The debate over the environmental impact of genetically modified (GM) crops is growing increasingly complex, intense, and extremely emotional. It is further complicated as new research is published. Are GM crops safe for the environment?
This Pocket K attempts to shed light on this issue by addressing basic questions regarding GM crops and the environment.
Assessing the environmental impact of GM crops is often difficult as many factors are considered. Some scientists focus on the potential risks of GM crops, while others emphasize their potential benefits. Just what are the issues and how can we address them?
What is the current environmental situation?
A growing population, global warming, and loss of biodiversity are having a tremendous impact on our environment.
By the year 2020, there will be 8 billion people living on this planet. This means that in the next 20 years, population is expected to increase by 2 billion. Feeding these people will mean massive changes in the production, distribution, and stability of food products.
Unfortunately, cropland and population are not uniformly distributed. For example, China has only 7% of the world’s productive land but 20-25% of the world’s population. This situation is aggravated by diminishing cropland due to erosion, fewer renewable resources, less water, and a reduced population working the land.
The destruction of wilderness and forests and continued use of coal and oil have led to a steady increase in carbon dioxide levels resulting in global warming. It is predicted that the average global temperature will rise by 2-3 ºC by the year 2100 with increasing fluctuations in weather conditions. Climate change can radically alter rainfall patterns and therefore require the migration of people and shifts in agricultural practices.
Further, an increasing human population is responsible for wilderness destruction, water quality problems, and diversion of water. The loss of habitat has resulted in many species being displaced.
Thus, to conserve forests, habitats, and biodiversity, it is necessary to ensure that future food requirements come only from cropland currently in use.
What are the environmental benefits of GM crops?
One of the significant environmental benefits of GM crops is the dramatic reduction in pesticide use, with the size of the reduction varying between crops and introduced trait.
- In 2000, total global reduction in pesticide use was estimated at 22.3 million kg of formulated product as a result of using herbicide tolerant GM soybean, seed rape, cotton and corn varieties and insect protected GM cotton; the deployment of insect-resistant Bt varieties was estimated to have reduced the total world use of insecticides by 14%.1
- In the USA, adoption of GM crops resulted in pesticide use reduction of 45.6 million pounds in 2001 (Gianessi et al. 2002).2
- Use of Bt cotton in China has led to a 60-80% reduction in the use of foliar insecticides3 and an estimated 15,000 tons reduction in pesticide use.4
- Herbicide tolerant soybean farmers in North America are able to spray less to control weeds and use no-till or conservation-till cultivation systems.5,6,7
- Reduced use of pesticides can significantly decrease their effects on water quality through run-off and leaching of residues into surface and groundwater. For example, run-off water from US fields planted with Bt cotton was virtually free of insecticides during a four-year US Department of Agriculture study.
- GM crops can significantly improve crop yields, so that more food can be grown on less land area. For example, in the US, 66 million bushels of corn were saved from the corn borer in 1999.6
How are GM crops assessed for environmental safety?
GM crops are thoroughly evaluated for environmental effects before entering the marketplace. They are assessed by many stakeholders in accordance with principles developed by environmental experts around the world.8,9,10 Among those who conduct risk assessment procedures are the developers of GM crops, regulatory bodies, and academic scientists.
Most countries use similar risk assessment procedures in considering the interactions between a GM crop and its environment. These include information about the role of the introduced gene, and the effect that it brings into the recipient plant. Also addressed are specific questions about unintentional effects such as:
- impact on non-target organisms in the environment
- whether the modified crop might persist in the environment longer than usual or invade new habitats
- likelihood and consequences of a gene being transferred unintentionally from the modified crop to other species
What are the potential risks?
Potential of the introduced genes to outcross to weedy relatives as well as the potential to create weedy species
Outcrossing is the unintentional breeding of a domestic crop with a related plant. A major environmental concern associated with GM crops is their potential to create new weeds through outcrossing with wild relatives or simply by persisting in the wild themselves.
The potential for the above to happen can and is assessed prior to introduction and is monitored after the crop is planted as well. A ten-year study initiated in 1990 demonstrated that there is no increased risk of invasiveness or persistence in wild habitats for GM crops (oilseed rape, potatoes, corn, and sugarbeet) and traits (herbicide tolerance, insect protection) tested when compared to their unmodified counterparts.11 The researchers stated, however, that these results “do not mean that genetic modifications could not increase weediness or invasiveness of crop plants, but they do indicate that productive crops are unlikely to survive for long outside cultivation.” It is therefore important, as regulations require, to evaluate individual GM crops on a case-by-case basis.
