Environmental protection

Homepage > Environmental Protection > Genetic Modification (GM) > Farm Scale Evaluations

GM Crop Farm-Scale Evaluations:
Background Papers

A review of the safety assessment of T25 maize for placing on the market in Europe

GM Policy and Regulation Unit, Department for Environment, Food and Rural Affairs
(amended February 2002)

Introduction

  1. The purpose of this paper is to explain the safety assessments that have been conducted on T25 maize as part of its regulatory approval in Europe for cultivation, feed and food uses. There has been criticism of these assessments, and the scientific evidence that underpins them, leading to calls for T25 maize to be banned. The safety of this maize is being re-evaluated in the light of the main concerns expressed 1. The current view of the independent UK advisory committees for the environment (ACRE 2), food (ACNFP 3) and animal feed (ACAF 4) is that T25 maize poses no greater risk to health, livestock or the environment than conventional non-GM maize varieties.
  2. The Government believes that GM crops and foods should not be used unless it can reasonably be concluded that they do not pose an unacceptable risk to human health or the environment. In applying this policy a precautionary approach is taken. The Government will not agree to the release of a GM product where there is significant uncertainty and further information or testing is needed. All relevant points of safety have to be satisfactorily addressed before approval would be given. Similarly, if important new information is presented about the safety of a GM product that already has marketing approval then it will be re-assessed. If necessary, the Government would act to revoke a product approval if the detailed evidence justified this.

Background on T25 GM Maize

T25 maize has been genetically modified to be tolerant to the herbicide glufosinate ammonium. This is achieved by expressing the PAT enzyme in the maize to inactivate the herbicide. T25 maize can therefore survive application of glufosinate that would kill other maize plants. The rationale behind this GM maize is to provide farmers with a different approach to weed control. It has been suggested that the use of T25 maize will reduce the number of herbicides used on maize to the benefit of wildlife. Others fear it will lead to greater weed control and a net loss in biodiversity.

  1. T25 is the code number given to a type GM maize produced by Aventis CropScience GmbH (formerly AgrEvo). T25 maize is tolerant to the widely used herbicide glufosinate ammonium, this being achieved by the insertion of a gene that makes the enzyme phosphinothricin acetyltransferase ('PAT'). PAT inactivates glufosinate (L-PPT) inside the plant rendering it non-toxic. T25 maize also contains a cauliflower mosaic virus promoter 5, but does not contain any functional antibiotic resistance marker genes 6.
  2. According to standard plant breeding practice, the original GM maize designated 'T25' has been bred with elite lines of maize to produce a number of T25 maize varieties that are suitable for commercial cultivation. In the UK T25 maize is most commonly known by the varietal name Chardon LL. A number of other varieties exist and in this paper 'T25 maize' is used as a generic term to describe this family of GM maize varieties.
  3. The concept behind T25 maize is that it offers a different approach to weed control from that used with conventional maize crops. Instead of several applications of different herbicides it may be possible to have a reduced number of sprays with one herbicide - glufosinate - and achieve the same level of weed control 7. Glufosinate is also less toxic to non-target organisms and less persistent in the environment than some of the herbicides, such as atrazine, currently used to control weeds in commercial maize crops. It has been suggested that the more refined timing of spray application possible with herbicide tolerant maize may yield environmental benefits relative to conventional maize, although this is by no means proven.
  4. The original T25 maize was first created in the late 1980s and has been undergoing development and evaluation since then. This means that the T25 maize being grown in trials today is the result of many generations of plant breeding 8, suggestive in itself of the stability and consistent performance of this particular genetic modification. This long period of development also points to the fact that a great deal of scientific work and assessment has been done on T25 maize. In a document of this size it is not possible to review all of this information or to summarise adequately the full dossier of data on T25 maize submitted to the European regulatory authorities (15 appendices in total). However, all of the regulatory information is available for public scrutiny (see details at the end of this paper on where to obtain further information).

Marketing approval for T25 maize under EU Directive 90/220/EEC: cultivation and feed uses.

The release and marketing of GM crops in Europe is controlled by Directive 90/220/EEC. Under the Directive no GMOs can be released without the proper consent and a detailed risk assessment to ensure that there will be no adverse effects on human health or the environment. T25 maize has full marketing consent in Europe for cultivation, feed and food uses. AgrEvo submitted the notification for marketing approval to the French authorities in 1995. France conducted a detailed evaluation and concluded that the notification met the requirements of the Directive and T25 maize posed little or no risk. The other Member States, including the UK, then conducted their own reviews of the notification. Member States agreed with France and European-wide marketing consent for T25 maize was issued in August 1998.

