EK-35
Midwest Industrial
Supply
Synthetic liquid
Tall-oil pitch (<60%, CASRN 8016-81-7)
Severely hydrotreated, high viscosity, synthetic isoalkane (>10%, CASRN 72623-86-0)
Alkyl polyamines (<4%, proprietary CASRN)
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Section 3-Targeted Literature Review
Table 1. Palliatives Used in Alaska and Included in the 2015 Literature Review: Product Names, Manufacturers, Types, and Chemical
Compositions
Product Name
Manufacturer
Type
Chemical Composition / CASRN
EnviroKleen
Midwest Industrial
Supply
Synthetic liquid
Polyolefin (<60%, CASRN 9003-27-4)
Severely hydrotreated, high viscosity, synthetic isoalkane (>10%, CASRN 72623-86-0)
Freedom Binder
400
Freedom Industries
Organic
nonpetroleum-based
(tall oil)
Water (30-60%)
Tall-oil pitch (30-60%, CASRN 8016-81-7)
Surfactant blend (1-10%, proprietary CASRN)
Liquidow
Occidental Chemical
Corporation
Salt-based
Water (53-72%)
Calcium chloride (28-42%, CASRN 10043-52-4)
Potassium chloride (<3%, CASRN 7447-40-7)
Sodium chloride (<2%, CASRN 7647-14-5)
LSP-400
3M
Polymer
Water (44-54%)
Olefin acrylate polymer (33-39%, proprietary CASRN)
Ammonium alkyl sulfate (2-6%, proprietary CASRN)
Ethyl lactate (1-5%, proprietary CASRN)
Alkyl ester (1-5%, proprietary CASRN)
Sodium alkyl ether sulfate (1-2%, proprietary CASRN)
Permazyme
(11X)
Pacific Enzymes
Enzyme
Proprietary blend of enzymes
Soil Sement
Midwest Industrial
Supply
Polymer
Water (50-95%)
Acrylic and vinyl acetate polymer (5-50%, non-hazardous)
Soiltac
Soilworks
Polymer
Copolymer of vinyl acetate, ethylene and vinyl ester with mineral fillers and protective colloid
liquid product
Synthetic vinyl copolymer dispersion (55%, non-hazardous)
Water (45%)
Top Seal
Soils Control
International
Enzyme
Copolymers, vinyl acrylic, water, and proprietary formulations
Vinyl acetate (<0.1%, CASRN 108-05-4)
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Section 3-Targeted Literature Review
Data collection involved the following overall steps:
1. Searching for and compiling relevant publicly available resources (e.g., published literature) documented
between 2015 and 2019 that pertain to the palliatives of interest.
2. Reviewing summaries for data sources obtained during the previous effort to identify supplemental content
for the palliatives of interest in this task.
3. Contacting subject matter experts and palliative manufacturers to seek palliative-specific information not
located via publicly available sources.
The following subsections describe specific information-gathering activities, which mirrored the overall process
followed in 2015 for continuity. Figure 1 highlights each step in the process.
3.1.1. Primary Documentation Search
ERG gathered palliative-specific information from various online sources. This process involved searching publicly
available databases and websites using a similar assemblage of relevant keywords and search strings developed
during the previous effort, but with some refinements based on the targeted nature of this particular follow-on
literature search (e.g., documentation published from 2015-present, searching on specific palliatives already known
to be used in Alaska). The following search tools were used:
Google Scholar (https://scholar.google.com/).
Scientific search engines including the U. S. National Library of Medicine' s PubMed
(https://www.ncbi.nim.nih.gov/pnbmed). Hazardous Substances Data Bank (HSDB;
http://toxnet.nim.nih.gov/cgi-bin/sis/titmigen7HSDB) and PubChem (https://pnbefaem.nebi.nlm.nih.gov/)..
State reference sources: Alaska Department of Environmental Conservation (lit!p://dec.alaska. gov/).
University of Alaska Fairbanks/Alaska University Transportation Center (http://antc.naf.edn/pnblicationsA.
and Alaska Department of Transportation and Public Facilities (http://www.dot.state.ak.nsA.
Google (https://www.google.com).
Websites for manufacturers of palliatives included in Table 1.
For this effort, the strategy for identifying relevant keywords and keyword search strings focused on the specific
palliatives of interest and the desired types of information to collect. The process for each of these is summarized
below.
General search terms comprised some combination of the words listed below.
o Where: Alaska.
o What: dust palliative, dust suppressant, dust control, dust abatement.
o Details: fate and transport, toxicity, environmental effect, environmental impact, human health,
subsistence, regulation.
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Section 3-Targeted Literature Review
Figure 1. Process to Collect and Document Information on Palliatives Used in Alaska
3-7
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Section 3-Targeted Literature Review
Palliative general search terms consisted of some assemblage of the words listed below.
o What: dust palliative, dust suppressant.
o Details: fate and transport, toxicity, environmental effect, environmental impact, human health.
Palliative-specific searches to identify the most current safety data sheets (SDSs) for each product
consisted of performing searches on Google and palliative manufacturing websites, using a combination of
the words listed below.
o What: palliative name.
o Details: manufacturer, safety data sheet, SDS.
Palliative-specific searches for those palliatives from Table 1 with no publicly available information
consisted of some assemblage of the words listed below.
o What: Alastac, AlastaSeal, Dust-Off, Freedom Binder 400, LSP-400.
o Details: fate and transport, toxicity, environmental effect, exposure, health.
Additional targeted efforts were conducted. These included searching:
o Individual terms on Alaska state websites: dust palliative, dust suppressant, dust control, dust
abatement, dust suppression, and road dust management.
o PubChem and TOXNET for each of the 17 palliative names as well as non-proprietary chemical
names/CASRNs for palliatives with no available data.
o Summaries developed for the publications reviewed during the extensive 2015 literature review
effort. Any relevant palliative-specific toxicity data was sought for palliatives included in Table 1.
When searching for reference literature, the process involved reviewing abstracts, identifying references most likely
to contain relevant information, and obtaining full-text references when possible. Throughout the literature search
process, ERG compiled relevant information about each reference in an Excel-based bibliographic database (e.g.,
author, date, title, URL [if applicable], full citation, and summary notes for the reference).
While some reference materials were available online in their entirety, others were limited to abstracts or brief
summaries. To complete the primary literature search, ERG established a tiered approach for reviewing and
compiling relevant information, which applied to all documents reviewed under this task order. The process
included searching online databases for references potentially relevant to palliatives and project objectives (Step 1),
targeting documents that could be useful based on a review of abstracts and other information (Step 2), obtaining
and reviewing full references for those deemed relevant (Step 3), summarizing the information contained (Step 4),
and flagging whether the references contained information on chemical make-up of palliatives, relative toxicity
values, newer regulations or advisories applicable to palliative use and exposure, and any mention of frequency of
specific palliative use in Alaska. Toxicity information gleaned from the published literature and the palliative
manufacturing SDSs was compiled into a table. Each step of the documentation search process is summarized in
Table 2.
Table 2. Steps for Primary Documentation Search Using Online Data Sources
e4 >
step
1
Search online data sources (e.g., Google Scholar, PubMed) using keywords and keyword search
strings.
2
Review abstracts and summary information for each reference.
Flag sources of information relevant for project-specific needs.
3
If accessible, obtain and review the full reference, and cite and summarize it in the bibliographic
database.
4
Search online data sources to obtain the most current SDS for each palliative.
5
Populate the bibliographic database with SDS reference information.
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Section 3-Targeted Literature Review
3.1.2. Consultation with Palliative Manufacturers and a Subject Matter Expert
As part of the literature search effort, ERG reached out to manufacturers and a subject matter expert to seek toxicity
data for the palliatives with no publicly available toxicity information. No palliative-specific toxicity information
was obtained for 5 of the 17 palliatives (Alastac, AlastaSeal, Dust-Off, Freedom Binder 400, and LSP-400) during
this process.
