Summary of public comments received on the draft screening assessment and risk management scope for thallium and its compounds

Comments on the draft Screening Assessment and Risk Management Scope (RMS) for Thallium and its compounds, assessed under the Chemicals Management Plan (CMP), were submitted by the Canadian Network for Human Health and the Environment (CNHHE) and Saskatchewan Environmental Society (SES), the Mining Association of Canada (MAC), and Teck Metals Ltd. – Trail Operations.

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

General comments

Comment summary 1: The largest sources of releases to the environment from the metal mining sector are now closed. How are historic releases to be considered in answering whether a substance “enters or may enter”?

Response 1: Historical releases were assessed to determine if thallium may enter the environment in a quantity or concentration that could pose a risk to the environment. Historical (up to 2016) releases from a closed facility (metal mining site 3, MM3) indicate that thallium is being released in its wastewater at levels of potential ecological concern. A discussion acknowledging closure of the facility and a reduction in receiving water concentrations post-operation was added to the uncertainties section of the report (7.3.4). Data that are more recent would help characterize the current situation at the facility.

Methodology

Comment summary 2: Releases of thallium to water from the base metals smelters (BMS) sector are low and unlikely to pose a risk to the environment. While two facilities did have elevated risk quotients (RQs), one had a marginal exceedance at a near-field discharge point, and the other facility is now closed and was releasing to a marine environment wherein thallium toxicity would be further mitigated by potassium [which could not be accounted for in the predicted no-effect concentration (PNEC) development].

Response 2: The exposure scenario for the BMS sector has been updated with the most recent data. Two BMS facilities (BMS6 and BMS8) showed potential for ecological concern from releases of thallium in wastewater effluent.

BMS6 had a median RQ of 2.5. BMS8 (Facility 3 in the draft screening assessment) recently ceased operation; however, wastewater discharged from the facility from 2016-2018 resulted in calculated thallium concentrations in the exposure area that exceed the PNEC significantly with RQs of 110 to 320.

A statement has been added to the assessment indicating that for most facilities, releases of thallium are limited and are unlikely to pose ecological concern, but a small number of facilities may release thallium to an extent that is of ecological concern.

Comment summary 3: The Method Detection Limits (MDLs) reported in the assessment ranged from 0.002 μg/L to 10 μg/L, relative to a PNEC of 0.8 μg/L. For higher MDLs a substituted value of ½ MDL is unlikely to be appropriately representative of the true value. It is recommended to provide an indication via a footnote which specific maximum values are non-detect values with elevated detection limits or consider removal of these values from the analysis.

Response 3: The thallium exposure analysis in Section 7.2.3 (metal mining) has been updated in the final assessment. Non-detects with a MDL above the PNEC of 0.8 µg/L are considered uncertain. Text is also provided in the assessment where a substituted value of ½ MDL has been applied for non-detectable concentrations. Instances where thallium concentrations are non-detectable with a MDL above the thallium PNEC of 0.8 µg/L are indicated in the exposure analysis (Section 7.3.1) and uncertainties are discussed (Section 7.3.4) in the assessment.

Comment summary 4: The closure of Facility 3 in the metal mining sector should be indicated.

Response 4: Clarification was made in the assessment to reflect that Facility MM3 has ceased operation.

Comment summary 5: The detection frequency in Figure 7-2 should align with the Alt-table for Figure 7-2 in section 7.2.3.

Response 5: Noted. Figure 7-2 has been updated in the assessment.

Comment summary 6: The table For Figure 7-2 should have a table number and title. The range of MDLs should be provided for each dataset.

Response 6: Noted. The table has been updated to identify MDLs in the dataset.

Comment summary 7: The assessment noted that less than 30% of metal mining facilities reported thallium concentrations in 2013 – 2017 voluntarily. Only a single facility has elevated RQs (see section 7.3.1). In contrast, the analysis of the wastewater treatment sector (WWTS) was based on only 21 facilities out of a possible 3500 WWTS.

Response 7: The exposure analysis for the metal mining sector has been updated to include additional data that are available for approximately 86% of metal mining facilities up to 2020. Only MM3 showed consistently elevated risk quotients, though PNEC exceedances were observed at additional sites. A statement has been added to the assessment indicating that thallium environmental releases from metal mining and base metals smelting are limited and are unlikely to pose ecological harm for most facilities on the basis of the information available.

