Research shows dangers of chemical mixes

Dr Goran Jamal, a consultant neurologist, has argued that organophosphates (OPs) cause long-term damage to people exposed to the chemicals at work and in their homes. Now he is helping to prepare a court case in the United States which will try to establish whether children suffered from an OP made by the Dow Chemical Company.

Any chemical company will argue that if a product is used safely and at the recommended doses, then there will be no harmful side-effects. But that ignores a new discovery made by scientists in the United States which Dr Jamal suggests could change thinking about the toxic effects of OP chemicals.
At Duke University in North Carolina, Mohammed Abou-Donia, professor of neuro-biology and neuro-toxicology, and his team looked at the effects of a combination of three chemicals on laboratory hens. One of these chemicals – the OP chlorpyrifos – is central to the case involving Dow. The scientists established levels at which the chemicals had no effect on the nervous system of hens when used on their own.

Toxicity levels increase
They also established the lethal dose for chlorpyrifos. Their next finding was extraordinary: when they combined three compounds which had proved to be safe used at the correct levels on their own, the toxicity shot up. ‘When they combined three compounds at safe level for chlorpyrifos and the others, they produced an effect on the laboratory animals which was equivalent to the lethal dose of chlorpyrifos,’ said Dr Jamal, who is at the West London Regional Neuro-Science Centre, part of Imperial College’s School of Medicine. ‘In other words, this combination effect multiplied the toxicity of the available chlorpyrifos by hundreds of times.’
In their laboratory, Professor Abou-Donia’s team had demonstrated an effect for people which groups such as Friends of the Earth have always said happens in the environment: combinations of toxic pesticides are far more damaging than any compound acting on its own. Apart from chlorpyrifos, Professor Abou-Donia’s team used permethrin, a synthetic pyrethroid (SP), and DEET, an insect repellant which Dr Jamal said was not toxic by itself. All three compounds were used by UK and US troops in the Gulf War.

Every-day exposure
‘In real life, arable and livestock farmers in the UK use this sort of combination of products – OPs, SPs and organochlorines – during the year,’ said Dr Jamal. ‘We found this when we visited farms during the Institute of Occupational Medicine study on OPs. Unfortunately, no-one is telling farmers about this combination effect because it has never been tested as part of establishing the chemicals’ safety and there are no hazard warning labels on the chemical containers about this possible effect.’ OPs also contained solvent combinations which are toxic by themselves but their combination effect with the active ingredients is unknown.
When chemicals combine in this way, said Dr Jamal, they have three effects on people: some chemicals bind to enzymes which de-toxify the body and make them unavailable to do their work on other chemicals expressed simultaneously. ‘This is rather like releasing 200 criminals in London and taking away the police officers who are usually on duty,’ said Dr Jamal. ‘There is bound to be some damage.’