Toxic Effects Of Polluted Water In The Yellow River On Bufo Raddei In Lanzhou Region

In the present study, the natural population of Bufo raddei Strauch in Liujiaxia Region (LJXR, a relatively unpolluted region) and Lanzhou Region (LZR, a mixed-polluted region by oils and phenols) were studied, including the population density, the sex ratio, the reproductivity (the number of eggs laid and the relative male gonad weight), the relative weight of liver, kidney and lipid body, the diet composition of adult B. raddei, the hatching ratio, the survival and malformation rates of B. raddei tadpoles, the micronucleus (MN) frequency in erythrocytes, the DNA damage in erythrocytes and liver cells, the degree of DNA methylation in liver cells, the malondialdehyde (MDA) content and the total antioxidant capacity (TAC) in liver cells of adult B. raddei. The results showed that:1. There were no significant differences (P>0.05) on the diet composition, the relative lipid body and male gonad weight of adult B. raddei between LJXR and LZR, which indicates that oils and phenols in LZR had no significant toxic effects on the diet composition, nutritional status and male reproductive activity of B. raddei.2. Oils and phenols in LZR decreased the eggs laid per female and survival of tadpoles, increased the mortality and malformation rate (P<0.01), which could directly induce B. raddei population decline. What's more, the alteration of sex ratio could indirectly influence B. raddei population.3. The body weight and body length of adult B. raddei in LZR decreased, and the relative weight of liver and kidney increased (P<0.05), which implies that the toad provides more energy for detoxification, thus less energy for reproduction -which could indirectly induce the decline of B. raddei population.4. In LZR, the population density of B. raddei was significantly (P<0.05) lower than that in LJXR at the same sampling month, which suggests that oils and phenols might play an important role in the decline of amphibian populations. 5. The MN frequency in erythrocytes of B. raddei from LZR was significantly higher than that from LJXR at the same sampling month (P<0.01), which implies that oils and phenols had a strong mutagenecity on amphibians.6. Similar to the results of MN frequency, the DNA damage in erythrocytes and liver cells of B. raddei from LZR was significantly higher than that from LJXR (P<0.05), further evidence for which oils and phenols were genotoxic to amphibians. In LZR, the MDA content increased while the TAC decreased in liver cells of B. raddei (P<0.05), which suggests that oils and phenols induced oxidative stress and DNA damage.7. The degree of DNA methylation in liver cells of B. raddei from LZR was significantly lower than that from LJXR (P<0.05), implying that oils and phenols had a strong carcinogenic potential on amphibians.8. The results from both comet assay and DNA methylation detection on liver cells showed that the genotoxicity varied significantly with oil and/or phenol concentrations, suggesting that these two methods are relatively sensitive and suitable for monitoring the genotoxicity of oils and phenols on amphibians. The significantly positive correlations between DNA damage and concentrations of oil and/or phenol existed in liver cells but erythrocytes, implying that liver is more suitable as a sentinel tissue for the assessment of genotoxic impact of oils and phenols under low-level contamination conditions.9. The genotoxicity effects of oils and phenols on B. raddei were concentration-depended. When the concentrations of oils and phenols decreased, the degree of genetic damage lightened, which suggests that the genetic damage could be repaired if the degree of pollution could be decreased.In conclusion, the present study explores the ecotoxic and genotoxic effects of oils and phenols on B. raddei, reveals the toxic mechanism of oils and phenols on B. raddei, and provides a scientific method for oils and phenols pollution monitoring.