Exposure scenarios for other sectors, including pulp and paper, oil sands, landfills, and wastewater treatment systems were also explored. The available data did not show potential for ecological risk from these sectors. However, it is acknowledged that the data available for these sectors may not be as comprehensive as that available for the metal mining and BMS sectors.

Comment summary 8: For Smelter Facility 2, the near-site sampling at Discharge site III would not typically be included in the overall monitoring program for this facility. More frequent sampling is conducted at Exposure 2 station, identified as the initial dilution zone located 0.23 km downstream of CII outfall, and 0.72 km downstream of CIII outfall. The geometric mean, median and 95th percentile of the data (n = 59 samples) at Exposure 2 station are all less than the PNEC.

Response 8: Transient sampling of Discharge sites II, III, and IV from 2011 (Ecoscape Environmental consultants Ltd. and Larratt Aquatic Consulting Ltd. 2014), internal information, and effluent concentration data from NPRI (2019) suggested that thallium has been released at Discharge site III at a much higher concentration compared to Discharge site II, where a regular monitoring program was conducted. Exposure 2 station is further away from the discharging point of main concern and may underestimate thallium exposure at the most exposed area.

Comment summary 9: Additional monitoring data are provided by the BMS Facility 2 for Exposure Site 2 from 2015-2016. The calculated PEC value based on NPRI data in the draft assessment for this time period should be substituted by the monitoring data.

Response 9: The exposure analysis for this facility (BMS7 in the final assessment) has been updated. For Exposure Site 2, as the measured concentrations were approximately 0.72 km further from the discharging site of concern (Discharge site III), NPRI effluent data were used as an additional line of evidence to estimate potential ecological risk for an exposure area closer to the discharge point of main concern.

Comment summary 10: BMS Facility 3 (BMS8 in the final assessment) is believed to be closed (late in 2019) and this should be indicated in the assessment. The facility has made considerable efforts to reduce its thallium releases to water in the last few years (2016-2018), as indicated by NPRI data. The facility also releases to a marine environment where high potassium content has potential to mitigate toxicity.

It should be stated if a dilution factor of 10 is applied in the predicted PEC value.

Response 10: The final screening assessment has been updated with the new information (NPRI effluent concentrations from 2016-2018) and indicates how the PEC values were calculated. Calculation of PECs from the effluent concentrations involved applying a dilution factor of 10 and adding the site-specific background concentration where the facility is located. PECs calculated for Facility BMS8 using effluent concentrations reported to NPRI showed significant PNEC exceedance, with RQs from 110 to 320, which indicates the potential for ecological concern.

See the response below under Ecological Effects regarding potential for potassium mitigation effects.

Comment summary 11: Data presented in Table 7-6 (see section 7.2.4) for Facility 2 have been mischaracterized.

Only one sample (March 28, 2013) should be identified with total and dissolved thallium concentrations above the PNEC.

This BMS facility has been conducting an extensive Aquatic Effects Monitoring Program (AEMP) in the receiving river as a requirement of its provincial effluent permit since 2011. No community-level adverse effects would be attributable to the impacts of the operations.

Response 11: Exposure analysis for this facility (Facility BMS7 in the final assessment) has been updated to include additional surface water concentrations from 2015-2016 (in addition to data before 2013) and duplicate values were identified and removed.

Further discussion of surface water concentrations at exposure areas has been added, including for the lines of evidence that were considered in the analysis of Discharging site III (the discharge point of concern) and uncertainties with the characterization of potential ecological concern.

Comment summary 12: Accurate monitoring data should supersede the estimates derived in the final assessment.

Response 12: Both monitoring (i.e., measured) and estimated data are considered in a weight of evidence approach in the assessment. Measured concentrations are, in general, preferred in the exposure analysis. For example, estimates derived from NPRI data were used as an additional line of evidence for the exposure scenario for Facility BMS7, as measured thallium concentrations did not fully reflect the contribution near effluent-discharging site III, where a higher quantity of thallium was released.

Information and data updates

Comment summary 13: New data collected under the Metal and Diamond Mining Effluent Regulations (MDMER) amendment should be incorporated into the final assessment. The assessment should also take into account the closure of the facilities identified.

Response 13: Thallium concentration data submitted in the most recent Environmental Effect Monitoring (EEM) reporting period (2021) under the MDMER has been included in the assessment. Facilities that are closed and/or have temporarily ceased production, but that continue to release effluents, are identified in the assessment.