3.2. Findings
This section synthesizes the findings of the targeted literature review effort. ERG conducted more than 150 search
queries to obtain relevant information published since the 2015 effort. Using our institutional knowledge and subject
matter experience, ERG evaluated the results of these queries in online websites, and identified literature considered
relevant in the bibliographic database. Using the targeted search terms and short time frame window (2015-2019),
ERG cataloged nine new resources relevant to the topics of interest, with eight marked as relevant to the project
scope and requiring a full review. Articles deemed relevant were those that provided information directly related to
the project objectives, goals, and research questions (e.g., dealt with palliative toxicity, included details on palliative
chemical make-up, specifically referenced the palliatives of interest). ERG deemed articles irrelevant if they fell
outside of this scope (e.g., referred to palliative performance, summarized information on dust effects). In searching
the literature review summary results from the past effort, ERG identified 16 articles relevant to the current project
goals, and these were evaluated for relevant toxicity data. Updated SDSs were located for 6 of the 17 palliatives,
with the previously obtained SDSs for the remaining palliatives still the most applicable.
As stated, the goal of this targeted search was to identity information in newer references related to toxicity,
chemical make-up of palliatives, newer regulations or advisories applicable to palliative use and exposure, and any
mention of frequency of specific palliative use in Alaska. Results are presented in the following subsections by these
topics.
3.2.1. Palliative Toxicity
Of utmost concern to EPA for this project was identifying toxicity values (human and environmental) to support the
ability to conduct a computational evaluation of potential toxicity (discussed in Section 5), and thereby enabling the
Agency to address the stated concerns of Alaska Natives about the potential harm from exposures to palliatives used
in the state. Table 3 summarizes whether toxicity data were found for each of the 17 palliatives, narrowed down by
toxicity data for fish, mammals, plants, invertebrates, and other aquatic species.
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Section 3-Targeted Literature Review
Table 3. Available Toxicity Data for the Subject Palliatives
Product Name
Available Toxicity Data
References
Fish
Mammals
Plants
Invertebrates
Other Aquatic Species
Alastac*
Yes
Yes
No
No
No
Apun, LLC, 2009
AlastaSeal
No
No
No
No
No
Apun, LLC, 2010
DirtGlue
Yes
No
No
Yes
No
GeoCHEM, Inc., 2010
Dowflake
Yes
Yes
Yes
Yes
No
Occidental Chemical Corporation, 2016a
Durasoil
Yes
No
Yes
Yes
Yes
Soilworks, 2019
Dustaway
No
Yes
No
No
No
Author unknown, 2017
Dust-Off
No
No
No
No
No
Cargill Salt, 2002
Earth Armour
No
Yes
No
No
No
Midwest Industrial Supply, Inc., 2010
EK-35
Yes
No
No
Yes
No
Midwest Industrial Supply, Inc., 2015a; Midwest
Industrial Supply, Inc., 2017
EnviroKleen
Yes
Yes
No
Yes
No
Midwest Industrial Supply, Inc., 2015b; Steevens et
al., 2007; TSL, Tri-State Laboratories, 2002
Freedom Binder
400
No
No
No
No
No
Freedom Industries, 2009
Liquidow
Yes
Yes
Yes
Yes
No
Occidental Chemical Corporation, 2016b
LSP-400
No
No
No
No
No
3M, 2010
Permazyme (11X)
No
No
No
Yes
No
Hobe Associates, 2015
Soil Sement
Yes
No
No
Yes
No
Midwest Industrial Supply, Inc., 2015c, 2015d
Soiltac
Yes
No
Yes
Yes
Yes
Soilworks, 2018a, 2018b
Top Seal
Yes
Yes
No
Yes
Yes
Rocky Mountain Remediation Services, LLC, 1996;
Soils Control International, Inc., 2006
*Data identified for Alastac were presented on the product's SDS to show the toxicity of various lignosulfonates (the chemical composition of this palliative), but
are not necessarily specific to this exact palliative formulation.
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Section 3-Targeted Literature Review
Cells populated with a "Yes" are those species for which toxicity data were located for a particular palliative. As
noted and shown in the table, aquatic toxicity testing data were available for more of the palliatives than mammalian
toxicity data. No toxicity data were found for AlastaSeal, Dust-Off, Freedom Binder, and LSP-400. ERG provided
the full compilation of specific toxicity data to EPA as a separate deliverable titled "Bibliographic Database and
Toxicity Table."
3.2.2. Chemical Make-up of Palliatives
This targeted literature search identified a few publications that mention chemical constituents in particular
palliatives (e.g., sodium chloride, calcium chloride), but did not provide chemical make-up information specific to
the 17 palliatives included inEPA's investigation. The chemical compositions of the 17 dust palliative products and
ingredient CASRNs, when available (i.e., are not proprietary ingredients), were identified from their SDSs (see
Table 1).
3 .2 .3. Newer Regulations or Advisories Applicable to Palliative Use and Exposure
One document obtained during the targeted literature search (Jones, 2017) mentions the topic of regulations or
advisories related to palliatives. This report evaluated available guidelines in the United States related to selecting,
identifying, and applying various dust palliatives. Jones (2017) reported that the U.S. does not have any official
specifications related to chemical-based palliatives but identifies that palliative suppliers must adhere to the Federal
Highway Administration requirements for chemical treatments on unpaved roads. These requirements are referred to
as "Standard Specifications for the Construction of Roads and Bridges on Federal Highway Projects" (FHWA,
2014). Jones (2017) also states that chemical-based products used on unpaved roads cannot exhibit "the
characteristic of toxicity", per U.S. EPA's Resource Conservation Recovery Act (RCRA).
3.2.4. Frequency of Specific Palliative Use in Alaska
ERG's targeted literature search identified no additional publications that documented frequency of specific
palliative use in Alaska beyond what was documented in EPA's 2015 effort (see EPA, 2016 for more information).
EPA did locate one report that summarized a pilot project involving the use of EnviroKleen and Durasoil on sections
of road in the Native Village of Ruby. The purpose of this pilot project was to measure PMio concentrations in
ambient air before and after palliative application (ADEC, 2017).
3.3. Data Gaps/Research Needs
This literature search effort yielded some details related to the targeted topics of interest, but information gaps and
research needs remain. The bullets below highlight remaining gaps on the specific topics explored.
No toxicity data were found for four of the palliatives: AlastaSeal, Dust-Off, Freedom Binder, and LSP-
400.
Limited mammalian toxicity data are available for the subject palliatives.
The chemical compositions of the dust palliative products and ingredient CASRNs were not available in all
cases due to some having proprietary formulations.
No data were found on direct human health effects associated with exposure to palliatives applied in the
environment.
The possible effects of palliatives on subsistence food sources are not well understood or documented in
the published literature.
No federal, state, or other regulations were identified that pertain to palliative use specifically in Alaska.
While there are some rules that can generally apply to the use of palliatives, no new data were identified
during this follow-on search related to guidelines or advisories in place that apply to palliative use and
exposure.
The frequency of specific palliative use in Alaska is not well documented in the published literature.
3-11
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Section 4-Selection of Three Palliatives for the Computational Evaluation of Toxicity
4. Selection of Three PaSSiatives for the ComputationaS Evaluation of
Toxicity
The process for selecting the three palliatives for the computational evaluation involved an examination of the
literature search findings and consultations with subject matter experts (see Section 4.1.4). The approach used, and
the ultimate palliative selection, are summarized in the sections that follow.
4.1. Approach
To pinpoint the most appropriate three palliatives for inclusion, ERG examined the targeted literature search
findings by considering the focused topics summarized in Sections 4.1.1 through 4.1.3 and reaching out to subject
matter experts (see Section 4.1.4).
