How safe is Bt-cotton?
Facts allay fear
The success story of Bt
cotton has opened the doors wide for the Bt crops in india. T
M Manjunath, Consultant, AgriBiotech and IPM, explains about
the scientific process involved in developing Bt crops, their
speciality and the safety regulation processes.
Bt-cotton is a
well-researched product and any science-based, rather than aggressive
and emotional, debate is welcome. Blind opposition and creating
suspicion and fear through unsubstantiated allegations have no place in
science. An attempt is made in this article to put across certain
biological and regulatory facts so as to clear any doubts about the
safety of Bt-cotton and other Bt-crops.
Why is Bt safe to
Bt-cotton, incorporated with the insecticidal gene(s) derived from the
soil bacterium, bacillus thuringiensis, has been specifically developed
to control cotton bollworms - not sucking pests, diseases, etc. - which
have haunted cotton growers for several decades.
Specificity: The cry (crystalline) proteins expressed by the introduced
genes in cotton tissues are lepidopteron (moth and butterfly group)
that are unique and require certain specific conditions for their
activity. These include:
The protein has to be ingested by the target insects as it has no
contact effect; ingestion takes place when caterpillars feed on any
part of Bt-cotton plant. The protein requires an alkaline
intestine with a pH of at least 9.5 for its activation and effective
processing; and there should be specific receptors in the
mid-gut epithelium cells of the target insect for protein-binding that
eventually leads to death of the incumbent caterpillars.
All these conditions are available in bollworms and therefore the
caterpillars succumb when they feed on Bt-cotton plants. The protein
cannot act in human or animal intestine because it is acidic, pH is
very low and lacks specific receptors. This has been demonstrated
during regulatory tests in India and other countries. Experimental
animals like mice, rats, rabbits, sheep, etc. fed with unusually high
doses (500, 1000 and 4300 mg/kg body weight) of Bt protein showed no
acute toxic effect on their health. These animals were found to be
substantially equivalent to those not fed with cry protein in respect
of body weight, food consumption and other respects. Based on such
scientific data, the US Environmental Protection Agency (EPA) has
concluded “toxicity and infectivity risks of cry proteins to
non-target organisms like avian, freshwater fish, freshwater aquatic
invertebrates, estuarine and marine animals, arthropod
predators/parasitoids, honey bees, annelids, and mammalian wildlife
will be minimal to non-existent…”
In spite of such clean certification by responsible bodies, serious
allegations continue to be made by a select group against the safety of
Bt-crops. Bt-cotton was implicated for mass
mortality of sheep purported to have fed on the foliage of this crop in
Warangal, Andhra Pradesh. However, GEAC, which examined the data
submitted by the Centre for Sustainable Agriculture (CSA), opined
during its 68th meeting held in May 2005, that the report was
highly exaggerated and was based more on hearsay than on scientific
facts. In spite of this, the reactionaries continue to quote such
examples and try to scare the farmers.
Bt-protein in soil: The cry proteins produced in Bt-cotton are found to
degrade when crop residues are incorporated into the soil. Thus, the
impact of these crops on environment, soil flora or fauna is
negligible. This is further supported by the long history of safe use
of Bt microbial spray formulations to control insect pests on a variety
of crops all over the world for more than 50 years.
Cross pollination and
The potential movement of transgenes from Bt-crops into related weeds
through pollen flow is one of the concerns. This issue has been
addressed for Bt-cotton and experimentally demonstrated that there is
no significant risk of such gene transfer.
In India, cotton has only one close weed relative. It is Gossypium
stocksii. It is found in northern Gujarat where cotton is not
cultivated. Besides, there is no record of bollworms feeding on this
weed and also there is no other major lepidopteron common to both
cotton and this weed. Further, the cotton pollen is heavy and cannot
move beyond a few meters away from cotton fields. Therefore, the
possibility of gene transfer and the development of ‘super
weed’ is a remote possibility. Even in other countries and
with other Bt-crops, there is no evidence that ‘super
weeds’ have ever developed over the past decade.
In India, we have two types of cotton: the American cotton (Gossypium
hirsutum and G barbadense) and the ‘desi’ (local)
cotton (Gossypium herbaceum and G arboreum). All the Bt-cotton hybrids
developed in India are G hirsutum. The American cotton is tetraploid in
genetic makeup whereas the ‘desi’ cotton is
diploid. There is no reproductive compatibility between the two. Even
if cross pollination occurs between the tetraploid and diploid cotton
plants, the zygotic embryo will not develop. This holds good for other
unrelated plant species as well. The terms such as ‘gene
pollution’ and ‘gene contamination’ are
mere jargons in this case.
