Developmental toxicity and inhibition of the fungicide hymexazol to melanin biosynthesis in zebrafish embryos.

Hymexazol is an efficacious and widely used fungicide. However, its environmental toxicological assessment has not been well documented. It had no report of its toxicity to fish embryo. Fish embryo acute toxicity tests are highly predictive of aquatic embryotoxicity outcome. In this study, zebrafish (Danio rerio) embryos were exposed to hymexazol at varying concentrations for the study of the developmental toxicity, melanin biosynthesis, biochemical and transcriptional endpoints. The embryotoxicity tests indicated that the 96h LC50 value of hymexazol was 649mg/L with a 95% confidence interval range of 632-667mg/L. Hymexazol at concentrations of 417-738mg/L decreased the heart rate and increased the voluntary swing. Hymexazol inhibited normal development at concentrations above 554mg/L. the 96h EC50 was 411mg/L. Hymexazol in a concentration range of 417-738mg/L induced cardiac edema and yolk sac edema. Exposure of hymexazol at such concentrations to zebrafish embryos for 48h decreased the pigment area density compared with the no hymexazol control. Tyrosinase activity was inhibited by hymexazol relative to the untreated control. The P53 mRNA expression level in embryos upon exposure to 480mg/L or greater of hymexazol was significantly higher than that of the control. The results indicated that hymexazol has quite low acute toxicity and low embryotoxicity to zebrafish.

Toxic effects of indoxacarb enantiomers on the embryonic development and induction of apoptosis in zebrafish larvae (Danio rerio).

Indoxacarb is a highly potent insecticide widely used to control Lepidoptera insects in vegetable, tea, cotton, and rice fields. It can run off into aquatic environments. It is consisted of two enantiomers. Environmental risks and aquatic toxicity of indoxacarb enantiomers have not been fully investigated. In this study, zebrafish (Danio rerio) embryos were exposed to varying concentrations of (-)-R-indoxacarb and (+)-S-indoxacarb until 96-h post-fertilization (hpf) to assess the embryonic toxicity. (-)-R-indoxacarb was 1.3-fold more toxic than (+)-S-isomer to zebrafish embryos at 96 hpf. (-)-R-indoxacarb exhibited reduction in body length and pericardial edema compared with (+)-S-indoxacarb. (-)-R-indoxacarb decreased the hatching rate sixfold greater than (+)-S-indoxacarb. The rate of pericardial edema induced by (-)-R-indoxacarb was 2.5 times greater than that by (+)-S-indoxacarb. The heart rate of the larvae exposed to (-)-R-indoxacarb was 30% lower than that to (+)-S-indoxacarb. In addition, exposure to the chiral isomers resulted in significant increases in apoptosis; interestingly (-)-R-indoxacarb induced apoptosis in the heart area, whereas (+)-S-indoxacarb induced apoptosis in the head area. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 7-16, 2017.