Joint toxic effects of naphthalene and cadmium on zebrafish superoxide dismutase

Persistent Organic Pollutants (POPs) and heavy metal are two kinds of important pollutants in marine environments. Individual toxicity of naphthalene (one of POPs) or cadmium (a heavy metal) has been examined and reported, yet the joint toxic effects of them haven´t been studied. Since chemicals usually exist as mixtures at low level concentrations in real environment, joint toxic effects on living organisms may give a more objective assessment on their real toxicity. In this study, adult zebrafish were exposed to above two substances individually or simultaneously at the concentration of 1/8 LC₅₀ for 24 hours. Individual toxicity results showed the activity of superoxide dismutase (SOD) in zebrafish muscle increased significantly after 2-hour of naphthalene exposure and 4-hour of cadmium exposure, indicating naphthalene impact on SOD prior to cadmium. Result of the joint action modes varied depending on different time points. Antagonistic effect was observed at the time points of 2 and 4 hours, while synergistic action displayed at the subsequent time points of 8 to 24 hours.