The high rates were found where the concentration of workers was highest. Researchers say that the population mix could have caused an epidemic of childhood infection which, for unknown reasons, led to leukaemia in rare cases.
The findings may also account for the higher than normal number of childhood leukaemias near the Dounreay nuclear reactor and research facility and other clusters near nuclear sites. Dounreay was within the area which was studied.
The findings of the research team, led by Dr Leo Kinlen, director of the Cancer Research Campaign's Epidemiology Unit in Oxford, reinforce the belief that population movement and some unknown strain of infection is the most likely cause of leukaemia clusters near nuclear installations.
In the study, published in tomorrow's British Medical Journal, the impact of 30,000 oil workers has been assessed. It says that thousands of North Sea workers were housed in specially built camps providing a 'striking example of population mixing'. Many came from Tyneside and Teesside, or from Glasgow and the Clyde, with others from the remote Scottish highlands. While few children lived close to the work sites, visits home by adults could have spread the effects of the population mix.
The oil workers were grouped into three categories, depending on the ratio of workers to members of the local working male population. Where the concentration was highest there was a significant increase in leukaemia rates in children aged up to four.
In this age group, researchers found nearly twice as many cases between 1979 and 1983 - 31 when 16.26 would have been expected.
Dr Kinlen said studies have shown that the increased number of leukaemias cannot be attributed to a parent working in the nuclear industry or irradiation of a parent before the child was born. 'Furthermore, other evidence weighs strongly against radioactive discharges as the cause.'
He said: 'The present findings suggest that the excess is due to the population mixing associated with the oil industry causing an epidemic of infection of which childhood leukaemia is an uncommon response.'
Three children aged up to four with leukaemia living within 25 miles of Dounreay were born in the area. But there were no children affected aged more than four. Dr Kinlen said this could indicate that the older children had gained immunity to the unknown infection when younger.Reuse content