Legacy and emerging per- and polyfluoroalkyl substances (PFASs) in Dagang Oilfield: Multimedia distribution and contributions of unknown precursors

A systematic survey was conducted on twenty-six per- and polyfluoroalkyl substances (PFASs) in fifty-one paired samples of surface water, sediment, and soil from Dagang Oilfield, Tianjin, China. Perfluorooctanoic acid, perfluorooctane sulfonic acid, p-perfluorous nonenoxybenzenesulfonate (OBS), and 6:2 fluorotelomer sulfonamidoalkyl betaine (6:2 FTAB) were ubiquitous in the oilfield with field log Kd of 1.3?2.2, indicating a high partition potential from surface water to sediment. Total petroleum hydrocarbons (TPH) are a predictor for PFAS contamination at oilfield. The concentrations of OBS and 6:2 FTAB were higher in surface water and sediment with elevated TPH level. With total oxidizable precursor assay, unknown precursors for C2?C3 perfluoroalkyl carboxylic acids (PFCAs) (57?99 mol%) contributed more than those for C4?C12 PFCAs in the three mediums. The unknown C4-, C6-, and C8-based precursors tended to be precursors for perfluoroalkyl sulfonates at the oilfield, and C8 fluorotelomer-based precursors particularly occurred in the surface water. The concentrations of C4- and C8-based precursors were found positively correlated with TPH levels (r = 0.67?0.72, p < 0.05), while C6 precursors may also come from other sources. Further studies are necessary to clarify the mass balance and risk assessment for unknown PFASs.

Automated summary

The study conducted in Dagang Oilfield, Tianjin, China, revealed that PFASs were widespread and correlated with TPH levels, with C4 and C8 precursors showing a positive correlation with TPH levels, while C6 precursors may come from other sources. Further research is needed to clarify the mass balance and risk assessment of unknown PFASs.