Acute, chronic, and embryonic toxicity of bifenazate in Biomphalaria glabrata

Bifenazate is a widely used acaricide for controlling mite pests in fruit trees, vegetables, and ornamental plants. With its increasing application in agricultural production, the potential for bifenazate to enter aquatic environments and pose risks to non-target aquatic organisms has raised growing concern. However, studies on its toxic effects in freshwater mollusks remain limited. In this study, the freshwater gastropod Biomphalaria glabrata was used as a model organism to systematically evaluate the acute, chronic, and embryonic toxicity of bifenazate. The results of a 96 h acute exposure showed that the LC₅₀ of bifenazate for adult B. glabrata was 9.536 mg/L, indicating moderate acute toxicity. Exposure induced pronounced stress responses, including shell contraction, increased mucus secretion, and abnormal behavior, accompanied by hemocyte structural damage, altered acetylcholinesterase (AChE) activity, and dysregulation of antioxidant-related gene expression. In the 21-day chronic exposure, bifenazate at concentrations of 0.1-1 mg/L significantly inhibited growth, reduced hemocyte density, and induced vacuolar degeneration in the hepatopancreas as well as structural damage to the gonads, thereby impairing physiological condition and reproductive function. Embryotoxicity assays further demonstrated that bifenazate exhibited high toxicity to B. glabrata embryos, with a 216 h LC₅₀ of 0.2313 mg/L. Complete mortality was observed at 0.3 mg/L, with most embryos arrested at early developmental stages. Overall, bifenazate induces significant acute, chronic, and developmental toxicity in B. glabrata, with early life stages showing higher sensitivity. These findings provide experimental evidence for understanding the toxicological characteristics and potential ecological risks of bifenazate to freshwater mollusks.