Determination of inorganic selenium species [Se(IV) and Se(VI)] in tube well water samples in Punjab, India

Abstract

Tube-well water samples in several parts of the Northeastern region of Indian Punjab, where extensive cases of selenosis were reported earlier, have been analyzed for Se(IV) and Se(VI). The total selenium in tube well water samples range from 12 to 93 mg L-1. No speciation information has been reported so far in these water samples. Bioavailability of selenium from water is affected by its various chemical forms. As selenate and selenite are the dominant forms of Se in water, an ion-chromatography- inductively coupled plasma mass spectrometry (IC- ICPMS) method was developed for the on-line separation of selenite [Se(IV)] and selenate [Se(VI)] and their determination in the tube well water samples. The selenium species were separated using an anion exchange column. A good baseline separation of both the species was obtained within 11 minutes. The detection limits for the Se species are Se(IV) = 0.3 μgL-1 and Se(VI) = 0.8 μg L-1. An eluent suppressor was used after the analytical column to reduce the salt content of the eluent: NaOH and the water sample. The dominant selenium species identified in these tube well water samples was found to be Se(VI). The concentration of total inorganic selenium in many of the water samples analyzed in this study exceeded the WHO limit (10 μg L-1).