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. 2022 Mar 15:812:151479.
doi: 10.1016/j.scitotenv.2021.151479. Epub 2021 Nov 9.

Analysis of the novel NCWELL database highlights two decades of co-occurrence of toxic metals in North Carolina private well water: Public health and environmental justice implications

Lauren A Eaves  1 , Alexander P Keil  2 , Julia E Rager  3 , Andrew George  4 , Rebecca C Fry  5
Affiliations

Analysis of the novel NCWELL database highlights two decades of co-occurrence of toxic metals in North Carolina private well water: Public health and environmental justice implications

Lauren A Eaves et al. Sci Total Environ. .

Abstract

Private well users are particularly vulnerable to metal exposure as they are not protected by the Safe Drinking Water Act. In North Carolina (NC), approximately 2.4 million individuals rely on private well water. In the present study, we constructed the NCWELL database: a comprehensive database of 117,960 geocoded well water tests over twenty-years in NC inclusive of 28 metals/metalloids. The NCWELL database was analyzed to identify areas of concern for single and co-occurring toxic metal contamination of private wells in NC. County-level population-at-risk rankings were calculated by combining toxic metal levels and the proportion of residents relying on well water. Additionally, k-means analysis was used to identify counties with critical co-occurrence of toxic metals. In the NCWELL database, inorganic arsenic (iAs) and lead (Pb) were detected above the EPA standards of 10 and 15 ppb in over 2500 and over 3000 tests, respectively. Shockingly, iAs was observed at levels up to 806 ppb and Pb at levels up to 105,440 ppb. Manganese (Mn) was detected above the EPA lifetime Health Advisory Limit in 4.9% and above the secondary Maximum Contaminant Level in 24.3% of all well water tests in NC, with a maximum concentration of 46,300 ppb reported. Mixtures-based analysis identified four distinct clusters of counties, one demonstrating high iAs and Mn and another with high Pb. Over the twenty-year period, metal levels remained high, indicative of sustained contamination in areas of concern. This study provides a novel database for researchers and concerned citizens in NC, demonstrates a methodology for identifying priority geographic regions for single and multiple contaminants, and has environmental justice implications in NC where metal exposure via private well water remains a serious public health concern.

Keywords: Arsenic; Geocoding; K-means clustering; Lead; Manganese; Private wells.

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Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1.
Figure 1.. Maps of North Carolina representing the average levels of (A) arsenic, (B) manganese and (C) lead within counties across North Carolina.
The maps on the left represent the mean concentration within a county, based on quartiles (indicated by the color-shading), and the numbers in the county indicate the number of tests from that county, summarizing well water tests from October 19, 1998, to May 20, 2019. The maps on the right show the percentage of tests that recorded concentrations at or above the EPA MCL standard (for iAs and Pb) or the EPA Health Advisory Limit (for Mn) within a county, indicated by the color-shading. County-level and census-tract level maps of additional metals of particular interest (cadmium, chromium, copper, mercury, and zinc) can be found in Supporting Information.
Figure 2.
Figure 2.. Correlation between county mean metal levels.
The color gradient indicates the Spearman correlation coefficient with blue indicating a positive association. Significant (p<0.05) correlations are indicated with an * (p<0.05). All metals with at least one well water test for all 100 counties were included in the correlation analysis.
Figure 3.
Figure 3.. Bivariate maps of North Carolina demonstrating key correlated pairs of metals in which one metal is toxic.
Maps show the mean concentrations (in ppb) of (A) arsenic and manganese and (B) lead and copper, by tertiles, summarizing well water tests from October 19, 1998, to May 20, 2019.
Figure 4.
Figure 4.. Four clusters of counties representing distinct profiles of county-level mean concentrations for metals with toxic properties were derived.
(A) a map of North Carolina demonstrating the spatial distributions of the clusters, (B) A bar graph demonstrating the mean of the z-score standardized mean concentration of each metal for the counties within each of the three clusters (y=0 represents the state mean) (C) boxplots of the distribution of the percentage of tests over the EPA MCL/SMCL/HAL within the counties in each cluster for each metal.
Figure 5.
Figure 5.. The top twenty-five counties for percentage of exceedances of the EPA MCL/HAL for (A) arsenic, (B) manganese and (C) lead.
Counties are ranked by the percentage of well tests reported that exceed the standard over the entire data collection period. The color-scale, indicated by the legend below each plot, indicate the percentage of exceedances of the MCL (iAs, PB) or HAL (Mn) for each year. The percentage of exceedances of the EPA MCL/HAL for the entire state for each year are represented by the top row in each plot.
See this image and copyright information in PMC

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