2020 FCSNW logo


Poster Presentations: Human Health and Ecological Risk Assessment
Assessing Human Health Risks of Non-Cancer Effects Due to Short-Duration and Intermittent Exposures to Chemicals at Contaminated Sites
Case Study A: Assessment of Antimony
Nicole Somers, Sanya Petrovic, Asish Mohapatra, Angela Li-Muller
Health Canada
The objective of this presentation is to share a chemical-specific case study demonstrating that some dose averaging may be acceptable for antimony due to chemical-specific attributes such as bioaccumulation and biological clearance rates.  
Abstract

Background
Existing risk assessment methods for contaminated sites typically address chronic daily exposures. Due to the unique usage patterns associated with some federal properties, access to these sites can routinely be for short and/or intermittent periods. Some risk assessments include calculations of average exposures experienced during these short intervals over longer periods of time. This practice, referred to as dose averaging, can potentially underestimate human health risks. As displayed in this three-part poster series, dose averaging of antimony may be acceptable in a risk assessment where the exposure is intermittent with the inclusion of chemical-specific rationale to illustrate that the dose averaging performed would not underestimate potential risk for this substance.

Objectives and Approach
Health Canada’s Contaminated Sites Division has developed guidance which involves assessing site-specific and chemical-specific data using a tiered framework to determine whether or not the use of dose averaging may be appropriate. Antimony ores are naturally occurring and may be extracted from the environment through mining processes. However, it can also be produced as an unintentional by-product of metal smelting operations where it is used in conjunction with other metals to manufacture products including lead batteries, sheet and pipe metal, bearings and solder. This chemical-specific case study uses concepts from the framework to highlight issues that risk assessors may encounter when evaluating exposures to antimony at a contaminated site, highlighting the assessment of short duration and intermittent exposures to elevated levels of antimony in soils. Key factors affecting antimony toxicity such as the actual exposure period, elimination kinetics and persistence of effects will be presented.

Results and Conclusions
This chemical-specific case study demonstrates that some dose averaging may be acceptable for antimony due to chemical-specific attributes such as bioaccumulation and biological clearance rates. Due to the two-phase clearance and average half-life of antimony, under some intermittent exposure scenarios the metal may not be cleared from the body fully before the next exposure occurs resulting in a buildup of antimony in the body. The development of this proposed case study is intended to illustrate how health risks may be underestimated through the use of dose averaging when sufficient time has not elapsed between exposure periods to clear a substance from the body. Other key factors resulting in potentially divergent risk outcomes will also be reviewed, including a discussion on which factors should be considered and included as part of the scientific rationale to support a human health risk assessment.

Nicole Somers, Health Risk Assessment and Toxicology Specialist, Contaminated Sites Division, Health Canada
Nicole Somers is a Health Risk Assessment and Toxicology Specialist with the Contaminated Sites Division at Health Canada.

Assessing Human Health Risks of Non-Cancer Effects Due to Short-Duration and Intermittent Exposures to Chemicals at Contaminated Sites
Case Study B: Assessment of Tetrachloroethylene
Asish Mohapatra, Nicole Somers, Sanya Petrovic, Angela Li-Muller
Health Canada
The objective of this presentation is to share a chemical-specific case study demonstrates that dose averaging is not acceptable for tetrachloroethylene.  
Abstract

Background
Existing risk assessment methods for contaminated sites typically address chronic daily exposures. Due to the unique usage patterns associated with some federal properties, access to these sites can routinely be for short and/or intermittent periods. Some risk assessments include calculations of average exposures experienced during these short intervals over longer periods of time. This practice, referred to as dose averaging, can potentially underestimate human health risks. As displayed in this three-part poster series, dose averaging of tetrachloroethylene (PERC) cannot be supported in a risk assessment based on chemical-specific rationale which illustrates that any dose averaging performed would likely underestimate potential risk for this substance.

