Of genes, grain, and grocers

The risks and realities of engineered crops

Laura Tangley / US News and World Report 10apr00

It's spring planting time, and Dennis Mitchell faces a dilemma. On the one hand, the South Dakota farmer likes the hardiness of the genetically altered corn and soybeans he has sown on his 3,300 acres since 1997. Even so, Mitchell is thinking he'll cut back on the high-tech crops this season. Why? "We just don't know if customers are going to buy them," Mitchell says simply.

For the first time since the seeds burst on the scene four years ago, many American farmers are expected to decrease the amount of land they dedicate to genetically modified crops–now about 76 million acres. It's not because the plants have performed poorly–they haven't–but rather because consumers, who fear the crops are harmful to human health and the environment, may refuse to buy them. While final statistics will not be available until well after seeds are in the ground, internal surveys conducted by farming interest groups indicate that members may cut back on bioengineered crops by about 20 percent this year. According to Gary Goldberg of the American Corn Growers Association, farmers already have lost more than $200 million in European exports. Now opposition to "Frankenfood" is intensifying in this country as well. Last week, some 1,500 biotech protesters demonstrated at a scientific conference in Boston. And while small amounts of altered crops already are found in a variety of U.S. foods, several major companies– including Frito-Lay, Gerber, and IAMS pet foods–say they will no longer use genetically modified ingredients in their products.

Time will tell. But are consumer fears about the safety of genetically engineered crops justified? Scientific evidence for either safety or risk is hard to come by–in part because large-scale, long-term trials have not been conducted. Yet recent controversy has spawned a flurry of new research, including a National Academy of Sciences study scheduled for release this week. Early results suggest that while some concerns about engineered crops are exaggerated, others, particularly worries about the environment, may be justified. Plant pathologist Jane Rissler of the Union of Concerned Scientists says, "We're discovering that when you look for evidence of environmental risk, you find it."

There is no evidence that any genetically modified food has harmed a human being. One of the critics' biggest concerns is that manipulating a crop's genome could enhance plant toxins in unexpected ways, by accidentally switching on or off another, nontarget gene. For example, a controversial study by Scottish researcher Arpad Pusztai, published last fall in the Lancet, found that rats fed potatoes that had been genetically modified to kill pests suffered health problems ranging from stunted growth to damaged immune systems. But industry scientists, who conduct their own trials before releasing a product, say they never would have commercialized the gene that Pusztai tested because it produces a protein known to be toxic.

Another concern is that people who suffer from allergies may inadvertently be exposed to a protein they react to–if a nut or shellfish gene ended up in corn, for example. Although the Food and Drug Administration requires companies to screen genetically modified products for known allergens, critics worry that new problem proteins could easily slip through the system, especially if they're produced by genes not naturally found in food.

Most biotech protests are fueled by such concerns over human health. But many biologists worry more about how genetically altered crops may affect the environment. One risk is that genes designed to give crops a competitive advantage–such as insect resistance–may be passed to related wild plants with which they interbreed, spawning new "superweeds." For example, biologists have found that a herbicide-tolerant canola cross-pollinates with a related weed, producing herbicide-tolerant descendants. And in a study recently published in Molecular Ecology, Allison Snow of Ohio State University reports that the physiological costs of this new trait are "negligible," suggesting that it may persist and spawn more troublesome weeds.

But the public worries more about biotech's impact on animals, even lowly insects. In a well-known study that ignited international controversy last year, John Losey of Cornell University found that monarch butterflies fed milkweed dusted with pollen from engineered corn either died or developed abnormally. In the Midwest, milkweed, the monarch's favorite food, grows in and around cornfields. Research is now underway to find out how often caterpillars and engineered corn come together.

Interrupting nature. Entomologists point out that the engineered corn contains a toxin–derived from a soil bacterium and known as Bt–chosen for its lethality to moth and butterfly larvae, so the monarch results are not surprising. More unexpectedly, Angelika Hilbeck of the Swiss Federal Research Station for Agroecology and Agriculture recently published studies showing that Bt also kills larvae of green lacewings–beneficial bugs that feed on crop pests. By planting Bt crops, says Hilbeck, "we risk disrupting the regulatory mechanisms that naturally keep pests in check."

Other studies suggest that Bt crops may also disrupt the below-ground ecosystems that keep soil fertile. In research published last winter in Nature, Guenther Stotzky of New York University discovered that Bt corn leaches the toxin through its roots and that the poison remains lethal for months. In another report, Katherine Donegan of the Oregon-based Dynamac Corp. found inexplicable changes in both soil chemistry and microbial life after Bt crops decompose.

But for many farmers, the most frightening risk of insecticide-producing crops is that long-term exposure to high doses of Bt will help bugs develop resistance to the chemical, which has long been used in small amounts as a safe, natural pesticide. To slow the evolution of resistance, the Environmental Protection Agency in January issued rules requiring farmers who plant Bt corn to sow at least 20 percent of their fields in traditional varieties. The agency also asked farmers to voluntarily plant conventional corn around the edges of their fields to protect monarch butterflies. Indeed, as evidence of risk and public jitters mount, more restrictions on altered crops are expected in the future.