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.
l 2005; Hill et. al 2005; Karadede and ?nl? 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 o 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.Heavvy 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 ollution status of the water and is a useful tool in studying the biological role of the 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 ollution 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 toxicity of these metals which can provide biological information to control the water quality. Bioassays are now being recognized as the best measure to determine the toxicity limit and establishing a safe concentration of the toxicant hich can be tolerated by the fish.The purpose of the acute toxicity test with fish species is to help in the assessment of the possible risk to similar species in natural environments, as an aid in the determination of possible water quality criteria for regulatory purposes, and for use in correlation with acute testing of other species for comparative purposes. Toxicity studies also help in studying the harmful effects of these metals on other vertebrates too; on the whole it indicates to what extent these toxic elements can harm the biota and proves a threat to the environment.
Sprague 1969) Zebrafish has been a prominent model vertebrate in a variety of biological disciplines (Hallare et. al 2004; Hill et. al 2005; Johnson et. al 2007; Krone et. al 1997a; Lele et.
al 1996; Wu et. al 2009). Substantial information gathered from developmental and genetic research, together with near-completion of the zebrafish genome project, has placed zebrafish in an attractive position for use as a toxicological model.There is a clear potential for zebrafish to provide valuable new insights into chemical toxicity, drug discovery, and human disease using recent dvances in forward and reverse genetic techniques coupled with large-scale, high- throughput screening (Hill et.
al 2005; Lele et. al 1996). There is a level of concentration of heavy metals that could be present in the water and would not be toxic to the fish.Since the zebrafish is a well known model for toxicological research, exposing it to a variety of heavy metals at varying known concentrations in the water sample would help us determine the best possible concentration at which the fish would survive thereby being able to standardize the degree of the metal accumulation in the water that would not be lethal to the fish.
The zebrafish, being freshwater fish, are exposed to waters containing heavy metals, and as a result tend to live under stress conditions which could have an effect or even alter to an extent their normal body functions.Assessment of the early changes induced by exposure to the different stress conditions could be observed both externally as well as internally. External examinations would include behavior, reproduction, motility, colour of the gills, feeding pattern, etc. There are a group of proteins known as stress proteins that are expressed when the fish tend to live in any kind of stress onditions. Heat shock proteins are implicated in cellular protection and it is suggested that they may play a role in normal growth and development.
It is believed elevation of temperature and probably restore cell functions during recovery from stress. (Misra et. al 1988) Heat-shock proteins which are usually measured in times of stress can also be determined to observe the rate of stress at which the model organism is subjected. The most abundant heat shock protein is a 70kDa protein. A variety of heat shock proteins including Hsp47, Hsp 70, Hsp 90alpha and Hsp 90beta nd the heat shock transcription factor Hsf 1 have been identified and cloned from zebrafish (Graser et.
al 1996; Krone et. al 1997a,b; Rabergh et. al 2000).Other internal observations would include the activity of various enzymes like Catalase, Glutathione- S-Transferase, Superoxide Dismutase, Acteylcholinesterase etc.
Bioaccumulation of heavy metals in the various organs and tissues of the fish could also be studied and reported. Once the standardizing of the levels of the heavy metals that the zebrafish would be able to survive in is complete, then the zebrafish could then be subjected to number of polluted water samples from around Mumbai so as to reveal the heavy metal content of these waters and its toxicity and determine the danger it poses to the aquatic ecosystem.
