Contemporary contamination and risk of persistent organic pollutants in sediments of an urbanised estuarine and coastal ecosystem

Estuaries are particularly at risk from persistent organic pollutants (POPs), since they form the boundary between freshwater and marine environments. We investigated spatial and seasonal trends of 7 organochlorine pesticides (OCs), 35 polychlorinated biphenyls (PCBs), and 25 polybrominated diphenyl ethers (PBDEs) in sediments (n = 155) from a range of sites in an urbanised and industrialised estuary (the Forth, south-east Scotland). PCBs (∑PCB mean concentration 3.3 ng g−1 ww, detection frequency 86%) and OCs (∑OC mean 2.5 ng g−1 ww; DF 95%) were the most abundant and frequently detected POPs, with PBDEs less widespread and at lower concentrations (∑PBDE mean 0.17 ng g−1 ww, DF 59%). POP profiles reflected historic patterns of production and use, and, for PCBs, congener-specific degradation profiles. PCB congeners 28, 118, 149, 101, 153, and 138, and the pesticides DDE (a breakdown product of DDT) and hexachlorobenzene were amongst the most frequently detected and abundant compounds. We found no evidence for seasonal variation in ∑OC and ∑PBDE concentrations, although ∑PCB and some individual compounds, e.g. dieldrin, exhibited seasonal differences. Key drivers of POP fate were sediment organic matter and distance from source areas. The weight of evidence suggested that the majority of POPs pose a relatively low risk in the estuary. However some compounds, e.g. Lindane exceeded the Probable Effect Level in 8% of samples. This work demonstrates the spatial variation in presence and potential risk of POPs in the UK environment and the need to continue to monitor the levels of these contaminants.