Risks of Genetic Engineering
Technologies usually involve risks, and sometimes those risks turn out to be unexpected ones. DDT, for example, turned out to accumulate in fish and thin the shells of fish-eating birds like eagles and ospreys. And chlorofluorocarbons turned out to float into the upper atmosphere and destroy ozone, a chemical that shields the earth from dangerous radiation.
What harmful effects might turn out to be associated with the use of genetically engineered (GE) organisms? This is not a simple question. Answering it requires that we understand complex biological and ecological systems.
So far, scientists know of no inherent, generic harms associated with GE organisms. For example, it is not true that all GE foods are toxic or that all engineered organisms are likely to proliferate if released into the environment.
But specific enginereed organisms may have specific harmful effects by virtue of the novel gene combinations they possess. This means that the risks of genetically engineered organisms may vary widely, and therefore must be assessed on a case-by-case basis.
So far, scientists have identified a number of ways in which GE organisms could adversely affect both human health and the environment. Once the risks are identified and can be detected by regulators, the next step is risk assessment: determining how likely potential harms are to occur.
In addition to risks that we can envision and attempt to assess, GE may pose risks that we simply do not know enough to identify. This possibility does not in itself justify trying to suppress the technology, but it does put a substantial burden on its advocates to demonstrate benefits.
Health Risks
New Allergens in the Food Supply
GE crops could produce new allergens in foods, which sensitive persons would not know to avoid. For instance, a gene for one of the many allergenic proteins found in milk might be transferred into vegetables such as carrots. A mother who knows better than to give her sensitive child milk would not realize that she needed to avoid GE carrots with the allergenic milk protein. This problem is unique to GE, because it alone can transfer proteins to completely unrelated species—often from organisms that have never been consumed as foods.
Research has substantiated concerns about GE rendering previously safe foods allergenic. For instance, a University of Nebraska study showed that soybeans engineered to contain Brazil nut proteins cause reactions in people allergic to Brazil nuts. Scientists have limited ability to predict whether a particular protein will be a food allergen, so importing proteins—particularly from non-food sources—is a gamble with respect to their allergenicity.
Antibiotic Resistance
Most genetically engineered plant foods carry fully functioning antibiotic-resistance genes, which are used as "selectable markers" early in the engineering process, helping to select cells that have taken up the foreign genes. Such genes could have two harmful effects. First, eating these foods could reduce the effectiveness of antibiotics to fight disease if the antibiotics are taken at the same time as the foods. Second, the resistance genes could be transferred to human or animal pathogens, making them impervious to antibiotics—an effect that has already been demonstrated experimentally in the human digestive system.
Production of New Toxins
Many organisms have the ability to produce toxic substances, which help to defend them from predators. Some plants contain inactive genetic pathways leading to toxic substances, and new genetic material introduced through GE could reactivate these pathways or otherwise increase the plant's production of toxic substances. This might happen, for instance, if on/off signals associated with an introduced gene are located on the genome in places where they could turn on the previously inactive genes for producing the toxins.
Concentration of Toxic Metals
Some genes added to crops can remove heavy metals like mercury from the soil and sequester them in the plant tissue. This allows the use of municipal sludge, which contains toxic heavy metals, as fertilizer. The crops are engineered to concentrate the heavy metals in parts of the plant that are not eaten—a tomato's roots or a potato's leaves, for example. This is done through genetic on/off switches that operate only on specific tissues. However, if the on/off switches are not completely turned off in edible tissues, there is a risk of contamination. There are also environmental risks associated with the handling and disposal of the contaminated parts of plants after harvesting.
Enhancement of the Environment for Toxic Fungi
Although most GE health risks result from adding new genetic material to organisms, the removal of genes and gene products can also cause problems. For example, GE might be used to produce decaffeinated coffee beans by deleting or turning off genes associated with caffeine production. But caffeine helps protect coffee beans against fungi. Beans that are unable to produce caffeine might be coated with fungi, which can produce toxins. Fungal toxins, such as aflatoxin, are potent human toxins that can remain active through processes of food preparation.
Environmental Risks
Increased Weediness
Serious weed problems can result when a plant is introduced—either accidentally or intentionally—into an environment where it inhibits crop yields or disrupts ecosystems. GE has the potential to create weed problems by adding traits that enable a plant to thrive unaided in environments where it becomes a new weed. One example would be drought-tolerant turfgrass or switchgrass, which may become invasive in drier environments.
