A battery of 20 bioassays was applied to assess test and endpoint performance in detecting the toxic potential of 15 freshwater sediment samples collected in the St. Lawrence River/Great Lakes systems. The bioassays included 18 micro-scale assays performed either on whole sediment, pore water or sediment organic extracts, as well as two standardized whole sediment bioassays undertaken with macroinvertebrates (Chironomus riparius and Hyalella azteca). Physical and chemical parameters of selected sediments were also analyzed to aid in the interpretation of results. Several qualitative and quantitative criteria were established for evaluating the reliability and usefulness of the micro-scale bioassays in predicting sediment toxicity based on a two-tier system. In Tier 1, micro-scale testing results were compared for general concordance with those of the benthic bioassays, benthic community structure index and with sediment contaminant levels. Micro-assays which complied with Tier 1 standards were further evaluated via a Tier 2 process consisting of selected (quantitative and qualitative) scientific and practical criteria. Of the 20 bioassays investigated, the two benthic assays and seven micro-scale assays successfully passed the double-tiered assessment. Micro-scale tests whose results most closely matched those of the benthic tests for appraisal of whole sediment toxicity, sediment contamination level and benthic community structure index included three bacterial assays (ATP assay, a micro-plate adaptation of the Microtox® assay, SOS Chromotest™), one algal assay (algal solid-phase test) and three micro-invertebrate assays (Thamnotoxkit™ F, Daphtoxkit™ F and Hydra assay). Two selected batteries, composed of the seven micro-scale assays and benthic invertebrate bioassays, are proposed for cost-effective appraisal of freshwater sediment toxicity.

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