www.checkbiotech.org ; www.raupp.info ; www.czu.cz

The global area planted with genetically engineered (GE) crops has
consistently increased each year since GE crops were first commercially
cultivated in 1996, reaching 90 million hectares in 2005, December 2006 by
Olivier Sanvido, Mich?le Stark, Jörg Romeis and Franz Bigler.

Five countries (USA, Argentina, Brazil, Canada and China) are growing
nearly 95% of the total area of these crops. In contrast the adoption of GE
crops in Europe was much less intense. This situation is probably going to
change, since the European Union (EU) entered the first GE maize varieties
expressing insecticidal proteins from Bacillus thuringiensis (Bt) into the
Common EU Catalogue of Varieties in September 2004. It is generally expected
that Bt-maize will also be commercially grown in EU countries other than
Spain, where commercial GE crop cultivation started in 1998. Several
countries such as France, Germany, Portugal, and the Czech Republic started
growing Bt-maize in 2005. Compared to Spain, where approximately 12% of the
total maize area grown in 2004 (representing 58,000 ha) was planted with
Bt-maize, the acreage in these countries is, however, very limited and
accounts for less than 1,000 ha each.

GE crops, modern agricultural systems and the environment
Concerns have been raised that the commercial cultivation of GE crops could
result in adverse effects on the environment.1 We have therefore reviewed
the scientific knowledge on environmental impacts of GE crops deriving from
ten years of worldwide experimental field research and commercial
cultivation.2 Our study focused on the currently commercially available GE
crops that could be relevant for agriculture in Western and Central Europe
(i.e., maize, oilseed rape, and soybean), and on the two main GE traits that
are currently commercialized, herbicide tolerance (HT) and insect resistance
(IR). The sources of information included peer-reviewed scientific journals,
scientific books, reports from countries with extensive GE crop cultivation,
as well as reports from international organizations.

Potential impacts of GE crops should be put in relation to the environmental
impacts of modern agricultural practices that took place during the last
decades. Independent from the use of GE crops, modern agricultural systems
have profound impacts on all environmental resources, including negative
impacts on biodiversity. Several changes in the management of agricultural
land over the last century have resulted in a decline in the biodiversity
within agro-ecosystems.3,4

Effects of GE crops on non-target organisms
There are concerns that insect-resistant GE crops expressing Cry-proteins
from Bacillus thuringiensis (Bt) could harm organisms other than the pest(s)
targeted by the toxin. The published large-scale studies in Bt crops
assessing possible non-target effects on arthropods have only revealed
subtle shifts in the arthropod community, which can be explained by a lack
of the target pest resulting from the effective control by the Bt crops.5 No
adverse effects on non-target natural enemies resulting from direct toxicity
of the expressed Bt toxins have so far been observed in laboratory studies
and in the field. There is evidence that the Bt crops grown today are more
target-specific and have fewer side effects on non-target organisms than
most current insecticides used.

While the adoption of Bt maize has resulted in only modest reductions in
insecticide applications due to the small area of conventional maize treated
with insecticides against the European Corn Borer, the commercial
cultivation of Bt cotton has resulted both in a substantial reduction in
quantity and in number of insecticide applications.6 In addition to direct
environmental benefits such as fewer non-target effects and reduced
pesticide inputs in water, demonstrable health benefits have been documented
for farm workers in developing countries due to less chemical insecticide
spraying in Bt cotton.7

Impacts of GE crops on soil ecosystems
Similarly to non-target effects above ground, concerns were raised that Bt
crops could have effects on soil organisms. Bt toxins enter the soil system
primarily via root exudation and via plant remains after harvest. Both
degradation and inactivation of the Bt toxin vary, depending on parameters
such as temperature and soil type. The initial degradation of the toxin is
rapid, while a low percentage (< 2%) may remain in the soil ecosystem
following one growing season. Bt toxins have been shown to bind to clay and
humic acid compounds; however, no accumulation of toxins has been observed
after several years of cultivation of Bt crops.

Population sizes and community structure of soil organisms are subject to
both natural seasonal variation and to variations caused by the agricultural
system (soil type, plant age, crops, cultivars, and crop rotation). Neither
laboratory nor field studies have shown lethal or sublethal effects of Bt
toxins on nontarget soil organisms such as earthworms, collembola, mites,
woodlice, or nematodes. Some differences in total numbers and community
structure have been described for microorganisms. The ecological
significance of the observed differences is not clear. Because most studies
have not assessed the natural variation occurring in agricultural systems,
it is generally difficult to establish whether the differences between Bt
and non-Bt crops were exceeding this variation. The only study considering
natural variation suggests that observed effects lie within this variation
and that the differences between conventional cultivars outweigh the
observed influences of Bt crops.8

Gene flow from GE crops to wild relatives
There is general scientific agreement that gene flow from GE crops to
sexually compatible wild relatives can occur.9 Experimental studies have
shown that GE crops are capable of spontaneously mating with wild relatives,
however at rates in the order of what would be expected for non-transgenic
crops. Few studies have shown that GE herbicide tolerant (GEHT) oilseed rape
(Brassica napus) can form F1 hybrids with wild turnip (Brassica rapa) at low
frequency under natural conditions. Questions remain whether these
transgenes would cause ecologically relevant changes in recipient plant
populations. Although there is a low probability that increased weediness
due to gene flow could occur, it is unlikely that GEHT weeds would create
greater agricultural problems than conventional weeds. Farmers can generally
choose among several herbicides for the cultivation of a given crop and they
have further a set of options within a crop rotation to control or manage
weeds.

