Part 3 of 4 (Part 1, Part 2, Part 4)
by Rachel Massey (Environmental Research Foundation)
As we saw in REHN #716, genetically engineered crops now planted in the U.S. and worldwide are mostly designed to tolerate herbicides or to kill insects or other pests. A small percentage is designed for other purposes such as resisting infection by certain viruses.
Here we will look at some of the threats genetically engineered crops pose to ecosystems.
Pesticidal crops may be toxic to nontarget organisms - organisms they were not designed to kill. For example, BT corn designed to kill the European corn borer can also be toxic to other closely related insects, including butterflies and moths.
Monarch butterfly larvae feed on milkweed, which often grows in or near corn fields. In a laboratory, scientists found that monarch larvae feeding on milkweed dusted with BT corn pollen grew more slowly and died at a higher rate than larvae that were not exposed to the toxic pollen.[1]
Another study found these effects were likely to occur outside the laboratory as well. Researchers placed potted milkweed plants in fields of BT corn and measured the number of BT pollen grains that were deposited on the milkweed leaves. Monarch larvae exposed to BT corn pollen at these levels had high death rates compared with larvae exposed to non-engineered corn pollen or placed on milkweed leaves with no pollen.[2]
The U.S. Environmental Protection Agency (EPA) now expresses concern about the effects of BT corn pollen on monarchs and other butterfly species, including the endangered Karner Blue butterfly.[3] EPA has asked companies to submit data on these effects, but this "data call-in" occurred four years AFTER EPA allowed BT corn to be used on U.S. farms.[2,pg.13]
BT corn may also harm the green lacewing, a beneficial insect that eats agricultural pests. The lacewing may be affected by the toxin in the digestive systems of insects that have eaten BT corn but have not been killed by it.[4] This example shows how non-target effects may interfere with a chain of predator-prey relationships, disrupting the natural balance that keeps pest populations under control.
BT crops may also affect non-target organisms by changing soil chemistry. A 1999 article in Nature reported that the roots of BT corn plants released BT toxin into soil. The researchers found that 90 to 95% of susceptible insect larvae exposed to the substance released from the roots died after 5 days.[5]
The use of BT crops can also promote the development of BT-resistant pest populations. As we saw in REHN #716, organic farmers use BT sprays occasionally as a natural insecticide to combat severe pest outbreaks. BT crops, in contrast, generally expose insects to BT toxins day after day, whether or not there is a major infestation.
These conditions increase the likelihood that BT-resistant insects will evolve. The widespread appearance of BT-resistant insect pests would mean the loss of one of the most valuable tools available to organic farmers for dealing with serious pest outbreaks.[6,pg.139]
Herbicide-tolerant crops are designed to make it easier for farmers to use certain herbicides. A 1999 study of soybean farming in the U.S. midwest found that farmers planting Roundup Ready soybeans used 2 to 5 times as many pounds of herbicide per acre as farmers using conventional systems, and ten times as much herbicide as farmers using Integrated Weed Management systems, which are intended to reduce the need for chemical herbicides.[7,pg.2]
Glyphosate, the active ingredient in Roundup, can sometimes persist in soil over long periods of time[8] and may affect the growth of beneficial soil bacteria, among other environmental effects.[9] A recent, unpublished study conducted at the University of Missouri suggests that applications of Roundup to Roundup Ready crops may be associated with elevated levels of soil fungi that sometimes cause plant diseases.[10]
More hazards may lie ahead as new products of genetic engineering come to market. According to the New York Times, Scott Company is collaborating with Monsanto to develop Roundup Ready grass for lawns.[11] Studies suggest that Roundup exposures can be harmful to human health. For example, exposure to glyphosate herbicides may be associated with increased occurrence of non-Hodgkins lymphoma, a cancer of white blood cells.[12] (See REHN #660.)
And a study published last August in Environmental Health Perspectives found that in a laboratory, Roundup exposure interfered with sex hormone production in cells of testicular tumors taken from mice.[13] If the introduction of Roundup Ready grass leads to increased use of Roundup on lawns, children's exposure to the herbicide could rise.
In some cases, genetically engineered crops might become problem weeds, disrupting existing ecosystems. A recent study published in Nature found that some genetically engineered crops are unlikely to become problem weeds.
Researchers planted genetically engineered crops that were available in 1990 and monitored their growth for ten years. Many of the plants simply died out, and those that did survive showed no signs of spreading.[14] But some crop plants, such as canola, survive well on their own without human intervention.
In Canada, genetically engineered canola plants designed to resist various herbicides appear to have exchanged genetic material so that some canola plants now can survive exposure to two or three herbicides. These plants with multiple herbicide resistance can be difficult for farmers to control.[6,pgs.122-123]
Genetically engineered virus-resistant crops are supposed to reduce problems from viral infections, but in some cases they could make those problems worse. Virus-resistant crops are created by adding virus genes to the plant's existing genetic material. If a genetically engineered crop resistant to one virus is infected by another virus, the genetic material from the two viruses may sometimes interact to produce new virus types, which could be more harmful or could infect a wider range of plants than the original.[15,pgs.59-68]
All the hazards discussed above are compounded by the problem of genetic pollution. Many crop plants disperse genetic material through pollen, which may be carried by the wind or by pollinators such as bees.
This means genetically engineered plants may "share" their genetic material with other, non-engineered plants.
For example, pollen from genetically engineered corn can blow into a neighboring field and pollinate conventional corn. Because of genetic pollution, some organic farmers whose fields border genetically engineered crops may no longer be able to certify their crops as organic.[6,pg.127]
In animals, sexual reproduction between different species is usually impossible. In a few cases, reproduction between closely related species can occur but the offspring are generally sterile. For example, a horse and a donkey can mate to produce a mule, but mules cannot reproduce.
In contrast, many plants are able to reproduce sexually with related species, and the offspring of these combinations are often fertile. When crop plants grow near wild plants to which they are related, they may reproduce with these plants. This means that genetic material inserted into a crop plant can find its way into wild plant populations.
A recent article in Science reviews the literature on "ecological risks and benefits" of genetically engineered crops and confirms what advocates of precaution have been saying for years: we lack basic information on how genetically engineered crops may affect ecosystems.[16]
Here are a few examples of what scientists do not know about ecological effects of genetically engineered crops:
No published studies have looked at whether novel genes introduced into crops have become established in populations of wild relatives.[16, pg. 2088]
We know that BT toxin can be released from the roots of BT corn plants, but no published studies have looked at the ecological consequences of adding BT toxin to soil in this way. [16, pg. 2089]
As we have seen, BT toxin in the digestive systems of plant-eating insects may affect the predator insects that eat them. Right now it is impossible to model how an ecosystem might change due to these effects on predators, the authors say.[16, pg. 2089]
Scientists are currently unable to estimate the likelihood that planting genetically engineered virus-resistant crops will lead to the development of new types of plant viruses. [16, pg. 2089]
A precautionary approach would require that we investigate these questions before, rather than after, permitting large-scale commercial cultivation of genetically engineered crops.
Rachel's Environment & Health News February 15, 2001
References
Part 4
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