Topics: Topics: Environmental Impact of GM Crops

The science review centres on particular scientific topics being debated widely by the science community and others. The Forum closed for contributions on 15 October.

This section of the science review considers the status of our current knowledge about how GM plants behave in the environment. It endeavours to identify what we know, what we do not know and whether the ecological tools available can fill in identified knowledge gaps. It also seeks to identify approaches to minimising risks from hitherto unidentified risks. The issues are wide-ranging. A few examples are listed which have been debated by scientists over recent years engaged in GM research, and these are mentioned to help prime the review. We hope that scientists working in areas outside GM will make contributions that might offer insights.

The experience of invasive species provides a warning as to how damaging the introduction of new organisms can be to the environment and the impetus to try and predict how new organisms, in this case genetically modified ones, will behave before they are released. Rhododendrons (introduced to the United Kingdom) provide a good example of an introduced plant, which has escaped from gardens, and become a serious problem in many semi-natural areas of United Kingdom where it has out-competed and displaced other plants. Can we predict what makes a plant invasive?

Organisms live in communities and interact with one another. For example, a genetically modified plant growing in a field will, during the course of a growing season, come in contact with a myriad of organisms both above and below ground. There can be direct, indirect, immediate and delayed interactions. In the face of this how can predictions be made as to how genetically modified plants will behave in the environment when released?

It has been suggested that a complete environmental audit of all these environmental interactions to assess the impact of genetically modified organisms is needed before they are released. Is this a realistic proposition? Is it necessary? Can one simply assume that interaction between, for example, oilseed rape and its environment are the norm and use this as the basis for focussing the assessment on the effect of the GM trait that has been introduced into the recipient plant? If we accept this approach - focusing the risk assessments on identifying novel interactions arising from the inserted transgene - how do we identify the relevant ecological interactions?

Identifying relevant ecological interactions is similar to the issues raised at another level of organisation - evaluating how a transgene in a new genetic background will behave through its interaction with other resident genes. Is a complete metabolic audit required to come to meaningful conclusions in this situation? Molecular tools to describe in fine detail the composition of organisms are under development and can detect very small differences between wild type and GM organism (see section on food and feed safety). A key question is how such data would be used in safety assessments. By analogy, what tools do ecologists have to determine how GM plants will behave in the environment?

Some GM crops may be beneficial to wildlife. They may offer more efficient utilisation of nutrients and result in reduced inputs of fertilisers, or require lower applications of pest, fungal and weed control agents (insecticides, fungicides, herbicides). If a GMO seems to offer both environmental risks and benefits can science help us weigh one against the other?

Some claim that GM crops will produce economic benefits for farmers who use them. To the extent that this is the case then it could mean that not only would GM crops replace their conventional relatives (eg GM oil seed rape might be grown in places where conventional oil seed rape is currently grown) but also that GM crops might be grown more frequently in rotations (eg that industrial GM oil seed rape might replace set aside in rotations) or that GM crops might be grown in parts of the country where their conventional relative is rarely grown (eg GM oil seed rape might be grown in pastural areas in the west of the country where there is currently little arable farming). Such land use changes might have far-reaching impacts on biodiversity, landscape quality, water quality, soil quality etc.

If you are also interested in this aspect of the science review, you are encouraged to visit the economics component of the GM dialogue being undertaken by the Strategy Unit which has been asked to carry out a study into the overall costs and benefits associated with the growing of GM crops, including their effect on conventional and organic farming interests.

Key issues

  • What is environmental harm and how do we measure it?
  • What is biodiversity?
  • How do we measure soil biodiversity?
  • Not all change is detrimental, so when is a change in biodiversity harmful and when is it beneficial?
  • What are the appropriate base lines for comparing GM crops?
  • Non-target and indirect effects. How can we evaluate these? Is ecology too complex to do this?
  • Insect and disease-resistant crops lead to the rapid development of resistant insects and diseases. Will GM traits encourage this?
  • What makes a plant invasive? Will GM traits encourage this?
  • What experiments have already been done on the behaviour of GM crops in the environment?
  • What approaches can be used to provide a link between the short-term ecological issues and the long-term evolutionary implications?
  • Where there is uncertainty, what contribution can GM plant design, monitoring or agronomic practices make to minimise this?
  • In some countries GM agriculture is commonplace. What scientific studies have been done to monitor the impact of GM agriculture on the environment in these countries and are these studies relevant to the United Kingdom?
  • What sorts of effects on the environment are irreversible? Do we have examples from current agricultural systems?
  • How can delayed environmental effects be detected? Are there relevant approaches used in other areas of environmental science?
  • Can we be optimistic that the relevant experiments to fill identified knowledge gaps can be constructed, or is the natural world so complex and chaotic that we can have little security in predicting how genetically modified organisms will behave in the environment?
  • the management regime associated with a GM crop, for example herbicide or insecticide use, is part of the package that needs to be assessed when examining the environmental impacts of GM crops - how can this be done?
  • GM crops could dramatically influence the economics of land use and thus change cropping patterns and crop rotations - they could even lead to completely different crops being grown in different parts of the country. How can the potential impacts on biodiversity, landscape, pesticide pollution of watercourses etc of future land use change be assessed?


Potential Wider Impact on Farmland Wildlife

Criteria to gauge harm

Guidelines for growing newly developed herbicide tolerant crops.

Insect-resistant transgenic plants in a multi-tropic context

Gene stacking in herbicide tolerant oilseed rape: lessons form the North American Experience.

Avoiding complexity and simplifying environmental risk assessment. Guidance prepared by the Advisory Committee on Releases to the Environment (ACRE) on principles of best practice in GM crops design which includes reference to the possibilities of avoiding identifiable and unidentifiable risks.

Monarch larvae sensitivity to Bacillus thuringiensis-purified proteins and pollen.
Richard L. Hellmich, Corn Insects and Crop Genetics Unit, Agricultural Research Service-U.S. Department of Agriculture, Ames, Iowa

Impact of Bt corn pollen on monarch butterfly populations: A risk assessment.
Mark K. Sears, Department of Environmental Biology, University of Guelph, Ontario, Canada

Corn pollen deposition on milkweeds in and near cornfields.
John M. Pleasants, Department of Zoology and Genetics, Iowa State University, Ames

Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies.
Diane E. Stanley-Horn, Department of Environmental Biology, University of Guelph, Ontario, Canada

Temporal and spatial overlap between monarch larvae and corn pollen.
Karen S. Oberhauser; Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota

Effects of exposure to event 176 Bacillus thuringiensis corn pollen on monarch and black swallowtail caterpillars under field conditions.
M. R. Berenbaum, Department of Entomology, University of Illinois at Urbana-Champaign, Urbana, Illionois

A Report on a Paper Concerning the Diversity of Bacterial Communities Associated with Conventional and Genetically Modified Herbicide Tolerant Oilseed Rape - Advice of the Advisory Committee on Releases to the Environment under Section 124 of the Environmental Protection Act 1990

Defra Research Report 17: The Risks and Consequences of Gene Transfer from Genetically-Manipulated micro-organisms in the Environment (Adobe Acrobat format, 100kb)