|In 1995, The Scottish Office Environment Department commissioned a multi-disciplinary research team at the University of Aberdeen to assess the implications of radium contamination at Dalgety Bay, to consider the level and risk which it presents to members of the public in relation to acceptable levels and to review the options for reducing the contamination if that were necessary.|
- The majority of those using the area surveyed by the research were local people visiting it for recreational activities. No particular group was identified as being at greater risk than any other but some parts of the area surveyed were visited far more than others.
- There were variations in the ambient radiation dose rate values measured at Dalgety Bay but these were found to be well within normal levels.
- The highest ambient dose rate found at Dalgety Bay was only two-thirds of that found naturally in Aberdeen.
- The radium contamination is not present as a layer in the sediment but is randomly distributed as particles.
- The number of radioactive particles found in the area surveyed was very small and thus the risk of coming into contact with such a particle is very low.
- The risk of inhalation of a radioactive particle is very low because most particles in the foreshore material are not small enough to inhale.
- The maximum fatal risk per year from inhaling or swallowing a radioactive particle to any user of the area surveyed was negligible and was calculated as clearly less than one in a million.
- Skin contact with a particle for an extended period could produce a very small burn similar in nature and severity to a fire ash burn of a similar size.
|The radium contamination of Dalgety Bay was originally found in 1990 and particles were removed as far as possible. The contamination was in the form of active particles containing radium-226 which were associated with clinker-like material. Radium-226 is a naturally occurring radioactive element which can be found throughout the rocks and soils of Scotland. Areas with igneous rocks such as granite tend to have higher levels than others. The Radium-226 contamination at Dalgety Bay, however, was not naturally occurring as the radium had, for some purpose, been concentrated before incineration had taken place. Subsequent monitoring identified a small but recurrent problem in that some new particles were found in areas from which particles had previously been removed. A research programme was therefore instigated in 1995 to look at the radium contamination and to suggest possible ways forward.|
|About the research|
|The research involved a survey of usage to provide a detailed profile of patterns of use and type of user; a field survey and sampling programme to identify the current extent and distribution of radioactive contaminated materials; laboratory studies to determine the chemical content of the samples taken from the area, and leaching studies to establish how long it would take for the radioactive components to dissolve out of the particles found when exposed to sea water and hydrochloric acid. In the light of these data an assessment was made of the maximum risk members of the local community were exposed to should they inhale or swallow a contaminated particle. These have been compared to a target risk suitable for use in environmental contamination situations.|
|The usage survey which took place over a 6 week period in the summer of 1995, involved an observational survey of patterns of usage, and the interviewing of a sample of users in the area. The survey allowed any areas with a higher likelihood of occupation or any activities with a higher potential for exposure to the contaminated particles to be identified. Care was then taken to cover these areas and activities in some detail during the fieldwork to ensure that a full assessment could be made of any risk associated with them.|
|The areas originally designated for the survey were restricted to the woods and the foreshore in front of them, the public car park and paths around the boat-house and the slipway area in front of the boat-house. Following the usage survey and to answer local queries, the area surveyed was extended to include the sandy area in the harbour. In total, some two-thirds of the foreshore at Dalgety Bay was intensively surveyed. The field survey and sampling programme was undertaken in October 1995 with a second visit to the site in December 1995. The survey measured both the sediment activity and the ambient dose rate in the areas identified. Areas of sediment which gave an anomalous reading were further investigated to establish the exact location and depth of the source. Where possible, the source was then taken to the laboratory for further analysis. Core samples were also taken to determine the particle size and depth distribution, if any, of the contamination.|
|The risk to the population from ingestion of radium-226 varies with age. The research therefore evaluated the risk for 3 representative age groups - adults, 10 year old children and one year old infants. A target risk figure of a risk of death of one in a million was adopted as the figure below which people consider the risk to be of little concern. This figure takes account of both the risk of swallowing or inhaling a particle and the risk of death should the event occur.|
