Introduction. Transgenic, or ‘genetically-modified’ crops are those
created when genes, the hereditary units of living things, are moved into
a plant from another species. In many cases the genes used to create transgenic
crops come from bacteria or viruses.
In 1999, transgenic crops were grown on 63.1 million acres in the U.S.,
constituting 72% of the global acreage of these crops. The seven most widely-grown
transgenic crops grown in 1999 were, in descending order of acreage: soybean,
corn, cotton, canola, potato, squash and papaya. Transgenic soybean and
corn accounted for 54% and 28% of global transgenic crop acreage, respectively;
cotton and canola each occupied approximately 9% of this acreage; potato,
squash and papaya each occupied less than 1% of this acreage in 1999. (James,
C. 1999. Global Status of Commercialized Transgenic Crops: 1999. ISAAABriefs
No.12: Preview. ISAAA: Ithaca, NY. www.isaaa.org/)
To date there are at least 38 commercially-available varieties of transgenic
seeds, including the crops listed above as well as vegetables such as chicory,
sweet corn and tomato (Union of Concerned Scientists, www.ucsusa.org/agriculture/gen.market.html).
More transgenic crops are likely to be available soon, as field trials
have been approved with transgenic barley, broccoli, carrot, cranberry,
eggplant, gladiolus, grape, pea, pepper, raspberry, strawberry, sugarcane,
sweetgum, sweet potato, watermelon and wheat. (www.aphis.usda.gov/bbep/bp/newsletter.html)
The majority of transgenic crops contain one of two genetically modified
traits: an insecticidal toxin from the ‘B.t.’ bacterium, or resistance
to an herbicide. However, resistance to viruses, altered oil content, and
altered ripening are among other characteristics that have been bio-engineered
into commercially-available crop plants.
The risks posed by transgenic crops, whether the risks outweigh the
benefits, who bears the risk and who reaps the benefit are subjects of
debate. There is factual evidence that can be used to support a wide range
of viewpoints, so consensus among scientists in the forseeable future is
unlikely. In part, that is because there are many possible risks and assessing
them involves extrapolating from the evidence available and drawing conclusions
that are inherently subjective.
Because transgenic crops in agriculture interface with the natural environment
on such a large scale, many of the concerns about them are quite distinct
from those relating to genetically engineered animals, medicines, and industrial
products. Thus, concerns about transgenic crops warrant a separate discussion.
Below is a summary of these concerns.
Questionable Pest Control Benefits. Transgenic crops offer agronomic
benefits, or farmers would not be adopting them so rapidly. The benefits
of herbicide-resistant crops include: improved control of problem weeds,
use of fewer types of herbicides and the simplification of weed management
strategies. The benefits of Bt-crops include: control of specific insect
pests (such as European corn borer or Colorado potato beetle) without the
need for other management or material inputs, and reduced levels of mycotoxins
in crops because insect feeding and tissue damage is reduced. There are
many other benefits that may result from the use of transgenic crops that
do not relate directly to pest management, such as increased vitamin levels.
One concern about the use of herbicide-tolerant and Bt-crops for pest
management is that these technologies may diminish the need for agro-ecosystem
approaches to pest management such as crop rotation. The history of pest
management shows that long-term success requires a diversified system that
spreads the burden across differing mixes of chemical, biological, genetic,
and cultural practices. Reliance on a single approach to pest management
will fail because pests successfully evolve and thrive in response to single
approaches. (C.M. Benbrook, 1999. World food system challenges and opportunities:
GMOs, biodiversity, and lessons from America's heartland. www.pmac.net/IWFS.pdf)
Already, resistance problems are being reported with herbicide-tolerant
crops. Volunteer canola resistant to three different herbicide-tolerant
canola systems (RoundUp, Liberty and Pursuit) has been found in a field
in northern Alberta. (M. MacArthur. Feb. 10, 2000. Triple-resistant canola
weeds found in Alberta, Canada. February 10, 2000.Western Producer. www.producer.com/articles/20000210/news/20000210news01.html)
In some cases, Bt-containing crops and herbicide-resistant varieties
(such as ‘RoundUp-Ready’) are being promoted and used in a way that tends
to reduce diversity on the farm. In harsh terms, this could be called the
‘dumbing down’ of pest management. For example, Monsanto ads aimed at farmers
using transgenic crops claim that RoundUp is “the only weed control you'll
ever need". (Iowa State University, herbicide ad "hall of shame".
www.weeds.iastate.edu/weednews/roundupcottonad.htm)
Economic Impact on Farmers. The use of transgenic crops by farmers is
usually accompanied by higher seed cost, and it may result in yield reductions.
