A Swiss company accidentally sold unapproved genetically modified seed corn in the US for four years. The mistake resulted in about 133 million kilograms of the corn making its way into the food chain.

Officials for the company, Syngenta, and the US Environmental Protection Agency insist there is no danger to human health. But the EPA and the US Department of Agriculture are investigating to see if any laws or regulations were broken. The EPA confirmed the investigation was underway in a statement to the journal Nature.

Between 2001 and 2004, Syngenta accidentally sold an unapproved corn variety called Bt 10, mistaking it for the approved variety Bt 11. Both varieties produce a bacterial toxin that kills insects, using the same inserted gene and producing the same protein. The only difference is the location of the inserted gene, Syngenta says.

The company says it discovered the mistake for itself when it switched to a new quality control system that tests for DNA directly. Previously it had tested only for proteins, which meant the two varieties appeared identical.

In all, about 15,000 hectares in four US states were planted with the unapproved variety. This amounts to about 0.01% of the corn grown in the US over those four years. On average, about 70% of corn in the US is fed to animals, while the other 30% is consumed directly by people.

Allergic reactions

In 2000 a GM corn variety called Starlink was discovered in the human food supply, even though it was approved only for use in animal feed because of possible allergic reactions in humans. That discovery prompted a massive recall and new methods for segregating GM and non-GM corn. It also raised concerns among overseas buyers of US corn.

Critics say the Bt 10 release demonstrates that regulations and methods for controlling GM crops are still faulty.

"This really makes us wonder what else is in corn that has not been approved but that has been field tested. It seems that companies either won't or can't control it," says Jane Rissler, a senior scientist at the Union of Concerned Scientists in Washington, DC, US.

The Starlink contamination was originally discovered by the environmental group Friends of the Earth and Bill Freese, an FoE research analyst, says regulators should not assume the unapproved variety is harmless without further testing.

"The US government should immediately institute a testing programme, at Syngenta's expense, to remove Bt 10-contaminated grain, seed stocks and processed foods from the food chain," he adds.