Determination of the transfer of tritium to crops fertilised with contaminated sewage sludge

Authorised discharges of radionuclides into sewers can result in contamination of the sludge, and so provide a pathway by which radionuclides can enter the foodchain. Specific data on the uptake of radionuclides from sludge amended land into crops is scarce. A study has been undertaken to generate data on tritium uptake by crops grown in soil amended with tritium contaminated sewage sludge using a range of soil types and crops common to the UK. The study was performed over two years. The concentration of tritium in soil fell throughout the study. It was therefore not possible to quantify individual soil to crop transfer in terms of conventional concentration ratios. Instead, an aggregated transfer quotient was estimated relating the concentration in the edible part of the crop in Bq kg-1 to the original amount of activity applied to the soil in Bq m-2. The values obtained were broadly similar at for all crop and soil types studied, being about 2 10-4 m2 kg-1. The observed values depend on factors such as temperature and rainfall, and so they should not be used in generalised radiological assessments. They are however indicative of the small amounts of tritium transferred to crops from amended soil.