Abstract
The assessment of river water quality has been made by physico-chemical and biological analyses. The role of plankton as indicators of freshwater contamination by heavy metals viz. zinc, iron, manganese, cadmium, lead and nickel has been studied through the computation of regression models. Significant variations in the concentration of heavy metals in water were due to changes in the volume of untreated industrial effluents and domestic sewage added continuously to the river system through. various effluent discharging tributaries. The concentrations of all heavy metals in water, except cadmium and mercury, were found significantly higher than the safe limits described by EPA (USA) for freshwater fisheries. The occurrence of all the heavy metals was negatively and significantly dependent upon the pH of water. The river water, throughout the stretch under study, was alkaline, however, decrease in pH of water significantly increased the heavy metal toxicity of water. Water temperature was another important factor which correlated positively and significantly (P < 0.01) with the occurrence of all heavy metals in river water. The uptake and accumulation of all the heavy metals (except lead) by the plankton were positively and significantly dependent on water temperature' also. The phytoplankton genera, viz. Bumilleria, Cladophora, Chlorella, Fragilaria, Synedra, Scendesmus, Tabellaria and Zygnema showed direct relationships with the intensity of metal pollution. Among zooplankton, Brachionus and Polyarthra were almost absent at highly polluted sampling stations. However, the genera viz. Aphanizomenon, Bacillaria, Closterium, Cyclopedia, Cocconeis, Cosmarium, Chrococus, Denticulla, Euglena, Spirulina, Spirogyra and Volvox showed considerable tolerance against heavy metal toxicity. Keratella and Filinia appeared to be the tolerant genera against heavy metal toxicity while Cyclops and Philodena were found as the sensitive forms. Metal ions in plankton have also shown direct relationships with the intensity ofwater pollution. Key words: heavy metals, plankton, regression, toxicity
