Separation of selenium species released from Se-exposed algae

We have assessed a fractionation scheme for selenium species that separates Se-containing amino acids and other organoselenium compounds in aqueous samples. We investigated the retention of standard solutions of selenate (Se⁺⁶), selenite (Se⁺⁴), and selenomethionine (Se⁻²) by fractionation media (Sephadex A-25 ion-exchange resin, copper-treated Chelex-100 ligand-exchange resin, and activated charcoal) and by several types of membrane filters. The fractionation method successfully isolated Se from the standard solutions into appropriate fractions for radiometric quantitation of ⁷⁵Se. However, some filter media retained unacceptably large amounts of selenate and selenite. Mass balance microcosms were inoculated with green algae (Chlamydomonas">Chlamydomonasreinhardtii">reinhardtii) previously exposed to inorganic ⁷⁵Se, and the fractionation scheme was used to examine the release of ⁷⁵Se species into water and air. The results of the microcosm exposure indicate that seasonal blooms and crashes of phytoplankton populations may produce increased concentrations of organoselenium species.