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This study continued our previous work (Sai et al. in Bull Environ Contam Toxicol 95:157-163, 2015a) by analysing the effects of simazine on the liver histological structure and metamorphosis in the developing Xenopus laevis. Tadpoles (Nieuwkoop-Faber stage 46) were exposed to simazine at 0.1, 1.2, 11.0 and 100.9 μg/L for 100 days. When tadpoles were exposed to simazine at 11.0 and 100.9 µg/L, an increased mortality and damaged liver tissues were observed together with significant inhibition of percent of X. laevis completing metamorphosis on days 80 and 90 and prolonged time of completing metamorphosis. On the other hand, we found that simazine has no significant effects on liver weight and altered hepatosomatic index. Results of this study may be considered to inform risk assessment of the effects of simazine on the development of X. laevis.

Simazine was investigated for gene expression concurrent with simazine-induced phenotype changes during development of male Xenopus laevis. X. laevis tadpoles (Nieuwkoop-Faber stage 46) were exposed to 0.1, 1.2, 11.0 and 100.9 μg/L simazine for 100 days. The results showed that an increased mortality of X. laevis, decreased gonad weight and altered gonadosomatic index of males significantly (p<0.05) when exposed to simazine at 11.0 and 100.9 µg/L. Significant degeneration in testicular tissues was observed when tadpoles were exposed to simazine at 100.9 µg/L. To investigate the molecular mechanisms behind the testicular degeneration by simazine, we evaluated gene expression in animals treated with 100.9 µg/L simazine and found that 1,315 genes were significantly altered (454 upregulated, 861 downregulated). Genes involved in the cell cycle control, and amino acid metabolism pathways were significantly downregulated. These results indicate that simazine affects the related gene expressions which may be helpful for the understanding of the reason for the reproductive toxicity of simazine on male X. laevis.

Atrazine (AZ), a widely used herbicide has drawn attentions for its potential impacts on amphibians. This study aims to investigate the toxicity of AZ in Bufo bufo gargarizans Cantor (B. bufo gargarizans), a species of toad commonly found in China and countries in East Asia. We treated tadpoles with 0.1, 1, 10 and 100 μg/L AZ for 85 days and examined related parameters. The results showed that the mortality of the toads in the treatment group increased dramatically in a U-shaped dose-response relationship. The hindlimb extension and metamorphosis rate of the toads were significantly inhibited by AZ at 10 and 100 μg/L. Under the same condition, there were significant progressive changes in the testicular structures. Moreover, we found that AZ has no significant effects on growth, sex ratios, gonadal morphology, forelimb emergence and histology in the ovaries. Our results support the idea that environmental contaminants including AZ may be relevant to global amphibian decline.