Occurrence of cesium-137 and other radionuclides in the surface layers of soil in Ohio and Antarctica

The testing of nuclear weapons in the atmosphere in the 1960s and the accidental explosion of a nuclear reactor in 1986 near Chernobyl, Ukraine, caused large amounts of fission-product radionuclides to be deposited over most of the surface of the Earth. The present study was undertaken in order to compare the decay rates of ¹³⁷Cs in the surface layer of soil in central Ohio at 40°N and in Antarctica at 77°S latitude. The measurements were made by means of gamma-ray spectrometry on 10 gram samples of bulk soil collected from the surface. The results indicate that the decay rate of ¹³⁷Cs in the Ohio soil sample is (2.2 ± 0.8) X 10^-1 pico Curies/g, whereas the rate of decay of this radionuclide in the antarctic soil is below the limit of detection (<1 X 10^-2 pCi/g). In addition, roots in the Ohio soil do not contain detectable ¹³⁷Cs, confirming that this radionuclide is not absorbed by plant roots because of its strong sorption on the surfaces of clay minerals. Soils in Ohio and Antarctica do contain long-lived unstable ⁴⁰K, as well as short-lived unstable daughters of ²³⁸U (²¹⁴Pb and ²¹⁴Bi) and of ²³²Th (²²⁸Ac, ²¹²Pb, ²⁰⁸Tl, and ²²⁸Th). The apparent absence of ¹³⁷Cs in the surface layer of antarctic soils is most likely the result of nondeposition of radioactive fallout at the extreme southern latitudes of Antarctica.