TOXIC EFFECTS OF HEAVY METALS ON FISH

 TOXIC EFFECTS OF HEAVY METALS ON FISH

A great variety of pollutant affect the majority of water courses which receive domestic, industrial and agricultural effluent and these complex situations become especially apparent when considering toxicity. Toxicity tests are useful tools in pollution studies, the term pollution is defined as the deterioration in chemical, physical and biological properties of water brought about by human activities (Varshney, 1991).

Heavy metals can be divided into toxic (hazardous to living organisms) and essential (needed by living organism). Heavy metals like zinc, mercury, lead resulted to abnormal physical development (Zweieg et al 1999). Heavy metals bioaccumulate more in the visceral tissues of the fish than in the muscles and bone (Gbem et al., 2001).

Toxicity of the heavy metals is dependent on dosage (Oladimeji, 1983, Eicheler et al., 2006).

There are two types of toxicity which are: Acute toxicity and chronic toxicity.

Acute toxicity is defined as large doses of heavy metal toxicants and symptoms which result rapidly to death while chronic toxicity is gradually appearance of small doses of heavy metals which can also result to death (Venogopal and Luckey, 1978). There are various environmental and geochemical factors that influence availability of metals into water body. (Luoma 1983) they are:

 TEMPERATURE

For the majority of metals it is not possible to enter any relationship between toxicity and water temperature. Experiment data suggested that the toxicity of chromium, zinc and silver nitrate is independent of test temperature.

For salmonid fish exposed to silver nitrate there is increase in temperature, there is increase in toxicity of silver. The opposite appears to be true for salmonid species exposed to copper and non salmoind species exposed to cadmium with increased temperature being associated with reduced toxicity.

 pH

 Based on ph levels which are 7.0 and 8.0 for majority of freshwater animals such as fish, a few instances of effect of variation in ph have been assessed e.g the toxicity of chromium and vanadium to fresh water fishes increases as the ph is lowered. (Grande and Anderson, 1983) and (Peterson, and Mance 1987) also support this report by a study conducted on young life stages of salmo solar to cadmium, chromium, lead and nickel.

LIFE STAGE

 A common generalization applied to the toxicity of metals to aquatic is the statement that young life stages are more susceptible than the adult. However, this does not mean that eggs are the most sensitive life stage, several studies have considered the relative sensitivity of eggs and fryand for salmo solar eggs which are most sensitive to nicked but not to calcium, (Peterson, metealte and ray, 1983) or chromium (Grande, and Anderson, 1983). The post-hatch fry are more sensitive than eggs of PimephalesPromelas exposed to cadmium (Pickering and Gast, 1972) and of Cyprinuscarpio exposed to nickel (Blaylock and Frank, 1979). Whilst salmo gardneri eggs are more sensitive to selenium (Hodson spray and Blunt 1980). Although there is no secure generalization as to the sensitivities of the early life stages of fresh water fish, young life stages are still considered to be more sensitive to metals than adult fish due to their essentially transient nature.

 WATER HARDNESS

Water hardness is normally reported as total hardness and is usually recorded in mg/litre. Toxicity of metals decreases as water hardness increases, for all species of fish, increasing water hardness is associated with reduced toxicity. The effect of water hardness is similar for salmonid and non-salmonid species in relation to cadmium and zinc. However for nickel the effect of water hardness is much more significant for non-salmonid species

 INFLUENCE OF OTHER METALS:

The effects of heavy metals on man and animals can be additive, antagonistic (Ellis et al., 1989). For instance, zinc and copper are cadmium antagonistic and so adverse effects of high cadmium intake can reduce normal amounts of Zinc and copper in the body.

 ENVIRONMENTAL AND HEALTH RISKS BY HEAVY METALS

The heavy metals are accumulated in living organisms when they are taken up, and stored faster than they are broken down (metabolized) or excreted. They enter into the water supply by industrial and consumer materials, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers and groundwater. The three most pollutant/environmental heavy metals have been reported include Pb, Hg and Cd1, but some other heavy metals can also badly affect the environment. ‘Heavy metals toxicity’ has been reported to be caused by different means; e.g., from contamination of drinking-water (Pb pipes), high ambient air concentrations near emission sources, or from food chain. The heavy metals are poisonous since they bio accumulate. The bio accumulation means an increase in the level of a chemical/toxicant in a biological organism over time, compared to chemical/toxicant level in the environment. It is important to point out here that the most of the zoos which were once located on the outskirts of the cities and towns are now surrounded by human activities, such as vehicular traffic and industries. All these activities can cause heavy metal pollution, which may adversely affect the health and wellbeing of the wild animals housed in such protected areas3. The environmental and health risks caused by various pollutants heavy metals are described as follows

EFFECT OF LEAD (Pb) ON FISH HEALTH

 Lead (Pb) enters into the water body both from terrestrial sources and from the atmosphere, lead concentration in seawater are higher near the coast, especially in polluted area like the eastern coast of the irish sea where concentrations is as high as 5mg/l. (Bernhard and zattera, 1975). Lead concentration in coastal waters near urban centers generally range from about 25mg/l in ordinary coastal waters to 150mg/l in waters that are polluted with sewage. Much of the lead enters coastal waters is in the particulate form.

