Joint Toxicity Of Naphthalene And Cadmium On Zebrafish (Danio Renio)

Both naphthalene and cadmium are important marine pollutants. There are many reports on their individual toxicity, but almost no report on their joint toxicity. Joint toxicity is more helpful for the toxicity evaluation in real environment.In this thesis, adult zebrafish were used for joint toxicity study on naphthalene and cadmium. The activity of superoxide dismutase (SOD) was detected as a molecular indicator of oxidative stress, and the expression level of p53-mediated apoptosis pathway-related genes are indicators for cell damage and repair. Three kinds of exposures (Le. individual exposure to cadmium or naphthalene; simultaneous exposure to naphthalene and cadmium; short-term exposure of naphthalene prior to joint exposure) have been set up in order to reveal the possible mechanism of joint toxicity of these two chemicals.The following results have been obtained in this thesis:1. Significant increase of SOD activity was detected 2-hour earlier in zebrafish exposed to naphthalene than exposed to cadmium, suggesting SOD is more sensitive to naphthalene than cadmium.2. Compared with results of individual exposure, joint exposure showed antagonistic effects from 2 to 4 hours and synergistic effects from 4 to 24 hours.3. Results were more complicated in a 2-hour pre-exposure of naphthalene to joint exposure. In period of 3 to 6 hours after cadmium was added, SOD activity in zebrafish with joint exposure showed unobvious change compared with naphthalene exposure, but significant change compared with cadmium exposure. Above results indicated pre-treatment of naphthalene would induce a temporary adaptation to toxicants in zebrafish, resulting in the decrease of SOD sensitivity to cadmium.4. No obvious difference of SOD activity could be observed during 24 hour period in two different concentrations of cadmium exposure, while significant differences were observed from 16 hours in joint exposures with the same concentration of cadmium. This demonstrated SOD activity would be more sensitive to concentration difference in joint exposure. 5. Further investigations showed sod gene expression level was significantly decreased in zebrafish with joint exposure, and the suppression lasted longer than individual exposure to either naphthalene or cadmium, indicating joint toxicity is more serious than individual toxicity.6. Gene expression levels of p53, bcl2 and mdm2 were significantly decreased in zebrafish with joint exposure, and the suppression lasted longer than individual exposure. However, the expression profiles of these genes seemed no obvious relevance, indicating the complexity of joint toxicity mechanism of cadmium and naphthalene.