4.1.1. Products with the Least Available Toxicity Data
ERG identified the palliative products that had the least toxicity information available from the literature review.
The following five products had the least toxicity information available:
AlastaSeal: The manufacturer of this product, Apun, LLC, indicated it has not sold the product since 2013
or 2014, and had no palliative toxicity data to provide.
Alastac: Apun, LLC, the manufacturer of this product, has not sold it since 2013 or 2014. Apun, LLC had
no palliative-specific-toxicity data to provide. However, toxicity data were located in the palliative's SDS
related to palliatives with similar chemical make-up (i.e., lignosulfonate products), but data specific to this
exact palliative were not available.
Dust-Off: Contacts made to the manufacturer, Cargill, yielded no available toxicity information.
Freedom Binder 400: Freedom Industries, the manufacturer of this discontinued palliative, went out of
business in 2014.
LSP-400: The manufacturer of this palliative, 3M, reported that there is no toxicity data available for this
product, as it was not fully commercialized in the U.S.
4.1.2. Products with the Most Available Toxicity Data
ERG identified the palliative products that had the most toxicity information available from the literature review.
About the same amount of information was found for the following eight palliatives:
Dowflake
Durasoil
EK-35
EnviroKleen
Liquidow
Soil Sement
Soiltac
Top Seal
4.1.3. Frequency of Palliative Use in Alaska
To further inform the selection of three palliatives for the computational evaluation, EPA sought to hone in on the
frequency of use in Alaska for the 17 palliatives known to be used in the state. As noted in Section 3.2.4, ERG found
no additional information during the 2019 targeted literature search regarding frequency of use of palliatives in
Alaska, but EPA did locate one report that documented the pilot testing of Durasoil and EnviroKleen in a single
village (ADEC, 2017). As such, ERG considered information documented in the previous report (EPA, 2016) and
ADEC, 2017, which is summarized below.
Soil Sementฎ, Soiltac, Permazyme, and TopSealฎ have had a very limited number of applications in the
state, with testing sometimes representing the only application.
4-12
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Section 4-Selection of Three Palliatives for the Computational Evaluation of Toxicity
Calcium chloride has been the main type of product used on roads managed by Alaska DOT&PF; Alaska
DOT&PF records show that calcium chloride was applied to more than 800 miles of roads and highways
each year from 2005 to 2010.
The following palliatives were applied to village roads at least once during the 2005 to 2010 time period:
EnviroKleenฎ, Earth Armour, Soil-Sementฎ, LSP-400, Alastac, and AlastaSeal.
The following palliatives were applied to other non-village roads (i.e., roads not specified as village roads
in the source document) at least once during the 2005 to 2010 timeframe: EK35ฎ, EnviroKleenฎ,
Durasoilฎ, Soiltac, Top Sealฎ, Dustaway, and the now discontinued Freedom Binder 400.
EnviroKleen and Durasoil were both used on roads in the Native Village of Ruby in 2014.
Other products have been used in Alaska since 2010, such as the application of EK35ฎ and Durasoilฎ at
airports, but documentation of these uses is not readily available to the public.
These research findings indicate that salt-based products, specifically calcium chloride, are the main type of product
used on unpaved roads managed by the Alaska DOT&PF. Toxicity information on contaminants in salt-based
palliatives (calcium chloride, magnesium chloride, and sodium chloride) were identified in published reports
obtained during the literature search. Of the salt-based palliatives in Table 1, toxicity information is available for
Dowflake and Liquidow (main salt-based component: calcium chloride). No data were found specific to Dust-Off
(main salt-based component: magnesium chloride).
4.1.4. Input from Subject Matter Experts
To further aid in the selection process, EPA contacted two subject matter experts in palliative use in Alaska: Billy
Connor and David Barnes with the University of Alaska Fairbanks - Alaska University Transportation Center. EPA
shared the information collected during the targeted literature search and proposed three synthetic palliatives to
possibly include in the computational evaluation: Durasoil (manufactured by Soilworks), andEK-35 and
EnviroKleen (manufactured by Midwest Industrial Supply). The experts:
Confirmed that these three synthetic palliatives are commonly used in Alaska.
Indicated there is a lot of data already available on calcium chloride, magnesium chloride, and sodium
chloride from a number of documented sources, but less data available on synthetic products such as those
proposed.
Agreed that it would be beneficial to focus the computational evaluation of toxicity on Durasoil, EK-35,
and EnviroKleen.
4.2. Findings
Based on this detailed evaluation, EPA ultimately selected three synthetic liquid palliatives to focus on in the
computational evaluation of potential toxicity: Durasoil (manufactured by Soilworks), and EK-35 and EnviroKleen
(manufactured by Midwest Industrial Supply). EPA selected these palliatives based on the following considerations:
The previous research effort (EPA, 2016) found that synthetic fluids are some of the most appealing types
of palliatives for use in the state because of their product availability, cost, and effectiveness (Barnes and
Connor, 2014). In addition, non-salt-based chemical palliatives have gained popularity for several reasons,
such as their effectiveness at reducing dust and their relative price efficiency (Milne, 2015).
They are some of the most commonly used palliatives in the State of Alaska.
They have available laboratory toxicity testing data.
Their use and toxicity are not as well documented as commonly used salt-based palliatives.
The effectiveness of Durasoil and EnviroKleen was previously studied as part of an ADEC dust monitoring
study in the Native Village of Ruby and additional information on these products will build a more
complete knowledge base.
Subject matter experts concurred they were appropriate for inclusion.
4-13
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Section 4-Selection of Three Palliatives for the Computational Evaluation of Toxicity
4.3. Data Gaps
Available information indicates which palliatives were applied to village roads at least once, but the number of times
and locations that each type of palliative was used on village roads is still unknown. Using institutional knowledge
and input from subject matter experts, EPA was able to identify some of the most commonly used palliatives in
Alaska to include in the computational evaluation
4-14
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Section 5-Computational Evaluation of Potential Palliative Toxicity
5. Computational Evaluation of Potential Palliative Toxicity
This section summarizes the approach, findings for each step of the process, and data gaps/research needs for the
computational evaluation of potential palliative toxicity conducted for this project.
5.1. Approach
Evaluating the potential for human toxicity of these palliatives is limited by the lack of information on specific
chemical composition. Each palliative is a chemical mixture composed of a proprietary blend of organic compounds.
For example:
EnviroKleen is composed of a mixture of <60% polyolefin (CASRN 9003-27-4) and >10% of
hydrotreated, high viscosity, synthetic isoalkane (CASRN 72623-86-0).
EK-35 is a mixture of <60% tall-oil pitch (CASRN 8016-81-7), >10% severely hydrotreated, high
viscosity, synthetic isoalkane (CASRN 72623-86-0), and <4% of proprietary alkyl polyamines.
Durasoil is a proprietary blend of non-petroleum synthetic alkanes. No information is available on the
specific constituent compounds.
The toxicity information that is available for these palliatives is based on testing conducted on the whole product,
which helped us understand the potential toxicity of each product as it is intended to be used and applied.
Because we do not know the specific chemical constituents and their properties, ERG was unable to use traditional
computational toxicological methods such as quantitative structure activity relationship (QSAR) models for this
effort, as they rely on input of a specific chemical structure of a compound. However, ERG was able to employ
methods that are similar to QSAR-type approaches, which allow us to draw inferences from a wider range of
toxicity data. Using this approach, ERG evaluated the relative toxicity of the three subject palliatives while also
presenting results in units (doses) that are familiar to a general population.
Figure 2 shows the main objectives at a high level for the computational evaluation of potential toxicity for the three
subject palliatives.
