A rapid bioassay is presented for determining acute toxicity directly in soil. Modifying the Organisation for Economic Cooperation and Development (OECD) protocol 207, it uses a thin layer of moistened soil laid directly in the bottom of the bioassay jar into which the earthworms are placed and incubated. Examples are presented in comparisons between the soil contact bioassay vs. the filter paper bioassay run on Toxicity Characteristic Leaching Procedure (TCLP) extracts of pesticide contaminated soil and petroleum drilling cuttings. In 2,4-dichlorophenoxyacetic acid (2,4-D) contaminated soil (300mg/Kg), no mortality was found in soil extracts, but 100% mortality was found when exposed directly to soil. Treatment with the Daremend® product in five anaerobic/aerobic cycles slowly reduced the 24 h mortality (0%) but still showed 100% mortality at 48 h. However, severe sub-lethal effects (expulsion of celomic/bloody fluids) were reduced from 50% to 37%, and further treatment may reduce the toxicity to acceptable levels. The petroleum drilling cuttings treated by chemical oxidation (1.3% H2O2, w/w) and bioremediation (simulation of biopiles), showed a similar response, where 0% mortality in soil extracts was found, but 100% mortality with soil contact. Post-treatment with chemical oxidation resulted in a reduction in the soil contact bioassay to 3% and 13% mortality, within the accepted range (≤10%) of the OECD protocol. Observations are presented with respect to moisture control to prevent earthworm desiccation and recommendation for confirmation using the sub-chronic test in the OECD protocol but by testing the contaminated/treated soil itself rather than artificial soil.
Keywords: Acute toxicity; Agricultural science; Chemistry; Direct contact bioassay; Earthworm bioassay; Engineering; Environmental science; Mortality; Soil characterization; Soil remediation.
© 2019 Published by Elsevier Ltd.