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Safety of Bt-Cotton: Facts allay Fear

By T.M. Manjunath, Ph.D.
Consultant - AgriBiotech, "SUMA",
174 G-Block,
Sahakaranagar, Bangalore 560 092 (India).
Email: tmmanjunath1939@yahoo.com


Safety assessment and risk management have been accorded the highest priority for biotech products, both by the official regulatory authorities as well as by the product registrants. Every country which has permitted or in the process of commercialization of transgenic crops has developed necessary bio-safety guidelines. International efforts, including the Cartagena Protocol, have been formulated to bring about all the regulations on the same platform. Based on such protocols, which lay emphasis on the precautionary principle, all biotech products including transgenic crops, undergo a comprehensive and rigorous assessment process to demonstrate their safety and benefits before they are given due regulatory approvals. Bt-cotton has undergone and passed such tests, both in India and other countries, before it received approval for commercialization. Despite such efforts, there has been an endless debate in certain quarters on its safety and benefits. Some facts related to safety are discussed below.


Transgenic plants expressing insecticidal proteins derived from the common soil bacterium, Bacillus thuringiensis, popularly abbreviated as Bt, have been found to provide an environmentally safe and effective control of certain insect pests. The year 1996 may be considered a turning point in the history of agricultural biotechnology in general and crop protection in particular as three insect resistant Bt-crops, developed by Monsanto Company, had received approval for commercialization in the USA after these had satisfied the regulatory requirements. Bt-cotton was one of them along with Bt-corn and Bt-potato. It took about 14 years of intensive research and millions of dollars to develop this technology and prove its safety and benefits. Bt-cotton (Bollgard®) was incorporated with the lepidopteron specific Bollgard® Bt-gene, cry 1Ac, targeted against cotton bollworms. Subsequently, Bt-cotton was also introduced into other countries like Australia (1996), Argentina (1997), China (1997), Mexico (1998), South Africa (1998), Colombia (2002) and India (2002).

For Indian agricultural biotechnology, 26th March 2002 is significant because on that day, the GEAC (Genetic Engineering Approval Committee) of the Ministry of
Environment and Forests, Govt of India, approved Mahyco's (Maharashtra Hybrid Seed Company) Bt-cotton for commercial cultivation. This is the first, and until now the only,
agri-biotech product to receive such an approval in India. This approval was preceded by a large number of laboratory tests and more than 500 field trials, carried out in different agro-climatic regions from 1996-2001, to demonstrate the safety and benefits of Bt-cotton. Mahyco is Monsanto's technology partner in India and their Bt-cotton hybrids carried the same Bollgard® Bt gene, cry 1Ac, licensed from Monsanto.
In September and December 2002, an improved version of Bt-cotton, Bollgard® II, stacked with two Bt genes, cry 1Ac and cry 2Ab2, also developed by Monsanto, received regulatory approvals in Australia and the USA, respectively. Mahyco is carrying out regulatory trials with Bollgard® II also in India.

The major issues with Bt-cotton, as with other transgenic crops, are biosafety-related. These are discussed below under A) Safety Assessment and B) Risk Management.


Safety assessment were carried out with regard to a) potential of cry proteins for toxicity and allergenicity, b) cross pollination and gene flow, c) fate of Bt protein in soil and d) effect on non-target organisms. The results obtained from studies to address such issues are summarized below.


The cry (acronym for crystal) proteins expressed in the commercialised Bt-cotton developed by Monsanto include cry 1Ac in Bollgard® and cry 1Ac plus cry 2Ab2 (both stacked) in Bollgard® II. The cry 1 class of proteins have selective toxicity to certain category of insects, in this case bollworms, and require certain specific conditions for their effective action. The protein has to be ingested by the target insects which happens when the caterpillars feed on the transgenic plant tissues. It requires an alkaline pH of 9.5 or above for effective processing and also specific receptors (on the brush-border membrane of mid-gut epithelium cells of target insect) for binding before it can kill the target insect. All these conditions are available in bollworms and therefore the caterpillars succumb when they feed on Bt-cotton plant. The protein cannot act in the human or animal intestine because their intestine is acidic, pH is about 1.5 and there are no receptors. Hence, Bt protein is safe to such non-target organisms.

The cry proteins produced in Bt-cotton have been shown to rapidly degrade when crop residues are incorporated into the soil. Thus, the impact of these crops on environment and human safety is negligible. This is further supported by the long history of safe use of Bt microbial spray formulations for control of insect pests on a variety crops all over the world for more than 40 years.


