Transfer of Cobalt-60 to plants from soils treated with sewage sludge

The uptake of 60Co from soils fertilized with contaminated sewage sludge has been investigated under a variety of experimental conditions. A number of garden plots were prepared by thoroughly mixing sludge containing 60Co with farm soils from the Ottawa Valley. Edible plants were grown in the open on these plots under conditions approximating those in market gardens. The crops were harvested at maturity and were prepared for measurement of 60Co by drying portions of the roots, leaves, stems and fruit. The samples were counted on a large germanium detector which was capable of resolving 60Co from other gamma-emitting nuclides. Cobalt was readily taken up from contaminated sludge but was nonuniformly distributed in various parts of the plant. In general, the roots showed the highest levels while edible portions such as seeds and tubers had much lower concentrations. The uptake ratio, expressed as radioactivity in the sample to radioactivity in the soil, varied from 0.003 to 8 on a dry-weight basis. (author)