Submitted to: Chemosphere
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/9/2007
Publication Date: 4/24/2007
Citation: Gao, S., Tanji, K.K., Dahlgren, R.A., Herbel, M.J. 2007. Chemical Status Of Selenium In Evaporation Basins For Disposal Of Agricultural Drainage. Chemosphere. Interpretive Summary: Evaporation basins are widely used for disposal of agricultural drainage water in the hydrologically closed Tulare basin of the San Joaquin Valley in California. The high levels of selenium (Se) in the drainage water, however, have been an environmental concern because of its potential toxicity to migratory waterfowl. Selenium toxicity largely depends on its concentration as well as species and there have been no quantitative measurements for drainage disposal basins. This study determined Se concentration and speciation or chemical status in water and sediment in two evaporation basin facilities in Tulare Lake Drainage District. Results showed that these evaporation basins were able to reduce Se concentration in surface waters from agricultural drainage water inputs. However, biochemical transformations resulted in higher percentage of reduced species as selenite and organic Se that are more toxic than the dominated oxidized selenate species in drainage water from agricultural fields. The intensity of these transformations varied from basin to basin. Sediment served as a sink to immobilize Se. The results from this study provide important information to consider in developing sustainable agricultural production system in the San Joaquin Valley of California.
Technical Abstract: Evaporation basins (or ponds) are the most commonly used facilities to dispose selenium (Se)-laden agricultural drainage in the closed hydrologic basin portion of the San Joaquin Valley in California. However, there is a continuous concern on potential risk of Se in evaporation basin waters to water birds. In this study, we determined Se concentration and examined the chemical status of Se in both waters and sediments in two currently operating evaporation pond facilities in Tulare Lake Drainage District. Some of the saline ponds have been colonized by brine-shrimp (Artemia) that had been harvested since 2001. Se speciation including selenate (SeVI), selenite (SeIV), and organic Se (org-Se or Se–II)] in waters and soil extracts, and fractionation (soluble, adsorbed, organic matter (OM) associated, and Se(0) and other resistant forms) in sediments and organic-rich surface detrital layers from the decay of algal blooms were determined. Selenium in these vascular plant-absent ponds exhibited similar behavior as in vascular plant-present wetland systems, indicating that similar Se transformation processes and mechanisms had resulted in Se immobilization and the increase of reduced Se species [SeIV, org-Se and elemental Se (Se0)] from Se(VI) dominated inlet drainage water. Selenium concentrations in most pond waters were significantly lower than the influent drainage water. This decrease of Se concentration, however, was accompanied with an increase of reduced Se species. Selenium accumulated the most in sediments of the initial pond receiving drainage water. Brine-shrimp harvesting activities did not affect Se speciation but may have reduced accumulation in surface detrital and sediments.