Radiological assessment of the ribble estuary—II. Beta and gamma dose rates and doses to critical groups

The mean background beta dose and gamma kerma rates measured in the Ribble Estuary were 0.16 ± 0.14 μSvh−1 and 64 ± 8.5 nGyh−1, respectively. Maximum total dose rates arising from radionuclides discharged from BNFL Sellafield and Springfields were 130 nGyh−1 in air for gamma emissions at 1 m above the sediments and 19 μSvh−1 to skin for beta emissions at 30 cm above the sediment. The maximum gamma air kerma rate was principally comprised (64%) of Sellafield-derived radionuclides and was located on the established salt marshes. The beta dose is almost entirely (95%) due to Springfieldsʹ derived radionuclides and is associated with fine-grained sediments in the upper reaches of the estuary. By means of posted questionnaires, time-lapse video photography and person-to-person questioning, the habits of the people who use the Ribble Estuary principally for recreation were assessed. The results were used to calculate the effective dose and organ doses from external irradiation and inhalation exposure to radioactivity originating from both Sellafield and Springfields discharges. The maximum excess dose was 73 μSv year−1 for a walker and bird-watcher with an occupancy of 2080 h annually. This is half the dose received by the critical group (house boat dwellers) identified and assessed by MAFF. All other excess doses were below this value.