Science in Society Archive

GM Contamination Accelerating
No Co-Existence Possible

Untried and untested GM crops are out of the bottle even in the UK where no GM crops are commercially grown. Rhea Gala

GM crops, the vast majority engineered for just two traits - herbicide tolerance and Bt pesticide, or stacked with both - have been released on five continents for up to nine years, causing widespread contamination of food, feed, seed and the environment across the globe.

Genetically modified DNA from any part of a GM plant can enter the environment unobserved, for example, through pollen transfer to a conventional crop, through seed dispersal or plant decomposition and persistence in soil ecology.  The toxins encoded in the DNA also kill wildlife and contaminate soil and water, as do herbicides such as glyphosate and glufosinate ammonium that are an essential component of the herbicide tolerant crop system. 

Outcrossing between a GM crop plant and a wild relative and over dependence of the GM crop on herbicides to which the crop is tolerant, are causing a wave of “superweeds” to emerge in the US and elsewhere; the UK has reported a potential candidate earlier this year.      

UK’s herbicide tolerant weed hybrids

The UK government reported genetically modified herbicide tolerant (GMHT) hybrid weed seedlings at field trial sites earlier this year. One was a cross between Bayer’s GMHT oilseed rape (Brassica napus) and its distant relative the common arable weed, charlock (Sinapis arvensis), and two were hybrids of Brassica napus and B. rapa.

The findings, which were not announced, were nevertheless widely reported and somewhat exaggerated in the press [1] because many politicians and government scientists had repeatedly downplayed the possibility of GM gene transfer to wild relatives, the emergence of GM superweeds, or any other adverse effects of GM crops.  For example, in 2000 the EU Environment agency concluded, “ There appears to be general agreement that natural gene flow is not likely to occur between B. napus and S. arvensis”. The EU has an industry-sponsored forward plan for ‘coexistence’ in European countries for GM, conventional and organic crops to 2025 (“Beware the New Biotech Eurovision” SiS 24).

The report to DEFRA from the Centre for Ecology and Hydrology, Dorset, found that [2],  “The commercial growing of genetically modified, herbicide-tolerant oilseed rape is seen to result in the potential for the inserted gene to escape from the crop and become incorporated in the genomes of one or more related wild crucifer species, potentially giving a competitive advantage to the recipients.”

The “virtually impossible” already happened

The emergence of two GMHT B. napus and B. rapa hybrids was inevitable as B. rapa is a parent of the commercial variety B. napus and spontaneous hybrids are well known to occur.  Although the two plants generally do not share the same distribution, B. rapa may be overlooked because of its similarity to feral oilseed rape.  The finding of these hybrids and the GMHT charlock hybrid show that the difficulties of coexistence between GM and conventional crops will be insuperable. Despite that, the authors still concluded, “The risks of transfer of herbicide tolerance to wild relatives of oilseed rape appear to be minimal.”  But Dr Brian Johnson, an ecological geneticist and head of the Biotech Advisory Unit at English Nature, said that the charlock superweed would be fertile through its pollen to neighbouring plants [1]; and that charlock seeds can remain in the soil for 20 to 30 years before they germinate.

Huge problems of cross-contamination and herbicide resistance have arisen in countries like Canada and the US (see for example “GM sugar beet turned sour”, SiS 25; “Roundup Ready sudden death”, SiS 28).

Herbicide tolerant volunteers

Herbicide tolerant volunteers were found in the two years following the Farm Scale Evaluations, and they tend to persist, requiring control with toxic herbicides other than glufosinate ammonium.  The authors thought that volunteers may pose a greater risk for gene flow of the bar gene into the environment, than hybridization with wild relatives, especially if the same gene construct is introduced into other crop species.  They also pointed out that these problems “highlight implications for the EU threshold limits of GM content in oilseed rape crops set at 0.1 percent, 0.3 percent and 0.9 percent for organic seed, certified seed and food & feed, respectively” [2]. 

GM contamination lasts at least 15 years in soil

The BRIGHT report [3] on a study in the UK begun in 1998 with funding from Monsanto, Bayer CropScience, BASF, and Agrovista UK Ltd, among others, tried to underplay problems to wildlife from GM crops; but found that when HTGM sugar beet followed HTGM winter oilseed rape, additional herbicides were needed to control volunteer rape.

There were also problems with crossbreeding between herbicide tolerant varieties of rape, producing seeds resistant to more than one herbicide, and making management of minimal herbicide regimes very tricky even for experienced practitioners. 

The authors of BRIGHT have since looked further into the problem of persistence of GM seeds in seedbanks in a new study on the population dynamics of volunteer rape, Brassica napus, comparing two GMHT winter oilseed rape cultivars and two conventional cultivars [4]. 

They found that seed remaining in the field after harvest averaged 3 575 seeds per square metre but ranged from less than 2 000 up to more than 10 000 seeds. There was a rapid decline in seed number during the first few months after harvest; a mean loss of 60 percent of seeds thought to be removed by wildlife.  But in subsequent seasons, the seedbank declined much more slowly at four of the five sites, at about 20 percent per year.  The models predicted a 95 percent seed loss after approximately nine years, resulting in nearly 200 seeds per square metre, which would give rise to at least two HT rape volunteers nine years after the original crop was sown. This predicts the emergence of an average of one plant per square metre after 15 years.

Although there was no difference between the four cultivars in either the number of seeds shed at harvest or in their subsequent persistence, the importance of the persistence of GM rape seeds, simply in the context of the coexistence of GM and non-GM crops is a clear cause for concern. The researchers concluded that the density of more than two volunteers per square metre would exceed the European Union threshold of 0.9 percent adventitious presence of GM seeds in a non-GM crop, if the subsequent crop were conventional.