Objectives and Approach
Health Canada’s Contaminated Sites Division has developed guidance which involves assessing site-specific and chemical-specific data using a tiered framework to determine whether or not the use of dose averaging may be appropriate. PERC is a volatile solvent that is highly mobile in the environment and can break down into a number of highly toxic daughter products via reductive dechlorination including trichloroethylene (TCE) and vinyl chloride. Elevated levels of PERC at contaminated sites are often the result of anthropogenic activities including metal degreasing, dry-cleaning and in aerospace applications. This chemical-specific case study uses concepts from the framework to highlight issues that risk assessors may encounter when evaluating PERC at a contaminated site, highlighting the assessment of short duration and intermittent exposures to elevated levels of PERC in soil. Key factors affecting PERC toxicity such as the actual exposure period, elimination kinetics and persistence of effects will be presented.

Results and Conclusions
This chemical-specific case study demonstrates that dose averaging is not acceptable for PERC. Neurobehavioral effects of PERC have been observed at low levels of exposure for all durations tested, indicating that the toxicity of PERC is related to peak concentration rather than the length of the exposure. This has resulted in the application of the same oral toxicity reference value (TRV) for acute, intermediate and chronic exposure durations. The development of this proposed case study is intended to illustrate how dose-averaging PERC over short periods of time may lead to underestimates of health risks. Other key factors resulting in potentially divergent risk outcomes will also be reviewed, including a discussion on which factors should be considered and included as part of the scientific rationale to support a human health risk assessment.

Asish Mohapatra, Health Risk Assessment and Toxicology Specialist, Contaminated Sites Division, Health Canada
Asish Mohapatra is a Health Risk Assessment and Toxicology Specialist in the Contaminated Sites Division at Health Canada.

Assessing Human Health Risks of Non-Cancer Effects Due to Short-Duration and Intermittent Exposures to Chemicals at Contaminated Sites
Case Study C: Assessment of Polychlorinated Dibenzo-p-dioxins
Sanya Petrovic, Nicole Somers, Asish Mohapatra, Angela Li-Muller
Health Canada
The objective of this presentation is to share a chemical-specific case study demonstrates that some dose averaging may be acceptable for dioxins due to chemical-specific attributes such as long half-life and persistence in the environment.  
Abstract

Background
Existing risk assessment methods for contaminated sites typically address chronic daily exposures. Due to the unique usage patterns associated with some federal properties, access to these sites can routinely be for short and/or intermittent periods. Some risk assessments include calculations of average exposures experienced during these short intervals over longer periods of time. This practice, referred to as dose averaging, can potentially underestimate human health risks. As displayed in this three-part poster series, dose averaging of polychlorinated dibenzo-p-dioxins (dioxins) may be acceptable in a risk assessment with the inclusion of chemical-specific rationale to illustrate that the dose averaging performed would not underestimate potential risk for this substance.

Objectives and Approach
Health Canada’s Contaminated Sites Division has developed guidance which involves assessing site-specific and chemical-specific data using a tiered framework to determine whether or not the use of dose averaging may be appropriate. Dioxins are a family of approximately 75 related chemical compounds often found as mixtures in the environment. Elevated levels of these compounds at contaminated sites are often the result of anthropogenic activities including bleaching processes at pulp and paper mills or on-site incineration practices. This chemical-specific case study uses concepts from the framework to highlight issues that risk assessors may encounter when evaluating dioxins at a contaminated site, highlighting the assessment of short duration and intermittent exposures to elevated levels of dioxins in soils. Key factors affecting dioxin toxicity such as the actual exposure period, elimination kinetics and persistence of effects will be presented.

Results and Conclusions
This chemical-specific case study demonstrates that some dose averaging may be acceptable for dioxins due to chemical-specific attributes such as long half-life and persistence in the environment. Use of the Joint Expert Committee on Food Additives (JECFA)/World Health Organization (WHO) tolerable monthly intake for oral exposure, as well as other key factors resulting in potentially divergent risk outcomes will also be reviewed. The development of this proposed case study is intended to illustrate how health risks may be underestimated through the use of dose averaging, including a discussion on which factors should be considered and included as part of the scientific rationale to support a human health risk assessment.

Sanya Petrovic, Unit Head, Contaminated Sites Division, Health Canada
Sanya Petrovic is a Unit Head for the Contaminated Sites Division at Health Canada.

