Influence of multiwall carbon nanotubes on the toxicity of 17β-estradiol in the early life stages of zebrafish.

Due to increasing use and release, both multiwall carbon nanotubes (MWCNTs) and 17β-estradiol (E2) may co-exist and interact with each other in aquatic environments. However, little is known about their combined effects on non-target organisms, especially in the presence of other environmental factors. In this study, the interplay between MWCNTs and E2 in the early life stages of zebrafish was investigated, focusing on the alterations in estrogenic responses with and without other environmental factors. There were no significant differences in the hatchability, mortality, or physical development of zebrafish in any treatments. Compared with E2 exposure, the E2-induced estrogenic responses (vtg1, vtg3, and esr1 genes) in zebrafish were markedly reduced to baseline by the presence of MWCNTs in most cases, indicating a strong protective effect. Furthermore, this inhibitive effect was not significantly changed by the preloading of natural organic matter (NOM) on MWCNTs. Nevertheless, the addition of ammonia nitrogen in the mixtures of MWCNTs and E2 alleviated the protective effect of MWCNTs, resuscitating the E2-induced estrogenic responses in zebrafish. These findings highlight the influence of carbon nanomaterials on the bioavailability of co-contaminants in organisms. The widespread environmental factors in natural environments should also be taken into consideration when the combined toxicity of nanomaterials and contaminants is discussed.