Additional risk characterization document in support of the draft screening assessment for zinc and its compounds
Official title: Additional Risk Characterization Document in Support of the Draft Screening Assessment for Zinc and its Compounds - Pulp and paper sector exposure and risk characterization
Environment and Climate Change Canada
A draft of the screening assessment for zinc and its compounds was published June 29, 2019. This document contains additional information to support the finalization of the screening assessment of zinc and its compounds and includes data identified or generated since the publication of the draft screening assessment.
The scope of this additional risk characterization document is limited to assessing potential ecological concerns from releases of zinc from pulp, paper, and paperboard mills in Canada. During the development of the draft screening assessment for zinc and its compounds, limited data on the releases of zinc to the environment from this sector were available. The data and analysis herein have been published to provide the opportunity for public comment on the new information prior to it being considered in the final screening assessment of zinc and its compounds, and if appropriate, the corresponding risk management approach document.
Zinc is a naturally occurring substance and is an essential element to plants and other forms of life. Zinc may be present in the organic matter feedstock used in pulp and paper processes, fuel sources (e.g., waste-derived fuels, gases, and oils) used in pulp and paper mills, or in substances used in pulp and paper processes (bleaching, fillers, additives, brighteners, etc.).
There were no responses to Notices issued under section 71 of the Canadian Environmental Protection Act, 1999 (CEPA) for the import or manufacture of any surveyed zinc-containing substance associated with the North American Industrial Classification System (NAICS) Code 3221 (Pulp, paper, and paperboard mills). There were, however, responses that zinc-containing substances are found in paper products, mixtures or manufactured items.
Predicted environmental concentrations for surface water derived from effluent quality monitoring data were found to exceed the predicted no-effect concentrations at certain pulp and paper mills.
On the basis of the information available, a limited number of pulp and paper mills had elevated risk quotients, indicating the potential for ecological harm from zinc.
Pursuant to sections 68 or 74 of the Canadian Environmental Protection Act, 1999 (CEPA), the Minister of the Environment and the Minister of Health conducted a screening assessment of zinc and its compounds. A draft of the screening assessment for zinc and its compounds was published June 29, 2019 (ECCC, HC 2019).
This document contains additional information to support the finalization of the screening assessment of zinc and its compounds. This includes data identified or generated since the publication of the draft screening assessment. Relevant data were identified up to April 2020. Targeted literature searches were conducted up to May 2020.
The scope of this additional risk characterization document is limited to assessing potential ecological concerns from releases of zinc from pulp, paper, and paperboard mills in Canada. During the development of the draft screening assessment for zinc and its compounds, limited data on the releases of zinc to the environment from this sector were available.
The data and analysis herein have been published to provide the opportunity for public comment on the new information prior to it being considered in the final screening assessment of zinc and its compounds, and if appropriate, the corresponding risk management approach document.
2. Sources and uses
Metals are naturally occurring and several are essential elements to plants and other forms of life, and thus metals may be present in the organic matter feedstock used in pulp and paper processes (Melanson 2000). Metals may also be present in fuel sources (e.g., waste-derived fuels, gases, and oils) used in pulp and paper mills (ECCC, HC 2017; Statistics Canada 2007), or metal-containing substances may be intentionally used in the process (bleaching, fillers, additives, brighteners, etc.). Pulp and paper mill effluent can therefore contain a number of metals, including zinc.
2.1 Information submitted in response to a CEPA section 71 survey
There were no responses to Notices issued under Section 71 of CEPA for the import or manufacture of any surveyed zinc-containing substance associated with the North American Industrial Classification System (NAICS) Code 3221 (Pulp, paper, and paperboard mills) (Canada 2009; Canada 2012; Canada 2017). There were, however, responses that zinc-containing substances are found in paper products, mixtures or manufactured items.
3. Releases to the environment
Pulp, paper and paperboard mills (e.g., as represented by the NAICS code 3221) were noted in the draft screening assessment as a sector releasing relatively large quantities of zinc to water, second only to releases from wastewater (ECCC, HC 2019). NPRI release data for 2016 and 2017 (NPRI 2020) became available after publication of the draft screening assessment and will be added to the final screening assessment. Additionally, effluent concentrations became available from the NPRI, where facilities reported direct discharge of substances to water in 2016 or 2017 as determined by continuous emission monitoring, predictive emission monitoring, or source testing.