Applying Health Canada’s Framework for Human Health Risk Assessment of Federal Sites Impacted with PFAS
Sue-Jin An, Thalia Zis, Nicole Somers, Christine Levicki, Luigi Lorusso
Health Canada
The objective of this presentation is to outline Health Canada’s recommended HHRA methodology for PFAS-impacted federal sites, as well as Health Canada’s human health screening values for PFAS in soil and groundwater. Examples will be included to demonstrate practical considerations and updates based on the evolving science in the PFAS field.  
Abstract

Background
Health Canada develops guidance on human health risk assessment (HHRA) of federal contaminated sites. In recent years, per- and polyfluoroalkyl substances (PFAS) have been the focus of much attention due to their persistence in the environment and their unique chemical properties. These substances are thermally and chemically stable, resistant to biotic or abiotic degradation (except in cases of precursor transformations) and have been found in areas distant from their originating sources. PFAS surfactants have seen widespread use as coating ingredients for textiles, paper products and cookware, and in aqueous film forming foams (AFFF) for firefighting activities where suppression of hydrocarbon fuel fires is required. Many of the ongoing PFAS investigations conducted at federal contaminated sites have been associated with firefighting training and maintenance activities. The need for tools to help assess potentially impacted sites became apparent when these substances were detected in soil and water as a result of historical and current activities.

Objective/Approach
As the science pertaining to PFAS and contaminated sites is growing rapidly, Health Canada’s Contaminated Sites Division has developed a framework to guide undertaking of HHRAs for federal sites impacted with PFAS. The poster will outline Health Canada’s recommended HHRA methodology for PFAS-impacted federal sites, as well as Health Canada’s human health screening values for PFAS in soil and groundwater. Examples will be included to demonstrate practical considerations and updates based on the evolving science in the PFAS field.

Mapping of Contaminants in Buried and Non-buried Structures and Works
Cristian Graf, Stantec Consulting Limited
The objective of this presentation is to discuss the development of an inventory of hazardous materials and to map the existing contaminants for Jacques Cartier and Champlain Bridges Incorporated and the proactive management of information having an environmental impact or impacts on health and safety.  
Abstract

As part of its sustainable development policy, Jacques Cartier and Champlain Bridges Incorporated (JCCBI) wanted to develop a tool to “manage in a systematic manner” the infrastructures on its territory and to ensure “safety and sustainability”. Stantec Consulting Limited has been hired to conduct an inventory of the hazardous materials and to map the existing contaminants using a Java management programming interface (JMAP).

The purpose of the mandate was to gather the available information and complete the missing information using a site survey in order to put in place a database of the contaminants present in the targeted structures. This database will make it possible to proactively manage the information that has an environmental/health-safety impact, enabling JCCBI to remain ahead of the issues presented by the presence of contaminants. The discovery of contaminants in materials or equipment during a project can have a major impact on the project, namely in terms of timeframes and budget.

The five sectors targeted by the contract are the following:

• Jacques-Cartier Bridge;
• Honoré-Mercier Bridge (federal section);
• Champlain Bridge ice-control structure;
• Melocheville Tunnel;
• Bonaventure Highway (federal section).

The scope of the work is limited to buried and non-buried structures and works and does not include the management of contaminated soil.

Contaminants targeted:

• Materials likely to contain asbestos (MLCAs);
• Lead in paint;
• Equipment that may contain mercury;
• Equipment that may contain polychlorinated biphenyls (PCBs);
• Materials likely to contain silica.

Objectives
As part of this mandate, the various steps and activities to be implemented for each of the targeted structures and works were completed in accordance with the following objectives:

• Develop an overall picture of the presence of contaminants using the documents provided by JCCBI;
• Complete the overall picture for the works and structures where there is a lack of information through field characterizations and inspections;
• Map and compile the information regarding contamination using the database taken from the characterization results and site inspections;
• Provide JCCBI with an overview of the contamination in the targeted structures and the means for ensuring effective tracking (recommendations, tools and programs).

