Such incidents have led to the disruption of trade between countries with shipments of grain, cereal and other crops being blocked by importing countries and destroyed or returned to the country of origin.
Trace amounts of GM crops become mixed with non-GM food by accident during field production, processing, packing, storage and transportation.
No international basis
Currently, there is no international agreement defining or quantifying "low level", therefore the interpretation varies from country to country. In many countries it is interpreted as any level at which detection is possible, such as very low trace levels, while in other countries case-by-case decisions are taken on what level is acceptable.
In the first survey of its kind , 75 out of 193 FAO member countries responded to questions on low levels of GM crops in international food and animal feed trade.
It revealed 198 incidents of low levels of GM crops mixed into non-GM crops in the 10 years up to 2012, with a jump in cases between 2009 and 2012 when 138 out of the incidents were reported. The highest number of incidents involved linseed, rice, maize and papaya
It also found that shipments with low levels of GM crops originated mainly from the US, Canada and China, although other countries also accidentally shipped such crops. Once detected, most shipments were destroyed or returned to the exporting country.
"The numbers of incidents are small relative to the millions of tonnes of food and feed traded every day," said Renata Clarke, the FAO’s senior food safety officer, who was behind the survey.
"We were surprised to see incidents from every region. It seems the more testing and more monitoring they do, the more incidents they find."
Three national approaches
Although testing technology has become more sensitive, it is notable that 37 out of the 75 countries who responded said they have little or no capacity to detect GMOs, leading many of them to ask the FAO to help improve their capacity for detection.
The study also found that 30 countries produce GM crops, either for research or commercial production or both, with GM crops are being developed. While 17 countries still do not have any food safety, feed safety or environmental regulations on GM crops, 55 have zero-tolerance policy for unauthorised GM crops.
A further 38 countries consider the different policies on GMOs between trading partners is an important factor in contributing to the trade risk posed by the presence of low levels of GM crops in some traded foods.
In most countries, there are no generally applicable low-level GMO policies, legislation or regulations yet in place. Different options have been used when setting such policy, including a zero tolerance policy, a low threshold policy and a case-by-case policy.