In natural habitats, no long-term introgression of transgenes into wild
plant populations leading to the extinction of any wild plant taxa has been
observed to date. Transgenes conferring herbicide tolerance are unlikely to
confer a benefit in natural habitats because these genes are selectively
neutral in natural environments, whereas insect resistance genes could
increase fitness if pests contribute to the control of natural plant
populations.

Invasiveness of GE crops into natural habitats
Despite the concern that GE crops could invade natural habitats, brought up
early in the discussion on potential environmental risk related to the
release of GE crops, it seems that modern crop varieties generally stay
domesticated. There is no evidence at present that the extensive cultivation
of GEHT oilseed rape over several years in Western Canada has resulted in a
widespread dispersal of volunteer oilseed rape carrying herbicide-tolerance
traits. Although one study found triple-herbicide resistant, and another
study reported double-herbicide resistant, oilseed rape volunteers in
Western Canada, the general lack of reported multiple-resistant volunteers
suggests that these volunteers are being controlled by chemical and
non-chemical management strategies, and are therefore not an agronomic
concern to most farmers. Furthermore, there is currently no evidence that
GEHT oilseed rape has become feral and invaded natural habitats.

Impacts of GE crops on pest and weed management
Impacts of GE crops on pest and weed management practices and their
potential ecological consequences are usually difficult to assess, because
they are generally influenced by many interacting factors and often only
show up after an extended period of time. Numerous weed species evolved
resistance to a number of herbicides long before the introduction of GEHT
crops.10 The experiences available from regions growing GEHT crops on a
large scale confirm that the development of herbicide resistances in weeds
is not primarily a question of genetic modification, but of the crop- and
herbicide management applied by farmers. Despite extensive cultivation of
GEHT oilseed rape in Canada, no weed species has so far been observed being
tolerant to the herbicides glyphosate and glufosinate. In continuously
cultivated GEHT soybeans in the United States, in contrast, many fields have
been treated only with glyphosate, which increases the pressure for the
selection of resistant biotypes. As a consequence, three years after the
introduction of GEHT soybean varieties, glyphosate-resistant horseweed
(Conyza canadensis) has been detected. Although farmers have to add another
herbicide to glyphosate to control the resistant weed species, there are
alternatives to glyphosate for most weed species that are highly effective
and provide good flexibility in application timing. There is, however, no
question that glyphosate-resistant weeds will increase the costs of weed
management for farmers.

The adoption of GEHT crops has allowed the use of a single broad spectrum
herbicide that may reduce the need for costly herbicide combinations.
Glyphosate and glufosinate are generally considered toxicologically more
benign, being in particular less toxic to humans and the environment than
many of the herbicides they replace. In addition, the adoption of GEHT crops
has often facilitated the change to conservation tillage agriculture.
Growers using conservation tillage have reduced their tillage operations,
thus preventing soil erosion and soil degradation.

The results of the UK Farm Scale Evaluations (FSE) showed that weed biomass
and numbers of some invertebrate groups were reduced under GEHT management
in sugar beet and oilseed rape and increased in maize compared with
conventional treatments.11 These differences were related to the weed
management of both conventional and GEHT systems. Highly effective weed
control practices, such as those chosen for the GEHT crops in the FSE, lead
to low numbers of weed seeds and insects. Fewer insects and decreased weed
seed might reduce the numbers of birds that depend on these insects and
seeds as a food source. The FSE assumed no other changes in field management
than GEHT crops replacing non-GE varieties. However, other cropping systems
such as conservation tillage are possible, resulting in a greater
availability of crop residues and weed seeds and, in consequence, improving
food supplies for insects, birds, and small mammals.12

Conclusions
The risks GE crops pose for the environment, and especially for
biodiversity, have been extensively assessed worldwide during the past ten
years of commercial cultivation. Consequently, substantial scientific data
on environmental effects of the currently commercialized GE crops is
available today, and will further be obtained given that several research
programs are underway in a number of countries. The data available so far
provide no scientific evidence that the commercial cultivation of GE crops
has caused environmental harm. Nevertheless, a number of issues related to
the interpretation of scientific data on effects of GE crops on the
environment are debated controversially. To a certain extent, this is due to
the inherent fact that scientific data is always characterized by
uncertainties, and that predictions on potential long-term or cumulative
effects are difficult. Uncertainties can either be related to the
circumstance that there is not yet a sufficient data basis provided for an
assessment of consequences (the "unknown"), or to the fact that the
questions posed are out of reach for scientific methods (the "unknowable").
Although some might argue that experience and solid scientific knowledge are
still lacking, the debate is generally not purely due to a lack of
scientific data, but more to an ambiguous interpretations of what is
considered an ecologically relevant effect of GE crops. The interpretation
of study results is thereby often challenged by the absence of a defined
baseline to evaluate environmental effects of GE crops in the context of
modern agricultural systems. There is thus a need to develop scientific
criteria to assist regulatory authorities when deciding whether
environmental effects of GE crops are considered relevant.

When discussing the risks of GE crops, one has to recognize that the real
choice for farmers and consumers is not between a GE technology that may
have risks and a completely safe alternative. The real choice is between GE
crops and current conventional pest and weed management practices, all
possibly having positive and negative outcomes. To ensure that a policy is
truly precautionary, one should therefore compare the risk of adopting a
technology against the risk of not adopting it.13 We thus believe that both
benefits and risks of GE crop systems should be compared with those of
current agricultural practices.

Acknowledgements
We would like to thank the Swiss Expert Committee for Biosafety for major
funding of the study.

The study is publicly available on the internet via the following link:
[www.art.admin.ch]

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