Interaction of Zinc, Cadmium, Copper, Endosulphan and Dimethoate Pesticides on Fresh Water Fish Channa Punctatus

Introduction

Man is responsible for drastically altering the natural resources through his intelligence. He has tried to improve the quality of life through industrial, agricultural and urban development and thus control his own evolutionary process. It is estimated that about 800-1000 tons of pollutants are being ejected into the atmosphere each day by all the big cities of our country. Agriculturists in their bid to improve the quality and quantity of food products have been using fertilizers and chemical pesticides indiscriminately. Such indiscriminate use may result in nutritional imbalance of the soil, which ultimately will reflect in men and animals in that area. Therefore, increasing industrialization and developmental programs lead to continued addition of pollutants to the environment. Environmental pollution by heavy metals has increased in recent years due to extensive use of heavy metals in agricultural, chemical and industrial processes and has become a threat to living organisms. Pesticides are used extensively throughout the world in agricultural and public health programs. The contribution of pesticides to agriculture and public health has been substantial, but their injudicious use has created serious problems.

Contamination of soil and water is caused often by chemical mixtures than by single pollutants. Common examples of mixed chemical pollutants include gasoline; crude oil and land fill leachates. Although these mixtures consist essentially of organic compounds, other pollutant mixtures may include both organic and inorganic chemicals such as B heavy metals. Even in cases where a site is contaminated by only one pollutant, the generation of degradation products, such as humic acid changes the chemical makeup of the soil and water at the site so that they are better described as mixtures. Therefore, the toxicity of mixtures or combinations acquires great significance.

The interactions among trace metals and pesticides possibly due to their competition for a common binding site are very well known and the most studied interactions are in the following groups: copper - molybdenum; copper - iron - zinc; cadmium - zinc - copper - iron; selenium - mercury - arsenic - cadmium; manganese -selenium; cadmium - Endosulfan; cadmium - Dimethoate; quinalphos - cypermethrin. The interaction between cadmium and zinc results in removal of cadmium from active sites when zinc is present in excess but when cadmium is in excess, it displaces zinc from its metallo enzymes and produces toxicity. Genus Valgum syndrome in Andhra Pradesh is a well known example of toxic manifestation due to metal interaction. Excessive intake of molybdenum along with fluoride led to depletion of the body reserves of the essential metal copper.

No interaction or “independent joint action” occurs when the toxicants have similar mode of action. But when they act independently, the resulting toxicity of the mixture is the sum of the toxicities of individual toxicants present. Under ‘interactive action’ the effect may be either synergistic (more than additive) or antagonistic (less than additive). These interactions occur when one toxicant alters the toxicity of other toxicants present, which may be due to interaction between the toxicants involved or between the individual toxicant and the physiological systems of the organisms. The former case may involve the alteration of chemical structure or chemical speciation, while the latter may involve alteration in the distribution, excretion or transformation of one toxicant by the other.

