Risks posed by GMOs

THE main types of risks posed by GMOs can be classified as health risks and environmental risks. Although a few risks associated with the use of genetically modified crops have been observed, no long-term studies have been done yet. What is the evidence so far?

Health risks

Allergies: There is a worry that the introduction of novel gene products with new proteins will cause allergic responses. The expression of Brazil nut protein in soybean confirmed that genetic engineering can lead to the expression of allergenic proteins.

Toxicity: The possible introduction or increase of toxic compounds might increase toxicity. As novel proteins produced in plants have the potential to cause human toxicity, further test and scrutiny are needed.

Pleiotropic effects: Previously unknown protein combinations may have unforeseen secondary effects in food plants. While further monitoring is needed, no significant secondary effects have been found from commercially available transgenic plants or products.

Antibiotic resistance: Concern has been expressed about antibiotic markers such as kanamycin that are used in plant transformation. These are still used to treat infections in humans, and increased exposure to them might cause infections to become resistant to antibiotics, rendering these medicines ineffective. While no definitive evidence has been found to support the theory that the use of antibiotic markers harms humans, alternatives are becoming available rapidly and are increasingly useful for food crop development.

Environmental risks

Unintended effects on non-target species: Although laboratory studies have reported damage to the larvae of monarch butterfly feeding on the pollen from Bt plants, no studies have shown an actual negative effect on butterfly densities in the wild. Further research is needed.

Effects of gene flow to close relatives: Pollen dispersal can lead to gene flow, but only trace amounts are dispersed more than a few hundred feet. The transfer of conventionally bred or transgenic resistance traits to weedy relatives could worsen weed problems, but such problems have not been observed or adequately studied.

Increased weediness: Some new traits introduced into crops - such as pest or pathogen resistance - could cause transgenic crops to become problem weeds. This could result in serious economic and ecological harm to farm or wildlife habitats.

Pests developing resistance to pest-protected plants: Insects, weeds and microbes have the potential to overcome most of the control options available to farmers, with significant environmental impacts. But management approaches can be used to delay pest adaptations.

Concerns about virus-resistant crops: Engineered plants containing virus resistance may facilitate the creation of new viral strains, introduce new transmission characteristics or cause changes in susceptibility to other, but related, viruses. Engineered plants are unlikely to present problems that are different from those associated with traditional breeding for virus resistance.

Threats to biodiversity: Gene exchange could spread to wild relatives that are rare or endangered, especially if the exchange happens in centres of crop diversity. Scientists must increase their awareness of these and other problems arising from potential gene flow from genetically modified crops.

Source: Human Development Report, UNDP, 2001.