Nationwide reconnaissance of contaminants of emerging concern in source and treated drinking waters of the United States

Abstract

When chemical or microbial contaminants are assessed for potential effect or possible regulation in ambient and drinking waters, a critical first step is determining if the contaminants occur and if they are at concentrations that may cause human or ecological health concerns. To this end, source and treated drinking water samples from 29 drinking water treatment plants (DWTPs) were analyzed as part of a two-phase study to determine whether chemical and microbial constituents, many of which are considered contaminants of emerging concern, were detectable in the waters. Of the 84 chemicals monitored in the 9 Phase I DWTPs, 27 were detected at least once in the source water, and 21 were detected at least once in treated drinking water. In Phase II, which was a broader and more comprehensive assessment, 247 chemical and microbial analytes were measured in 25 DWTPs, with 148 detected at least once in the source water, and 121 detected at least once in the treated drinking water. The frequency of detection was often related to the analyte's contaminant class, as pharmaceuticals and anthropogenic waste indicators tended to be infrequently detected and more easily removed during treatment, while per and polyfluoroalkyl substances and inorganic constituents were both more frequently detected and, overall, more resistant to treatment. The data collected as part of this project will be used to help inform evaluation of unregulated contaminants in surface water, groundwater, and drinking water.

Keywords: Contaminants of emerging concern; Drinking water; Microorganisms; Pharmaceuticals; Source water.

Fig. 1.

Qualitative frequency of detection for analytes monitored in both Phases I and II. Number of analytes in each class - total, 77; pharmaceuticals, 24; anthropogenic waste indicators, 53.

Fig. 2.

Qualitative detections of all Phase II analytes and watershed characteristics. The qualitative detections ranked according the number of source water analytes detected. The watershed characteristics table lists the type of source water (R, river or stream; L, lake or reservoir; G, groundwater (includes under the influence of surface water)), as well as size and use characteristics of the watershed.

Fig. 3.

Qualitative detections in each Phase II DWTP, separated by chemical/microbial class. Number of analytes in each class: pharmaceuticals, 121; PFASs, 17; AWIs, 55; inorganics, 40; microorganisms, 14.

Fig. 4.

Concentrations summed by chemical class at each Phase IIDWTP. For these figures, lithium is treated as an inorganic analyte instead of a pharmaceutical due to differences in units (μg/L for lithium versus ng/L for the other pharmaceuticals). Inorganics were divided between those with μg/L and mg/L concentrations (see Supplementary information Table 2 for analytes in each class).

Fig. 5.

Normalized chemical concentrations. Concentrations in each chemical class were normalized to the location with the greatest concentration. The summed normalized concentration figure is the sum of the normalized concentrations of five chemical class subunits (pharmaceuticals, PFASs, AWIs, inorganics with μg/L units and inorganics with mg/L units).