The potential for horizontal gene transfer from Bt-crops was also
considered and evaluated. Various sub-species or strains of
Bacillus thuringiensis naturally occur in soil and therefore various
cry genes have been available for long periods of time for any
potential horizontal transfer from this bacterium to other soil
species. Therefore, Bt crops, including cotton, are not adding anything
new to the already existing flux of cry genes among the soil
microorganisms. There is no evidence that horizontal gene transfer has
occurred from plants to microbes.
Pest populations exposed to Bt-crops continuously for several years
have the potential to develop resistance to cry proteins. Resistance is
not unique to Bt-crops. In view of this, proactive insect
resistance management strategies have been developed and are in
place. A key element of these plans is that growers should
plant sufficient acreage of non-Bt crops to serve as a refuge for
producing Bt-sensitive insects. The refuge strategy is designed to
ensure that Bt-susceptible insects will be available to mate with
Bt-resistant insects. The offspring of these mating will be
Bt-susceptible, thus mitigating the spread of resistance in the
population. Gene pyramiding, optimum dose and deployment of Bt-crops as
one of the components of integrated pest management are the other
options for Insect Resistance Management (IRM).
Growing refuge has been made as one of the conditions while giving
approval for Bt-cotton in India. In India,
Helicoverpa armigera, besides cotton, has a large number of
alternative hosts like chickpea, pigeonpea, tomato, sunflower, maize
and sorghum, which are grown in the same area at the same time as
cotton. These would serve as natural refugia, thereby helping
IRM. The fact is that although Bt-cotton has been under large scale
commercial cultivation for many years, there has been no indication of
any pest resistance to Bt protein expressed within the plant.
This is very encouraging.
The above scientific information clearly indicate that Bt is safe to
non-target organisms and environment. Yet, the reactionaries continue
to hurl allegations, question the competence of regulators, confuse
politicians, scare the farmers and demand a ban on a well-researched
scientific product! It is a puzzle what would satisfy them! Those who
demand a ban owe a responsibility to furnish supporting scientific data
to GEAC, for scrutiny and appropriate decision. Mere public agitation
and press statements have no credibility in science.
An annotated bibliography of more than 200 peer reviewed world
literature on biosafety and related issues associated with GE/GM crops
was prepared and reviewed way back in 2003. There was hardly any
scientific paper that found Bt-crops as unsafe to humans or
environment. In subsequent years, many more scientific papers have been
published in reputed journals in support of this technology. The
anti-biotech papers are mostly published in newspapers and magazines
without being reviewed by experts.
Bt-technology has already lasted for more than a decade in several
countries and in India since 2002, bringing substantial environmental
and economic benefits to farmers with no negative consequences
whatsoever. It is the responsibility of the scientists and regulators
to sustain these benefits. If we close the doors for new technologies,
fearing the opposition and speculated risks, we cannot make any
progress and solve our problems.
There was hardly any scientific paper that found Bt-crops as unsafe to
humans or environment.
Blind opposition and creating suspicion and fear through
unsubstantiated allegations have no place in science.
Those who demand a ban owe a responsibility to furnish supporting
scientific data to GEAC, for scrutiny and appropriate decision.
If we close the doors for new technologies, fearing the opposition and
speculated risks, we cannot make any progress and solve our
Beegle, C.C. and Yamamoto, T. 1992. History of Bacillus thuringiensis
Berliner research and development. Can. Entomol., 124: 587-616.
Fred S. Betz, Bruce G. Hammond and Roy L. Fuchs (2000).
Safety and Advantages of Bacillus thuringiensis-Protected Plants to
Control Insect Pests. Regulatory Toxicology and Pharmacology, 32 :
GEAC (Genetic Engineering Approval Committee), 2006.
James, C. 2007. Global Status of Commercialized Biotech/GM
Crops: 2007. ISAAA Briefs No. 37, 225 pp. ISAAA: Ithaca, NY.
Manjunath, T. M. 2007. Q & A on Bt-Cotton in India. Answers to
More than 70 Questions on All Aspects. All India Crop Biotechnology
Association, New Delhi, 78 pp.
Sean Weaver and Michael Morris, 2003. Annotated Bibliography of
Scientific Publications On The Risks Associated With Genetic
Modification. Morris School of Earth Sciences Research Report No. 21.
Victoria University of Wellington. May 2003.