New Allergens in the Food Supply
Transgenic crops could bring new allergens into foods that sensitive individuals would not know to avoid. An example is transferring the gene for one of the many allergenic proteins found in milk into vegetables like carrots. Mothers who know to avoid giving their sensitive children milk would not know to avoid giving them transgenic carrots containing milk proteins. The problem is unique to genetic engineering because it alone can transfer proteins across species boundaries into completely unrelated organisms.
Genetic engineering routinely moves proteins into the food supply from organisms that have never been consumed as foods. Some of those proteins could be food allergens, since virtually all known food allergens are proteins. Recent research substantiates concerns about genetic engineering rendering previously safe foods allergenic. A study by scientists at the University of Nebraska shows that soybeans genetically engineered to contain Brazil-nut proteins cause reactions in individuals allergic to Brazil nuts.
Scientists have limited ability to predict whether a particular protein will be a food allergen, if consumed by humans. The only sure way to determine whether protein will be an allergen is through experience. Thus importing proteins, particularly from nonfood sources, is a gamble with respect to their allergenicity.
Antibiotic Resistance
Genetic engineering often uses genes for antibiotic resistance as "selectable markers." Early in the engineering process, these markers help select cells that have taken up foreign genes. Although they have no further use, the genes continue to be expressed in plant tissues. Most genetically engineered plant foods carry fully functioning antibiotic-resistance genes.
The presence of antibiotic-resistance genes in foods could have two harmful effects. First, eating these foods could reduce the effectiveness of antibiotics to fight disease when these antibiotics are taken with meals. Antibiotic-resistance genes produce enzymes that can degrade antibiotics. If a tomato with an antibiotic-resistance gene is eaten at the same time as an antibiotic, it could destroy the antibiotic in the stomach.
Second, the resistance genes could be transferred to human or animal pathogens, making them impervious to antibiotics. If transfer were to occur, it could aggravate the already serious health problem of antibiotic-resistant disease organisms. Although unmediated transfers of genetic material from plants to bacteria are highly unlikely, any possibility that they may occur requires careful scrutiny in light of the seriousness of antibiotic resistance.
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In addition, the widespread presence of antibiotic-resistance genes in engineered food suggests that as the number of genetically engineered products grows, the effects of antibiotic resistance should be analyzed cumulatively across the food supply.
Production of New Toxins
Many organisms have the ability to produce toxic substances. For plants, such substances help to defend stationary organisms from the many predators in their environment. In some cases, plants contain inactive pathways leading to toxic substances. Addition of new genetic material through genetic engineering could reactivate these inactive pathways or otherwise increase the levels of toxic substances within the plants. This could happen, for example, if the on/off signals associated with the introduced gene were located on the genome in places where they could turn on the previously inactive genes.
Concentration of Toxic Metals
Some of the new genes being added to crops can remove heavy metals like mercury from the soil and concentrate them in the plant tissue. The purpose of creating such crops is to make possible the use of municipal sludge as fertilizer. Sludge contains useful plant nutrients, but often cannot be used as fertilizer because it is contaminated with toxic heavy metals. The idea is to engineer plants to remove and sequester those metals in inedible parts of plants. In a tomato, for example, the metals would be sequestered in the roots; in potatoes in the leaves. Turning on the genes in only some parts of the plants requires the use of genetic on/off switches that turn on only in specific tissues, like leaves.
Such products pose risks of contaminating foods with high levels of toxic metals if the on/off switches are not completely turned off in edible tissues. There are also environmental risks associated with the handling and disposal of the metal-contaminated parts of plants after harvesting.
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