  1. The deliberate release, including import, of genetically modified organisms (GMOs) is governed principally by EU Directive 90/220/EEC 9. This stipulates that GMOs must not be released without prior approval, and that consent will not be granted unless a detailed risk assessment confirms that there will be no adverse effect on human health or the environment.
  2. There are two types of GMO release consent under Directive 90/220: 'Part B' for research and development purposes and 'Part C' for placing on the market. As this paper focuses on the evaluation of T25 maize for Part C marketing consent a brief description of that process may be helpful. Applications (or 'notifications' as they are called in the Directive) for Part C approval are submitted initially to any one of the 15 EU Member States. This Member State then takes the lead in reviewing the notification in detail and forming an opinion. If that opinion is favourable (i.e. the notification dossier meets the requirements of the Directive and the GMO will have no adverse effects on health or the environment) the dossier will be forwarded to the European Commission and the other Member States. The other Member States then also evaluate the notification, with the benefit of knowing that the lead Member State has already considered the matter in detail and has recommended that it be approved. If there are no objections the lead Member State issues the marketing consent which applies throughout the EU. If objections are raised there is provision for all Member States to meet to resolve the issues, with a final decision being taken if necessary by the Council of Environment Ministers.
  3. Twelve GM plants already have Part C marketing approval. These include soya beans, oilseed rape, chicory, carnations and three types of GM maize - besides T25. The maize varieties and soya are already imported in bulk into Europe for processing and use in animal feed.

Part C consent for T25 maize

  1. A marketing notification for T25 maize was submitted to the French authorities in 1995. Permission was sought for the maize to be cultivated (grown from seed) in Europe or imported as grain and for the material from either source to be processed into food and animal feed. French scientists and regulatory authorities evaluated the T25 dossier and concluded that T25 maize was safe for the environment, human health and as animal feed. France therefore forwarded the dossier to the European Commission with a favourable opinion, at which stage the other Member States received the dossier to conduct their own independent safety assessments.
  2. In the UK ACRE (environment) and ACNFP (food safety) assessed the T25 dossier in 1996. Both committees concurred with the opinion of the French and were content that T25 maize posed little or no risk to human health or the environment. Some Member States raised specific points or had questions about the T25 dossier and further information was supplied subsequently to address the issues raised. Following this wide assessment by Member States, it was agreed at European Community level that a marketing consent should be granted, and France finally issued this in August 1998.
  3. The following paragraphs look more closely at particular aspects of the T25 maize risk assessment as considered by ACRE, ACNFP and, more recently, ACAF. Most of the points covered relate to issues that were considered at the time of the original T25 Part C notification. Others concern points that have been raised subsequently but refer to data and experimental details in the notification dossier.
  4. The Government welcomes an open debate about the risk assessment of GMOs and the related science. But while it is right that reported criticisms of some aspects of the T25 maize safety assessment made by a few scientists are given due consideration, they should be seen in the context that across the EU as a whole very many scientists have looked at this GM crop and not identified any serious concerns. On this basis, therefore, it is reasonable to conclude that the overriding balance of scientific opinion supports the view that this maize poses no more risk to people, animals or the environment than non-GM bred maize lines.

Assessment of T25 maize for environmental safety

Maize is not a persistent or invasive crop and despite being grown widely has not become a weed. There are no sexually compatible wild relatives of maize in Europe and so T25 maize cannot transfer genes via cross-pollination to wild plants. Nor is it likely to transfer the PAT enzyme gene to soil organisms by horizontal gene transfer and, even if it did, no harm would be likely to arise because soil micro-organisms already carry such genes and no extra selective advantage would be gained.

Evidence presented by AgrEvo to support the marketing of T25 maize indicates that PAT will not interfere with the normal biochemical pathways in maize leading to unexpected effects. It will also have no adverse impact on non-target organisms including bees and other beneficial insects. The PAT enzyme is not present in T25 maize pollen.

Concern has been expressed about the impact on biodiversity of the herbicide management regimes used with herbicide tolerant maize and other crops. This is being tested in the Farm Scale Evaluations. There will be no commercial growing of these GM crops until the FSEs are complete, and only then if the herbicide use associated with them is assessed as causing no unacceptable environmental effects.

Potential for T25 maize to disseminate, establish and survive in the environment

  1. Although maize is cultivated widely it has never become a weed in Europe or the United States, nor is there any historic evidence that it can compete with wild plants and invade natural habitats. In the agricultural environment, maize is dependent upon human intervention to ensure its survival. It is an annual plant that dies at the end of the season and can only propagate by seed. In cultivated maize the seed is harvested before it can be shed onto the ground and it has no sexually compatible wild relatives in Europe.
  2. Against this background, ACRE considered whether the introduction of the pat gene into T25 maize would enhance its capacity to survive, establish and invade habitats. The Committee reviewed the behaviour of T25 maize under field conditions and, in particular, data presented on morphological studies 10 and agronomic performance from field trials in the USA and Europe. Studies presented in the dossier included experiments on flowering time, plant height, yield, survival and persistence 11 and susceptibility to other approved herbicides. Laboratory studies on seed germination rates were also presented. The experiments demonstrated that T25 maize is indistinguishable from standard conventionally bred maize varieties. Further, like conventional maize, T25 is extremely susceptible to cold and frost and cannot survive the normal winter in the UK. The few volunteer maize plants that originate from dropped seed at harvest are controlled easily.
  3. ACRE agreed that based on these numerous lines of evidence there is no indication that there had been any direct or indirect effect of the genetic modification on the ability of the maize to survive or out-compete wild plants. The T25 maize is no more likely to be invasive or weedy than non-GM maize varieties currently on the market. Published research supports ACRE's view that glufosinate tolerant maize and other herbicide-tolerant plants are unlikely to persist as weeds 12.

