Risks of Genetic Engineering

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Risks of Genetic Engineering

 

Potential

Harms to Health

Potential

Environmental Harms

Risk

Assessment

 

http://www.ucsusa.org/food_and_agriculture/science_and_impacts/impacts_genetic_engineering/risks-of-genetic-engineering.html

Many previous technologies have proved to have adverse effects

unexpected by their developers. 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 or release of genetically engineered organisms?

This is not an easy question. Being able to answer it depends on

understanding complex biological and ecological systems. So far,

scientists know of no generic harms associated with genetically

engineered organisms. For example, it is not true that all genetically

engineered foods are toxic or that all released engineered organisms

are likely to proliferate in the environment. But specific engineered

organisms may be harmful by virtue of the novel gene combinations they

possess. This means that the risks of genetically engineered organisms

must be assessed case by case and that these risks can differ greatly

from one gene-organism combination to another.

So far, scientists have identified a number of ways in which

genetically engineered organisms could potentially adversely impact

both human health and the environment. Once the potential harms are

identified, the question becomes how likely are they to occur. The

answer to this question falls into the arena of risk assessment.

In addition to posing risks of harm that we can envision and attempt

to assess, genetic engineering may also pose risks that we simply do

not know enough to identify. The recognition of this possibility does

not by itself justify stopping the technology, but does put a

substantial burden on those who wish to go forward to demonstrate

benefits.

1. Potential Harms to

Health

 

New

Allergens in the Food Supply

Antibiotic

Resistance

Production

of New Toxins

Concentration

of Toxic Metals

Enhancement

of the Environment for Toxic Fungi

Unknown

Harms to Health

 

Here are the some examples of the potential adverse effects of

genetically engineered organisms may have on human health. Most of

these examples are associated with the growth and consumption of

genetically engineered crops. Different risks would be associated with

genetically engineered animals and, like the risks associated with

plants, would depend largely on the new traits introduced into the

organism.

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.

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.

Enhancement

of the Environment for Toxic Fungi

Although for the most part health risks are the result of the

genetic material newly added to organisms, it is also possible for the

removal of genes and gene products to cause problems. For example,

genetic engineering 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.

Unknown Harms to Health

As with any new technology, the full set of risks associated with

genetic engineering have almost certainly not been identified. The

ability to imagine what might go wrong with a technology is limited by

the currently incomplete understanding of physiology, genetics, and

nutrition.

2. Potential

Environmental Harms

 

Increased

Weediness

Gene

Transfer to Wild or Weedy Relatives

Change

in Herbicide Use Patterns

Squandering

of Valuable Pest Susceptibility Genes

Poisoned

Wildlife

Creation

of New or Worse Viruses

Unknown

Harms to the Environment

 

 

Increased Weediness

One way of thinking generally about the environmental harm that

genetically engineered plants might do is to consider that they might

become weeds. Here, weeds means all plants in places where humans do

not want them. The term covers everything from Johnson grass choking

crops in fields to kudzu blanketing trees to melaleuca trees invading

the Everglades. In each case, the plants are growing unaided by humans

in places where they are having unwanted effects. In agriculture, weeds

can severely inhibit crop yield. In unmanaged environments, like the

Everglades, invading trees can displace natural flora and upset whole

ecosystems.

Some weeds result from the accidental introduction of alien plants,

but many were the result of purposeful introductions for agricultural

and horticultural purposes. Some of the plants intentionally introduced

into the United States that have become serious weeds are Johnson

grass, multiflora rose, and kudzu. A new combination of traits produced

as a result of genetic engineering might enable crops to thrive unaided

in the environment in circumstances where they would then be considered

new or worse weeds. One example would be a rice plant engineered to be

salt-tolerant that escaped cultivation and invaded nearby marine

estuaries.

Gene Transfer

to Wild or Weedy Relatives

Novel genes placed in crops will not necessarily stay in

agricultural fields. If relatives of the altered crops are growing near

the field, the new gene can easily move via pollen into those plants.

The new traits might confer on wild or weedy relatives of crop plants

the ability to thrive in unwanted places, making them weeds as defined

above. For example, a gene changing the oil composition of a crop might

move into nearby weedy relatives in which the new oil composition would

enable the seeds to survive the winter. Overwintering might allow the

plant to become a weed or might intensify weedy properties it already

possesses.

Change in Herbicide

Use Patterns

Crops genetically engineered to be resistant to chemical herbicides

are tightly linked to the use of particular chemical pesticides.

Adoption of these crops could therefore lead to changes in the mix of

chemical herbicides used across the country. To the extent that

chemical herbicides differ in their environmental toxicity, these

changing patterns could result in greater levels of environmental harm

overall. In addition, widespread use of herbicide-tolerant crops could

lead to the rapid evolution of resistance to herbicides in weeds,

either as a result of increased exposure to the herbicide or as a

result of the transfer of the herbicide trait to weedy relatives of

crops. Again, since herbicides differ in their environmental harm, loss

of some herbicides may be detrimental to the environment overall.

Squandering

of Valuable Pest Susceptibility Genes

Many insects contain genes that render them susceptible to

pesticides. Often these susceptibility genes predominate in natural

populations of insects. These genes are a valuable natural resource

because they allow pesticides to remain as effective pest-control

tools. The more benign the pesticide, the more valuable the genes that

make pests susceptible to it.

Certain genetically engineered crops threaten the continued

susceptibility of pests to one of nature's most valuable pesticides:

the Bacillus thuringiensis or Bt toxin. These "Bt crops" are

genetically engineered to contain a gene for the Bt toxin. Because the

crops produce the toxin in most plant tissues 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.

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 and transcapsidation.

Recombination can occur between the plant-produced viral genes and

closely related genes of incoming viruses. Such recombination may

produce viruses that can infect a wider range of hosts or that may be

more virulent than the parent viruses.

Transcapsidation involves the encapsulation of the genetic material

of one virus by the plant-produced viral proteins. Such hybrid viruses

could transfer viral genetic material to a new host plant that it could

not otherwise infect. Except in rare circumstances, this would be a

one-time-only effect, because the viral genetic material carries no

genes for the foreign proteins within which it was encapsulated and

would not be able to produce a second generation of hybrid viruses.

Unknown Harms to the

Environment

As with human health risks, it is unlikely that all potential harms

to the environment have been identified. Each of the potential harms

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. At this point,

biology and ecology are too poorly understood to be certain that

question has been answered comprehensively.

3. Risk Assessment

Having identified a list of possible harms that might occur as a

result of using or releasing genetically engineered organisms, the next

question is how likely are any of these to occur? Like the original

"brainstorming" of potential harms, the answer to this question 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. For example, the approval of the first genetically

engineered squash by the United States Department of Agriculture

involved a controversial risk assessment.

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 are done by scientists and

policymakers in the relevant agencies (USDA or EPA) with 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 for generation of list of possible harms to be assessed.