Tracing Anthropogenic Metal(loid) Contaminants in the Environment Using Geochemical, Radiogenic, and Radioactive Isotopic Tools

Coal combustion residuals (CCRs or coal ash), phosphate rocks and fertilizers, and leaded gasoline and lead-based paint represent major anthropogenic sources of metal and metalloid (i.e., metal(loid)) contaminants released to the environment. This dissertation aims to characterize the compositions of trace elements and radiogenic isotopes (Pb, Sr) of these anthropogenic sources and further explore their individual applicability and/or conjunctive utility with radioactive isotopes (228Ra, 226Ra, 137Cs, and 210Pb) in tracing the origin, timing, and impacts of metal(loid) contamination at various scales and in multiple environmental settings.The trace element compositions and isotopic signatures of Pb and Sr in fly ash originating from coals of different coal basins in the United States were characterized. In addition, an extended database of the Pb isotope fingerprints of coal and coal ash from China and India – the world’s top two coal producers and consumers – was established, combining newly measured values of coal and coal ash samples in this dissertation and data compiled from the literature. The results showed that (1) the Pb isotope signature of coal fly ash is distinctive from the isotope compositions of both the legacy anthropogenic Pb sources (i.e., leaded gasoline and lead-based paint) as well as natural Pb, which can be used for detecting fly ash contamination in the environment; (2) the 87Sr/86Sr ratio of bulk coal fly ash is distinctive from that of water-soluble fraction, which reflects the heterogenous distribution of Sr in fly ash and indicates the different uses of 87Sr/86Sr ratio for tracing its contamination in different environmental settings (i.e., terrestrial versus aquatic); and (3) the integrative use of trace elements, Ra isotopes (228Ra/226Ra), and Pb isotopes can further improve the detection of trace levels of coal fly ash dispersed in the environment. Through the integration of geochemical and isotopic tools (i.e., trace element distribution and 87Sr/86Sr ratio) with morphological and magnetic observations, this dissertation revealed the decades of historical and current unmonitored releases of coal ash and associated metal(loid) contaminants from the inadequate coal ash disposal units to the adjacent freshwater lakes across North Carolina (NC). The temporal distribution and evolution of coal ash contamination in the lake sediments were constructed by 137Cs- and 210Pb-based chronology techniques. The contributions of coal fly ash to the total Pb accumulation in the sediments of these contaminated lakes were quantified using a Bayesian-based Pb isotope mixing model, and the results suggested that regionally Pb contamination from fly ash can significantly outweigh the Pb input of atmospheric deposition (i.e., leaded gasoline) in the environment. Furthermore, the Pb isotope compositions of coal fly ash from China, India, and the U.S. were constrained and the fluxes of Pb associated with coal fly ash disposal in the three countries were estimated, laying the groundwork for future research on the impacts of coal ash on the Pb biogeochemical cycles at larger scales. Additionally, this dissertation reported the first set of data on the Pb isotope compositions along with rare earth elements and yttrium (REY) of phosphate rocks and fertilizers sourced from different regions and origins around the world. The geological imprints reflected in the geochemical and Pb isotopic fingerprints of the phosphate rocks were discussed and their potential utilizations and limitations in tracing phosphate-associated metal(loid) contamination in the environment were evaluated. This lays the groundwork for future local and regional studies on tracing the impacts of metal(loid) contaminants from phosphate rock mining and phosphate fertilizer application. Furthermore, this dissertation showcased a holistic assessment of the legacy anthropogenic contamination of Pb and other metal(loid)s in urban soils from Durham, NC, whereby fallout radionuclides 137Cs and 210Pb were proposed as potential indicators of the extent of soil disturbances that can impact the mobilization and redistribution of metal(loid) contaminants. The imprints of distinctive Pb isotopic fingerprints of leaded gasoline and lead-based paint in the soils reflected the persistent presence of these legacy sources in the urban environment of today, and the potential bioavailability of toxic metal(loid)s in the contaminated soils upon oral ingestion was assessed via in vitro arrays.