1



## Summary of External Peer Review and Public Comments **and Disposition** 

This document summarizes the public and peer review comments that EPA’s Office of Pollution Prevent and Toxics (OPPT) received on the external review draft **TSCA Work Plan Chemical Risk Assessment for ATO.**  It also provides EPA/OPPT’s response to the comment s receive from the public and the peer review panel.

EPA/OPPT appreciates the valuable input provided by the public and peer review panel. The input resulted in substantial revisions to the risk assessment

Peer review charge questions 1 are used to categorize the peer review and public comments into specific issues related to four main themes.

• General Issues on the Risk Assessment Document

• Use of fate, transport and bioavailability informat ion

• Environmental Exposure Assessment

• Hazard and Dose‐Response Assessments

• Risk Characterization

1 These are the questions that EPA/OPPT submitted to the panel to guide the peer review process.2

**1 Issue 1: Overall Clarity of the Assessment** 

The charge question under Issue 1 asked the peer re view panel to comment on the following:

**Please comment on the clarity, strengths and weakne sses of the risk assessment and**  **provide specific suggestions for how it may be impr oved.** 

**1.1 Terminology** 

**Comment:** Peer reviewers stated that proper risk assessment terminology and organization were not used in the ATO risk assessme nt and suggested that it be
restructured to follow EPA’s Risk Framework Guidanc e.

**Response:** The revised ATO assessment has been revised extensi vely, including to better align basic terminology and structure with EPA’s Gu idelines for Ecological Risk

Assessment.

**Comment:** Both public and peer review comments questioned t he use of descriptive terms such as, “conservative”, “sensitive”, “robust ” and “persistent” and requested that
these terms be defined.

**Response:** Descriptive terms have been further clarified or r emoved from the assessment except where these descriptive terms are clearly de fined.

**Comment:** Peer reviewers requested clarification for descrip tive terms used to characterize persistence and bioaccumulation potent ial ( **e.g** ., “low”, “moderate”, and “high”).

**Response:** EPA/OPPT has removed to PBT predictions and descrip tors used in draft assessment and included description of relevant dat a that informs persistence and
bioaccumulation in the fate section.

**Comment:** The acronym “COC” can be interpreted as “chemical of concern” or
“contaminant of concern” instead of the risk assess ment’s intended meaning of
“concentration of concern”.

**Response:** This acronym is clearly defined at the beginning of the document in the Glossary of Terms and Abbreviations section.

**1.2 Scope** 

**Comment:** Public and peer review comments suggested that the report be referred to as a scoping or screening assessment, because it is ba sed on conservative assumptions.3

**Response:** EPA/OPPT acknowledges the conservative assumptions used in the ATO risk assessment. In response to this comment, additional clarifying language has been added in Chapter 1 and the risk characterization Chapter 3, which states that this evaluation is based on available data and modeling; models are de scribed and referenced.

**Comment:** Public and peer review comments indicated that the risk assessment goals, objectives and scope were not adequately described in the report ( **i**

. **e** ., the assessment should be distinguished as either a nationwide, reg ional, or site specific assessment of past, current or future risks).

**Response:** EPA/OPPT has made significant revisions to the ATO risk assessment to improve the clarity of the document. **Chapter 1** of the final risk assessment has been restructured to include additional sections describing Problem Form ulation, Conceptual Model and the Analysis Plan for ATO; all of these address the iss ue of scope and scale of the assessment.

**Comment:** Peer reviewers identified the focus on aquatic ecos ystems as a weakness of the ATO assessment (because most of the reported an timony releases are to terrestrial systems) and suggested that risks associated with l and disposal be evaluated as part of
the assessment.

**Response:** In response to this comment, the problem formulatio n section of Chapter 1 has been updated to provide further explanation for why risks to terrestrial and specifically, soil‐dwelling organisms were not eval uated. During scoping, all potential exposure pathways were considered and risks to aqua tic and benthic organisms were identified as a primary concern. The terrestrial co mpartment was not assessed due to limitations in the available monitoring data for so il which precluded a meaningful risk estimation. EPA/OPPT acknowledges that most of the reported antimony releases are to land; however, land disposal of antimony‐containing materials is expected to represent a minor exposure pathway based on: 1) the limited bio accessibility of antimony in soil and 2) existing land disposal regulations under other s tatues (CERLA and RCRA). Previous evaluations of the land disposal pathway (discussed in sections 3.1.2 and 4.1.3.4 of the European Union Risk Assessment Report support this conclusion.

**1.3 Problem formulation** 

**Comment:** A lack of clarity was observed in the risk assessme nt’s problem formulation, with some peer reviewers stating that this step was skipped.

