London

Europe this week introduced stringent rules for the labelling of food that contains genetically modified organisms. But in most countries the labels will take months to appear — and questions remain about how they will be implemented.

The rules, which are imposed by the European Union and came into effect on 19 April, are intended to aid consumer acceptance of genetically modified food in Europe. They may help to defuse a US complaint to the World Trade Organization (WTO) that Europe is unfairly blocking imports of transgenic food.

Food containing more than 0.9% genetically modified ingredients must be clearly labelled as doing so, the rules say. If the ingredients are awaiting final approval as being safe to eat, that threshold falls to 0.5%.

“This is the biggest piece of legislation in the food industry for 20 years,” says Richard Werran, head of Cert ID, a firm based in Fairfield, Iowa, that is offering to test food for its transgenic content.

Britain, Germany and the Netherlands are expected to implement the regulations in stores within a few months, but other nations may take longer.

The rules require food to be tracked from its source through manufacture to the point of sale. Manufacturers and packagers will also have to test food directly for traces of genetically modified organisms. A network of laboratories set up and operated by the European Commission (EC) has developed a series of standard tests.

The Institute for Health and Consumer Protection, part of the EC's Joint Research Centre in Ispra, Italy, has led the development of these tests, which use polymerase chain reaction technology to search for modified DNA.

But the tests do not work with the refined products, such as oil or sugar, of some genetically modified organisms because they may contain no transgenic DNA, so figures for food containing these will depend on manufacturers' supply-chain records.

Many retailers doubt that customers will buy food products labelled as genetically modified, and some refuse to stock them. Analysts are unsure whether the new rules will make any difference to consumer acceptance — or to the United States' complaint to the WTO.