Association Between Occurrence of Per- and Polyfluoroalkyl Substances in Public Water Systems and Socioeconomic Status in North Carolina
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Background: Exposure to Per- and polyfluoroalkyl substances (PFAS) is associated with health risks. However, the joint spatial distribution of PFAS and socioeconomic status (SES) is not known. This study examines the joint distribution of PFAS and SES in North Carolina.
Methods:
Hierarchical clustering was used to cluster 2010 census block groups based on features including urbanicity, education, income, housing, poverty, unemployment, and occupation. Seven resulting SES “clusters” were ranked from highest to lowest SES based on the input variables with Social Vulnerability Index used to validate rankings. Clusters were linked to public water systems (PWS) based on the PWS serving a zip code intersecting that cluster. PFAS occurrence data was obtained from the Third Unregulated Contaminant Rule which tested all large PWS and a representative sample of small and medium PWS. Percent of zip codes served by a PWS testing positive for PFAS are reported.
Results:
Clusters were further grouped into 3 SES categories (high, medium, and low) to facilitate comparisons. As compared to the low SES clusters, high SES clusters were more urban, had lower unemployment, and greater percentage of White residents, even though race was not included in the clustering. PFAS were observed 1.99 times more frequently in high SES clusters as compared to low (29.3% vs 14.7%) and 1.38 times more frequently as compared to medium SES (29.3% vs 21.2%). All differences were highly significant using chi-squared tests, and robust to requiring 50% of a PWS zip code to be in a cluster for assignment.
Conclusion:
Based on PWS testing, PFAS may occur more commonly in higher SES areas. This analysis did not account for homes on well water which might be more commonly be found in rural, lower SES areas. The drivers of this relationship and its relevance for understanding PFAS and environmental justice remain to be fully explored. This abstract does not necessarily reflect US EPA policy.