**Response:** Problem formulation was conducted for the ATO asses sment; however, in response to this comment, the description of this s tep has been expanded in Chapter 1.4

**Comment:** Peer reviewers stated that a conceptual model which would have guided the analysis (and provided some justification for why c ertain environmental compartments were excluded) was absent from the assessment.

**Response:** To increase transparency, a conceptual model has been added in Chapter 1.

**Comment:** Public and peer review comments indicated that th e assumptions about sources of ATO releases and potential contact with ecological receptors were not clearly communicated in the report.

**Response:** In response to this comment, the discussion of pote ntial release sources has been expanded and a conceptual model has been added in Chapter 1 and in the analysis approach in Chapter 3. In addition, to increase tr ansparency, further discussion of the primary assessment assumptions has been added to th e exposure assessment.

**Comment:** Public and peer review comments indicated that use of a “worst‐case
scenario” was not well communicated in the risk ass essment.

**Response:** In response to this comment, the risk characterizat ion section has been updated to include additional clarifying language a bout assumptions used in the problem formulation and risk characterization that conveys this point. Furthermore, where conservative assumptions or data selections were ma de regarding exposure or hazard, they are noted.

**Comment:** Peer reviewers stated that more attention should be placed on assessment endpoints ( **i.e** ., hazard benchmarks) and data quality objectives.

**Response:** In response to this comment, Data evaluation criter ia are stated and referenced in Chapter 3. Briefly, data adequacy cri teria include, but are not limited to: test substance identification, number of organism i n each dose/concentration group, dose/concentration level, route/type of exposure, d uration of exposure, species, controls (for additional details, see EPA, 1999). Studies co nducted according to established EPA or OECD Guidelines as well as studies using other prot ocols were included if they met data adequacy criteria. EPA/OPPT has also added addition al detail to the tables to clarify the
critical elements of each hazard benchmark includin g test type/guideline used, toxicity endpoint and effect.

**1.4 Environmental Assessment** 

**Comment:** One peer reviewer stated that Chapter 3 of the report should be reorganized to include a discussion of all acute endpoints, fol lowed by a discussion of all chronic endpoints.5

**Response:** EPA/OPPT has revised the Ecological Hazard Assessme nt section to include separate sections acute and chronic toxicity to aqu atic organisms. For sediment‐and soil‐ dwelling organism, all available data were chronic data, so no acute discussion was
included.

**Comment:** Public and peer review comments indicated that the following should be added to the ATO report: 1) the criteria for study selection, 2) a general summary of the hazard and exposure data, and 3) conclusions drawn from previous assessments.

**Response:** The draft ATO document referenced a general adheren ce to internationally accepted guidelines ( **e.g** ., OECD, OPPTS, ASTM, etc) as the main criteria for study selection; however, EPA/OPPT agrees that further di scussion of these topics may serve to strengthen the assessment. In response to this comm ent, a more transparent discussion of the available hazard information, including spec ific criteria used for study selection and conclusions drawn from previous assessments, has be en added to the environmental hazards section including revised study summary tab les.

**Comment:** Peer reviewers noted that a comprehensive discussio n of antimony speciation and how it impacts environmental fate, transport, b ioavailability, biotransformation, and bioaccumulation potential is absent from the report

.

**Response:** EPA/OPPT has revised the Environmental Fate section . It includes discussion of fate of antimony in water, sediment, soil and ai r. In addition, a detailed discussion of environmental bioavailability, transformation and b ioaccumulation of antimony has been
included.

**1.5 Environmental Risk Characterization** 

**Comment:** Peer reviewers requested further justification for the decision to use a deterministic approach based on single point estima tes, rather than a probability distribution for the exposure concentration and res ponse functions.

**Response:** Exposure and hazard data currently available for AT O are limited and largely inadequate for a probabilistic approach. However, a probabilistic approach was utilized for modeling releases from TRI facilities to estima te environmental water concentrations. EPA/OPPT maintains that a deterministic approach is most appropriate for evaluating the exposure concentration and response functions when data are limited, as is the case with
the available hazard data.6

**2 Issue 2: Characterization of Environmental Exposure**  **s Based on Release Data**

The charge questions under Issue 2 asked the peer r eview panel to comment on the following:

**During project scoping, OPPT identified ATO use as a synergist in halogenated flame**  **retardants as the focus of this assessment. EPA’s 2 010 Toxic Release Inventory (TRI) was**  **used to obtain information on water releases associ ated with this end-use scenario. Data**  **collection was refined using the North American Ind ustry 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 AT O is not specifically listed on the**  **TRI, data reported under the broader category of ‘A ntimony compounds’ were used as a**  **surrogate for ATO in this assessment. ATO surface w ater concentrations were predicted**  **using a screening level tool (E-FAST2), to model wa ter releases reported by selected TRI**  **facilities.**

**2.1 Use of TRI data for Antimony compounds** 

**Comment** : Peer reviewers stated that Industry reported TRI data should not be the sole source of antimony release information due to the i nherent limitations in this dataset ( **e.g** ., inconsistent and/or incomplete release informati on, and the lack of verification).

