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The Ecological Impacts of Agricultural Biotechnology

Miguel Altieri


Biotechnology may someday be considered a safe agricultural tool but studies suggest it may have harmful ecological consequences, such as:

  • spreading genetically engineered genes to indigenous plants
  • increasing toxicity, which may move through the food chain
  • disrupting nature’s system of pest control
  • creating new weeds or virus strains

February 2001


The cassava makes up part of the diet of nearly 600 million people worldwide. By inserting a bacterial version of the gene for starch production, scientists have come up with a super-sized cassava. Photo: David Monniaux.

Transgenic crops (GMCs: genetically modified crops), main products of agricultural biotechnology, are increasingly becoming a dominant feature of the agricultural landscapes of the USA and other countries such as China, Argentina, Mexico and Canada.

Nearly half of American farms grow GMCs (genetically modified crops).
  • Worldwide, the areas planted to transgenic crops jumped more than twenty-fold in the past six years, from3 million hectares in 1996 to nearly 44.2 million hectares in 2000. 10
  • In the USA, Argentina and Canada, over half of the average for major crops such as soybean, corn and canola are planted in transgenic varieties.
  • Herbicide resistant crops (HRCs) and insect resistant crops (Bt crops) accounted respectively for 59 and 15 percent of the total global area of all transgenic crops in 2000.
Big business claims GMCs will reduce the use of chemical pesticides.

Transnational corporations (TNCs) such as Monsanto, DuPont, and Novartis, the main proponents of biotechnology, argue that carefully planned introduction of these crops should reduce or even eliminate the enormous crop losses due to weeds, insect pests, and pathogens. In fact, they argue that the use of such crops will have added beneficial effects on the environment by significantly reducing the use of agrochemicals.13 However, ecological theory predicts that as long as transgenic crops follow closely the pesticide paradigm prevalent in modern agriculture, such biotechnological products will do nothing but reinforce the pesticide treadmill in agroecosystems, thus legitimizing the concerns that many environmentalists and some scientists have expressed regarding the possible environmental risks of genetically engineered organisms. In fact, there are several widely accepted environmental drawbacks associated with the rapid deployment and widespread commercialization of such crops in large monocultures, including:3,21,25

Pests show rapid evolution in resisting the pesticide properties of GMCs.
Toxic buildup in GMCs harms useful insects.
  • the spread of transgenes to related weeds or conspecifics via crop-weed hybridization

  • reduction of the fitness of non-target organisms through the acquisition of transgenic traits via hybridization

  • the rapid evolution of resistance of insect pests such as Lepidoptera to Bt

  • accumulation of the insecticidal Bt toxin, which remains active in the soil after the crop is ploughed under and binds tightly to clays and humic acids;

  • disruption of natural control of insect pests through intertrophic-level effects of the Bt toxin on predators

  • unanticipated effects on non-target herbivorous insects (i.e., monarch butterflies) through deposition of transgenic pollen on foliage of surrounding wild vegetation14

  • vector-mediated horizontal gene transfer and recombination to create new pathogenic organisms

This paper will focus on the known effects of the two dominant types of GMCs: herbicide resistant crops (HRCs) and insect resistant crops (Bt).

Biotechnology, agrodiversity and farmers’ options

Monoculture, or farming only one crop, can lead to economic disaster and hunger.

The spread of transgenic crops threatens crop diversity by promoting monocultures which leads to environmental simplification and genetic erosion. History has repeatedly shown that uniformity characterizing agricultural areas sown to a smaller number of varieties is a source of increased risk for farmers, as the genetically homogeneous fields may be more vulnerable to disease and pest attack.22

Farmers have many choices, other than biotechnology, that work.

Several people think that HRCs and Bt crops have been a poor choice of traits to feature the technology, given predicted environmental problems and the issue of resistance evolution. In fact, there is enough evidence to suggest that both these types of crops are not really needed to address the problems they were designed to solve. On the contrary, they tend to reduce the pest management options available to farmers. There are many alternative approaches, (e.g., rotations, polycultures, cover crops, biological control, etc.) that farmers can use to effectively regulate the insect and weed populations that are being targeted by the biotechnology industry. To the extent that transgenic crops further entrench the current monocultural system, they impede farmers from using a plethora of alternative methods. 2

Ecological effects of HRCs

Gene flow

Are we altering the genetic structure of living things in the name of utility and profit?

