Summary of public comments received on the draft screening assessment for antimony-containing substances

Comments on the Draft Screening Assessment (dSAR) for Antimony-containing Substances, assessed under the Chemicals Management Plan (CMP), were submitted by the Canadian Consumer Specialty Products Association, the Canadian Network for Human Health and Environment, the Saskatchewan Environmental Society, and a private citizen.

Summarized public comments and responses are provided below, organized by topic:

Overarching

Summarized comment Summarized response
The approach using “total” antimony as a surrogate for a number of different compounds needs to be clearly explained. Some exposure sources were assessed based on measurements of total antimony, which is identified as an uncertainty in the assessment. The application of measured total antimony concentrations as a surrogate for the exposure to 11 individual substances is a conservative approach.
The use of “total” antimony in this assessment is suitably conservative for the inorganic compounds. However, there needs to be consideration of varying properties between organometallic compounds and inorganic compounds, as the “total” may underestimate the effect of organic antimony. A detailed analysis of available exposure and human and ecological hazard data for each substance in the group was conducted. It was determined that the selected endpoints were conservative and, therefore, protective of adverse effects from exposure to the general population and to the environment, including the organic and organometallic antimony substances.
There needs to be more justification provided when using a read-across approach for the antimony substances with limited data. Where available, the human health assessment used the most relevant exposure and hazard data for individual antimony substances to which Canadians are exposed. Otherwise, data from trivalent and pentavalent forms of antimony for which there is an exposure in the general population were used. Justification for the use of read-across in the ecological assessment is documented in the Science Approach Document (SciAD): Ecological Risk Classification of Inorganic Substances (ERC-I) (ECCC 2018).
The draft screening assessment is clear and provides a brief description of the hazard data for antimony. The exposure information should be published in a more permanent form. Noted.

Ecological assessment

Summarized comment Summarized response
In the assessment of ecological harm, there needs to be consideration of additional pathways such as transport of antimony from soil to plant, or transfer through the food chain, even if briefly. The Screening Assessment of Antimony Trioxide (Canada 2010) found the aquatic and terrestrial bioaccumulation potential of antimony to be low. This evaluation was not revisited for the ERC-I SciAD (ECCC 2018) or the present assessment of 11 substances.
There is a major omission in that no uncertainties were identified for the ecological assessment. This needs to be remedied. Uncertainties for the ecological assessment are described in the ERC-I SciAD (ECCC 2018).

Human health assessment

Summarized comment Summarized response
More information is needed to explain that health effects associated with nano scale antimony are not being considered in this screening assessment. Having been alerted to the possibility of nano scale antimony, the reader needs to have confidence that health effects that are not assessed here will be addressed elsewhere. The measured total antimony concentrations in the environment or human biomonitoring could include engineered nanomaterials containing antimony. However, there is little evidence that any of the 11 substances assessed would be commercially encountered as engineered nanoscale particles. Additionally, nanomaterials are being more broadly addressed as a separate CMP initiative. Therefore, the potential for differential effects of nanoscale antimony were not considered in this screening assessment.
Although it is understood that uses of certain antimony compounds in homeopathic remedies are outside the scope of this assessment, it is suggested that more information regarding regulations of these compounds for this use be provided in the screening assessment. The screening assessment does not list or describe all available data; rather only key relevant data are highlighted to support the risk assessment of antimony substances in the group that have potential for exposure by the  general population of Canada. The details of the licensed homeopathic medicines can be found at Health Canada’s Natural and Non-prescription Health Products Directorate (NNHPD).
Was occupational exposure taken into consideration when assessing the potential to cause harm to human health? Screening assessments conducted under CEPA are based on the best available data. Under the CMP, they focus on risks of exposure to the general population, rather than risks of exposures in the workplace. Hazards related to chemicals used in the workplace are defined within the Workplace Hazardous Materials Information System (WHMIS).
The screening assessment should use a critical No Observed Adverse Effect Level (NOAEL) of 0.06 mg Sb/kg-bw/day for rats consuming antimony potassium tartrate (APT) from Poon et al. 1998, instead of the NOAEL of 49 mg Sb/kg-bw/day based on sodium hexahydroxoantimonate. The human health assessment considers the most relevant critical endpoint for trivalent and pentavalent antimony substances for which there is an oral exposure in the general population. The NOAEL of 0.06 mg Sb/kg-bw/day was based on APT, which is expected to have minimal exposure to Canadians. Therefore, this endpoint is not considered a critical endpoint for risk characterization of antimony substances in the group.
The estimates for dermal absorption are very uncertain, and infant exposure levels may be rather high due to use of antimony as a flame retardant. In the absence of adequate dermal toxicity studies, the oral NOAEL of 49 mg Sb/kg-bw/day was selected for the risk characterization of dermal exposure to both trivalent and pentavalent antimony substances. A relative dermal to oral absorption value of 10% was applied to the dermal exposure estimates, including exposure by the infants, to account for differences in oral and dermal absorption.
Aquaglyceroporins were not mentioned in the Draft Screening Assessment report, although evidence suggests they have an important role in the distribution of antimony in the body and hence in its toxic effects. The additional information submitted was considered and the assessment was revised accordingly.
The Draft Screening Assessment report indicates that average oral absorption of antimony from the substances to which the public is exposed will be much less than the absorption of antimony in animal studies using antimony chloride or APT.  However, this low absorption is not adequately supported by evidence. The gastrointestinal absorption fractions in the SAR were updated with recommended values for antimony substances from the International Commission on Radiological Protection (ICRP 1981).
Some animal studies suggest that dermal application of antimony can result in considerable absorption and significant toxicity. Systemic exposure from the dermal route was not considered significant based on low solubility of most antimony-containing substances. Therefore, a dermal to oral relative absorption factor of 0.1 (10%) was used in the screening assessment report (SAR), which is consistent with the Federal Contaminated Site Risk Assessment in Canada, Part I: Guidance On Human Health Preliminary Quantitative Risk Assessment (PQRA).
The analysis of infant exposure to antimony raises concern. Infants with irritated sore skin could be susceptible to excessive absorption of antimony used as flame retardants in mattress covers. Oral intake from infants sucking on plush toys or cloth may also be a concern.   A revised Screening Assessment report using the oral NOAEL of about 0.06 mg Sb/kg-bw/day would be expected to find the margin of exposure (MOE) is too small for infants. Infant exposure to antimony was determined using different exposure scenarios: oral (exposure to environmental media, food, water and mouthing of textile); dermal (sleepers and mattress covers) and inhalation (environmental media). The resulting margins of exposure for those exposure scenarios are considered adequate to protect infants from harmful effects of exposure to antimony substances. 
The revised Screening Assessment report should include information from Merck’s 1899 Manual of the Matria Medica, on the acute doses of APT that were given to humans as medicine to elicit vomiting in the early 1900s and the 1800s. The assessment does not list or describe all available data; rather only key relevant data are highlighted to support the risk assessment of antimony substances in the group that have potential for exposure to Canadians. Available evidence suggests that the Canadian general population is not significantly exposed to APT. 

