Assessing Risks Arising from Contamination of the Aquatic Environment with Bt Toxin from GM Corn - Essay Example

? INTRODUCTION Anyone familiar with modern agriculture in the context of crop science is most likely aware of, and acquainted with BT products. Specifically Bacillus Thuringiensis toxin products affecting insects, primarily larva as an internalized pesticide. Throughout the American Midwest, widescale agriculture has reshaped the terrain, and corn (maize) is a predominant product, as is evidenced by the 35 million hectares which are planted annually in the United States. (Tank, 2010) The majority of this corn crop has been genetically modified for pest resistance. (National Agriculture Statistics Service, 2009) Hypothesis: To find out the impact of BT toxins on the aquatic environment if used without extensive risk assessment. What is the first impression you get when you hear the term, “Genetically Modified Food”? In recent years, speculation has renewed over the full effects, and possible consequences of genetic modification of organisms for the production, and augmentation of human food supplies. It is worthwhile to identify the specificities of the techniques involved to produce BT crops, as well as other biotech innovations. To understand potential environmental and biological risk factors involved we must delve into precisely what does and does not occur with genetically modified crops. This study will explore techniques involved in producing genetically modified foods, their importance to agriculture, and the nature of the BT molecule/toxin. In addition, two other research projects will be summarized which explore possible side effects of BT toxin dispersing into the environment, as well as the frequency of that dispersal in the water table. BT technology must be a subject of discussion, both due to the popularity of this technique, by which pesticides can be incorporated directly into plant tissues constitutively – and the possible far-reaching ramifications of such an inclusion. Both of these studies focus on corn/maize due to its prevalence – but virtually any vegetable that has utility for humans is a possible target for genetic modification, in the interest of greater profit towards an increase in the human food supply. GENETIC MODIFICATION Genetically modified organism(GMO): An organism is "genetically modified", if it’s genetic material has been changed in a way that does not occur under natural conditions through cross-breeding or natural recombination. Bacillus thuringiensis (Bt) is a spore forming bacterium that produces crystals protein (cry proteins), which are toxic to many species of insects. (University of California San Diego) GM crops are made using technology which allows Bt toxins to be introduced into crops, making them resistant to pests. For centuries, human beings have attempted to incorporate desired traits both in animals and plants of human utility. Selective breeding has been employed to both as a means of eliminating undesirable traits, such as excessive ferocity in certain breeds of dogs, and greater sugar content as well as size increases for fruits and vegetables. Using ancient techniques agriculture was limited to working within a single species in order to identify desirable, and undesirable traits - and then through successive generations to concentrate those virtues within the species that proved of highest economic benefit to humanity. Or as the case may be, to winnow out those traits that ran counter to human interests. Genetic modification broadens the set of tools available to agriculture, agribusiness, and eventually to animal husbandry. What if we were not limited by the genes within a single species? What if it were possible to use genes from virtually any species and incorporate them into crops? Perhaps the particular globular proteins present in a deep-sea fish which prevent their body fluids from freezing in the ocean depths might be replicated, and incorporated into food crops in order to prevent their spoilage during winter freezes? strawberries courtesy USDA,  Perhaps the particular globular proteins present in a deep-sea fish which prevent their body fluids from freezing in the ocean depths might be replicated, and incorporated into food crops in order to prevent their spoilage during winter freezes? (Sierra Club, 2001) genetic modification allows us to transfer genes in between species. This takes advantage of the universality of the genetic code between all forms of life, even between different kingdoms of life. It is possible for genes encoding beef proteins to be transferred to micro organisms for production, this method allows flavoring proteins normally gained through the slaughter of bovines to be produced safely by bacterial colonies, to the same overall effect – in order to aid the production of cheese. (Border, 1998) The products approved in the United Kingdom for instance, involving genetic modification including maize, tomato paste, and the aforementioned cheese incorporating beef proteins. Brewers and bakers yeast also subject to genetic modification have been approved. (Jones, 1997) , (Jones, 1996) A variety of plants have been