Sediment Studies Provide Key Information on the Need to Treat Sewage Discharged to Sea by a Major Canadian City

Abstract

Relatively untreated (screened) municipal wastes from the City of Victoria, B.C. and environs are discharged to the sea as effluent from two long outfall pipes, only one of which (Macaulay Point) discharges to a depositional zone. Sediments along transects away from the Macaulay Point outfall were collected and the following parameters determined: contamination (selected chemicals of concern), toxicity (polychaete survival and growth, amphipod survival, and bivalve larvae abnormalities), and benthic infaunal community structure. Significant sediment contamination was restricted to within 100-400 m of the outfall with the exception of high PAH contamination due to the shipwreck of a collier in 1891. Sediment toxicity was restricted to effects on growth and development, also within 100-400 m of the outfall; survival was near control levels even at the outfall terminus. Benthic infaunal community structure indicated “moderate pollution” within 100 m of the outfall and showed a classic organic enrichment pattern of increasing species richness and lower abundance with distance from the outfall. Overall, the impact of the outfall on the sediments is minimal, highly restricted in extent, and not of major environmental concern. A public referendum, conducted after the release of this and of other scientific studies, resulted in the deferral of primary effluent treatment.