Fipronil and its transformation products in the Pearl River Estuary: Spatial distribution, bioaccumulation, trophic...

Fipronil, a widely applied phenylpyrazole insecticide, has been increasingly detected in aquatic environments, raising concerns regarding its potential ecological and human health impacts. This study systematically investigated the occurrence, bioaccumulation, trophic transfer, and ecological risks of fipronil and its transformation products (FIPs) in the Pearl River Estuary (PRE), a critical subtropical estuarine system in Southern China. Fipronil and two transformation products, including fipronil sulfone and fipronil sulfide, were ubiquitously detected in both surface and bottom waters, with total concentrations ranging from 0.826 to 6.23 ng/L. In sediments, fipronil and fipronil sulfone were present at total concentrations between 0.033 and 0.165 ng/g dw. Ecological risk assessment indicated medium to high risk levels for FIPs in both water and sediment compartments. Furthermore, fipronil and three transformation products (fipronil sulfone, fipronil desulfinyl, and fipronil sulfide) were detected in 15 fish species and two shrimp species, with total concentrations ranging from 0.121 to 1.396 ng/g ww. Trophic magnification factors (TMFs) suggested weak biomagnification potential of FIPs in the estuarine food web. Human health risk assessment based on seafood consumption revealed low estimated daily intake (EDI) levels, with hazard quotients (HQs) significantly below 1, indicating negligible non-carcinogenic risk to local populations. These findings underscore the need for continued monitoring and regulatory oversight of fipronil contamination in estuarine environments to safeguard ecological integrity and public health.