Chronic toxic effects of chloroxylenol exposure on Rana chensinensis: Insights from endochondral ossfication.

Chloroxylenol (para‑chloro-meta-xylenol, PCMX), is a widely used antimicrobial agent and can remain in the aquatic environment. Although toxicity studies related to PCMX on the aquatic animals like zebrafish and Brachionus koreanus have been reported, there are few reports in the ecological risk of amphibians. In this study, the toxicity of different concentration (143, 14.3, 1.43 μg/L) of PCMX treatments on the endochondral ossification and body condition of Rana chensiensis tadpoles was investigated at environmentally relevant concentrations during metamorphosis. The chronic exposure of PCMX decreased bone length and ossification of limbs, caused changes of thyroid gland structure and ossification related gene expression levels. Besides, we found that R. chensiensis developed rheumatoid arthritis. Therefore, these results provided valuable evidence that the ecological risk of PCMX that will negatively affect the body condition, thyroid hormones homeostasis and skeletal development of R. chensiensis tadpoles.