Risk of transfer of herbicide tolerance trait from T25 maize to wild plants

  1. Transfer of genes between plants occurs via cross-pollination between sexually compatible individuals. In Europe, maize has no sexually compatible wild relatives. Therefore, ACRE concluded that the risk of gene escape to wild relatives is zero.

Direct and indirect effects on non-target organisms including bees

  1. Information was submitted in the notification dossier on monitoring the susceptibility of T25 maize to a range of pests and diseases over three growing seasons in field trials. There were no differences in the susceptibility of T25 maize varieties compared with non-GM maize varieties and no evidence therefore that T25 maize was any more toxic or harmful to pests (and the beneficial creatures that eat them). Neither did T25 show any differences in susceptibility to diseases compared to non-GM maize.
  2. In reviewing the environmental risk assessment ACRE has concluded that bees are very unlikely to be at risk from T25 maize for two main reasons. First, exposure of bees to the PAT enzyme is unlikely because bees rarely visit maize and, even if they did, tests have shown that the PAT enzyme is absent from pollen. Second, there is no reason to believe that even if bees ingest PAT that it is toxic to them 13. In this respect, it is difficult to see a mechanism whereby PAT could be toxic. Tests show that PAT is very specific for the inactivation of glufosinate (L-PPT) 14 and is therefore very unlikely to interfere with bee digestion or other normal metabolic pathways.
  3. It has also been suggested that bees are at risk from horizontal gene transfer (see below for a detailed consideration of HGT) of the PAT gene from pollen. This view is based on work by Dr Hans-Hinrich Kaatz 15 which appeared to show that bacteria in the intestinal tract of bees could take up the PAT gene when the bees were exposed to GM plants. This work has not yet been published and so it is difficult for ACRE to give a detailed view, but until then there is no reason to disagree with the press notice from the German researchers who conducted the work that there is little or no risk to bees or to human health.

Horizontal gene transfer of T25 maize transgenes to soil bacteria

  1. ACRE considers the possibility of horizontal gene transfer (HGT) 16 as a matter of course for all applications for the release of GM plants. ACRE's general view is that the likelihood of genes moving from plants to soil bacteria is very low and that the environmental consequences (if it did occur) with T25 maize would be negligible.
  2. In reaching this view on HGT from T25 maize ACRE took the following considerations into account:
    • The pat gene is derived from a soil borne Streptomyces bacterium 17,which is not considered to be a pathogen of humans, animals or plants
    • Streptomyces bacteria live in UK soils and PAT is already part of the soil ecosystem. Its transfer by HGT would not therefore impact on background levels of PAT already in soil bacteria.
    • Experiments have shown that HGT from GM plants to soil micro-organisms is very unlikely 18.
    • In the unlikely event that the T25 maize pat gene is transferred to a soil bacterium then it would not be expressed. This is because it is linked to the cauliflower mosaic virus promoter that expresses genes in plants - not bacteria. Also, the pat gene has been altered 19 in the laboratory from one that is expressed well in bacteria to one that it is expressed more efficiently in plants. The changes have not altered the PAT protein but the 'new' gene would be expressed poorly in bacteria.

Possible production of unintended and unidentified biochemical products

  1. The transfer of T25 maize genes via cross-pollination to plants other than maize is not possible in Europe because wild sexually compatible relatives do not grow here; cross-pollination leading to hybrid kernel development is possible between Chardon LL and other maize varieties. However, it is unlikely that this will lead to the production of unexpected toxins or allergens because, given the detailed knowledge of the gene and the very specific enzyme/substrate mode of action of PAT, there is no rational basis for supposing that hybridisation (cross-pollination) would alter the metabolism of the hybrid other than to confer glufosinate tolerance. In tests the PAT enzyme is very specific for its target, glufosinate, and is incapable of reacting with other, even closely related, compounds. It is unlikely therefore to interfere with other plant processes. Cross-pollination would introduce the PAT gene into the hybrid in the same chromosomal environment as it was in the original variety.