Figure 2. Main Objectives for the Computational Evaluation of Potential Toxicity
For the first main objective, ERG collected toxicity data for Durasoil, EK-35, and EnviroKleen using online
resources and personal communication with the manufacturers (Midwest Industrial Supply and Soilworks).
Additional scientific approaches were used to convert the available aquatic toxicity values (available as fish L('50s])
for Durasoil, EK-35, and EnviroKleen to mammal toxicity values (oral rat LD50s-), making them relatable to human
exposures.
1 LC50 = concentration that causes death in 50% of tested organisms within a certain time period
2 LD50 = dose expected to cause death in 50% of tested organisms within a certain time period
5-15
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Section 5-Computational Evaluation of Potential Palliative Toxicity
ERG prepared the following step-by-step process to meet the other three main objectives:
1. Compare the ecological toxicity for endpoints consistent across all three palliatives (50% lethal
concentrations [LC50s])
2. Compare the ecological toxicity endpoints (LC50s) to familiar household products using LC50s
3. Extrapolate ecological toxicity endpoints (LC50s) to mammalian toxicity endpoints (50% lethal doses
[LD50s])
4. Compare the mammalian toxicity endpoints to familiar household products using LD50s
5. Extrapolate mammalian toxicity endpoints (LD50s) to human equivalent doses (HEDs)
6. Present the toxicity of palliatives using established toxicity scales
5.2. Findings
This section provides the findings for each step conducted during the computational evaluation.
5.2.1. Step 1: Compare Ecological Toxicity Using Available Data
ERG compiled all available toxicity data for Durasoil, EK-35, and EnviroKleen that were obtained via online
resources and personal communication with manufacturers.3 Based on a review of available information, ERG
identified that ecological toxicity tests have been conducted under acute and chronic exposure conditions for all
three palliatives as whole products. Table 4 provides all the test results of these studies for two fish species (rainbow
trout and fathead minnow), three invertebrates (mysid shrimp, two types of water flea, and earthworms), and
bacterium.
Based on the palliative-specific toxicity data shown in Table 4, the most sensitive endpoints varied across
palliatives:
For Durasoil the most sensitive endpoint (the lowest toxicity value) was for 7-day IC25 of growth in mysid
shrimp observed at concentrations of >1,000 mg/L. The IC25 is a point estimate of the toxic concentration
that would cause a 25% reduction in a non-lethal biological measurement. For this toxicity assessment,
1,000 mg/L was the maximum concentration tested, and so an estimated value of >1,000 mg/L was applied
as the IC25. For fish, the most sensitive endpoint was a 96-hour LC50 of >2,000 mg/L for survival of
rainbow trout and a 7-day IC25 for growth of >2,000 mg/L for fathead minnow. This does not necessarily
mean Durasoil is not potentially toxic, just that the concentration that would elicit changes in
growth/reproduction and survival in the tested aquatic species are greater than 1,000 mg/L and 2,000 mg/L,
respectively.
For EK-35, the most sensitive endpoint was for a 7-day lowest observed effect concentration (LOEC) for
growth/reproduction in rainbow trout of >10 mg/L. The LOEC for survival was measured as 20 mg/L. The
7-day no observed effect concentration (NOEC) for both growth/reproduction and for survival was
estimated to be 10 mg/L. Therefore, together the evidence suggests detrimental effects for
growth/reproduction and survival start occurring in rainbow trout exposed to between 10 and 20 mg/L of
EK-35.
For EnviroKleen, LOECs and LC50s were estimated to be >1,000 mg/L across species, exposure scenarios,
and health endpoints. The corresponding NOECs were all estimated to be 1,000 mg/L. Taken together, this
means that no toxicity endpoint was observed at the maximum concentration used across these toxicity
assessments. This does not necessarily mean EnviroKleen is not potentially toxic, just that the
concentration that would elicit changes in growth/reproduction and survival in the tested aquatic species are
greater than 1,000 mg/L.
3 Data are based on the most current manufacturers' safety data sheets (SDSs), with more specifics on those toxicity
values gleaned from the additional references cited, when available. For Durasoil, based on laboratory data collected
over time (and provided to ERG by the manufacturer), testing results reported as IC25s and IC50s were assumed to
be based on toxicity growth tests.
5-16
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Table 4. Toxicity of Durasoil, EK-35, and EnviroKleen
Species
Toxicity Measure
Durasoil3
EK-35b-c'd
EnviroKleend'(,J
Fish
Rainbow Trout
96-hour LC50 (survival)
>2,000 mg/L
30 mg/L
>1,000 mg/L
(iOncorhynchus mykiss)
96-hour NOEC (survival)
-
-
1,000 mg/L
96-hour LOEC (survival)
-
-
>1,000 mg/L
7-day LC50 (survival)
-
23 mg/L
>1,000 mg/L
7-day NOEC (survival)
-
10 mg/L
1,000 mg/L
7-day LOEC (survival)
-
20 mg/L
>1,000 mg/L
7-day LC50 (growth/reproduction)
-
> 10 mg/L
>1,000 mg/L
7-day NOEC (growth/reproduction)
-
10 mg/L
1,000 mg/L
7-day LOEC (growth/reproduction)
-
> 10 mg/L
>1,000 mg/L
Fathead Minnow
96-hour LC50 (survival)
-
271 mg/L
>1,000 mg/L
(Pimephales promelas)
96-hour NOEC (survival)
-
125 mg/L
1,000 mg/L
96-hour LOEC (survival)
-
250 mg/L
>1,000 mg/L
7-day LC50 (survival)
>28,000 mg/L
97.3 mg/L
>1,000 mg/L
7-day NOEC (survival)
-
31.3 mg/L
1,000 mg/L
7-day LOEC (survival)
-
62.5 mg/L
>1,000 mg/L
7-day LC50 (growth/reproduction)
-
114 mg/L
>1,000 mg/L
7-day NOEC (growth/reproduction)
-
31.3 mg/L
1,000 mg/L
7-day LOEC (growth/reproduction)
-
62.5 mg/L
>1,000 mg/L
7-day IC25 (growth)
>2,000 mg/L
-
-
7-day IC50 (growth)
>39,000 mg/L
-
-
Invertebrates
Mysid Shrimp
96-hr LC50 (survival)
-
Ill mg/L
>1,000 mg/L
(Americamysis bahia)
96-hr NOEC (survival)
-
63 mg/L
1,000 mg/L
96-hr LOEC (survival)
-
130 mg/L
>1,000 mg/L
7-day LC50 (survival)
>2,000 mg/L
58.6 mg/L
>1,000 mg/L
7-day NOEC (survival)
-
25 mg/L
1,000 mg/L
7-day LOEC (survival)
-
50 mg/L
>1,000 mg/L
7-day LC50 (growth/reproduction)
-
>50 mg/L
>1,000 mg/L
7-day NOEC (growth/reproduction)
-
50 mg/L
1,000 mg/L
7-day LOEC (growth/reproduction)
-
>50 mg/L
>1,000 mg/L
7-day IC25 (growth)
>1,000 mg/L
-
-
Water Flea
48-hour LC50 (survival)
18,000 mg/L
-
-
(Daphnia magna)
Water Flea
48- hr LC50 (survival)
-
>1,000 mg/L
>1,000 mg/L
(Ceriodaphnia dubia)
48-hr NOEC (survival)
-
1,000 mg/L
1,000 mg/L
48-hr LOEC (survival)
-
>1,000 mg/L
>1,000 mg/L
7-day LC50 (survival)
-
>1,000 mg/L
>1,000 mg/L
7-day NOEC (survival)
-
500 mg/L
1,000 mg/L
7-day LOEC (survival)
-
1,000 mg/L
>1,000 mg/L
5-17
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Table 4. Toxicity of Durasoil, EK-35, and EnviroKleen
Species
Toxicity Measure
Durasoil3
EK-35b'c-d
EnviroKleend'('J
Water Flea
7-day LC50 (growth/reproduction)
-
375 mg/L
>1,000 mg/L
(Ceriodaphnia dubia)
7-day NOEC (growth/reproduction)
-
250 mg/L
1,000 mg/L
[continued]
7-day LOEC (growth/reproduction)
-
500 mg/L
>1,000 mg/L
Earthworm
14-day LC50 (survival)
>670,000 mg/L
-
-
(Eisenia andrei)
Other
Bacterium
15-minute IC50 (growth)
>500,000 mg/L
-
-
(Alii vibrio fischeri)
Notes:
indicates no data are available
IC25 = Point estimate of toxic concentration that would cause a 25% reduction in non-lethal biological
measurement
IC50 = Point estimate of toxic concentration that would cause a 50% reduction in non-lethal biological
measurement
LC50 = Lethal Concentration, 50%
LOEC = Lowest Observable Effects Concentration
mg/L = milligrams per liter
NOEC = No Observable Effects Concentration
References:
a Soilworks. 2019. Durasoil safety data sheet. Revised April 2, 2019.