developed to incorporate the BT gene, as will be described in the following section. The modification of plants in this way is growing increasingly common. (Wong et al. 1992) Other methods include the strategic deactivation of particular genes for commercial utility. Such is the deactivation of the polyphenol oxidase gene in potatoes, which has been found to eliminate the discoloration from bruising. (Bachem, 1994) Potatoes are among a variety of crops subjected to successful BT modification, in this case to engender resistance to the Colorado Potato Beetle. (Perlak et al. 1993.) As mentioned above, it is possible to grow beef proteins in bacteria to transfer those qualities to other foods without actually killing the animal, and other methods also allow renewable sources of other biological products, such as drugs and vaccines through plant and animal media. Other cattle and sheep, can be genetically adapted to produce pharmaceutical compounds in their milk. (Coghlan, 1995.) , (Henninghausen, 1998), (Kiernan, 1996) Photo courtesy of Foodylife.com The basic techniques by which this is commonly done employ variations on the following methods: Recombinant DNA techniques: by which viral vectors or bacterial plasmids are assembled carrying the desired gene which is then inserted into the host cell, which expresses those genes accordingly. Microinjection: it is possible to isolate genetic material and using the proper instrumentation to directly insert it within the nucleus of an active cell. Electrochemical poration: certain chemical compounds and mild currents of electricity can change the confirmation of the cell membrane, and the nucleus itself allowing a fluid media containing novel genetic information to pass into the host cell. Also, certain promoter elements in plant DNA may be chemically activated. (Williams et al, 1992) Bioballistics: slivers of metal with genetic information adhered to it can be launched shotgun style against the host cell. Pre-existing mechanisms will transfer the genetic material to the nucleus upon entry to the cell. Sometimes known as biolistics (Union of concerned scientists, 2003) Biolistics assembly: This picture was taken from http://www.agr.okstate.edu/ptf/chambergun.html - the Oklahoma Plant Transformation Facility. The particles are fired through the gas acceleration tube, through the rupture disk and into the target tissue. . From: http://www.gateshead.gov.uk/Care%20and%20Health/Food%20Safety/Genetically.aspx Toxins in transgenic byproducts may affect headwater stream ecosystems Among the drawbacks is a risk of what these toxins may do to other insects nowhere near a cornfield, should the BT toxin disseminate through headwaters. (Rosi-Marshall et al. 2007) – Which will be discussed below in further detail. The objective being to quantify the effect from BT products entering aquatic ecosystems in the Midwest. METHODS Inputs of corn by-products measured to 12 typical headwater streams in agricultural region of N. Indiana in 2005/2006. Quantified downstream transport distances of corn by-products during base flow conditions. Laboratory feeding studies; examine effect of Bt corn by-products on selected aquatic insects commonly found in headwater streams. While numerous studies have demonstrated the effectiveness, and possible economic utility of BT toxins, when constitutively incorporated into the tissues of crop plants transgenically, we must turn our attention to the potential side effects. BT can destroy insects, prevent their larva from living long enough to do damage to crop plants. But when large-scale cultivation of genetically modified crops becomes widespread, it is indeed possible that some trace of their genetic material will enter the ecosystem. (Douville, 2007) Contrary to earlier predictions, that plant byproducts would remain on the same field that produced them, (National Research Council, 2000) data suggests that pollen and detritus from transgenic plants can filter into the ground and water. While there is little reason to think that dispersal of the BT toxin poses any direct risk to humans the very effectiveness of the toxin in controlling insects could lead to widespread consequences to native animal populations that must be weighed. Prior studies did not take into account populations of the stream dwelling insects, which might be closely related – phylogenetically to the target pest species, as is the case with trichopterans. Corn in particular, constitutively expressing the BT toxin gene can proliferate its pollen into headwater streams, the problem inherent in this dispersal being that non-target insect populations living in association with the waters may die, or suffer stunted growth simply due to the proximity of BT corn pollen. Theoretically, widespread damage to non-target insect populations could have detrimental effects upon the food chain – for the other organisms that may depend upon those insects for their own food source. (Rosi-Marshall et al. 2007) Agricultural runoff invariably carries crop byproducts, (Stone et al. 2005) and given the proximity to local bodies of water that is a necessity in large-scale agriculture any form of seed, pollen, or