OZONE, as well as causing breathing difficulties, could give you cancer. Government researchers in the US have uncovered the first serious evidence that the highly reactive gas, which is used in industry and which forms photochemical smogs in summer, might be carcinogenic. Although British government advisers are playing down the findings, Germany鈥檚 health and safety scientists are recommending that ozone should be reclassified as a 鈥渟uspected carcinogen鈥�.
A study for the US Department of 午夜福利1000集合鈥檚 National Toxicology Program, funded partly by the car industry, found 鈥渟ome evidence of carcinogenic activity of ozone鈥� in female mice. Females that inhaled air containing 2000 micrograms per cubic metre of ozone for two years developed tumours of the lung and bronchial tubes at twice the rate of female mice that inhaled no ozone. Smaller increases in cancer rates were found among females exposed to 1000 micrograms per cubic metre.
Although the same exposures produced an increased incidence of cancers in male mice, the trend was 鈥渓ess striking鈥�. The researchers found no evidence of a carcinogenic effect in rats. 鈥淭here appears to be a consistent increase in the incidence of pulmonary neoplasms in mice with increasing ozone exposure, and it is more pronounced in females than in males,鈥� they conclude.
Advertisement
But in Britain, the 午夜福利1000集合 and Safety Executive鈥檚 latest review of occupational ozone exposure, published this month, plays down the American results, arguing that it 鈥渟howed no carcinogenicity in rats and male mice and only equivocal response for lung tumours in female mice鈥�. The HSE has decided not to classify ozone as a carcinogen, and in fact plans to abolish the present limit of 200 micrograms per cubic metre averaged over eight hours for people who are exposed to ozone at work.
At the same time, because ozone is a known lung irritant, the HSE wants the present exposure limit averaged over 15 minutes to be reduced from 600 micrograms per cubic metre to 400. According to the HSE, welders and some workers in the water, printing and food industries can be exposed to ozone. Office workers who use photocopiers are the largest group at risk. If photocopiers are kept in poorly ventilated rooms, levels of ozone can reach 1000 micrograms per cubic metre. 鈥淲e have considered the very limited evidence in the US report and we think that our proposed new limit should be adequate,鈥� says a spokesman for the HSE.
By contrast, the German government鈥檚 scientific advisory committee on occupational health standards says that the American findings have convinced it to recommend that ozone be redefined as a 鈥渟uspected carcinogen鈥�. In standards due to be published in July, the committee will press for Germany鈥檚 eight-hour occupational safety limit of 200 micrograms per cubic metre to be lowered, although it will not recommend a specific alternative.
There is not enough evidence on ozone鈥檚 carcinogenicity to support a specific standard, says one of the committee鈥檚 toxicologists, Hermann Kappus of Berlin University鈥檚 Virchow Clinic. But he expects the German government to take a political decision to tighten the existing limit. He says that there is also laboratory evidence that ozone can damage DNA in mammalian cells. 鈥淲e must take these indications of a carcinogenic effect seriously,鈥� Kappus says.
Kappus says that one potential problem, to which little attention has been paid, is the ozone concentrations that passengers and crew are exposed to in high-flying aircraft. Air circulated in the cabins of modern aircraft is taken from the stratosphere, where ozone concentrations can be high. The German airline Lufthansa says it introduced catalytic converters six years ago to reduce ozone intake on its long-haul flights. British Airways cannot say what the ozone levels in its aircraft are, but insists that they are 鈥渘ot a problem鈥�.
The American study, which became available to health and safety experts in Europe two months ago, found no significant evidence of carcinogenic effects on mice exposed to 240 micrograms of ozone per cubic metre of air. Because of ozone鈥檚 ability to cause breathing difficulties at such levels, the WHO鈥檚 safety guideline is 100 micrograms per cubic metre 鈥� a concentration that is often exceeded during long sunny spells in Europe. Ozone is a particular problem during still summer weather because the gas is generated by the action of sunlight on hydrocarbons and nitrogen oxides in traffic fumes.
Levels of up to 240 micrograms per cubic metre were measured in Britain and Germany during the hot spell in the first week of May. In response to public anxiety, German federal environment minister, Angela Merkel, promised action before the end of this month. She wants to ban older, dirtier vehicles whenever ozone concentrations exceed a certain limit.
But what the trigger level might be and what exceptions might be allowed are the subject of fierce dispute in the German Cabinet. Last week, objections from the industry minister G眉nter Rexrodt and the transport minister Matthias Wissmann, forced Merkel to cancel a press conference at the last minute, just as she was about to announce details of her proposals.