Severn Sound Sediment Chemistry and Bioassessment, 1988–1990

Abstract Fine-grained sediment in the embayments of Severn Sound contains metals that exceed the Ontario Ministry of the Environment's lowest effect level, the level at which some disturbance of the sediment dwelling community can be expected. Sediment in Penetang Bay has concentrations of Cr that are above the provincial Severe Effect Level, the level at which a compound is expected to be detrimental to the majority of benthic species. Nevertheless, chronic sediment bioassays resulted in little measurable sublethal toxicity. Based on evidence from weak acid extraction of metals from sediment, the lack of toxicity may be due to the limited bioavailability of metals. The potential for metals to enter the food web was suggested by metal bioaccumulation observed for test species. Chromium and Ni concentrations in mayflies were significantly correlated with total Cr and Ni in sediment, and Zn and Cu tissue concentrations were not correlated with total metals in sediment. In general, the bioaccumulation of Cd, Cr, Cu, Ni and Pb by test species was more strongly correlated with extractable metals and with metals in the <63 µm size fraction than with total metals in bulk sediment, demonstrating that the total sediment pool of metals was not biologically available. Remedial actions for sediment in Severn Sound should focus on source control and natural sediment recovery, given the lack of sublethal chronic toxicity. Confirmation that active sources are not present and an ability to predict the natural recovery period for marginally contaminated regions would assist in fully restoring the sound.