Is eating food from transgenic crops a health hazard? An experiment carried out in Scotland, where rats fed for ten days on transgenic potatoes containing a lectin gene from snowdrops appeared to develop internal organ damage, is often cited in support of this claim, although this particular study has been widely criticized by other scientists as being too small-scale and inconclusive (Ewen and Pusztai 1999). Some transgenes may pose human health risks when consumed: for example, a project to insert a brazil nut protein gene into soybean was halted when early tests showed that people allergic to nuts reacted to the modified soy products (Nordlee et al. 1996). This demonstrates the need to consider potential health effects in new transgenic crops, but it also shows that proper testing can identify risks. Although almost half the US soybean crop, and a quarter of US corn, now consists of transgenic varieties (which means that we have all been eating transgenic food products for some time) there is as yet no single case reported of anyone suffering health effects as a result. For more information see Kaeppler 2000 or Thompson 2000.

Can antibiotic resistance genes used as markers in transgenic crops be transferred to pathogenic bacteria? The chain of events that would be necessary for such a transfer is quite unlikely, and there is no evidence that it occurs. However, in response to concerns about this remote possibility scientists are starting to use alternative marker genes in transgenic plants, such as the GFP gene which makes the plant fluoresce when placed under UV light. A detailed 1998 report by the U.S. Food and Drug Administrations on the use of antibiotic resistance genes is available at Kaeppler 2000.

Are transgenic crops a threat to other organisms in the environment? Bt corn, which contains a bacterial gene enabling the plants to manufacture a substance toxic to the larvae of butterflies and moths but harmless to other organisms, has been a target of criticism since a laboratory study published last year showed that Bt corn pollen dusted onto milkweed leaves was harmful to monarch butterfly larvae feeding on them (Losey et al. 1999). Follow-up studies have shown that pollen from Bt corn rarely reaches toxic levels on milkweed in the field even when monarch butterfly larvae are feeding on plants adjacent to a corn field (Strickland 1999). Planting Bt corn also greatly reduces or eliminates the need for spraying with pesticides which are far more damaging to non-target insect populations.

Will pollen from transgenic crops contaminate non-transgenic crop varieties? More information is needed about the extent of this risk for different crops. However, a recently completed study at the University of Maine found that cross-pollination of conventional corn by transgenic corn grown in an adjacent plot was 1% at a distance of 100 feet and declined to zero at a distance of 1000 feet. This suggests that it will be quite feasible to prevent the transfer of transgenes to non-transgenic varieties by following recommended planting distances, just as is currently done to maintain purity with conventional varieties. See also Barton and Dracup 2000.

Will herbicide-resistant transgenic crops create "superweeds"? This is a real threat where transgenic crops containing a herbicide-resistance gene grow alongside closely related weed species, such as wild mustards in canola or jointed goatgrass in wheat. Gene movement from crop to weed through pollen transfer has been demonstrated for both of these crops. Proposals to reduce the risk of creating transgenic "superweeds" include linking herbicide-resistance genes to other genes which are harmless to the crop but damaging to a weed, such as genes which affect seed dormancy or prevent flowering in the next generation. Thus if a weed did acquire a herbicide-resistance gene from a transgenic crop, its offspring would not survive to spread the herbicide resistance through the weed population.

Do transgenic crops reduce biodiversity? It has been argued that transgenic crops will replace traditional crop varieties, especially in developing countries, causing loss of biological diversity. This risk is real, but not restricted to transgenic crops. Farmers around the world have adopted new commercial varieties in the past and they will continue to do so as long as it is to their advantage. What is needed is better conservation of traditional crop varieties in danger of being lost, so that the useful genes they contain can be preserved.

Will insect pests become resistant to Bt toxins? A major concern is that the widespread planting of transgenic crops containing the insecticidal Bt gene will expose many more insect pests to the Bt toxin, accelerating the development of Bt resistance in pest populations. We already know this can happen: Bt resistance has been widely documented in the diamondback moth (Plutella xylostella), a major pest of vegetable crops, in the US and in some Asian countries. This resulted from many years of growers using Bt as an environmentally-friendly insecticidal spray. Decreased susceptibility to Bt has recently been documented in soybean loopers collected from Bt cotton, indicating that resistance can arise from exposure to transgenic crops (see Mascarenhas et al. 1998). Strategies such as the use of non-transgenic "refuge"areas have been proposed to prevent or slow the development of Bt resistance in pest populations - for more information on this topic go to the Current Transgenic Products section of this website and click on Insect Resistance to Bt Toxins at the top of the page. See also Barton and Dracup 2000.

Will the widespread adoption of transgenic crops lead to increased corporate control of the world's food supply? Research and development leading to the production of transgenic crop varieties is expensive and requires resources unavailable to many developing countries. Critics of the technology point out that ownership and control of the transgenic crops currently grown is in the hands of a small number of powerful corporations, which often impose restrictive conditions on farmers buying their seed. This trend has been accelerated by the widespread patenting of plant genes and germplasm in the US and some other countries. For more detailed discussion of some of these issues, see AgBioForum Vol.1 No.2 (Fall 1998), available at http://www.agbioforum.org/ under Archives Jordan 2000.