Ecological effects

Comment summary 14: It is understood that potassium as a toxicity modifying factor (TMF) could not be incorporated in the PNEC in the assessment due to inadequate data available.

Response 14: Noted. The mitigation effects of potassium require further study, as different responses have been seen with different types of organisms. For example, available data (Table 7-2) suggest that acute toxicity of thallium to marine algae is in a similar range as the toxicity values shown for freshwater algae, despite the higher potassium levels in the study with the marine algae.

A recent study on potassium as a TMF for thallium by Nagel et al. (2021) also suggested the likelihood of differences in toxic mechanisms even among freshwater crustacean species, and between short- and long-term exposures.

Comment summary 15: Considering the importance of high potassium levels in the marine environment, it is recommended that the current PNEC not be put forth as an updated Federal Environmental Quality Guideline (FEQG) until this TMF is included.

Response 15: Noted.

Comment summary 16: It is agreed that Thallium (I) should be the focus of the effects assessment and the CCME approach should be followed.

Response 16: Noted.

Comment summary 17: A footnote should be provided to Table A-1 to indicate any studies where thallium speciation is uncertain. The possible effect on the HC5 of the Species Sensitivity Distribution (SSD) should be discussed due to noticeably higher toxicity of Thallium (III) than Thallium (I).

Response 17: As discussed in section 7.1.3, Tl(I) was stable in aquatic toxicity tests, whilst Tl(III) was converted to Tl(I) during toxicity tests of 21 days. Potential conversion of Tl(I) to Tl(III) is likely not present under laboratory toxicity test conditions. Attributing effects observed in toxicity studies to Tl(I) when speciation was not specified is therefore practicable and not expected to be overly conservative. A discussion of the possible effect of Tl(III) on the CTV has been added in section 7.3.4 (Sensitivity of conclusion to key uncertainties).

Comment summary 18: Use of the unpublished study in the SSD should be further supported for data quality.

Response 18: Revisions were made to clarify that the study has been evaluated as acceptable quality. However, the endpoint used in the SSD was not presented in the published journal paper, but was obtained through personal communication with the author.

Comment summary 19: Additional information should be provided related to fit at the lower end of the acute SSD curve, relative to other models.

Response 19: The logistic model was selected because it had the lowest mean sum of squared error (MSE), indicating that it had the best fit at the lower end of the SSD curve when compared with the other models.

Comment summary 20: It is unfortunate that data gaps precluded a chronic SSD approach. The assessment factor-approach used in the assessment is more conservative than a HC5 generated from an SSD.

Response 20: Internal analyses comparing the assessment factor approach (Okonski et al. 2021) to SSDs resulted in comparable PNEC values. However, the SSD approach is considered to have a higher level of confidence.

Comment summary 21: It is agreed that the marine dataset is too limited to derive a guideline using a SSD approach. The marine PNEC is likely to be conservative with the assessment factor approach and without accounting for potassium as TMF. More discussion on this is recommended.

Response 21: Additional discussion has been added in section 7.3.4 (Sensitivity of conclusion to key uncertainties).

Ecological risk characterization

Comment summary 22: Thallium releases are unlikely to be widespread for the metal mining sector, as only 1 facility has elevated Risk Quotients. In addition, the said facility is now closed.

Response 22: A statement has been added to the assessment indicating that thallium release from only a small number of facilities in the metal mining and base metals smelting sectors may cause potential ecological harm.

Comment summary 23: The PEC presented for smelter Facility 3 in the screening assessment was predicted and should be re-worded to indicate such.

Response 23: The PECs for this facility (BMS8 in the final assessment) were re-calculated based on the annual effluent data submitted to the NPRI (2021). Data for BMS8 have been noted as predicted, where applicable.

Comment summary 24: The comprehensive biological monitoring data that are collected under the MDMER for mines of concern should be included in the assessment to reflect a true weight of evidence.

Response 24: Water quality data required under Schedule 5 of the MDMER were considered the most relevant lines of evidence for the metal mining and BMS sectors as they directly reflect exposures to the thallium moiety. Effluent toxicity tests and biological monitoring represent an important source of information for assessing the adequacy of the MDMER for protecting the aquatic environment. The studies are designed to determine effects from metal mining effluent (rather than specific contaminants). In the most recent national assessment of Environmental Effects Monitoring (EEM) for metal mines a majority of the mines evaluated had reported effects and thallium was identified in one investigation of cause for a base metal mine.

