Wristwatches of the sort given to servicemen during the Second World War can emit radiation far above safe levels, according to new research by experts from the University of Northampton and Kingston University.
The paints used to make their dials glow in the dark are known to emit radon gas – and this work is the first to determine just how harmful such items can be.
Radon exposure is a leading cause of lung cancer deaths, and the fear is the families of ex-serviceman or collectors might be at risk from such time pieces.
In this study, a collection of 30 antique, radium-dial watches gave rise to radon concentrations 134 times greater than the UK’s recommended ‘safe’ level when kept in a space the size of a typical boxroom.
In addition, three of the watches in poor condition gave rise individually to radon concentrations – when kept in the same poorly ventilated room – well in excess of the threshold where Public Health England would recommend remediation.
The authors, Dr Robin Crockett, University of Northampton, and Professor Gavin Gillmore, Kingston University, warn these levels are high enough to be dangerous even in much larger spaces, such as whole houses.
Dr Crockett said: “These results show that the radon emitted from individual watches can potentially pose a serious cancer risk. This is of concern because in addition to military watches being particularly prized by collectors, many individual radium-dial watches are kept as mementoes by ex-servicemen and their descendants.
“They have the potential to pose a significant health hazard to themselves and their families. Smokers are particularly at risk.”
Professor Gillmore, who is Head of Energy at Kingston University, added that due to the age and condition of many of the watches in this study, opening up such watches without taking appropriate precautions is not recommended.
“Loose paint fragments will contain radium particles which could be ingested,” he said. “As this is a strong alpha emitter there is a potentially serious health risk for those who do this.”
Radon is a colourless and odourless radioactive gas, formed by the radioactive decay of small amounts of uranium that occur naturally in all rocks and soils. It often seeps into homes where it can then reach dangerous levels.
In the UK, radon is the second biggest cause of lung cancer deaths after smoking, with over 1,100 fatalities every year.
This new study looked at potential sources of radon gas found within the home.
It found granite (as used in kitchen tops or door stops), a uranium glass dish, and an art deco-inspired Fiesta-ware ceramic teapot were all found to be within safe levels.
However, the dials on bedside clocks, compasses, and airplane instruments from the period will all be radioactive, if they too were manufactured using radioluminescent paint, said Dr Crockett.
“The watches tested were a mix of British, Swiss and American made items, manufactured between the nineteen twenties and sixties, but we know these sort of paints were used into the seventies,” he added.
“There are potentially millions of these watches in circulation.”
The entire watch collection gave rise to a hazardous radon concentration approximately 67 times the Domestic Action Level of 200 Becquerels per cubic metre (Bq/m3), and more than 130 times greater than the Domestic Target Level.
Three watches in particularly poor condition gave very high readings.
A Swiss-made pocket watch gave an individual reading of more than 1,200 Bq/m3,whilst two of the wristwatches gave rise to hazardous radon concentrations in excess of 200 Bq/m3 each.
The average radon level in UK homes amounts to 20 Bq/m3 which for most people is about half their total radiation exposure.
Public Health England recommends that radon levels should be reduced in homes where the average is more than 200 Bq/m3, preferably to 100 Bq/m3 or less.
The study is published as part of a recently released volume from the Geological Society entitled ‘Radon, Health and Natural Hazards’, the culmination of a five year global project funded by UNESCO, the International Union of Geological Sciences, and the International Geoscience Programme.
The initiative brought together scientists with an interest in radon from over 20 European countries, the Americas, Asia and the Middle East.