High radiocesium levels in granite outcrop vegetation and reductions through time.

Levels of fallout radiocesium in vegetation were examined on three granite outcrops and a forested area in the Georgia piedmont during 1976-1980. Mean values averaged 4.3 times higher in three species collected on an outcrop than in the same species collected on clay soils in a nearby pine-hardwood forest. Levels in reindeer moss (Cladonia spp.) were significantly (p less than 0.01) lower in species that formed deep, entangled tufts with abundant, slender branches. Cesium levels decreased by as much as 90% from the mid-1960s but were virtually unchanged in the late 1970s. Dry-weight levels in mushrooms reached 18,470 Bq kg-1 (499.2 pCi g-1). Radiation levels in outcrop vegetation were higher than values found anywhere in the piedmont and were comparable to levels reported in plants from the sterile sandy soils of the temperate region coastal plains. These data fit well with earlier reported values and correlate well with the availability of atmospheric fallout. Outcrops can be used as sensitive environmental barometers for some contaminants.