210Pb, 210Po, 226Ra, U and Th in arable crops and ovine liver: variations in concentrations in the United Kingdom and resultant doses.

Concentrations of a range of naturally occurring radionuclides have been determined in the same crops grown at two sites in the UK. Ovine liver has also been studied. One site was in an area where concentrations in soil are typical of the UK (the 'control' site) and the other in an area where levels were well above average (the 'test' site). For an average adult consumer of all of the foodstuffs studied, the doses from consumption for the test site were about 4 times higher than those for the control site. However, the differences were small compared with the variability in overall doses from natural background across the UK. 210Pb and 210Po were important contributors to doses for both sites, but at the test site the contribution from 226Ra was also significant. Of the foodstuffs studied, consumption of leafy vegetables and liver gave the highest doses. The doses from leafy vegetables were sensitive to the weather conditions prior to harvesting. Consequently, rigorous monitoring programmes should be based on several samples collected throughout the year; extrapolations based on a single annual sample are unlikely to be reliable.

Speciation of plutonium in potato and the gastrointestinal transfer of plutonium and americium from potato.

Complexation of Pu(IV) and Am(III) by naturally occurring agents such as citrate and phytate might enhance their uptake from the digestive tract. However, the extent to which they enhance the gastrointestinal uptake of actinides from foodstuffs is far from resolved, as this study shows. Investigations of the chemical forms of Pu(IV) and Am(III), by gel permeation chromatography, in simulated digests of potato tubers naturally radiolabelled with 239Pu(IV) and 241Am(III) have shown that neither citrate nor phytate appear to determine their chemical forms. Therefore, it is possible that these are not the complexing anions which determine the gastrointestinal transfer of these radioelements from potato meal. Isotachophoretic analyses of the juices pressed from tubers and solutions prepared by simulated digestion of potato tubers have demonstrated the presence of several low molecular weight anions. These anions might be complexing agents because they possess an isotachophoretic mobility similar to that of citrate; some of these anions remain unidentified. Whereas 239Pu and 241Am were used in the foregoing studies, 238Pu and 241Am were used to produce either in vitro or naturally radiolabelled potatoes for gastrointestinal transfer measurements using rats and hamsters. Gastrointestinal transfer values of 0.13 +/- 0.05% (mean +/- standard error of mean) and 0.16 +/- 0.06% were determined with rats for the uptake of 238Pu and 241Am, respectively, from naturally labelled potato meal. Higher gastrointestinal transfer values were obtained for hamsters: for 238Pu and 241Am the transfer values from naturally labelled meal were 0.25 +/- 0.08% and 0.33 +/- 0.07%, respectively. Similar values were observed for uptake from in vitro labelled potato meal. On the basis of the similarity of the values for the naturally labelled potato meal and for the 'spiked' potato meal it would appear that biological incorporation is not necessary for the binding of the actinides to the ligands which will determine gastrointestinal transfer.