Scope of the Work
A summary of the tasks completed as part of this mandate is presented below:

• Document review: The objective of this task was to establish an inventory of the available data and assess their relevance and quality. Furthermore, the document review served to create an overview of the contaminants present or potentially present in the targeted sectors;
• Drafting of an action plan and organization of the work: prepare and plan the activities to be implemented for each of the sectors targeted by this study;

• Complete an inventory and mapping of the contaminants:

• Complete an inventory of the structures and identify the contaminants potentially present through a document review;
• Prepare an investigations program;
• Complete the field work (inspections and surveys);
• Mesh the inspection results with JCCBI’s internal mapping and information management tool;
• Prepare the characterization reports and the summary report, a response program and recommendations.

PFOS Fish and Shellfish Consumption at Two AFFF Case Studies – Understanding and Communicating Risk
Amy Quintin and Antony Rodolakis
Wood
The objective of this presentation is to illustrate the importance of the CSM and site setting in understanding and communicating risk. The setting is particularly relevant for PFAS sites with fish and/or shellfish present, as potential human health risks may vary widely from site to site, particularly between freshwater and estuarine environments. Understanding the setting and existing advisories is key to communicating risk to stakeholders.  
Abstract

Background/Objectives
Per- and polyfluoroalkyl substances (PFAS) have been detected in fish and shellfish globally, in particular perfluorooctane sulfonate (PFOS). PFOS bioaccumulates and enters the human food chain through seafood ingestion. This human health exposure pathway is frequently evaluated when PFOS contamination is encountered near an aquatic environment. An understanding of the site conceptual site model (CSM) and site setting is necessary to evaluate and communicate the results.

Approach/Activities
This study considers implications to human health at two case study sites, with over 100 aquatic samples collected at each site. Both sites were impacted by historical aqueous film forming foam (AFFF), and both were in close proximity to aquatic environments with fish and shellfish present. The first site was near a freshwater and estuarine river. The second site was on a peninsula surrounded by estuarine waters. Recreational fishing and shellfish harvesting takes place near both sites.

Results/Lessons Learned
Bioaccumulation patterns and potential risk outcomes were found to vary between freshwater and estuarine environments. At the first site, concentrations in estuarine fish tissue concentrations were generally below screening values. At the second site, potential risks from consumption of fish tissue within estuarine waters were ruled out based on the migratory species present. At the first site, PFOS concentrations in freshwater fish within the river were found vary significantly, with some concentrations above screening values in specific species. At both sites, shellfish concentrations in the estuarine environments were below human health screening values. The results of each investigation were considered within the context of existing consumption advisories and local consumption habits, which were incorporated into the final recommendations. The overall context of screening level exceedances is fundamental to understanding and communicating potential risks to stakeholders.

Amy Quintin, Senior Human Health Risk Assessor, Wood
Amy Quintin is a human health risk assessor with over fifteen years of experience. Her role is to lead and review multi-media human health risk assessments for common and emerging contaminants under state, federal and international programs. She provides risk assessment support for all elements of the site management process, from reviewing initial sampling plans to developing remediation strategy decisions.

Human Health Risk Assessment of Lead at Federal Sites
Gillian Dunlop and Tania Noble
Stantec Consulting Limited
The objective of this presentation is to use a case study to outline what the new Health Canada Lead toxicological reference value means in terms of calculated risk levels and remediation requirements.  
Abstract

Health Canada has released guidance on lead toxicity and risk, within the Guidelines for Canadian Drinking Water, Guideline Technical Document, Lead. Health Canada (2019) contains a review of lead toxicity and a new toxicity value for evaluating non-carcinogenic human health risks for lead. In recognition that the development effects associated with lead do not appear to have a threshold, a slope factor of 2500 (mg/kg-d)-1 is recommended when evaluating health risks for lead. The slope factor is based on an endpoint of mild intellectual disability expressed as a decrement in IQ points. This new slope factor was used to evaluate human health risks due to lead at the Fisheries and Oceans Canada Great Duck Island Lightstation Site.

