Screening level ecological risk assessment of heavy metals and biocides in seawater at an active ship repair drydock

The Esquimalt Graving Dock is an active ship repair facility and drydock located in Esquimalt Harbour near Victoria, British Columbia. During drydock operations, vessels are floated in (ingress), the drydock opening is closed, and seawater is pumped out (pump-down). Vessel repair activities including sandblasting, power-washing, welding, and painting are then conducted in accordance with the facility environmental management system that requires containment and off-site disposal of waste materials. After repairs are completed, seawater is pumped into the drydock and the vessel is floated out (egress), completing a full docking/undocking cycle. Monitoring was conducted to assess the quality of water discharged to the waterlot during vessel ingress, drydock pump-down, vessel egress, and during auxiliary pumping. Metals and tributyltin were found at concentrations exceeding generic water quality guidelines. The objective of this study was to conduct a screening level (preliminary) ecological risk assessment of the drydock discharges including problem formulation, exposure assessment, effects assessment, and risk characterization. Key elements included censored data analysis, wildlife food-chain modelling, and literature-based toxicological reference values ranging from no-observed adverse effect levels (NOAEL's) to a 50% effects concentration (EC50), in most cases multiplied by a safety factor of 0.1. Exposures were conservatively assumed to be chronic (long-term). Hazard quotient values greater than 1 indicated the potential for adverse effects to marine plants/algae and fish from copper, and for marine invertebrates to copper, zinc, and tributyltin. Hazard quotients for marine mammals and marine birds were less than 1. Considering all lines of evidence including background conditions, bioavailability, and the intermittent nature of the discharges, it was concluded that risks of adverse effects were either negligible (marine mammals and birds) or low (plants/algae, invertebrates, and fish). To address uncertainties, recommendations included monitoring using passive samplers to determine long-term average concentrations, additional characterization of background water quality, and consideration of other substances such as booster biocides and fluoropolymer or per-and polyfluoroalkyl substances (PFAS).