Soil property-dependent toxicity and oxidative stress induced by perfluorooctanoic acid in Caenorhabditis elegans

Perfluorooctanoic acid (PFOA), a persistent organic pollutant frequently detected in soils, has received increasing attention due to growing demands for soil environmental guideline values that ensure acceptable ecological risk. However, systematic evaluations of PFOA ecotoxicity under realistic soil conditions remain limited. In this study, Caenorhabditis elegans (C. elegans) was used as a model soil organism, following ISO 10872, to assess PFOA-induced effects on growth, fertility, and reproduction after seven days of exposure in six representative Chinese soils. Oxidative stress responses were also measured, including reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT). PFOA exposure significantly inhibited all biological endpoints, with EC₅₀ values of 28 ∼ 59 mg·kg⁻¹ for growth, 19 ∼ 53 mg·kg⁻¹ for fertility (expressed as the percentage of gravid adults), and 19 ∼ 39 mg·kg⁻¹ for reproduction. Soil physicochemical properties strongly influenced toxicity. Stepwise regression analysis identified cation exchange capacity (CEC), organic matter (OM), and free Fe oxides (Fe_FO) as major predictors of growth toxicity, explaining 89.7 % of the variance (P < 0.05). For fertility and reproduction, total Fe (Fe_total) was the primary determinant, while the addition of pH, amorphous Fe/Al oxides (Fe_AO, Al_AO), and total Al (Al_total) further improved model performance. PFOA also induced pronounced oxidative stress, evidenced by increased ROS and MDA levels and biphasic SOD and CAT responses, indicating disruption of antioxidant defenses at higher exposures. Overall, these findings clarify how soil geochemistry modulates the bioavailability and ecological toxicity of PFOA, providing essential evidence for developing soil quality standards, environmental guideline values, and improved ecological risk assessments.