|The majority of those interviewed were regular users from the local area and tended to use the area throughout the year. The most common activities found were watching boats (44%), walking (40%), walking the dog (38%), sitting on the beach (33%) and sailing (29%).|
|Field survey and sampling programme|
|The radiation readings taken did not vary significantly between the land and the foreshore sites, with lower readings noted on the mudflats. Only a very low proportion of fines (particles small enough to inhale) were found in each sediment sample, which suggests that there would be a low risk of members of the public inhaling fine material. The depth distribution of the sediment showed no distinct patterns of radium-226 distribution, indicating that contamination is not present as a layer, but is more randomly distributed as particles.|
|Physical Turbulence etc|
|The intertidal sediments and foreshore may be affected by tidal patterns in the bay. Increased wave action (eg during storms) may erode the bank and redistribute contamination or break it into smaller particles. Sediment can be turned over by burrowing organisms, or by human activity such as bait digging, which creates the possibility that contaminated particles under the surface can be moved to the surface and into the water column. Major engineering works which involved excavation of any areas would expose the workers involved to an elevated risk of inhalation or swallowing a particle.|
|It was not possible to identify the actual source of radium activity as the samples studied showed that the material had been thoroughly incinerated, which had largely destroyed its original physical form. The presence of copper in samples suggests that electrical items may have been combusted, whereas the presence of part of a porcelain crucible in one sample could suggest that laboratory techniques were also being used in the work area. Leaching studies showed that progressive slow solubilisation of the radioactive species was taking place, indicating therefore that the contamination activity can be expected to diminish slowly as a result of dissolution. These leaching studies also measured the amount of radium-226 which could be released following swallowing of a particle by the hydrochloric acid which is found in the stomach.|
|It is not possible, due to the inhomogeneity of the material, to suggest a rate for the dissolution, but if, for example, the material collected is about 50 years old, it is likely that leaching will require centuries to dissolve and disperse the radioactive components.|
|Assessment of potential risk to humans|
|The ambient dose rates measured in the area were found to be well below those measured in other parts of Scotland (two-thirds of those measured in Aberdeen) and are therefore of no concern. Application of a worst case scenario indicated that the doses that could be received following the swallowing or inhalation of a particle were not negligible. These doses were, however, no more than those that could be received during some diagnostic x-ray examinations. When the risk of actually inhaling or swallowing a particle is also taken into account the total risk of death in a year is clearly less than the one in a million target risk for all 3 groups considered. Consideration of the effect a particle would have if left on the skin for 24 hours, indicated that a small radiation burn may be produced. This burn would be very similar in severity and nature to an ember burn from a wood fire.|
|Options for action|
|Although the target risk of one in a million was not exceeded, the research team recommend that some precautionary measures should be undertaken which would further reduce all risks and might allay any remaining public concern.|
|Several sediment treatment options are available for radioactive contamination, including extraction of the soil, soil washing, biological treatment, covering with a top layer of material, restricting access to the site and a clean-up of accessible particles.|
|Restriction on access to the Dalgety Bay foreshore is, in the light of the research findings, considered unnecessary. However, the research team recommend that: |
- an intensive survey/decontamination exercise is undertaken to locate and remove as many of the particles as possible and to understand further the extent of the contamination.
- systematic monitoring should be carried out, perhaps on a yearly basis, to ascertain radioactive contamination levels in the area.
- during any decontamination work or work activity which involves digging or disturbing the sediment, normal precautions should be employed to reduce the risk of workers ingesting or inhaling particles that may be present.
|"Assessment of the Implications of Radium Contamination of Dalgety Bay Beach and Foreshore", the research report summarised in this Research Findings, may be purchased (price £10 per copy).|
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|Further copies of this Research Findings may be obtained from: |
The Scottish Office Central Research Unit
Area 2J CRU
Telephone: 0131-244 7562