4. Potential to cause ecological harm
Hazard characterization is described in section 7.3 of the draft screening assessment (ECCC, HC 2019). Briefly, the long-term Canadian Water Quality Guideline (CWQG) for the Protection of Aquatic Life, and Interim Sediment Quality Guidelines (ISQG), were selected as the predicted no-effect concentrations (PNECs) for aquatic and sediment compartment hazard characterization, respectively (CCME 2018a; CCME 2018b; CCME 1999). No extrapolations beyond the stated toxicity modifying factor (TMF) domain of the CWQG were made, consistent with analyses in the draft screening assessment for other sectors.
5. Ecological exposure assessment
The ecological exposure assessment considered exposure data from each of the four sources described below.
Pulp, paper and paperboard mills is one of the main sectors reporting releases of zinc and its compounds to the NPRI, and particularly to the aquatic compartment for the majority of facilities. Annual average effluent total zinc (Zn-T) concentrations were available for 2016 or 2017 from the NPRI for 11 facilities, determined by the source testing method (NPRI 2020).
The Canadian pulp and paper sector includes facilities (mills) that produce a range of products including paper, cardboard, newsprint, and pulp. These mills are subject to the Pulp and Paper Effluent Regulations (PPER) under the Fisheries Act (Canada 2018). However, zinc is not a required parameter for effluent monitoring under Schedule II part 1(1) of those regulations, nor is water quality monitoring required. However, a limited number of Environmental Effects Monitoring (EEM) interpretive report and study design documents were found to contain concentrations of zinc measured in effluent, or in surface waters of exposure and reference areas (e.g., as part of broader site characterization, or as part of an Investigation of Cause) (EEM 2020). Measured concentrations of dissolved zinc (Zn-D) and Zn-T in exposure areas and corresponding reference areas were limited to 4 and 5 facilities, respectively, with very limited sample sizes and limited temporal availability. Measured concentrations of Zn-T in effluent were available for 14 facilities. Measured concentrations of Zn-T in sediment in an exposure area and corresponding reference area were identified for a single facility (EEM 2020).
Monthly (approximately) effluent Zn-T concentrations reported to the Quebec Ministère de l’Environnement et de la Lutte contre les changements climatiques (MELCC) for 2013 to 2018 were also available for five facilities of interest identified from the PPER-EEM data set (MELCC 2020a). When discrepancies were noted between effluent concentrations found in PPER-EEM documents and effluent concentrations submitted to MELCC, data submitted to MELCC were taken as correct (personal communication, email from the Forest Products and Fisheries Act Division, Environment and Climate Change Canada, to the Ecological Assessment Division, Environment and Climate Change Canada, dated May 15, 2020; unreferenced). Additional TMFs were collected from the Banque de données sur la qualité du milieu aquatique (BQMA) (available for dissolved organic carbon (DOC) and pH only) as a refinement replacing ecozone geometric means. BQMA data were extracted from the MELCC Atlas interactif de la qualité des eaux et des écosystèmes aquatiques for monitoring stations identified as being in relevant proximity to the facilities or representing similar conditions to the exposure or reference areas (e.g., as identified by an EEM interpretive report or study design document) (MELCC 2020b). Annual average zinc concentrations in effluents (e.g., leachates) from pulp and paper landfill sites were also available from the MELCC Atlas des pressions sur le milieu aquatique (MELCC 2020c). Data were available for 13 effluent streams from 11 facilities between 2013 and 2018.
In addition, zinc exposure data were provided by the National Council for Air and Stream Improvement (NCASI), who designed, coordinated, and managed a sampling campaign (August 2018 to January 2019) of 30 facilities representing 2 mill process categories (mechanical and chemical), different wood fibre sources, and covering 4 ecozones (NCASI 2020). Zn-T and Zn-D concentrations in effluent, and Zn-T, Zn-D, pH, and hardness in ambient or intake waters were available from 17 chemical mills and 13 mechanical mills. PNECs were derived using pH and hardness for the corresponding ambient or intake water, and ecozone geometric mean DOC values, as TMFs.
