Direct and indirect metal contamination of estuarine sediments by boat paint particles

Surface and subsurface estuarine sediments close to a cluster of abandoned boats have been fractionated (between <250 and 5000 μm) and analysed microscopically for paint particles. Paints were encountered in all samples, with concentrations calculated for whole sediment samples up to 1450 per kg (dry weight). X-ray fluorescence (XRF) analysis of paint particles retained by the coarsest (>5000 μm) size fraction revealed heterogeneous concentrations of Ba, Cu, Pb, Sn and Zn that reflect pigments and antifoulants used in various recent and historical antifouling and above waterline boat paints. Analysis of sediments by XRF revelated heterogeneous distributions of these metals between locations, size fractions and depths, and among replicate measurements at different positions of the same sample. Consequently, no relationship with grain size (evaluated using Rb as a proxy) was evident and concentrations often greatly exceeded predicted effect levels for sediments. Re-analysis of sediments after paint particles had been manually removed revealed no statistical difference in median concentrations for Cu, Pb and Zn but significantly lower concentrations for Ba and Sn. This suggests that paint particles contribute directly to the contamination of sediment by Ba and Sn, but indirectly, through leaching and adsorption, to contamination by Cu, Pb and Zn. These two types of association have implications for metal persistence and bioavailability in sediment, and raise questions about how sediment quality should be assessed in the presence of particulate contaminants.