Assessment of the acute toxicity of crude oils in soils using earthworms, microtox®, and plants

The assessment of soil quality resulting from a chemical or oil spill and/or remediation effort may be obtained by evaluating the toxicity to soil organisms. To enhance our understanding of the soil quality resulting from laboratory and field oil spill remediation, we have assessed three soil toxicity test methods. Heavy, medium and light crude oils (API gravity 16–18, 30 and 53) were spiked into two soils in the laboratory. The earthworm (Eisenia foetida) 14-d lethality assay, the modified Microbics Microtox® Solid-Phase assay, and the 14-d plant seed germination and growth assays were tested with combinations of crude oils and soils. Earthworms were 1.4 to 14 times more sensitive than Microtox and 1.3 to >77 times more sensitive than plants to the oily soils. Light oil in the silty low organic carbon soil was generally the most toxic, while heavy oil in the sandy high organic carbon soil was least toxic. The bioassay techniques were demonstrated to be sensitive indicators of soil quality and may be used to evaluate the quality of remediated oily soils.