ARSENIC BIOGEOCHEMISTRY IN THE HUMBER ESTUARY, UK

Sampling campaigns have been carried out in the Humber Estuary to asse ss the spatial and temporal distributions of arsenic species and their fluxes to the North Sea. Axial concentrations of dissolved inorganic arsenic displayed conservative behaviour down-estuary of an industrial source. There was no evidence of methylated species in the low-salini ty region in mid-summer, due to high turbidities, which impacted on ph ytoplankton activity. At the estuary entrance dissolved inorganic arse nic concentrations were directly related to salinity over each of four tidal cycles, covering seasonal variability in estuarine conditions. Arsenic partition coefficients, for suspended particulate matter, show ed no systematic trend with salinity but were linearly related to iron inputs, possibly from industrial sources. During spring, in the lower estuary, dissolved inorganic arsenic was accompanied by trace quantit ies (approximately 0.03 mug l-1) of dimethylarsenic. In mid-summer, wh en the water temperatures were approximately 18-degrees-C and at high salinity, both dimethylarsenic and monomethylarsenic were present, wit h the former species having the greater concentrations. The fraction o f total arsenic as methylated species increased from 0% in winter to 2 % in spring to 12% in mid-summer. Seasonal fluxes of dissolved inorgan ic arsenic increased from 55 kg day-1 in winter to 20 kg day-1 in spri ng and 13 kg day-1 in mid-summer but fluxes of dissolved methylated sp ecies were < 1 kg day-1. Particulate fluxes were in the range 70-100 k g day-1 in winter, 13 kg day-1 in spring and < 1 kg day-1 in mid-summe r. The significance of arsenic fluxes to the North Sea is discussed, t ogether with the predictive modelling of arsenic behaviour in the Humb er Estuary and Plume.