How pesticide contaminates the ground water
Ground water is a source of water which presents below surface of water. While pesticide is the term used to kill pests .But in one side we are getting benefits from pesticide by controlling pests of crops .But in the other side we sacrificed environmental interest. Ground water is a big and best source of drinking so it is much used as drinking water in the world. If we just count united state of America 50 million people used ground water as a drinking water. It is found that 97% of American which are living in rural areas is used ground water as a drinking source. Total water used by livestock is 55% and 40 % of water which is used in irrigating crops in ground water. According to survey in 1980 use of ground water is increased 158 percent. While the use of surface water is only increase up to 107 percent. But due to excessive use of pesticide for control of pest play a major role in ground water contamination as the use of pesticide involves in ground water contamination.
Human activities are mostly source of ground water contamination. Problem of ground water contamination is attracted by peoples towards itself. According to latest survey in America 80 percent of American people considered ground water as national problem while 54 American people considered ground water contamination as a community problem. The question can arise how pesticide pollute ground water by entering into it.
How pesticide get enter into groundwater?
During the world war two excessive use of pesticide were done. So as a result of leaching of pesticide it contaminated ground water. Pesticide can enter into ground water due to practices of users which is used pesticide for control of pest, due to soil type if soil has less organic matter than more chances of leaching of pesticide to ground water, if distance of ground water is less from surface than more chances of contamination, also depend n chemical nature of pesticide etc. If we briefly discussed practices of users which is often caused ground water contamination. If user not follow the label direction which is given on product means if this product is made for control of rodent and we used it for control of crop pests so this may be more toxic and enter into ground water and cause hazard to human, animals etc. Some farmers used above the limit which is recommended so overdosing can cause ground water contamination. Application method of user also influences contamination of ground water .Application method influence spreading of pesticide from one location to another. Bach siphoning also influence contamination of ground water. As a result of back siphoning pesticide introduced in ground water. If source of water is near the pesticide storage it may also synergize the contamination of ground water.
Ability of pesticide to contaminate water:
There are three main factors of pesticide due to these factors pesticide may damage more or more deteriorate the quality f ground water. First factor is solubility .Solubility can be defined as tendency of pesticide to dissolve in water. If solubility of pesticide to dissolve in water is more than pesticide can easily moved with water from one place to another and due to more solubility more chances of leaching of pesticide because as water leach down pesticide also leach with water because pesticide is dissolved in water. If pesticide is less soluble in water then pesticide remains in surface and less chances of leach down because pesticide does not moved underground with water due to mixing in water.
Second factor is adsorption of pesticide with soil particles. If greater the adsorption rate then pesticide with water than movement of pesticide is difficult through the soil because of pesticide binds with particles of soil. So ultimately less leaching of pesticide to ground water is occurred. If the adsorption rate of pesticide with soil particles is less than pesticide freely move through soil surface and ultimately less chances of leaching of pesticide to ground water.
Third very important factor of pesticide which greatly influence in contamination of ground water is pesticide persistence .Pesticide persistence can be defined pesticide ability to resist against break down either by chemical and by microbial way. If the pesticide more persistent than that pesticide remained in the environment for longer period of time so greater the chance of mixing with water and ultimately leach down into ground water and cause ground water contamination. If the pesticide less persistent than it remained in environment for shorter period of time so it favors to environment and ultimately less chances of leaching down of pesticide into ground water.
Ground water contamination also depends on crop .We can also say crop age. Contamination of ground water due to pesticide is less in large plants because large plants consume surplus amount of water so due to this factor pesticide is not much leach down into ground water and less chances of contamination. But in smaller plants consumption f water is less so pesticide present in water can move or leach down into ground water and cause ground water contamination. So we should use of pesticide according to size of plant or according to recommended dose.
If the root zone of plant abundant in microbial community which is present in soil then more chances of break down or biodegradation of pesticide by microbial mean, then less chance of leach down of pesticide to ground water and ultimately less chances of contamination. but in the other case if soil under root zone of plant is less in microbial community because it depend on soil type weather soil favors growth of microbial community .If microbial community deficient than less breakdown or bio degradation by means of microbial community. So pesticide remains in water or surface of soil and more chances of leaching down of pesticide into ground water and cause ground water contamination.
Contamination depend on soil factors:
First factor is soil texture, If sand content is more than particles of soil is not bounded closely to each other .So that type of soil pesticide easily moved through soil surface. S more chances of contamination of ground water by pesticide .But if soil is clayey than it tight closely pesticide particle into it, so less leaching of pesticide into ground water. Other factor is permeability means how pesticide can easily pass through surface of soil. If water easily passed through surface than more movement of pesticide with water and more chances of leach down of pesticide into ground water and more chance of contamination .If water is not easily moved through surface of soil than pesticide is not easily moved through soil surface so less chances of contamination. Third factor is soil organic matter if more organic matter content in soil than organic matter hold pesticide and prevent to leach down of pesticide into ground water. If less organic matter content in soil than capacity to hold pesticide is low so pesticide leach down into ground water and cause ground water contamination.
Conclusion of all this discussion is that excessive use of pesticide effected human badly. Because application of pesticide is not just on pest and it does not affected only pest which we want to control it also effect environment by following way because it mixed with water and some water absorbed by plant and some water move run off and pesticide spreading to another area so it effect surface water and some water leach down through aquifers and reached to ground water and ground water contaminated with pesticide.
Ultimate effect is that ground water is a rich source of fresh drinking water so one big source of drinking water is damage due to pesticide use and if people used this contaminated water as a drinking water so it cause damage to human being and other animal but human more effected because it is a ultimate consumer .
So solution of that problem is that firstly we avoid use f pesticide and used pest management practices and keep in mind that chemical control is a last option. If no choice other than pesticide than used pesticides with less persistence means they easily breakdown either by photo degradation or chemical degradation or by means of microbes. So if less persistent (e.g. pyrethroids) (pesticide less chances of leaching down of pesticide with water so ultimately less chance of contamination of ground water with pesticides so due to that less effect of pesticide on ground water and on living things (animals, human) which have big consumer of ground water.
Muhammad Wasim Akram ( Department of Entomology, UOS)
Hafiz Ali Hassan Raza Shah (Department of Entomology, UOs)
Rao Adeel Ur Rehman (Department of Soil Science, UOS)
Moeen Ahmad (Department of Food Science, GCUF, Sahiwal)
Muhammad Qaisar Naeem Khan (Department of Plant Pathology, UOS)