Selenium assimilation and volatilization from selenocyanate-treated Indian mustard and muskgrass

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 muM SeCN- removed 30% (w/v) of the Se supplied in 5 d, accumulating 554 and 86 mug 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 mug 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.