Les Levidow, Susan Carr and David Wield (left) describe how legislating on genetically modified food is giving the European Union a headache

Since the 1980s there has been a wide-ranging debate about the hazards involved in releasing genetically modified organisms. Biotechnologists claim merely to correct genetic deficiencies, thus improving natural processes; they promise environmentally friendly products for protecting crops, even for "feeding the world". Environmentalist critics foresee genetically modified organisms aggravating the existing problem of technological dependency; for example, their use might supplement the familiar "pesticide treadmill" with a "genetic treadmill" of technical fixes.

The European Commission's Deliberate Release Directive 90/220 aimed to address this by linking environmental precaution with "harmonised procedures" among member states for market approval of products based on genetically modified organisms. But despite this, every marketing application has undergone a disputes procedure.

For example, Plant Genetic Systems requested market approval for a herbicide-tolerant oilseed rape. When our Department of the Environment recommended approval, some member states objected that the herbicide-tolerance gene might spread and generate herbicide-tolerant weeds, thus potentially restricting options for weed-control methods and for future agricultural policy.

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In another difficult case, Ciba-Geigy requested market approval for a maize plant that contained genes for both an insecticide (a Bt toxin) and herbicide-tolerance. When France recommended market approval, some members objected that the product could intensify selection pressure for insects resistant to the naturally occurring toxin, thus eliminating a safe alternative to chemical pesticides.

In both cases, member states disagreed over the statutory relevance of so-called "secondary effects". Proponents of market approval argued that the directive encompasses only "product safety", that is, the direct ecological effects of the modified organism or its inserted genes. Others emphasised the requirement that all appropriate measures be taken "to avoid adverse effects on human health and the environment", which they interpreted to encompass agricultural practices in using the product.

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Beneath the stances lies an ambiguity in defining and anticipating the relevant "adverse effects". For the oilseed rape, UK regulators judged that spread of the herbicide-tolerance gene could not cause harm to agriculture, because other effective herbicides were available. Yet DoE advisers regarded some potential effects as "borderline cases", somewhere between environmental harm and agricultural problems. Moreover, after recommending market approval of the product, the DoE itself funded large-scale safety trials.

A related ambiguity operates in France. For herbicide-tolerant oilseed rape, the French advisory committee perceived "no uncertainties about an identified or potential risk". Rather, it emphasised "unknowns about socioeconomic consequences', that is, the prospect of generating herbicide-tolerant weeds. Citing those unknowns, the committee recommended market approval be granted only on a five-year basis, with mandatory monitoring of commercial usage. According to the committee chairman: "The term 'environment' should be understood in a broad sense: herbicide-resistant weeds can be an environmental problem for the relevant agrosystem ..." Thus "environmental harm" has been flexibly defined, even by the same advisers, depending upon the precautionary measures to be justified.

In that way, the herbicide-tolerant oilseed rape also illustrates difficulties in applying the "step-by-step principle", which the EC directive had incorporated as a means to obtain safety data before large-scale releases. Should commercial use count as the final "step", or as an intermediate "step" P in effect, as a large-scale experiment? Despite proposals that post-market monitoring be legally required, such a precaution has been relegated to a voluntary basis, as if it were unnecessary to prevent environmental harm.

Market approvals also involve disputes over what labelling (if any) to require. Some member states argue that labelling may be required only "in relation to the risk assessment"; yet market approval implies products are safe, regardless of how they are used. Other member states demand that products are labelled as "genetically modified", regardless of their safety. Similarly, non-governmental organisations have demanded that any novel food be labelled to ensure informed choice.

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In all those ways genetically modified organisms risk regulation has had contested boundaries. It faces the difficult task of harmonising the basis of market approval, while overcoming the legitimacy problems of biotechnology.

From Precautionary to Risk-Based Regulation: the Case of GMO Releases, funded by Britain's Economic and Social Research Council.

Les Levidow, Susan Carr and David Wield, centre for technology strategy, Open University.