Uptake of natural and anthropogenic actinides in vegetable crops grown on a contaminated lake bed

Activity concentrations and plant/soil concentration ratios (CRs) of 239,240Pu, 241Am, 244Cm, 232Th, and 238U were determined for three vegetable crops grown on an exposed, contaminated lake bed of a former reactor cooling reservoir in South Carolina, USA. The crops included greens and tubers of turnips (Brassica rapa var. white-globe), bush beans (Phaseolus vulgaris), and husks and kernels of sweet corn (Zea mays var. silver queen). Although all plots were fertilized, some received K2SO4, while others received no K2SO4. The K2SO4 fertilizer treatment generally lowered activity concentrations for 241Am, 244Cm, 232Th and 238U, but differences were statistically significant for 241Am and 244Cm only. Highly significant differences occurred in activity concentrations among actinides and among crops. In general, turnip greens exhibited the highest uptake for each of the actinides measured, while corn kernels had the least. For turnip greens, geometric mean CRs ranged from 2.3×10-3 for 239,240Pu to 5.3×10-2 for 241Am (no K2SO4 fertilizer). For corn kernels, geometric mean CRs ranged from 2.1×10-5 for 239,240Pu and 232Th to 1.5×10-3 for 244Cm (no K fertilizer). In general, CRs across all crops for the actinides were in the order: 244Cm>241Am>238U>232Th >239,240Pu. Lifetime health risks from consuming crops contaminated with anthropogenic actinides were similar to the risks from naturally occurring actinides in the same crops (total 2×10-6); however, these risks were only 0.3% of the risk from consuming the same crops contaminated with 137Cs.