Effects of environmentally relevant concentrations of carbendazim, either alone or combined with benzophenone-3, on testicular development in Xenopus laevis.

The fungicide carbendazim (CBZ), widely present in aquatic environments, has been reported to disrupt testicular development in rodents, yet its impacts on amphibians remain poorly understood. Here, we investigated the effects of environmentally-relevant concentrations of CBZ (1, 10, 100 μg/L) on early testicular development in Xenopus laevis following exposure from Nieuwkoop-Faber (NF) stages 45/46 to 52 in Experiment I. While all the concentrations of CBZ inhibited tadpole development, 10 and 100 μg/L CBZ caused retarded testicular development, which was characterized by morphological abnormality, suppressed cell proliferation and reduced germ cells, along with downregulation of testis-biased genes and upregulation of ovary-biased genes in certain concentration groups. Although 1 μg/L CBZ did not lead to significant changes in these testicular parameters, their declining trends are of concern, especially when considering its combined exposure with other contaminants. Thus, we conducted Experiment II to address the combined effects of 1 μg/L CBZ with the UV filter benzophenone-3 (BP-3), which was reported to affect testicular development in X. laevis, on testicular development from stages 45/46 to 66. As expected, we found that co-exposure to 1 μg/L CBZ and 2.28 μg/L BP-3 produced smaller testis size accompanied with fewer germ cells compared to the control, while alone exposure had no significant effects on the two parameters, exhibiting a synergistic effect on testicular development. Besides, their combined exposure also exerted synergistic effects with regard to metamorphic delay, increased liver weight and hepatic histological changes. Our findings emphasize the impacts of environmentally relevant concentrations of CBZ alone or in combination with UV-filters on testicular development, highlighting the ecological risk of these contaminants especially their mixtures for amphibians, which warrants continued attention.