TOXICITY OF CONTAMINATED SEDIMENTS IN DILUTION SERIES WITH CONTROL SEDIMENTS

The use of dilutions has been the foundation of our approach for asses sing contaminated water, and accordingly, it may be important to estab lish similar or parallel approaches for sediment dilutions. Test organ ism responses to dilution gradients can identify the degree of necessa ry sediment alteration to reduce the toxicity. Using whole sediment di lutions to represent the complex interactions of in situ sediments can identify the toxicity, but the selection of the appropriate diluent f or the contaminated sediment may affect the results and conclusions dr awn. Contaminated whole sediments were examined to evaluate the toxici ty of dilutions of sediments with a diversity of test organisms. Dilut ions of the contaminated sediments were prepared with differing diluen ts that varied in organic carbon content, particle size distribution, and volatile solids. Studies were conducted using four macroinvertebra tes and a vascular, rooted plant. Responses by some test organisms fol lowed a sigmoidal dose-response curve, but others followed a U-shaped curve. Initial dilutions reduced toxicity as expected, but further dil ution resulted in an increase in toxicity. The type of diluent used wa s an important factor in assessing the sediment toxicity, because the control soil reduced toxicity more effectively than sand as a diluent of the same sediment. Using sediment chemical and physical characteris tics as an indicator of sediment dilution may not be as useful as chem ical analysis of contaminants, but warrants further investigation.