GMO Free Seeds Action in Brussels, © Greenpeace / Philip Reynaers

Genetically engineered (GE - also called genetically modified, GM) crops raise many concerns, particularly for the environment. One of the main concerns for consumers, farmers and traders is contamination from GE crops. Now, a comprehensive review of recorded GE contamination incidents has been published in a scientific journal by Greenpeace and GeneWatch.

GeneWatch and Greenpeace maintain a website, the GM Contamination Register, that records incidents of contamination caused by GE crops dating back to 1997 (just after GE crops were first commercially grown). By the end of 2013, nearly 400 incidents were recorded. The review analyses these incidents by crop and by country. It reveals some interesting patterns of GE contamination and the limitations to what we know about how contamination happens and how it is detected.

Action Against Illegal GE Maize in France, © Pierre Baelen / Greenpeace

Contamination from GE crops occurs, not only from commercial growing, but also from field trials and illegal plantings. The review details eight cases of contamination from GE crops (including GE rice, GE grass, GE papaya and GE pharmaceutical crops) that were at the experimental stages of development (i.e. not authorized for commercial growing anywhere in the world). In most cases no risk assessment for food and environmental safety had been performed on these GE crops. Experimental GE animals were also reported entering human the food chain, making a total of nine cases of contamination from unauthorized GE organisms.

The three main commercially grown GE crops for food and/or animal feed (oilseed rape, soya and maize) have all been associated with GE contamination incidents over the past 17 years. However, GE rice has the highest number of incidents of contamination, accounting for a third of all cases, despite the fact it has never been grown commercially. We think this is, at least in part, related to the extensive monitoring for unauthorized rice in rice imports, once the GE contamination was discovered.

Some countries, such as Germany, report a high number of contamination incidents but this may be more related to a more extensive monitoring regime than other countries. We do not know how many GE contamination incidents might have gone unnoticed but we do know that, for many experimental GE crops, there is no methodology available that allows for testing of contamination.

Finally, the persistence of GE contamination varies considerably between cases. Some are seemingly ongoing (e.g. GE grass), whilst others appear to have ceased (e.g. US GE Liberty Link rice). In some cases at least, we think that governments and companies have made efforts to eliminate GE contamination, and this has been successful.

In conclusion, GE contamination happens when GE crops are grown outdoors. The only way to prevent GE contamination is to keep genetically engineered organisms in secure containment use, such as laboratories or specialised greenhouses.

Dr. Janet Cotter is a Senior Scientist at the Greenpeace International Science Unit.

Becky Price is a Consultant at GeneWatch UK.