Source Investigation for Lead and Cadmium with Possible Barium Clustering in Durham County

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Title: Source Investigation for Lead and Cadmium with Possible Barium Clustering in Durham County
Author: Lopez, Alberto
Abstract: ABSTRACT SOURCE INVESTIGATION FOR LEAD AND CADMIUM WITH POSSIBLE BARIUM CLUSTERING IN DURHAM COUNTY Background: Heavy metals like lead (Pb), cadmium (Cd), and barium (Ba) are pervasive contaminants found in many environments and may pose long-term health risks. A study previously conducted in Durham County, North Carolina (NC), obtained peripheral blood from 310 pregnant women at the 12-week gestational stage. Blood samples were analyzed for heavy metals and spatial distributions. The results showed elevated Pb and Cd concentrations that were spatially clustered in an urban neighborhood in Durham County. The objective of this study was to investigate the possible sources of the metal clusters (Pb and Cd) and to analyze the same dataset for the spatial distribution of Ba and for its co-occurrence with other metals. Methods: Publicly available tax data for Durham County, NC, including parcel identification numbers, addresses, year built, built usage, and state of repair, as well as U.S. Census data were used to investigate possible sources of Pb and Cd. Geospatial clustering analysis and mapping were performed using the Hot Spot Analysis (Getis-Ord Gi*) to determine if clustering of Ba was observed. Results: When considering both Pb and Cd clusters, the percentage of dwellings built before 1978, when Pb based paints were banned, was 85.4%. Seventy-nine percent of Pb and 45% of Cd cluster homes were of average build quality, while 21% of Pb and 55% of Cd cluster homes were built of lower than average quality. The median home income for the Pb cluster included 72% (n= 16) at very low income (≤ $32,000) and 28% (n=6) at low income ($32,000 to $46,000). All median incomes in the Cd clusters were categorized as being very low (≤ $32,000). The geospatial cluster analysis indicated that there were five potential hot spots. The median level and interquartile range (IQR) (ng/g) for all participants were 14.50 and 10.03 – 22.46. The median blood concentration within the hot spots was 21.05 ng/g (IQR 16.22 - 31.49 ng/g). The median Ba blood concentration for participants at and above the 90th percentile was 56.63 ng/g. Metals co-occurred with Ba, with the most frequent co-occurrences with Ba being with Cd. Participants with Ba at or above the 90th percentile had an average of 3.4 metals that also occurred at or above the 90th percentile. In the Ba cluster, the average was 3.0 metals. Conclusion: The source of Pb and Cd was not conclusively identified, but the ages of the homes in the previously identified clusters indicate that paint may be the source of exposure. The presence of five probable Ba hot spots was identified, with Cd possibly co-occurring with Ba in some clusters. Additional investigations are required to confirm Pb and Cd sources and to further assess Ba exposures. The Ba exposure investigation should consider regional geology, exploring industries in Durham County that may be generating emissions that may then travel long distances, and an evaluation of possible occupational sources.
Date: 2017-12-14

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