Benoxacor caused developmental and cardiac toxicity in zebrafish larvae

Benoxacor (BN) is a highly effective antidote of dichloroacetamide herbicides generally used to protect crops from herbicidal damage. As a commonly used agrochemical, this herbicide antidote is continuously discharged in watercourses thus causing toxicity to aquatic organisms, and ultimately leading to contamination of the food chain. To date, its potential toxicity to the cardiac development of aquatic organisms has not been evaluated. In the present study, we have selected the zebrafish as a model to study the impact of BN on embryonic developmental and cardiac toxicity. The zebrafish embryos were exposed in 0.5, 1.0 and 2.0 mg/L BN from 5.5 to 72 h post-fertilization (hpf). The results indicated that the exposure to BN led to increased mortality and diminished heart and hatching rates in the embryos. BN exposure also brought pericardial edema (PE) and linear stretching of heart. Besides, exposure to BN induced an excessive accumulation of reactive oxygen species (ROS) in the zebrafish embryos and abnormal activities of the antioxidant enzymes, including catalase (CAT) and malondialdehyde (MDA). Moreover, exposure to BN caused serious cardiac toxicity of the embryos, accompanied by abnormality of heart development- and apoptosis-related genes. Surprisingly, astaxanthin (ASTA), as a common antioxidant, was found to be able to partially rescue the cardiac toxicity caused by BN, which indicated that ROS are probably the major reason for the resulting cardiotoxicity in zebrafish embryos. Our results suggest the need for a comprehensive safety evaluation of the regular consumption of benoxacor, which provides scientific basis for the development of health standards and assessment of potential risk in aquatic organisms or even human.

Developmental toxicity and transcriptome analysis of zebrafish (Danio rerio) embryos following exposure to chiral herbicide safener benoxacor

Benoxacor, a chiral herbicide safener for S-metolachlor, has been detected in streams. However, the potential risk this poses to aquatic ecosystems is not clear. This study used zebrafish (Danio rerio) embryos as a model to assess the enantioselective toxicity of benoxacor and its effects on biological activity and development from 2 h to 96 h post-fertilization (hpf). Results showed that benoxacor had negative effects on hatchability, malformations, and mortality. Compared to either individual enantiomer, embryos exposed to Rac-benoxacor had higher acute and developmental toxicities, glutathione S-transferase (GST) and glutathione peroxidase (GPx) enzyme activities, and nrf 2 expression levels. They also had lower superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) enzyme activity and krt 17, tbx 16, osx, cat, bcl 2, bax, and ifn expression levels. High-throughput RNA sequencing revealed that Rac-benoxacor had a greater effect on gene regulation than either enantiomer. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses demonstrated that changes in oxidoreductase activity, cellular lipid metabolic process, and catalytic activity related genes may be due to the enantioselective effects of benoxacor isomers. These results suggest that the ecotoxicology data and safety knowledge about the effects of chiral benoxacor on zebrafish should be considered in future environmental risk evaluation.