Dry deposition of gaseous radioiodine and particulate radiocaesium onto leafy vegetables

Abstract

Radionuclides released to the atmosphere during dry weather (e.g. after a nuclear accident) may contaminate vegetable foods and cause exposure to humans via the food chain. To obtain experimental data for an appropriate assessment of this exposure path, dry deposition of radionuclides to leafy vegetables was studied under homogeneous and controlled greenhouse conditions. Gaseous 131I-tracer in predominant elemental form and particulate 134Cs-tracer at about 1 μm diameter were used to identify susceptible vegetable species with regard to contamination by these radionuclides. The persistence was examined by washing the harvested product with water. The vegetables tested were spinach ( Spinacia oleracea), butterhead lettuce ( Lactuca sativa var. capitata), endive ( Cichorium endivia), leaf lettuce ( Lactuca sativa var. crispa), curly kale ( Brassica oleracea convar. acephala) and white cabbage ( Brassica oleracea convar. capitata). The variation of radionuclides deposited onto each vegetable was evaluated statistically using the non-parametric Kruskal–Wallis Test and the U-test of Mann–Whitney. Significant differences in deposited 131I and 134Cs activity concentration were found among the vegetable species. For 131I, the deposition velocity to spinach normalized to the biomass of the vegetation was 0.5–0.9 cm 3 g − 1 s − 1 which was the highest among all species. The particulate 134Cs deposition velocity of 0.09 cm 3 g − 1 s − 1 was the highest for curly kale, which has rough and structured leaves. The lowest deposition velocity was onto white cabbage: 0.02 cm 3 g − 1 s − 1 (iodine) and 0.003 cm 3 g − 1 s − 1 (caesium). For all species, the gaseous iodine deposition was significantly higher compared to the particulate caesium deposition. The deposition depends on the sensitive parameters leaf area, stomatal aperture, and plant morphology. Decontamination by washing with water was very limited for iodine but up to a factor of two for caesium.