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The biggest experiment ever carried out to evaluate the environmental impact of genetically modified (GM) crops has concluded that it is impossible to draw a general conclusion about whether such crops are safe or dangerous for wildlife.

The researchers who carried out the experiments – the findings of which were announced in London today (16 October) – say that the impact depends on a variety of factors, including the specific genetic traits introduced into the crops, and the way in which herbicide use is altered.

While they found that, in some cases, the use of GM crops reduce the amount of wildlife, in other cases –  namely the use of GM maize – wildlife was actually increased.

But the researchers emphasise that any judgement of the environmental impact of GM crops can only be made on a case-by-case basis. And they add that this applies as much to developing as to developed nations.

These conclusions have emerged from a comprehensive set of farm trials that were launched in Britain three years ago and carried out at about 60 sites across the country in an attempt to address concern about the potential impact of GM crops on the environment.

The researchers studied three different crops – oilseed rape, beet and maize. They looked at the impact on local biodiversity (for example on natural vegetation and on bird and insect life) of growing conventional varieties of each crop compared to varieties that had been genetically modified to resist weed-killers.

In the case of oilseed rape and beet, they found that the farming practices involved in growing the GM varieties were more harmful to many groups of wildlife than growing the conventional varieties, as the practice led to a greater reduction in the natural vegetation that such wildlife requires.

In contrast, the cultivation of GM varieties of maize caused less overall damage to the natural vegetation (as it resulted in reduced weed-killer use) and therefore proved to be beneficial to the local wildlife, which used such vegetation for food and shelter.

"The results of these studies reveal significant difference in the effect on biodiversity when managing genetically modified herbicide-tolerant crops, as compared to conventional varieties," said Les Firbank of the Centre for Hydrology and Ecology, who co-ordinated the project. "One important conclusion is that each new application of GM crop technology must be looked at on a case-by-case basis using a rational, evidence-based approach."

The results of the studies of the GM oilseed rape and beet crops have been quickly picked by anti-GM groups in the United Kingdom, who argue that it confirms their fears that the widespread use of such crops in Britain would have a damaging, and irreversible, impact on the countryside.

"If we grow herbicide-tolerant crops here, it may be the final nail in the coffin for some species," says Sue Mayer, director of GeneWatch UK. She points out that the new results contrast sharply with the conclusions of government science advisors in 1997 that GM oilseed rape presented no threat to the environment.

In contrast, the results have been welcome by the agri-biotech industry, who argue that they vindicate its own position that it would be wrong to apply a blanket ban on all GM crops in Britain, and that each proposed crop should be judged individually on its potential environmental impact.

"These results confirm that the flexibility of GM crops allows them to be grown in a way that benefits the environment," says Paul Rylott of the Agricultural Biotechnology Council. “These studies show that claims that GM crops will wipe out our wildlife are not supported by the evidence. On the contrary, they show that GM crops are more flexible and can enhance biodiversity."

John Pidgin, the manager of one of the set of trials, says that although it would be wrong to extrapolate the results of the trials directly to developing countries, the main implication – that the impact of a GM crop depends heavily on the specific characteristics of the crop and the way that it is grown – remains valid.

Click here for more details on the trials (including the full text of the papers)
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