https://www.soilworks.com/media/115319/sdsl501001-durasoil-safety-data-sheet-en-.pdf.
b Midwest Industrial Supply, Inc. 2015. EK35 Series safety data sheet. Revised May 21, 2015.
http://midwestind.com/wp-content/yploads/MW EK35 Series SDS.pdf.
c Midwest Industrial Supply, Inc. 2017. Environmental data for EK35 synthetic organic dust control.
http://midwestind.com/wp-content/uploads/MW EK35-Environmental-Data.pdf.
d ABC Laboratories, Inc. 2003. Study title: 7-day survival and growth tests of dust suppression products EK-35 and
EnviroKleen to the rainbow trout, oncorhynchus mykiss, determined under static removal conditions. Provided by
Cheryl Detloff, Midwest Chemist.
e Midwest Industrial Supply, Inc. 2015. EnviroKleen safety data sheet. Revised May 22, 2015.
http://midwestind.com/wp-content/yploads/MW EnviroKleen SDS.pdf.
f ABC Laboratories. 2002. EnviroKleen environmental data, acute and chronic aquatic toxicity. Provided by Cheryl
Detloff, Midwest Chemist.
ERG evaluated all the available toxicity data and identified toxicity endpoints that were consistently measured
across the three palliatives for the same given species and duration of exposure (shown in Table 5). These endpoints
include the 96-hour LC50 for rainbow trout, 7-day LC50 for the fathead minnow, and 7-day LC50 for the mysid
shrimp. An examination of the toxicity data for these specific endpoints indicates that EK-35 is more toxic than
Durasoil and EnviroKleen because it consistently has the lowest toxicity value. Of the three common toxicity
endpoints, the most sensitive is the 96-hour LC50 for rainbow trout, which indicates that 50% of trout died when
exposed to EK-35 at a concentration of 30 mg/L for 96 hours. For EnviroKleen and Durasoil, the 96-hour LC50s for
survival were not observed at the maximum concentrations tested and were therefore estimated to be >2,000 mg/L
and >1,000 mg/L, respectively. This rainbow trout acute toxicity endpoint, as well as the other two chronic toxicity
endpoints (7-day LC50 for fathead minnow and 7-day LC50 for mysid shrimp), suggest that EK-35 has the potential
to be more toxic than both Durasoil and EnviroKleen.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Table 5. Common Toxicity Measures for Durasoil, EK-35, and EnviroKleen
Toxicity Endpoint
Durasoil3
EK-35"
EnviroKleen0
96-hour LC50 (survival) for rainbow trout
(Oncorhynchus my kiss)
>2,000 mg/L
30 mg/L
>1,000 mg/L
7-day LC50 (survival) for fathead
minnow (Pimephales promelas)
>28,000 mg/L
97.3 mg/L
>1,000 mg/L
7-day LC50 (survival) for mysid shrimp
(.Americamysis bahia)
>2,000 mg/L
58.6 mg/L
>1,000 mg/L
References:
aSoilworks. 2019. Durasoil safety data sheet. Revised April 2, 2019.
https://www.soilworks.com/media/115319/sdsl501001-durasoil-safetv-data-sheet-en-.pdf.
b Midwest Industrial Supply, Inc. 2015. EK35 Series safety data sheet. Revised May 21, 2015.
http://midwestind.com/wp-content/uploads/MW EK35 Series SDS.pdf.
c Midwest Industrial Supply, Inc. 2015. EnviroKleen safety data sheet. Revised May 22, 2015.
http://midwestind.com/wp-content/uploads/MW EnviroKleen Series SDS.pdf.
There is no clear way to distinguish between the toxicity of Durasoil and EnviroKleen given these data, as LC50s
were not observed for both palliatives at the maximum concentrations tested. However, the toxicity tests for
Durasoil used a maximum concentration that was greater than the toxicity tests for EnviroKleen, providing evidence
to suggest that Durasoil likely has the lower toxicity of the two.
To provide added perspective. Figure 3 compares the toxicity values presented in Table 5 to EPA's ecotoxicity scale
for aquatic organisms (EPA, 2017). Based on this toxicity scale for the three common toxicity measures across the
subject palliatives, the aquatic toxicity results presented for Durasoil and EnviroKleen for 96-hour LC50s for
rainbow trout, 7-day LC50s for fathead minnow, and 7-day LC50s for mysid shrimp all are at least a factor of 10
greater than 100, indicating they are practically non-toxic to aquatic organisms. The LC50s for EK-35 for these three
endpoints ranged from 30 mg/L to 97.3 mg/L, falling within EPA's slightly toxic range for aquatic toxicity. These
toxicity levels mean that Durasoil, EK-35, and EnviroKleen are unlikely to adversely affect the survival of fish in
the enviromnent where they would most likely be present at much lower concentrations.
Figure 3. Comparison of Palliative Ecotoxicity to EPA's Ecotoxicity Scale for Aquatic Organisms
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Section 5-Computational Evaluation of Potential Palliative Toxicity
5.2.2. Step 2: Compare Ecological Toxicity of Palliatives (LC50s) to Familiar Household
Products
ERG collected information from manufacturers' SDSs on the ecological toxicity of an array of common household
products. The 96-hour LC50s for rainbow trout survival for the three palliatives were then compared to common
household products to help put the relative toxicity information into context for a broader audience. Of note, while
data for the palliatives were based on whole products, the household data were based on the primary active
ingredient of each product. ERG conducted a sweep to locate available toxicity data for a plethora of commonly
used household products. Aquatic toxicity data were identified to enable comparisons between products and one
endpoint across all three palliatives: 96-hour LC50s for rainbow trout survival. The products included air freshener
& deodorizer, bar soap, hand & body lotion, hand sanitizer, no-rinse body wash, and salt. The LC50s for these
products are displayed in Table 6.
Table 6. LC50 Rainbow Trout Toxicity of Household Items
Common Household Product
Active Ingredient (percent in
product, if known)
96-hour LC50
Rainbow Trout (Oncorhynchus
mykiss) (mg/L)
Air Freshener & Deodorizer
Acetone, 60-80%
4,740-6,330
Bar Soap
Glycerin, 1-10%
50
Hand & Body Lotion
Glycerol, proprietary
percentage
67,500
Hand Sanitizer
Ethanol, 50-75%
42
No-rinse Body Wash
Propylene glycol, proprietary
percentage
40,613
Salt
Sodium chloride, 98.5-99.5%
2,800
information was obtained from product SDSs.
LC50s presented in the SDSs in the unit of mL/L were converted to mg/L.
