Developmental reproductive toxicity and endocrine activity of propiconazole in the Xenopus tropicalis model

Environmental pollutants and especially endocrine disrupting chemicals (EDCs) are implicated as one of the drivers of the amphibian declines. To advance the understanding of the risks of EDCs to amphibians, methods to determine endocrine-linked adverse effects are needed. The aims were to 1) develop a partial life-cycle assaywith themodel frog Xenopus tropicalis to determine endocrine perturbation and adverse developmental effects, and 2) determine effects of propiconazole in this assay. Propiconazole is a pesticidewithmultiple endocrine modes of action in vitro. Its potential endocrine activity and adverse effects in amphibians remain to be elucidated. Tadpoles were exposed to 0, 33 and 384 mu g propiconazole/L during critical developmental windows until completed metamorphosis. At metamorphosis, a sub-sample of animals was analysed for endpoints for disruption of estrogen/androgen (sex ratio, brain aromatase activity) and thyroid pathways (time to metamorphosis). The remaining individuals were kept unexposed for 2 months post-metamorphosis to analyze effects on sexual development including gonadal and Mullerian duct maturity and gametogenesis. At metamorphosis, brain aromatase activity was significantly increased in the high-dose group compared to control. In both propiconazole groups, an increased proportion of individuals reached metamorphosis faster than the mean time for controls, suggesting a stimulatory effect on the thyroid system. At 2 months post-metamorphosis, testis size, sperm and Mullerian duct maturity were reduced in the low-dose males, and the liver somatic index in males was increased in both propiconazole groups, compared with controls. In conclusion, our results show that propiconazole exposure caused endocrine perturbations and subsequent hepatic and reproductive effects evident at puberty, indicating persistent disruption of metabolism and male reproductive function. Our findings advance the development of methodology to determine endocrine and adverse effects of EDCs. Moreover, they increase the understanding of endocrine perturbations and consequent risk of adverse effects of azoles in amphibians. (C) 2020 The Authors. Published by Elsevier B.V.

Automated summary

The study utilized the model frog Xenopus tropicalis to investigate the effects of propiconazole exposure on endocrine perturbations and subsequent adverse effects. It was found that propiconazole increased brain aromatase activity and accelerated metamorphosis in tadpoles, indicating a stimulatory effect on the thyroid system. However, at puberty, hepatic and reproductive effects were evident, suggesting persistent disruption of metabolism and male reproductive function.