This presentation will summarize what the new lead slope factor means in terms of site-specific target levels for different land uses, and how different exposure point concentrations can be correlated with theoretical IQ decrements. For federal custodians with lead-impacted sites, the presentation will provide a useful update on the most recent Health Canada guidance on lead, and how that may affect calculated risk levels and remediation requirements.

Gillian Dunlop, Risk Assessor, Environmental Services, Stantec Consulting Limited
Gillian Dunlop is a risk assessor in Stantec Consulting Limited's Environmental Services team. Since the start of her consulting career in 2007, Gillian has worked on numerous human health and ecological risk assessments. With extensive experience at federal contaminated sites, she has carried out risk assessment projects for numerous custodial departments in various provinces. Gillian has completed many risk assessments under Ontario Regulation 153/04 and is familiar with the Ontario regulatory process. Gillian is a recognized toxicologist by the Ontario Ministry of the Environment, Conservation and Parks, and has completed Maximum Concentration Level Assessments that have achieved regulatory approval. Gillian has conducted risk assessments for a variety of sites (e.g., residential, commercial, industrial and sensitive) and chemical groups (e.g., inorganics, organics, radionuclides) for all types of environmental media (e.g., soil, soil vapour, groundwater, surface water and sediment). Gillian has prepared the multi-media health assessment component of environmental assessments for mining, oil and gas and power projects. Gillian has a B.Sc. from the University of Guelph in Environmental Science and a Ph.D. from the University of Toronto in Chemistry.

Critical Review and Update of Relative Potency Values for Selected Carcinogenic PAHs
Lynne Haber1, Alison Pecquet1, Melissa K. Vincent1,2, Yvette Bonvalot3, Louise White3
1University of Cincinnati
2Cardno ChemRisk
3Health Canada
The objective of this presentation is to share Health Canada’s critical review and analysis of the relative potency approach widely used to estimate risks of PAH-containing mixtures in human health risk assessments. Based on the findings, a multi-faceted approach for understanding the potency of PAH mixtures will be presented, involving mixture characterization, new indicators of PAH mixtures and alternative methods such as in vitro, or other short-term testing.  
Abstract

The human health risks of chemical mixtures containing polycyclic aromatic hydrocarbons (PAHs) are estimated using relative potency (RPF)/potency equivalence (PEF) factors, based on the ratio of the potencies of the target PAH and benzo[a]pyrene (B[a]P). In this work, Health Canada reviewed the US Environmental Protection Agency (EPA) (2010) draft RPF approach for PAH mixtures and the EPA Science Advisory Board (SAB) comments on that draft, with the goal of applying the SAB recommendations to update the PEFs for eight carcinogenic PAHs with published exposure guidelines and for several additional carcinogenic PAHs. Based on the SAB recommendations, the analyses focused on carcinogenicity studies using environmentally relevant exposure routes that provided data for both the target PAH and B[a]P (or an appropriate surrogate); 48 study/chemical combinations met these initial criteria. Of these, only three studies (one testing five of the subject PAHs) met the additional dose-response criteria: (1) inclusion of multiple dose levels of both the target PAH and B[a]P; and, (2) having a tumor response of 50% or less at the lowest or only dose tested. Only one chemical (cyclopenta[c,d]pyrene) had multiple studies that met the criteria. The lack of available studies meeting the criteria highlights the large uncertainties in the published RPFs/PEFs, and we discuss the potential for a multidisciplinary stepwise alternative risk assessment approach.

Louise White, Contaminated Site Program, Health Canada
Louise White has worked for Health Canada's Contaminated Site Program for the past 14 years. She has also worked on contaminant assessment and other contaminant issues for Environment Canada, Fisheries and Oceans Canada and Canadian Wildlife Service.

Updated Health Canada Supplemental Guidance for Soil Vapour Intrusion Assessment at Contaminated Sites
Christine Levicki, Thalia Zis, Sue-Jin An, Lindsay Smith-Munoz
Health Canada
The objective of this presentation is to present Health Canada's updated Supplemental Guidance for Soil Vapour Intrusion Assessment at Contaminated Sites.  
Abstract

Health Canada’s Contaminated Sites Division has updated its 2010 Supplemental Guidance for Soil Vapour Intrusion Assessment at Contaminated Sites to incorporate the most recent science, and, to the level practicable, adopt elements from A Protocol for the Derivation of Soil Vapour Quality Guidelines for Protection of Human Exposures via Inhalation of Vapours (CCME, 2014). This Health Canada supplemental guidance allows for incorporation of consistent scientific information in evaluating potential human health risks associated with the inhalation of indoor air vapours originating from subsurface contamination in groundwater or soil at federal contaminated sites.

