The relative sensitivities and discrimination abilities of the Daphnia magna 48-h lethality assay of sediment pore water, the Photobacterium phosphoreum 15-min bioluminescence inhibition (Microtox@) assay of sediment pore water and the Chironomus tentans 10-d growth reduction assay of whole Detroit River sediments were investigated and predictive relationships developed. While all three assays demonstrated the toxicity of some sediments and all of them identified the most and least toxic sediments, the D. magna lethality assay was the least sensitive and discriminatory. The Microtoxa assay was the most sensitive. Based on lethality, the C. tentans assay was less sensitive than D. magna, but growth inhibition was sensitive and the most discriminatory of the three assays. Chironomids were not observed in the sediments that caused a 30% decrease in growth of C. tentans relative to that on control sediment in which chironomids were observed. This sediment toxicity is also approximately that which kills D. magna. Some locations were deemed very toxic by one or two assays but not toxic by the others. The results of all of the assays were correlated, but none of the assays accurately predicted the results of the other two. It was concluded that the D. magna lethality test could be used to predict which sediments were so toxic that benthic insects would not be expected to be present. A principal components analysis demonstrated that the MicrotoxO assay gave sufficiently different information that it could be included in a battery of sediment toxicity tests designed to accurately classify the toxicities of sediments.

The ultimate goal of toxicity testing is to monitor or predict the effects of single compounds, elements or mixtures on the long-term health of individual organisms, populations, communities and ecosystems. Unfortunately, one does not always have all of the information required to determine the long-term or 'chronic' effects of toxicants on the survival, growth or reproduction of aquatic organisms. For this reason, the chronic effects of toxicants are often inferred or estimated from observations made during short-term or 'acute' field or laboratory studies, which may be conducted at greater concentrations of toxicant. The observations made in the short-term studies are then related to the chronic effects by some statistical relationship. There are basically two approaches: 1) The long-term effects on a parameter, such as survival (lethality.) are predicted from observations on the same parameter, during short-term exposures; 2) Alternatively, the response of one parameter to long-term exposures of a toxicant can be predicted from the short-term responses of a different parameter. In this report we present several different examples ofboth types of methods for estimating chronic responses from information on more short-term responses and discuss the rationale, advantages and disadvantages of each. We also report on two biochemical indicators; energetic substrates and RNA/DNA ratio. These indicators both act as sensitive, integrative measures of sublethal effects of contaminants during both acute and chronic exposures.

The relative sensitivities of bioassays to determine the toxicity of sediments were investigated and three methods of making the sample dilutions required to generate dose-response relationships were compared. The assays studied were: (a) Microtoxa, a 15-min assay of Photobacterium phosphoreum bioluminescence inhibition by pore water; (b) 48-h Daphnia magna lethality test in pore water; (c) 10-d subchronic assay of lethality to and reduction of weight gain by Chironomus tentans performed in either whole sediment or pore water; (d) 168-h acute lethality assay of Hexugenia limbata in either whole sediment or pore water. The three methods of diluting sediments were: (a) extracting pore water from the toxic location and dilution with pore water from the control station; (b) diluting whole sediment from the toxic location with control whole sediment from a reference location, then extracting pore water; and (c) diluting toxic, whole sediment with whole sediment from a reference location, then using the whole sediment in bioassays. Based on lethality, H. limbata was the most sensitive organism to the toxicity of Detroit River sediment. Lethality of D. magna in pore water was similar to that of H. limbata in whole sediment and can be used to predict effects of whole sediment toxicity to H. limbata. The concentration required to cause a 50% reduction in C. tentans growth (10-d EC50) was approximately that which caused 50% lethality of D. magna and was similar to the toxicity that restricts benthic invertebrate colonization of contaminated sediments. While the three dilution techniques gave similar results with some assays, they gave very different results in other assays. The dose-response relationships determined by the three dilution techniques would be expected to vary with sediment, toxicant and bioassay type, and the dose-response relationship derived from each technique needs to be interpreted accordingly.

The relative sensitivities of bioassays to determine the toxicity of sediments were investigated and three methods of making the sample dilutions required to generate dose‐response relationships were compared. The assays studied were: (a) Microtox®, a 15‐min assay of Photobacterium phosphoreum bioluminescence inhibition by pore water; (b) 48‐h Daphnia magna lethality test in pore water; (c) 10‐d subchronic assay of lethality to and reduction of weight gain by Chironomus tentans performed in either whole sediment or pore water; (d) 168‐h acute lethality assay of Hexagenia limbata in either whole sediment or pore water. The three methods of diluting sediments were: (a) extracting pore water from the toxic location and dilution with pore water from the control station; (b) diluting whole sediment from the toxic location with control whole sediment from a reference location, then extracting pore water; and (c) diluting toxic, whole sediment with whole sediment from a reference location, then using the whole sediment in bioassays. Based on lethality, H. limbata was the most sensitive organism to the toxicity of Detroit River sediment. Lethality of D. magna in pore water was similar to that of H. limbata in whole sediment and can be used to predict effects of whole sediment toxicity to H. limbata. The concentration required to cause a 50% reduction in C. tentans growth (10‐d EC50) was approximately that which caused 50% lethality of D. magna (48‐h LC50) and was similar to the toxicity that restricts benthic invertebrate colonization of contaminated sediments. While the three dilution techniques gave similar results with some assays, they gave very different results in other assays. The dose‐response relationships determined by the three dilution techniques would be expected to vary with sediment, toxicant and bioassay type, and the dose‐response relationship derived from each technique needs to be interpreted accordingly.

No abstract