Just as it occurs between traditionally improved crops and wild relatives, pollen mediates gene flow between GMCs and wild relatives or conspecifics despite all possible efforts to reduce it. Little is known about the long-term persistence of crop genes in wild populations or about the impact of fitness-related crop genes on the population dynamics of weedy relatives. The main concern with transgenes that confer significant biological advantages is that they may transform wild/weed plants into new or worse weeds.

Hybridization of HRCs with populations of free living relatives will make these plants increasingly difficult to control, especially if they are already recognized as agricultural weeds and if they acquire resistance to widely used herbicides. For example:

  • Transgenic resistance to glufosinate can be passed on from Brassica napus to populations of weedy Brassica napa, and persist under natural conditions. 25
  • In Europe there is a major concern about the possibility of pollen transfer of herbicide tolerant genes from Brassica oilseeds to Brassica nigra and Sinapis arvensis. 8

Economic and agronomic implications

The majority of GMCs have been engineered to repel unwanted plants or weeds.

World-wide in 2000, transgenic herbicide resistant crops were planted on 74% of the 44.2 million hectares devoted to transgenic crops. 10 In North America, transgenic glufosinate resistant cultivars of canola and corn, and transgenic glyphosate resistant cultivars of soybean, corn, cotton, and canola are now commercially available. Bromoxynil resistant transgenic cotton has also been developed. The so-called Round-up ready soybeans are the most prevalent GMCs.

Transgenic herbicide resistance in crop plants simplifies chemically based weed management because it typically involves compounds that are active on a very broad spectrum of weed species. Post-emergence application timing for these materials fits well with reduced or zero-tillage production methods, which can conserve soil and reduce fuel and tillage costs.6

However, HRCs also have significant problems.

Editor’s note: Sales of biotechnology products are reaching $60 billion/year.
  • Reliance on HRCs perpetuates the weed resistance problems and species shifts that are common to conventional herbicide based approaches.

  • Herbicide resistance becomes more of a problem as the number of herbicide modes of action to which weeds are exposed becomes fewer and fewer, a trend that HRCs may exacerbate due to market forces.

  • Given industry pressures to increase herbicide sales, acreage treated with broad-spectrum herbicides will expand, exacerbating the resistance problem. For example, it has been projected that the acreage treated with glyphosate will increase to nearly 150 million acres. Although glyphosate is considered less prone to weed resistance, the increased use of the herbicide will result in weed resistance, even if more slowly, as it has been already documented with Australian populations of annual ryegrass, quackgrass, birdsfoot trefoil and Cirsium arvense.7

  • Perhaps the greatest problem of using HRCs to solve weed problems is that they steer efforts away from crop diversification and help to maintain cropping systems dominated by one or two annual species. Crop diversification can

    • reduce the need for herbicides
    • improve soil and water quality
    • minimize requirements for synthetic nitrogen fertilizer
    • regulate insect pest and pathogen populations
    • increase crop yields and reduce yield variance.

Thus, to the extent that transgenic HRCs inhibit the adoption of diversified cropping systems that include rotational crops, cover crops and green manure, they hinder the development of sustainable agriculture.

Ecological risks of Bt crops

The number of crops engineered for insect resistance is on the rise.

Based on the fact that more than 500 species of pests have already evolved resistance to conventional insecticides, pests can also evolve resistance to Bt toxins present in transgenic crops. No one questions if Bt resistance will develop, the question is now how fast it will develop. Susceptibility to Bt toxins can therefore be viewed as a natural resource that could be quickly depleted by inappropriate use of Bt crops.15 However, cautiously restricted use of these crops should substantially delay the evolution of resistance. But is cautious use of Bt crops possible given commercial pressures that have resulted in a rapid rollout of Bt crops reaching 8.2 million hectares worldwide in 2000?

Organic farmers can produce a significant yield without insecticides.

The refuge strategy of setting aside 20-30% of land to non-Bt crops to delay resistance is very difficult to implement regionally. Data from the Midwest shows that Bt corn saves on some insecticide use and yields are 2.4 Bu/acre higher than conventional corn but only under high European corn borer infestations (USDA 1999). On the other hand organic corn growers use no insecticides and obtain yields (4.8-9 t/ha) similar or slightly higher than conventional farmers (5.0-7.l t/ha).16

GMCs may have unintended victims, such as the monarch butterfly or lacewing.

