On Science: Frankenfood: Are genetically modified crops safe?
This article first appeared in the St. Louis Beacon, July 1, 2009 - We are living in a world of molecular agriculture, with genetically engineered foods now a common part of our daily lives. The advantages afforded by genetic engineering are cheaper and more nutritious foods. But what are the disadvantages, the potential costs and dangers, of genetic engineering? Many people, including influential activists and members of the scientific community, have expressed concern that genetically engineered products administered to plants or animals might, for unforeseen reasons, turn out to be dangerous for consumers.
Should we be eating "Frankenfood"? What kind of unforeseen impact on the ecosystem might "improved" crops have?
With genetically modified (GM) foods so much in evidence, these questions have led to considerable controversy and protest. The intense feelings generated by this dispute point to the need for consumers like you and me to understand how one measures the risks associated with the genetic engineering of plants.
Two sets of risks need to be considered: The first stems from eating genetically modified foods; the other concerns potential ecological effects.
Is Eating Genetically Modified Food Dangerous?
Bioengineers modify crops in two quite different ways. One class of gene modification makes the crop easier to grow; a second class of modification is intended to improve the food itself. Many consumers worry that either sort of genetically modified food may have been rendered dangerous.
The introduction of herbicide-resistant crops is an example of the first class of modification, producing a GM version that is easier to grow (herbicides kill weeds while not harming the crop). Is the crop that results nutritionally different? No.
The real issue, of course, is whether the gene modification that renders crop plants herbicide-resistant involves introducing novel proteins with potentially dangerous consequences. Could introduced proteins like the enzyme making crops herbicide resistant become allergens, causing a potentially fatal immune reaction in some people?
Because the potential danger of allergic reactions is quite real, every time a protein-encoding gene is introduced into a GM crop it is necessary to carry out extensive tests of the introduced protein's allergen potential.
This same issue arises each time a gene is added to a crop plant. Thorough tests for allergenicity are required by the EPA before any GM crop is approved for human consumption. No GM crop currently being produced in the United States contains a protein that acts as an allergen to humans.
On this score, then, the risk of bioengineering to the food supply seems to be slight, so long as adequate testing of new varieties continues.
Are GM Crops Harmful to the Environment?
Those concerned about the environmental consequences of the widespread use of GM crops raise three legitimate concerns that merit careful evaluation:
!. Harm to Other Organisms. The first concern is the possibility of unintentional harm to other organisms. This issue is seen most clearly in the case of crops like GM corn. Results from a small laboratory experiment suggested that pollen from GM corn could harm larvae from the Monarch butterfly, which is, like the corn borer, a lepidopteran insect. While this preliminary report received considerable publicity, subsequent studies suggest little possibility of harm. Monarch butterflies lay their eggs on milkweed, not corn, and field management ensures that there is little if any milkweed growing in or near cornfields. In field tests, few Monarch larvae are found there.
Farmers focus on the fact that GM cornfields do not need to be sprayed with chemical pesticides to control the corn borer. An estimated $9 billion in damage is caused annually by the application of pesticides in the United States, and billions of insects and other animals, including an estimated 67 million birds, are killed each year by pesticides.
In a serious attempt to learn whether GM crops are a danger to other organisms, the British government undertook a comprehensive three-year "farm-scale evaluation" of the effects of GM-herbicide-resistant beet, corn and oilseed crops on biodiversity (in this instance, numbers of kinds of insects). In the study, 60 fields each of beets, corn and rape (oilseed) were split between conventional varieties and genetically modified herbicide-tolerant strains.
In a report released in 2003, the results "reveal significant differences in the effect on biodiversity when managing genetically herbicide-resistant crops as compared to conventional varieties." The report showed that weeds are important sources of food and shelter for insects; because GM crops allow farmers to get rid of weeds more effectively, they have a greater impact on insect populations. In brief, they found that weed-killing herbicides killed weeds. There were no other adverse affects.
2. Resistance. All insecticides used in agriculture share the problem that pests eventually evolve resistance to them, in much the same way that bacterial populations evolve resistance to antibiotics. Use of the insecticide creates a selective pressure favoring mutations that make the pest resistant to it. This is true of chemical pesticides, and also of internal insecticides produced by gene-modified Bt corn.
Will pests eventually become resistant to the Bt toxin, just as many have become resistant to the high levels of chemical pesticide we sprayed on crops? This is certainly a possibility, as a few species of insects have developed resistance to Bt when it was sprayed directly on crops in years past. However, despite the widespread use of Bt crops like corn, soybeans and cotton since 1996, there are as of yet no cases of insects developing resistance to Bt plants in the field. Still, because of this possibility farmers are required to plant at least 20 percent non-Bt crops alongside Bt crops to provide refuges where insect populations are not under selection pressure and in this way to slow the development of resistance. It is very important that this requirement be met. If ignored, Bt-resistant insect pests may appear in future fields.
3. Gene Flow. How about the possibility that introduced genes will pass from GM crops to their wild or weedy relatives?
This sort of gene flow happens naturally all the time, and so this is a legitimate question. For the first round of major GM crops, there is usually no potential relative around to receive the modified gene from the GM crop. There are no wild relatives of soybeans in Europe, for example. Thus, there can be no gene escape from GM soybeans in Europe, any more than genes can flow from you to your pet dog or cat.
For secondary crops only now being gene-modified, the risks are more tangible. There is mounting evidence that passage of modified genes to other plants can be significant, and the possibility that it might occur must be carefully evaluated.
In 2004, Environmental Protection Agency scientists planted eight fields in central Oregon (400 acres in all) with genetically modified creeping bentgrass (Agrostis stolonifera). Bentgrass is widely planted on golf course greens because it can be closely mowed. But normal bentgrass is particularly susceptible to weeds, and so requires extensive chemical spraying. The GM form of creeping bentgrass being tested by the EPA had been made resistant to the herbicide glyphosate, which would eliminate the need for most of the spraying. Just spray the herbicide and only the bentgrass can grow.
Tracking the spread of GM pollen from these eight fields, the EPA scientists collected seeds from potted "sentinel" bentgrass plants and from natural plants, grew them to seedling stage, and examined the DNA of the seedling plants for the glyphosate-resistance gene.
In one field, a total of 178 A. stolonifera plants were placed outside the golf course, many of them downwind. An additional 69 bentgrass individuals were found to be already growing downwind, most of them the related species A. gigantea.
Seeds were collected from each of these plants, and the DNA of resulting seedlings tested for the presence of the gene introduced into the GM golf-course grass.
The gene was found in the potted bentgrass plants up to 13 miles away, and in the wild relative grasses nearly nine miles away from the fields! With no room for doubt or wiggle in the conclusion, the gene introduced into GM bentgrass was freely passing to related species miles away.
Might the spread of the glyphosate-resistance gene to surrounding grasses create hard-to-kill "superweeds," or would it be easy to use other weedkillers to control any newly resistant plants? However one interprets its findings, this study suggests that it may be difficult to control GM secondary crops from interbreeding with surrounding relatives to create new hybrids.
It would be nice if, in each and every instance, the potential for secondary spread of an introduced gene could be evaluated on each farm before the crop is planted, but in practice that is not going to happen. The government may in the future requite that GM secondary crops be evaluated for the potential for spread, mapping the distribution of known wild relatives.
However, I cannot help but ask "So what?" If a wild relative of a GM crop inadvertently becomes resistant to glyphosate or some other agricultural herbicide or insecticide, what if any possible difference would it make? Think about that. That question is the one government regulators should be investigating.
George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner.
Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability. He has authored more than 50 scientific publications and seven texts.
As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.
Copyright George Johnson