Thus there may be no additional profit, or there may be a net economic
loss, despite short-term savings in pest management costs. In 1998, the
Leopold Center at Iowa State University conducted a survey of 800
Iowa farmers, representing a random selection of 62 continuous corn fields,
315 rotated corn fields, and 365 soybean fields. For soybeans, non-GM varieties
yielded more than GM varieties (an average 51.21 bushels per acre compared
to 49.26). Herbicide costs were 30% less for farmers who grew GM soybeans,
but much of the savings went toward higher seed costs. Returns to land
and labor were almost identical. For corn, Bt varieties yielded an average
160.4 bushels per acre, compared to 147.7 for non-Bt varieties. Farmers
still applied insecticides on 12% of their Bt corn fields, compared to
18% for farmers with non-Bt corn. The biggest cost differences were in
seed: an average $39.62 per acre for Bt corn, compared to $29.96 per acre
for non-Bt corn. After labor and other costs, Bt corn earned farmers only
an additional $3.97 per acre, which was not considered to be a statistically
significant difference. (Duffy, M. 1999. Does planting GMO seed boost farmer’s
profits? www.leopold.iastate.edu/fall99leoletterindex.html)
A University of Wisconsin report analyzed soybean yield trials from
8 states in the northern U.S. It concluded: “The average yield of RoundUp
Ready varieties ranged from 14% less to 13% more than conventional varieties
in 40 performance tests conducted by universities in 1998. When averaged
across all tests, RoundUp Ready varieties were 4% lower in yield than conventional
varieties. It is anticipated that soybean growers will continue to increase
acreage planted to RoundUp Ready varieties and will sacrifice yield for
ease of weed control.” (Oplinger, E.S., M.J. Martinka and K.A. Schmitz.
1999. Performance of transgenic soybeans in the northern U.S. www.biotech-info.net/soybean_performance.pdf)
A recent study by Purdue university suggests that in general the current
premiums charged for Bt seed are higher than the expected value of the
protection offered by the seed. (Hyde, J., M. A. Martin, P.V. Preckel and
C. R. Edwards. The economics of Bt corn: adoption implications. www.agcom.purdue.edu/AgCom/Pubs/ID/ID-219/ID-219.html)
The rapid adoption of transgenic varieties has taken place without independent
field testing prior their commercial release, perhaps due to the
rush to bring them to market in order to recoup the sizeable investment
in their development. Historically, seed companies provided samples of
new crop varieties to land grant university researchers to include in their
variety trials, and new varieties were not available to farmers until their
performance had been evaluated against other top varieties. Agronomists
now say they are not even able to get transgenic varieties upon request
from companies in the year they are first introduced (Magdoff, F., Director
of the Northeast USDA Sustainable Agriculture Research and Education program,
personal communication).
Unintended crop attributes. ‘Pleiotropic effects’ may occur when new
genes are inserted into plants to give the plants desirable new traits
(i.e. more than one change may occur in a plant as a result of the new
gene). The US Food and Drug Administration (FDA) policy regulating transgenic
crops assumes that pleiotropic effects will not occur, and that genetically
modified crops are ‘substantially equivalent’ to conventional crops. This
policy was implemented despite concerns raised by government scientists
that it failed to adequately address risks to the environment or to animal
and human health posed by pleiotropic effects.
Memos written by FDA scientific staff indicate that pleiotropic effects
may indeed occur when new genes are inserted into food crops: “Until more
of these experimental plants have a wider environmental distribution, it
would be premature for FDA to summarily dismiss pleiotropy" and "Pleiotropic
effects occur in genetically engineered plants... at frequencies up to
30%. Most of these effects can be managed by the subsequent breeding and
selection procedures. Nevertheless, some undesirable effects such as increased
levels of known naturally occurring toxicants, appearance of new, not previously
identified toxicants, increased capability of concentrating toxic substances
from the environment (e.g., pesticides or heavy metals), and undesirable
alterations in the levels of nutrients may escape breeders' attention unless
genetically engineered plants are evaluated specifically for these changes.
