Concentrations and laboratory quality-assurance data for six unregulated contaminants measured in source and finished drinking-water samples collected from public water systems throughout Minnesota by using ELISA and MS-based analytical methods

The U.S. Geological Survey, in cooperation with the Minnesota Department of Health, conducted a study to determine the occurrence of six unregulated contaminants in source and finished drinking-water samples collected from 67 public water supply systems throughout Minnesota. Minnesota relies on groundwater and surface water sources for drinking water. Land use, such as wastewater discharge and agriculture, is a factor that determines groundwater and surface water quality. The public water supply systems were categorized based on whether the source water is from surface water or groundwater. Groundwater sites were further categorized by expected sources of contamination based on land use: wastewater, agriculture, and mix of wastewater and agriculture. The 67 public water supply systems sampled during this study were composed of 16 surface water (SW), 22 groundwater influenced by wastewater (GWWW), 21 groundwater influenced by agriculture (GWAg), and 8 groundwater influenced by both wastewater and agriculture (GWWW/Ag) facility types. Minnesota finished drinking water from public water supply systems is seldom directly from the source without some degree of treatment. Typically, treatment is to satisfy regulatory requirements or provide aesthetic value rather than designed for the removal of unregulated contaminants. To identify the presence of unregulated contaminants in source and finished drinking water from public water supply facilities, water samples were analyzed for three commonly detected pesticides (atrazine, imidacloprid, and pyrethroids) and three commonly detected pharmaceuticals (caffeine, carbamazepine, and sulfamethoxazole). Concentrations of three target contaminants (atrazine, imidacloprid, and pyrethroids) plus several immunologically similar contaminants and/or three target pharmaceuticals (caffeine, carbamazepine, and sulfamethoxazole) plus several immunologically similar contaminants were determined in source and finished drinking-water samples collected from 22 GWWW, 21 GWAg, 8 GWWW/Ag, and 16 SW public water supply facilities. The target contaminant plus immunologically similar contaminants (as defined by ELISA specifications) are referred to as contaminant groups. Note that each contaminant group may represent a different set of compounds across analyzing laboratories. Samples collected from SW (66 samples) and GWWW/Ag (16 samples) public water supply facilities were analyzed for all six contaminant groups. Samples collected from GWAg (40 samples) facilities were analyzed for the three pesticide groups and samples collected from GWWW (40 samples) facilities were analyzed for the three pharmaceutical groups. A total of 162 water-quality samples were analyzed by three different laboratory entities. All samples were analyzed at the USGS Upper Midwest Water Science Center using the enzyme-linked immunosorbent assay (ELISA) analytical method. All samples were analyzed at the U.S. Geological Survey National Water Quality Laboratory (NWQL) where samples collected for pesticide analysis were analyzed by direct aqueous injection with liquid chromatography and tandem mass spectrometry (LC-MS/MS), except for the target contaminant, atrazine (ATZ1), and samples collected for pharmaceuticals and ATZ1 analysis were analyzed by direct aqueous injection with high performance liquid chromatography and tandem mass spectrometry (HPLC/MS/MS). Samples were also analyzed for select pharmaceuticals at SGS AXYS Services Ltd. (AXYS) by LC-MS/MS. These data are a part of the associated U.S. Geological Survey Scientific Investigations Report 2022-5066 (https://doi.org/10.3133/sir20225066).