Assessment of Mumbai Waters for Heavy Metal Toxicity Using Zebrafish as Model Organisms

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INTRODUCTION
The ever increasing population in the world today has led to the mounting of sewage, refuse and industrial waste everywhere. This waste has no place where it could be discarded and now it has found its way into the water bodies polluting the water and thereby creating a threat to the marine flora and fauna. In the environment, organisms are usually exposed not just to a single pollutant but rather to a mixture of these chemicals. Mumbai is one of the busiest metropolitans in the country today housing over a million people alone and the garbage generated daily needs to be dumped somewhere. Mumbai, the capital of economic development, has been under deep stress due to industrial, commercial and population growth. Infrastructural facilities are not adequate to cater to the needs of the people. The environmental status of the coastal region around Mumbai has deteriorated due to wastewater discharges (Dhage et. al 2005). Toxic discharges by illegal means now find its way into the creeks and lakes which are often flushed out into the sea. The escalating accumulation of heavy metals is a hazard to life underwater and is amplifying the mortality rate of the fishes and other aquatic fauna. This buildup of waste in the waters not only affects the aquatic life but also mankind both directly and indirectly. Fish is considered as one of the main protein sources of food for humans. Water pollution leads to affecting fish with toxic metals resulting from different sources like accidental spillage of chemical wastes, periodic precipitation contaminated with air borne pollutants, discharge of industrial or sewerage effluents, agricultural drainage and domestic wastewater. Toxicity with heavy metals to humans as a result of fish contamination has led to many studies on heavy metals in fish (Rashed 2000). Contamination of aquatic ecosystems with heavy metals has been receiving increased worldwide attention due to their harmful effects on human health and other organisms in the environment. Most of the studies dealing with toxic effects of metals deal with single metal species, while the aquatic ecosystems are typically exposed to mixtures of metals. (Demirak et. al 2005; Hill et. al 2005; Karadede and Ünlü 1999) Hence, in order to provide data supporting the usefulness of freshwater fish as indicators of heavy metal pollution, it has been proposed in the present study to investigate the bioaccumulation of these heavy metals in selected organs of these fish (Palaniappan et. al 2008). The presence of toxic materials in ecosystems is presently related with increased concentrations of heavy metals ions which enter the water sources with sewage waters. Heavy metals tend to accumulate in advanced organisms through bio-magnification effects in the food chain. Thus they can enter into human body, and accumulate in the human tissues to pose chronic toxicity (Qiao-qiao et. al 2007). The bioaccumulation of metals in fish is an index of the pollution status of the water and is a useful tool in studying the biological role of the metals present at elevated levels in the fish. When fish are exposed to waters containing metals they tend to take up the dissolved metal ions and accumulate them in the various organs which would ultimately be fatal to the fish in certain cases. Accumulation of these toxic metals usually occur in the muscles, gills, liver, kidney etc. at different amounts which could be determined by analyzing the tissues separately in order to ascertain the total uptake and accumulation of these metals in the organs. There is an urgent need to define a safe amount of chemicals to control pollution and to protect humans from slow poisoning through fish consumption. To protect the aquatic fauna especially food fishes, some criterion should be developed for the safe disposal of waste. Besides the study of the physicochemical and biological conditions of the affected area, laboratory experiments are necessary to determine the...
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