Trends in heavy metals, polychlorinated biphenyls and toxicity from sediment cores of the inner River Thames estuary, London, UK†
River islands (Ait or Eyot) within the inner tidal Thames serve as unique recorders of current and historical estuarine chemical pollution. Sediment cores from Chiswick Ait were assessed for contamination using Microtox® solid phase bioassay, stable isotopes (δ13C, δ15N), heavy metals and polychlorinated biphenyls (PCBs). Microtox® classified these sediments as non-toxic to moderately toxic and bulk isotopes identified a change in organic input. Metals Cu, Zn, Cr, Ni, Cd, Hg and Ag showed parallel rise, peak and fall profiles which when allied to a 207/208Pb and 137Cs based chronology supported major changes in trace metal contributions corresponding to approximate input times of 1940 (rise), 1963 (peak) and 1985 (fall). Metals ranged from Cu 15 to 373 mg kg−1 (mean 141 mg kg−1), Zn 137 to 1331 mg kg−1 (mean 576 mg kg−1), Cr 14–351 mg kg−1 (mean 156 mg kg−1), Pb 10 to 1506 mg kg−1 (mean 402 mg kg−1), As 1 to 107 (mean 38 mg kg−1), Ni 11 to 113 mg kg−1 (mean 63 mg kg−1), Cd 0.2 to 53 mg kg−1 (mean 9 mg kg−1), Hg 1 to 8 mg kg−1 (mean 4.6 mg kg−1) and Ag from 0.7 to 50 mg kg−1 (mean 7.5 mg kg−1). Down core total PCBs ranged from 10.5 to 121 μg kg−1 and mean of 39 μg kg−1. The rise, peak and fall of Cu, Zn, Cr, Ni, Cd and Ag pollution matched local sewage works' treatment discharge records. Whereas the Hg, Pb and As profiles were disconnected, reflecting alternative historic sources and or partitioning behaviour. Comparison to marine sediment quality guidelines indicate that Zn, Pb, Ni, Cd and Hg exceed action level 2, whereas sedimentary Cu, Cr and As concentrations were above action level 1 (no action) but below action level 2 (further investigation required). The river islands of the tidal Thames capture a unique contaminant chemistry record due in part to their location in the tidal frame (salinity minimum) and close proximity to west London.