Environmental Health - Toxic Substances
Watershed- and Regional-Scale Contamination
Watershed- and regional-scale investigations are developed to address contamination problems typical of specific land uses or human activities that may pose a threat to human and environmental health throughout significant parts of the Nation. Current watershed- and regional-scale investigations address contamination from agricultural chemicals in the Midwest corn belt; cotton agriculture across the southern U.S.; human activities in estuarine ecosystems; historic hard-rock mining in watersheds in mountain terrain and southwestern alluvial basins; and mercury emissions on aquatic ecosystems.
In some cases, these investigations involve characterizing contaminant sources and their mechanisms for affecting aquatic ecosystems. This is the case in ongoing investigations of watersheds that may be affected by hundreds of abandoned mine sites. In some cases, watershed- and regional-scale investigations involve widespread detection of mixtures of contaminants or contaminant transformation products at levels near or below existing water-quality standards or advisories. This is the case in investigations of agricultural land uses which have documented that mixtures of pesticides and their metabolites accumulate to significantly higher levels than the individual parent compounds. In still other cases, these investigations identify chemicals in environmental samples for which standards have not yet been developed. In these cases, the Program provides information to resource managers and regulators that is useful for developing new water-quality standards or registering use of new chemicals, such as new pesticides or industrial chemicals.
These investigations complement the National Water-Quality Assessment (NAWQA) Program, which has the goal of assessing the status and trends of the quality of the Nation's ground- and surface-water resources. The Toxics Program watershed- and regional-scale investigations focus rapidly on new issues, emerging contaminants, and understanding the processes that affect whether a chemical may be of widespread concern. This information is used for planning future NAWQA Program activities.
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