A new technique for testing DNA could transform civil litigation cases by supporting or refuting people’s claims that their health has been damaged by exposure to toxic chemicals.

Samples of DNA are taken from a healthy person and exposed to the chemical in question to see which genes are affected. This is then used as a blueprint against which a claimant’s DNA can be compared.

The technique is expected to transform the quality of evidence in civil cases. It could dramatically reduce the time it takes to settle cases where miners, industrial workers and others seek compensation for illnesses caused by exposure to asbestos, coal dust or other environmental toxins.

Such cases can often run for decades, or rely on evidence only available from a postmortem examination.

DNA evidence from living persons could also potentially eradicate false claims, ensuring that compensation is paid only to those whose health has actually been affected.

Last night solicitors welcomed the advance, saying that DNA evidence could provide a “litmus test” for compensation claims. It will be up to individual judges to decide, case by case, if such evidence is admissible.

Claims for diseases caused by asbestos are rising and not expected to peak until at least 2010.

Pat Troop, chief executive of the Health Protection Agency, told The Times recently that with more than 100,000 chemicals currently circulating in the environment, the lack of knowledge of the health impact was a serious concern.

It is one of the key topics to be discussed at the agency’s annual conference, which takes place this week.

Bruce Gillis, the scientist who developed the technique, said that it would allow some people to win cases they might otherwise have lost, while others would find themselves with no case because their diseases were not caused by the chemicals to which they were exposed.

While DNA evidence is a mainstay in criminal prosecutions, it makes very rare appearances in civil courts – such as when victims of rape or other crimes sue their alleged attackers.

In California, courts have heard more than 20 cases that used evidence from the technique, developed at the University of Illinois College of Medicine by Dr Gillis and his colleagues.

In one case, a worker at a company selling tyres sued his employers alleging that he had suffered illness as a result of exposure to benzene. Liberty Mutual, the employer’s insurers, spent $12,500 on the test, which proved that his illness was not caused by benzene, saving an estimated $2 million (£1 million) in damages.

In other cases, the DNA technique worked to the benefit of claimants. “A man had been exposed to a mixture of eight chemicals and developed gall bladder cancer,” Dr Gillis said. “None of the chemicals was a carcinogen on its own, but we showed that in combination they increased the activity of cancer-causing genes.

“This was a case where we truly answered an important question. The man’s heirs won the case – he, unfortunately, had already died.”

The technique, called msds1, uses commercially available DNA micro-arrays to work out which of thousands of genes are affected by exposure to a certain chemical. The arrays consist of thousands of pits containing fragments of DNA which highlight the effects of dangerous chemicals.

For example, benzene – a common pollutant found in petrol that can cause leuakaemia – was found to affect about 150 genes, half of which were increased in activity (upregulated) and the other half reduced (down-regulated). The pattern of activation provides a “fingerprint” of how benzene affects blood cells. This can then be compared with the pattern found by testing the plaintiff’s blood cells. If they match, the plaintiff’s injury was caused by benzene; if not, it was not.

The court can be shown a simplified graphical display of the genes that are affected, laid alongside the results from the plaintiff. A match or lack of a match is plain to see.

Dr Gillis can also trace the pattern of release of signalling chemicals called cytokines triggered by an injury or an exposure to a chemical. In one case in the US, a nurse said that an injury was causing her such extreme pain that she could not work. However, tests showed that she was not expressing the cytokines that would be triggered by pain, enabling the defence to claim successfully that the pain did not exist.

Apart from the cost of testing and judges’ discretion, there would be few impediments to using similar evidence in a British court, lawyers said.

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