leavings of transgenic plants must be evaluated for its environmental impact. And indeed, research indicates that transgenic byproducts from BT corn do last long enough, insufficient quantities to be available for microbial metabolism, and ingestion by a variety of insect species, and further dispersal caused by storm systems. This has the potential to affect organisms far from the cornfield. (Rosi-Marshall et al. 2007). The decomposition process of plant material is an important linchpin in aquatic ecosystems. A combination of microorganisms and mechanical abrasion makes available a needed source of nutrients in freshwater systems, of which plant detritus is an integral component. Within a river system, this is an important transfer of nutritional energy from upstream to downstream. (Minshall et al. 1983) Research indicates that while it is possible for aquatic insect species that live in association with freshwater algae to be negatively impacted by BT runoff, in terms of overall fitness and fertility – a study by Rosi-Marshall et al. Indicates that commonly expressed levels of BT toxin do not show appreciable differences in insect mortality, but levels 2 to 3 times higher than the maximum observed aerial output can damage the population, and would in theory – limit the food source of native fish and amphibian predators. (Rosi-Marshall et al. 2007). Still, ecosystem degradation and an influx of nutrients, typically the result of nitrogen-based fertilizers can create ecological imbalances in freshwater systems, (Cooper, 1993), (Allan, 2004) and the potential exists for BT runoff to serve as an additional ecological stressor. Results: Corn pollen - aerially deposited into all streams; inputs 0.1 to 1.0 g m_2 Inputs corn by-products –highly variable at 12 streams. Distances: crop litter inc. leaves and cobs: 0.38 to 180 m, pollen traveled from 20 to 60m Factor high influence: stream discharge. No difference between Bt and non-Bt corn litter breakdown rates Toxin effect on lepidopteran (butterflies and moths), dipteran (true flies), and coleopteran (beetles) pests To summarize, we know the toxin-containing corn detritus is deposited by River systems throughout a broad territory far beyond the cornfield itself. BT corn, and corn byproducts can have a negative impact on the biota of rivers and streams, especially insects. Within the headwaters, nutrient enrichment and habitat degradation is a concern. BT corn products can serve as an additional stress factor upon the ecosystem. Limitations: The amount of pollen found from BT corn was low. The toxin levels found to be dangerous in the lab did not occur within the environment outside. The BT toxins can still arise from pesticides, not only from transgenic crops. There can also be variance on the BT endotoxin, this is a distinction that was not explored. The article makes insufficient justification for adverse effects downstream. (TANK ET AL. 2010) TRANSGENIC CORN RESIDUE This study examined the residue of transgenic corn, and what occurs when corn litter disseminates through streams and rivers throughout the Midwest. Of the corn crop in the United States in 2009, 63% of it was genetically modified, containing insecticidal proteins from BT. (Cry1Ab), relevant because 82% of stream sites were adjacent to corn fields. Knowing that it is possible for maize detritus to filter into the freshwater streams from agricultural runoff, it is worth investigating to what extent transgenic DNA from maize can penetrate the ecosystem, and in what quantities. This is a necessary prerequisite before an adequate determination of ecological impact can be derived. The Cry1Ab protein, originating from BT-modified crops, has been found at detectable amounts during a survey of 217 stream sites in Indiana. Out of this number in 86% of the waters investigated contained identifiable corn residues. (Tank, 2010) source: (Tank et al. 2010) During the stream study, 50 sites were found with detectable levels of Cry1AB protein, with levels at or above 6 ng/L. However, it is difficult to use these results and generalize about distribution or contamination of water-tables with BT. There appears to a disparity between corn byproducts filtering into the aquatic environment, and presence of Cry1AB protein. The BT toxin exists in some places where corn byproducts were not detected. While the transgenic protein was invariably found within 500 m of a corn field, investigators were unable to agree upon a pattern of distribution. Attempts were also made to trace the origins of Cry1AB contamination of stream water to upstream sources, but the patterns of distribution did not appear consistent. Nonetheless it is apparent that maize detritus is a common factor in freshwater streams throughout the Midwest. Among transported particulate matter these corn byproducts make up of 17% of the organic carbon budget in freshwater streams connected to agricultural lands. And this contribution becomes greater during thunderstorms. Six months after harvest, corn detritus is common in freshwater stream channels in the target area of northwestern Indiana. (Dalzell, 2005) , (Tank et al, 2010) And it is logical to project similar