Cases of traded food and feed being contaminated with low levels of GMOs have soared around the world in the past five years.

Between 2002 and 2012 there were 198 incidents of traces of GM crops found mixed with non-GM crops and 70% of cases were reported since 2009.

The shipments had to be destroyed or sent back to the exporting country if that particular GM crop was not allowed.

Most of the cases originated in the USA, China and Canada, with linseed, rice, maize and papaya involved in the majority of incidents, according to the survey by the Food and Agriculture Organisation of the United Nations (FAO).

In the four months to this February, China rejected 887,000t of American maize because it included traces of an unapproved GM variety.

See also: Owen Paterson backs EU proposals to fast-track GM crops

FAO senior food safety officer Renata Clarke said the more testing and monitoring countries did, they more incidents they found.

“The numbers of incidents are small relative to the millions of tonnes of food and feed traded every day,” she said.

“But because trade disruptions may be very costly and given the reported increase in the occurrence of these disruptions, the FAO conducted this survey and is holding a technical consultation to try to start a dialogue between countries on the issue.”

Of the 75 countries surveyed, only 30 were producing GM crops for either research or commercial production.

There are no food, feed or environmental regulations on GM crops in 17 countries, but 55 nations had a zero-tolerance policy on unauthorised varieties.

GM and non-GM crops can become mixed accidentally by being grown in close proximity or during processing, packing, storage and transportation.