Mixing between GM and non-GM varieties has already caused serious economic losses for producers in lost sales and exports. But the consequences of mixing will be much more serious with new crops that are altered to produce pharmaceuticals and industrial chemicals, the scientists argue. The crops could harm human health and be toxic to wild animals.
"What would be the impact societally, economically if for example, cornflakes were contaminated by some sort of drug or chemical? I think it would be a vast impact economically," said Karen Perry Stillerman, senior food and environment programme analyst with the Union of Concerned Scientists.
"I think it's really hard to say [what impact contamination would have] because there is a variety of different drugs and chemicals that might be manufactured in plants this way," she added. "Our perception is that some of them might be toxic, but all of them would certainly cause tremendous economic upheaval."
The group presented its findings at the American Association for the Advancement of Science conference in Boston.
Huge research effort
Up to now, commercial GM varieties have been restricted mainly to modifications for herbicide tolerance or resistance to pests. But a huge research effort is going into a new generation of crops that are genetically modified to produce drugs, hormones, vaccines and industrial chemicals such as the precursors of plastics.
Although public opinion in Britain and the rest of Europe remains firmly against GM crops in general, it is more favourable to crops with medical benefits. But the Union of Concerned Scientists said that these are precisely the crops that pose the greatest risks if they exchange genes with wild relatives or conventional versions of the same crop.
So-called "pharma crops" can offer advantages over current methods of drug manufacture. Vaccines produced this way could be grown cheaply in developing countries and simply given to patients in the food. That would remove the need for sterile needles and refrigerators to keep vaccine doses cold - a major obstacle for delivering therapies in poor countries.
Prof Paul Gepts, a plant geneticist at the University of California, Davis, said past experience suggests that "contamination" events cannot be avoided. "Gene flow is really a regular occurrence among plants. So if you put a gene out there it's going to escape. It's going to go to other varieties of the same crop or to its wild relatives," he said. "It's clear that zero contamination is impossible at present."
Major economic losses
There have been a handful of examples in the US and elsewhere of genes from GM varieties not cleared for human consumption getting into nearby food crops and hence the human food chain. This has led to major economic losses for producers in lost sales, exports and clean-up costs, but there have been no proven cases of damage to human health.
"With the products we are talking about, there's the potential for that to be much more serious than what we have seen so far," said Prof Robert Wisner at Iowa State University.
According to Gepts, most of the ideas for keeping crops apart are inadequate, because pollen and seed are carried on the wind, by animals and birds and on farm machinery. He said the only way to be sure that food crops would not be contaminated by drug genes or genes for industrial chemicals would be to use non-food crops such as tobacco.
Alternatively, GM food plants could be grown in greenhouses or underground to prevent pollen escaping, he said.
Call for ban
The Union of Concerned Scientists is calling on the US Department of Agriculture to ban the growth of GM pharma crops outdoors unless they are species that are not eaten by people or livestock.
The USDA is currently putting together new guidelines on GM that are expected to be completed by the end of the year. Currently, no GM crops that produce industrial chemicals or pharma crops are grown commercially, although there are some field trials under way in the US.
Similar issues will apply in the UK and Europe if pharma crops are approved. So far, though, only a handful of GM crop varieties are grown in Europe.
© 2008 The Guardian