Such evaluations should be performed on a case-by-case basis, i.e., every
transformant should be evaluated before it enters the marketplace." Instead
of heeding theses concerns, FDA issued biotech food rules that assume no
pleiotropic effects will occur, therefore no additional safety testing
of transgenic crops is required. (See internal FDA memos at: www.bio-integrity.org/list.html)
Pleiotropic effects may enhance the competitiveness of transgenic crops
once they are released into the environment. Transgenic Arabidopsis lines
were found in field studies to be 20 times more likely to outcross than
the untransformed plants. Thus, the transgenic plants have a dramatically
increased ability to donate pollen to nearby plants. The authors state
that it is unlikely that this increase in outcrossing was due to genetic
mutation, because two independently transformed lines both showed higher
levels of outcrossing. This has implications regarding the risk of releasing
transgenic crops into the environment. (Wichmann, G., C.B. Purrington,
and J.Bergelson. 1998. Male promiscuity is increased in transgenic Arabidopsis.
9th International Conference on Arabidopsis Research University of Wisconsin,
Madison June 24 - 29, 1998)
Transfer of modified genes to weeds. The movement of plant pollen could
confer traits from transgenic crops to their weedy relatives. Most of the
major crops in the US co-occur with at least one wild weedy relative with
which they have some degree of sexual compatibility (Ellstrand, N.C. 1996.
Potential for crop transgene escape and persistence in weedy populations.
www.nbiap.vt.edu/brarg/cris/grant9403.html) While some crops lack wild
relatives, such as corn, other crops, such as strawberry, canola, and cucurbits
have the potential to transfer genes to weedy relatives in the northeast,
over distances that depend on wind and insect pollination patterns. Little
research has examined this risk in the field, but it has been confirmed
that gene flow between cultivated and wild beet can occur. (Bartsch D,
Lehnen M, Clegg J, Pohl-Orf M, Schuphan I, and Ellstrand NC. 1999. Impact
of gene flow from cultivated beet on genetic diversity of wild sea beet
populations. Molecular Ecology 8(11):1733-1741)
Even some proponents of plant biotechnology are calling for more responsible
management of transgenic crops in order to prevent them from interbreeding
with nearby weeds (Gressel J. 1999. Tandem constructs: preventing the rise
of superweeds. Trends in Biotechnology 17(9):361-366.)
A recent British survey of the literature summarizes the nature of pollen
dispersal by 5 crops and the risk of cross-pollination with wild or cultivated
relatives. “Oil seed rape (canola) presents a high risk for cross-pollination
between source and recipient fields. It is inter-fertile with a number
of wild relatives found in the UK and introgression of transgenes seems
likely. Pollen dispersal has been recorded at up to 4km by insects (some
20 fold higher than the recommended isolation distances), and to 3km by
the air flow. Notable potential exists for cross-pollination with feral
populations which are common in the UK, giving rise to well distributed
further sources of possible contamination.”
“Sugar beet presents a medium to high risk for cross pollination both
with other stands and with wild relatives. Sugar beet crops are biennial
and do not normally flower within the harvesting regime, although some
'bolters' will flower giving the potential for limited gene flow from the
beet crop. In areas producing sugar beet seed flowering is a necessity
and here the risk of cross pollination increases accordingly. The pollen
produced can be spread extensively on the airflow (significant quantities
have been recorded at distances up to 800m) and by insects.”
“Maize presents a medium to high level of risk for cross pollination
with other maize crops as the pollen can spread on the airflow. Pollen
distribution, as determined by outcrossing between different maize varieties,
has been recorded at up to 800m. Maize also presents a medium to
high risk for the inclusion of pollen into honey. However, the crop is
not interfertile with any UK wild or crop relatives. The percentage of
cross breeding with other maize crops in the vicinity will depend on factors
such as separation distance, local barriers to pollen movement, such as
woods and hedges, local climate and topography.”
“Wheat and potato can be described as low risk for contamination from
genetically modified varieties. Wheat has limited potential for outcrossing
even with proximal plants and is not inter-fertile with wild or crop relatives
in the UK. Potato is a tuber crop, that is also planted as a seed tuber.
