Environmental impacts of GM crops3. A synthesis of available data on environmental impacts of Bt maize and HT oilseed rape within European cropping systems has been produced
SIGMEA reviewed the (a) impacts of gene flow and introgression on within-and-between-species plant diversity and (b) the wider ecological implications of growing Bt maize and HT oilseed rape. It linked several important ‘impact’ studies, notably those in Spain on Bt maize[1] and in the UK on HT beet, maize and oilseed rape[2], and was closely associated with the EU ECOGEN project on Bt maize[3].
The approaches to studying environmental impacts in SIGMEA were based on the key elements described in the US Environmental Protection Agency Guidelines of 1998 and the European Food Safety Authority Guidance Document of 2006. The 'exposure' and the 'effect' were considered for a range of ecological indicators of the in-field soil and food web, including soil biophysical status, soil micro- and meso-fauna, plant species, functional groups and assemblages (as affected by introgression and field management, e.g. herbicide), plant-feeding invertebrates and other invertebrate functional or trophic groups. There was little evidence available to SIGMEA (and little evidence generally) of wider effects on, for example, biogeochemical cycles and the quality of water or air. The conclusions reached by SIGMEA for the main crops studied are as follows:
• Maize (Bt varieties, targeted at corn borers). There appears to be no reason on grounds of biosafety not to increase the scale of growing. The most consistent finding is that Bt maize in field trials and crop production in Europe to date had no systematic or reproducible effects on any of the invertebrates or soil organisms studied over a time period of several years. In contrast, over similar time periods, other agronomic factors did have large and measurable effects on the same organisms. Appropriate monitoring should be in place, especially for resistance development in corn borers, and potential effects on certain sensitive non-target biotic groups should be considered in greater depth.
• Oilseed rape (HT varieties, tolerant to glufosinate ammonium or glyphosate). The ranking of HT oilseed rape against the comparator, usually the conventional crop and agronomy, varied with the local context. Negative effects occurred where a) the herbicides used in HT cropping caused a systematic depletion of the weed flora and dependent invertebrates resulting in reductions in biodiversity within fields, and b) the presence of HT volunteers limited future options for use of herbicides and the growing of certain crops such as beans in which volunteers are difficult to control. Positive effects may occur due to the herbicides used with HT cropping being less toxic to non-weed organisms than most other herbicides and crop protection chemicals. Nevertheless, the ecological effects of HT crops compared to non-HT in the same production system are generally smaller than those due to differences between crop species, season of sowing or agronomic practices.
• Beet. The various types of beet - crop, weed, feral, wild - are in genetic contact through seed and pollen. Wild beet needs proactive conservation, since it is a biologically interesting plant form of restricted habitat, a source of genes for future beet breeding and a source of annual impurities in crop beets. HT beet cultivation could also deplete biodiversity within fields for the same reasons as discussed for HT oilseed rape.
In summary, statistically significant effects of GMHT cropping on ecological processes or organisms have been obtained in the field, but most effects are smaller than or at most comparable to those due to general agronomic operations. There is an increasing consensus that future assessment of GM crops considers both negative and positive impacts of GM cropping in a more holistic way than previously. Most important, standards and criteria for environmentally resilient cropping systems are needed against which GM cropping and its non-GM comparator can be assessed. Setting such environmental standards is now an absolute priority.
[1]Monitoring programme of Bt maize in Spain: Farinos et al., 2008. Diversity and seasonal phenology of aboveground arthropods in conventional and transgenic maize crops in Central Spain. Biological Control, Volume 44, Issue 3, March 2008, Pages 362-371
[2]Farm Scale Evaluation : Firbank et al., 2003. An introduction to the Farm Scale evaluations of genetically modified herbicide-tolerant crops. Journal of Applied Ecology 40, 2-16.
[3] FP5 project ECOGEN (www.ecogen.dk/reports) - PH Krogh & B. Griffiths, 2007. ECOGEN: soil ecological and economic evaluation of Genetically Modified Crops. Pedobiologia 51 (2007) 171—173
Writing:
A. Messéan (INRA)
Creation date: 21 May 2009 Update: 28 May 2009 |