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New analysis links dioxin to cancer

作者:艾灯籍    发布时间:2019-03-04 07:14:04    

By STEPHANIE YANCHINKSI CAREFUL detective work by a West German epidemiologist may have established the first clearcut evidence of a direct link between exposure to dioxins and cancer in humans. Friedemann Rohleder, an independent specialist, has produced a report detailing an unexpectedly high incidence of cancer among workers exposed to dioxins during an industrial accident at a chemicals plant in 1953. The plant, operated by the West German company BASF, made trichlorophenol. Rohleder claims the company presented the data in a way that disguised the cancers. Dioxins, unwanted chemical by-products of many combustion processes, poison some laboratory animals outright, and can cause cancer in others. Large doses of dioxins cause chloracne, a serious skin ailment, in humans. Partly because they have always had to rely on unreliable data, toxicologists have never established unequivocally whether exposure to dioxins can give people cancer or other long-term sickness. The incident which Rohleder reviewed occurred on 17 November 1953 after a runaway chemical reaction at a plant operated by BASF in Ludwigshafen. The reaction released dioxins into the factory and its neighbourhood. An investigation of the mortalilty records of the exposed workers published in 1985 on behalf of the Born Berufsgenossenschaft (BG) – the industry association which handles liability claims – became the foundation for refusing compensation to workers. It dismissed associations between exposure to dioxin and cancer. The BG report rekindled controversy about dioxin within the German scientific community, and spurred victims and their families to take their cases to the courts. Eventually, the government invited Rohleder, an epidemiologist, to evaluate the evidence independently. The report of his findings provoked controversy at an international symposium on dioxins in Toronto, Canada, late last month. Rohleder compared three sets of data: one, from BASF’s medical department, formed the basis of the pivotal study in 1985 for the BG; a second, from the state medical officer of commerce, was based on earlier data collected by the BG; and a third set recently collected by the BG in response to a growing clamour to re-examine the evidence. All sets of data originated from the medical departments of BASF. The data for the original BASF study mentioned 153 workers classed as having been exposed to dioxin. The most recent data say that only 122 people were exposed. Rohleder compared the medical histories of individuals on both lists, and concluded that BASF included in its list 20 supervisors who he believes were not exposed. Another such comparison revealed that the company listed 18 workers as suffering from dermatitis – a milder skin infection – when the BG reported clear cases of chloracne, a sign of dioxin poisoning. The study gauged exposure to dioxin by examining the severity of the skin disease. But Rohleder says that because many of the skin ailments were ‘misclassified’, the investigators found no clear relationship between exposure and skin disease. They then argued against any relationship between dioxin exposure and cancer mortality, although their own research revealed an unexpectedly high incidence of deaths from cancer in the group with chloracne. In his own evaluation, Rohleder investigated BASF’s 153 workers but eliminated the 20 supervisors. He also eliminated the only two women in the sample, making the final group sufficiently uniform for standard epidemiological analysis. Rohleder grouped together neoplasms of the larynx, trachea, bronchi and lung and other cancers of the respiratory organs. He observed 8 deaths from cancer, instead of the expected 3.01, giving a statistically significant standardised mortality ratio of 2.66. By adding cancers of the digestive tract in a similar fashion he found an identical ratio. Despite the small size of the sample Rohleder concludes that: ‘This analysis adds further evidence to an association between dioxin exposure and human malignancy.’ When contacted by New Scientist this week,

 

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