Mineral dusts from the desiccated playa of Owens Lake, Calif., contain elevated concentrations of many heavy metals. To assess the element sources and possible hazards to humans, other animals, and plants, we are (1) analyzing trace-element contents of the fine-grained mineral and soluble fractions of deposited dust, playa sediment, and aerosol samples collected during dust storms, and (2) using SEM microbeam and microprobe techniques.

Dusts and aerosols are strongly enriched in sulfate from soluble sodium sulfate in playa sediment: elemental S concentrations in saline dust events can be as high as 10 %. Potentially toxic elements in the <50 µm fraction of deposited dust include (conc. in ppm): As (10-50), Cr (17-56), Cu (£ 22), Mo (0.5-3), Ni (£ 16), Pb (50-400), Sb (6-14), Th (10-16), and U (3-8). Deionized water leach tests of the dusts (20:1 liquid:solid by wt., initial leach pH~5, 5-min. shake) show these metals are quite soluble and bioavailable (i.e., dissolved As, Mo, and U as high as 2700, 650, and 170 µg/L, respectively).

Dust-deposition rates of some metals and sulfates in Owens Valley equal or exceed rates in industrialized areas of the world. Much Owens Lake dust is <10 µm in diameter, and SEM studies reveal abundant submicron particles. Given composition, size, and deposition rates (1991-1998 average of 150 g/m2/yr of fine dust at one site), a large fraction of these metals could be transported hundreds of kilometers and easily respired. Terminal lake basins such as Owens Valley could be globally important sources of metal-bearing dusts. The health and ecological effects of these dusts and aerosols are poorly known but of potential concern.