A reconsideration of the safety of fenoxycarb (IGR) in soil environment: The toxicity of fenoxycarb to Yuukianura szeptyckii (Collembola)

Abstract

Fenoxycarb, a juvenile hormone agonist has been widely used to control various insect pests in agriculture. Fenoxycarb has been considered environmentally safe because it degrades quickly and has lower mammalian toxicity compared with many conventional pesticides. To date, fenoxycarb is reported safe for soil organisms, but this conclusion is based solely on toxicity studies with Folsomia candida (Collembola) and Eisenia fetida (earth-worm). The aim of this study was to investigate the toxic effect of fenoxycarb on Yuukianura szeptyckii (Collembola) to assess further whether this chemical is environmentally safe or not. After 28 d of exposure of fenoxycarb in the soil, adult survival and juvenile production were assessed. The median lethal concentration (LC50) value for adult was 955.2 mg/kg and the median effective concentration (EC50) and no observed effect concentration (NOEC) value for juvenile production was 0.2 mg/kg and < 0.15 mg/kg, respectively. The effect of fenoxycarb on egg production and hatching rate was evaluated using a compressed soil substrate. A significant reduction in egg production was observed at 300 mg/kg or more, and the hatching rate was significantly reduced at 0.15 mg/kg or more. These results indicated that the adverse effects of fenoxycarb on juvenile production at concentrations of 0.15, 9.4, and 75 mg/kg were mainly due to a reduced hatching rate. The toxicity/exposure ratio (TER) for fenoxycarb in Y. szeptyckii was < 5, indicating risk to Y. szeptyckii from fenoxycarb residues in soil. This study suggests that fenoxycarb poses high potential risk to Y. szeptyckii at environmentally relevant concentrations. Thus, further research, such as higher tier study is needed to clarify fenoxycarb risk in soil ecosystems.