There is little potential for the introgression of transgenes into the
harvested potato tuber and the species is not inter-fertile with any UK
wild or crop relatives.”
“Much published work relies on small field trials (including GM trials).
Evidence indicates that the extent of gene flow between GM and non-GM fields,
and between GM and feral populations depends mainly on the scale of pollen
release and dispersal, and on the distances between source and recipient
populations. The potential impact (including cross pollination and inclusion
in honey) of pollen from GM crops increases notably with the size and number
of fields planted.” (Treu, R. and J. Emberlin. 2000. Pollen dispersal
in the crops maize, oil seed rape, potatoes, sugarbeet and wheat - evidence
from publications. Soil Association, 40-56 Victoria Street, Bristol BS1
6BY, UK. www.soilassociation.org)
Contamination of organic farms and food. Organic farming standards do
not allow the use of genetically modifed organisms, including transgenic
crops. Organic farmers, processors and distributors stand to lose markets
and income if their organic products are de-certified due to genetic contamination.
Such contamination can be identified by a variety of commercially-available
tests that range in price from $6 to $400, depending on what type of genetic
material is tested for. Genetic contamination can occur in a variety of
ways, on the farm, at the grain elevators, during transportation, and during
food processing. Organically-grown crops such as corn or canola may become
contaminated if they are cross-pollinated by wind-blown pollen from transgenic
crops in nearby fields, although this is not much of a threat for plants
like soybeans that self-pollinate. (Bett, K.S. 1999. Mounting evidence
of genetic pollution from GE crops growing evidence of widespread GMO contamination.
From: Environmental Science and Technology. www.purefood.org/ge/gepollution.cfm)
Terra Prima, a company that sells organic corn chips, used DNA testing
to prove that corn grown by a certified organic farmer in Texas was contaminated
by cross-pollination from a nearby field where Bt corn was grown. The company
was forced to destroy $87,000 worth of its chips because the contamination
did not come to light until after the corn was made into chips; it is a
plaintiff in a lawsuit filed against EPA this February alleging that the
agency registered genetically engineered crops without adequately considering
their health and environmental impacts. (K.S. Bett. 1999. Mounting Evidence
of Genetic Pollution from GE Crops Growing Evidence of Widespread GMO.
www.purefood.org/ge/gepollution.cfm)
No system of field production can absolutely guarantee the purity of
the seeds or plants produced. Low but acceptable levels of contamination
of organic crops need to be identified and measures identified to achieve
them. The best means of reducing the potential for contamination by GM
pollen is for organic producers and/or transgenic crop producers to isolate
their crops by an appropriate distance. Crop isolation distances have already
been established for the production of seed of high genetic purity, and
these (or specific multiples of these) could be used as a basis for the
production of organic crops, for example, seed corn production requires
an isolation distance of 666 feet.(Moyes, C.L. and P.J. Dale. 1999. Organic
farming and gene transfer from genetically modified crops. MAFF Research
Project OF0157, John Innes Centre, UK. www.gmissues.org/orgreport/gmissues%5B1%5D.htm)
Besides potential contamination from neighboring farms, transgenic crops
are sometimes grown unintentionally on farms - organic and conventional.
For example, a non-organic vegetable farmer in Vermont recently told me
‘he was horrified’ to learn he had been growing transgenic squash varieties
without knowing it. (The varieties had been purchased because they were
described in seed catalogs as virus-resistant but no mention was made of
their being transgenic). Unintentional planting of transgenic seed might
also occur if contamination happens during seed production. (Skinner, D.
and R.N. Peaden. 1993. Risk of transgenic alfalfa disemination during seed
production. www.nbiap.vt.edu/brarg/cris/grant9302.html)
To prevent contamination, handling practices throughout the food system
must preserve the separated identity of organic and non-organic products.
Because some businesses require products they purchase to be certified
to contain less than 0.1% or even 0.01% of genetically modified organisms,
carelessness such as not properly cleaning out a weighing bin can lead
to contamination. People involved in moving organic products want to protect
their interests so they have begun testing at different points along the
way from farm to table.