**Response:** EPA/OPPT reviewed all data sources mentioned in the ATO peer review report; however, most of the reported information was not u seful for a TSCA‐related assessment because it was too generic with regard to the sourc e of antimony. EPA/OPPT examined numerous reports and databases during the search fo r relevant release data, and concluded that TRI provided the best available rele ase information because it is the only
database that differentiates between the release of antimony compounds and that of elemental antimony, and allows for characterization of environmental releases across industry sectors. The caveats and limitations assoc iated with use of TRI data are explicitly
discussed in the ATO assessment.

**Comment:** One peer reviewer suggested that the assessment b e revised to include a qualitative discussion of emissions from other rele ase sources ( **e.g** ., ammunition, brake linings) and waste disposal scenarios.

**Response:** In response to this comment, the problem formulatio n section in Chapter 1 has been further revised to clearly articulate the decision logic used to narrow the scope
of the assessment to ATO use as a flame retardant s ynergist. This ATO assessment is not intended to present an extensive overview of antimo ny emissions from all sources across the US and was focused on the highest potential exp osures/releases related to TSCA.

**Comment:** Peer reviewers requested that all TRI‐related mat erial be consolidated within the Exposure section of the ATO risk assessment.7

**Response:** TRI information is now presented predominantly in t he exposure with some mention of the modeled outputs in the risk characte rization section.

**Comment:** Peer reviewers stated that sample collection deta ils ( **e.g** ., distance between sampling sites and TRI facilities) should be report ed for the soil data set and an overview of antimony concentrations in biosolids should be i ncluded in the report within the context of potential application to agricultural or rangeland soils.

**Response:** As stated in the ATO risk characterization, EPA/OPPT evaluated the available hazard and exposure data for soil and determined th at it was inadequate to support a quantitative risk evaluation. Due to data limitatio ns this pathway was not assessed quantitatively in this assessment and therefore sam ple collection details were deemed

unnecessary.

**2.2 Modeling Approach and Assumptions** 

**Comment:** Peer reviewers requested that all model input data and assumptions be provided in the risk assessment.

**Response:** EPA/OPPT has provided modeling input data including the name of receiving stream, and stream flow, in Appendix B of the revis ed assessment.

**Comment:** One peer reviewer stated that use of TRI data in the model violated many conditions and assumptions of the model and represe nted an inappropriate use of the data. Specifically, E‐FAST2 requires information on the total number of release days per year, which TRI data do not provide.

**Response:** EPA/OPPT disagrees with the assertion that TRI data are inappropriate for use in (or violate conditions of) the E‐FAST2 model. Wh ile TRI data do not include the total number of release days per year, EPA/OPPT developed an approach, including two scenarios, for putting TRI release data into a rele ase days per year context (see next comment). The limitations of the ATO exposure asses sment are explicitly acknowledged in the data limitations and uncertainty section. T hese limitations which are predicated on conservative assumptions does not preclude use of t he E‐FAST2 model for estimating surface water concentrations at the identified poin ts of release. All model assumptions are clearly articulated in the exposure section of the ATO assessment.

**Comment:** Peer reviewers requested further clarification for why the 250‐ and 24‐day/yr release scenarios were selected, and whether the 24 ‐day/yr release scenario reflects 24 consecutive days of release.

**Response:** EPA/OPPT has included more detailed explanation for the release scenarios in the Exposure Assessment section of the revised asse ssment. Briefly, because the TRI data do not include specific information on patterns of release, two hypothetical release8

scenarios were developed to provide an upper and lo wer bound for the range of daily
releases that could be used to estimate surface wat er concentrations. This allowed for comparisons between estimates based on higher daily release amounts incurred over a shorter time interval ( **e.g.** , 24 consecutive days) and a less extreme situation in which lower daily release amounts are incurred over a lon ger time interval.

**Comment:** Peer reviewers requested further discussion of the exposure analysis and
more information on how the Probabilistic Dilution Model and E‐FAST2 model work.

**Response:** The exposure assessment has been revised to include additional discussion on
the Probabilistic Dilution Model and E‐FAST2. In ad dition, detailed information on these models is publicly available on EPA’s website: http://www.epa.gov/oppt/exposure/pubs/efast.htm , a link to which is also provide in the
revised document.

