Review on environmental selenium: Occurrence, public health implications and biological treatment strategies

Selenium is an essential toxin that functions as essential micronutrient for maintaining good health with a small safety margin, but is toxic at slightly higher concentrations or doses. It is being distributed throughout the environment, including mines, water, plants, soils, wastewater and the atmosphere. A multi-sectorial studies should be required to eliminate the toxic effects of Se and retain its public health benefits through the application of various treatment strategies from the contaminated environment. Amongst them, the biological techniques by inoculating several Se-respiring microorganisms in removing Se-laden wastewater have received worldwide attention. The treatment performance of the reviewed biological technologies (bioreactors systems) have been performed higher removal efficiency, but their sustainability in continuous processes depends on the effects of operational parameters. Both in small- and large-scale operations, the phytoremediation techniques utilizing microalgae and artificial wetlands performed a considerable Se elimination efficiency. This paper provides a critical review on the occurrence of selenium, public health significance of selenium to be used as an essential micronutrient and supplement for patients with various diseases (including those with HIV-AIDS and COVID-19), its toxicity, and the biological selenium treatment technologies investigated at laboratory and currently in use at pilot, and full-scale processes.