The highlights of the updated guidance will be presented and include the following:

• A multiple lines of evidence approach to allow for flexibility in assessing the vapour intrusion pathway at federal contaminated sites.
• Additional detail on the recommended environmental data to assess the vapour intrusion pathway.
• Generic default input values for the Johnson & Ettinger (1991) model harmonized to the degree practicable with those in the CCME (2014) protocol for the derivation of soil vapour quality guidelines.
• Presentation of the J&E-derived vapour attenuation factors in a simplified and user-friendly manner.
• An update to the vertical and lateral screening distances for volatile contaminants which bioattenuate.
• An updated approach for adjusting attenuation factors for bioattenuation.
• Additional detail to guide the use of default sub-slab attenuation factors adopted from CCME (2014).

Christine Levicki, Environmental Specialist, Contaminated Sites Division, Health Canada
Christine Levicki is an Environmental Specialist with Health Canada's Contaminated Sites Division.

A Discussion of the Pitfalls of a Poorly Constructed Conceptual Site Model and the Implications on Risk Conclusions and Management Objectives – A Case Study Using a Detailed Aquatic Risk Assessment at a Former Military Airport
Brett Lucas, Ahmadreza Mehjoo, Blair McDonald
Golder Associates Ltd.
The objective of this presentation is to present on the importance of developing a robust conceptual site model to ensure that contaminant sources, pathways and routes of exposure are properly characterized and assessed. If this is not properly characterized, this can have significant implications on remediation objectives and risk conclusions.  
Abstract

A preliminary quantitative risk assessment (PQRA) of the shoreline area of a local airport (confidential location) was previously conducted. The airport was constructed during World War II and had previously been used as a staging area for US Military operations during transportation to Alaska. The site is currently the location of a local airport used primarily for chartered flights. The results of the original PQRA concluded that elevated concentrations of dichlorodiphenyltrichloroethane (DDT) in sediment and fish tissue could represent an unacceptable risk to human and ecological receptors. The previous PQRA theorized that the likely source of DDT to the aquatic environment was a combination of groundwater discharges from upland landfills, and historical loading of DDT as a result of leakage from improper disposal of drums in the adjacent lake. Golder Associates Ltd. (Golder) conducted a review of the previous PQRA and identified several data gaps and opportunities for refinement of the conceptual site model and risk assessment. Golder conducted supplemental sampling (fish, surficial sediment, sediment cores, benthic invertebrates, and upland soil, groundwater and porewater) using a tiered approach to manage costs while focusing analyses on key outcomes observed during the staged processing of the data. They then used the data collected during the supplemental sampling to refine the conceptual site model to provide direction for a detailed quantitative risk assessment (DQRA). The intent of a conceptual site model is to help communicate the relationship between contaminant sources, pathways and receptors. During the data gap assessment, a total of four plausible scenarios were identified for release of DDT to the lake including: groundwater discharge from upland dump sites; contaminated soil runoff from affected upland areas; release from improper disposal of drums in the lake; and, direct aerial application. It was determined through review of the available literature that aerial application of DDT to the lake may have occurred between 1949 and 1969 to control insects.

The sampling data confirmed that elevated DDT concentrations in sediment and fish tissues were found within the area of interest, however significant concentrations were also found at other in-lake locations and at a regional reference lake. The results highlight the importance of properly developing your conceptual site model to understand contaminant release mechanisms and exposure pathways. A properly developed conceptual site model is key to accurately investigating and characterizing risk and has important site management implications. The results of this investigation were important in identifying that observed contamination may be the result of a larger regional condition influenced by historical aerial application of DDT. These conclusions have significant implications for remediation planning because without the regional context identified in the updated conceptual site model, reclamation activities would have likely focused on a more localized approach (e.g., dredging), which would not have effectively managed the full extent of contamination.

