EXPLORING SPATIAL RELATIONSHIPS BETWEEN LIGNITE-BEARING AQUIFERS, TOTAL ORGANIC CARBON, AND END-STAGE RENAL DISEASE IN THE US GULF COAST

In the Gulf Coast region of the United States, low-rank coals (lignite) are hydraulically connected to drinking water supplies. High incidences of end-stage renal disease (ESRD), a chronic kidney disease, occur in this region and cases have been spatially correlated with drinking water withdrawal from aquifers that contain lignite. While past work has looked at incidence rates at the county level, this study used zip code level data for higher spatial resolution. We also explored the spatial variation of total organic carbon (TOC) in groundwater and its relationship to both lignite beds and incidences of ESRD in Texas, Louisiana, and Arkansas. We hypothesized that TOC levels would be higher in lignite-bearing aquifers and that rates of ESRD would be higher in zip codes situated on these aquifers. The USGS Water Quality Portal was used to gather TOC concentrations in groundwater from 1990-1999 to explore the relationship between long-term exposure to these compounds that may be related to incidences of ESRD. ESRD data at the zip code level were queried from the United States Renal Data System. In general, lignite-hosting aquifers had higher rates of ESRD in regions without lignite; however, a lack of precision in the publicly-available TOC data limited the broader impacts of the study. Additionally, we found that zip codes with small populations produce unstable rate estimates and show calculation bias for small zip-code areas and small populations. Thus, the subsequent spatial analyses (hot spot and geographically weighted regression) did not reflect accurate rates of incidence across the study area. This work using zip code level data supports previous work done at the county level and preliminary results show a spatial correlation between lignite deposits, TOC, and ESRD incident rates in the Gulf Coast region of the US. Future work will focus on spatial smoothing methods using zip code-rates before proceeding with additional spatial analyses.