The Cauliflower Mosaic Virus Promoter and possible gene silencing/DNA rearrangements

  1. ACRE has considered the cauliflower mosaic virus (CaMV) 35S promoter on a number of occasions and in particular reviewed the paper by Ho et al., (1999) 20. This paper concerns the ability of the CaMV 35S promoter to recombine with other viruses and the role that it may play in horizontal gene transfer. The paper is a review of the scientific literature on the CaMV promoter and advances the hypothesis that a 'recombination hotspot' predisposes the promoter to recombination with viruses and other DNA sequences. It is suggested that this may lead to new pathogenic viruses, unexpected and harmful over expression of plant genes or might even lead to cancer. ACRE considered the article and whether the central theories had any implications for the release of GM plants like T25 containing the CaMV 35S promoter. It concluded that this paper does not challenge current scientific understanding or indicate that the CaMV 35S promoter, as used in genetic modification, is inherently unsafe 21. The CaMV 35S promoter used in GM plants represents an extremely low risk to human health and the environment.
  2. It has been suggested that genetic modification is a fundamentally uncertain process that may give rise to unforeseen effects, insofar that the transgenic material might be inserted unstably into the DNA sequence. Whatever the general merits of this argument, this is not a problem in respect of T25 maize because it has been bred over many successive generations and selected by breeders for its stable and reliable characteristics.
  3. It has also been suggested that the random insertion of the transgene (the foreign DNA inserted into the plant) into a plant genome may disrupt normal plant genes and lead to unexpected effects. While this may be true, plant breeding and selection in the laboratory and glasshouse make it very unlikely to be an issue with T25 maize. Furthermore, a number of studies (see below) have analysed the composition of T25 maize and found no difference from the range of variation expected in conventional maize varieties. ACRE has looked at the specific issue of unpredictable insertion of DNA sequences in the genome and considered the activity of transposable elements. These are pieces of DNA that occur naturally in many plants, including maize, and which can move at low frequency from one genetic location to another. Transposable elements have the potential to 'jump' into and disrupt normal maize genes and have been doing so (naturally) for millennia with no apparent ill effect. This is similar to the possible disruptive effect that the insertion of a transgene might have.

Impact of the agricultural management practices associated with T25 maize

  1. At the time T25 maize came forward for marketing approval, Directive 90/220/EEC did not formally require any consideration of the potential wider effects of the changes in farm management practice that might be associated with a GM plant (as opposed to the safety of the GM plant itself). In the case of T25 there is an issue as to whether the herbicide regime to be used by farmers who grow the crop might have a negative impact on biodiversity, relative to the herbicide regimes for non-GM maize crops.
  2. This gap in the risk assessment was recognised, and it was the need to ensure consideration of the possible effect of the intended herbicide regimes for T25 maize, and other herbicide-tolerant plants, that led the Government, in agreement with the industry group SCIMAC 22, to establish the Farm Scale Evaluation (FSE) programme 23. There will be no commercial growing of GM crops until the FSEs are complete and only then if the associated herbicide use is assessed as causing no unacceptable effects on the environment.
  3. The regulatory approval of glufosinate for use on T25 maize is not part of the assessment under 90/220/EEC, but it is an extremely important and related issue. Pesticide approval is a matter for the regulatory authorities under Directive 91/414 and in the UK the Advisory Committee on Pesticides (ACP) advises Ministers on whether an approval should be given. ACRE has forged close links with the ACP and its environment panel to ensure that the environmental impact of the chemicals that might be used on GM crops are taken properly into account.

Assessment of T25 maize for safety to human health

As part of the risk assessment for T25 maize ACRE has evaluated the risks to people who come directly or indirectly into contact with the GM maize or its pollen, giving particular consideration to possible toxicity or allergic reactions. ACRE's consideration of human health aspects is separate from that of the food safety assessment undertaken by ACNFP.

The composition of T25 maize is the same as any other maize apart from the presence of the PAT enzyme. Tests have shown that PAT is rapidly degraded in the digestive system and there is no reason to believe that it is allergenic or toxic. T25 maize pollen does not contain the PAT enzyme.

Safety of the genes inserted into T25 maize

  1. As noted, T25 maize contains a novel gene that makes the PAT enzyme needed to inactivate the herbicide glufosinate. Clearly maize does not normally make this enzyme and so risk assessment focussed initially on whether or not PAT is likely to cause allergic reactions or be toxic. Experimental analysis presented in the part C notification dossier indicates strongly that the PAT enzyme is readily digested in human gastric fluids and is broken down quickly by heat and acids. One scientist has recently criticised part of these studies and expressed the view that the pH of the acid was wrong 24. Whatever the merits of this view the fact remains that the same studies have been reviewed by many independent experts across the 15 Member States (and again recently by ACAF) and none were concerned that the pH used was inappropriate. However, it must be recognised that tests like this are only an indicator of how rapidly a protein might be degraded in the stomach and they are not designed or intended to be a detailed simulation of an animal's digestive system. Acid digestion studies therefore make a contribution to the various threads of evidence in the risk assessment package but the assessment does not depend upon these experiments alone.
  2. Rapid degradation by heat and acids are features that make PAT very unlikely to be allergenic. The proteins in food and pollen that typically cause allergic reactions tend to be very stable and resistant to digestion, strong acids and heat. Well known allergens in peanuts and shellfish are good examples of such proteins. PAT is not like this. Furthermore, the PAT protein sequence was compared to the sequences of thousands of other proteins. None of the proteins with which PAT shared some similarity are known as allergens or toxins.
  3. It is relevant here again that biochemically the PAT enzyme is known to be highly specific for glufosinate and does not react with other related compounds. It is specific to inactivating glufosinate and is very unlikely to also interfere with other processes in T25 maize in unexpected ways or lead to unexpected toxins/allergens.