Brett Lucas, Environmental Scientist, Environmental Remediation and Water Group, Golder Associates Ltd.
Brett Lucas is an environmental scientist in Golder's Environmental Remediation and Water Group. He holds a Master's of Science degree in environmental toxicology and is a Registered Professional Biologist with the BC College of Applied Biology. His areas of expertise include: human health and ecological risk assessments; aquatic and marine toxicology; environmental effects monitoring; toxicity identification evaluations; site-specific water quality guideline development; contaminated sites; and, paleolimnology.

The Importance of Considering the Conceptual Site Model when Selecting Lines of Evidence Used in an Aquatic Risk Assessment
Brett Lucas, Ahmadreza Mehjoo, Blair McDonald
Golder Associates Ltd.
The objective of this presentation is to highlight the importance of selecting appropriate lines of evidence that relate back to a robust understanding of the conceptual site model.  
Abstract

A preliminary quantitative risk assessment (PQRA) of the shoreline area of a local airport (confidential location) was previously conducted. The airport was constructed during World War II and had previously been used as a staging area for US Military operations during transportation to Alaska. The site is currently the location of a local airport used primarily for chartered flights. The results of the original PQRA concluded that elevated concentrations of dichlorodiphenyltrichloroethane (DDT) in sediment and fish tissue could represent an unacceptable risk to human and ecological receptors. The previous PQRA theorized that the likely source of DDT to the aquatic environment was a combination of groundwater discharges from upland landfills, and historical loading of DDT as a result of leakage from improper disposal of drums in the adjacent lake. Golder Associates Ltd. (Golder) conducted a review of the previous PQRA and identified several data gaps and opportunities for refinement of the conceptual site model and risk assessment. Golder conducted supplemental sampling (fish, surficial sediment, sediment cores, benthic invertebrates, and upland soil, groundwater and porewater) using a tiered approach to manage costs while focusing analyses on key outcomes that would reduce uncertainty with respect to previously identified risk conclusions. A key objective of the current DQRA was to incorporate site-specific data to replace conservative assumptions made in the previous PQRA. The goal was to avoid unnecessary physical remediation of areas where risk from contamination could be managed in place. The DQRA used a modified weight-of-evidence approach to integrate sediment chemistry, toxicity, and benthic community data into risk conclusions for benthic organisms that aligned with the updated understanding of the conceptual site model. This approach provided clarity on the level of sediment contamination, the likely source, and the bioavailability of DDT in sediments. Risks to fish were evaluated using a chain of evidence approach to integrate various lines of evidence related to dietary exposure, bioaccumulation and fish health. The results confirmed that northern pike, lake trout, and whitefish were accumulating DDT in their tissues, although direct effects on fish health indices were less apparent. These fish tissue results were then used to assess potential health risks to humans and semi-aquatic wildlife (mammals and birds) from potential exposure to DDT accumulating in the food-web.

The sampling data confirmed that elevated DDT concentrations in sediment and fish tissues were found within the area of interest, however significant concentrations were also found at other in-lake locations and at a regional reference lake. The DQRA determined that ecological health risks were less than previously reported in the PQRA. The results highlight the importance of selecting appropriate lines of evidence that align with a robust understanding of the conceptual site model. By continually referring back to the conceptual site model (i.e., source and exposure pathways) at each stage of the risk assessment, uncertainty in risk conclusions were reduced.

Brett Lucas, Environmental Scientist, Environmental Remediation and Water Group, Golder Associates Ltd.
Brett Lucas is an environmental scientist in Golder's Environmental Remediation and Water Group. He holds a Master's of Science degree in environmental toxicology and is a Registered Professional Biologist with the BC College of Applied Biology. His areas of expertise include: human health and ecological risk assessments; aquatic and marine toxicology; environmental effects monitoring; toxicity identification evaluations; site-specific water quality guideline development; contaminated sites; and, paleolimnology.

Questions en

fb icon   Twitter icon   linkedIn icon