Comment summary 25: The effect of closure of the facilities that had highest releases of thallium to the environment should be discussed.

Response 25: The closure of the facilities has been discussed in the assessment.

Comment summary 26: The sensitivity analysis conducted for the detection limit substitution approach is important and appreciated.

Response 26: Noted.

Human health assessment

Comment summary 27: The approach taken to assess risk to human health in the draft screening assessment does not adequately account for uncertainties regarding effects of thallium on children, during in utero development, and on reproduction. The epidemiological studies used for the derivation of HBM-I value do not provide sufficient evidence for the safety of thallium exposure in these subpopulations.

Response 27: The health effects assessment is based upon the best and most relevant information, including information on reproductive and developmental effects. The HBM-I value used in the health effects assessment is expected to be protective of reproductive and developmental effects.

An epidemiological study used in the HBM-1 derivation included both children and pregnant women (Brockhaus et al. 1981). A follow-up study (Dolgner et al. 1983) evaluated developmental effects in the same population. The results of the study indicated that it is unlikely that there is a causal relationship between thallium exposure and congenital birth defects. The assessment was updated with additional details from these studies.

Comment summary 28: Available information on the levels of thallium in urine suggest that the Canadian general public is not exposed to excessive levels of thallium.

Response 28: Agreed.

Comment summary 29: There are no Canadian biomonitoring data available for children under 3 years old. Children aged 1-4 have the highest dietary intake of thallium per kilogram of body weight.

Response 29: This uncertainty is described in section 8.1 of the assessment. Although there are no biomonitoring data for children under 3 years old, the HBM-I value incorporates data from children 1 year and older and the 95^th percentile urine concentrations in the Canadian population are more than 10-fold lower than the HBM-I value.

Comment summary 30: Dietary intake estimates of toddlers exceed the US EPA (2009) reference dose (RfD) and therefore, raise high concern for thallium exposure.

Response 30: The health effects assessment is based upon the best and most relevant available information. Uncertainties associated with the U.S. EPA RfD included the biological relevance of the effect, low dose selection, and inconsistencies in the interpretation and reporting of data.

Comment summary 31: The WHO-IPS (1996) states “that there are no good data to suggest that infants or pregnant women are more sensitive to effects of thallium” than the general population.

Response 31: Noted.

Comment summary 32: Thallium and lead have a similar toxicity profile, as both are neurotoxicants. Therefore, consideration should be given to the possibility that thallium could represent a threat to nervous system development.

Response 32: The best and most relevant available data were considered, including data on neurotoxicity. Although both thallium and lead can cause neurotoxicity following exposure, there is no direct evidence that indicates that thallium and lead have the same mechanism of action. In addition, developmental effects were considered in the derivation of the HBM-I value.

Comment summary 33: The use of thallium in food packaging in Canada is a concern and consideration should be given to eliminating this use.

Response 33: Biomonitoring data provides a biologically relevant, integrated measure of exposure that occurs across multiple routes and sources, including food packaging. Population-level human biomonitoring data demonstrate that exposure to thallium in Canada is low.

Comment summary 34: There should be tests to evaluate thallium exposure to Canadians that are likely to have higher levels of exposure, including people with occupational exposure to thallium and those living near some mine and smelter operations.

Response 34: Assessments conducted under CEPA 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 Government of Canada is currently working with the provinces and territories to explore ways to enhance the protection of workers from exposure to chemicals by integrating and leveraging the information, tools, and/or technical expertise of the Chemicals Management Plan and Health Canada’s Workplace Hazardous Products Program.

The assessment was based on the best and most relevant biomonitoring data. Although biomonitoring data in Canadians living in the vicinity of point sources of thallium are currently lacking, there is more than a 10-fold gap between the 95^th percentile concentrations in Canadians and the HBM-1 level. Exposures above the HBM-1 level are not anticipated.

Comment summary 35: The screening assessment should not use the German HBM-I value due to uncertainties associated with the health effects of thallium exposure, including developmental and reproductive effects, genotoxicity and carcinogenicity.

Response 35: The human health effects assessment was based on the best and most relevant available data. HBM-I values are health-based biomonitoring guidance values established by the German Human Biomonitoring Commission. Toxicity associated with thallium exposure including developmental and reproductive effects were been considered by the German Human Biomonitoring Commission during development of this guidance value.

