Environmental Hazards of Genetically Engineered Plants


Biological Pollution

Genetically engineered (GE) plants are created by splicing foreign genetic material into plant genomes, creating new organisms that could never arise in nature. The most common form of gene-splicing is quite similar to the process of viral infection. The gene is first cobbled together with pieces of unstable DNA from disease-causing viruses and bacteria, which are required to "infect" the target plant with the desired gene, overcome the plant’s defense mechanisms against foreign DNA, and force the plant to express the inserted gene. Once inserted, both the gene and its viral helpers are passed on to future generations; they may mutate, recombine with viruses, or be transferred "horizontally" to other organisms, with unknown and largely unstudied consequences. While chemical toxins may be cleaned up, genetic engineering truly gives pollution a life of its own.

Chemical Dependence

Almost two-thirds of genetically engineered crops grown on a commercial basis in the United States have been modified to tolerate certain proprietary herbicides or weedkillers. Crops such as corn, soy and canola have been genetically engineered to withstand otherwise lethal doses of chemical pesticides. Farmers, therefore, can douse their fields with herbicides without having to worry about killing their crops.

Herbicide-tolerant crops contradict the claim that genetic engineering will help the environment. Instead of moving farmers away from their dependence on chemical pesticides, the crops actually encourage pesticide use – a threat to our drinking water, our food and to wildlife. A report by Benbrook Consulting in July 1999, which reviewed more that 8,200 university-run field tests on herbicide-resistant crops, found that farmers planting Roundup Ready soybeans used two to five times more herbicides than conventional soybean farmers.


It has been shown that herbicide-resistance genes can spread to related plants in pollen carried by bees or the wind. Researchers have found evidence for this in the case of canola and sugar beet in Europe. In Canada, volunteer canola resistant to three different herbicides resulted from such uncontrollable cross-breeding between plants resistant to one herbicide each.

These superweeds can be difficult and expensive for farmers to eradicate. They could displace existing species of plants, destroying local ecosystems and threatening biodiversity.

Research in the UK has shown that pollen from GE crops can contaminate fields up to 4 km away, creating serious liability problems for farmers growing crops for the expanding markets in non-GE and organic foods.

Herbicide-resistant crops, themselves, may also become weeds if they grow in places where humans don’t want them. We already have examples of the consequences of intentionally introducing non-native plants into the environment. Kudzu and Johnson grass, for example, were both introduced into the United States and today have become serious weeds.

Pesticide Plants

Second in acreage only to herbicide-resistant crops, pesticide plants are engineered to produce toxin in all their tissues, including the edible grain. Pesticide plants are produced by means of a "gene gun," which is used to "shoot" a toxin-producing gene taken from a soil bacterium – Bacillus thuringiensis (Bt) – directly into the tissue of corn, canola, potatoes and cotton to make the plants poisonous to insects. About 25% of the U.S. corn crop is now planted in Bt varieties. Proponents of genetic engineering argue that Bt crops will reduce the need for insecticides and therefore spare the environment. In fact, the transformation of plants into pesticides is a terribly misguided development with ominous implications for the health of the ecosystem.

Effects on non-target organisms:

The toxin gene found naturally in Bt bacteria produces an inactive "protoxin" that is activated by the gastric juices of certain insects; the activated toxin then destroys their digestive tracts and kills the insects. In contrast, genetically engineered plants produce an active toxin that does not require activation.

In 1999, scientists at Cornell University revealed that pollen from genetically engineered Bt corn can kill Monarch butterflies. The findings of this lab study have since been confirmed in an ongoing field study at Iowa State University.

New research also shows that the Bt toxin can leach through plant roots into the soil where it binds to soil particles and remains active for up to 250 days, possibly harming soil micro-organisms and disrupting the soil ecology.

Evidence shows that Bt crops may also affect beneficial predator insects such as lacewings and ladybirds when they eat insects that have been feeding on genetically engineered plants.

A Threat to Organic Agriculture

Bt crops also pose a threat to organic agriculture. Organic farmers have long used the Bt toxin in a natural spray as a component of an integrated pest management scheme. The spray targets specific pests and is non-toxic to mammals. However, plants that continually produce the Bt insecticide will exert strong selective pressure on insects to develop resistance to the insecticide. As insects evolve resistance to Bt toxins, organic farmers will be stripped of one of their most valuable tools.

Many scientists believe that efforts to slow the development of resistance in pests are ineffectual. The main strategy involves planting "refuges" of non-Bt crops interspersed among the genentically engineered fields, with the goal of diluting resistant insect populations with susceptible individuals.

A recent article in the journal Science found that a common pest of cotton was able to build up resistance to the Bt plant pesticide very quickly. The US EPA subsequently announced that refuges of non-GM crops needed to be increased by 20 to 50 percent of the total area in order to prevent the build-up of resistance in the insect population.



1 Chevre et al, 1998. "Characterisation of Backcross Generations Obtained Under Field Conditions from Oilseed Rape Wild Radish F-1 Interspecific Hybrids: An Assessment

2 Thompson, C.E. et al, 1999 "Regional patterns of gene flow and its consequences for GM oilseed rape" in Gene Flow and Agriculture: Relevance for Transgenic crops; British Crop Protection Council Symposium Proceedings No. 72. Ed. P.J.W. Lutman

3 Losey, J.E. et al,1999 "Transgenic Pollen Harms Monarch Larvae" Nature, 399: 214, May 20, 1999

4 Saxena, D., Flores, S.& Stotzky, G. 1999 "Transgenic Plants: Insecticidal Toxin in Root Exudates from Bt Corn" Nature, 402: 480

5 Hillbeck, A. et al, 1998 "Effects of Transgenic Bacillus thuringiensis corn-fed prey on mortality and development time of immature Chrysoperla carnea;" Environmental Entomology Vol 27 (2): 480-487.

6 Tabashnik, B.E. et al 2000 "Resistance to Bt Toxins" Science 7/1/2000, p.287