The presence of arsenic (As) in drinking water is a major global public health issue. Chlorella vulgaris (C.vulgaris) is a common green alga that tolerates high levels of As. Focused sonication was used to extract previously unidentified As-GS/PC complexes from C. vulgaris and their integrity was confirmed by HPLC online with simultaneous HR-ICP-MS and ES-MS/MS detection. The response of C. vulgaris when challenged with As(III), As(V) and dimethylarsinic acid (DMA) was assessed through experiments on toxicity, adsorption, efflux, speciation of arsenic (reduction, oxidation and chelation with GSH/PC) and compartmentalisation (flow cytometry). C. vulgaris cells did not produce any As-GS/PC complexes when exposed to As(V) which may indicate that a reduction step is needed for As(V) complexation with GSH/PC. Cells formed DMASV-GS upon exposure to DMA, but this is not part of a detoxification mechanism. It was found that As(III) triggers the formation of arsenic complexes with PC and homophytochelatins (hPC) and their compartmentalisation in vacuoles. The potential of C. vulgaris to bio-remediate arsenic from water is highly selective for the more toxic As(III) (for human life) without the potential hazard to reduce As(V) to As(III)
