GENET archive


2-Plants: Biotechnology and comparative risk assessment of GE wheat

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SOURCE: ISB News Report, USA, by Robert K. D. Peterson
DATE:   Feb 2006

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Considerable attention has been paid to potential risks and risk
assessment approaches for genetically engineered (GE) organisms. In
recent years, a number of regulatory agencies around the world have been
formulating assessment procedures to ensure the acceptable environmental
safety of GE organisms. Although there are exceptions, these procedures
typically follow conventional risk assessment steps, including
formulation of the problem, assessment of the effects, assessment of the
exposures, and characterization of the risks.

Risk assessments for GE organisms, especially GE crops, have ranged from
simple, qualitative characterizations to complex, quantitative
characterizations. Regardless of the type or complexity of the
assessment, nearly all risk assessments of GE crops address the risk of
the crop as a standalone system, without formally and systematically
considering the ecological or human-health risks posed by alternative
crops and cropping systems.

Risks for crops and cropping systems posed by organic, conventional, and
mutagenic approaches typically are not compared to GE crops and systems.
This is interesting because many other environmental risk assessments and
decisions in the U.S. are presented as part of governmentally mandated
Environmental Impact Statements or Environmental Assessments. A hallmark
of those assessments is the analysis of alternatives (albeit not
typically formalized, comparative risk assessments) to the proposed
action. Formal comparative risk analyses of alternatives would be
valuable for decision-making about, and public communication of, genetic
engineering technologies. Comparative risk analysis can provide a broader
perspective from which to consider risks and benefits posed by genetic

In Peterson and Hulting1 and Peterson and Shama2, we compared multiple
aspects of risk associated with different wheat production systems in the
U.S. and Canada using the risk assessment paradigm. We chose to examine
risk issues associated with wheat because wheat varieties using genetic
engineering are just now emerging. Wheat varieties produced using these
biotechnologies have lagged behind other crop species, but are now being
developed in the case of genetic engineering and are being grown
commercially in the case of mutagenic techniques. Therefore, this
provided us with a unique opportunity to assess comparatively the
potential environmental risks (human health, ecological, and livestock
risks) associated with the different biotechnology and conventional wheat
production systems.


For our assessments, we used tier 1 quantitative and qualitative risk
assessment methods to compare specific environmental risks associated
with genetically engineered, mutagenic, and conventional wheat production
systems (specifically herbicide and protein risks) in Canada and the U.S.
Risk assessment typically utilizes a tiered modeling approach extending
from deterministic models (Tier 1) based on conservative assumptions to
probabilistic models (Tier 4) using refined assumptions3. In risk
assessment, conservative assumptions in lower-tier assessments represent
overestimates of effect and exposure; therefore, the resulting
quantitative risk values typically are conservative and err on the side
of environmental safety.

Herbicide-tolerant wheat varieties have been produced using both
genetically engineered (DNA recombination) and chemically induced DNA
mutation techniques. Replacement of traditional herbicides with
glyphosate in a glyphosate-tolerant (genetically engineered) wheat system
or imazamox in an imidazolinone-tolerant (mutagenic) wheat system may
alter environmental risks associated with weed management. Additionally,
because both systems rely on plants that express novel proteins, the
proteins and plants themselves may impose risks.

For the conventional wheat system, herbicides were considered as the only
stressor in our assessment. Therefore, the conventional wheat production
system served as a baseline in our analysis. For the glyphosate-tolerant
wheat system, herbicides and the transgenic protein were the stressors.
For the imidazolinone-tolerant wheat system, herbicides and the mutated
protein were the stressors. The primary stressors then potentially
affected the systems through human health (dietary exposure for the
biotech proteins and herbicides, and applicator risk for the herbicides),
livestock, and ecological effects. The effects we considered in this
assessment reflected primary impacts. Therefore, we presented only direct
effects of the stressors on the human and ecological receptors. We did
not consider economic risks or agronomic risks, such as pollen-mediated
and mechanical mixing of wheat grain from different production systems,
pollen-mediated gene flow to wild or weedy relatives of wheat, fallow
management with herbicides, herbicide resistance in target weeds, and
herbicide rotation risks to alternate crops.

Herbicide risk

The herbicide active ingredients evaluated in this study included 2,4-
dichlorophenoxy acetic acid (2,4-D), bromoxynil, clodinafop, clopyralid,
dicamba, fenoxaprop, flucarbazone, MCPA, metsulfuron, thifensulfuron,
tralkoxydim, triallate, triasulfuron, tribenuron, and trifluralin. These
active ingredients were chosen because they are used on a relatively
large percentage of spring wheat acres in the U.S. and Canada. Risk
associated with glyphosate and imazamox also was evaluated because of
their use in glyphosate-tolerant and imidazolinone-tolerant wheat.

