ACCUMULATION OF CESIUM-137 AND SR-90 IN PONDEROSA PINE AND MONTEREY PINE-SEEDLINGS

Because ponderosa pine [Pinus ponderosa (Dougl. ex Laws)] and Monterey pine (P. radiata D Don) have exceptionally fast growth rates and their abscised needles are not readily dispersed by wind, these species may be valuable for removing radioisotopes from contaminated soils. Ponderosa and Monterey pine seedlings were tested for their ability to accumulate Cs-137 and Sr-90-characteristic radioisotopes of nuclear fallout-from contaminated soil. Seedlings were grown for 3 mo in 165 cm3 sphagnum peat moss/perlite (1:1 V/V) in a growth chamber. In Exp. 1, seedling accumulation of CS-137 and Sr-90 after 1 mo of exposure was measured. In Exp. 2, seedling accumulation of the radioisotopes during different-length exposures was measured. Seedling accumulation of Cs-137 and Sr-90 at different concentrations of the radioisotopes in the growth medium was measured in Exp. 3. Ponderosa pine accumulated 6.3% of the Cs-137 and 1.5% of the Sr-90 present in the growth medium after 1 mo; Monterey pine accumulated 8.3% of the Cs-137 and 4.5% of the Sr-90. Accumulation of Cs-137 and Sr-90 by both coniferous species was curvilinearly related to duration of exposure. Accumulation of Cs-137 and Sr-90 by both species increased with increasing concentration in the growth medium and correlated curvilinearly with radioisotope concentration in the growth medium. Large areas throughout the world are contaminated with Cs-137 and Sr-90 as a result of nuclear weapons testing or atomic reactor accidents. The ability of trees to sequester and store Cs-137 and Sr-90 introduces the possibility of using reforestation to remediate contaminated soils.