Effects of Single, Binary and Quinary Mixtures of Phenanthrene and Its N-PAHs on Eisenia fetida in Soil

It is now acknowledged that aromatic hydrocarbons present in contaminated soils occur in mixtures. The effect of single, binary and quinary mixtures of phenanthrene and selected nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) were investigated on the survival, growth and behavioural index of earthworms ( Eisenia fetida ) over a 21-day incubation in soil. The results showed that the LC 50 values ranged from (not detected) ND–329.3 mg kg −1 (single mixture), ND–219.8 mg kg −1 (binary mixtures) to 148.4 mg kg −1 (quinary mixture), while the EC 50 values (based on weight loss) ranged from 13.3–148.4 mg kg −1 (single mixture), 63.8–148.4 mg kg −1 (binary mixture) to 24.2 mg kg −1 (quinary mixture). Greater impacts were recorded where N-PAHs are present with phenanthrene. Further, behavioural index of E. fetida was affected after 24-h exposure to N-PAH-amended soils. Among the N-PAHs however, benzo[h]quinoline recorded the greatest impact on the survival, growth and behavioural index of E. fetida in soil. Findings from this study showed that three ring-N-PAHs are more toxic than phenanthrene as expected from their physico-chemical properties. The binary and quinary mixtures of phenanthrene and N-PAHs in soil intensified toxicity, suggesting that PAHs-N-PAHs mixtures represent greater risk to soil biota.