Metal contamination in sediments of an estuary impacted by discharges of antifouling waste (Yealm, southwest England)

The Yealm is a small, protected estuary in southwest England. A paint-testing laboratory on the estuary operated from the 1920s until 2011 but sometime in 2015 or 2016, an unauthorised discharge of antifouling waste occurred. In this study, concentrations of metals and forms thereof associated with contemporary and historical antifouling formulations (As, Cu, Hg, Pb, Sn, Zn, organic Hg, organic Sn), along with other elements of geochemical or anthropogenic interest, were measured in fractionated (<180 μm) surface sediments at different distances from the discharge. Close to the discharge, concentrations of organic-Sn, representative of tributyltin, exceeded a level that requires material disposal in landfill; here and upestuary, concentrations of Cu and Hg exceeded respective predicted effect levels for estuarine sediments. Analysis of paint flakes isolated from sediments outside the laboratory revealed similar chemical signatures (high concentrations of Cu in most flakes and high levels of Hg and Sn in several cases), consistent with antifouling paint being the cause of contamination. Concentrations of Cu, Hg and organic Sn in sections of a dated core sampled close to the discharge exhibited enrichment since the opening of the laboratory nearly 100 years ago, with distinctive peaks for Hg and organic Sn coincident with periods shortly after these biocidal metals began to be phased out or restricted. These observations suggest that historical waste discharges may have been important and that any remediation measures will be challenging. The general observations might also be applicable to other facilities where contemporary and legacy antifouling waste is commonly discharged to sediments (e.g., boatyards).