3.4. Contamination of Annual Crops

Abstract

Results are presented from the Nordic countries dealing with the uptake of radiocaesium from soil in annual crops after the Chernobyl accident. Barley, potato, carrot, cabbage and pea were selected as suitable representatives of Nordic annual crops. The transfer of radiocaesium to man from these annual crops was generally low. Common experience was that levels after the first year decreased considerably in the agricultural ecosystems, because of the absence of fresh direct fallout and the rapid, strong fixing of caesium in most soil types. Thereafter the rate of decrease was very uncertain with a large variation between localities. Agricultural practices inhibit uptake and especially resuspension by deeper placement of the contaminated surface soil. Only in areas with highly organic soils, low in clay, potassium and pH, can considerable uptake through roots take place. Examples of such places with an enhanced uptake from soil are the Swedish peat study sites in the Gävle region, and the Faroe Islands. In such areas the addition of potassium can be recommended in cases of severe contamination. Reliable effective ecological halflifes (T1/2cco) for content of radiocaesium in the treated species cannot be calculated from the material available. A cautious estimate of T1/2 of about 5–10 years in the period from 1987 and until today seems reasonable. Results indicate the longest T1/2cco for the Danish and Finnish mineral soils, and the shortest for the Swedish and Faroese organic soils. Aarkrog (1992) states that the ecological halflife for Chernobyl 137 Cs in the Danish total diet is 3 years. The content of radiocaesium is lower in barley grain than in the vegetable species. Carrots had a lower uptake to the edible parts than vegetable species where other parts than the root are used. These uptake patterns correspond well with what is generally assumed.