Based on this endpoint comparison, EK-35 has a lower LC50 (30 mg/L) and is therefore more toxic than all of the
household products listed in Table 6. The evaluative data show that Durasoil and EnviroKleen are less toxic than
hand sanitizer and bar soap. However, a judgement cannot be made on the relative toxicity of Durasoil and
EnviroKleen compared to the remaining household products because LC50s were not observed at the maximum
concentrations tested in these palliative aquatic toxicity assessments (2,000 mg/L and 1,000 mg/L, respectively).
5.2.3. Step 3: Extrapolate Ecological Toxicity Data (LC50s) to Mammalian Toxicity (LD50s)
The available toxicity data for each palliative (shown in Table 4) are primarily from studies conducted with fish or
invertebrates. No mammalian toxicity data, such as 50% lethal doses (LD50s), were available for the palliatives as
whole products. However, methods have been developed to relate LC50s in non-mammalian species to LD50s in
mammals (Delistraty et al., 1998; Hodson, 1985; Janardan et al., 1984; Kaiser and Esterby, 1991; Zolotarev et al.,
2017). These methods involve developing regression models from a large collection of paired observations of
LC50s, for example in fish, and LD50s in rats from toxicity studies on a wide range of chemicals. Table 7 presents a
summary of regression models published in the scientific literature that were developed to relate LC50s in rainbow
trout to rat LD50s.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Table 7. Regressions for Fish LC50s and Rat LD50s
Reference
Test Chemicals
Na
Y Variableb
X Variable"
Slope
Intercept
rc
Janardan et al.
1984
Priority Pollutants
24
Rat LD50
(mmol/kg)
Fathead
Minnow LC50
(nmol/L)
0.35
-0.161
0.63
Janardan et al.
1984
Priority pollutants
and pesticides
combined
64
Male Rat
LD50
(mmol/kg)
Fathead
Minnow LC50
(nmol/L)
0.33
-0.34
0.58
Janardan et al.
1984
Priority pollutants
and pesticides
combined
64
Female Rat
LD50
(mmol/kg)
Fathead
Minnow LC50
(nmol/L)
0.36
-0.259
0.67
Janardan et al.
1984
Chlorinated
pesticides
12
Male Rat
LD50
(mmol/kg)
Fathead
Minnow LC50
(nmol/L)
0.59
0.192
0.999
Janardan et al.
1984
Chlorinated
pesticides
12
Female Rat
LD50
(mmol/kg)
Fathead
Minnow LC50
(nmol/L)
0.28
0.38
0.999
Hodson 1985
Phenols, benzenes,
anilines, solvents,
misc.
15
Rat LD50
(mmol/kg)
Trout LC50
(mmol/L)
0.7086
1.6553
0.62
Kaiser and
Esterby 1991
Variety of chemical
lasses
91
Rat LD50
(mmol/kg)
Fathead
Minnow LC50
(mmol/L)
0.36
-1.16
0.583
Delistraty et al.
1998
Pesticides and non-
pesticides
213
Trout LC50
(mmol/L)
Rat LD50
(mmol/kg)
0.722
-2.16
0.512
a The number of chemicals used in developing the regression model
bLD50s and LC50s were logged for regression analyses
0 Correlation coefficient
mmol/kg = millimoles per kilogram
|imol/L = micromoles per liter
The regression models in Table 7 were based on data from individual chemicals with known properties, and the
models are often improved by including these properties as covariates. For example, a compound's octanol-water
partition coefficient (lgP or logKow) has been established as an important covariate in predicting a mammalian
LD50 from a fish LC50. This is because the partition coefficient is a measure of hydrophobicity, and very
hydrophobic compounds tend to accumulate in fish to a much greater degree than in mammals.
An additional limitation of the regression models presented in Table 7 is that they were fit to data in molar units.
Because toxicological effects occur at the molecular level, molar units are most appropriate when comparing
toxicities of different compounds. However, without knowing the constituent composition of each palliative, ERG
did not know the molecular weight of each compound within each palliative, which meant we are unable to use the
regression equations from Table 7 directly. Instead, we used a similar approach and developed a regression model
based on the units of the available toxicity data, mg/L (as opposed to molar units).
ERG developed two regression models that predict mammalian toxicity (LD50s) using the available LC50 fish
toxicity data from Table 5 for the three subject dust palliatives. The two regression models were based on data sets
from two studies that included paired fish LC50s and rat LD50s. The steps for developing these models were as
follows:
Zolotarev et al. (2017) present paired zebra fish LC50s and rat LD50s for 50 compounds in units of mg/L
and mg/kg, respectively. These data were log transformed and ERG ran a regression on the data in Excel
using Excel's Data Analysis Toolpak. The regression model was significant (p = 0.000096), though the
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Section 5-Computational Evaluation of Potential Palliative Toxicity
model has limited explanatory power (correlation coefficient, r = 0.52). Results are shown in Figure 4. The
regression equation from this model fit is: LogLD50 = 0.278*LogLC50 + 2.614.
Figure 4. Regression Based on Data from Zolotarev et al. (2017)
Zolotarev et al. 2017 Data
Logl_D50 Linear (Logl_D50)
y = 0.2782x +2.6143
D
A
3#
f
d
9
1
ft
W
#
n
6
4
2
ซ, c
) :
ป L
i e
-?
Zebra Fish LogLC50
Hodson (1985) presents paired rainbow trout LC50s and rat LD50s for 14 compounds in units of mmol/L
and mmol/kg. ERG looked up molar densities for each of these chemicals and used these values to convert
from molar units into mg/L and mg/kg. These data were log transformed and a regression was run on the
data in Excel using Excel's Data Analysis Toolpak. The regression model was significant (p = 0.045),
though the model has limited explanatory power (r = 0.54). Results are shown in Figure 5. The
regression equation from this model fit is: LogLD50 = 0.369*LogLC50 + 2.51.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Figure 5. Regression Based on Data from Hodson (1985)
Hodson 1985 Data
LogLD50 (mg/kg) Linear (Logl_D50 (mg/kg))
y = 0.3691x + 2.51
3.5
d
3.
2
1.5
1
-10 12
Rainbow Trout LogLC50
The fact that these two models were significant demonstrates that there is an association between fish LC50s and rat
LD50s. This allowed ERG to extrapolate from the limited toxicity data available for each palliative. Keeping in
mind that the correlation from these models was not large, we could still form a first order approximation.
Therefore, the regression equations from each model were used to extrapolate LD50s for the two fish endpoints (96-
hour survival LC50s for rainbow trout and 7-day survival LC50s for fathead minnow) from Table 8. Of note, the
shrimp toxicity values were not used to predict LD50s because the two data sets used in developing the regression
models were based on fish toxicity data.
Table 8 shows the predicted rat LD50s that result from applying these models to the toxicity data for the three
palliatives.
Table 8. Predicted Rat LD50s in mg/kg for the Three Palliatives
Model
Toxicity Endpoint
Durasoil3
EK-35"
EnviroKleen0
Model based on Zolotarev et
al. 2017 data
Rat LD50 (extrapolated from 96-
hour LC50 for rainbow trout)
>3,409
1,060
>2,811
Rat LD50 (extrapolated from 7-day
LC50 for fathead minnow)
>7,104
1,470
>2,811
Model based on Hodson
1985 data
Rat LD50 (extrapolated from 96-
hour LC50 for rainbow trout)
>5,351
1,136
>4,143
Rat LD50 (extrapolated from 7-day
LC50 for fathead minnow)
>14,173
1,753
>4,143
The two models produced surprisingly similar results. This can be seen when comparing the regression equations
above, or by looking at the range of predicted LD50 values for EnviroKleen, which had the same LC50 inputs for
both rainbow trout and fathead minnow of >1,000 mg/kg. The two models produced predicted LD50s that ranged
from >2,811 to >4,143 mg/kg, a factor difference of approximately 1.5. Still, the predicted mammalian toxicity
values in Table 8 vary depending on which regression model and LC50 input were used. The variation seen in
predicted LD50s is greatest for Durasoil, primarily because the input values for this palliative had the greatest range
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Section 5-Computational Evaluation of Potential Palliative Toxicity
(from >2,000 mg/kg for the 96-hour LC50 for rainbow trout to >28,000 mg/kg for the 7-day LC50 for fathead
minnow). The predicted LD50 values for EK-35 had the smallest range from 1,060 mg/kg to 1,753 mg/kg.
