Environmental occurrence of perfluorooctanesulfonic acid from sulfluramid-based ant bait usage and its ecotoxicological risks

In laboratory trials, sulfluramid (N-ethyl perfluorooctane sulfonamide; EtFOSA) has been shown to degrade into perfluorooctanesulfonic acid (PFOS) under aerobic conditions, including in Brazilian agricultural soils. Thus, we aimed to investigate the environmental occurrence of PFOS in agricultural areas mostly used for forestry, where sulfluramid-based ant baits are primarily used. Surface water, groundwater, and sediment samples were collected from selected micro-watersheds, primarily used for forest plantation, and PFOS and its precursors were assessed by ultra-performance liquid chromatography coupled to a triple quadrupole mass spectrometer. PFOS was the most frequently detected compound, present in 76 % of surface water samples, with concentrations up to 50.6 ng L⁻¹. EtFOSA and perfluorooctane sulfonamide (FOSA) were also detected, but at lower frequencies and concentrations. The highest PFOS concentrations were found in the watershed with mixed urban/industrial and agricultural activities, indicating multiple contamination sources. However, groundwater samples from monitoring wells inside planted forests of Pine and Eucalyptus also showed detectable PFOS contamination, likely due to the biodegradation of EtFOSA from ant bait applications. Sediment samples revealed seasonal variations, with higher detection rates during the dry season, suggesting a high-mobility of the studied compounds. Risk assessment using the risk quotient (RQ) approach indicated that all measured PFOS concentrations exceeded the European Union's annual average environmental quality standard (AA-EQS) for inland surface waters, posing potential risks to aquatic biota. This study endorses the need for ongoing monitoring, regulations, and safer pest control alternatives to mitigate PFOS contamination and its environmental risks.