Organic and colloidal selenium in Southern Chesapeake Bay and adjacent waters

Abstract

River water, estuarine water and coastal seawater were collected and filtered through glass-fiber filters. Subsamples of these three types of waters were subsequently passed through AMICON DIAFLO ultrafilters (UM 2, YM 5 and YM 10) individually. The filtrates were analyzed for dissolved selenium with and without oxidation by irradiation with ultraviolet (UV) light and for dissolved organic carbon (DOC). The concentration of organic selenium is calculated as the difference in the concentrations of selenium with and without UV oxidation. The contribution of colloidal inorganic selenium to total dissolved inorganic selenium decreases with increasing salinity. Colloidal inorganic selenium constitutes 77, 40 and 0% of the total dissolved inorganic selenium in river water, estuarine water and coastal seawater, respectively. Most of the colloidal inorganic selenium is found in material having nominal molecular weights (NMW) between 1000 and 5000. Organic selenium is detected in all three types of waters. The ratio of organic to inorganic selenium ranges from 0.66 to 1.58. The lowest ratio was observed in river water. Colloidal organic selenium was also found in all three types of waters. Its contribution to total dissolved organic selenium again decreases with increasing salinity. Colloidal organic selenium constitutes 70, 64 and 35% of total dissolved organic selenium in river water, estuarine water and coastal seawater, respectively. Most of the organic selenium is found in material having low NMW. For a given sample, except in the subsample of river water containing material with NMW above 10 000, the concentrations of organic selenium in the filtrates are linearly related to those of DOC.