Acceleration of insect pest resistance to B.t. is thought by many scientists
to be likely since the selective pressure created by millions of acres
of transgenic-Bt crops vastly exceeds that posed by traditional application
of Bt pesticides. Bt is the most important bio-pesticide in the world,
used to control caterpillar and beetle larvae such as European corn borer
and Colorado potato beetle. It is an valuable tool for conventional growers
practicing IPM, as well as for organic and transitional growers (Lipson,
M. 1999. Transgenic Bt crops, pest resistance and the organic grower. Organic
Farming Research Foundation, Information Bulletin No. 6). In February 1999,
Greenpeace and a coalition of over 70 plaintiffs, including the Center
for Food Safety and the International Federation of Organic Agricultural
Movements, sued the EPA, charging the agency with the wanton destruction
of the world's most important biological pesticide.
In response to concerns that transgenic-Bt crops may be accelerating
the evolution of pesticide resistant insects, the EPA has announced new
restrictions on GE corn and cotton cultivation. The new restrictions, which
became effective January 14, 2000, require registrants to ensure that growers
plant a minimum of 20% of their acreage in non-Bt corn refuges. For corn
grown in cotton areas, the non-Bt refuge requirement is increased to at
least 50 percent. (www.epa.gov/pesticides/biopesticides)
Escape and spread of transgenic crops. Researchers at the University
of North Carolina and the University of Georgia performed a field experiment
in which Bt-transgenic and non-transgenic canola plants were planted in
natural vegetation and semi-cultivated plots and subjected to various insect
selection pressure in the form of herbivory. In the semi-cultivated plots,
medium to high levels of defoliation decreased survivorship of non-transgenic
plants relative to Bt-transgenic plants, and increased differential reproduction
in favor of Bt plants. “Thus, where suitable habitat is available, such
as roadsides, fallow fields, and field edges, there is a strong likelihood
of enhanced ecological risk associated with the release of certain transgene/crop
combinations such as insecticidal canola.” (Stewart, C.N Jr.,
J.N. All, P.L. Raymer and S. Ramachandran. 1996. Inceased fitness
of transgenic insecticidal canola under insect selection pressure. www.nbiap.vt.edu/brarg/brasym96/stewart96.htm)
Negative Effects on Non-Target organisms. In the case of crops engineered
to contain the Bt toxin to kill foliar pests, below-ground insects may
be affected as well, since all the cells of the plant contain the toxin.
Biologically active Bt toxin has been found to be released from the roots
of Bt corn into growth medium and into the soil environment. It has been
suggested that the toxin may accumulate in soil under continuous cultivation
of Bt corn and that this accumulation may lead to unanticipated impacts
on non-target organisms in the soil. (Saxena, D., S. Flores and G. Stotzky.
1999. Insecticidal toxin in root exudates from Bt corn. Nature 402:480)
Another study examined the post-harvest effects of an insecticidal protein
in transgenic tobacco residues. Compared to unmodified (parent plant) tobacco
residues, transgenic residues that were buried in soil altered the species
composition of the soil biota responsible for organic matter decomposition
and nutrient cycling. The population of fungal feeding nematodes, which
have been shown to influence N mineralization and plant growth, was altered
by the transgenic residues. (Donegan, K.K., R.J. Seidler, V.J. Fieland,
D.L. Schaller, C.J. Palm, L.M. Ganio, D.M. Cardwell, and Y.Steinberger.
1997. Decomposition of genetically engineered tobacco under field conditions:
persistence of proteinase inhibitor I product and effects on soil microbial
respiration and protozoa, nematode and microarthropod populations. J. Applied
Ecology 34:767-777)
A Scottish study found that ladybugs which fed on aphids that had fed
on transgenic potatoes produced up to 30% fewer progeny and lived only
half as long as ladybugs feeding on aphids which had fed on conventional
potatoes. (Birch, A.N.E., I.E. Geoghegan, M.E.N. Majerus, C. Hackette and
J. Allen. 1997. Interactions between plant resistance genes, pest aphid
populations and beneficial aphid predators. Scottish Crop Research Institute
Annual Report. pp. 68-72). Similar evidence of ecological ramification
was reported from the Swiss Federal Research Station for Agroecology and
Agriculture. They found that the Bt endotoxin from transgenic corn killed
most corn borers, but the green lacewings which fed on the corn borers
were also killed. In subsequent studies, they found that 50% more lacewings
died after consuming catepillers fed on Bt than consuming the purified
Bt directly. (Hilbeck, A., M. Baumgartner, P.M. Fried and F.Bigler. 1998.
