ARSENIC IN THE THAMES PLUME, UK

Dissolved and particulate arsenic species have been determined in the Thames Estuary and Plume. During February 1989 only dissolved inorgani c 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 w as 28.2 +/- 14.0 nM and about 8% of the total dissolved arsenic concen trations comprised the methylated species monomethylarsenic (mean 0.52 +/- 0.22 nM) and dimethylarsenic (mean 1.85 +/- 1.70 nM). Concentrati ons of arsenic in suspended particulate matter were 89 +/- 39 nmol g(- 1) in February and 61 +/- 12 nmol g(-1) in July. Partition coefficient s (K(D)s) for arsenic were about 10(3) litre kg(-1) and were an order of magnitude lower than those for the Humber Plume. Fluxes of dissolve d 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. T he concentrations of dissolved inorganic arsenic in sediment porewater s were Jive times higher than those in the water column indicating dif fusional fluxes from the sediments amounting to 1.2-2.6 kg d(-1) over the whole plume. The results were synthesised as an annual arsenic bud get for the Thames Plume, which showed that cycling of arsenic by phyt oplankton was the dominant process. (C) 1997 Elsevier Science Ltd.