Environmentally relevant concentrations of butachlor inhibited the development of the green toad (Bufotes viridis sitibundus) during the incubation period.

Abstract

Butachlor is one of the most widely used herbicides in agricultural areas throughout the world. Studies have measured the toxicity of butachlor in single life stages of amphibians, however, less attention has been paid to the impacts of this herbicide on various life stages. Therefore, we collected the eggs of the green toad Bufotes viridis sitibundus from a clean environment with no history of pesticides. We then exposed the collected eggs to environmentally relevant concentrations of butachlor (1.5, 1, 0.8, 0.6, 0.4, and 0.1 mg/L) and measured the growth, survival, and development of green toads during the incubation period. We also measured five different responses i.e., length at the beginning of metamorphosis (LBM), length at the formation of forelimb bud (LFF), length at the end of metamorphosis (LEM), weight at the beginning of metamorphosis (WBM), and weight at the end of metamorphosis (WEM) during the incubation period. The survival rate showed an indirect relationship with butachlor concentrations. The longest development duration was recorded for toads reared in the control (110 days), while the shortest duration (9 days) was observed in the highest butachlor concentration (i.e., 1.5 mg/L), with the highest mortality recorded in this treatment- all the eggs dying by days 11 and 9 after the start of incubation. We found a significant difference between the survival of toads in butachlor treatments and the control group (P < 0.05). We observed a significant difference between treatments and the control group in LBM, LFF, LEM, and WEM (P < 0.05), except WBM (P > 0.05). Our findings highlight that butachlor, at environmentally relevant concentrations, inhibited the development of the green toad and mitigated the survival of eggs and larvae, resulting in the unsuccessful completion of development before metamorphosis, a critical life stage.