Dual enantioselective effect of the insecticide bifenthrin on locomotor behavior and development in embryonic-larval zebrafish

Bifenthrin (BF) is a synthetic pyrethroid that targets the nervous system of insects and may have adverse effects on the behavior and development of nontarget organisms. However, no reports have been issued on the effects of different enantiomers on locomotor behavior for synthetic pyrethroids (SPs) in zebrafish, and whether locomotor activity is associated with the developmental toxicities remains unclear. In this study, enantioselectivity of BF (1S and 1R) on the acute locomotor activity and developmental toxicities of embryonic-larval zebrafish were first evaluated. The results indicated that 1R-BF was more toxic, causing morphological impairments, with a 96-h median effective concentration (EC50) of 226 μg/L for pericardial edema and 145 μg/L for curved body axis. Administration of 20μg/L of one enantiomer of BF had differential effects on the locomotor activity of zebrafish larvae at 4 d postfertilization (dpf) under alternating light and dark conditions. Larvae treated with 1R-BF were not sensitive to the alteration of light to dark, and the locomotor activities were reduced to a level similar to that observed in light, which otherwise increased rapidly and markedly. However, 1S-BF did not alter the general pattern of zebrafish response to the light or dark compared with the control. The results demonstrated that the differential effects on development might have contributed to the enantioselectivity in the locomotor activity. The consistency of enantioselectivity with insecticidal activity may also indicate a common mode of action. Furthermore, 1R-BF accelerated the spontaneous movement and hatching process, whereas 1S-BF seemed to be inhibitory. The results suggest the need to link behavioral changes to developmental toxicities in order to achieve more comprehensive health risk assessments of chiral pesticides.