For the exposure assessment, measured concentrations of zinc in exposure and reference areas, where available, were taken directly as predicted environmental concentrations (PECs) (EEM 2020). Measured concentrations of Zn-D were preferred for calculating PECs, with measured concentrations of Zn-T being used in their absence. When measured concentrations in the receiving environment (and corresponding reference environments) were not available, zinc concentrations were modeled from effluent concentrations. Effluent concentrations from each data source (NPRI 2020; EEM 2020; MELCC 2020a; MELCC 2020b; NCASI 2020) were used to calculate modelled PECs according to the equation below. Non-detect measurements were replaced with half of the method detection limit. Non-detects were prevalent in surface water measurements (>50% of samples), but were rare in effluent quality monitoring (~1% of samples).
PEC (μg/L) = Cb (μg/L) + ((Ceff (μg/L) – Cb (μg/L)) / (Rf (L/d) / Reff (L/d)))
Where Cb is the background concentration of zinc. For defining background concentrations, concentrations of zinc in the receiving water (upstream of the final discharge point) were preferred, followed by concentrations in the intake water and by the median ecozone background concentration. Ceff is the concentration of zinc in effluent. The term Rf/Reff represents dilution of the effluent into the receiving water, where Reff is the effluent flow rate and Rf is the 10th percentile of the receiving water flow. Data collected for other recent screening assessments indicate that the standard maximum effective dilution factor of 10 is applied to the vast majority of direct discharging pulp and paper mills. Therefore, the term Rf/Reff was replaced with 10 to calculate PECs for this sector. Geometric means of ecozone TMFs were used to derive corresponding PNECs. The identification of ambient zinc concentrations and TMFs is described in section 7.4 of the draft screening assessment (ECCC, HC 2019) or were obtained from MELCC (2020b), as described above.
Calculated average PEC ranges for each data source described above are available in Table 6‑1. Specific calculated Zn-D PECs from the NCASI dataset are shown in Figure 5‑1.
Long form description
Figure 5-1 uses box plots to summarize dissolved zinc concentrations for exposure areas and corresponding reference areas. The sample sizes, detection frequencies, minima, medians, and maxima are shown in the following table:
|Facility Number and Type||Sample size (n)||Detection frequency (%)||Minimum||Median||Maximum|
|F1 EXP Chemical||1||100||3.9||3.9||3.9|
|F1 REF Chemical||NAa||NAa||1.7||1.7||1.7|
|F2 EXP Mechanical||3||100||190||200||200|
|F2 REF Mechanical||1||100||120||120||120|
|F3 EXP Mechanical||3||100||21||22||22|
|F3 REF Mechanical||3||33||0.50||0.50||0.50|
|F4 EXP Chemical||3||0||1.4||2.0||2.4|
|F4 REF Chemical||3||0||0.50||0.50||0.50|
|F5 EXP Chemical||3||100||3.4||3.4||3.5|
|F5 REF Chemical||2||100||2.2||2.6||2.9|
|F6 EXP Chemical||1||0||2.2||2.2||2.2|
|F6 REF Chemical||3||33||0.50||0.50||4.6|
|F7 EXP Chemical||1||100||6.3||6.3||6.3|
|F7 REF Chemical||NA a||NA a||1.7||1.7||1.7|
|F8 EXP Chemical||2||0||1.1||1.9||2.6|
|F8 REF Chemical||3||33||0.50||0.50||1.2|
|F9 EXP Mechanical||2||100||11||26||26|
|F9 REF Mechanical||3||100||7.0||7.2||7.2|
|F10 EXP Mechanical||3||100||23||23||23|
|F10 REF Mechanical||3||67||0.50||2.2||2.2|
|F11 EXP Mechanical||3||100||37||37||37|
|F11 REF Mechanical||1||100||0.50||0.50||0.50|
|F12 EXP Mechanical||3||100||4.6||5.5||5.5|
|F12 REF Mechanical||3||0||0.50||0.50||0.50|
|F13 EXP Mechanical||3||100||14||15||15|
|F13 REF Mechanical||1||100||4.6||4.6||4.6|
|F14 EXP Chemical||3||33||1.4||1.4||2.0|
|F14 REF Chemical||3||0||0.50||0.50||0.50|
|F15 EXP Chemical||3||100||4.2||4.3||4.5|
|F15 REF Chemical||2||50||0.50||2.9||5.3|
|F16 EXP Mechanical||3||100||12||14||14|
|F16 REF Mechanical||3||33||0.50||0.50||0.50|
|F17 EXP Chemical||3||100||4.7||4.8||5.0|
