As part of its mission to evaluate the Nation's water resources, the U.S. Geological Survey has initiated various studies to identify and characterize the distribution of a wide range of organic compounds including pesticides, human and veterinary pharmaceuticals, hormonally active compounds, household chemicals, and personal-care products in surface and ground water. These studies range in scale from nationwide and regional programs such as those of the Toxics Hydrology and National Water-Quality Assessment Programs, to local studies conducted in cooperation with municipal governments. These efforts have required development of analytical methods for extraction and analysis of trace levels of target compounds as well as identification of their metabolites and degradation products. In many cases, the parent compound undergoes rapid transformations such as loss of ethyl or isopropyl groups in the case of triazine herbicides, or hydrolysis and conjugation in the case of antibiotics and hormones.
The distribution of these compounds in water is associated with use and disposal patterns. Pesticides, especially herbicides and their degradation products, have been identified in surface water and ground water in agricultural regions of the United States. Veterinary antibiotics and hormones have been identified in ground water and surface water near animal feeding operations and in association with land application of animal wastes. Pharmaceutical compounds and personal-care products have been identified in wastewater outfalls and drinking-water supplies. Many surface-water supplies are downstream from wastewater-treatment plant outfalls, particularly in urban and coastal areas. Wastewater-treatment processes are primarily designed to disinfect wastewater and decrease the concentrations of oxygen-demanding substances rather than to remove trace organic contaminants. Hence, wastewater is a potential source of a variety of organic compounds in downstream water supplies. Several studies have shown that drinking-water treatment processes do not fully remove some of these organic compounds.
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