The importance of quality control in validating concentrations of contaminants of emerging concern in source and treated drinking water samples

Abstract

A national-scale survey of 247 contaminants of emerging concern (CECs), including organic and inorganic chemical compounds, and microbial contaminants, was conducted in source and treated drinking water samples from 25 treatment plants across the United States. Multiple methods were used to determine these CECs, including six analytical methods to measure 174 pharmaceuticals, personal care products, and pesticides. A three-component quality assurance/quality control (QA/QC) program was designed for the subset of 174 CECs which allowed us to assess and compare performances of the methods used. The three components included: 1) a common field QA/QC protocol and sample design, 2) individual investigator-developed method-specific QA/QC protocols, and 3) a suite of 46 method comparison analytes that were determined in two or more analytical methods. Overall method performance for the 174 organic chemical CECs was assessed by comparing spiked recoveries in reagent, source, and treated water over a two-year period. In addition to the 247 CECs reported in the larger drinking water study, another 48 pharmaceutical compounds measured did not consistently meet predetermined quality standards. Methodologies that did not seem suitable for these analytes are overviewed. The need to exclude analytes based on method performance demonstrates the importance of additional QA/QC protocols.

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

Fig. 1.

Distribution of the median recoveries of all analytes in each of six methods, determined in laboratory fortified blank samples (LFB). The number of LFBs varied between methods and is indicated as number of replicates analyzed for each. The number of analytes in each method is indicated in parentheses beneath each boxplot. The boxplots display the mean (center dot), 50th percentile (center bar), 25th and 75th percentile (bottom and top of box, respectively), and the 10th and 90th percentile (bottom and top whisker, respectively). Specific method details can be found in Table 1.

Fig. 2.

Distribution of median recoveries of all analytes in each of six methods, determined in 25 source water Laboratory Fortified Matrix samples (LFM). The number of analytes per method is indicated in parentheses, and specific method details can be found in Table 1.

Fig. 3.

Distribution of median recoveries of all analytes in each of six methods, determined in 25 treated water Laboratory Fortified Matrix samples (LFM). The number of analytes per method is indicated in parentheses, and specific method details can be found in Table 1.

Fig. 4.

A comparison of the quantitative frequency of detection in source and treated drinking water for 22 intermethod comparator analytes (ICA) quantified in at least one environmental sample (n = 25 for all analytes).