AN ASSESSMENT OF LEVEL OF SOME OF HEAVY METALS IN FISH

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AN ASSESSMENT OF LEVEL OF SOME OF HEAVY METALS IN FISH

CHAPTER ONE

INTRODUCTION

Background of the study

Effect of heavy metals on aquatic life:

Fish is high in omega-3 and protein that the human body needs to stay healthy. However, potentially dangerous heavy metals are absorbed into the body tissues of fish that are transferred to humans on consumption of this affected fish. Good quality of food for human consumption can only be produced in an environment free from contamination and pollution. Fish are of great economic importance, but are affected immensely by various chemicals including heavy metals directly or indirectly in different ways. Several reports indicate high mortality of juvenile fish and reduced breeding potential of adults after long term exposure to heavy metals8. The freshwater fish, Labeo rohita is of great commercial importance because it is the most common fish widely consumed worldwide. Therefore, it can be a good model to study the responses to heavy metal contaminations. Histopathological studies on fish are a noteworthy and promising field to understand the structural organization occurs in the organs due to pollutants in the environment. These structural changes vary with the body parts, nature of the pollutant, medium and duration of exposure. Water quality characteristics also influence histopathological manifestations of toxic effects2. The structural changes in the organs at microscopic cellular and organ level leads to alterations of the function systems. Hence the main objective of this study is to provide insight into the source of heavy metals and their harmful effects on environment and living organisms.

Heavy metal toxicity has proved to be a major threat as several health risks are associated with it. These metals have hardly any biological role to play in the human body but on the contrary their toxic effect causes malfunctioning of the body system. These elements may sometimes act as pseudo elements of the body, interfering with the metabolic processes that occur in the body. They accumulate in the body resulting into chronic diseases. In order to maintain public health, measures have been taken to control and prevent by treating metal toxicity occurring at various levels like occupational exposure, accidents and environmental factors. Metal toxicity depends on the absorbed dose, its route as well as duration of exposure. These heavy metals bind with protein sites which are not meant for them, by displacing original metals from their natural binding sites causing malfunctioning of cells by their toxicity. Oxidative deterioration of biological macromolecules is primarily due to binding of heavy metals to the DNA and nuclear proteins. Industrial waste contain large number of toxicants such as salts of heavy metals, acids, organic matter, pesticides and even cyanides which deteriorate the physico-chemical characteristics of water. These pollutants build up in the food chain and are responsible for adverse effects and even death of the organisms in the aquatic system. Fish serve as biomarkers of environmental pollution as studies on the overall health are widely carried out in order to evaluate the physiological changes of aquatic ecosystems. Heavy metals are generally referred to as those metals which possess a specific density of above 5 gm/cm3 and adversely affect the environment and living organisms. These metals are quintessential to maintain various biochemical and physiological functions in living organisms in very low concentrations only. These metals prove to be noxious when they exceed certain threshold concentrations. Heavy metals are significant environmental pollutants and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional and environmental reasons. The most commonly found heavy metals in waste water include copper, nickel, zinc, cobalt and cadmium all of which cause risks for human health and environment. Heavy metal toxicity can lower energy levels and damage the functioning of brain, lungs, kidney, liver and blood composition and other important organs. Long term exposure to high concentrations lead to gradual and progressive physical, muscular and neurological degenerative processes that initiate disease like multiple sclerosis, Parkinson’s, Alzheimer’s and muscular dystrophy. Repeated long term exposure of some metals and their compounds may cause cancer.

Copper:

Copper is a trace element which is essential for the function of specific protein enzymes. However, at high concentrations it is toxic to the organisms. The increasing industrial activities and the use of CuSO4 as a fungicide in agricultural practices as well as in the control of algae and pathogens in fish culture ponds have increased the copper concentrations in aquatic systems. It is used in combination with lime and water as a protective agent3. Copper sulphate is very toxic to fish. Its toxicity to fish varies with the species and the physical and chemical characteristics of the water9.

Nickel:

Nickel finds numerous applications in many industries because of its resistance to corrosion, high strength and durability, pleasing appearance, good thermal and electrical conductivity and its ability in forming alloys with other metals. The production of alloys accounts for approximately 75% of total nickel consumption6, 7, 10. The pathogenesis of nickel toxicity is relatively complex because of the large number of chemical and physical forms.

Zinc:

Zinc, an essential trace metal becomes toxic when in the nutritional supply it becomes excessive. The main uses of zinc are in the manufacture of galvanized iron, bronze, white paint, rubber, glazes, enamel glass, paper, as a wood preservative (ZnCl2, fungicidal action), petrochemicals, and fertilizers and in steam generation power plants6. Some zinc is released into the environment by natural processes, but most comes from activities of people like mining, steel production, coal burning, and

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Cobalt:

Cobalt is found in meteorites. Elemental cobalt is a hard, silvery grey metal. However, cobalt is usually found in the environment combined with other elements such as oxygen, sulfur, and arsenic. Small amounts of these chemical compounds can be found in rocks, soil and plants, Cobalt metal is usually mixed with other metals to form alloys, these alloys are used in a number of military and industrial applications such as aircraft engines, magnets, and grinding and cutting tools. Cobalt compounds are used as colorants in glass, ceramics, and paints, as catalysts, and as paint driers. Cobalt colorants have a characteristic blue color; however, not all cobalt compounds are blue. Cobalt compounds are also used as trace element additives in agriculture and medicine.

Cadmium:

This metal was first used in World War I as a substitute for tin and in paint industries as a pigment. Today, it is also being widely used in rechargeable batteries, for production of special alloys, and is also present in tobacco smoke. About three-fourths of cadmium is used in alkaline batteries as an electrode component, the remaining part is used in coatings, pigments and in plating works and also as a plastic stabilizer. Humans may get exposed to this metal primarily by inhalation and ingestion and can suffer from acute and chronic intoxication.

1.2 Statement of the problem

Conditions like wrinkled cell membrane damaged or enlarged nucleus and vacullation lead either to anemic condition of animals or death in the long run. Anemic conditions and less iron content have been reported in fish, bird and mammal following exposure to pollutants by several researchers.

Heavy metals likecadmium (Cd), nickel (Ni), chromium (Cr)and lead (Pb) were tested in different organs like gills, livers, kidneys and flesh tissues of the control fish enduring in natural water system. And most of the metals are present in edible portion of fish. Humans are also affected by eating fish and can cause a few of health problems.The levels of toxic elements in different fishes depend on the fish sex,age, season and place. The pollution of waterways with anthropogenic activities are the major cause of aquatic loss and imbalanced food chain.