Survival of earthworms in soil exposed to mixture of petroleum products spiked with manure

Abstract

Petroleum hydrocarbon contamination poses a serious threat to soil ecosystems and may limit the effectiveness of earthworm-assisted bioremediation. This study investigated the survival of two earthworm species, Eudrilus eugeniae (epigeic) and Alma millsoni (endogeic), in soil contaminated with varying concentrations of a mixture of petroleum products (MPP). It also evaluated the effect of poultry manure amendment on their survival. Sandy loam soil was contaminated with MPP at concentrations of 0, 2, 5, 10, 15, 20, and 25 g per 500 g of soil, with or without poultry manure amendment (10 g per 500 g of soil). Survival was monitored over a 30-day exposure period. Two-way and three-way ANOVA were used to evaluate the effects of species, contamination level, and poultry manure amendment on survival. Petroleum contamination significantly reduced earthworm survival in a concentration-dependent manner (P < 0.001). In unamended soil, E. eugeniae exhibited survival rates of 100, 70, and 20% at 2, 5, and 10 g MPP, respectively, whereas A. millsoni recorded survival rates of 90%, 40%, and 0% at the same concentrations. In unamended soil, complete mortality occurred in both species at MPP concentrations ≥15 g per 500 g of soil. Poultry manure amendment significantly improved survival (P < 0.05), increasing the earthworms' tolerance to petroleum contamination. In amended soil, E. eugeniae maintained survival rates of 100, 100, 40, and 10% at 2, 5, 10, and 15 g MPP, respectively, while A. millsoni recorded survival rates of 100, 60, and 10% at 2, 5, and 10 g MPP, respectively. Throughout the study, E. eugeniae consistently demonstrated greater tolerance to petroleum contamination than A. millsoni. These findings indicate that poultry manure can mitigate petroleum toxicity and enhance earthworm survival, thereby improving the potential of vermiremediation in moderately contaminated soils. E. eugeniae is therefore recommended as the more suitable species for the bioremediation of petroleum-contaminated soils.