|F17 REF Chemical||3||33||0.50||0.50||1.4|
|F18 EXP Chemical||3||100||10||10||11|
|F18 REF Chemical||3||100||2.7||9.8||12|
|F19 EXP Chemical||3||100||2.6||2.7||3.7|
|F19 REF Chemical||3||100||1.6||1.7||2.1|
|F21 EXP Chemical||3||100||2.9||3.1||3.4|
|F21 REF Chemical||3||33||0.5||0.5||1.7|
|F22 EXP Chemical||3||100||10||15||16|
|F22 REF Chemical||3||100||1.0||1.2||1.7|
|F23 EXP Mechanical||3||100||10||11||11|
|F23 REF Mechanical||3||100||1.5||1.7||1.7|
|F24 EXP Mechanical||2||100||7.6||7.8||7.8|
|F24 REF Mechanical||2||100||3.1||3.1||3.1|
|F25 EXP Mechanical||3||100||26||27||27|
|F25 REF Mechanical||3||100||1.2||1.4||1.4|
|F26 EXP Chemical||2||100||6.6||7.0||7.5|
|F26 REF Chemical||3||67||0.50||1.9||4.2|
|F27 EXP Chemical||3||100||2.2||2.6||2.7|
|F27 REF Chemical||3||0||0.50||0.50||0.50|
|F28 EXP Mechanical||3||100||50||52||52|
|F28 REF Mechanical||1||0||0.50||0.50||0.50|
|F29 EXP Chemical||2||100||6.6||6.6||6.6|
|F29 REF Chemical||3||100||1.9||2.2||3.1|
|F30 EXP Mechanical||3||67||4.6||5.3||5.3|
|F30 REF Mechanical||3||100||4.2||4.6||4.6|
|F31 EXP Chemical||3||100||8.0||8.4||8.5|
|F31 REF Chemical||3||100||6.8||7.0||8.4|
a Data for this site were not available, therefore the national average of ecozone median background concentrations was applied.
6. Characterization of ecological risk
The approach to the characterization of ecological risk is described in section 7.5 of the draft screening assessment (ECCC, HC 2019).
6.1 Risk quotient analysis
Ecological risk characterization for the pulp and paper sector considered exposure data from each of the four sources described in section 5 of this report: reporting of zinc surface water measurements and effluent concentrations in interpretive reports submitted under the EEM provisions of the PPER (EEM 2020), average zinc effluent concentrations reported from source testing methods to the NPRI (NPRI 2020), effluent concentrations available from the Ministère de l’Environnement et de la Lutte contre les changements climatiques (MELCC 2020a,c), and a voluntary sampling campaign and study organized by NCASI which collected zinc concentrations in effluent, and ambient and intake waters (NCASI 2020).
Environmental monitoring data gathered in the exposure areas of pulp and paper mills were limited to that found to be reported under the EEM provisions of the PPER (EEM 2020). Zn-D concentrations in exposure and corresponding reference areas of four facilities were low, with the largest median RQ equal to 0.09, and the maximum individual RQ equal to 0.23. Effluent Zn-T concentrations were somewhat more available in the EEM dataset. Effluent concentrations from EEM reports were replaced with equivalent effluent data submitted to MELCC for matching sample dates, when available, to address discrepancies for certain facilities. RQs calculated from effluent modelling were frequently elevated for 5 of 14 facilities where data were available. The frequency of PNEC exceedance across these five facilities ranged from 38% to 100%. However, of the facilities associated with elevated RQs, only 2 release their effluent to fresh water. The other 3 facilities release effluents to fluvial estuary or estuarine environments. Since “it is not appropriate to apply the zinc freshwater guideline to marine or estuarine environments” (CCME 2018), the strength of inference from RQs for these latter facilities may be reduced.
A potential TMF refinement was considered for the facilities associated with elevated PPER-EEM effluent modelling risk quotients using Banque de données sur la qualité du milieu aquatique (BQMA) monitoring data medians (available for DOC and pH only) as a local refinement replacing ecozone geometric means. However, in terms of the frequency of PNEC exceedances, the refinement of TMFs using BQMA data did not significantly change the outcome for any of the 5 facilities with elevated RQs (i.e., RQs remained elevated).
