Comparison of toxicity detected by five bioassays during bioremediation of diesel fuel-spiked soils

Biodegradation of petroleum contaminants is an effective and generally inexpensive approach for reducing their concentrations in soils. However, little information is available on the toxicological status of contaminated soils and the fate of target hydrocarbons following bioremediation. Four texturally distinct soils were contaminated with diesel fuel and bioremediated in microcosms at 22°C, with moisture contents of 85% of soil water holding capacity, and nitrogen (N) and/or phosphorus (P) nutrient amendments. The progress of bioremediation was monitored using chemical and toxicological analyses. Soil toxicity was measured using five short-term bioassays: seed germination, red blood cell hemolysis, solid-phase Microtox, SOS-chromotest, and Toxi-chromotest. Reductions in target compound concentration were not always predictive of reductions in soil toxicity. Conflicting trends were indicated by the toxicity test results. For example, total petroleum hydrocarbon analysis revealed decreased hydrocarbon concentrations in all four soils following bioremediation but seed germination and seedling emergence data indicated increased soil toxicity. In contrast, the Microtox test data indicated decreased toxicity in two of the four soils. These results suggest that measurements of target contaminant concentrations should be complemented with several different soil toxicity bioassays, particularly when evaluating the ability of bioremediation to reduce the adverse effects of contaminants in soil. © 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 117–126, 1998