**Comment:** In order to help readers understand the geographic relationship between the monitoring data and TRI facilities, peer reviewers suggested that the report provide the HUC‐12 code for watersheds impacted by selected TRI facilities, and specific locations for the water monitoring data used in the exposure asse ssment.

**Response:** As stated in the Exposure Assessment, none of the i dentified TRI facilities and environmental monitoring sites were located within the same watershed. As noted in the assessment, the monitoring data were collected for many reasons that are not linked to TRI facilities. It was clear based on the 8‐digit s cale (HUC‐8) used in this report, that the selected TRI facilities were many miles away from t he environmental monitoring sites. As such, additional refinement with more detailed info rmation at the HUC 12‐digit level would not significantly improve the assessment nor change the conclusions stated
therein.

**2.3 Alternative Data Sources** 

**Comment:** One peer reviewer suggested that data from TOXNET and CTD be used to identify point source discharge data gaps for air, water, and soil in order to improve the accuracy of the estimated environmental releases re ported in the 2010 TRI.

**Response:** Unlike TRI, these databases do not contain point so urce discharge data. These sources are used primarily by Superfund cleanup pro grams and are not applicable to the
TSCA‐related use scenarios evaluated in this assess ment. Therefore, these data sources
were not included in the revised assessment.

**2.4 Alternative Approaches** 

**Comment:** One peer reviewer stated that: 1) risk e **s** timation should be based on antimony trichloride rather than the total release of antimony compounds reported in9

the 2010 TRI; 2) antimony trichloride can be presum ed to be entirely trivalent antimony, whereas the TRI data for antimony compounds have an unknown composition of antimony ions; and 3) trivalent antimony is the mor e toxic form of dissolved antimony and will result in overestimates of the toxicity as sociated with TRI discharges.

**Response:** Given the available market and use information for antimony and related compounds, EPA/OPPT maintains that ATO is the most relevant substance for risk estimation. EPA/OPPT found no conclusive scientific to adequately support the assertion of increased toxicity to ecological organisms follo wing exposure to trivalent versus pentavalent antimony. Because ATO is poorly soluble , antimony trichloride has been used as a surrogate to address data gaps for hazard char acterization; however, antimony trichloride acidifies soil and water compartments, and therefore may be considered less reflective of conditions expected in the ambient en vironment. Only if experimental conditions are normalized ( **e.g** ., ecologically relevant pH/ionic strength), can th e reported effects be considered relevant for predicting what may occur under ambient conditions in
the environment.

**Comment:** One peer reviewer stated that the risk assessment would benefit from a broader characterization that considers critical ph ases in the lifecycle of products rather than focusing solely on the largest manufacturing a nd use sector.

**Response:** The ATO assessment focused on use scenarios that co uld be addressed based on the information currently available. A life cycl e analysis is unlikely to change the stated risk findings. A lifecycle assessment was beyond th e scope of this assessment because of limitations in the database for all the relevant pa thways and receptors required for lifecycle assessment.10

**3 Issue 3: Characterization of Environmental Exposure**  **s Based on Monitoring Data**

The charge questions under Issue 3 asked the peer r eview panel to comment on the following:

**OPPT used environmental monitoring information obta ined from the U.S. Geological**  **Survey- National Water Information System and EPA's STORET database to evaluate**  **Antimony levels in environmental media. Data collec tion was limited to states (n=10)**  **with TRI facilities (n=14) having NAICS codes corre sponding to ATO use as a synergist in**  **halogenated flame retardants.**

**3.1 The Use of Large Monitoring Datasets** 

**Comment:** Peer reviewers stated that information presented i n the ATO risk assessment was not representative of other locations in the US , and suggested that monitoring data obtained from other states (in addition to those in itially selected) be included.

**Response:** EPA/OPPT acknowledges the data limitations and unce rtainties associated with the exposure assessment used for the ATO asses sment. The purpose of this effort was to refine the analysis so that it focused speci fically on TSCA‐related uses. EPA/OPPT did not intentionally limit the analysis to 10 stat es; however, areas with the highest reported environmental releases (i.e., from industr ies that potentially use or produce ATO as a synergist in halogenated flame retardants base d on TRI reporting) were located in these areas. It was found that these TRI facility r elease sites were not located within watersheds where the available monitoring data were collected. Therefore, the monitoring data was not used for quantitative risk characterization, but only as a line of evidence support the risk conclusions.

**Comment:** Peer reviewers suggested that a query of hydrologi c unit codes (HUCs) rather
than states would allow EPA to better assess whethe r antimony discharges are causing environmental risk and requested that the HUC‐12 co de be included in Table 3‐2.