Elevated risk quotients were calculated from NPRI effluent concentrations for 4 of 11 facilities in 2016 or 2017. However, 3 of these facilities release their effluent to fluvial estuary or estuarine environments.
Risk characterization for the pulp and paper sector also considered effluent, ambient or raw intake monitoring of Zn-D, Zn-T, pH, and hardness, submitted for samples from 30 Canadian facilities from August 2018 to January 2019 (NCASI 2020). Facility-specific PNECs were calculated using pH and hardness data for respective ambient waters and representative ecozone DOC values. Zn-D RQs for modelled exposure and ambient waters are presented in Figure 6-1 (NCASI 2020).
Long form description
Figure 6-1 uses box plots to summarize risk quotients based on dissolved zinc concentrations for exposure areas and corresponding reference areas. The sample sizes, detection frequencies, minima, medians, and maxima are shown in the following table:
|Facility Number and Type||Sample size (n)||Detection frequency (%)||Minimum||Median||Maximum|
|F1 EXP Chemical||1||100||0.074||0.074||0.074|
|F1 REF Chemical||NAa||NAa||0.032||0.032||0.032|
|F2 EXP Mechanical||3||100||1.7||1.7||1.7|
|F2 REF Mechanical||1||100||1.0||1.0||1.0|
|F3 EXP Mechanical||3||100||0.21||0.22||0.22|
|F3 REF Mechanical||3||33||0.0049||0.0049||0.0049|
|F4 EXP Chemical||3||0||0.062||0.089||0.089|
|F4 REF Chemical||3||0||0.022||0.022||0.022|
|F5 EXP Chemical||3||100||0.073||0.073||0.073|
|F5 REF Chemical||2||100||0.047||0.054||0.054|
|F6 EXP Chemical||1||0||0.038||0.038||0.038|
|F6 REF Chemical||3||33||0.0086||0.0086||0.0086|
|F7 EXP Chemical||1||100||0.34||0.34||0.34|
|F7 REF Chemical||NAa||NAa||0.091||0.091||0.091|
|F8 EXP Chemical||2||0||0.11||0.18||0.18|
|F8 REF Chemical||3||33||0.048||0.048||0.048|
|F9 EXP Mechanical||2||100||0.52||1.2||1.2|
|F9 REF Mechanical||3||100||0.34||0.34||0.34|
|F10 EXP Mechanical||3||100||1.25||1.3||1.3|
|F10 REF Mechanical||3||67||0.027||0.12||0.12|
|F11 EXP Mechanical||3||100||2.0||2.0||2.0|
|F11 REF Mechanical||1||100||0.027||0.027||0.027|
|F12 EXP Mechanical||3||100||0.13||0.15||0.15|
|F12 REF Mechanical||3||0||0.014||0.014||0.014|
|F13 EXP Mechanical||3||100||1.8||2.0||2.0|
|F13 REF Mechanical||1||100||0.59||0.59||0.59|
|F14 EXP Chemical||3||33||0.032||0.032||0.032|
|F14 REF Chemical||3||0||0.011||0.011||0.011|
|F15 EXP Chemical||3||100||0.14||0.14||0.14|
|F15 REF Chemical||2||50||0.016||0.093||0.093|
|F16 EXP Mechanical||3||100||0.14||0.16||0.16|
|F16 REF Mechanical||3||33||0.0057||0.0057||0.0057|
|F17 EXP Chemical||3||100||0.18||0.18||0.18|
|F17 REF Chemical||3||33||0.019||0.019||0.019|
|F18 EXP Chemical||3||100||0.46||0.46||0.46|
|F18 REF Chemical||3||100||0.12||0.44||0.44|
|F19 EXP Chemical||3||100||0.14||0.15||0.15|
|F19 REF Chemical||3||100||0.089||0.094||0.094|
|F21 EXP Chemical||3||100||0.056||0.060||0.060|
|F21 REF Chemical||3||33||0.0096||0.0096||0.0096|
|F22 EXP Chemical||3||100||0.56||0.86||0.86|
|F22 REF Chemical||3||100||0.056||0.067||0.067|
|F23 EXP Mechanical||3||100||0.50||0.52||0.52|
|F23 REF Mechanical||3||100||0.071||0.081||0.081|
|F24 EXP Mechanical||2||100||0.27||0.28||0.28|
|F24 REF Mechanical||2||100||0.11||0.11||0.11|
|F25 EXP Mechanical||3||100||0.68||0.71||0.71|
|F25 REF Mechanical||3||100||0.031||0.036||0.036|
|F26 EXP Chemical||2||100||0.33||0.35||0.35|
|F26 REF Chemical||3||67||0.025||0.095||0.095|
|F27 EXP Chemical||3||100||0.18||0.21||0.21|
|F27 REF Chemical||3||0||0.040||0.040||0.040|
|F28 EXP Mechanical||3||100||1.9||2.0||2.0|
|F28 REF Mechanical||1||0||0.019||0.019||0.019|
|F29 EXP Chemical||2||100||0.66||0.66||0.66|
|F29 REF Chemical||3||100||0.19||0.22||0.22|
|F30 EXP Mechanical||3||67||0.22||0.26||0.26|
|F30 REF Mechanical||3||100||0.20||0.22||0.22|
|F31 EXP Chemical||3||100||0.77||0.80||0.80|
|F31 REF Chemical||3||100||0.65||0.67||0.67|
a Data for this site were not available, therefore the national average of ecozone median background concentrations was applied.
