ABSTRACT
Soils and rocks contain the Uranium and Thorium Series, headed by 238U (t1/24.468 109 yr) and 232Th (t1/21.4051010 yr), respectively. The natural forces of erosion and weathering reduce the particle size of the host rock or soil and surface winds suspend the small particles. These are removed from the atmosphere by the usual scavenging processes. It is known that “dust storms” resulting from desertification carry material for thousands of kilometers and in some instances around the world. The distribution of uranium and thorium in the terrestrial environment is relatively constant at 2-3 µg U g1 (25-36 mBq 238U g1) of soil and 10 µg Th g1 (4 mBq 232Th g1) of soil.1,2 There are geographical areas that do have higher concentrations and have had the deposits exploited for commercial purposes. The bulk of the atmospheric inventory of uranium is soil derived from the earth’s surface. Additional sources of uranium are emissions from energy-generating plants (coal, oil, nuclear), fallout resuspension from atmospheric nuclear weapons
tests, satellite failures, and nuclear-related accidents.3 Atmospheric thorium is also derived from soil resuspension and, to a lesser degree, energy-related emissions.