The limited number of studies on the genotoxicity of thallium compounds provide inconsistent results regarding genotoxic potential, and the evidence for the carcinogenicity of thallium is inadequate for classification. This uncertainty was taken into consideration during the derivation of the HBM-I value. In addition, this uncertainty is described in section 8.1 of the assessment.

Conclusion

Comment summary 36: Disagree that metal mining and base metal smelting merit identification as sectors denoting concern in the report.

Response 36: The assessment has been updated to indicate that only a small number of facilities in the metal mining and BMS sectors release thallium at levels of potential ecological concern.

Comment summary 37: The draft screening assessment correctly concludes that there is a risk to the environment from thallium and its compounds. Therefore, “Thallium and its compounds” should be added to Schedule 1 of CEPA.

Response 37: Noted.

Comment summary 38: The evidence for listing metal mining as a sector of interest may be weak due to only approximately one-third (39) of facilities being considered, which is described as a data gap. The single facility exhibiting an elevated RQ is now closed, hence, emissions to water will be greatly reduced. We believe that the data analysis presented indicates it is unlikely that additional mining facilities would be of concern to the environment.

Response 38: The exposure analysis has been updated to include the latest data reported under the MDMER EEM provisions and to the NPRI, representing 86% of metal mining facilities in operation between 2004 and 2020. The closure of Facility MM3 and a potential reduction in releases post-closure is discussed in the assessment. The assessment has also been updated to clarify that more recent monitoring data for Facility MM3 and monitoring data for BMS8 would help address uncertainties.

Risk management

Comment summary 39: The information requested for thallium concentrations in surface water for metal mining should be available in standard EEM reports under MDMER, and hence this request is not necessary.

It is requested to remove the data request on benthic organism tissue residue sampling for the BMS sector due to a lack of standardized tissue residue effects data for thallium and historic impacts for older smelting facilities.

Response 39: The information request for mines reporting to MDMER was removed. The data request for benthic organism tissue for BMS was also removed.

Comment summary 40: There is a risk management instrument already in place to manage releases of thallium from metal mines due to a new requirement to monitor thallium in effluent under the Metal and Diamond Mining Effluent Regulations (MDMER) under the Fisheries Act. This amendment came into effect in June of 2018, and is supported by mandatory Environmental Effects Monitoring (EEM). As a result, metal mines may not pose a risk to the environment based on current data.

Response 40: The risk assessment considers the latest information submitted under the MDMER and to the NPRI (2021). On the basis of this information, the assessment concluded that there is a risk to the environment from a small number of facilities in the metal mining and base metals smelting sectors.

The proposed risk management action is to review information received from regulated mines in response to environmental effects monitoring requirements under the MDMER, to determine if additional regulatory or non-regulatory risk management is appropriate.

Comment summary 41: Editorial revision suggested for the last paragraph of Section 2.1.

Response 41: Noted and change made to a “small number of”.

Comment summary 42: A stakeholder would like to discuss the proposed comprehensive strategy to manage metals assessed as toxic under the third phase of the CMP.

Response 42: ECCC met with the stakeholder in November 2020 to discuss this strategy.

Comment summary 43: A statement should be added to reflect that only a single facility of the 39 mining facilities with thallium data had concentrations above the PNEC, and this facility is now closed.

Response 43: The assessment was updated and considers the latest information submitted for 157 metal ore mining and milling sites that conduct EEM (2021) under the MDMER and three additional facilities which reported to the NPRI (2021). While one facility had consistently higher RQs, other facilities had some data points above the PNEC and may also be of potential concern. The assessment contains a statement that only a small number of facilities involved in metal mining and base metal smelting are of potential ecological concern.

The RM approach document reflects the findings of the final risk assessment.

Comment summary 44: High-quality monitoring data for mining facilities will become available through the Schedule 5 MDMER amendment that came into effect in June of 2018. A statement should be made in the RMA that analysis of that data will be conducted in advance of any decisions related to the need for additional risk management instruments, particularly with the existing risk management tools related to this sector, such as the MDMER.

Response 44: The RM action proposed includes review of the data submitted by the MDMER. Section 3.3.1 of the Risk Management Approach indicates that ECCC will review the information received from regulated mines in response to environmental effects monitoring requirements under MDMER to determine if additional regulatory or non-regulatory risk management of effluents from metal mines is appropriate for one or more assessed metals, this includes thallium.

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