Risk quotients calculated from MELCC pulp and paper landfill effluent data (MELCC 2020c) for 13 effluent streams reported by 11 facilities show a low frequency of PNEC exceedances, particularly in recent years.
Lastly, sediment data were also found to be reported to the PPER-EEM for a single facility (EEM 2020). Calculated sediment RQs for this facility were not elevated and were very similar in the exposure and reference area.
A summary of PECs, corresponding PNECs, and RQs for all data sources identified for the pulp and paper sector is presented in Table 6‑1. Overall, a limited number of pulp and paper mills show potential for ecological harm from zinc based on effluent concentration modelling as evidenced by elevated risk quotients at some facilities, particularly from the NCASI dataset which contains the largest representation of facilities and reports the preferred fraction for risk characterization (i.e., Zn-D). Conversely, the limited amount of monitoring data available for both Zn-D and Zn-T in exposure and corresponding reference areas, and modelled exposure from landfill effluent data, suggest a limited potential for ecological harm. Taken together, there is a potential for ecological harm from a limited number of facilities in the pulp and paper sector from zinc.
|Dataset||Condition||Analyte||Number of facilities||Year||Range of average PECs||Range of average PNECs||Range of average RQs|
|NCASI||Ambient||Zn-D||30||2018||0.5 to 120b||7.8 to 110b||0.011 to 1.1|
|NCASI||Exposure||Zn-D||30||2018||1.6 to 200b||7.8 to 110b||0.036 to 2.2|
|NCASI||Ambient||Zn-T||30||2018||1.5 to 110b||7.8 to 110b||0.013 to 2.8|
|NCASI||Exposure||Zn-T||30||2018||3.7 to 120b||7.8 to 110b||0.063 to 3.2|
|NPRI||Exposure||Zn-Ta||11||2016 and 2017||3.7 to 95b||6.0 to 48b||0.077 to 3.8|
|PPER-EEM Water quality||Reference||Zn-D||5||2012 to 2018 (non-continuous)||0.50 to 2.5b||11 to 36b||0.016 to 0.088|
|PPER-EEM Water quality||Exposure||Zn-D||4||2012 to 2018 (non-continuous)||0.73 to 2.5b||11 to 39b||0.016 to 0.10|
|PPER-EEM Water quality||Reference||Zn-T||6||2012 to 2018 (non-continuous)||2.4 to 24b||8.3 to 36b||0.065 to 0.80|
|PPER-EEM Water quality||Exposure||Zn-T||5||2012 to 2018 (non-continuous)||2.9 to 6.7b||9.1 to 39b||0.096 to 0.52|
|PPER-EEM Effluent||Exposure||Zn-D||4||2012 to 2018 (non-continuous)||2.1 to 4.2b||8.6 to 45b||0.047 to 0.48|
|PPER-EEM Effluent (supplemented with MELCC effluent data)||Exposure||Zn-T||14||2012 to 2018 (non-continuous)||3.4 to 63b||8.8 to 45b||0.16 to 4.3|
|PPER-EEM Sediment||Reference||Zn-T||1||2014 to 2015||96c||123c||0.78|
|PPER-EEM Sediment||Exposure||Zn-T||1||2014 to 2015||92c||123c||0.75|
|MELCC Landfill effluent||Exposure||Zn-Ta||11||2013 to 2018||3.7 to 8.8b||16 to 18b||0.24 to 0.63|
Abbreviations: PEC, predicted environmental concentration; PNEC, predicted no effect concentration; RQ, risk quotient; Zn-D, dissolved zinc; Zn-T, total zinc.
