important environmental benefits with little or no risk. Genetically modified organisms (GMOs) have been the subject of debate for many years, with many people either completely for or completely against their mass production and sale. But what exactly is a GMO? It is defined as an organism whose characteristics have been altered by the insertion of a gene from another organism using genetic engineering techniques, usually to give the recipient more desirable traits for human exploitation. In agriculture, this is most often increased pest or herbicide resistance in genetically modified (GM) crops.
The question of risk associated with GM crops has divided opinion amongst both experts and the public; however there still does not seem to be any conclusive evidence for either benefits or risks on the environment where these organisms are cultivated.
This essay will address some of the popular issues raised with regard to environmental benefits and risks and try to weigh up the pros and cons of GMOs in agriculture.
With the ever-increasing human population, our planet is being put under more and more pressure as we try to keep up with the demands for resources. It is estimated that food production will have to increase by 70% by 2050 to provide the predicted 9.1 billion people with enough food (Food and Agriculture Organization (FAO), 2009). But with the continued expansion of human populations, we shall also see a further shortage of land suitable for agriculture. The answer to these problems came when genetic engineering allowed us to customise an organism’s characteristics to our desires; increasing crop yield, or reducing damage by pests, thereby allowing a greater quantity of crop to be harvested from the same amount of land.
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One of the main characteristics desired in a cultivated crop plant is a resistance to pests such as insects and weeds. Since their introduction in 1947, there has been a steady increase in the use of synthetic pesticides to reduce crop losses caused by insects, weeds and diseases (Phipps and Park, 2002). However, an estimated 43% of total world production of the major crops is lost each year, with a further 10% lost after harvesting (Oerke et al. 1995). The use of pesticides has been linked to negative effects in the environment; the loss of UK farmland biodiversity such as insects and bird species and the change in food sources of farmland birds (Ewald and Aebischer, 1999). In GM crops, insect resistance is achieved within the plant DNA itself, so the need for the spraying of pesticides is much reduced. The most common gene selected for insect resistance is extracted from a bacterium called Bacillus thuringiensis because it produces toxins which are sensitive to a specific group of insects including the European corn borer, corn earworm, south-western corn borer and corn rootworm (Schuler et al. 1998). Plants containing this gene are called Bt varieties. In 2000, out of a global total of 5.3 million hectares of cotton grown, 3.2 million hectares were Bt varieties (James, 2000). China is one of the largest producers of cotton, with cotton farmers relying heavily on pesticides, however, in a survey conducted during 1999 and 2000, pesticide use on cotton plants was reduced on average from 55kg (on non-Bt varieties) to 16kg (on Bt varieties) per hectare, and the number of times sprayed was reduced from 20 to 7. Also, the survey reported that the use of toxic organochlorines and organophosphates was almost completely stopped (Huang et al. 2001). This evidence is supportive of the use of insect resistant GM crops because there is less need for the use of pesticides which have a negative effect on the biodiversity of the environment. However, this method may result in the evolution of resistant pests, which would make the GM crop redundant and therefore re-establish the need for stronger pesticides until a substitute is found for the Bt gene (Hails, 2000). Furthermore, an Australian study has discovered that Bt toxin is found in the roots of modified plants at similar concentrations found in the leaves. This means that the toxins can pass into the soil easily, not only from degrading leaf matter, but also directly from the roots and could potentially lead to an accumulation of toxin in the soil or in the organisms which digest it; insect larvae and microbes. In this way, GM crops could have an indirect impact on biodiversity of insects (and their predators), non-target plants and the soil environment about which we still have only limited knowledge (Vadakattu and Watson, 2004).
Alongside pesticide resistance, the other main desired trait of engineered crops is a tolerance to herbicides. 63.7% of GM crops grown in 2005 were engineered with herbicide tolerance (James, 2005). The plants are modified to be resistant to one powerful herbicide called glyphosate, which means that farmers can grow the crop and spray it with one application of glyphosate herbicide to kill any weeds, but the crop itself will not be affected. This is advantageous because it reduces the cost to the farmer and also reduces the run-off of sprayed herbicides into the surrounding ecosystem (Whitman, 2000). The average reduction in herbicide use on GM soybeans in the USA when studied proved to be around 10%, and although it made 16 herbicides redundant, the usage of glyphosate increased 5-fold (Phipps and Park, 2002). The biggest risk associated with herbicide resistance comes from potential gene transfer across species to close relatives, thereby creating an unregulated hybrid of a GM plant. If this relative is considered a weed, resistance to the herbicide will result in a ‘super weed’, where it cannot be killed using glyphosate and farmers must revert back to physical processes such as tilling, which in turn accelerates soil erosion and nutrient leeching (Hail, 2000). Yet there is remarkable evidence from canola oil seed farmers in Canada of the positive effects of growing the herbicide tolerant (Ht) variety; in 2000, when 55% of all canola grown was Ht, the total amount of herbicide used was reduced by 6 million kg, 31.2 million litres of diesel fuel were saved which in turn saved Canadian $13.1 million and 110,000 tonnes of carbon dioxide being released into the atmosphere (Canola Council of Canada, 2000). The report also described how farmers have adopted a zero or minimal tillage strategy to control weeds, which has the environmental benefits of less soil erosion and less carbon released into the atmosphere; it is estimated that 1 million tonnes of carbon dioxide are no longer released, so one could say that GM crops may help reduce the rate of global climate change. At present, it appears that there are important benefits and disadvantages of herbicide tolerance, but that more research into the probability of hybridisation with non-desired species should be carried out in order to establish a balanced argument. Currently, the advantages seem to outweigh the disadvantages, but this situation may change in the future if resistance spreads to other species.