Because the Hodson model was developed from rainbow trout toxicity data, an argument can be made that this is the
more appropriate model to use when extrapolating from a rainbow trout LC50. The Zolotarev et al. (2017) model
was based on zebra fish data but was developed from a much larger number of chemicals and conducted more
recently. Neither model used fathead minnow data, however.
While no mammalian toxicity data were available for the palliatives as whole products, for the EnviroKleen
palliative only, ERG was able to obtain LD50 toxicity on its two chemical constituents. Those data are presented
here to offer additional perspective. LD50s were available for two different raw materials that make up
EnviroKleen: polyolefin and a synthetic isoalkane. The synthetic fluid had a rat oral LD50 >5,000 mg/kg, and
polyolefin (polyisobutylene) had a rat oral LD50 >5,000 mg/kg. Thus, while the available LD50s are not
representative of mammalian toxicity on the full palliative composition, these two materials make up 100% of
EnviroKleen at proprietary proportions and therefore are good indicators of the potential toxicity of the palliative.
The LD50 values here are consistent with the predicted values presented in Table 8.
5.2.4. Step 4: Compare Mammalian Toxicity Data (LD50s) to Common Household Products
In the previous Step 2, ERG compared 96-hour LC50s in rainbow trout between the three subject palliatives and a
variety of common household products. In Step 4, ERG compared the predicted oral rat LD50s for the three
palliatives to oral rat LD50s for the same products as in Step 2, as well as a few additional common household
products for which only LD50s were available (see Table 9). While Step 2 involved comparing LC50s for the
palliatives to common household products, this LD50 comparison was performed because an LD50 dose is an easier
to understand toxicity metric for humans than an LC50, which is an aquatic toxicity concentration. The findings of
this comparison are presented below:
EK-35: Aspirin (1,500 mg/kg) and bug spray (1,747 mg/kg) fall within the predicted LD50 range for EK-
35 (1,060 mg/kg to 1,753 mg/kg), but EK-35 is more toxic than the other household products except for
laundry detergent.
Durasoil: Components of air freshener & deodorizer, baby foaming shampoo & wash, bar soap, hand and
body lotion, and hand sanitizer all fall within the lower bounds of Durasoil's predicted toxicity range
(>3,409 mg/kg to >14,173 mg/kg). Aspirin (1,500 mg/kg), bug spray (1,747 mg/kg), and laundry detergent
(333 mg/kg) are more toxic than Durasoil.
EnviroKleen: LD50s for aspirin, bug spray, and laundry detergent fall below the lower bounds of
EnviroKleen's predicted toxicity range (>2,811 mg/kg to >4,143 mg/kg), meaning EnviroKleen's predicted
toxicity is lower than these products.
It is worth noting that Durasoil and EnviroKleen are more difficult to assess because the extrapolated LD50s are
based on their LC50s, for which ERG only knew that their toxicity was above a certain tested maximum
concentration. However, as summarized above, we can more confidently speak to the household product LD50s that
fall within the predicted LD50 ranges for the palliatives and to those below those ranges.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Table 9. Oral Rat LD50 Toxicity of Household Items
Common Household Product
Active Ingredient
Oral LD50 Rat (mg/kg)
Air Freshener & Deodorizer
Acetone, 60-80%
5,800
Antiperspirant/Deodorant Spray
Propylene glycol, 3-7%
20,000
Aspirin
Acetylsalicylic acid, 100%
1,500
Baby Foaming Shampoo & Wash
Mixture of ingredients
>5,000
Bar Soap
Glycerin, 1-10%
12,600
Bug Spray (mixture of ingredients)
Mixture of ingredients
1,747
Hand & Body Lotion
Glycerol, proprietary percentage
12,600
Hand Sanitizer
Ethanol, 50-75%
7,060
Liquid Laundry Detergent
Caustic potash, 45%
333
No-rinse Body Wash
Propylene glycol, proprietary
percentage
20,000
Salt
Sodium chloride, 98.5-99.5%
>3,000
5.2.5. Step 5: Extrapolate Mammalian Toxicity (LD50s) to HEDs
The toxicity of each substance can further be interpreted by converting the extrapolated mammalian doses (LD50s)
into human equivalent doses (HEDs) based on allometric equations, which relate body weight and surface area
between species. This method is commonly used in risk assessments, for example in deriving oral reference doses,
and allows for an easier to understand metric of toxicity in terms of human exposure (EPA, 2010).
The EPA-recommended equation for calculating an HED is: Laboratory animal exposure (mg/kg) x DAF = HED
(mg/kg), where DAF is the Dosimetric Adjustment Factor, a factor that relates the body weight of the test animal to
that of the human. For rats, the recommended DAF is 0.24. To account for interspecies variability, an uncertainty
factor of 3 is also applied. Table 10 shows the calculated HEDs derived from the predicted LD50s.
Table 10. Human Equivalent Doses in mg/kg
Model
Toxicity Endpoint
Durasoil
EK-35
EnviroKleen
Model based on
Zolotarev et al. 2017
data
Rat LD50 (extrapolated from
96-hour LC50 for rainbow trout)
>273
85
>225
Rat LD50 (extrapolated from 7-
day LC50 for fathead minnow)
>568
118
>225
Model based on
Hodson 1985 data
Rat LD50 (extrapolated from
96-hour LC50 for rainbow trout)
>428
91
>331
Rat LD50 (extrapolated from 7-
day LC50 for fathead minnow)
>1,134
140
>331
5.2.6. Step 6: Present the Toxicity of Palliatives Using Established Toxicity Scales
To better understand the toxicity of the predicted LD50s for humans, ERG compared the estimated range of
predicted palliative LD50s (Durasoil: >3,409 to >14,173 mg/kg, EK-35: 1,060 to 1,753 mg/kg, and EnviroKleen:
>2,811 to >4,143 mg/kg) to the established Hodge and Sterner (1943) toxicity scale (see
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Figure 6 and Table 11). This scale rates toxicity from extremely toxic to relatively harmless using a total of four
levels in between (for a total of six). Based on that scale, EK-35 is classified as slightly toxic, corresponding to a
probable lethal dose in humans of ingesting approximately a pint. While precise estimates of LD50 for Durasoil and
EnviroKleen are not available, at their most toxic estimate (the lowest predicted LD50), EnviroKleen would also be
classified as slightly toxic, whereas Durasoil would be either classified as slightly toxic or practically non-toxic
depending on which model estimate was used. A practically non-toxic classification would correspond to a probable
lethal dose in humans of ingesting a quart. The actual toxicity of Durasoil and EnviroKleen, however, is not truly
known and predictions are limited by the available toxicity data.
Table 11. Toxicity Classes of Predicted Palliative LD50s, Using the Hodge and Sterner Scale
Predicted LD50s in mg/kg
Toxicity
Commonly Used
Oral Rat LD50 Scale
(from Table 8)
Probable Lethal Dose in
Rating
Term
Range in mg/kg
Humans
Durasoil*
EK-35
EnviroKleen*
Extremely Toxic
1 or less
1 grain (a taste, a drop)
Highly Toxic
1-50
4 mL (1 tsp)
Moderately Toxic
50-500
30 mL (1 fl. oz.)
