Characterization and spatial distribution of organic-contaminated sediment derived from historical industrial effluents.

Organic sediment contaminants [polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/Fs), and polycyclic aromatic hydrocarbons (PAHs)] were assessed using secondary monitoring data from a former tidal estuary (Boat Harbour) impacted by historical industrial effluents. Spatiotemporal characterization of PCDD/Fs and PAHs in sediments was conducted to inform a sediment remediation program designed to return this contaminated aquatic site back to a tidal lagoon. Spatiotemporal variations of sediment PCDD/F and PAH concentrations across Boat Harbour and off-site reference locations were assessed using secondary monitoring data collected between 1992 and 2015. Sediment PCDD/F toxic equivalency (TEQ) and PAH concentrations were compared to sediment quality guidelines. Sediment PCDD/F concentrations exceeded the highest effect thresholds posing severe ecological health risks. High sediment PCDD/F concentrations have persisted in Boat Harbour despite implementation of Pulp and Paper Mill Effluent Chlorinated Dioxins and Furans Regulations in 1992. PAH concentrations varied greatly. Five individual PAH compounds frequently exceeded severe effect thresholds, in contrast to total PAHs, which were below severe effect thresholds. Forensic analysis using PAH diagnostic ratios suggests pyrogenic PAHs derived from wood processes or coal combustion were likely sources. Twenty-five years of monitoring data revealed large data gaps in our understanding of sediment characteristics in Boat Harbour. Gaps included spatial (vertical and horizontal) and temporal variations, presenting challenges for remediation to accurately delineate sediment contaminants. Deeper horizons were poorly characterized compared to shallow sediments (0-15 cm). Historical secondary monitoring data showed that spatial coverage across Boat Harbour was inadequate. Due to severe ecological health risks associated with high sediment PCDD/F concentrations, remediation of the entire sediment inventory is recommended. Detailed vertical and horizontal sampling within Boat Harbour, establishment of local baseline concentrations, and additional sampling in down-gradient-receiving environments for a suite of contaminants are required to better characterize sediments prior to remediation.