Effects of cis-bifenthrin enantiomers on the growth, behavioral, biomarkers of oxidative damage and bioaccumulation in Xenopus laevis

Chirality should be taken into consideration when assessing the effect of synthetic pyrethroids to aquatic environmental safety. In our study, 96 h acute toxicity assay showed that enantiomers of cis-BF had an addictive effect of toxicity on Xenopus laevis and R-cis-bifenthrin(R-cis-BF) had higher acute toxicity than S-cis-BF. In chronic assay, R-cis-BF exerted more toxic effect on behavior and development of tadpoles than S-cis-BF, and there was also enantioselective effect of cis-BF on antioxidant enzyme and LDH activity. Besides, thyroid development was also affected at the gene and hormone level, with varied effects observed with different exposure enantiomers. Moreover, in the enantioselective accumulation and tissue distribution of enantiomer assays, results showed that R-cis-BF had higher affinity to organisms than S-cis-BF. This study provided the evidence that chiral pesticides enantioselectively affected development of amphibians, and also shed light on the understanding of enantioselectivity in both acute and chronic eco-toxicities to improve risk assessment and regulation of chiral pesticides.

Thyroid hormone related gene transcription in southern sand flathead (Platycephalus bassensis) is associated with environmental mercury and arsenic exposure

Arsenic (As) and mercury (Hg) are ubiquitous elements known to disrupt thyroid function in vertebrates. To explore the underlying mechanisms of Hg and As on the fish thyroid system, we investigated the associations between muscle concentrations of Hg and As with thyroid-related gene transcription in flathead (Platycephalus bassensis) from a contaminated estuary. We sampled fish at several sites to determine the hepatic expression of genes including deiodinases (D1 and D2), transthyretin (TTR), thyroid hormone receptors (TRα and TRβ) and related them to Hg and As levels in the same individuals. Negative correlations were observed between Hg levels and D2, TTR, TRα and TRβ, whereas positive associations were found between As concentrations and TTR and TRβ. These results suggest that Hg and As exposures from environmental pollution affect the regulation of genes important for normal thyroid function in fish. These thyroid-related genes could be used as biomarkers for monitoring environmental thyroid-hormone disrupting chemicals.