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OPPT Proposed Draft Charge to External Peer Reviewers for the review of the TSCA 

Workplan Chemical Risk Assessment of ATO

December 2012

This assessment evaluated the environmental risks that may be associated with ATO use as a 

synergist in halogenated flame retardants. Human health risks were determined to be of low 

concern; the available hazard data are summarized in an appendix. 

Issue 1. Overall Clarity of the Assessment. Chapter 1 provides the scope of the assessment 

and a brief introduction. Supporting information on chemistry, fate, and uses are provided 

in Chapter 2 and the exposure, hazard, and risk characterizations are presented in 

Chapter 3. Additional supporting information is available in the appendices.

Question 1-1. Please comment on the clarity and strengths and weaknesses of the risk 

assessment and provide specific suggestions regarding how this may be improved. 

Issue 2. Characterization of Environmental Exposures Based on Release Data. During 

project scoping, OPPT identified ATO use as a synergist in halogenated flame retardants 

as the focus of this assessment. EPA’s 2010 Toxic Release Inventory (TRI) was used to 

obtain information on water releases associated with this end-use scenario. Data collection 

was refined using the North American Industry Classification System (NAICS) codes to 

identify a subset of TRI facilities (i.e., those indicating production, processing or use of 

ATO-containing flame retardants). Because ATO is not specifically listed on the TRI, data

reported under the broader category of ‘antimony compounds’ were used as a surrogate 

for ATO in this assessment. ATO surface water concentrations were predicted using a 

screening level tool (E-FAST2), to model water releases reported by selected TRI facilities.

Question 2-1: TRI information reported for ‘antimony compounds’ was used to estimate 

ATO releases associated with its use as a synergist in halogenated flame retardants. Please 

comment on this approach. 

Question 2-2: Because TRI does not indicate the number of days associated with reported 

releases, two exposure scenarios were developed (assuming the total water releases reported 

in the 2010 TRI occurred over a period of 250 days or, a more conservative scenario of 24

days to provide a range of predicted water concentrations for comparison with hazard 

benchmarks (concentrations of concern) identified for aquatic organisms. Please comment 

on the assumptions used to develop modeling scenarios using EPA’s E-FAST2 model to 

assess aquatic exposures to ATO. 

Question 2-3: Please comment on the approach EPA used to estimate environmental 

releases resulting from uses of ATO as a synergist in flame-retardant chemicals. Are there 

other data sources or approaches that EPA should consider to estimate environmental 

releases of ATO in this end-use? If so, please provide citations or data for consideration in 

further revision of the draft assessment.
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Issue 3. Characterization of Environmental Exposures Based on Monitoring Data. OPPT 

used environmental monitoring information obtained from the U.S. Geological SurveyNational Water Information System and EPA's STORET database to evaluate antimony 

levels in environmental media. Data collection was limited to states (n=10) with TRI 

facilities (n=14) having NAICS codes corresponding to ATO uses as a synergist in 

halogenated flame retardants. 

Question 3-1: Please comment on the use of these large monitoring data sets to characterize 

ecological exposures to ATO use as a synergist in flame retardants and their 

representativeness for other locations in the US. 

Question 3-2: Are there other major sources of environmental monitoring data (or other 

pertinent information) that EPA should incorporate in the exposure assessment? If so, please 

provide the necessary citations and/or data for inclusion in the revised document. 

Question 3-3: Are there concerns or limitations in these data sets that may impact their 

utility for risk assessment? 

Issue 4. Fate, Transport and Bioavailability. Information available in the published 

literature regarding the chemistry, fate and transport of ATO is used qualitatively to assess 

bioavailability to ecological organisms. There is a lack of site-specific data on geochemistry 

that would inform specification and availability antimony compounds in its toxic forms for 

environmental receptors.

Question 4-1: Please comment on the use of this information in the ATO assessment. Are 

there other data sources that EPA should consider? 

Issue 5. Environmental Hazard Assessment. The available hazard information was 

critically evaluated based on specific test guidelines, accepted endpoints used to assess 

ecotoxicity, and the amount of detail provided in each study report. Hazard benchmarks 

(i.e., concentrations of concern) were subsequently derived using the most robust 

ecotoxicity studies and conservative ecotoxicity values identified in the published literature. 

Acceptable toxicity data were not available for ATO for both chronic and acute exposures 

in all media. For this reason, toxicity data for antimony trichloride is used to characterize 

hazards to water, soil, and sediment dwelling organisms. This is not expected to 

significantly impact the findings of this assessment because (1) upon dissolution, antimony 

compounds release antimony ions, and it is the fate and toxicity associated with the total 

antimony ion concentration that is of most importance when assessing the toxicity of 

antimony in environmental media and (2) both the oxide and chloride salts of antimony 

produce comparable amounts of antimony ions upon dissolution in water.

Question 5-1: What other factors should EPA consider in evaluating the potential risks of 

concern for ecological organisms from antimony species? Please comment on the use of 

toxicity data for antimony trichloride to characterize hazards to water, soil, and sediment 

dwelling organisms. 
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Issue 6. Environmental Risk Characterization. The ATO assessment evaluates risks of 

concern posed to ecological organisms as a result of ATO use as a synergist in halogenated 

flame retardants. Generally speaking, risks are indicated when antimony levels in 

environmental media (as indicated by environmental monitoring and industrial release 

information) exceed the hazard benchmarks (i.e., concentrations of concern) identified for 

ecological organisms in water, soil and sediment. This approach resulted in very few 

instances where the concern concentrations for water or sediment dwelling organisms were 

exceeded (< 1%). No exceedances of the hazard benchmarks for soil dwelling organisms 

were identified. The uncertainties/limitations of this approach are discussed in the ATO 

document.

Question 6-1: Please comment on the implicit assumption that antimony concentrations 

measured in environmental media reflect many different inputs (i.e., from various end use

applications and other types of antimony compounds in addition to ATO) and how this could 

impact the risk estimation. 

Question 6-2: The findings reported in this assessment hinge on the assumption that a 

‘conservative’ scenario has been presented (based on the assumption that all releases of 

various types of antimony compounds have been attributed to ATO use in flame retardants) 

and as such, reflect a conservative estimate of risk of exposure to ATO. Please comment on 

validity of this assumption and the likelihood that the actual risks of concern posed to 

ecological organisms have been over (or under) estimated.

Question 6-3: Please comment on the data set used to evaluate exposures to soil-dwelling 

organisms and the limitations and/or uncertainties in estimating risk to soil-dwelling 

organisms. Please provide comment on additional data sources, surrogate/related chemicals, 

or approaches to estimate risks under data poor conditions?