Assessment of T25 maize for animal feed safety

Member States concluded in 1996 that T25 maize was safe for use in animal feed. The UK Advisory Committee on Animal Feedingstuffs has looked again recently at the available data. ACAF is content that T25 maize grain or its products pose no more risk as animal feed than non-GM maize varieties. The composition of T25 maize in essential nutrients is within the range expected from non-GM maize. Toxicity tests with rats and feeding studies with chickens indicate that PAT is not acutely toxic and the grain is nutritionally equivalent to other maize varieties.

The data on the composition of T25 maize silage were limited and it was not possible for ACAF to be sure that the silage is compositionally equivalent to that of other maize varieties. Although the available data do indicate that T25 maize silage is the same as other maize, and there is no reason to believe it is unsafe, ACRE agrees that its equivalence should be confirmed. Further information has been sought from Aventis to resolve this matter. No commercial T25 maize silage will, in any case, be fed to animals in the UK before the end of the Farm Scale Evaluations, and only then if the Government is entirely satisfied with its safety.

  1. The marketing consent for T25 maize covers its use as animal feed. Livestock would consume this maize primarily as whole crop silage but also as processed or unprocessed grain. In 1996 ACRE took account of feed safety aspects of T25 maize as did ACNFP. Following this consideration the UK agreed with France (as the lead competent authority) that T25 maize could be used safely as, or in, animal feed. The European Commission's Scientific Committee on Plants confirmed this view 25. Since the 1998 EU approval of T25 the maize grain, produced largely in North America, may have been imported into Europe and used in animal feeds. However no commercial maize silage produced from the T25 event has been fed to animals in this country
  2. Since the original consideration of T25 maize for regulatory approval, the Government has established a new expert committee - ACAF - specifically to provide independent expert advice on all issues relating to the safety and use of animal feedingstuffs. The Secretariat for ACAF is shared by the Food Standards Agency and Defra.
  3. ACRE has asked ACAF to look again at the assessment of T25 maize as animal feed, in the light of the safety criticisms made in the written representations to the public hearing on the proposed addition of Chardon LL (a T25 variety) to the National Seeds List. Some 250 written objections to the proposed listing were received, many citing animal feed concerns. The hearing is currently adjourned while the status of Chardon LL in the National List process is clarified.
  4. Members of the ACAF sub-group that specialises in GMO-related issues therefore looked at T25 maize in detail last year. They were critical of some aspects of the information provided in support of the animal feed safety. But on the basis of all of the available data, they saw nothing to indicate that T25 maize grain or its products pose any more risk to animals or humans if used in animal feed than non-GM maize varieties.
  5. However, the current available data are not sufficient to conclude that T25 maize silage is 'compositionally equivalent' to that of other maize varieties. It is unlikely that T25 silage is unsafe to feed to animals but ACRE agrees that its equivalence should be confirmed (the available data are already pointing in that direction) before it can be said with confidence that T25 maize silage is of a low risk. Further information has been sought from Aventis to resolve this matter. No commercial T25 maize silage will, in any case, be fed to animals in the UK before the end of the Farm Scale Evaluations and only then if the Government is entirely satisfied with its safety.
  6. The following paragraphs explain the evidence presented in the Part C notification on the feed safety of T25 maize and the main subsequent considerations.

Toxicity tests

  1. To assess the toxicity of the PAT protein, Aventis (then AgrEvo) carried out a repeated dose oral toxicity test on rats in which rat body weights, organ weight and food consumption were measured. Studies in the T25 dossier show that these parameters were unaffected in rats fed the PAT protein, and there was no evidence of mammalian toxicity. The fact that these studies were conducted for 14 days has been criticised by some observers as being too short. But this is a recognised process whereby test animals are fed 'large' amounts of a specific substance over a relatively short period and monitored for any toxic effects. After two weeks of this regime, there was no apparent effect on the animals and so confidence can be gained that PAT is not acutely toxic.
  2. The rat studies were not entirely without criticism from ACAF. ACAF Members considered that the origin of the PAT protein fed to rats was obscure and the use of activity units and weight of PAT did not allow the level of exposure to be determined accurately. However, taking these factors into account, the data did imply that the dose of PAT given to rats was some 5000-fold greater that normal dietary exposure. If this is the case (and it is still to be confirmed) then the study is a test of acute toxicity and would allow a No Observed Adverse Effect Level (NOAEL) to be set above any reasonable level for concern.
  3. In addition to feeding studies involving the pure protein, Aventis submitted the results of tests on broiler chickens fed the T25 maize itself. This test was essentially a comparison of growth rate between two groups of birds fed with T25 maize grain or non-transgenic grain over a period of 40 days. During such a period the weights of the birds would normally increase substantially (15-fold in the first 18 days) and so nutritional equivalence and 'wholesomeness' of the non-GM and the GM feed can be readily compared.
  4. In this particular experiment, 280 birds were assigned to two groups - one group (140 birds) was fed a diet that contained T25 maize and the other group (140 birds) was fed a diet that contained ordinary maize.
  5. The mortality rates of birds reared by this type of broiler chicken production method are high, up to 8 percent. And so, not unexpectedly, there were mortalities during this experiment too. In an experiment of this size, one would expect up to 11 birds to die in each group of 140 (8%).
  6. In this particular experiment, the mortality rate in birds fed GM maize was 7% (10 out of 140), that of birds fed non-GM maize was 3.6% (5 out of 140). Some people have expressed concern over these values, but both are within the expected range for chickens reared in these conditions (up to 8%).
  7. However the crucial question is whether or not this difference in mortality is biologically significant? The numbers of chickens dying was very small irrespective of their diets and the mortality varied a great deal between the different rearing rooms used in the experiment. This sort of variation among mortality data is typical of such experiments, but it does mean that it is not possible to prove that small differences between birds fed on different diets have not arisen simply by chance.
  8. In most cases, where a dietary factor affects mortality rates in chickens, the surviving chickens in the test group show evidence of other impacts such as decreased weight gain.. In the reported experiment, there were no significant differences noted in weight gain and feed intake among the surviving chickens. The lack of difference in weight gain between the two groups indicates that the difference in mortality rates was more likely to be due to chance than to any dietary effect.
  9. The weight gain and feed intake results from this test support the hypothesis that the two maize diets are nutritionally equivalent.

