NRPB-W49: Non-technical summary

Non-technical summary

Models are often used to assess the radiation dose to man from radionuclides in the environment. One example would be the authorised discharge of naturally occurring radionuclides. This is because the discharges might not add significantly to the concentrations of these radionuclides already in the environment, and so assessments could not then be based simply on measurements. Some of these models use transfer factors (TFs) to predict the movement of radionuclides along environmental pathways. TFs are simply quotients of activities in the relevant media at equilibrium. For example, the soil-to-crop TF is the activity concentration in the crop divided by the activity concentration in its associated soil, expressed on a fresh or dry mass basis.

In this review, a range of naturally occurring radionuclides was considered and published information on TFs was compiled. The study was confined to transfer along the soil-crop and feed-animal pathways. The evaluation also included studies of the transfer of activity into the plant after it had been deposited on to the surfaces of outer leaves - a process known as translocation.

Naturally occurring radionuclides have not been studied to the same extent as their man-made counterparts. About 190 potentially useful individual references were located and the data were critically reviewed. In some cases the original authors were contacted to obtain clarification or additional information. Only those studies where the environment was similar to that of the UK were used to derive best-estimate values. In practice, this meant that less than 30% of the publications provided useful information. For many types of crop, only a few datasets could be located, and even fewer data could be found for the transfer of feed to animal products.

The best estimate values produced from this review were compared with the current values and assumptions used in FARMLAND, the model used by NRPB to predict transfer along terrestrial foodchains. The comparison indicated that in some cases changes in TF values need to be considered, and that the assumptions regarding the translocation of polonium (Po) and lead (Pb) should be revised. The review also enabled some important research requirements to be identified.

Last reviewed: 1 September 2009