Slightly Toxic
500-5,000
>3,409 to
>14,173
1,060 to
1,753
>2,811
to >4,143
600 mL (1 pint)
Practically Non-toxic
5,000-15,000
1 liter (or 1 quart)
Relatively Harmless
15,000 or more
1 liter (or 1 quart)
*Toxicity values for Durasoil and EnviroKleen represent lower bounds and could be larger (less toxic) than the
values reported here.
The Hodge and Sterner scale is referenced in various sources, such as
https://www.ccohs.ca/oshanswers/cheniicals/ld50.htniL
5.2.7. Computational Evaluation Conclusions
The approach described herein allowed ERG to put the limited available aquatic toxicity data for three subject
palliatives into perspective in terms of relative toxicity and human exposure. Based on our extrapolations, these
three palliatives fall into the "slightly toxic" to "practically non-toxic" categories for human exposure using an
established toxicity scale. Using this established toxicity scale, it is estimated that there is a 50% chance of death for
humans who consumed 1 pint (slightly toxic) to 1 quart (practically non-toxic) of pure palliative product. In the
environment, they are greatly diluted. It is unlikely that subsistence foods near roads would be a conduit for
ingesting this much of the palliative product. For example, the LC50s for fish would not be of concern to Alaska
Native people because even if palliatives were to runoff into nearby water bodies, they would be greatly diluted.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Figure 6. Hodge and Sterner Toxicity Scale: LD50s (in mg/kg)
for Palliatives and Household Products
Palliative
Predicted
LD50s
Toxicity Scale
by Oral Rat LD50s
Extremely Toxic
LD50 = <1
(a taste, a drop)
Highly Toxic
LD50 = 1-50 ฎ
(1 teaspoon)
D
Common
Household
Product LDSQs
Moderately Toxic
LD50 = 50 - 500
(1 fluid ounce)
U
Laundry detergent
(333)
r
EK-35
(1,060-1,753)
EnviroKleen*
(>2,811->4,143)
Durasoil*
(>3,409->14,173)
Slightly Toxic
LD50 = 500 - 5,000
(1 pint)
Aspirin
(1,500)
Bug spray
(1,747)
Salt
(>3,000)
Durasoil*
(>3,409->14,173)
Practically Non-Toxic
LD50 - 5,000 -15,000
(1 quart)
Baby foaming shampoo & wash
(>5,000)
Air freshener & deodorizer ฆ -
(5,800)
- Km
Hand sanitizer
5 (7,060)
ป I
Bar soap
(12,600)
Hand & body lotion
I (12,600)
J
Relatively Harmless
LD50 = >15,000
(21 quart)
(20,000)
fflji
Vafifec
No-rinse body wash
Hซjy*vSa5li
(20,000)
11II7
All numerical values are LD50s in units of milligrams per kilogram (mg/kg).
*Toxicity values for Durasoil and EnviroKleen represent lower bounds and could be larger (less toxic) than the
values reported here. The extrapolated LD50s are based on their LC50s, for which it is only known that their toxicity
is above a certain tested maximum concentration, which is why ">" symbols are applied to the ranges. Durasoil falls
into two categories, based on its wide range of predicted LD50s.
The Hodge and Sterner scale is referenced in various sources, such as
https://www.ccohs.ca/oshanswers/chemicals/ld50.html.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
Overall, EK-35 was found to be the most toxic of the three palliatives. Because LC50s were not observed at the
maximum concentrations tested for Durasoil and EnviroKleen, ERG cannot definitively say which of the two
palliatives is more toxic. However, based on the maximum concentrations tested during toxicity assessments, there
is evidence to suggest that Durasoil likely has a lower toxicity than EnviroKleen. To give an idea of how
comparatively toxic the palliatives are, the established Hodge and Sterner Toxicity Scale was used to compare the
predicted palliative LD50s to LD50s for household products.(Figure 6). Specifically,
This comparison to household products revealed that EK-35 was more toxic than the active ingredients of
most household products evaluated. The most toxic estimate for EK-35 fell in the same toxicity range as
aspirin and bug spray, but was more toxic than other household products examined (e.g., bar soap) except
for laundry detergent.
Durasoil was in the same toxicity range of products like baby foaming shampoo and wash, bar soap, and
hand sanitizer, and was less toxic than aspirin, bug spray, and laundry detergent.
EnviroKleen's predicted toxicity was lower than aspirin, bug spray, and laundry detergent, and within the
same toxicity range as salt.
This comparative analysis between the estimated toxicity of these three palliatives and common household products
shows that Durasoil and EnviroKleen in their pure, undiluted form are not more toxic than many commonly used
household items.
5.3. Data Gaps/Research Needs
As with all scientific approaches of this nature, there are some limitations that need to be acknowledged with the
computational evaluation of potential toxicity. The identified limitations include the following:
The specific chemical composition of each dust palliative is proprietary, which prevented the ability to
conduct chemical-specific analyses.
Computational approaches such as QSAR rely on understanding the chemical structure of a compound to
better understand its behavior given structurally-similar compounds. Though these data were unavailable,
ERG was able to employ computational methods to evaluate relative toxicity.
Mammalian toxicity data were not available for the three subject dust palliatives as whole products.
Based on available data, specific adverse human or ecotoxic effects associated with these palliatives are
unknown.
There are inherent uncertainties in any type of extrapolation approach, such as that used here to extrapolate
LC50 aquatic concentrations to LD50 mammalian doses. For example, a model is only as good as the test
dataset. That is, extrapolating information for chemicals that are very different than the compounds used to
develop the model would not be appropriate. However, the two different models used in the approach
above led to similar results, which provides evidence for their predictions.
Toxicity endpoints for two of the palliatives (Durasoil and EnviroKleen) were reported as being greater
than the maximum concentration tested, so the exact toxicity levels were unknown. Not knowing the actual
concentrations for the LC50s limited our ability to conclusively compare these palliatives to many of the
household products.
The regression models were originally developed using data from individual chemicals with known
properties. These models are improved by including chemical-specific properties as covariates. Fortius
effort, chemical-specific information to include in the model was not available.
The regression models reported in the literature were fit to data in molar units. ERG compensated for this
limitation by using a similar approach and developing a regression model based on the units of our toxicity
data, mg/L (as opposed to molar units).
Toxicity data presented in the SDSs for household products were often based on the main ingredients, not
the whole product as for the palliative toxicity data.
When comparing LC50s, aquatic data for household products were only located in SDSs for one of the
three common endpoints for acute toxicity: 96-hour LC50 in rainbow trout.
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Section 5-Computational Evaluation of Potential Palliative Toxicity
To address some of these limitations, additional toxicity data for these palliatives is desired. Specifically, studies
should evaluate the toxicity of these palliatives to mammals at endpoints beyond lethality. This additional data
would provide for a more direct evaluation of the potential toxicity of these three palliatives to humans. Moreover,
having the actual levels at which certain endpoints occur for Durasoil and EnviroKleen would allow for calculating
actual estimates of toxicity, rather than needing to use the available upper bound data based on the maximum
concentrations tested.
5-29
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Section 6-References
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Section 6-References
UAF (University of Alaska Fairbanks)/AUTC (Alaska University Transportation Center). 2013. Dust Control for
Unpaved Roads and Runways in Rural Alaska.
http://www.dot.state.ak.ns/stwddes/research/assets/pdf/tb001 dust.pdf.
Withycombe, E., and Dulla, R. 2006. Alaska Rural Dust Control Alternatives. Prepared for ADEC. Report No.
SR2006-03-03. Sacramento, CA: Sierra Research, Inc. https://dec.alaska.gov/media/7468/diist-control~report~
032006.pdf.
Zolotarev, K.V., N.F. Belyaeva, A.N. Mikhailov, and M.V. Mikhailova. 2017. Dependence between LD50 for
rodents and LC50 for adult fish and fish embryos. Bull Exp Biol Med, 162(4):445-450.
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