Evaluating the techniques for a tiered testing approach to dredged sediment assessment - A study over a metal concentration gradient

A sediment quality triad approach was used to evaluate Environment Canada's battery of marine bioassays and the proposed pass/fail criteria along a me tals gradient in Belledune Harbour, New Brunswick, Canada. Most assays perf ormed consistently, but certain tests provided less response than expected at the more contaminated stations (amphipod survival and light reduction in photoluminescent bacteria tests passed according to proposed pass/fail cri teria). Echinoid fertilization tests were quite sensitive. Bioaccumulation of lead and benthic community structure were related to bulk sediment value s (at alpha = 0.1). Test interpretation criteria appear reasonable, but as the response rate was low in certain tests, further assessment is recommend ed. With respect to species suitability, only the clam Macoma balthica used in the bioaccumulation test was thought to be less than optimal for routin e use on a large scale because of practical handling and cost consideration s. Canadian draft Interim Sediment Quality Guidelines, which the Disposal a t Sea Program may use for screening purposes in a tiered testing approach, were used in this study as the chemical benchmarks to select test stations on the basis of the relative probability of effects. Guidelines at the thre shold effects level (TEL) performed well in the study as levels below which unacceptable biological effects were unlikely to occur. The ratio of simul taneously extractable metals to acid volatile sulfides was also used in add ition to the guideline levels to help explain responses (or lack thereon al ong the gradient. Each of the chemical approaches was useful in the predict ion/explanation of some but not all of the responses seen in the toxicity a nd/or benthic community results.