BT crops and beneficial insects

Bacillus thuringiensis proteins are becoming ubiquitous, highly bioactive substances in agroecosystems. Most non-target herbivores colonizing Bt crops in the field ingest plant tissue containing Bt protein which they can pass on to their natural enemies in a more or less processed form. Polyphagous natural enemies (polyphagous: subsisting on many kinds of foods) that move between crop cultures are found to frequently encounter Bt-containing non-target herbivorous prey in more than one crop. This is a major ecological concern given previous studies that documented that Cry1 Ab adversely affected the predaceous lacewing Chrysoperla carnea reared on Bt corn-fed prey larvae.9

These findings are problematic for small farmers in developing countries who rely on insect pest control, which involves a complexity of predators in their mixed cropping systems.1 Research shows that natural enemies can be affected directly through inter-trophic level effects of the toxin present in Bt crops. This raises serious concerns about the potential disruption of natural pest control, as polyphagous predators will encounter Bt-containing, non-target prey that move within and between crop cultivars throughout the crop season. Disrupted biocontrol mechanisms will likely result in increased crop losses due to pests or to the increased use of pesticides by farmers with consequent health and environmental hazards.

Effects on the soil ecosystem

The possibilities for soil biota to be exposed to transgenic products are very high. The little research conducted in this area has already demonstrated:4, 18, 23

Toxins from GMCs remain active in the soil, decreasing soil fertility.
  • There is long term persistence of insecticidal products (Bt and proteinase inhibitors) in soil.
  • The insecticidal toxin produced by Bacillus thuringiensis subsp. kurskatki remain active in the soil, where it binds rapidly and tightly to clays and humic acids.
  • The bound toxin retains its insecticidal properties and is protected against microbial degradation by being bound to soil particles, persisting in various soils for at least 234 days.
  • The presence of the toxin in exudates from Bt corn and verified that it was active in an insecticidal bioassay using larvae of the tobacco hornworm.

Given the persistence and the possible presence of exudates, there is potential for prolonged exposure of the microbial and invertebrate community to such toxins, and therefore studies should evaluate the effects of transgenic plants on both microbial and invertebrate communities and the ecological processes they mediate.3

If transgenic crops substantially alter soil biota and affect processes such as soil organic matter decomposition and mineralization, this would be of serious concern to organic farmers and most poor farmers in the developing world. These farmers cannot purchase or don’t want to use expensive chemical fertilizers. They rely instead on local residues, organic matter and especially soil organisms for soil fertility (e.g., key invertebrate, fungal or bacterial species) which can be affected by the soil bound toxin. Soil fertility could be dramatically reduced if crop leachates inhibit the activity of the soil biota and slow down natural rates of decomposition and nutrient release.

General Conclusions and Recommendations

The available independently generated scientific information suggests that

The long-term impacts of GMCs are not yet known.
  • the massive use of transgenic crops poses substantial potential risks from an ecological point of view *the ecological effects are not limited to pest resistance and creation of new weeds or virus strains11
  • transgenic crops can produce environmental toxins that move through the food chain and also may end up in the soil and water affecting invertebrates and probably ecological processes such as nutrient cycling3
  • no one can really predict the long-term impacts that will result from such massive deployment of such crops.

Not enough research has been done to evaluate the environmental and health risks of transgenic crops, an unfortunate trend. Most scientists feel that such knowledge is crucial to have before biotechnological innovations are implemented. There is a clear need to further assess the severity, magnitude and scope of risks associated with the massive field deployment of transgenic crops. Much of the evaluation of risks must move beyond comparing GMC fields and conventionally managed systems to include alternative cropping systems featuring crop diversity and low-external input approaches. This will allow real risk/benefit analysis of transgenic crops in relation to known and effective alternatives.

The loss of agricultural diversity may lead to disaster in developing countries.

Moreover, the large-scale landscape homogenization with transgenic crops will exacerbate the ecological problems already associated with monoculture agriculture. Unquestioned expansion of this technology into developing countries may not be wise or desirable. There is strength in the agricultural diversity of many of these countries, and it should not be inhibited or reduced by extensive monoculture, especially when consequences of doing so results in serious social and environmental problems.2

The repeated use of transgenic crops in an area may result in cumulative effects such as those resulting from the buildup of toxins in soils. For this reason, risk assessment studies not only have to be of an ecological nature in order to capture effects on ecosystem processes, but also of sufficient duration so that probable accumulative effects can be detected. The application of multiple diagnostic methods will provide the most sensitive and comprehensive assessment of the potential ecological impact of transgenic crops.

Conclusion: agricultural biotechnology is driven by profit, not by scientific research.

