| Abstract: | Arsenic speciation in the Itchen estuary and Southampton Water (UK) has been shown to vary seasonally, with detectable (>0.02μg As dm?3) dissolved arsenic(III) and methylated arsenic only being present from May to early October. This corresponds to the time period during which water temperatures exceed 12°C. For the remainder of the year, inorganic arsenic(V) was the only detectable species. At its peak, ca 30% of the dissolved arsenic was present as methylated forms with dimethylarsenic (DMAs) being the predominant bioarsenical. Significant quantities of monomethyl-arsenic (MMAs) and inorganic arsenic(III) were also present, however. The concentrations of the bioarsenical species varied with position in the estuary and generally increased with salinity. Measurements made during the period of peak algal activity implicated the highsalinity area of the estuary as the most probable region in which the methylated arsenicals are generated. At some sites, a distinct lag was observed between the appearance of dimethylarsenic and the detection of arsenic(III)and monomethylarsenic. Chlorophyll a concentration proved to be a poor predictor of the appearance of reduced and methylated arsenic in the water column. Possible sources of dissolved methylated arsenic are discussed. |
