The radiological impact of discharges of natural radionuclides from a phosphate plant in the United Kingdom

Abstract

Discharges of natural radionuclides in liquid effluents from a phosphate ore processing plant in the United Kingdom (UK) have been made to the Irish Sea since 1954. Recently the plant has begun to import crude phosphoric acid and discharges have been substantially reduced. Environmental monitoring of seafood began in the late 1980s. Initial estimates showed that a high rate of consumers of seafood were receiving exposures of ∼0.3 mSv y −1. In this paper, an oceanographic model is used to hindcast exposures since 1954 and to forecast trends in the future. Using new dosimetric data derived from a human uptake study at this laboratory, exposures of local seafood consumers were cautiously predicted to have risen to 3 mSv y −1 in 1963, peaking at 6 mSv y −1 in 1983 and falling to 0.04 mSv y −1 after the reduction in discharges in the early 1990s. Most of these doses were due to 210Po in crustaceans and molluscs. The model predicts a quick return to near background concentrations in the environment during the early 1990s. Environmental measurements have shown a slower, though significant, reduction in concentrations. External radiation from radionuclides absorbed onto fine sediments is identified as another source of exposure deserving further study. Taking into account the pessimistic nature of the assumptions in the assessment, it is unlikely that exposures exceeded the dose limit of 5 mSv y −1 due to the operation of the plant.