Mixtures of Organic and Inorganic Chemicals Characterized in Water from the Taps of Residences in the Greater Chicago Area— Science to Understand Contaminant Exposures in Drinking Water

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As a component of ongoing research with a coalition of partners, including the U.S. Geological Survey U.S. Environmental Protection Agency, National Institute of Environmental Health Sciences, Colorado School of Mines, University of Illinois Chicago, and University of South Carolina, water was collected from the taps of 45 Chicago-area residences and analyzed for 540 organic and 35 inorganic chemicals contaminants.  In addition, the untreated  drinking water source in Lake Michigan and treated water before entry to conveyance infrastructure for the Greater Chicago Area were analyzed for comparison. This pilot study in the Chicago area complements a 2016 reconnaissance study of 12 business and 13 residential tapwaters in 11 States throughout the United States. 

As a reflection of the efficacy of water treatment by the Chicago area drinking water facilities, no Federal drinking water standards were exceeded in any sample collected and 90 percent of organic chemicals analyzed were not detected in treated tapwater samples. Consistent with previous findings from a reconnaissance study in homes and businesses throughout the United States, low-level concentrations of disinfection byproducts (DBPs), per/polyfluoroalkyl substances (PFASs), and pesticides were frequently detected (greater than 90 percent of the samples in this study). Although no enforceable standards were exceeded, drinking water goals used to manage public drinking water supplies for arsenic, lead, uranium, and two DBPs (bromodichloromethane and tribromomethane) were exceeded. 

Person collecting a water sample from a residential tap

U.S. Geological Survey scientist collecting a water sample from a home faucet for analyses of inorganic and organic chemicals.  They use an integrated approach to understand drinking water from its sources, through watersheds, aquifers, and infrastructure to tap water where human exposure could occur.(Credit: Paul Bradley, U. S. Geological Survey. Public domain.)

While the results of this study emphasize the high quality and effective treatment of the drinking water in the area sampled, the results also demonstrate the potential for human exposure to low concentrations of chemical mixtures that are not commonly monitored or assessed at the point of exposure (tapwater). Although beyond the scope of this investigation, this study reveals a potential data gap in drinking water exposure assessments potentially needed for public health and for epidemiological and other researchers studying pathologic and toxicologic disease. The study results also provide information about sources and potential changes in contaminants as water moves from Lake Michigan to residential taps, including incoming contaminants that may be in the untreated source waters, chemical additions or removals through the treatment process, and changes through infrastructure and plumbing carrying treated water to tap.  This information can be used to identify targeted mitigation efforts that most efficiently reduce human exposure. 

Science needed for decision makers who maintain the safety of U.S. drinking water supplies includes a broader understanding of how processes such as increased reuse of wastewaters in watersheds and aquifers, aging drinking-water infrastructure, legacy plumbing materials, and disinfection processes may affect contaminant exposures from drinking water.   Although water purveyors consistently monitor more than 100 chemical and microbial contaminants as part of compliance requirements under the Safe Drinking Water Act, there is a recognized lack of comprehensive data on other known, or suspected, contaminant mixtures in drinking water at the point of exposure in residences. The U.S. Geological Survey’s  Water and Wastewater Infrastructure team studies contaminants and pathogens in water resources from their sources through watersheds, aquifers, and infrastructure to human and wildlife exposures and uses that information to develop decision tools that protect human and wildlife health. 



This research was funded by the U.S. Geological Survey’s Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology) in cooperation with the U.S. Environmental Protection Agency,  National Institute of Environmental Health Sciences, Colorado School of Mines, University of Illinois Chicago, and University of South Carolina.