Movement and distribution of radionuclides on granitic outcrops within the Georgia piedmont.

Abstract

From 1962 through 1964, radioactive fallout in parts of the southeastern U.S. has been detected in greater quantity than in many other places of the country. Flatrock ecosystems in Georgia retain very little rainwater; most run-off water flows through a series of communities which filter and retain fallout radionuclides. When fallout-bearing water flowed over barren rocks, lowland communities always held more radionuclides than upland communities. Usually, however, upland communities removed particular isotopes from surplus run-off water. Parmelia conspersa, an “upland” lichen, had higher concentrations of 137Cs (up to 300 pCi/g dry wt.) than any other plant in 1964. Viguiera porteri, an aster, held the largest concentrations of 90Sr (up to 125 pCi/g). Concentrations of fallout were higher in upland Juniperus virginiana than in lowland populations, although the spectrum of isotopes at both sites was similar. Even though each granitic outcrop as a whole is a relatively simple ecological system, it consists of smaller systems wherein the dynamics of radioisotope movements and bioaccumulation can be understood only in terms of intimate familiarity with each little system contributing to the whole. Maximum concentration levels for any component have not been ascertained; nevertheless, accumulation of isotopes within Parmelia and Viguiera may well indicate the extent to which fallout has become an environmental “contaminant” in the Southeast.