Mycotoxins

  1. Infection of Maize kernels by fungi can produce toxins that are harmful to humans and animals eating infected maize. To ensure that the genetic modification had not unexpectedly increased susceptibility to fungi, field experiments were conducted. The results show that T25 maize was no more susceptible to infection than commercial maize varieties.

Composition and nutritional analyses

  1. Compositional analysis of T25 maize grain showed that it is no different from other maize varieties in essential nutrients and anti-nutrients, and all measured values fell within the range reported for commercial maize varieties 26. Analyses included consideration of fatty acids and amino acids as well as phytic acid, which is a naturally occurring maize anti-nutrient. It is important to note that conventionally bred maize varieties, which often show great variation in composition, nutritional value and/or natural toxins, are not subjected to the same level of scrutiny as T25 maize and other GM varieties.

  2. As outlined above, ACAF experts considered that the current data did not allow the conclusion that T25 maize silage was equivalent to the silage from other maize varieties. The available data gave no cause for concern, but were insufficient on their own. More information is needed and in ACAF's view this could be secured by the provision of sufficient additional analytical data to allow substantial equivalence to be concluded for silage as well for the kernel. Alternatively, data from a feeding study made with dairy cattle could be used to demonstrate the wholesomeness of the silage and a lack of any effect on milk production and composition. Milk production data is usually taken as a relatively sensitive indicator of body condition.

Cattle feeding studies

  1. The fact that no feeding studies have been carried out with T25 maize on cattle or sheep has been claimed to represent a serious weakness in the risk assessment process. ACAF has made its position of animal feed trials clear. The Committee recognises the value of animal feeding studies on target species, particularly for determining nutritional adequacy. However, it has not called for animal tests in all cases, but is committed to adopting the most effective safety assessment techniques for each case. Having reassessed T25 maize, ACAF is not of the view that feeding studies on T25 silage must be done and is content for the necessary safety data to be obtained by another route. A comparison of the composition of T25 with commercially grown maize varieties is in this case an appropriate and sufficient route. This is because supporting information about PAT (its biochemistry, natural occurrence in soil, fate in gastric juices, dissimilarity to known toxins and allergens) give no indication that it will be harmful to livestock.

Food safety and approval of T25 maize under the European Novel Foods Regulations 258/97

Ingredients derived from T25 maize were cleared for food use in the UK following a full safety assessment by the ACNFP

  1. Processed ingredients derived from T25 maize such as starch and glucose syrup were cleared for food use in the UK in February 1997 following a full safety assessment by the ACNFP 27.
  2. This assessment, which was carried out before the EU Novel Foods Regulation 258/97 came into effect, is equivalent to that now used under the Regulation. The EU rules allow a company to notify the European Commission of its intention to market a product which is considered to be substantially equivalent to an existing food or food ingredient. Aventis therefore notified the Commission of its intention to market products from T25 based on the ACNFP's full safety assessment. The concept of substantial equivalence allows for a comparison between the modified food or food ingredient and its unmodified counterpart. This comparison is based on the food's composition, nutritional value, metabolism, intended use and the level of any undesirable substances it contains.

Other considerations with T25 maize: 'Contamination' of non-GM maize by cross-pollination.

The separation distances being applied to the Farm Scale Evaluations of T25 maize will ensure that any GM presence due to cross-pollination in the neighbouring crops or silage is less than 1%. In most field situations the level will be considerably less than 1%. The separation distances are based on the best available science and internationally recognised criteria for plant breeding.

  1. Although not a safety issue the potential for T25 maize to cross-pollinate neighbouring maize crops is covered here for the sake of completeness and because there has been confusion surrounding the scientific data relating to separation distances and cross-pollination.