**Response:** HUCs, unlike TRI data, do not allow for the identif ication of environmental
releases that can be associated with TSCA‐related u ses. Therefore, extensive query of monitoring data that cannot be linked to TSCA‐relat ed antimony use is beyond the scope
of this assessment.

**Comment:** Peer reviewers noted a discrepancy in the timeframe associated with the environmental monitoring information and industry r eported release data used in the exposure assessment. Questions regarding the use of historical data for this risk
assessment were also raised.

**Response:** Although the historical monitoring data may be usef ul for inclusion in a weight‐of‐evidence approach, it was not used for ri sk characterization in the revised11

assessment. In response to this comment, the ATO do cument has been revised to explicitly state that the historical monitoring dat a were not use to evaluate current risks

**.**

**Comment:** One peer reviewer noted that measured antimony conc entrations were not considered within the context of background levels that occur naturally in the environment and suggested that a literature search be conducted to find published articles reporting antimony concentrations in the a mbient environment.

**Response:** EPA/OPPT conducted additional literature searches o n background antimony concentrations. Distribution patterns for antimony are largely dominated by natural variation, and a high sample density is required to establish a reliable baseline levels in
the ambient environment. Because the available moni toring data are limited (in terms of the number of sites sampled over a given area), ant imony levels reported in the USGS data set or other published literature may not accu rately reflect natural background concentrations. In addition, regional differences i n geochemistry and weather conditions, as well as variations in analytical and sampling te chniques, make direct comparisons difficult. It is important to note however, that th e measured and predicted antimony concentrations reported in the ATO risk assessment are low and do not indicate a concern for elevated background concentrations.

**Comment:** Peer reviewers suggested that the monitoring data c ollected for the ATO risk assessment should include waste disposal areas beca use they are the largest release sources by mass.

**Response:** Limited and rather uncertain data are available reg arding the occurrence of ATO in waste materials and emissions that may be pr oduced by various disposal methods. This exposure pathway is not expected to present th e greatest potential for environmental exposure due the limited bioavailabil ity of antimony in the soil and terrestrial compartment, as well as current regulat ory, reclamation and recycling activities. In response to this comment, further ex planation for the decision not to include the waste disposal exposure scenario in this assess ment has been added to the problem formulation section of Chapter 1.

**Comment:** Peer reviewers noted that the monitoring sites for the STORET and USGS data do not correspond to any of the discharge locations reported to TRI and suggested that this information was used for purposes not original ly intended.

**Response:** EPA/OPPT acknowledges the lack of spatial overlap b etween the TRI facilities and monitoring data, and the basic utility of the i nformation gleaned from these datasets. Despite the conservative assumptions underpinning t his assessment, the environmental monitoring data obtained from these databases showe d very few instances where ambient antimony concentrations exceeded or even ca me near the identified hazard
benchmarks that would otherwise indicate a concern for ecological organisms. While this12

is informative and provided as a comparison to the findings linked to the TRI facilities, its use in quantitative risk estimation has been deemph asized in the risk characterization.

**3.2 Data Set Limitations** 

**Comment:** Peer reviewers noted that STORET data do not undergo quality assurance review and require no standard methodology or level s of quantification. It was suggested that spatially and temporally unrelated data be use d with caution in the risk assessment.

**Response:** EPA/OPPT agrees that spatially and temporally unrel ated data should be used with caution. EPA/OPPT found that these TRI facilit y release sites were not located within watersheds where the available monitoring data were collected. Therefore, the monitoring data was not used for quantitative risk characterization, but only as a line of evidence support the risk conclusions.

**Comment:** One peer reviewer stated that the report lacked an exploratory data analysis ( **i.e** ., distribution type, breaks in the information, sp atial patterns in the regions).

**Response:** Given the stated data limitations in the spatial ov erlap between the TRI facilities and the monitoring data it is unclear ho w this would improve risk
characterization.13

**4 Issue 4: Fate, Transport and Bioavailability** 

The charge questions under Issue 4 asked the peer r eview panel to comment on the following:

**Information available in the published literature r egarding the chemistry, fate and**  **transport of ATO is used qualitatively to assess bi oavailability to ecological organisms.**  **There is a lack of site-specific data on geochemist ry that would inform specification and**  **availability [of] Antimony compounds in [their] tox ic forms for environmental receptors.** 

**4.1 Role of Environmental Factors on Antimony Bioavaila**  **bility and Transformation**

**Comment:** Peer reviewers noted that Environment Canada’s rec ent review of environmental fate and bioavailability issues for a ntimony and the European Union Risk Assessment Report provide additional reference info rmation that could inform the ATO assessment. It was suggested that the discussion re garding effects of environmental factors on antimony bioavailability and transformat ion be supplemented with a summary table indicating how bioavailability is affected by these factors.