The question of hybridisation has always surrounded GM crops, but the risk of a hybrid plant surviving in the natural environment and establishing a population has always been considered extremely small. The potential for a crop to hybridise with a weed is dependent on numerous factors: the relatedness of the species, geographical location and sexual compatibility to name a few. However, even if a GM crop were to hybridise with a weed relative, the resulting cross would be dependent on a different set of factors in order to be successful and reproduce; it must overcome all normal plant limiting factors such as competition, nutrients, light etc. but also be able to reproduce itself and survive over many generations. The likelihood of a hybrid surviving in the wild is extremely small, yet it is important to remember that the risk does exist and that such a plant would have a higher fitness, be potentially more invasive and likely out compete its relatives, resulting in extinction through hybridisation (Conner et al. 2003).
In fact, extinction caused by the introduction of GM crops is a larger problem than originally anticipated. Farmers all over the world are favouring high-yield, Ht and pest resistant crops which gain more profit than their natural relatives, resulting in uniform monocultures. Currently, 1350 traditional crop species face extinction, with an average of 2 species being lost every week, because they are being replaced with engineered versions of themselves (FAO, 2003).
Genetic engineering does not stop with crops. There exist today GM trees designed for better quality timber or ease of paper production, and GM plants used in biofuels. Much research is being done on GM animals for use as a food source and use in medicine, although none have yet been licensed to be sold. From an environmental point of view, one of the most interesting applications of GM comes in the form of phytoremediation. Scientists have genetically engineered bacteria to clean polluted and contaminated soil, and plants which can take up heavy metal residues from the soil (Meagher, 2006).
Conclusion
There has been and still is much debate over the safety of GMOs, with particular emphasis on GM crops because they have the potential to alter ecosystems, and because they ultimately end up on our plates. While the effects on human health are substantially risky, they are beyond the topic of this essay.
The cultivation of GM crops has become more widespread since their introduction, with 25 countries now growing them commercially and many more growing them on a trial basis (James, 2008). With continuing research into genes, it seems inevitable that genetic engineering of crops will continue in order to produce the best, most desirable crop possible, while also minimising the environmental impacts.
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There is evidence for both sides of the argument concerning benefits and risks to the environment, however, not all GM plants behave the same way. The advantages of Ht canola in Canada are obvious, yet in other species the tolerance is not so great and additional spraying is still required. This may be down to geographical location, soil type or farming practise, but it is important to remember that there is no uniform behaviour of GM crops. The environmental benefit of pest resistance is a reduced use of pesticides thereby increasing biodiversity by only targeting specific problem pests instead of killing all the insects in the vicinity. However, this is met with many potential risks such as; accumulation of Bt toxin in the soil which may reduce soil biodiversity, possible evolution of resistance in target pest species and the need to stack genes for resistance to pests which are not affected by the Bt toxin. The environmental benefits of Ht crops include reduced spraying of herbicides which in turn will reduce run off and contamination of water sources, reduced tilling of soil which decreases soil erosion and requires less mechanical management of fields, which means less carbon dioxide released into the atmosphere to contribute to global warming. The main risk of Ht crops is the potential for hybridisation and invasion of a resistant weed species. From this analysis, we can see that one modified crop may have more advantages than disadvantages, yet for another gene there are more disadvantages than advantages.
It is difficult to know what to think about the situation. While we still do not know the impacts these crops may have on the environment and the ecosystems they exist in, some may say that we should not grow them until we know more, but will we ever know how they will behave in the natural environment if we only experiment with them in a laboratory?
To conclude with my own opinion, looking at the bigger picture, GM crops will not offer us any environmental benefits because ultimately they are grown for human consumption, meaning the human population will continue increasing because food is not a limiting factor. More food will result in more people, which will lead to the continued exploitation and destruction of our planet. As a species, we have overcome the forces of natural selection through the development of medicine and with the expanding use of GM crops, it looks like we are set to overcome the limiting factor of food availability.
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