For a recent study involving separation distances see Perry, J.N. (2002) Sensitive dependencies and separation distances for GMHT crops. Proceedings of the Royal Society, Biological Sciences, 269, 1176-1179.

This paper concerns separation distances, which are used to create buffer zones to reduce the chance of unwanted cross-pollination. It uses a simple mathematical model to simulate an arable landscape with an organic and a GM crop of the same species, with fields separated by a statutory separation distance to reduce the chance of cross-pollination. The EU and the UK Government are reviewing these statutory separation distances. The Government policy is to ensure the coexistence of GM, organic and conventional farming, should GM become commercialized. This study shows that a major increase in separation distances may greatly decrease the amount of land available to grow both organic and GMHT crops, and thereby have serious implications for a policy of coexistence.

(See also the New Scientist article by James Randerson, from the 18 May 2002 issue.)

Download a reproduced version of the New Scientist article.





Other relevant recent results, not detailed in this paper, relate to the relationship between achievable threshold percent GM contamination and separation distance for unusually long-range pollination, such as that mediated by convection currents, turbulent conditions or weather fronts or by insects. I presented a paper on this at a workshop at the recent SETAC 2002 meeting. Very simple mathematical models may be built in the form of a mixture of two frequency distributions, to represent the effect of this long-range mechanism when it operates simultaneously with the more usual, relatively short-range, wind-borne transport responsible for most pollination. Such models demonstrate that if as few as 1 in 100 pollination events are mediated by the former, this may have a profound and deleterious impact on the ability to force contamination thresholds to very low levels, and that, depending on the threshold levels required, this might only be achieved with separation distances of the order of kilometres. Models are required because current data does not exist to relate adequately separation distances to pollination thresholds for values of the former above about 200m and values of the latter below about 0.5%. Such data is necessarily expensive to obtain, because of the need to obtain adequate precision for events occurring with such small probabilities, but is required urgently to inform policy and deliver reliable consumer choice. The Government Department DEFRA is funding such studies within Oil Seed Rape, in a project led by our colleague Geoff Squire of SCRI. Possibly the most extensive set of data yet available was published in the journal Science in 2002, collected by Mary Rieger and colleagues in Australia. Here you can download Rieger's paper, and a commentary on it.











I was invited to give evidence to The Agriculture and Environment Biotechnology Commission (AEBC) concerning this work on separation distances, thresholds for cross-pollination, and co-existence at their meeting on 12 September 2002. The AEBC was set up in June 2000 with a remit to provide the UK Government and Devolved Administrations with independent, strategic advice on developments in biotechnology and their implications for agriculture and the environment. It attempts to look at the broad picture, taking ethical and social issues into account, as well as the science. The AEBC works alongside the Human Genetics Commission (HGC) which advises on how new developments in human genetics will impact on people and health care, and the Food Standards Agency (FSA) which is the body responsible for food safety, including GM food. Most AEBC meetings are held in public, at a variety of locations in the UK. This one covered two days and was held in Edinburgh. Mike Wilkinson of the University of Reading gave evidence with me, on gene flow to wild relatives - see the agenda for details. Here is a brief summary of what happened, taken from the AEBC website:

1. The Chair welcomed Professor Perry and Dr Wilkinson to the meeting, to give evidence about issues being considered by the AEBC consumer choice group.
There is a full record of their presentations and of the discussion which followed
on the AEBC website.

2. Professor Perry said that if separation distances were increased then there may be limited space to grow both organic and GM herbicide tolerant crops simultaneously and that this might conflict with the Government’s stated policy of co-existence. He also said that a decline in cross-pollination at relatively short range may not apply at greater distances and a small amount of long-distance pollination mediated by unusual weather events or insects may have a relatively big effect. In these circumstances, separation distances of the order of kilometres might be required to force thresholds to very low levels. He pointed out that an increase in purity by whatever factor increased the costs of testing by about the same factor.

3. Dr Wilkinson explained the ethos and context of his work. He was involved in looking at how geneflows could be studied for unwanted ecological change in the natural environment. He did not consider contamination from one field to the next to be a big environmental issue but he did see it as an agricultural and political one. He believed it would be important to obtain an estimate of long range geneflow in order to enable a more accurate overall estimate of the number of hybrids. He saw farm practice and seed contamination as far more important issues than field to field contamination.

4. The Chair thanked Professor Perry and Dr Wilkinson for the clarity of their presentations and for assisting the Commission with its understanding of the issues and their complexity.

You can download this .pdf file to see the full transcript of the evidence presented.








The published version of the work on the mixture of two frequency distributions, referred to above, appeared as a book chapter in: GM Crops, the Scientists Speak edited by Brian J. Ford FIBiol FLS, which comprised talks given at a symposium in Cambridge in 2002.
Perry, J.N. (2003) GM Crops and the Environment. Chapter 6 in: GM Crops, the Scientists Speak, (Proceedings of the Cambridge Society for the Application of Research, Symposium on GM Food, Churchill College, Cambridge, 23 March 2002), edited by B.J. Ford , ISBN 0-9543595-2-6, Cambridge: Rothay House (in press, due June 2003).

The Cambridge Society for the Application of Research was founded in 1956. Its aim is to provide a forum for scientists to meet and discuss topics of interest. It also organises a series of meetings throughout the year, to which the general public is welcome to attend.



In addition to my own chapter the book includes contributions from:
Brian Ford, Professor Sir Sam Edwards, Professor Malcolm Grant,
Colin Merritt, Sir John Marsh, Mike Gasson & Professor Sir Brian Heap.
The first edition, ISBN 0-9543595-2-6, is in hardback, priced at £14.95, although a paperback edition, ISBN 0-9543595-3-4, is scheduled for publication during late-2003, priced at £10.95.
Further details from the Rothay House website;
you can order the book by email.