Selenium Assimilation and Volatilization from Selenocyanate-Treated Indian Mustard and Muskgrass

Abstract

Selenocyanate (SeCN(-)) is a major contaminant in the effluents from some oil refineries, power plants, and in mine drainage water. In this study, we determined the potential of Indian mustard (Brassica juncea) and muskgrass (a macroalga, Chara canescens) for SeCN(-) phytoremediation in upland and wetland situations, respectively. The tolerance of Indian mustard to toxic levels of SeCN(-) was similar to or higher than other toxic forms of Se. Indian mustard treated with 20 microM SeCN(-) removed 30% (w/v) of the Se supplied in 5 d, accumulating 554 and 86 microg of Se g(-1) dry weight in roots and shoots, respectively. Under similar conditions, muskgrass removed approximately 9% (w/v) of the Se supplied as SeCN(-) and accumulated 27 microg of Se g(-1) dry weight. A biochemical pathway for SeCN(-) degradation was proposed for Indian mustard. Indian mustard and muskgrass efficiently degraded SeCN(-) as none of the Se accumulated by either organism remained in this form. Indian mustard accumulated predominantly organic Se, whereas muskgrass contained Se mainly as selenite and organic Se forms. Indian mustard produced volatile Se from SeCN(-) in the form of less toxic dimethylselenide. Se volatilization by Indian mustard accounted for only 0.7% (w/v) of the SeCN(-) removed, likely because the biochemical steps in the production of dimethylselenide from organic Se were rate limiting. Indian mustard is promising for the phytoremediation of SeCN(-) -contaminated soil and water because of its remarkable abilities to phytoextract SeCN(-) and degrade all the accumulated SeCN(-) to other Se forms.

Selenium accumulation and metabolism in algae

“…In macroalgae, no essential selenoproteins have been identified so far, but Se volatilization has been observed (de Souza et al, 2002). The metabolic fate of Se in these organisms needs more investigation, as the identification of Se-metabolites produced by macroalgae may be of crucial importance to shade light on Se utilization strategies by these organisms.…”

“…Despite macroalgae generally accumulate lower levels of Se compared to unicellular algae, they can be used in Se phytoremediation technologies as Se bioindicators or players in Se removal (de Souza et al, 2002). Chara canescens, for instance, was tested for its capacity to accumulate Se deriving from the drainage water of a farmland (Lin et al, 2002), whereas Cladophora hutchinsiae is recognized as a suitable biosorbent organism for treating Se(IV) ions-containing wastewaters by virtue of its low-cost biomass and high sorption capacity (Tuzen and Sari, 2010).…”

Novel macroalgae (seaweed) biorefinery systems for integrated chemical, protein, salt, nutrient and mineral extractions and environmental protection by green synthesis and life cycle sustainability assessments

“…Therefore, contamination control in aquatic systems and soil prevents the presence of many heavy and carcinogen metals in the food supply or in the environmental in general. However, the performance of macroalgae in terms of removal rate of toxic metals from soil or sludge is lower compared to terrestrial plants 17,18 . Figure 3 illustrates the mechanisms of (bio)phytoremediation by macroalgae during their growth phase 19 .…”

Solar Photocatalytic Removal of Selenite, Selenate, and Selenocyanate Species

“…Multiple sources that add selenium to natural water bodies include agricultural activities , leaching from mining practices , application of selenium containing chemicals in numerous industries, and wastewater streams from petroleum refineries and power plants . Though typically selenite (SeO 3 2− ) and selenate (SeO 4 2− ) account for most Se‐species in selenium contaminated water bodies however selenocyanate (SeCN − ) is another dominant Se‐species in specific industrial effluents including those from petroleum refineries, mining, and power plants using fossil fuels . The danger posed by such selenium contamination is also reflected by stringent environmental regulations .…”