Effects of transgenic Bacillus thuringiensis corn-fed prey on mortality
and development time of immature Chrysoperla carnea. Environmental Entomology
27(2):480-487) Some ecologists suspect that the aphids in this study had
sequestered the Bt endotoxin and succeeded in transferring it to predators.
Cauliflower mosaic viral (CaMV) promoter is used in practically all
current transgenic crops released commercially or undergoing field trials.
Concern has been raised about the safety of transgenic plants containing
CaMV promoters. Although CaMV itself infects only dicotyledons, its promoter
is ‘promiscuous’ and functions efficiently in monocotyledons, conifers,
green algae, yeasts and E. coli. The transfer of CaMV promoter to other
species could also give rise to unpredictable effects on gene expression,
which may negatively impact the ecosystem as a whole. It is suggested that
such transfer might occur if ‘naked’ or ‘free’ is DNA in released into
the environment and taken up by the cells of another organism. Thus, some
scientists recommend that all transgenic crops containing CaMV 35S or similar
promoters should be immediately withdrawn from commercial production or
open field trials, and that all products derived from such crops containing
transgenic DNA should also be immediately withdrawn from sale and from
use for human consumption or animal feed. (Ho, Mae-Wan, A.Ryan and J.Cummins.
1999. Cauliflower mosaic viral promoter — a recipe for disaster? Microbial
Ecology in Health and Disease 1999; 11(4). www.scup.no/mehd/ho)
Food Safety. There are several concerns about how consumption of transgenic
crops may negatively affect human health. These have to do with the potential
for allergins to be accidentally introduced in new crop varieties, and
with the potential to promote antibiotic and virus resistance in people
and animals. (M.Hanson and J.Halloran. 1999. Jeopardizing the future? Genetic
engineering, food and the environment. Consumer Policy Institute/Consumers
Union). There is some evidence that a genetically engineered soybean containing
a Brazil nut gene could cause allergic reactions to humans (Nordlee J.A.,
S.L.Taylor, J.A.Townsend, L.A.Thomas and R.K. Bush. 1996. Identification
of a Brazil-nut allergen in transgenic soybeans. The New England Journal
of Medicine, 334(11):726-728)
Market Implications. It is well know that markets for American crops
in Europe have been reduced due to the use of trangenic crops. A 1999 survey
indicates that many mainstream farmers now feel that the risks associated
with planting GMOs may be too great. Farmers mention the loss of export
and domestic markets, questions over cross-pollination, testing and certification,
concern over grain elevator insistence on segregation and premiums being
offered for GMO-free crops, as driving corn grower demand for alternatives
to GMOs. In addition, grain elevators are expressing apprehension over
the costs to segregate because their facilities are not equipped for separate
dumping and drying. These concerns prompt the forecast of a dramatic reduction
in GMO-corn acreage. (American Corn Growers Assn., www.acga.org/news/1999/092099.htm)
Consumer acceptance of transgenic crops in the domestic marketplace
may also be a problem for farmers. A survey by the International Food Information
Council, a Washington DC foundation, indicates that consumers are not well-informed
about genetically engineered foods. However, even when asked questions
biased toward favorable responses, such as how likely they would be to
buy biotech foods that “required fewer pesticide sprays”, or “tasted better
or fresher”, a significant portion (21 to 43%) of the 1,000 people interviewed
still said they would not be likely to purchase such food. (U.S. Consumer
Attitudes Toward Food Biotechnology. Wirthlin Group Quorum Surveys.
http://ificinfo.health.org/foodbiotech/survey.htm)
Conclusion. The rapid adoption of transgenic crops poses some significant
risks to ecosystems, as well as some economic risks to farmers. In my opinion,
it does not appear that these risks have been managed with sufficient caution,
especially since the potential long-term benefits to farmers and consumers
are not compelling. Organic farmers in particular are at risk, due to the
lack of measures to protect them from losses due to genetic contamination.
While transgenic crops may simplify management for conventional farmers,
they also create economic risk because marketplace acceptance of trangenic
crops is currently weak and may worsen. Transgenic crops do not support
a sustainable approach to crop production that emphasizes 1) ago-ecosystem
based management of pests and nutrients and 2) farm profitability derived
from strong markets that are built on meeting the consumer’s desires. |