**Response:** EPA/OPPT has revised the Environmental Fate section . It includes discussion of fate of antimony in water, sediment, soil and air. In addition, a detailed discussion of environmental bioavailability, transformation and b ioaccumulation of antimony has been
included.

**Comment:** One peer reviewer recommended that EPA use equati ons rather than single values to quantify antimony’s BAF. Others noted tha t mining studies have measured antimony concentrations in soils and plants and tha t the principles for soil sequestration and uptake would be similar and could therefore pro vide general estimates for Antimony’s BAF.

**Response:** EPA/OPPT could find no appropriate equations for ca lculating BAFs for metalloids and as a matter of principle this not re commended in EPA’s metals assessment guidance. In response to this comment, EPA/OPPT has included monitoring information from areas near an antimony emitting smelter to pro vide additional insights regarding antimony uptake, and the potential for bioaccumulat ion in the food chain.

**Comment:** One peer reviewer stated that EPA should explore t he literature for studies on antimony pertaining to storage and use facilities, previous mining operations, or accidents along transportation routes.

**Response:** EPA/OPPT’s work plan assessments focus on its TSCA authority, which does not include evaluations of these types of scenarios ; however, the monitoring information collected near an antimony emitting smelter has bee n included in the assessment for context. The revised assessment also speaks to thes e pathways and the respective regulatory authorities which already regulate them.14

**Comment:** One peer reviewer stated that EPA could use inform ation about antimony bioaccessibility and bioavailability in the peer‐re viewed literature to adjust total antimony
concentrations in the environment to bioaccessible concentrations.

**Response:** While site‐specific parameters may provide some qua litative context, this information cannot be used quantitatively to determ ine the bioavailable fraction of antimony, because it is a function of many differen t environmental conditions ( **e.g** ., pH, temperature, geochemistry, matrix components, meteo rological conditions), that can vary seasonally and temporally. Clarification of th is myriad of contributing factors has
been included in the revised assessment.

**4.2 Environmental fate** 

**Comment:** One peer reviewer requested clarification for why antimony’s behavior in air
and marine waters is relevant to its behavior in fr esh water.

**Response:** As stated in the EU RAR, deposition from combustion sources is expected to be a major source of antimony deposition in marine and freshwater systems. Combustion or incineration processes are likely to transform Anti mony compounds to ATO regardless of the pre‐incinerated form of antimony. This will rel ease ATO into the air where it can undergo additional transformation and long range tr ansport before being deposited to surface waters or soils through wet and dry deposit ion. This assessment did not focus specifically on this pathway. Evaluation of monitor ing information would have taken into account deposition from air sources but there is no way to provide source attribution at the present time.

**Comment:** One peer reviewer stated that no obvious attempt was made to understand the fate, transport, and bioavailability of ATO at the sites considered.

**Response:** This is not a site specific risk assessment; howeve r, a qualitative discussion of antimony fate, transport, and bioavailability can b e found in the fate section.

**Comment:** One peer reviewer stated that fugacity modeling sho uld be applicable to ATO and recommended that EPA identify two to three site s, characterize the routes of exposure, and conduct fugacity modeling.

**Response:** Fugacity modeling is not applicable to inorganic su bstances having a negligible vapor pressure, negligible Henry’s Law constant and no octanol water partition coefficient. As noted in the Environment Canada Rep ort on ATO: “...Typical mass balance fugacity modeling is also not applicable to Antimon y trioxide or to the metal ions that are released from it on dissolution, because, as for ot her non‐volatile chemicals, these substances exert zero partial pressure and fugacity in air...”15

**Comment:** One peer reviewer stated that the partitioning of antimony between particles
and water was not discussed in the fate section of the ATO risk assessment, and alluded to existing data which indicates that most antimony is present in the dissolved phase.

**Response:** Site‐specific parameters can impact solubility; how ever, EPA/OPPT disagrees
with the assertion that most antimony is present in the dissolved phas e upon release into the environment. Based on reported sediment‐water p artition coefficients, antimony is expected to sorb to solid particles in aquatic medi a and precipitate out of solution. As reported in the EU RAR (section 3.1.3.1.3), the sol ubility of antimony in soil (and its bioaccessibility to soil‐dwelling organisms) is lim ited due to the formation of a Ca‐ antimonate precipitate. In response to this comment , additional discussion of how the sediment water partition coefficient relates to sol ution chemistry has been added to the

Fate section.

**4.3 Bioaccumulation** 

**Comment:** One peer reviewer suggested that the Bioaccumulatio n section be organized into BCF and BAF for soil and water separately.

