Yes, they are.
All flowering plants produce pollen and plant breeders have always been aware of the implications of pollen movement. When growing a specific crop with certain desirable properties, they take steps to prevent cross-pollination from other plants. For this reason plant breeders set isolation distances between crops. For example, commercial (non-GM) crops of industrial-quality oilseed rape must be separated from edible oilseed rape by at least 50 metres. Seed crops of oilseed rape have to be separated by 200 metres. Such isolation distances - set by the OECD - have been in use for many years and have always worked to the certified international standards.
Isolation distances have generated considerable discussion in relation to GM crops but the behaviour of pollen from GM plants is no different from that of ‘conventional’ (herbicide-tolerant) plants. The current regulations on isolation distances between GM and conventional crops have therefore been based on those routinely used by plant breeders.
Pollen can be blown by the wind or carried by insects to other flowers. How far it travels effectively depends on the amount of pollen produced. Research on pollen movement shows that most travels no more than a few metres: even from a large field of a crop such as oilseed rape, 97 per cent falls to the ground within 1 metre. However, minute amounts of pollen (whether GM or non-GM) will travel further.
The potential for a pollen grain to fertilise other plants depends on:
1. How long it has been in the air; pollen is not particularly hardy and loses its ability to pollinate quite rapidly;
2. The amount of pollen produced by the potential recipient crop. If the recipient is producing plenty of its own pollen, a few grains from elsewhere are unlikely to fertilise any of the available seed. However, if the recipient is a single, isolated plant the chance of fertilisation increases;
3. The weather. As most hay-fever sufferers will testify, hot sunny weather results in more pollen movement. But the pollen also loses its viability more quickly. In the wet, much of the pollen is washed out of the air and does not travel far;
4. Finally, the recipient plant must be sexually compatible, in flower and unfertilised.
Isolation distances and GM crops
The distance depends on the crop. Only GM oilseed rape, maize and sugar/fodder beet were grown in farm scale trials.
Sugar beet is a biennial plant and, as such, does not flower in the first year when it is harvested (it is grown for its root). It is a requirement of the GM approval process that any flowering GM sugar beet plants are removed. Pollen flow is, therefore, not an issue with this crop and the isolation distance has been set at 6 metres.
Oilseed rape and maize do produce pollen and the current isolation distances are 50 metres unless the adjacent crop is an organic one, in which case the distance is 200 metres.
The recent mixing of non-GM oilseed rape with around one per cent of a GM variety has caused people to question whether the current isolation distances are adequate. However, it has not been definitively stated that this incident was due to cross-pollination. The current isolation distances have been in use for many years and have been perfectly satisfactory for ‘conventional’ crops, keeping the level of cross-pollination well below the accepted standard of one per cent. This level of cross-pollination should be acceptable: one per cent is the threshold level set by the EU for the content of GM ingredients in “GM-free” foods.
Isolation between any crops to give absolutely zero mixing is impossible and that is true in both directions. GM farmers, having paid a premium price for their higher quality seed, do not want it contaminated by poorer quality pollen from “organic” crops or elsewhere. But they, too, will have to live with a threshold; isolation is no more possible for them than for anybody else.