Separation distances employed in the Farm Scale Evaluations of T25 maize

  1. The separation distances being applied to the Farm Scale Evaluations of T25 maize aim to minimise cross-pollination with any neighbouring maize or sweetcorn crops. They will help to ensure that any GM presence due to cross-pollination in the neighbouring crops or silage is less than 1%. In most field situations the level will be considerably less than 1%, although this cannot be guaranteed in unusual weather conditions.
  2. The current FSE separation distances take account of a review of the available scientific evidence and literature in this area in 2000 by the National Institute of Agricultural Botany (NIAB) 28. Confusion has arisen because work carried out for the Soil Association by the National Pollen Research Unit (NPRU) 29 appears to contradict the NIAB report and the basis for the current separation distances. This has led some in the organic sector (and others) to call for much greater distances to protect organic farmers. The apparent contradiction between the NIAB and NPRU studies is essentially due to the fact that the former is concerned with the actual frequency of cross-pollination over distance, whereas the latter focuses on absolute distance of pollen dispersal. The ability of pollen to travel large distances is not the same as the frequency with which it results in cross-pollination.

ACRE advice in relation to the separation distances for T25 maize

  1. Similar confusion arises in respect of claims that ACRE has failed to modify its risk assessment advice for T25 maize in response to the NPRU data and, in particular, that ACRE was wrong in its 1998 advice concerning the likely cross-pollination of organic sweetcorn growing near a field trial of T25 maize in Devon 30.
  2. In this case ACRE was asked to advise on a very specific field situation and took into account local topography, size and number of maize plots (pollen dilution was a key issue as only 6 plots out of approximately 1800 were GM at the Devon site). ACRE concluded that in this specific case at a separation distance of 200 metres a cross-pollination frequency could be expected of no greater than 1 sweetcorn kernel in every 40,000 being a GM hybrid. By contrast, the NPRU report calculated that 1 kernel in 93 might be expected to be a hybrid at a separation distance of 200 metres, but crucially the NPRU report was not referring to any particular case. The authors qualified this estimate by stating that a whole variety of environmental factors could affect cross-pollination such as local topography, field size etc. These are precisely the factors that ACRE had taken into account in its 1998 advice to Ministers.
  3. ACRE subsequently reviewed the NPRU report to determine whether it raised any evidence not available when it advised on the Devon situation and whether its advice needing updating. ACRE accepted the main conclusions of the report that maize pollen can be carried by wind and insects for great distances, but the report did not provide any new information on the central issue on which ACRE had given advice previously which was on cross pollination frequency 31. The committee therefore did not alter its previous advice which is entirely consistent with the NPRU report.
  4. ACRE has also considered the issue of T25 maize cross-pollination and separation distances in relation to a request for advice from the National Assembly for Wales 32. After careful consideration ACRE endorsed the separation distances used in the FSEs and concluded that they were based on the best available science.
  5. The Government recognises that beyond the issue of safety there is a legitimate question surrounding the public acceptability of low levels of incidental GM presence in non-GM crops/food, and specifically what might be regarded as a reasonable threshold for GM presence. The Government is aware that there is a range of views on this matter and it is subject to ongoing consideration.

Further information

Detailed papers on the legal framework for GMO releases and the history and science of the Farm Scale Evaluations are available at: www.defra.gov.uk/environment/acre/index.htm

The public register entry for T25 (including the environmental risk assessment) can be viewed at Defra during office hours Monday to Friday 0900-17.00hrs at the address below or copies can be sent but first class post by phoning the public register enquiry line (below).

The full T25 dossier (15 appendices) is also available for scrutiny on the same basis as the public register entry.

GM Policy and Regulation unit
Defra
3/H8 Ashdown House
123 Victoria Street
London
SW1E 6DE
Public register enquiry line: 020 7082 8122
Email: biotech@defra.gsi.gov.uk

Alternatively you may submit further questions or comments by post or email to the above address.

1 Bad Science, Bad Decisions. Friends of the Earth briefing paper, www.foe.co.uk, and official proceedings of the Chardon LL public hearing, www.defra.gov.uk/planth/pvs/chardon/index.htm

2 Advisory Committee on Releases to the Environment.

3 Advisory Committee on Novel Foods and Processes.

4 Advisory Committee on Animal Feedingstuffs.

5 Also known as the CaMV 35S promoter, this is a small stretch of DNA used in most GM plants to switch on the inserted gene or genes.

6 T25 contains a fragment of an ampicillin antibiotic resistance gene. Experimental tests (RNA analysis - northern blots and enzyme assays) indicate that this gene fragment is not expressed in the T25 maize. This gene fragment is therefore inactive.

7 For a fuller discussion of this and related issues see: The Commercial Use of Genetically Modified Crops in the United Kingdom: the potential for wider impact on farmland wildlife. Advisory Committee on Releases to the Environment Annual report No 5: 1998. www.defra.gov.uk/environment/acre/index.htm

8 Aventis estimates 23 generations of breeding, with 40 different maize varieties world-wide now containing T25.

9 A revised Directive 2001/18/EC on GMO releases was adopted last year and will be fully implemented by October 2002. A detailed note on the regulatory framework for GMO releases is available at: www.defra.gov.uk/environment/acre/background/index.htm.

