Using trace elements and radionuclides distributions in soils to detect the possible presence of legacy coal combustion residuals disposal in North Carolina

Abstract:

The release of coal combustion residuals (CCRs) into the environment can pose ecological and human health risks, due the high concentrations of toxic trace metals and radionuclides in CCRs relative to naturally occurring sediments and soils. The legacy of CCR disposal at unregulated sites has raised public concerns about potential human health effects. In Mooresville, North Carolina the recent finding of a thyroid cancer cluster has heightened concern over possible CCRs in the local environment. In order to detect the possible presence of CCRs in soils, surface soils from residential areas and soil cores drilled at local schools were investigated through the systematic measurements of trace elements and radionuclides (Ra-226, Ra-228, and Pb-210). We used the geochemical fingerprint of CCRs originating from the combustion of Appalachian coals as a model for tracing CCR presence in soils, with reference to the chemistry of background soils measured across North Carolina as well as soils from similar geological formations to those found in Mooresville. Our data show that the trace metals in the analyzed soil samples were within the ranges expected for background soils under similar geological conditions, and the distribution of the trace metals were not consistent with the CCR distinctive geochemical fingerprint. The Th/U ratio in the analyzed soil samples (~4.3) were higher than the Th/U ratios in the Appalachian CCRs (~2), which was consistent with higher ²²⁸Ra/²²⁶Ra activity ratios (>1) in the soils relative to that of the Appalachian CCRs (~0.7). Overall, the data generated in the study suggest that the trace metals and radionuclides in the analyzed soil samples are largely controlled by the local geology and not the result of CCR disposal. Because of the differences between local background soils and Appalachian CCRs, the geochemical tools developed in this study can be used to detect the occurrence of CCR materials in soil with a resolution of around 10% CCR mixed with native soils.