It is recognised that GM crops should be grown in ways that prevent them from cross-breeding with conventional crops and contaminating the wider environment.  However, no containment methods to date have worked. This poses the question - Can GM crops be contained? 

Genes inserted into GM crops do not stay put; they have the ability to spread into the ecosystem. GM plants carry foreign genes in all parts of the plant (seeds, pollen, stems, leaves and roots) and therefore every part of a GM crop plant has the potential to pollute the environment. Pollen, seeds and crop residues can be spread naturally by wind, rain, birds and domestic and wild animals.

Human activity and the movement of machinery used to harvest, transport, store and market GM crops spread GM seeds and crop residues.  GM contamination levels can be so high they devastate whole areas or regions.  For instance, the cultivation of GM-free crops of maize, oilseed rape and soya is, for practical purposes, no longer possible anywhere in Canada.

(See chapter 7 in: Seeds of Doubt - North American farmers´ experiences of GM crops, Soil Association (2002), a report compiled by H. Warwick og G. Meziani.)