Gene Transfer
Novel genes engineered into crops can easily move via pollen to wild or weedy relatives of those crops that may be growing nearby. The new traits might confer on those relatives the ability to thrive in unwanted places. Several wild relatives of crops in the U.S., such as jointed goatgrass (a wheat relative), are already serious weeds—and gene transfer could exacerbate this problem. (A related but distinct problem is gene contamination of non-GE crops by nearby GE crops.)
Change in Herbicide Use Patterns
Widespread use of herbicide-tolerant crops has led to the rapid evolution of resistance to herbicides in weeds as a result of increased exposure to the herbicide. As these herbicides become less effective, farmers may increase their use of older, more toxic herbicides, with resulting environmental harm.
Squandering of Valuable Pest Susceptibility Genes
Many insects contain genes that render them susceptible to pesticides. These genes are a valuable natural resource because they allow pesticides to remain effective. "Bt crops," which are genetically engineered to contain a gene for the Bacillus thuringiensis (Bt) toxin—one of nature's most valuable pesticides—threaten the continued susceptibility of pests to the Bt toxin. Because the crops produce the toxin throughout the life cycle of the plant, pests are constantly exposed to it. This continuous exposure selects for the rare resistance genes in the pest population and in time will render the Bt pesticide useless, unless specific measures are instituted to avoid the development of such resistance. (Bt resistance has already been observed
Poisoned Wildlife
Addition of foreign genes to plants could also have serious consequences for wildlife in a number of circumstances. For example, engineering crop plants, such as tobacco or rice, to produce plastics or pharmaceuticals could endanger mice or deer who consume crop debris left in the fields after harvesting. Fish that have been engineered to contain metal-sequestering proteins (such fish have been suggested as living pollution clean-up devices) could be harmful if consumed by other fish or raccoons.
Creation of New (or Worse) Viruses
One of the most common applications of genetic engineering is the production of virus-tolerant crops. Such crops are produced by engineering components of viruses into the plant genomes. For reasons not well understood, plants producing viral components on their own are resistant to subsequent infection by those viruses. Such plants, however, pose other risks of creating new or worse viruses through two mechanisms: recombination, in which plant-produced viral genes and genes of incoming viruses recombine to produce viruses that are more virulent or can infect a wider range of hosts than the parent viruses; and transcapsidation, in which plant-produced viral proteins encapsulate the genetic material of another virus, producing a hybrid virus that could transfer viral genetic material to a new host platn that it could not otherwise infect.
Unknown Risks
Each of the risks described above is an answer to the question, "well, what might go wrong?" The answer to that question depends on how well scientists understand the organism and the environment into which it is released. And since that understanding is incomplete, it is unlikely that all potential harms to human health and the environment from the use of genetically engineered organisms have been identified.
Risk Assessment
How likely are any of these potential harms to occur? The answer to this question, again, depends greatly on how well the organisms and their interaction in the environment are understood. Risks must be assessed case by case as new applications of genetic engineering are introduced. In some circumstances, it is possible to assess risks with great confidence. For example, it is vanishingly unlikely that genetically engineered palm trees will thrive in the Arctic regardless of what genes have been added. But for many potential harms, the answers are far less certain.
Risk assessments can be complicated. Because even rigorous assessments involve numerous assumptions and judgment calls, they are often controversial when they are used to support particular government decisions.
Under the current US regulatory framework for biotechnology, some sort of risk assessment is routinely produced before decisions to allow commercialization of products under the Federal Plant Pest Act; the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA); and the Toxic Substances Control Act (TSCA). In the case of the Plant Pest Act, risk assessments are done according to the procedure specified by the National Environmental Policy Act (NEPA). Under NEPA, risk assessments could lead to full-blown environmental impact statements, but so far all evaluations of engineered agricultural organisms have led to the legal conclusion that no environmental impact statement is needed.
For the most part, risk assessments by scientists and policymakers in the relevant agencies (USDA or EPA) rely on information provided by the companies seeking the approvals. The public often has a brief opportunity to review and comment on the risk assessments.
There is no standard set of questions that risk assessments must answer because of the great range of potential impacts of biotechnology products. A risk assessment for a microbial pesticide, for example, would be substantially different from a risk assessment for genetically engineered salmon. Like all efforts at risk evaluation, risk assessments done for regulation depend on the base of scientific knowledge underlying the list of possible harms to be assessed.
