"Detections of contaminants do not necessarily indicate a concern for human health because USGS analytical methods can detect many contaminants at concentrations that are 100-fold to 1,000-fold lower than human-health benchmarks," said lead scientist Patricia Toccalino. "Assessing contaminants in these small amounts helps to track emerging issues in our water resources and to identify contaminants that may warrant inclusion in future monitoring."
Scientists tested water samples for 337 properties and chemical contaminants, including nutrients, radionuclides, trace elements, pesticides, solvents, gasoline hydrocarbons, disinfection by-products and manufacturing additives. This study did not assess pharmaceuticals or hormones.
Most (279) of the contaminants analyzed in this study are not federally regulated in finished drinking water under the Safe Drinking Water Act.
The USGS also sampled paired source and finished (treated) water from a smaller subset of 94 public wells. Findings showed that many man-made organic contaminants detected in source water generally were detected in finished water at similar concentrations. Organic contaminants detected in both treated and source water typically were detected at concentrations well below human-health benchmarks, however.
Additionally, the study shows that contaminants found in public wells usually co-occurred with other contaminants as mixtures. Mixtures can be a concern because the total combined toxicity of contaminants in water may be greater than that of any single contaminant. Mixtures of contaminants with concentrations approaching benchmarks were found in 84 percent of wells, but mixtures of contaminants above health benchmarks were found less frequently, in 4 percent of wells.
This USGS study identifies which contaminant mixtures may be of most concern in groundwater used for public-water supply and can help human-health researchers to target and prioritize
|Contact: Kara Capelli|
United States Geological Survey