Although biotechnology is an important tool, at this point alternative solutions exist to address the problems that current GMCs, developed mostly by profit motives, are designed to solve. The dramatic positive effects of rotations, multiple cropping, and biological control on crop health, environmental quality and agricultural productivity have been confirmed repeatedly by scientific research. Biotechnology should be considered as one more tool that can be used, provided the ecological risks are investigated and deemed acceptable, in conjunction with a host of other approaches to move agriculture towards sustainability.17

Miguel Altieri, Ph.D., teaches agroecology in the Department of Environmental Science, Policy and Management at University of California at Berkeley, and is a technical advisor to the Latin American Consortium on Agroecology and Development in Santiago. He is also the General Coordinator for the United Nations Development Programme’s Sustainable Agriculture Networking and Extension Programme. He has written numerous books and articles and has become an outspoken scientist on the ecological risks of agricultural biotechnology.

The Ecological Impacts of Agricultural Biotechnology

ActionBioscience Articles

Traits Introduced into Plants by Genetic Engineering

A brief overview of the traits being engineered in plants - from herbicide tolerance to improved nutritional value.

Council for Agricultural Science and Technology (CAST)

CAST is the science source for food, agricultural, and environmental information in the USA.

Agriculture Network Information Center (AgNIC)

AgNIC is a guide to quality agricultural information on the Internet as selected by the National Agricultural Library, Land-Grant Universities, and other institutions.

The Nature Institute

Provides commentaries on new developments in genetics and genetic engineering, and promotes a holistic approach to seeing and understanding nature and technology.

USDA Agricultural Biotechnology: Questions and Answers

Breeders have been evaluating new products developed through agricultural biotechnology for centuries. In addition to these efforts, the United States Department of Agriculture (USDA), the Environmental Protection Agency (EPA), and the Food and Drug Administration (FDA) work to ensure that crops produced through genetic engineering for commercial use are properly tested and studied to make sure they pose no significant risk to consumers or the environment. Learn the answers to popular AG Biotech questions, as well as gain access to useful resources, including a biotechnology glossary.

Biotechnology Offers U.S. Farmers Promises and Problems

To get to this interesting article, click on archives and then Spring 1999 issue.

DNA from bacteria in GMOs

A study summary that claims GE crops contain bacterial DNA that may be hazardous to health.

31 Critical Questions in Agricultural Biotechnology

A compilation of answers to 31 frequently asked questions about biotechnology.

Transgenics Crops

The National Sustainable Agriculture Information Service provides an introduction and overview of transgenic crops—including potential problems. Furthermore, the site provides many useful resources. The second link provides a factsheet of the Genetically Modified Crops in the United States.

Read a book

High Tech Harvest: Understanding Genetically Modified Food Plantsby Paul Lurquin, a biologist, clearly explains modern plant genetics and genetically engineered crops worldwide (Westview Press, 2002).

Organic Consumers Association

Join one of the organization’s many campaigns for “food safety, organic agriculture, fair trade, and sustainability.”

Agricultural Biotechnology

Articles and other resources from Purdue University. A good primer on the subject.

Genetic Engineering Action Network (GEAN)

GEAN is is a network of grassroots activists, non-governmental organizations, and scientists who are active on issues in biotechnology. The second link takes you to their resources page with links to other activist organizations, such as Greenpeace and GRAIN.

Lesson Title: Biotechnology: An Agricultural Dilemma
Levels: high school - undergraduate
Summary: This lesson examines potential benefits and risks of genetically modified crops (GMCs). Students can debate the environmental risks of GMCs, develop an action plan to save farmland from superweeds, participate in a public meeting to determine the fate of select GMCs in India, create ads promoting GMCs … and more!_

Download/view lesson. (To open the lesson’s PDF file, you need Adobe Acrobat Reader free software.)

Useful links for educators

  • » Agriculture in the Classroom
    Lesson plans and other resources for educators teaching about agriculture. This program is coordinated by the United States Department of Agriculture.