The potential movement of transgenes from Bt-plants into related weeds, through pollen flow, has been one of the concerns. This issue has been addressed for each Bt-crop that has been approved and experimentally demonstrated that there is no significant risk of capture and expression of any Bt cry gene by wild or weedy relatives of cotton, corn, or potato. The low risk has been ascribed to sexual incompatibility (due to differences in chromosome number) and differences in crop phenology (i.e., periodicity or timing of events within an organism's life cycle as related to climate, e.g., flowering time) and habitat.

Weed relatives of cotton are very few. In the USA, Gossypium tomentosum is a weed related to cotton, but it is found only Hawaii and is already on the decline. Nevertheless, there is restriction on growing Bt-cotton in Hawaii as a precautionary measure. In India, cotton has only one weed relative, Gossypium comstocksii. It is found only in the northern part of Gujarat where cotton is not cultivated. Moreover, there is no serious lepidopteron common to this weed and any economic crops. Thus, it poses no problem. In India, Bt gene has been introduced into hybrids developed from the new world cotton species (Gossypium hirsutum and G. barbadens) which are tetraploid. These cannot cross pollinate with the 'Desi' (local) cotton (G. arboreum and G. herbaceum) as they are diploid and lack reproductive compatibility.

The potential for horizontal gene transfer from Bt-crops was also considered and evaluated. Various sub-species or strains of Bacillus thuringiensis already 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 micro-organisms. There is no evidence that horizontal gene transfer has occurred from plants to microbes.


It is feared that soil organisms may be affected on being exposed to cry proteins being leached from roots of Bt-crops or from incorporation of above-ground plant tissues into soil after harvest, or by the pollen deposited on soil. Exposure may occur by feeding on living or dead Bt roots or, theoretically, by ingestion or absorption after secretion of cry protein into soil. Experiments have been conducted to determine the amount and persistence of cry protein in the soil and the data reviewed by the regulatory authorities. It is concluded that Bt insecticidal proteins cannot bio-accumulate causing delayed effects.

An accumulation through the food chain is therefore not expected to take place and there are no data to support this possibility for proteinaceous substances. The basic biological
properties of proteins also make Bt cry proteins readily susceptible to metabolic, microbial and abiotic degradation once they are ingested and excreted into the environment. Although there are reports of soil binding under certain circumstances, the bound cry proteins are also reported to be rapidly degraded by microbes upon elution from soil.


Another apprehension is that non-target organisms exposed to Bt cry proteins expressed in transgenic plants may suffer from undesirable deleterious effects. Several experimental studies were carried out to examine this issue.

Experimental animals like mice, rats, rabbits and sheep fed with unusually high doses (500, 1000 and 4300 mg/kg body weight) of cry1Ac protein showed no acute toxic effect on their health. These animals were found to be substantially equivalent to those not fed with cry 1Ac in respect of body weight, food consumption and other respects.

Proximate analysis showed that there was no difference between Bt-cotton and its non-Bt counter part in terms of protein, carbohydrates, ash and moisture contents. Forage composition of Bt-cotton is substantially equivalent to non-Bt cotton in respect of gossypol and other acid contents.

The U.S. Environmental Protection Agency (EPA) has concluded "that 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 at the label use-rates of registered B. thuringiensis active ingredients." This provides strong support that cry proteins produced in Bt-crops approved for commercial cultivation will pose low risk to non-target organisms. A published report of toxicity to monarch butterfly caterpillars when force-fed with un-naturally high doses of Bt protein from Bt corn in the laboratory does not hold good for the natural situation where such high levels on plants are highly improbable.

In India, as per the direction of Department of Biotechnology (DBT), several studies relating to bio-safety were conducted. Feed-safety studies of Bt cottonseed meal were carried out with goats, buffalos, cows, rabbits, birds and fish. The results revealed that the animals fed with Bt-cottonseed meal showed no ill-effects and were comparable to control animals in the various tests. These studies were carried out at the Industrial Toxicological Research Institute (ITRC), Lucknow; National Dairy Research Institute, Karnal; Central Institute of Fisheries Education, Mumbai; Central Avian Research Institute, Bareily; National Institute of Nutrition, Hyderabad: and Govind Vallabh Pant University for Agriculture and Technology, Pantnagar. In short, the various feed-safety studies conducted showed Bt cottonseed meal to be substantially equivalent to the non-Bt counterpart.

Studies were also conducted on the effect of leachate from Bt cotton plant on soil rhizosphere and non-rhizosphere microflora, soil collembola and earthworms. The results showed no difference between the soils obtained from Bt and non-Bt plants.

There was a mischievous propaganda that Bt cotton contained the so-called 'Terminator Technology.' Experiments were also conducted to demonstrate that it was not true.