Synergism is caused by various biological activities of chemicals depending mainly on whether the agents have the same or different sites of primary action and whether or not the presence of one chemical influences the amount of other agent reaching their sites of action (interactive or non interactive). Combined treatment may result in simple addition. The compounds that belong to the same class and have a common target organ show linear additive effects, whereas compounds with the same target organ but different metabolic pathways may produce less than additive response. Synergistic mechanisms with simultaneous administration may involve one or more possibilities: a) Increase in uptake b) Enhanced metabolic activation c) Inhibition of DNA repair processes d) Increased proliferation of cells with DNA damage Geyer, et al. [1] provides an explanation for a 40-fold difference in the acute toxicity (LC50) of gamma hexachloro cyclohexane (gamma-HCH, Lindane) in 14 different fish species, based on well recognized principles of toxicokinetics and toxic dynamics in combination with a compilation of data from the literature and some original data. The 48h median lethal concentration (48-h LC50) of gamma-HCH in 14 fish species, belonging to 6 families, range from 22 to 900 micrograms/l. A significant positive linear relationship was found between lipid content (% of wet weight) and the 48-h LC50 of gamma- HCH in these fish species, revealing that the toxicity of gamma-HCH in various fish species is decreasing with increasing total lipid content. If median lethal concentrations are normalized for 1% lipid content, then the range of 48-h LC50s is reduced to between 18 and 32 micrograms/l. It is concluded that lipids of aquatic organisms can serve (among other functions) as a protective storage site against the toxic effects of gamma- HCH and, possibly, of other lipophilic, persistent organic chemicals which are bio concentrated in body lipids. Therefore, in organisms with higher lipid content, a smaller fraction of a lipophilic chemical will reach target organs (liver, lung, central and peripheral nerves, etc.) to cause adverse effects. Results suggest that this correlation can be used to extrapolate the acute toxicity (48-h LC50) of gamma-HCH to other fish species if their lipid content is known. Toxicity of Fenvalerate a synthetic pyrethroid to some fresh water fish species was evaluated by Satyavardhan [2]. The toxicity is determined by using both static and continuous flow through systems and also noticed some specific behavioral characteristics during the experimentation periods in different time intervals. The LC 50 values were calculated for 24h, 48h, 72h and 96h respectively. When the fish were exposed to sub lethal and lethal concentration of Fenvalerate, technical grade and 20% EC., they were migrated to the bottom of the test chamber immediately. This is because of the toxic stress. Their Schooling behavior was totally disturbed and they are swimming independently and this was followed by irregular, erratic and dangling movements with the imbalanced swimming activity. The swimming behavior was in a cork screw pattern and rotating along horizontal axis and followed by “S” jerks, sudden, rapid and non- directed sport of forward movement likely to be busted swimming. The fish were exhibited peculiar behavior that is the fish were trying to leap out from the test chamber which can be viewed as escape phenomenon. Respiratory disruption was observed due to cough and yawning this is because of toxic stress. They often barrel rolled or spiraled at regular intervals and engulfed the air through mouth before respiration ceased. A change in color of the gill lamellae from reddish to light brown with coagulation of excess mucous on the gill lamellae was observed. The symptoms of Fenvalerate poisoning in the fish include loss of schooling behavior, swimming near the upper surface, hyper activity, zigzag movement, loss of buoyancy, elevated cough, increased gill mucous secretion, flaring of the gill arches, head shaking and restlessness before death.

Materials and Methods

Healthy living specimens of the fresh water teleost fish Channa Punctatus were collected from the local ponds. Toxicants used in the experiments are zinc, cadmium, copper, Endosulfan and Dimethoate.

Healthy living specimen of freshwater teleost fish Channa Punctatus were collected from the local ponds and acclimatized to the laboratory conditions for 10 days in batches of 10 each were transferred to 4 glass aquarium and exposed for 96 hour to 3 different toxicants and 2 pesticides at their various concentrations (Zinc 18.62 mg/l, Cadmium 11.8mg/l, Copper 0.56 mg/l, Endosulfan 3.1ug and Dimethoate 14.84). After 96 hours exposure the mortality of the fish at each concentration was recorded. The fish were considered dead when they did not respond on being probed with a glass rod and respiration ceased. Table 1 lists the combinations of toxicants and their concentration used in toxicity studies. The sequence of administration of metals and pesticides was as follows: each aquarium containing 10 fish in tap water received first a corresponding concentration of the toxicant listed in Table 1 as the additive. Within the next 20 mm. a corresponding volume of solution listed as the ‘toxicant’ was added.

All experiments were run simultaneously for 96 hr and dead fishes were counted after every 8 hr intervals. A control experiment was also run for 96 hr in toxicant free tap water. All experiments were repeated three times at temperature varying between 20-25°C. From these experiments six combinations, zinc+cadmium, zinc+copper, cadmium+Endosulfan, zinc+Endosulfan, zinc+cadmium÷ copper+Endosulfan, zinc- cadmium+copper+Dimethoate were selected.

Conclusion

From these observations it is clear that in combination of cadmium and copper separately with Endosulfan, no mortality of fish was observed, showing antagonistic effect, while the presence of these two metals together with pesticides became very toxic (synergistic). Interaction between metals was also very toxic to fish except zinc+ cadmium combination where toxicity was reduced. Pesticides combination was found more than additive showing 50% mortality with in 42 hr instead of 48 hr, but even up to 96 hr the combination could not cause 100% mortality which suggests less than additive effect.