Effects of phenanthrene on the mortality, growth, and anti-oxidant system of earthworms ( Eisenia fetida) under laboratory conditions

Abstract

To assess the toxic effects of phenanthrene on earthworms, we exposed Eisenia fetida to artificial soils supplemented with different concentrations (0.5, 2.5, 12.5, mg kg −1 soil) of phenanthrene. The residual phenanthrene in the soil, the bioaccumulation of phenanthrene in earthworms, and the subsequent effects of phenanthrene on growth, anti-oxidant enzyme activities, and lipid peroxidation (LPO) were determined. The degradation rate of low concentrations of phenanthrene was faster than it was for higher concentrations, and the degradation half-life was 7.3 d (0.5 mg kg −1). Bioaccumulation of phenanthrene in the earthworms decreased the phenanthrene concentration in soils, and phenanthrene content in the earthworms significantly increased with increasing initial soil concentrations. Phenanthrene had a significant effect on E. fetida growth, and the 14-d LC 50 was calculated as 40.67 mg kg −1. Statistical analysis of the growth inhibition rate showed that the concentration and duration of exposure had significant effects on growth inhibition ( p < 0.001). Superoxide dismutase (SOD) activity increased at the beginning (2 and 7 d) and decreased in the end (14 and 28 d). Catalase (CAT) activity in all treatments was inhibited from 1 to 14 d of exposure. However, no significant perturbations in malondialdehyde (MDA) content were noted between control and phenanthrene-treated earthworms except after 2 d of exposure. These results revealed that bioaccumulation of phenanthrene in E. fetida caused concentration-dependent, sub-lethal toxicity. Growth and superoxide dismutase activity can be regarded as sensitive parameters for evaluating the toxicity of phenanthrene to earthworms.