Growth and reproductive toxicity of bisphenol A in Oikopleura dioica at environmentally relevant concentrations.

Bisphenol A (BPA), a known endocrine disruptor, is ubiquitous in various aquatic environments. Appendicularians are among the most abundant mesozooplankton populations and occupy a crucial niche in marine ecosystems. However, no toxicological data are available concerning the effects of BPA on this functional group. In this study, an evaluation of the toxicity of environmentally relevant levels of BPA (2.5-150 μg/L) on the appendicularian Oikopleura dioica, including its morphology and transcriptome, was conducted. Our results demonstrated the high sensitivity of O. dioica to BPA, with a LC of 142 μg/L. Exposure to 125 μg/L BPA significantly inhibited the somatic growth, gonadal development and reproduction of individuals, whereas exposure to an environmentally safe concentration (2.5 μg/L) affected female fecundity and fitness as well as male gene expression. The results of the transcriptomic analysis suggest that males were more sensitive to BPA stress at the molecular level. BPA exposure not only led to abnormal secretion of digestive enzymes and phospholipase A2, affecting the function of the digestive system and arachidonic acid but also significantly down-regulated the expression of mRNAs related to enzymes involved in carbohydrate and energy metabolism in males. These findings suggest that the current safe environmental concentrations may not be safe.