Problems and Recommendations in Using Algal Toxicity Testing to Evaluate Contaminated Sediments

Abstract

Algae were used to evaluate the toxicity of elutriates prepared from contaminated sediments from several Great Lakes Areas of Concern. A single-species laboratory toxicity test using Selenastrum capricornutum was adapted from the U.S. Environmental Protection Agency's standard 96-h algal assay procedure. This standard method was converted to a 24-h photosynthetic test requiring only 25-mL sample volumes. Algal cells were exposed to elutriates supplemented with nutrients and radioactive inorganic carbon. Toxicity was measured as carbon uptake relative to controls. All elutriates were stimulatory relative to the negative control. Stimulation complicated interpretation of results and prevented calculation of effective concentrations causing a decrease in algal photosynthesis. Samples could be classified as toxic or non-toxic based upon dilution series response curves; however, classical dose:response curves were rarely observed. Algal results generally supported those derived from Daphnia and Microtox tm tests. Successful use of algal bioassays to evaluate the toxicity of sediment elutriates will require development of a standard media or sediment extract which could serve as an acceptable negative control or diluent. This could reduce the confounding effect of nutrient stimulation, which complicates the use of algal toxicity testing in sediment toxicity assessments.