Uptake of 226Ra and 210Pb by food crops cultivated in a region of high natural radioactivity in Brazil

The Pocos de Caldas Plateau is a deeply weathered alkaline igneous intrusion of about 35 km diameter, in which several radioactive anomalies exist. The first Brazilian uranium mine and mill are located in this region. A study is in progress to assess the edible vegetable uptake of the most abundant natural radionuclides in the local environment and this paper reports the results for 226Ra and 210Pb. In farm soils, both nuclides have similar concentrations. The minimum values are comparable to those found in areas of normal radioactivity but the maximum concentrations are tenfold higher. 'Exchangeable' radium in soils ranges from 2.3% to 34.5% of the total. In the vegetables analyzed, 226Ra concentrations are slightly higher than those of 210Pb and the maximum values are also one order of magnitude greater than in normal regions. For both radionuclides, the average soil-to-plant concentration factors are of the order of 10-3 and 10-2, when related to total and to 'exchangeable' contents in soils, respectively. (author)