POTENTIAL 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
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.
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
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
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
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.