The Boat Harbour Effluent Treatment Facility (BHETF), located in Pictou Landing, Pictou County, Nova Scotia, is a 560-hectare impoundment used for over 50 years to treat effluent from a nearby pulp and paper mill. Dioxins and furans (D/F), polycyclic aromatic hydrocarbons (PAHs), and metals are the known contaminants of concern in sediment of the impoundment. A key component of the multiphase project was a Quantitative Human Health and Ecological Risk Assessment (QHHERA) to support an environmental impact assessment to identify areas of the BHETF requiring remediation for protection of ecological receptors and human health for intended future recreational and traditional usage. The overall objectives of the project include remediation of impacted sediment, returning the BHETF to a tidal estuary, and reconnecting the First Nations community to the land and waters of Boat Harbour. The ecological risk component of the QHHERA incorporated multiple lines of evidence and statistical analyses to evaluate risk to terrestrial and aquatic receptors. Specifically, passive sampling of pore water in freshwater and estuarine sediments was a key line of evidence for evaluating risk to benthic communities. Other lines of evidence to assess risk to benthic communities were sediment quality guidelines (SQGs) and equilibrium sediment benchmarks (ESBs).
Results/Conclusions
Pore water was collected using passive sampling devices deployed for 34 to 42 days, depending on the device and analyte. Pore water for analysis of metals and PAHs was collected in situ using peepers and SP3™ samplers provided by SiREM Technologies. Due to the slow kinetics of D/F partitioning between phases under low kinetic energy conditions, an ex‑situ passive sampling program was utilized to evaluate D/F in pore water. Samples were collected from the site and homogenized under laboratory conditions into a slurry using deionized water and sodium azide to prevent biological activity and prevent degradation of D/F. SP3TM samplers were added to the slurries, which were continuously agitated during the 42‑day equilibration period. For PAHs and D/F, the SP3TM samplers were pre‑loaded with performance reference compounds (PRCs) to estimate the degree of equilibrium reached and calculate freely‑dissolved concentrations in pore water. Comparison of concentrations in bulk sediment to SQGs, which were developed in the 1990s, identified a number of metals, PAHs, and D/F as posing risk to benthic communities. In contrast, freely dissolved concentrations in pore water, which is the most direct measure of bioavailability and exposure, were generally below water quality guidelines (WQGs) for protection of aquatic life.
