Oxidative stress biomarkers of the polychaete Nereis diversicolor exposed to cadmium and petroleum hydrocarbons.

Changes in the activity of antioxidant enzymes including superoxide dismutase (SOD) and peroxidase (POD) and in the content of soluble protein (SP) in Nereis diversicolor exposed to cadmium (Cd) and petroleum hydrocarbons (PHCs) were investigated under a laboratory condition. The results indicated that SOD activity in N. diversicolor exposed to Cd and PHCs significantly (P<0.05) increased with exposure time. This increase of SOD activity can be considered a sensitive biomarker of oxidative stress by Cd and PHCs. The decrease in POD activity and SP content in N. diversicolor could also sensitively reflect oxidative stress induced by Cd and PHCs. Concentration combination of Cd and PHCs had significant (P<0.05) influences on the activity of SOD and POD, as called double-dose dependent effects. There were highly significant (P<0.01) effects of exposure time on SOD activity in N. diversicolor at single or joint exposure of Cd and PHCs. Exposure time also resulted in significant differences in POD activity (P<0.05) and SP content (P<0.01) in N. diversicolor which was simultaneously exposed to Cd and PHCs, as called time-dependent effects. Compared with day 0, SOD activity in non-exposed N. diversicolor increased, possibly due to the effects of temperature. Therefore, the effects of pollutants with emphasis on abiotic parameters on the antioxidant defense system should be considered in future studies.