Cadmium biosorption and biomass production by two freshwater microalgae Scenedesmus acutus and Chlorella pyrenoidosa: An integrated approach.

Cadmium (Cd) contamination in different water bodies is a matter of serious concern, as it can cause biomagnification in our food chain up to several trophic levels. In this study, Cd toxicity was investigated in the micro-algae Chlorella pyrenoidosa and Scenedesmus acutus exposed to various concentrations of Cd for 96 h. The inhibitory and toxic effects of Cd on growth and photosynthetic parameters of algae were demonstrated. The bioremediation potentials of these algae were investigated and bioremoval mechanisms were confirmed using qualitative electron microscopic assay such as scanning/transmission electron microscope (S/TEM). The photochemical quenching (Fv/Fm), quantum yield (YII), relative electron transfer rate (rETR) and non-photochemical quenching (NPQ) were inhibited significantly and reduced by ≥ 50% of the control at MIC 50 values. The C. pyrenoidosa and S. acutus biomass have shown 30% and 20% reduction in carbon content and 10% and 12% reduction in nitrogen content at MIC50 values of Cd treatment, respectively. During bioremoval studies, C. pyrenoidosa and S. acutus have shown 45.45% and 57.14% Cd removal of Cd from initial concentration of 1.5 ppm. Out of total cadmium removal C. pyrenoidosa was reported 3% bioaccumulation and 97% biosorption. Whereas S. acutus showed 1.5% accumulation and 98.5% biosorption. The S/TEM images showed the surface accumulation and bioaccumulation of cadmium inside the cytoplasm, vacuoles, and chloroplast. Thus cultivating C. pyrenoidosa and S. acutus would be beneficial in Cd contaminated water bodies as they serve the dual purpose by Cd remediation and algal biomass production.