Phycoremediation and photosynthetic toxicity assessment of lead by two freshwater microalgae Scenedesmus acutus and Chlorella pyrenoidosa

Abstract

Heavy metal (HM) pollution is a serious agro‐economic concern and algae can be used as one of the bioremediating agents as it can grow in different water bodies. In this study the Scenedesmus acutus and Chlorella pyrenoidosa were exposed to various concentrations of Pb²⁺ for 96 h and a multidimensional toxicity assessment have been performed by pulse amplitude modulation technique (PAM) and Fourier Transform Infrared Spectroscopy (FTIR). High angle annular dark field, scanning transmission electron microscopy coupled energy dispersive spectroscopy (HAADF‐S/TEM‐EDS) detected intracellular localization of Pb²⁺, thus confirming algal bio‐accumulation abilities. Sensitivity assay demonstrated that 500 and 400 ppm of Pb²⁺ as minimum inhibitory concentrations (MIC50) for S. acutus and C. pyrenoidosa respectively which inhibited growth (OD) by >50% in 96 h. During bioremoval studies, S. acutus and C. pyrenoidosa were found to remove ~52 and ~32 of total Pb²⁺ respectively. The particulate analysis of Pb²⁺ by ICP‐OES, showed >99.5% biosorption capacity by both the species. The biomass characterization by FTIR showed the involvement of various cell wall functional groups such as hydroxyl, alkane and C=C groups in the biosorption of Pb²⁺ by both the species. The noninvasive chlorophyll fluorescence techniques provide a quick insight on heavy metal stress and can be adapted as a rapid detection tool to study the Pb²⁺ stress. S. acutus strain showed higher tolerance and higher bioremoval capacity than C. pyrenoidosa. However, both the species can be exploited for biosorption of Pb²⁺ from aquatic streams as an alternative way for low cost Pb²⁺recovery systems.