Pest populations exposed to Bt-crops continuously for several years have the potential to develop resistance to cry proteins. This phenomenon is not unique to Bt. In view of this, proactive insect resistance management (IRM) strategies have been developed and are in place so as to prevent or delay resistance development. A key element of these plans is that growers should plant sufficient non-Bt crops to serve as a refuge for producing Bt-susceptible insects. The recommendation includes growing 20% non-Bt cotton in the periphery of Bt-cotton as refuge and taking necessary control measures against bollworms in the refuge crop as and when required. The alternative is to grow only 5% non-Bt as refuge without taking any control measure. The refuge strategy is designed to ensure that Bt-susceptible insects will be available to mate with Bt-resistant insects, should they arise. The offspring of these mating will be Bt-susceptible, thus mitigating the spread of resistance in the population. Gene stacking or pyramiding, expression of optimum dose of Bt protein, and deployment of Bt-crops as one of the components of integrated pest management are the other options for IRM. Bollgard® II developed by Monsanto which has been approved for commercialization in Australia and the USA in 2002 is an example for gene stacking. This contains two Bt genes, cry 1Ac and cry 2Ab2. The proteins produced by these have different binding sites, thus making it very difficult for the pest to develop resistance to both the proteins simultaneously.

Planting refuge is recommended as mandatory in India as in the USA, Australia and other countries. In India, Helicoverpa armigera, by far the most predominant bollworm, besides cotton, has a large number of alternative host crops like chickpea, pigeonpea, tomato, sunflower, maize and sorghum which are substantially grown around the same area at the same time as cotton. These crops, especially chickpea and pigeonpea, support large populations of H. armigera, thereby serving as natural refuge and helping IRM. Further, as the area presently occupied by Bt-cotton is very small (about 6% of the total cotton area), a huge crop of non-Bt hybrids and varieties are also available as refuge. In view of this, whether there is need to deliberately grow non-Bt cotton as refuge needs to be re-examined.

In the last 8-9 years of large scale commercial cultivation of Bt-cotton in various countries (7.5 million hectares in 8 countries in the year 2004), there has been no evidence of field resistance to the in planta expressed Bt protein by bollworms. This is encouraging and monitoring should be continued.


Bt-cotton is a thoroughly researched biotech product that has undergone all the tests pertaining to bio-safety and agronomic traits as prescribed by the concerned regulatory authorities in each country including India. Its safety to environment, human, animals, and agriculture has been demonstrated through scientific studies. Since its first commercialization in the USA in 1996, the area under Bt-cotton has steadily increased from year to year and it occupied 7.5 million hectares (4.5 m ha by Bt alone and 3.0 m ha by Bt stacked with herbicide tolerance) in 8 countries by 2004. During these nine years, no untoward incident has occurred with regard to bio-safety or pest resistance. The major benefits from Bt-cotton include effective control of bollworms leading to significant yield increase, drastic reduction in chemical sprays and substantial increase in net profit to farmers. Efforts are being made to sustain these social, economical and environmental benefits. A few individuals who continue to doubt and indulge in an unending debate on the safety and benefits of Bt-cotton seem to overlook these facts and appear to be highly biased. Criticism based only speculation has no credibility. It should be backed by scientific evidence. If any one has any genuine issue or better suggestions for safety assessment, these should be addressed to the concerned regulatory authorities for necessary action. Helpful suggestion is progressive, but mere condemnation is destructive. There is always scope for improvement. We should not stop doing research for fear of imaginary risks, but always take necessary proactive steps to overcome the same. With regard to safety and benefits of Bt cotton, facts allay fear.


Anonymous. 2001. Bt Plant-Pesticides Biopesticides Registration Action Document, USDA, 89 pp.

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 : 156-173.

James, C. 2004. Global Status of Commercialized Biotech/GM Crops, 2004. ISAAA Briefs No. 32. Ithaca, New York.

Manjunath, T. M. 2004. Bt-Cotton: Safety Assessment, Risk Management and Cost-Benefit Analysis, pp. 366-369. In Khadi et al. (Eds) - "International Symposium on Strategies for Sustainable Cotton Production - A Global Vision", Vol. 1, Crop Improvement, 23-25 Novermber 2004, University of Agricultural Sciences, Dharwad, Karnataka (India), 482 pp.

Sarah L. Bates, Jian-Zhou Zhao, Richard T. Roush and Anthony M. Shelton. 2005. Insect Resistance Management in GM Crops: Past, Present and Future. Nature Biotechnology, 23 (1): 57-62.

Pisupati, B., Dharmaji, B. D. and Warner, E. 2002. Risk Assessment and Risk Management in Implementing the Cartagena Protocol: Proceedings of Asia Regional Workshop organized by IUCN-Regional Biodiversity Programme - Asia & Department of Biotechnology, Govt of India, 22-24 May 2002, New Delhi, 216pp.