Temporal ecological assessment of oil contaminated soils before and after bioremediation

Ecotoxicity methods were used to assess different soil and oil combinations before, during and after laboratory bioremediation with associated hydroca rbon analysis. Heavy, medium and light crude oil (API gravity 14, 30, and 5 5) was spiked (ca, 5% w/w) into two sandy soils in the laboratory having or ganic carbon concentrations of 0.3 (Norwood) and 4.7% (Norwood/Baccto). The earthworm (Eisenia fetida) 14-d lethality assay, the modified Microbics Mi crotox(R) Solid-Phase assay, and the 14-d plant seed germination and growth assays using corn, wheat and oats, were spiked and tested during a 360-d l aboratory remediation. Eisenia was the most sensitive of the three methods utilized with survival increasing throughout bioremediation with fastest to xicity reduction in the high carbon Norwood/Baccto soils where LC50's were 100% or greater at the end of 90-d whereas, >150-d were required to achieve a similar result in the low carbon soil. Analysis of the undiluted treatme nts with oily soil alone showed that earthworm survival was high after 90-d in all high organic carbon soils, and after eight months in the low carbon soils, except for the Norwood soil-light oil treatment, which required 360 -d to achieve 100% survival. The Microtox assay was less sensitive with EC5 0's 100% or greater observed after 90-d in high carbon soils and after 240- d for all low carbon soils. After bioremediation, no effects on seed germin ation were observed, although some plant growth inhibition effects remained . There was no direct correlation between total petroleum hydrocarbon conce ntrations and toxicity. (C) 1999 Elsevier Science Ltd. All rights reserved.