By Ruth Pollard
IT'S toxic enough to be classed as a carcinogen, but the jury is out on whether the gas ethylene oxide is behind what residents say is an unusually high rate of childhood cancers in a northern beaches area.
Under normal circumstances, there would be little prospect of children being exposed to the gas, said Bruce Armstrong, a professor of public health and medical foundation fellow at the Sydney Cancer Centre at Royal Prince Alfred Hospital.
Most exposure occurs in the workplace, and therefore, in adults, meaning there was no data available on the effects of exposure to the toxin in children, Professor Armstrong said.
"There is not one bit of evidence of this causing childhood cancer. However, there was sufficient evidence in experimental animals that it caused cancer [and] limited evidence in humans from occupational studies," he said.
The toxin causes chromosomal damage in animals and in exposed workers, leading the International Agency for Research on Cancer to declare ethylene oxide a carcinogen.
It was difficult to tell whether the seven reported cancer cases in the Mona Vale, Warriewood and Bayview area were related to the elevated emissions coming from the Unomedical plant, Professor Armstrong said.
"I couldn't be sure if there is a concentration of childhood cancer in the area or not … However, one puts more weight on more of a single kind of cancer."
In this instance, there was a case of leukaemia, and one of the rarer Ewing's carcinoma close to the Unomedical site, while a handful of other childhood cancers had been diagnosed in the surrounding areas over the past decade.
Leukaemia and lymphoma were the only two cancers linked to exposure to ethylene oxide, Professor Armstrong said.
Parents had a natural tendency to search for reasons for their child's illness, he said.
"Everybody is looking for an explanation for their cancer, but in kids you are always going to be saying, 'Why, why my kid, what happened?"'
Experts define a cancer cluster as a greater than expected number of cancer cases within a group of people, a geographical area or over a period of time.
Yet it was difficult to know when a number of cases concentrated in a particular area warranted an investigation into possible underlying causes, Andrew Penman, the chief executive officer of the NSW Cancer Council, said.
"Until you have done a formal analysis of the difference in rates between different areas and determine that it is so far beyond the realm of chance that it requires further investigation, you are not even at first base," Dr Penman said.
"Most clusters that are investigated are generally found to have no observable cause … it is a very, very frustrating area."