10 Morphological studies consider the way a modified plant grows, its shape and form, and whether this is the same as the unmodified plant.

11 Incidence of volunteer plants in following crops or in field margins.

12 Crawley, M.J., Brown, S.L., Hails, R.S., Kohn, D.D., & M.Rees. Transgenic crops in natural habitats. Nature, 2001 vol 409, pp 682-683.

13 It is important to note that the transgene itself is not directly toxic. Only the gene product could be toxic, so the fact that the gene is in the pollen is not an indicator of potential toxicity.

14 Glufosinate (L-PPT) inhibits glutamine synthetase in plants which leads to an accumulation of toxic levels of ammonia. PAT catalyses the acetylation of the free amino group of L-PPT to yield N-acetyl-L-PPT, a compound that does not inactivate glutamine synthetase. PAT is highly specific for L-PPT and does not acetylate other L-amino acids, nor does it acetylate D-PPT. In the presence of excess concentrations of L-amino acids, PAT is unaffected in its ability to acetylate L-PPT. In L-PPT tolerant plants which express relatively high levels of PAT, the main residue metabolite of L-PPT catabolism is N-acetyl-phosphinothricin

15 University of Jena and the Hans Knöll Institute for Natural Substance Research in Jena.

16 Horizontal gene transfer refers to a non-sexual transfer of genes between unrelated organisms. For example concern has been expressed that soil bacteria may pick up transgenes from GM plants and express them in their own cells.

17 The actinomyces, Streptomyces viridochromogenes, was the source of the pat gene in T25.

18 It has been claimed that research by Frank Gebhard & Kornelia Smalla (published in Applied and Environmental Microbiology 64 (4) 1550-1554, and FEMS Microbiology Ecology 28, 261-272) has shown that horizontal gene transfer between GM plants and bacterial can take place in the soil. These studies did not demonstrate, nor did they claim to provide evidence of, horizontal gene transfer under field conditions. ACRE reviewed these papers (www.defra.gov.uk/environment/acre/index.htm) and concluded that they provide important information on this issue and confirm advice given previously by ACRE on horizontal gene transfer.

19 To achieve efficient expression of bacterial genes in plants it is common for researchers to modify the DNA codon usage pattern to one that is more suitable for plants. The pat gene isolated from Streptomyces spp. has a high G/C content when compared to plant genes, and the native Streptomyces gene was therefore modified prior to introduction into maize. This resulted in increased expression levels of the PAT enzyme. This process does not change the amino acid sequence of the PAT enzyme.

20 Ho, M. W., Ryan, A., Cummins, J.,(1999). Cauliflower mosaic viral promoter - a recipe for disaster. Microbial Ecology in Health and Disease 11 (4)

21 www.defra.gov.uk/environment/acre/index.htm.

22 Supply Chain Initiative on Modified Agricultural Crops: the members of SCIMAC are the National Farmers Union, British Society of Plant Breeders, British Crop Protection Association, UK Agricultural Supply Trade Association and the British Sugar Beet Seed Producers Association.

23 Detailed papers on the legal framework for GMO releases and the history and science of the Farm Scale Evaluations are available: www.defra.gov.uk/environment/acre/index.htm

24 Bad Science, Bad Decisions. Friends of the Earth briefing paper, www.foe.co.uk

25 www.europa.eu.int/comm/food/fs/sc/scp/out04_enhtml

26 Some statistically significant differences were observed between the GM and non-GM varieties but all fell within the accepted range of values common for maize varieties. Animal feed experts felt that this was unlikely to be significant because livestock already experience these subtle differences in the composition of maize.

27 ACNFP 1996 Annual Report, Appendix II, pp 38-46

28 Report on the separation distances required to ensure cross-pollination is below specified limits in non-seed crops of sugar beet, maize and oilseed rape. J. Ingram. National Institute of Agricultural Botany. Published 3 August 2000.

29 Emberlin J., Adams-Groom, B. Tidmarsh, J. (1999) A Report on the Dispersal of Maize Pollen. National Pollen Research Unit, University College, Worcester. Report commission by and available from the Soil Association, Bristol House, 40-56 Victoria Street, Bristol, BS1 6BY

30 Advice for the secretary of State 23 June 1998. Genetically modified maize in national list trials adjacent to an organic farm in Devon www.defra.gov.uk/environment/acre/index.htm

31 Advice for The Secretary of State 25 March 1999. A Report on The Dispersal of Maize Pollen Compiled by the National Pollen Research Unit and Commissioned by The Soil Association www.defra.gov.uk/environment/acre/index.htm

32 www.defra.gov.uk/environment/acre/index.htm

Page published 25 February 2002;
Page last modified 7 October, 2003

Department for Environment, Food and Rural Affairs