The spatial structure and origin of trace metals and biological material in dust in the Salt Lake Valley, UT, USA

Abstract:

Exposure to metals and biological material via dust inhalation and ingestion may pose risks beyond respiratory distresses from dust inhalation. The Salt Lake Valley, which includes the Salt Lake City metropolitan area and the Great Salt Lake, frequently experiences dust events. However, we know little about the influence of this complex landscape on regional dust composition. To address this gap, we measured the geochemistry, toxicology, and biological community makeup of dust at high spatial resolution within the Salt Lake Valley and contextualized our measurements with data from our nascent dust database. We collected source sediments and dust using bulk deposition samplers at 15 sites situated across a land use gradient. We collected 56 samples over three multi-month time periods spanning 2018 and 2019. We subjected the <63 μm size fraction to a cold (22˚C) dilute (0.8M) nitric acid leach for 24 hours prior to geochemical analysis of the supernatant for major, minor, and trace element contents and ⁸⁷Sr/⁸⁶Sr ratios. We evaluated dust sample toxicity, characterized biological communities, and modeled dust transport. We observed a median (mean) dust flux of 0.84 g yr^-1 (1.74 g yr^-1). The <63 μm portion represents between 16% and 96% of dust mass. Higher dust fluxes occurred at sites proximal to the Great Salt Lake playa and contained more coarse-grained material. Both air transport modeling and ⁸⁷Sr/⁸⁶Sr ratios suggest that playa sediments constitute 50-90% of dust collected at four sites nearest the Great Salt Lake. Among these sites, biological community composition reflected proximity to the hypersaline north arm of the Great Salt Lake. We observed higher abundances of anthropogenic elements like Cr, Cu, Zn, Pb, La, and Ni in samplers situated in urban areas compared to low use areas and found the highest metals abundances in the lowest income areas. However, while inhalation and ingestion of certain metals may pose health risks, we did not find that metals concentrations correlated with dust toxicity. Instead, toxicity may be linked to seasonal abundance and transport of biological contributions from the Great Salt Lake. This study takes a multifaceted approach to unravel the drivers of dust composition in the region, the role the urban core plays in augmenting this signal, and the community health risks posed by dust.