Useful links for student research

In addition to the links in the “learn more” section above:

  1. Altieri, M.A. (1994). Biodiversity and Pest Management in Agroecosystems. Haworth Press, New York.
  2. Altieri, M.A. (1996). Agroecology: The science of sustainable agriculture. Westview Press, Boulder.
  3. Altieri M.A. (2000). “The ecological impacts of transgenic crops on agroecosystem health.” Ecosystem Health 6: 13-23.
  4. Donegan, K.K., C.J. Palm, V.J. Fieland, L.A. Porteous, L.M. Ganis, D.L. Scheller and R.J. Seidler (1995). “Changes in levels, species, and DNA fingerprints of soil microorganisms associated with cotton expressing the Bacillus thuringiensis var. Kurstaki endotoxin.” Applied Soil Ecology 2, 111-124.
  5. Donegan, K.K. and R.J. Seidler (1999). “Effects of transgenic plants on soil and plant microorganisms.” Recent Res. Devel. Microbiology 3: 415-424
  6. Duke, S.O. (1996). Herbicide resistant crops: agricultural, environmental, economic regulatory, and technical aspects, p. 420. Lewis Publishers, Boca Raton.
  7. Gill, D.S. (1995). “Development of herbicide resistance in annual ryegrass populations in the cropping belt of Western Australia.” Australian Journal of Exp. Agriculture 3, 67-72.
  8. Goldberg, R.J. (1992). “Environmental concerns with the development of herbicide-tolerant plants.” Weed Technology 6, 647-652.
  9. Hilbeck, A., M. Baumgartner, P.M. Fried, and F. Bigler (1998). “Effects of transgenic Bacillus thuringiensis corn fed prey on mortality and development time of immature Chysoperla carnea (Neuroptera: Chysopidae).” Environmental Entomology 27, 460-487.
  10. James, C. (2000). “Global review of commercialized transgenic crops: 2000. International Service for the Acquisition of Agri-Biotech Application.” ISSA Briefs No. 21-2000, Ithaca.
  11. Kendall, H.W., R. Beachy, T. Eismer, F. Gould, R. Herdt, P.H. Ravon, J. Schell, and M.S. Swaminathan (1997). “Bioengineering of crops.” Report of the World Bank Panel on transgenic crops, World Bank, Washington, D.C. p. 30.
  12. Kjellsson, G. and V. Simonson (1994). Methods for risk assessment of transgenic plants, p. 214. Birkhauser Verlag, Basil.
  13. Krimsky, S. and R.P. Wrubel (1996). Agricultural Biotechnology and the Environment: Science, Policy and Social Issues. University of Illinois Press, Urbana.
  14. Losey, J.E., L.S. Rayor and M.E. Cater (1999). “Transgenic pollen harms monarch larvae.” Nature 399, 241.
  15. Mellon, M and J. Rissler (1998). “Now or never: serious plans to save a natural pest control.” Union of Concerned Scientists. Washington DC.
  16. National Research Council (1984) Alternative Agriculture. National Academy Press. Washington DC.
  17. National Research Council (1996). “Ecologically based pest management.” National Academy of Sciences, Washington, DC.
  18. Palm, C.J., D.L. Schaller, K.K. Donegan and R.J. Seidler (1996). “Persistence in soil of transgenic plant produced Bacillus thurigiensis var. Kustaki endotoxin.” Canadian Journal of Microbiology (in press).
  19. Paoletti, M.G. and D. Pimentel (1996). “Genetic engineering in agriculture and the environment: Assessing risks and benefits.” BioScience 46, 665-671.
  20. Pimentel, D., M.S. Hunter, J.A. LaGrow, R.A. Efroymson, J.C. Landers, F.T. Mervis, C.A. McCarthy and A.E. Boyd (1989). “Benefits and risks of genetic engineering in agriculture.” BioScience 39, 606-614.
  21. Rissler, J. and M. Mellon (1996). The Ecological Risks of Engineered Crops. MIT Press, Cambridge.
  22. Robinson, R.A. (1996). “Return to resistance: Breeding crops to reduce pesticide resistance.” AgAccess, Davis.
  23. Saxena, D., S. Flores and G. Stotzky (1999). “Insecticidal toxin in root exudates from Bt corn.” Nature 401,480.
  24. Schuler, T.H., R.P.J. Potting, I. Dunholm, and G.M. Poppy (1999). “Parasitoid behavior and Bt plants.” Nature 400, 825.
  25. Snow, A.A. and P. Moran (1997). “Commercialization of transgenic plants: Potential ecological risks.” BioScience 47, 86-96.
  26. Steinbrecher, R.A. (1996). “From green to gene revolution: The environmental risks of genetically engineered crops.” The Ecologist 26, 273-282.
  27. Tabashnik, B.E. (1994). “Delaying insect adaptation to transgenic plants: Seed mixtures and refugia reconsidered.” Proc. R. Soc. London 255, 7-12.
  28. United States Department of Agriculture (1999). “Genetically engineered crops for pest management.” USDA Economic Research Service, Washington DC.


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