SPATIAL AND TEMPORAL VARIABILITY IN METAL BIOAVAILABILITY AND TOXICITY OF SEDIMENT FROM HAMILTON HARBOR, LAKE-ONTARIO

Trace metals in sediment from nearshore urban and industrialized centres of the Great Lakes are frequently at concentrations well above geological background values. Total metal content in sediment, however, is a weak predictor of sediment toxicity. This study examined the bioavailability of metals from Hamilton Harbour in Lake Ontario and considered variability in metal forms on a temporal basis. Sediment from regions within Hamilton Harbour is highly contaminated with metals; nevertheless, not all metal-contaminated sites were toxic to test organisms. Most sediment did elicit sublethal and/or lethal responses in bioassay organisms. Metal bioavailability, as measured by weak acid extractions, metal bioaccumulation by fathead minnows, and sediment toxicity, was greater in sediment collected in the fall as compared to sediment collected in the spring. Results of analyses of tissue residues in test organisms and the reduced toxicity observed in sediment collected from some stations in the spring as compared to the fall implicate trace metals and sediment oxygen demand as contributing to sediment toxicity. The suitability for colonization by benthic invertebrates of sediment in some areas of Hamilton Harbour appears to be limited by both contaminants and high sediment oxygen demand. Improving the oxygen regime of the harbour should result in improvements in the benthic invertebrate community directly, by providing a suitable oxygen regime for organisms less tolerant of temporal anoxia, and indirectly by decreasing metal bioavailability, possibly through the co-precipitation of trace metals with iron and manganese hydroxides.