Arsenic pollution is a major problem in the aquatic environment. In the present investigation, it has been found that micro algae can sequester heavy metals from water .The oxidation state of the metal play an important role in metal uptake capacity. Bioassay study was carried out using the diatom, Chaetoceros calcitrans . It was isolated from Cochin backwaters and its growth phase was determined. In the case of estuarine forms, salinity play an important role in the metal uptake and growth. In Cochin backwaters C. calcitrans is found to be dominant during the post monsoon period when the salinity ranged from 26 to 35 ppt. High salinity stimulates the metal uptake in C. calcitrans . The effect of different concentrations of Arsenic on the growth, productivity, pigments, proline and protein content were studied. The bio absorption ability of test species was studied. It was observed that Arsenic was found to be stimulating the growth upto 5ppm concentration and was toxic above 10 ppm. Even though an increase in biomass was observed due to initial metal uptake, gradually toxic effect was noticed in the metabolic activity of the cell. This was reflected in the end products of photosynthesis and different pigments. By suggesting the threshold level of toxicity of this metal, it will be easy for environmentalist and law makers to suggest a tolerance level. This pilot study can be used as a specific application in environmental biotechnology for the management of Arsenic pollution at low intensity by phyco remediation.

Arsenic, Chaetoceros calcitrans, protein and proline production, physiological parameters, Cochin backwaters