These results come in the same week as DEFRA’s report showing that the harmful effects on wildlife from GMHT crops in the Farm Scale Evaluations (see “GM crop fails final test” SiS 26) persist for at least two years [5]. Results showed that weed seedbanks following GMHT spring oilseed rape were significantly lower than following conventional crops over this period as was the case with winter oilseed rape [6]. Seedbanks following GMHT beet were also smaller providing empirical evidence for longer-term effects of GMHT cropping on farmland biodiversity [5]. Seedbanks for GMHT maize were higher than conventional, mostly probably due to the use of the now banned herbicide atrazine on the conventional crop.

Illegal contamination with GM material

These cases of environmental contamination with GM material have been detected in the UK where there is as yet no commercial planting of GM crops; emphasising that contamination in countries such as Canada, the US and Argentina - where GM monocultures are becoming, or are already the norm – is far more extensive (“Soya disaster in Latin America”, this issue). 

Though hardly reported in the mainstream press, well over 60 incidents of illegal or unlabelled GM contamination have been documented in 27 countries on five continents; eight of which occurred in the UK.  And those are only the recorded incidents [7]. The worst single contamination incident was of StarLink Maize, a GM variety approved only for animal feed which entered the human food chain in seven countries, the US, Canada, Egypt, Bolivia, Nicaragua, Japan and South Korea.

Moreover GM DNA is in the European human food chain via GM animal feed (“DNA in food and feed” SiS 23), but milk and meat are not labelled as such, and are considered safe by the UK Food Standards Agency.

Recent GM contamination in Europe

UK Member of Parliament Michael Meacher recently condemned seven years of secrecy over GM food and feed safety [8].  “On the seventh anniversary of the first disclosure of scientific concern about GM food safety I am supporting calls for freedom of access to the data used by the Government to approve GM foods.” Meacher said, “ Since the issue is the launching of GM products into the nation’s food supply that have never been independently tested, this is a public scandal of huge proportions.”

Next year the EU will decide how member countries will draft ‘coexistence laws’ for GM, conventional and organic crops to be grown together.  But at a conference in Bologna, Italy, in September, experts maintained such ‘co-existence’ to be biologically impossible.  Angelika Hilbeck of the Swiss Federal Institute of Technology Zurich said that [9], “[trying to prevent GMO contamination] starts with the seeds; you want to make sure you get uncontaminated seeds. This is the origin of everything, from there on the contamination multiplies.  For example, in Canada it is hardly possible to get GM-free canola seeds.”

News emerged in October about Monsanto’s massive illegal GM contamination of Romania.  The country has the largest GM cultivated landscape in Europe; officially half the 140 000 hectares of soya planted in 2005 is registered to be GM. However, according to representatives of farmers’ associations and even biotech giant Monsanto’s former Romanian manager, up to 90 percent of soya is GM. The core of the problem is due to genetically engineered crops contaminating the traditional cultures, as well as the illegal selling of GM soya seeds.  GM potatoes and plums were also found [10].

Greenpeace protesters stopped the 125 000 tonne bulk-carrier Étoile’s huge consignment of GM animal feed from the US from being unloaded in Bristol.  The feed was destined for British dairy cows to produce milk for the UK’s biggest supermarkets. Sainsbury's, Tesco, Asda, Waitrose and Morrisons all sell own-brand milk from cows fed on American GM feed.  The GM varieties were banned in Europe, but were found by expert laboratory analysts in samples taken from ships over the last two years.

Campaigners believe that only strict rules with liability regulations applied by governments can stop the unauthorised spread of GM seeds and products, which seems to be increasingly out of control all around the world.  Doreen Stabinsky of Greenpeace International says,  “If states do not act and set strict rules now GM crops will further contaminate lands, seeds and food around the world.”  But no Government or international agency has established a public record of contamination incidents or other problems associated with GM crops.  GeneWatch UK and Greenpeace International are launching the first on-line register of genetically modified contamination incidents. The on-line, searchable web site gives details of all the known cases of GM contamination of food, feed, seed and wild plants that have taken place worldwide [11]. 

Article first published 16/12/05


  1. “GM crop created superweed say scientists” Brown P. The Guardian. “5 July 2005.,2763,1535428,00.html
  2. Daniels R, Boffey C, Mogg R, Bond J, Clarke R.  The potential for dispersal of herbicide tolerant genes from genetically modified, herbicide tolerant oilseed rape crops to wild relatives.  Final report to DEFRA.  July 2005.
  3. Sweet J, Simpson E, Law J et al.  Botanical and rotational implications of genetically modified herbicide tolerance in winter oilseed rape and sugar beet. (BRIGHT Project). Nov 2004 http:///
  4. Lutman PJW et al , 2005. Persistence of seeds from crops of conventional and herbicide tolerant oilseed rape (Brassica napus). Proc.R.Soc. B. 272, 1909-1915 22 September 2005.
  5. Firbank LG, Rothery P, May MJ et al. Effects of genetically modified herbicide-tolerant cropping systems on weed seedbanks in two years of following crops.  Proc. R. Soc. B. 272, 1909–1915 August 2005
  6. Gala R.  GM crop fails final test” Science in Society 26, 2005.
  8. Michael Meacher condemns 7 years of secrecy over GM food and feed safety. 15 Aug 2005
  9. Experts maintain 'co-existence' of GM and GM-free crops biologically impossible
  10. GMW: GMOs Out of Control - Ex-Monsanto director speaks out in Romania. 10 Oct 05.
  11. Greenpeace 13 aquitted in GM trial;

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