Potential phytotoxicity of lead and cadmium to lemna minor grown in sewage stabilization ponds

The objective of this study is to develop a phytoassay for the heavy metal toxicity in ecotoxicological studies using Lemna minor. The results suggest that the assay is simple, and economical. Similar to fish or aquatic bioassay, the plant Lemna may also be used as an indicator species in the bioassay evaluation for aquatic system. The sensitivity of Lemna plants in terms of biochemical changes and enzyme activities to Cd(II) and Pb(II) was remarkably noticeable. The presence of Cd and Pb drastically decreased the catalase and protease activity and increased the peroxidase activity. The protein, carbohydrate and chlorophyll pigment content decreased where as the proline content increased with the concentration of both metals. Cadmium proved to be comparatively more toxic than lead. The antagonistic behaviour of cadmium and lead was observed in terms of the sensitivity of Lemna plants. Duckweed plants grown in the lowest concentration of cadmium and lead in sewage exhibited metal tolerance by budding after prolonged period of exposure. The results suggest that the bio-chemical changes and the enzyme activity in Lemna plants is a promising indicator of heavy metal toxicity. Duckweed assay should be further explored so that its value can be evaluated when more data are available.