Toxic effects of crude-oil-contaminated soil in aquatic environment on Carassius auratus and their hepatic antioxidant defense system

Under the indoor simulant conditions, toxic effects of crude-oil-contaminated soil which was put into aquatic environment on the young fishes Carassius auratus and their hepatic antioxidant system after a 20-d exposure were investigated. Results showed that the relationship between the mortality of C. auratus and the exposed doses could be divided to 3 phases: fishes exposed to the low dose groups (0.5--5.0 g/L) were dead due to the ingestion of crude-oil-contaminated soils in aquatic environment; at the medium dose groups (5.0--25.0 g/L) fishes were dead due to the penetration of toxic substances; at the high dose groups (25.0--50.0 g/L) fishes were dead due to environmental stress. The highest mortality and death speed were found in the 1.0 g/L dose group, and the death speed was sharply increased in the 50.0 g/L dose group in the late phase of the exposure. The activity of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) and the content of malaondialdehyde (MDA) in the hepatic tissues of C. auratus were induced significantly. The activity of SOD was first increased and then decreased, and was significantly inhibited in the 50.0 g/L dose group. The activity of CAT was highly induced, and restored to a little more than the control level when the exposed doses exceeded 10.0 g/L. The activity of GST was the most sensitive, it was significantly induced in all dose groups, and the highest elevation was up to 6 times in the 0.5 g/L dose group compared with the control. The MDA content was significantly elevated in the 50.0 g/L dose group, and the changes of the MDA content were opposite with the changes of the GST activity.