Fish as a Bio-Indicator of Freshwater Contamination by Metals

Abstract

The effect of the aquatic toxicity on the fate and dynamics of planktonic biomass including uptake and accumulation of heavy metals by the fish plankton and sediments have been studied with a view to assess its ill-effects on the river Ravi aquatic ecosystem. The assessment of eco-toxicity is difficult and complicated process, and therefore parameters by which it was measured are quantitative and relatively basic. However, long-term studies would be necessary for the continuous monitoring of such toxicity levels in water for sustainable conservative of aquatic resource, i.e., River Ravi, for freshwater fisheries, irrigation, sports and drinking water. The assessment of water quality has been made by physico-chemical and biological analyses. The role of both plankton and fish as indicators of fresh water contamination by metals has been studied through the computation of regression models. The two-year data on heavy metals toxicity levels at all sampling sites were compared with the standards prescribed by the EPA (USA) for safe freshwater fisheries. However, during last three months of the project, metals toxicity in water and their uptake and accumulation by the plankton and sediments were studied and possible relationships among these components of river ecosystem have been established. The current heavy metals toxicity of water at various points, viz. Farrukhabad nulla, Bakar Mandi nulla, Munshi Hospital nulla, Hudiara nulla, Taj company nulla and Degh fall are extremely high and there has been an increasing tendency towards accumulation of metals in fish, plankton and sediments in riverine ecosystem. Differential water utility patterns, cultural practices and waste-disposal procedures adopted by the public and sanitation authorities have resulted in considerable degradation of the river Ravi water throughout the stretch under investigation. At the same time this river still exhibits a potential for self-purification. However, if we consider rivers as the renal systems of the land spaces then this kidney system is close to the renal failure at river Ravi. Hence, it is imperative that appropriate steps should be taken by both the government and public agencies to restore river Ravi from effluent tributary to a natural riverine condition. During this research endeavor it has been observed that significant variation in the concentrations of heavy metals, in water, were due to changes in volumes of untreated industrial effluents and domestic sewage added continuously into the river through various effluent discharge tributaries. There was considerable deterioration in the quality of river water at discharge points of Farrukhabad nulla, Bakar Mandi nulla, Munshi Hospital nulla, Hudiara nulla, Taj company nulla and Degh fall. The quality of river water improved gradually onwards, after Bakar Mandi nulla, except at Khurd Pur (the point where Hudiara nulla enters river Ravi), where this river receives large quantities of wastes deteriorating its water quality. The gradual improvement in the quality of river water at Baloki Headworks was due to merging of less polluted tributary, i.e. Q.B. link canal, into river. The concentrations of all heavy metals except cadmium and mercury, in water samples at all the sampling stations, were found significantly higher than the safe limits for freshwater fisheries and drinking purpose as prescribed by EPA and PHSDWS (USA). All the three freshwater fish species, viz. Catla catla, labeo rohita and Cirrhina mrigala are on the verge of extinction in the river Ravi system. However, Catla catla at Shahdera toll tax bridge has vanished. Among phytoplankton, Burmilleria, Cladophora, Chlorella, Fragilaria, Synedra, Scendesmus, Tabellaria and Zygnema indicated direct relationships with the intensity of pollution at highly polluted sites. Among zooplankton, Brachionus and polyarthra were almost absent at highly polluted sampling stations. However, the genera, viz. Aphanizomenon, Bacillaria, Closterium, Cyclopedia, Coconeis, Cosmarium, Chrococus, denticulla, Euglena, Spirulina, Spirogyra and Volvox showed considerable tolerance against heavy metals toxicity. Keratella and Filina appeared to be tolerant genera against heavy metals toxicity while Cyclops and philodena were found as the sensitive forms. Th eproximate body composition of three fish species namely catla catla, Labeo rohita and Cirrhina mrigala showed increased total ash while both muscle proteins and fats decreased with increase in aquatic metals. Among the three species, Catla catla showed significantly higher ability to accumulate metals in the body than Labeo Rohita and Cirrhina mrigala. Metal ions in sediments and plankton have also shown direct relationships with the intensity of water pollution. Thus, the present investigation indicated that both plankton and sediments could act as indicators of freshwater contamination by metals in river ecosystem. However, there is a desperate need to further extend this project for another three years to obtain sufficient data on the heavy metal’s toxicity regarding the whole stretch of River Ravi.