Direct effects on non-target organisms
In May 1999, it was reported that pollen from Bacillus thuringiensis (Bt)-insect resistant corn had a negative impact on Monarch butterfly larvae. This report raised concerns and questions about potential risks to Monarchs and perhaps other non-target organisms. Some scientists, however, urged caution over the interpretation of the study because it reflects a different situation than that in the environment. The author indicated “Our study was conducted in the lab and, while it raises an important issue, it would be inappropriate to draw any conclusions about the risk to Monarch populations in the field solely on these initial results.”
A report from the US Environmental Protection Agency (EPA) indicated that the “data provide a weight of evidence indicating no unreasonable adverse effects of Bt proteins expressed in plants to non-target wildlife” Furthermore, a collaborative research effort by North American scientists has concluded that in most commercial hybrids, Bt expression in pollen is low, and laboratory and field studies show no acute toxic effects at any pollen density that would be encountered in the field..13
Development of insect resistance
Another concern over the use of Bt crops is that it will lead to the development of insect resistance to Bt. Insect resistance management plans have been developed by government, industry, and scientists to address this issue.
These plans include a requirement that every field of insect-resistant crops must have an associated refuge of non-GM crops in order for the insects to develop without selection to the insect resistant varieties.
Additional resistance management practices are also being developed by scientists all over the world.
The environmental and ecological concerns potentially associated with GM crops are evaluated prior to their release. In addition, monitoring and good agricultural systems are in place to detect and minimize potential risks. Comparisons among GM, conventional, and other agricultural practices, such as organic farming, will bring to light the relative risks and benefits of adopting GM crops.
- Phipps, R.H. and J.R. Park. 2002. Environmetal benefits of genetically modified crops: Global and European perspectives on their ability to reduce pesticide use, Journal of Animal and Feed Science, 11:1-18.
- Gianessi, L.P., C.S. Silvers, S. Sankula and J.E. Carpenter. 2002. Plant biotechnology: Current and potential impact for improving pest management in U.S. agriculture: An analysis of 40 case studies, National Center for Food and Agricultural Policy, Washington, D.C., June.
- Xia, J.Y., J.J. Cui, L.H. Ma, S.X. Dong, and X.F. Cui. 1999. The role of transgenic Bt cotton in integrated insect pest management. Acta Gossypii Sinica 11(2):57-64.
- Pray, C.E., D. Ma, J. Huang and F. Qiao. 2001. Impact of Bt cotton in China, World Development, 29:813-25
- American Soybean Association (ASA). Conservation Tillage Study, 2001.
- Carpenter, J.E. and Gianessi, L.P. “Agricultural Biotechnology: Updated benefit estimates.” National Center for Food and Agricultural Policy, 2001.
- Canola Council of Canada. “An agronomic and economic assessment of transgenic canola”. Canola Council of Canada: 1-95, 2001 www.canola-council.org/production/gmo1.html
- U.S. National Research Council, 1989. Field testing genetically modified organisms: Framework for decisions. Committee on Scientific Evaluation of the Introduction of Genetically Modified Microorganisms and Plants into the Environment. National Academy Press, Washington, D.C.
- Organization for Economic Cooperation and Development, 1992, Safety considerations for biotechnology, OECD, Paris, 50 pp.
- Government of Canada, 1994. Assessment criteria for determining environmental safety of plants with novel traits. Dir9408, Dec. 16, 1994. Plant Products Division, Plant Industry Directorate, Agriculture and Agri-food Canada.
- Crawley, M.J., Brown, S.L., Hails, R.S., Kohn, D.D. and Rees, M. 2001. Biotechnology: Transgenic crops in natural habitats. Nature, 409:682-683.
- U.S. Environmental Protection Agency, 2000. “Bt Biopesticides Registration Action Document Preliminary Risks and Benefits Sections Bacillus thuringiensis Plant-Pesticides.” www.epa.gov/scipoly/sap
- Sears, M., R.L. Hellmich, D.E. Stanley-Horn, K.S. Oberhauser, J.M. Pleasants, H.R. Mattila, B.D. Siegfried, and G.P. Dively. Impact of Bt corn pollen on monarch butterfly populations: A risk assessment. PNAS 98:11937-11942; plublished online before print as 10.1073/pnas.211329998.