Consequently, lead accumulates in coastal sediments, average deep ocean sediment concentrates range from 27 to 45mg lead per gram because of industrial discharges. The maximum admissible lead concentration in water is 0.004 to 0.008mg/l for salmonids and 0.07 for cyprinids.

In an experiment carried out by (Smith et al, 1976 and Sprague et al 1982) shows that chronic exposure of fish to lead produces characteristic response of black finning and spinal curvature. Both effects are initially reversible but severe, black finning develops into irreversible rotting of the fins. (Haider 1975).

Acute lead toxicity is characterized initially by damage to the gill epithelium, the affected fish are killed by suffocation. The characteristic symptoms of chronic lead toxicity include change in the blood parameters with severe damage to the erythrocytes and leucocytes, and degenerating changes in the system.

 EFFECTS OF LEAD ON HUMAN HEALTH

 The high levels of Pb may result in toxic effects in humans which in turn cause problems in the synthesis of haemoglobin (Hb), effects on kidneys, gastrointestinal tract(GIT), joints and reproductive system, and acute or chronic damage to nervous system. Target organs are the bones, brain, blood, kidneys, and thyroid gland. Accounts for most of the cases of pediatric heavy metal poisoning. Lead poisoning is the leading environmentally induced illness in children. At greatest risk are children under the age of six because they are undergoing rapid neurological and physical development. In the environment, lead bio-accumulates in most organisms and is toxic to plants, animals and micro-organisms. Young fish are more susceptible to lead poisoning than mature fish or eggs. Symptoms of lead toxicity in fish include spinal deformity and blackening of the caudal region (rear part of the fish).

 EFFECT OF COPPER (Cu) ON FISH HEALTH

Copper enters the marine environment because of waste water and atmospheric discharges from copper production, metal plating, textile production, and sewage outfall and from antifouling paint on ships. The principal sources are atmosphere fallout and antifouling point. These input usually have negligible effect on the open ocean but may have a significant effect on coastal waters.

Open seawater has copper concentration around 1mg/l but in polluted areas these maybe as high as 11mg/l. ship bottom paint has been found to produce very high concentration of copper in seawater and sediments in harbors.

Effects of copper on fish include:

a. Impair their sense of smell (olfaction)

b. Interfere with normal migration.

c. Impair their ability to fight disease (immune response).

d. Make breathing difficult

e. Disrupt osmoregulation

f. Impair their ability to sense vibrations via their lateral line canals (a sensory system that can help fish avoid predators)

g. Impair brain function

h. Change their enzyme activity, blood chemistry and metabolism

i. Can delay or accelerate natural hatch rates (Sorenson 1991)

EFFECT OF NICKEL (Ni) ON FISH HEALTH

 Nickel Ni is needed in small amounts to produce red blood cells (RBCs), but it becomes slightly toxic in excess quantity. Its chronic exposure can cause decrease in body weight, heart and liver damage, and skin irritation. In aquatic animals, the Ni is accumulated but its presence is not magnified along the food chains.

EFFECT OF CHROMIUM (Cr) ON FISH HEALTH

Chromium has wide range of adverse effects in aquatic organisms. In benthic invertebrates it has been observed that there is reduced fecundity and survival, growth inhibition, and abnormal movement patterns (U.S. EPA 1980b). Fish experienced reduced growth, chromosomal aberrations, reduced disease resistance, morphological changes. Chromium inhibits growth in duckweed and algae, reduces fecundity and survival of benthic invertebrates, and reduces growth of freshwater fingerlings. (Sindayigaya, et al. 1994; Sadiq 1992)

 Chromium Cr has been reported to be used in metal alloys and pigments for paints, cement, paper, rubber and other materials. The low level Cr can irritate skin and can produce ulcer. Its chronic exposure can produce kidney and liver damage. The Cr can also damage to circulatory and nerve tissues. In aquatic animals, it is normally accumulated and can cause toxicity to eating fish

EFFECT OF IRON (Fe) ON FISH HEALTH

 Iron (Fe) has an essential role as a constituent of enzymes such as cytochrome and catalase and of oxygen transporting proteins, such as haemoglobin and myglobin. In fresh waters iron is an important nutrient for algae and other organisms. Due to its abundance on the earth’s crust iron is almost in all fresh water body and often is of high concentration in water and sediment than other trace metals.

Higher concentration of iron has been long considered a problem and the uptake of iron in aquatic organism is of two sources which are food and water, the interchange between the two oxidation states of Fe has great influence on the relative proportion of these uptake routes. Dissolved Fe(II) and other metals are taken predominantly via water, whereas Fe(III) precipitates may significantly contribute to the dietary Fe concentrations of aquatic animals. Within the animals Fe is actively transported across the membrane by endocytosis. Ingestion accounts for most of the toxic effects of iron because iron is absorbed rapidly in the gastrointestinal tract. The corrosive nature of iron seems to further increase the absorption. Target organs are the liver, cardiovascular system, and kidneys. Elevated blood pressure; cognitive and neuro-behavioral effects in children & adults. Lead exposure in utero, in infancy and childhood may result in low birth rate, anaemia, neurological impairment, IQ deficits, renal alterations, colic, growth retardation or impaired metabolism of vitamin D.

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