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The Mexican government has confirmed earlier reports that transgenic maize is growing within the country’s borders and has apparently contaminated wild varieties, despite a national ban on the cultivation of genetically modified (GM) crops.

A government-commissioned study has shown that as many as 95 per cent of maize fields in the Mexican states of Oaxaca and Pueblo contain evidence of GM ‘contamination’— the highest level yet recorded.

The announcement — made yesterday (18 April) at the biodiversity convention meeting at the Hague, the Netherlands — is the latest twist in a heated scientific and political row over whether or not GM maize is contaminating wild strains in Mexico, the genetic home of maize.

The controversy erupted last November when David Quist and Ignacio Chapela from the University of California published a study in Nature that showed that DNA from GM maize had been found in wild varieties (see GM maize found 'contaminating' wild strains).

The findings have since been widely used by environmental groups and others as confirming the legitimacy of their concern about the potential effects of transgenic crops on plant biodiversity, considered essential for global food security.

But doubts about the scientific validity of the research led the journal earlier this month to withdraw its support for the study, concluding that there was insufficient evidence to justify its original publication of the paper (see Nature backtracks over GM maize controversy).

The new Mexican evidence, however, appears to support Quist and Chapela’s findings, and gives weight to environmentalists’ fears.

“Genetic contamination of wild Mexican varieties is taking place,” Exequiel Ezcurra, president of the National Ecology Institute at the Mexican environment ministry, told the Mexican newspaper La Reforma. “On average, 8 per cent of plants showed signs of GM contamination, although in other fields we found more than 10 per cent.”

The greatest levels of contamination were found near main roads and alongside commercially cultivated maize fields, whereas lower levels were found in more remote areas.

One explanation for the appearance of transgenic varieties of maize is that farmers may have planted maize imported into Mexico from the United States for use in tortillas, unaware that the grain was from GM crops.

According to Ezcurra, the Mexican study is planned to be published in a scientific journal after it has been carefully reviewed to avoid a repetition of the dispute over the scientific validity of the results that has dogged Quist and Chapela’s Nature paper.

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