Ground water agricultural chemical problem

In summary, there is a problem, more perceived than real, associated with the presence of agricultural chemicals in ground-water. To place these findings in perspective requires a guideline number based on health effects which would say to the media and the public that there should not be health concerns below a certain level. 

While both industrial and agricultural chemicals have been found in California ground waters, pesticides injected beneath the soil surface to control nematodes are a particular concern. The nematicide 1,2-dibromo-3-chloropropane (DBCP), which was banned in California in 1977, is the most serious example of this problem in California (1-2). Figure 1 shows the increase between 1979 and 1984 in the number of wells found to contain measurable quantities of DBCP. As of April 1984, 2522 wells contained DBCP, with over half these wells (1455) having concentrations in excess of 1.0 part per billion, the current California "action level". 

In order to answer the question are there any more DBCP-type problems out there awaiting discovery, the State Board in May 1980 established a Toxic Substances Control Program. A major focus of this program was development of an "early warning" priority chemicals project to (1) assess risks, (2) recommend water quality objectives, and (3) propose appropriate mitigation measures for agricultural and industrial chemicals most likely to adversely impact surface or ground water quality. 

Metals and their compounds persist in the environment and can be a serious problem in raw water treatment, especially from ground water sources or surface water with a high proportion of agricultural run-off content. They may accumulate in organisms, particularly those near the top of the food chain, and cause a range of toxic effects. Metallic ions present in raw water arise from the leaching of minerals in the ground, from industrial effluents and chemical processes, and from leachates from land fill sites and contaminated land. 

Although NOT is not usually thought of as a "toxic" chemical, it does cause several health problems including methemoglobinemia in infants (blue-baby syndrome) and may also be linked to stomach cancer. Agricultural runoff can lead to significant, potentially harmful, concentrations of NOT in ground or surface water. 

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