Arsenic in the Thames Plume, UK

Dissolved and pariculate arsenic species have been determined in the Thames Estuary and Plume. During February 1989 only dissolved inorganic arsenic was detected in the estuary (mean concentration 97.8 ± 5.7 nM) and the plume (mean concentration 43.7 ± 12.0 nM). In July 1990, the mean concentration of dissolved inorganic arsenic in the plume was 28.2 ± 14.0 nM and about 8% of the total dissolved arsenic concentrations comprised the methylated species monomethylarsenic (mean 0.52 ± 0.22 nM) and dimethylarsenic (mean 1.85 ± 1.70 nM). Concentrations of arsenic in suspended particulate matter were 89 ± 39 nmol g−1 in February and 61 ± 12 nmol g−1 in July. Partition coefficients (KDs) for arsenic were about 103 litre kg−1 and were an order of magnitude lower than those for the Humber Plume. Fluxes of dissolved inorganic arsenic form the estuary based on zero salinity end member concentrations were 22 kg d−1 in February and 7 kg d−1 in July. The concentrations of dissolved inorganic arsenic in sediment porewaters were five times higher than those in the water column indicating diffusional fluxes from the sediments amounting to 1.2–2.6 kg d−l over the whole plume. The results were synthesised as an annual arsenic budget for the Thames Plume, which showed that cycling of arsenic by phytoplankton was the dominant process.