Life cycle responses of earthworm, Eisenia fetida to soil contaminated with crude oil sludge containing polycyclic aromatic hydrocarbons (PAHs).

Crude oil sludge contamination and its disposal pose significant threats to aquatic and terrestrial ecosystems. This study assessed the ecological risks of crude oil sludge through polycyclic aromatic hydrocarbon (PAH) quantification and multi-endpoint toxicity evaluation in Eisenia fetida. High-performance liquid chromatography analysis of crude oil sludge from Ankaleshwar, India, revealed the presence of 3- to 5-ring PAHs at concentrations ranging from 0.02 to 10.35 μg/mL. The effects of crude oil sludge (0.01-500 g/kg) were examined across the earthworm life cycle, including cocoons, juveniles, and adults. Exposure to sludge caused a significant, concentration-dependent reduction in survival, biomass, and reproduction. Although cocoon exposure did not significantly affect hatchling numbers, it notably impaired adult reproduction by reducing hatchling counts. Juveniles displayed greater sensitivity, with mortality rates of 30-50 % at days 7 and 14, respectively, accompanied by decreased body weight following chronic exposure. In contrast, adult earthworms showed significant declines in cocoon production and juvenile formation without immediate effects on survival. Phenanthrene was the only PAH consistently detected in earthworm tissues, reaching concentrations up to 440.53 μg/g in adults and 0.212 μg/g in juveniles. Biochemical analyses revealed marked alterations in oxidative stress and neurotoxicity markers. Adults exhibited significant induction of antioxidant enzymes under chronic exposure, whereas juveniles showed minimal or reduced enzymatic responses, indicating stage-specific physiological resilience. Histological examination demonstrated concentration-dependent muscle degeneration and disruption of the gut epithelium. Overall, these findings identify phenanthrene as a key contributor to crude oil sludge toxicity and underscore the importance of assessing life-cycle responses in terrestrial ecotoxicology.