Temporal changes in gamma dose rates in the Esk Estuary, UK

Over the last 30 years there has been a reduction in the radioactive discharges from the UK’s Sellafield site. Radionuclide activity concentrations in the environment around Sellafield have declined as a result. However, routine monitoring results from the nearby Esk Estuary show a less clear trend, with fluctuations in gamma dose rate measurements being reported from year to year. A comprehensive survey (n = 576) of gamma dose rates in the Esk Estuary was undertaken in 2007 and the data compared to a similar survey carried out in 1989. There was a highly statistically significant decrease in the external gamma dose rates within the Esk Estuary between 1989 and 2007. The measured total gamma dose rate range in 2007 was 0.064 – 0.235 Gy h−1with a mean of 0.123 Gy h−1. This equates to a maximum exposure of 0.200 Sv h−1. There was no evidence of large-scale sediment redistribution under current conditions. However, there was limited evidence to suggest that part of the reason for the reduction in measured dose rates was the burial of contaminated sediment deposits by uncontaminated sediments transported by tidal processes.