Editorial

Summarized comment Summarized response
The physical and chemical properties section is brief and the transformation of antimony compounds in the environment needs to be addressed, with examples. Information on the physical and chemical properties of the antimony substances in this group that is needed to support the assessment approach is included in the SAR. More details are found in Table 2-1 and Appendix A. The antimony compounds in this assessment are generally expected to transform in the environment according to first principles approaches (for example, hard-soft acid base theory) and as better supported by empirical transformation data (e.g., Skeaff et al. 2013).  
The combination of a formula-based format and excessive use of acronyms makes the report difficult to read, especially since the report covers 11 different compounds. The tables provided are clear and helpful. However, there are instances where more explanation and/or justification for various assumptions need to be provided. In a few examples where information does not add anything, sections could be omitted without compromising the assessment. Noted. The acronyms in the assessment are defined at the first instance they appear. Additional justification has been provided in the assessment for various assumptions, where appropriate. 
The document contains certain editorial errors and some inconsistencies with referencing. Comments regarding the consistency of references and other editorial errors have been addressed. Comments regarding the spelling of chemical names were noted. However, DSL substance names have been applied consistently in the assessment to reflect the spelling used originally in the DSL.

Stakeholder engagement

Summarized comment Summarized response
Assistance is offered if additional information is needed. Noted.

Sources and uses

Summarized comment Summarized response
Import quantities are not an appropriate reference if they are expected to be more representative of antimony trioxide than the 11 substances in the antimony-containing substances group. International trade data were available for antimony-related Harmonized System (HS) codes. These codes are poorly related to the 11 substances within the scope of the assessment. However, as a conservative approach for ERC-I (ECCC 2018), these data were taken as reasonable worst-case assumptions of imports for the 11 substances.
Table 4-1 should be updated as it contains values that are 10 years old which may not be reflective of current production and import amounts due to economic fluctuations. Table 4-1 presents the most recent Canadian manufacturing and import data for these 11 substances that has been submitted pursuant to a section 71 survey of the Canadian Environmental Protection Act, 1999, or through voluntary data submission.

Conclusion

Summarized comment Summarized response
Conclusions concerning ecological and health effects are supported by material reviewed; however, there needs to be more detailed discussion about uncertainty and how uncertainties have been addressed. While uncertainties in the SAR have been identified, the assessment used a conservative approach in risk characterization of the 11 substances. Therefore, it is considered that the approach used in the screening assessment is adequately protective against the uncertainties in exposure and hazard databases.
The information presented in the document does not adequately support a conclusion that antimony-containing substances are not entering the environment in a way that constitutes or may constitute a danger to the health of Canadians. The assessment considered multiple routes of exposure using conservative parameters and conducted a conservative analysis of available effect data. Considering the margins of exposure and other lines of evidence, there is adequate support for the assessment conclusion.

References

Canada. 2010. Screening assessment for the Challenge: Antimony trioxide (antimony oxide): Chemical Abstracts Service Registry Number 1309-64-4. Ottawa (ON): Government of Canada. [accessed 2019 Jan].

[ECCC] Environment and Climate Change Canada. [modified 2018 May 4]. Science Approach Document: Ecological Risk Classification of Inorganic Substances. Gatineau (QC): Government of Canada. 

[ICRP] International Commission on Radiological Protection. 1981. Metabolic data for antimony. Limits for intakes of radionuclides by workers (ICRP Publication 30, Part 3). Ann ICRP 6(2/3):46-49.

Skeaff JM, Beaudoin R, Wang R, Joyce B. 2013. Transformation/Dissolution Examination of Antimony and Antimony Compounds with Speciation of the Transformation/Dissolution Solutions. Integrated Environmental Assessment and Management. 9(1): 98-113.

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