Toxicity of individual and combined effect of Mefenpyr di-ethyl safener and its co-herbicide, Fenoxaprop-P-ethyl, to zebrafish

Abstract

Mefenpyr diethyl (MEF), a supposed inert chemical, is a safener used in herbicide formulations with active ingredients such as Fenoxaprop-P-ethyl (FEN), has been found in surface water. Since the hazards of this safener, individually and in combination with its herbicide, toward non-target aquatic organisms, were not known,acute and chronic studies were conducted on various endpoints in embryos of zebrafish (Danio rerio). Endpoints during acute exposures included mortality and hatchability. During chronic exposures, the growth and survival of larvae were determined. Exposure to concentrations of MEF > 3 mg/L alone significantly decreased the rate of hatching, while exposure to FEN alone to > 3 mg/L had no significant effect on the rate of hatching. However, exposure to each of the chemicals individually caused some delay in hatching. When exposed in combination with FEN, adverse effects of MEF on the rate of hatching were mitigated in a dose-dependent manner. During the acute exposure to 3 mg/L, mortality was caused by MEF than FEN. During chronic exposures to 0.1 or 1.0 mg/L, MEF has more toxic potency than FEN. Both compounds caused some abnormalities, including pericardial edema, spinal curvature, tail malformation, and edema of the yoke sac. Based on the activities of SOD and GST, both MEF and FEN caused oxidative stress. FEN reduced the toxic potency of MEF when exposed together, but there were more deformities of greater severity in embryos exposed to MEF than those exposed to FEN. Molecular docking showed that both chemicals could potentially inhibit the activity of sex hormones and hatching enzymes. These results demonstrate that while classified as "inert", the safener, and FEN can cause various effects, including molecular responses and lethality and should be monitored and regulated.