Spent lubricant oil-contaminated soil toxicity to Eisenia andrei before and after bioremediation

Bioremediation is very efficient in biodegrading petroleum hydrocarbons. However, the decrease in these target contaminants in soils is not necessarily followed by a decrease in toxicity. The remaining contaminants can be enough to retain toxicity, while incomplete degradation of several compounds can generate sub-products, which can be even more toxic. In this context, the aim of this study was to assess acute and chronic toxicity in Eisenia andrei exposed to soil contaminated with 5% spent lubricant oil before and after 22 months of bioremediation in 150 L aerobic reactors. Applied bioremediation strategies were biostimulation (BIOS), bioaugmentation by adding mature compost from municipal solid waste (BIOA₁) and bioaugmentation by adding non-mature compost from municipal solid waste (BIOA₂). After 22 months, total petroleum hydrocarbons (TPH) were reduced 71% in BIOS and 73% in both BIOA₁ and BIOA₂. Polycyclic aromatic hydrocarbons (PAH) were reduced in about 98% in all treatments (BIOS, BIOA₁ and BIOA₂). At the 14^th day of exposure, mortality rates were 7 ± 2, 20 ± 0, 75 ± 25, 93 ± 12 and 100 ± 0% for Eisenia andrei exposed to CONT (soil with no oil addition), BIOS, OLU (soil newly contaminated with 5% spent oil), BIOA₁ and BIOA₂, respectively. After 14 days, surviving specimens in both BIOS and OLU soils exhibited anatomic deformations, less biomass than the controls, and decrease in juvenile forms and coelomocytes. After 28 days, the mortality rate for BIOS and OLU soils increased to 97 and 100%, respectively. Therefore, even with a reduction of 71-73% for TPH and 98% for PAH, toxic effects remained in all soils bioremediated, probably due to the remaining hydrocarbons and/or hydrocarbon biodegradation products. The results indicate that both chemical analyses and toxicological monitoring are required to follow-up soil remediation progress.