METHOD FOR DETECTING SELENIUM SPECIATION IN GROUNDWATER

To better understand the potential toxicity of Se, it is necessary to know the concentration of different Se ionic species (e.g., SeO32- and SeO42-). The hydride generation atomic absorption spectrophotometry ( HGAAS) method of Se analysis cannot separate Se into individual ionic species. ion chromatography (IC) can determine SeO32- and SeO42- conce ntrations simultaneously; however, common anions, such as sulfate (SO4 2-), in groundwater interferes with SeO32- and SeO42- speciation. The purpose of this study was to measure the concentration of ionic SeO32- and SeO42- species in groundwater, thereby determining the chemical s peciation of dissolved Se. Three groundwater samples with high concent rations of Mg2+ and SO42- were used in this study. The ionic SeO32- an d SeO42- species in groundwater samples were selectively adsorbed onto copper oxide (CuO) particles by lowering the pH to 5.5. These ionic s pecies were desorbed from the surface of CuO particles by increasing t he pH to 12.5. Subsequently, the concentrations of SeO32- and SeO42- i onic species in solutions were determined with HGAAS and IC. The effec t of divalent cations (e.g., Mg2+) on the concentration of SeO42- in a queous solutions was also evaluated. The dissolved Se concentration in three groundwater samples ranged from 22 to 151 mu g/ L. The CuO part icles extracted 97% of SeO32- from groundwater samples, suggesting tha t Se(IV) concentrations were dominated by the SeO32- ion. However, CuO particles extracted 80% of SeO42- from groundwater samples. These res ults suggest that Se(VI) concentrations consisted of SeO42- and metal SeO42- solution species. The dissolved Mg2+ in groundwater samples for med a strong neutral ion pair with SeO42- (MgSeO40), which was not ads orbed by the CuO particles. Overall chemical speciation of dissolved S e, extracted with CuO particles, suggests that groundwater samples con sisted of SeO32- (6-36%), SeO42- (32-65%), organic Se species (14-23%) , and neutral ion pairs (9-16%). An important aspect of the proposed m ethod is that CuO can be used in the field to extract both SeO32- and SeO42- ionic species from groundwater samples, and these species could be desorbed from CuO and measured using HGAAS or IC methods, dependin g upon the concentrations of these species.