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. 2018 Aug 15:633:1667-1678.
doi: 10.1016/j.scitotenv.2018.02.288. Epub 2018 Apr 15.

Spatial clustering of metal and metalloid mixtures in unregulated water sources on the Navajo Nation - Arizona, New Mexico, and Utah, USA

Joseph H Hoover  1 , Eric Coker  2 , Yolanda Barney  3 , Chris Shuey  4 , Johnnye Lewis  5
Affiliations

Spatial clustering of metal and metalloid mixtures in unregulated water sources on the Navajo Nation - Arizona, New Mexico, and Utah, USA

Joseph H Hoover et al. Sci Total Environ. .

Abstract

Contaminant mixtures are identified regularly in public and private drinking water supplies throughout the United States; however, the complex and often correlated nature of mixtures makes identification of relevant combinations challenging. This study employed a Bayesian clustering method to identify subgroups of water sources with similar metal and metalloid profiles. Additionally, a spatial scan statistic assessed spatial clustering of these subgroups and a human health metric was applied to investigate potential for human toxicity. These methods were applied to a dataset comprised of metal and metalloid measurements from unregulated water sources located on the Navajo Nation, in the southwest United States. Results indicated distinct subgroups of water sources with similar contaminant profiles and that some of these subgroups were spatially clustered. Several profiles had metal and metalloid concentrations that may have potential for human toxicity including arsenic, uranium, lead, manganese, and selenium. This approach may be useful for identifying mixtures in water sources, spatially evaluating the clusters, and help inform toxicological research investigating mixtures.

Keywords: Metal and metalloid mixtures; Spatial clustering; Unregulated water sources.

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Figures

Fig. 1
Fig. 1
Matrix illustrating the correlation coefficient (Spearman's ρ) for metals and metalloids measured in unregulated water sources.
Fig. 2
Fig. 2
Boxplot of select water contaminants, partitioned into clusters for comparison. The value below each boxplot indicates the percentage of sources with contaminant measurements below the limit of detection. Black horizontal lines for arsenic (As), manganese (Mn), selenium (Se), and uranium (U) indicate the overall median.
Fig. 3
Fig. 3
Overview map (3A) of the Navajo Nation in the southwest United States and locations of unregulated water sources classified into Water Quality Cluster 1, 2, or 3. In panel B, C and D the larger dots are unregulated sources classified into the WQC of interest and the smaller black dots are other tested unregulated sources with different WQC membership. The dashed polygons around subsets of water sources indicate a significant spatial cluster.
Fig. 4
Fig. 4
Locations of unregulated water sources classified into Water Quality Cluster 4, 5, 6 or 7. In each panel, the larger dots are unregulated sources classified into the WQC of interest and the smaller black dots are other tested unregulated sources with different WQC membership. The dashed polygons around subsets of water sources indicate a significant spatial cluster.
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