a Not explicitly reported, but assumed to represent total zinc concentrations.
b Units for these values are in µg Zn/L
c Units for these values are in mg Zn/kg
6.2 Consideration of the lines of evidence
The key lines of evidence supporting that releases of zinc from the pulp and paper sector show a potential for ecological harm are presented in Table 6-2. The level of confidence refers to the combined influence of data quality and variability, data gaps, causality, plausibility and any extrapolation required within the line of evidence. The relevance refers to the impact the line of evidence has when determining the potential to cause harm in the Canadian environment. Qualifiers used in the analysis ranged from low to high, with the assigned weight having five possible outcomes.
|Line of evidence||Level of confidence||Relevance in assessment||Weight assigned|
|PNECs derived with sample-specific TMF data||High||High||High|
|PNECs derived with ecozone TMF data||Moderate||High||Moderate to high|
|PNEC for benthic organisms in sediment||Moderate||Moderate||Moderate|
|PEC(s) based on measured data in surface water or sediments (PPER EEM reporting)||Low||High||Moderate|
|PEC(s) for surface waters based on effluent modelling (PPER EEM reporting; MELCC; NCASI; NPRI)||Moderate||High||Moderate to high|
|RQ(s) for surface waters based on measured PECs and PNECs derived with sample-specific TMF data||Low||High||Moderate|
|RQ(s) for surface waters based on modelled PECs and PNECs derived with ecozone TMF data||Moderate||High||Moderate to high|
|RQs for sediment||Low||Moderate||Low to moderate|
7. Uncertainties in the characterization of ecological risk
With ecological hazard characterization for zinc aligned with recent and robust CWQGs and the ISQG, most of the uncertainties in the characterization of ecological risk from the pulp and paper sector pertain to exposure characterization.
Water quality monitoring data from PPER-EEM interpretive reports and study design documents resulted in a sparse dataset representing a very small proportion of the sector. As this water quality monitoring dataset is very small, it is not robust enough to meaningfully extrapolate to all Canadian mills, as the potential for risk may be of greater or less proportion. The low RQs cannot be read across or presumed for the facilities where only modelled RQs from effluent data are available, some of which are elevated (i.e., greater than 1). The absence of a systematic reporting requirement for zinc in the PPER introduces considerable sampling bias in the available EEM dataset that cannot be readily quantified. More certainty in this analysis was provided by the NCASI study, not only for its greater representation of facilities in the sector, but also for measuring both Zn-D and Zn-T in effluents, and measuring Zn-D, Zn-T, pH, and hardness in ambient waters (raw intake water or receiving stream water upstream of the discharge point).
Some uncertainty in risk characterization may be introduced by the comparison of Zn-T concentrations to PNECs, which are generally intended for comparison to the less frequently measured Zn-D. To explore this uncertainty further, average effluent Zn-D and Zn-T concentrations, and average ambient Zn-D and Zn-T concentrations, with the same sample codes (NCASI 2020) were compared in beanplots (Figure 7-1). The beanplots indicate that in most cases average Zn-D and Zn-T effluent concentrations were similar, with the ratio of Zn-D to Zn-T in effluent frequently close to unity. This suggests that risk quotient calculations based on Zn-T in effluent may represent a reasonable worst-case approach for risk quotient calculations when data for Zn-D are lacking.
Long form description
Figure 7-1 uses the beanplot, beeswarm, and segments functions of R to display the relationships between average Zn-D and Zn-T in effluents with a sample size of 29, and between average Zn-D and Zn-T in ambient measurements with a sample size of 26, with the same sample code. Lines are drawn between points in each set of distributions to show that, in general, Zn-D and Zn-T measurements are similar in these matrices, particularly effluent. In the ambient measurement plot, Zn-T is more often greater than Zn-D, but by modest amounts.
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