Weathering of Lead in Fort Irwin Firing Range Soils

This paper investigates the physical and chemical transformation of metallic lead (Pb) in Ft. Irwin firing
range soils. Soil samples were collected from berms of two small arms firing ranges, an active one and an
abandoned one, located in the Mojave desert. Pb bullet fragments found in field samples were analyzed by
means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine the
mechanism of metal breakdown in desert climates. Moreover, in order to further elucidate metallic Pb
surface reactions, the process by which Pb fragments are subjected to field weathering conditions was
simulated in the laboratory by performing wetting and drying cycle tests on the surface of metallic Pb
specimens. Results indicated that metallic Pb bullet fragments recovered from the active range field
samples were primarily covered by surface layers of cerussite and hydrocerussite, but litharge was also
identified. In the abandoned range, hydrocerussite and metallic Pb were the predominant Pb species, but
laurionite was also identified. The wetting and drying test results also confirmed the predominant presence
of cerussite and hydrocerussite. In addition, the presence of copper (Cu). Overall, it seems that in these high
pH desert environments, Pb would eventually form insoluble secondary minerals and therefore, its mobility
is expected to be quite limited.