We characterized risks to the following ecological receptors: wild
mammals, birds, nontarget terrestrial plants, nontarget aquatic plants,
aquatic vertebrates, aquatic invertebrates, and groundwater. Ecological
risks were assessed by integrating toxicity and exposure. To do this,
risks to ecological receptors were assessed using the Risk Quotient (RQ)
Method. For each ecological receptor, an RQ was calculated by dividing
the Estimated Environmental Concentration (EEC) by the appropriate
toxicity endpoint (e.g., the LC50).

Transgenic protein risk

Risks for the glyphosate-tolerant CP4 EPSPS protein were determined
primarily using a qualitative weight-of-evidence approach. Effect and
exposure information for humans, livestock, and wildlife (such as
mammals, birds, and fish) was obtained from the scientific literature.
Other information was obtained from regulatory reports and submissions.

Mutated protein risk

As with the CP4 EPSPS protein, risks for the mutated imidazolinone-
tolerant AHAS protein were determined using a qualitative weight-of-
evidence approach. However, effect and exposure information for the
mutated AHAS protein is not available in the scientific literature.
Further, because it is a mutagenic trait and not a genetically engineered
trait, regulatory approvals are not required in the U.S. The regulatory
status of imidazolinone-tolerant wheat also limits the availability of
public information. In Canada, imidazolinone-tolerant wheat is regulated
as a novel trait by the Canadian Food Inspection Agency (CFIA) and Health
Canada. Therefore, we used the decision documents produced by these two
agencies for our risk assessment.


Both glyphosate and imazamox presented lower human health and ecological
risks than many other herbicides associated with conventional wheat
production systems. The differences in risks were most pronounced when
comparing glyphosate and imazamox to herbicides currently with
substantial market share. Current weight-of-evidence suggests that the
transgenic CP4 EPSPS protein present in glyphosate-tolerant wheat poses
negligible risk to humans, livestock, and wildlife. Risk for mutated AHAS
protein in imidazolinone-tolerant wheat most likely would be low, but
there were not sufficient effect and exposure data to adequately
characterize risk. Environmental risks for herbicides were more amenable
to quantitative assessments than for the transgenic CP4 EPSPS protein and
the mutated AHAS protein.

An important caveat emerges from our work: Tier 1 risk assessment
approaches have limited value for accurate quantifications of risk
because of their simplistic hazard and exposure assumptions. These
assumptions, which are highly conservative and err on the side of
environmental safety, typically are used for highlighting significant
versus negligible risks during preliminary decision-making and not for
determining actual site-specific risks. Therefore, our results should not
be used as representations of "actual" risks. To determine more realistic
risks, higher-tier assessments for these technologies should be used.
However, we believe quantitative and qualitative tier 1 approaches are
valuable for making direct comparisons between environmental stressors.

In our work, environmental risks for herbicides were more amenable to
quantitative assessments than for the transgenic CP4 EPSPS protein and
the mutated AHAS protein. Because of specificity and familiarity with
their native counterparts, evolving regulatory requirements, and the fact
that they are not pesticides, these proteins do not have the same
completeness of toxicity testing data as herbicides. We believe it is
important that minimum effect and exposure data (such as acute mammalian
toxicities to altered or inserted proteins) are generated and made
publicly available for all novel plant traits, including non-genetically
engineered approaches. These data would allow for independent, third-
party tier 1 assessments of risk and proper communication of those risks
to the public.

Although our assessment was not comprehensive, we believe the approach
demonstrates the potential risk-risk tradeoffs when implementing the
newer biotechnologies. We are currently applying similar comparative risk
approaches to plant-based pharmaceuticals. These types of comparative
biological risk assessments add valuable information, which subsequently
aid regulatory and public decision-making about biotechnology.


1. Peterson RKD and Hulting AW. (2004) A comparative ecological risk
assessment for herbicides used on spring wheat: the effect of glyphosate
when used within a glyphosate-tolerant wheat system. Weed Sci. 52, 834-844
2. Peterson RKD and Shama LM. (2005) A comparative risk assessment of
genetically engineered, mutagenic, and conventional wheat production
systems. Transgenic Res. 14, 859-875
3. [NRC] National Research Council (1983) Risk Assessment in the Federal
Government: Managing the Process. National Academy Press, Washington, DC.

Robert K. D. Peterson
Agricultural & Biological Risk Assessment
Dept. of Land Resources & Environmental Sciences
Montana State University
Bozeman, MT


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