Remediation and Bioremediation of Selenium‐Contaminated Waters

Abstract

Selenium (Se) is a trace element that occurs naturally in soils, water, biota, and food. It is nutritionally required, but Se in excess is toxic to aquatic‐associated wildlife such as fish and birds. Exposure to Se primarily occurs through the diet, not by direct exposure to water; therefore it is vital to account for the “biogeochemistry” of Se—the complex paths by which it moves from contaminated water up the foodweb. As a consequence, waterborne Se is an inappropriate focus for remediation, and this entry illustrates how such a focus can inadvertently misguide major remediation efforts. In fact, there is no fixed “target concentration” for remediation to achieve, as universally accepted water or tissue threshold concentrations for the protection of wildlife are likely to remain controversial for some time to come. This can stymie the traditional remediation strategies of containment, removal, or treatment. One approach to Se remediation that functions under changing regulatory limits is mitigation of wildlife impacts through “alternative” and “compensation” habitats. Also, strategies that take advantage of the natural biogeochemistry, such as algal volatilization of Se, may provide cost‐effective management of contaminated water; however, this approach must be combined with foodweb interruption to prevent Se bioaccumulation.

Selenium toxicity to survival and reproduction of Collembola and Enchytraeids in a sandy loam soil

“…The EC20 and EC50 values based on the toxicities of Se to the reproduction of F. candida and E. crypticus, respectively, were not only remarkably similar between these 2 species but were also similar to those established for the earthworm Eisenia andrei (3.4 and 3.9 mg/kg, respectively [35]). However, Se is also an essential trace element for many terrestrial species [6][7][8]. The EC50 value is provided for relative comparison with the EC50 values for other anionic contaminants because EC50 values are more commonly reported in the literature.…”

“…Much of the previous research published on the ecotoxicology of Se has focused primarily on aquatic or wetland systems [6][7][8][9][10][11], or microbial transformations of Se [12]. Much of the previous research published on the ecotoxicology of Se has focused primarily on aquatic or wetland systems [6][7][8][9][10][11], or microbial transformations of Se [12].…”

“…Selenium is relatively insoluble and immobile in its more reduced forms, but in more oxidized forms, particularly Se 4þ and Se 6þ , Se is mobile in aqueous solutions. In these more oxidized forms Se poses a substantial risk to aquatic organisms [6][7][8].…”

“…Notwithstanding the evidence for Se persistence in soil, data in the published literature were insufficient to establish the screening level concentrations for the assessment of ecological risks at Se-contaminated sites. Much of the previous research published on the ecotoxicology of Se has focused primarily on aquatic or wetland systems [6][7][8][9][10][11], or microbial transformations of Se [12]. Minimal information exists regarding the effects of Se on terrestrial invertebrates, with limited data established in insect feeding studies [13][14][15][16] and even less information on ecotoxicological effects of Se on soil invertebrates.…”

Microbial Transformations of Selenium Species of Relevance to Bioremediation

“…As more stringent regulations come into force in order to limit the discharge of Se-containing waste, the use of bioremediation technologies are preferable because they will offer more cost-effective approaches for the removal of the pollutant. There has been a growing interest in the use of microorganisms in remediating Secontaminated environments (96)(97)(98)(99). In this context, a number of studies have been carried out in order to exploit the use of Seoxyanion-reducing microorganisms in small/large-scale remediation schemes.…”