Comparing measured and modelled PFOS concentrations in a UK freshwater catchment and estimating emission rates

摘要

The lifecycle, sources and fate of perfluorooctane sulfonate (PFOS) continue to generate scientific and political interest,particularly since PFOS was listed by the Stockholm Convention and largely restricted in Europe. It continuesto be detected in aquatic environments, with only limited studies into the on-going sources. This paperexplores PFOS emissions discharged by the general population into a small catchment comprising two rivers inthe UK. A sampling campaignwas undertaken to improve our understanding of population-derived PFOS sourcesfrom sewage treatment plants (STPs) and in rivers. A corresponding modelling exercise allowed an emission estimateof 13 μg/day/per capita to be derived for the Aire and Calder rivers. PFOS emission was linked to STP dischargesbylinear regression of measured and modelled concntrations (R2= 0.49–0.85). The model was able toaccurately estimate the spatial trends of PFOS in the rivers, while predicted concentrations were within a factorof three based on per capita emission values taken from the literature. Measured PFOS concentrations in riverssuggested that emissions from STPs are partially dependent on treatment type, where plants with secondaryor tertiary treatment such as activated sludge processes emit less PFOS, possibly due to increased partitioningand retention. With refinements based on the type of treatment at each STP, predictions were furtherimproved. The total PFOS mass discharged annually via rivers from the UK has been estimated to be between215 and 310 kg, based on the per capita emission range derived in this study