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Volume 109: debated on Saturday 2 May 1987

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asked the Secretary of State for the Environment if he will list the 20 areas in England and Wales with the highest levels of naturally occurring radioactivity and the reasons why these levels occur in the areas concerned.

The largest source of exposure to naturally occuring radioactivity in England and Wales is from the build-up of radon gas in houses. For the country as a whole, the mean annual dose is 1 milliSievert per year (mSv/y). Higher than average doses arise because of geological factors, particularly the natural uranium content of the ground, and the permeability of the rock and soil to radon. The National Radiological Protection Board has been carrying out national and regional studies to identify houses where radon gives rise to high annual doses of radioactivity. The results are not necessarily representative of the housing stock as a whole in the area, as they represented a deliberate attempt to identify houses with high radon concentrations. But the areas identified by the NRPB with the highest mean indoor exposure to radon products are:

Location and CountyGrid SquareNumber of dwellings surveyedMean annual dose (mSv/y)
Eastern part of Sedgemoor, SomersetST 43156
North-eastern edge of Dartmoor, DevonSX 88441
Coast area of Mount's Bay, CornwallSW 52240
North-eastern edge of Dartmoor, DevonSX 781138
Coas area near Tintagel Head, CornwallSX 09137
West of St. Austell, CornwallSW 952135
Northern part of Dartmoor, DevonSX 68131
Northern edge of Dartmoor, DevonSX 79228
West of Truro, CornwallSW 74627
South of Camborne, CornwallSW 631327
Eastern edge of Dartmoor, DevonSX 771125

Location and County

Grid Square

Number of dwellings surveyed

Mean annual dose (mSv/y)

Northen part of Bodmin Moor, CornwallSX 18623
Southern edge of Dartmoor, DevonSX 651022
Central part of Dartmoor, DevonSX 67622
South-western edge of Dartmoor, Devon and CornwallSX 46221
Northern edge of Dartmoor, DevonSX 69520
Coast area north of St. Agnes Head, DevonSW 751419
Eastern edge of Dartmoor, Devon and CornwallSX 47618
North of Penzance, CornwallSW 43617
South-eastern edge of Dartmoor, DevonSX 761016

The fewer the number of dwellings surveyed, the less reliance should be given to the result.

Radon gives rise to doses of alpha radiation. The presence in the ground of minerals with radioactive content can also give rise to naturally occurring gamma radiation, but the doses received are much lower: the highest in England and Wales being less than 1 mSv/y.