**Response:** EPA/OPPT revised the Fate section in the final asse ssment to incorporate this suggestion.

**Comment:** State that site‐specific information on soil monito ring data can be used to investigate the transformation, bioavailability, an d bioaccumulation of antimony in terrestrial systems.

**Response:** This is not a site‐specific assessment, and there a re no quantitative methods available at this time which can accurately determi ne the bioavailable or bioaccessible fraction of antimony based on total concentrations reported in soils or sediments. In response to this comment, EPA/OPPT has updated the Fate section to include a qualitative discussion of antimony transformation i n the environment and how it can impact bioavailability to environmental receptors.16

**5 Issue 5: Environmental Hazard Assessment** 

Charge questions under Issue 5 asked the p eer review panel to comment on the following:

**The available hazard information was critically eva luated based on specific test**  **guidelines, accepted endpoints used to assess ecoto xicity, and the amount of detail**  **provided in each study report. 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 was used to characterize hazar ds to water, soil, and sediment**  **dwelling organisms. This is not expected to signifi cantly impact the findings of this**  **assessment because (1) upon dissolution, antimony c ompounds 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 a ntimony in environmental media and**  **(2) both the oxide and chloride salts of antimony p roduce comparable amounts of**  **antimony ions upon dissolution in water.**

**Comment:** One peer reviewer stated that toxicity data from st udies using ATO are not similar to toxicity data derived using antimony tri chloride (due to a difference in solubility which would require a greater amount of ATO to yiel d the same number of antimony ions as antimony trichloride), and requested a more in‐d epth discussion of these environmental chemistry issues.

**Response** : The data limitations and uncertainties associated w ith this approach are clearly stated in the environmental hazards and unc ertainty sections. EPA/OPPT understands that antimony trichloride, being more s oluble, will dissolve faster than ATO. As stated in the ATO assessment, the liberation of ions will be slower for ATO, therefore use of antimony trichloride as a surrogate for ATO represents a conservative approach for assessing aquatic hazards. In response to this comm ent, the environmental chemistry and hazard sections have been updated to include a more in‐depth discussion of antimony dissolution chemistry.

**Comment:** One peer reviewer stated that the toxicity data do not account for degradation or transformation of antimony that may occur in environmental media or as a result of interactions with other compounds.

**Response:** Antimony cannot be degraded in the environment, but may be transformed between different chemical phases, forms and oxidat ion states. These types of transformations generally do not occur within the t ime frame of an acute or chronic toxicity test and therefore are not expected to imp act test results. It is acknowledged however, that the test system should be allowed to reach equilibrium before testing, as the slow dissolution of ATO may create increasing p ressure on organisms over time. If toxicity testing is conducted immediately after ATO has been added to the test media, the resulting hazard effects may not accurately reflect those that would be expected at17

equilibrium. In response to this comment, clarifyin g text has been added to the hazard characterization and uncertainty sections to adequa tely convey this point.

**Comment:** One peer reviewer stated that the relative toxiciti es of pentavalent and trivalent antimony should be acknowledged in the re port.

**Response:** As mentioned above, EPA/OPPT located no reliable sc ientific evidence to definitively support an increased relative toxicity following environmental exposure to trivalent versus pentavalent forms of antimony. As stated in the ATO assessment, antimony does not occur as a single oxidation state in the ambient environment. The equilibrium for redox transitioning between trivale nt and pentavalent antimony varies with environmental conditions despite the theory th at only one oxidation state should prevail (EU‐RAR section 3.2.1). This precludes test ing of a single oxidation state, and is
one of the main reasons that the ATO assessment was based on the conservative assumption that all measured and monitored levels o f antimony represent the total dissolved antimony concentration (even though this clearly is not the case).

**Comment:** Peer reviewers stated that a thorough review of th e scientific literature should be conducted to supplement the toxicity data curren tly used in the report.

**Response:** EPA/OPPT reviewed the additional literature provide d in the peer review report and found much of this information not to be relevant and/or not particularly useful for various reasons, including the following : 1) studies failed to adhere to the criteria used to establish data adequacy as outline d in the ATO document, 2) did not use a relevant test organism, as described in the OECD te st guidelines, and/or 3) did not use ATO, antimony trichloride, or another relevant Anti mony moiety for testing purposes.

**5.1 Toxicity assessment** 

**Comment:** One peer reviewer requested further explanation o f the calculations used to
derive concern concentrations.

**Response:** The calculations used to derive concern concentrati ons are described in the Ecological Hazard Assessment and additional clarifi cation shave been added to describe the use of assessment and uncertainty factors.

