PFAS contaminants in surface waters, effluents, sediments and coastal food webs off the Solent coastline UK

Per- and polyfluoroalkyl substances (PFAS) are persistent coastal contaminants. Their distribution across environmental compartments and food webs remains poorly understood. The Solent is a densely urbanised tidal strait representative of industrialised coastal systems. Inputs from wastewater treatment plants, combined sewer overflows, and historic landfills create multiple PFAS pathways to the marine environment. We integrated our collected field samples (including surface waters, n = 3; and multiple biota species collected in triplicate) with regulatory monitoring datasets (sediment and archived biota) and wastewater effluent records to quantify PFAS across surface waters, sediments, treated wastewater effluent, and marine biota from the Solent. In sediments, ΣPFOS was present at the highest mean concentrations, at 0.5 μg kg−1 dry weight. Surface waters and effluents contained a broader mixture of short- and long-chain PFAS. Mean ΣPFOS concentrations in surface water reached 8.5 ng L−1, exceeding the UK/EU environmental quality standard for coastal waters (0.65 ng L−1). Treated effluent contained several short-chain PFAS, including PFHxA, PFBA, and PFBS, at mean concentrations of 1.3–5.9 ng L−1. PFOA (3.1–4.0 ng L−1) and PFOS (5.7–7.2 ng L−1) were also consistently detected. In biota, ΣPFOS exceeded the biota EQS (9.1 μg kg−1 wet weight) only in harbour porpoise liver, with a mean concentration of 341.39 μg kg−1. However, when expressed as PFOA-equivalents using EU relative potency factors (RPFs), most of the biota samples exceeded the EFSA benchmark of 77 ng/kg. However, twenty-three samples from Langstone harbour had no detectable PFAS. Multivariate analyses showed that PFAS composition varied among species but was not associated with literature-based trophic grouping (PERMANOVA R2 = 0.058, p > 0.05). Although ecological EQS exceedance was limited to PFOS in specific matrices, application of RPFs revealed widespread exceedance of mixture-based health benchmarks. These findings demonstrate that reliance on single-compound regulatory thresholds may underestimate cumulative PFAS risk in UK coastal systems. A mixture-based toxic equivalency approach exposes potential regulatory blind spots in current PFAS assessment frameworks.