Nanogeoscience

Abstract: Mercury (Hg) is an environmental contaminant that is neurotoxic to humans, particularly to individuals exposed through consumption of fish. In aquatic environments, Hg-sulfides, such as HgS nanoparticles, are precursors to methylmercury, the form of Hg that bioaccumulates in fish. Current knowledge is limited regarding processes through which HgS nanoparticles persist. The goals of this study were to: 1) synthesize uncapped HgS nanoparticles, 2) characterize these nanoparticles, and 3) test aggregation rates of nanoparticles in solutions simulating natural conditions. A novel aqueous synthesis process for uncapped nanoparticles was developed using a controlled precipitation process. The resulting metacinnabar-HgS(s) was characterized through transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction spectroscopy. Using dynamic light scattering, the aggregation rate of HgS nanoparticles was found to increase as salinity increased. Furthermore, the aggregation rate decreased in the presence of cysteine, an organic acid prevalent in sediment pore water. Through comparison of cysteine to a structurally similar organic acid, serine, it is believed that the sulfhydryl group in cysteine is responsible for controlling aggregation rates. By studying the biogeochemical processes of these ubiquitous nanoparticles in aquatic systems, this research has deepened the understanding of mercury in its aqueous phase and furthered the emerging field of nanogeoscience.