**Comment:** One peer reviewer stated that NOECs and LOECs are unreliable and should not be used in this risk assessment, and suggested it w ould be more appropriate to use an

EC x .

**Response:** It is clearly appropriate to estimate EC x values where the data are sufficient (‘fit‐for‐purpose’) and the percent effect level to be estimated has a firm biological basis; however, most studies available to assess hazard fo r ATO do not fit this profile. Many of18

these studies were not designed to quantify the pre cise concentration at which a specific size effect occurs, but to determine whether there is an effect that needs to be explored further. As such, regression models for these types of experiments (and the EC x estimates derived from them) offer little value. The advantag e associated with use of a NOEC/LOEC approach is that these values reflect actual tested concentrations obtained from toxicity studies which adhere to internationally accepted gu idelines for data quality (designed to ensure that only reliable studies are included in h azard characterization). In short, the uncertainty associated with use of interpolation (o r extrapolation) methods for derivation
of EC x values, and the questions surrounding data adequac y, and selection of the most appropriate effect level ( **i.e** ., EC 10 or EC 50 ), limit the utility of this approach.

**Comment:** Confidence intervals should accompany LC 50 values.

**Response:** EPA/OPPT has added this information, where availabl e, from the toxicity
studies summarized in the hazard characterization s ection.19

**6 Issue 6: Environmental Risk Characterization** 

Charge questions under Issue 6 asked the pe er review panel to comment on the following:

**The ATO assessment evaluates risks of concern posed to ecological organisms as a result**  **of ATO use as a synergist in halogenated flame reta rdants. Generally speaking, risks are**  **indicated when antimony levels in environmental med ia (as indicated by environmental**  **monitoring and industrial release information) exce ed the hazard benchmarks (i.e.,**  **concentrations of concern) identified for ecologica l organisms in water, soil and**  **sediment. This approach resulted in very few instan ces where the concern**  **concentrations for water or sediment dwelling organ isms were exceeded. No**  **exceedances of the hazard benchmarks for soil dwell ing organisms were identified. The**  **uncertainties/limitations of this approach are disc ussed in the ATO document.** 

**6.1 Limitations of Data and Analysis** 

**Comment:** Peer reviewers stated that the ATO report should st ate upfront that the USGS and STORET data are not from the primary watersheds of the TRI facilities. It was further
noted that an evaluation of data on a watershed bas is instead of a state basis could focus the report on whether the TRI facilities are contri buting to environmental risk, and decrease the relevance of other input pathways.

**Response:** The Environmental Exposure Assessment has been revi sed to include additional clarifying language which clearly states that the USGS and STORET data are not from the primary watersheds of the TRI facilities i dentified under the scope of this

assessment.

**Comment:** One peer reviewer requested that the ATO document state up front that statistical analyses were not performed on the expo sure data and that a comparison of all data points with hazard benchmarks was used to arri ve at a percentage of exceedances.

**Response:** EPA/OPPT has acknowledged that the divisor used to calculate the percentage of exceedances was the total number of samples obta ined from the USGS/STORET databases and that the exposure assessment was not a robust statistical analysis.

**Comment:** Peer reviewers noted that use of data older than 2 0 years is not
recommended for use in the ATO risk assessment.

**Response:** In response to this comment, additional clarifying language which states that
the ATO risk characterization was based on monitori ng data collected over the last three years has been added to the exposure and risk chara cterizations, and has provided
clarification on the data limitations and uncertain ty in the risk characterization section.20

**6.2 Scope** 

**Comment:** One peer reviewer noted that a discussion of the e ffects of long‐term antimony accumulation in sediments and soils is cur rently absent from the report.

**Response:** Land application of ATO is a complicated issue requ iring material flow analysis and model estimates of long‐term accumulation that would require considerable time and resources to generate. In response to this comm ent, additional language which clearly articulates that this issue was not address ed has been added in the Data Limitations and Uncertainty section.

**6.3 Risk Characterization** 

**Comment:** One peer reviewer suggested that a weight‐of‐eviden ce approach be used to balance the input information and help identify whi ch line of evidence is most likely contributing to an overestimate or underestimate of risk.

**Response:** In response to this comment, an expanded discussion of the available evidence, associated data limitations, expected imp acts of the assumptions employed in thee analysis and implications for associated risk estimates have been added in the risk
characterization section.

**Comment:** Peer reviewers stated that proper risk assessment terminology and organization were not used in the ATO risk assessme nt and suggested that it be
restructured to follow EPA’s Risk Framework Guidanc e.

**Response:** The revised ATO assessment has been revised extensi vely, including to better align basic terminology and structure with EPA’s Gu idelines for Ecological Risk

Assessment.