@ Asad, use of agrochemicals can reach water-bearing aquifers below ground from applications onto crop fields, seepage of contaminated surface water, accidental spills and leaks, improper disposal, and even through injection waste material into wells. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants from leaking fuel tanks or fuel or toxic chemical spills may enter the groundwater and contaminate the aquifer. Pesticide contamination of groundwater is a subject of national importance because groundwater is used for drinking water by about 50 percent of the Nation's population. Primary VOC pollutants found in groundwater include aromatic hydrocarbons such as BTEX compounds ( benzene, toluene, ethylbenzene and xylenes), and chlorinated solvents including tetrachloroethylene (PCE), trichloroethylene (TCE), and vinyl chloride (VC).

Thanks J. C. Tarafdar for informative response. This means dependence on ground water is increasing over time and it's quality is deteriorating which an alarm of danger for humans specifically.

Asad Ali Khan

Pesticides, like most other water contaminants, enter the hydrologic system from point sources, which are associated with specific points of release, and from nonpoint sources, which are diffuse and widely dispersed. Nonpoint sources are the dominant sources of pesticides found in streams and groundwater. Nonpoint sources include runoff to streams from agricultural and urban land, seepage to groundwater in areas where pesticides are used, and deposition of pesticides from the atmosphere. Potential point sources of pesticides include pesticide manufacturing plants, mixing-and-loading facilities, spills, wastewater recharge facilities (wells or basins), waste disposal sites, and sewage treatment plants. Once pesticides and their degradates (new compounds formed by the transformation of a pesticide by chemical or biological reactions) reach the atmosphere, streams, or groundwater, they move through the hydrologic system with air, water, or particles, depending on the chemical and physical properties of the compounds. 

When weighing management decisions for the protection of groundwater quality, it is important to consider the time lag between application of pesticides and fertilizers to the land and arrival of the chemicals at a well. This time lag generally decreases with increasing aquifer permeability and with decreasing depth to water. In response to reductions in chemical applications to the land, the quality of shallow groundwater will improve before the quality of deep groundwater, which could take decades.

We can say they pose a potential danger if they are consumed in large quantities, but, as any experienced scientist knows, you cannot draw factual conclusions unless scientific tests have been done. Some pesticides have had a designated Maximum Contaminant Limit (MCL) in drinking water set by the U.S. Environmental Protection Agency (EPA), but many have not. Also, the effect of combining more than one pesticide in drinking water might be different than the effects of each individual pesticide alone. It is another situation where we don't have sufficient scientific data to draw reliable conclusions.

Zainab Siddiqui thanks for useful answer.

The agrochemicals includes fertilizers, Mico- & Macro-nutrients, plant growth regulators, pesticides enter in the ground water in the crop farming areas . Excess of agro-chemicals are accumulated as ground water polluting it.

Thanks Madhukar Baburao Deshmukh for your worthwhile response about the issue under consideration.

Soluble pesticides were carried away by water molecules especially during the precipitation event by percolating downward into the soil layers and eventually reach surface waters and groundwater. Consequently, it degrades water quality and reduces the supply of clean water for potable water. Farms discharge large quantities of agrochemicals, organic matter, drug residues, sediments and saline drainage into water bodies. The resultant water pollution poses demonstrated risks to aquatic ecosystems, human health and productive activities. Agricultural practice often involves an intensive and incorrect use of pesticides and fertilizers. These chemicals can leach through the soil profile and contaminate groundwater, including drinking water. For this reason, an effective groundwater monitoring is strongly advisable. Pesticide and/or fertilizer bind to the soil particles in a process called sorption and are degraded by soil micro-organisms. The chemicals lower the surface tension and cause spreading of water drops on solid surfaces resulting in wetting of that surface. Pesticide and/or fertilizer bind to the soil particles in a process called sorption and are degraded by soil micro-organisms. The chemicals lower the surface tension and cause spreading of water drops on solid surfaces resulting in wetting of that surface. Chemical fertilizer overuse can contribute to soil acidification and soil crust, thereby reducing the content of organic matter, humus content, beneficial species, stunting plant growth, altering the pH of the soil, growing pests, and even leading to the release of greenhouse gases. This excess nitrogen and phosphorus can be washed from farm fields and into waterways during rain events and when snow melts, and can also leach through the soil and into groundwater over time. High levels of nitrogen and phosphorus can cause eutrophication of water bodies. Fertilizers kill soil microorganisms as the soil is not replenished. Chemical fertilizers get washed off through irrigation and rainfall as drainage and reach rivers, lakes, and streams and pollute them, disturbing the natural.