ABSTRACT
Human society during the past several centuries has created a large number of chemical substances that often find their way into the environment, either intentionally applied during agricultural practices, unintentionally released from leaking industrial and municipal waste disposal sites, or stemming from research or weapons production related activities. As many of these chemicals represent a significant health risk when they enter the food chain, contamination of both surface and subsurface water supplies has become a major issue. Modern agriculture uses an unprecedented number of chemicals, both in plant and animal production. A broad range of fertilizers, pesticides and fumigants are now routinely applied to agricultural lands, thus making agriculture one of the most important sources for non-point source pollution. The same is true for salts and toxic trace elements, which are often an unintended consequence of irrigation in arid and semiarid regions. While many agricultural chemicals are generally beneficial in surface soils, their leaching into the deeper vadose zone and groundwater may pose serious problems. Thus, management processes are being sought to keep fertilizers and pesticides in the root
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zone and prevent their transport into underlying or down-gradient water resources. Agriculture also increasingly uses a variety of pharmaceuticals and hormones in animal production many of which, along with pathogenic microorganisms, are being released to the environment through animal waste. Animal waste and wash water effluent, in turn, is frequently applied to agricultural lands. Potential concerns about the presence of pharmaceuticals and hormones in the environment include: (1) abnormal physiological processes and reproductive impairment; (2) increased incidences of cancer; (3) development of antibiotic resistant bacteria; and (4) increased toxicity of chemical mixtures. While the emphasis above is mostly on non-point source pollution by agricultural chemicals, similar problems arise with point-source pollution from industrial and municipal waste disposal sites, leaking underground storage tanks, chemicals spills, nuclear waste repositories, and mine tailings, among other sources.