circumstances throughout the corn belt of the American Midwest. It was noted above that BT toxin was found in all cases, within 500 m of corn field – results indicate that 91% of stream and river systems in Indiana fall within those parameters from a corn field. (Tank et al, 2010) With so much land in the Midwest devoted towards this single product – the consequences of its large-scale growth, and deposition on land and water should be investigated, as a possible source of organic carbon output within the water table, the consequences of which should be studied by further research. It is difficult to piece together a precise schedule by which a certain quantity of BT toxin will or will not disseminate throughout farmland according to proximity with a cornfield utilizing such crops; however the Cry1Ab protein can be readily found. Once corn pollen or husks containing components of the BT toxin filter into the ecosystem, a cascade of microbial metabolism, mechanical abrasion, and invertebrate ingestion allows these molecules to inculcate themselves in the biomass across a wide territory. (Rosi-Marshall et al. 2007) Freshwater streams expand the territory thus exposed to the protein, carrying it far beyond the same field that originated it. Diverse means are available by which corn detritus can find entry into far-ranging ecosystems, root exudates as well as raw maize biomass remain sources, as well as the possibility of transgenic pollen. (Rosi-Marshall et al. 2007), and the Cry1Ab protein appears capable of moving vertically through the soil. (Tank et al. 2010) The proteins composing the BT Toxin can and will remain in the surrounding environs long after harvest, and their dispersal encompasses a greater range than was previously supposed. (National Research Council, 2000) But the Tank study does not address whether and to what extent the proliferation of BT corn detritus may actually impact the environment; whether these proteins pose a threat to non-target species must be investigated by others. Outcome BT proteins can be leaked from detritus or soils, transported to streams through tile drains. When BT proteins are found in streams and rivers, there is a risk that it will affect aquatic species there. But more research is still needed to determine whether or not the concentration of BT proteins (Cry1Ab) detected in this study is likely to have an adverse affect on nontarget organisms. CONCLUSIONS & RISK ASSESSMENT Genetic modification of plant and animal food sources is not only profitable, but the day will come where it will become inevitable, if it is not already. Human history is replete with examples of soil productivity failing to keep pace with human hunger. Even the most cunning forms of selective breeding will reach absolute limits on the changes possible to a given plant or animal dependent on the alleles within the species. These are limitations that agri-science must – and has overcome in large part. Corn is integral to any far-reaching crop discussion for its prevalence, upon millions of hectares of land dominated by its cultivation. And corn would naturally be a beneficiary of Bacillus thuringiensis transgenic biotechnology. Here, the principle concern is that – while BT expressed as a gene-product of GM plants has the potential to save millions of dollars worldwide in pesticide costs, there remains a possibility of environmental risk. BT does a good job of controlling one of its target organisms, the European Corn Borer. A larva that begins to devour BT corn, or any larva that devours BT cotton-leaves, or a BT potato plant, or BT something else – will accumulate crystalline proteins in its gut that form a channel which will forcibly drain its tissues of their fluid contents, resulting in death long before the young insect can damage agri-business' bottom line. But more research needs to be conducted upon nontarget organisms, such as the caddisfly. A filter feeder that survives from biofilm off of submerged surfaces, one of the detritovores as mentioned previously, it has nothing to do with cornfields, does not attempt to harm corn crops but ecosystems could be disrupted if the leavings of transgenic corn damage the fitness/growth of this insect, or increase its mortality. The Caddisfly is an indicator species, sensitive to such contaminants. (McDonald et al. 1990) Another non-target species, the Waterflea can exhibit reduced fitness from a variety of toxins, also an indicator species. (Environmental business specialists, 2011) HOW BT WORKS Bacillus Thuringiensis is a gram positive, spore forming Saprophytic bacteria, commonly found wherever one might find natural soil decomposers. It also exists on plant surfaces. The proliferation of this bacteria is not restricted, and it can be isolated in soil samples across the globe, occasionally found in grain dusts, leaves and forest detritus. Bacillus thuringiensis assembles crystals during the dormant phase of its life cycle, which are inherently toxic to detritovores – which typically implies invertebrates feeding on plant debris, common to stream beds and forests. The insects targeted include: Lepidoptera, (Moths) Diptera,(Flies) Coleoptera (Beetles). (Rosi-Marshall et al. 2007) BT also is purported to have fungicidal properties. (Schnepf, 1998) The formation of endospores for the species is characterized by the presence of a Parasporal crystal. Upon ingestion by an insect, the alkalinity of the insect gut dissolves a portion of the molecule, and releases the active toxic. (Maagd, 1999) The Bacillus thuringiensis molecule is in essence, an insecticidal crystalline structure that attaches itself to the epithelium of the insect gut, then forces the opening of pores within the cell membranes. The completed quaternary structure of the molecule functions not unlike a suction pump against the lining of the larva's gut. This forcibly evacuates the fluid contents of the affected insect tissues, resulting in cell death. (Hofte & Whiteley, 1989) , (Glare & O'Callaghan, 2000) Schematic ribbon diagram structure of the CryA toxin. The three domains and their suggested functions are indicated. Shaded segments correspond to the five conserved sequence blocks (1–5). The position of the b-sheets of domain II are indicated near the protruding loops of each sheet. Source: http://www.mrc-lmb.cam.ac.uk/genomes/madanm/articles/dnashuff.htm. Accessed 11/19/2011 The significance of this development, is more than just any single spray-on pesticide. Through genetic engineering, it's possible for plants to naturally express this toxin within their own leaves. Thus when insect larva hatch and begin to feed upon the crop plant, their own food source kills their intestinal tract. And the larva does not last long enough to inflict significant damage on the plant. The toxin itself is a molecular match only for cellular receptors of the insect intestine, (van Rie et al. 1990), (Hofte & Whiteley, 1989) thus making the crop plants safe for human consumption. At one time, (the 1930's) the utility of the toxin was known, and spray-on applications were employed before transgenic techniques became possible. Superficial application was marginally effective, but had severe limits. The BT crystals proved to be unstable in UV light, certain boring pests might be unaffected by a surface spray, and multiple applications might be required throughout the growing season for full effectiveness – raising costs yet further. (Maagd, 1999) The graphic below (Maagd, 1999) underscores the financial value of the transgenic form of this molecule, constitutively expressed when compared with the expenditures worldwide for spray-on insecticides for crop plants. With transgenic technologies, pesticides can be made more potent, more direct in their action, and far cheaper – because the substance is not purchased and applied separately, but is produced by the plant's own DNA. The potential savings could be in the billions, dependent only upon the start-up costs of purchasing the GM seed. Considerable efforts have been underway since the early 90's and before to adapt BT genetics to a wide range of crop plants, including potatoes, tomatoes, and maize. (Fischoff et al.1987), (Perlak et al. 1993) , (Koziel, 1993), (Rosi-Marshall et al. 2007), (Vaeck, 1987) – as well as non-foods, such as cotton. (Perlak et al. 1990) RISKS As tons of corn grow heavy and ripe in America's fields, and as their husks and pollen drift into the local water supply, researchers fear that the BT proteins will permeate the ecosystem and kill off larva that were nowhere near the precious cornfield. This could affect the food supplies of fish and amphibians and damage local foodchains. Could. While the research indicates that corn detritus can spread far beyond the corn field, the Rosi-Marshall study had to boost the BT levels to more than twice the maximum observed concentration before the fitness of bystander insect species was adversely affected. This, in itself is not a compelling case for overarching restriction on BT biotech. Twice the normal humidity can harm fitness, twice the normal sunlight would certainly harm fitness. But the keyword here is 'normal.' BT toxin expressed in plant leaves decidedly isn't. While the numbers alone are not definitive proof that a threat exists; there is still the potential of what could be termed – death by a thousand cuts. Enough unnatural things, individually innocuous could snowball into a serious consequence through their very preponderance, or through unexpected synergism. Therefore, a robust estimate of the impact of BT toxins on aquatic life does not truly exist. Investigators in the Rosi-Marshall study have also found higher than normal ligning content in BT corn; confounding nutritional analyses as the detritus infiltrates into river-systems, including algae. The caddisfly is only one of many filter feeders that depends upon algae in freshwater ecosystems. The long-term reach of deviations in nutritional content could impact fitness in addition to, and separate from the potential for toxicity. Presently, there does not appear to be any evidence that BT poses any harm to fish, microbes, or large mammals – it only targets the midgut cells of certain insects. Still, mortality among bystander species will remove necessary food sources. Researchers within the past ten years display no confidence that corn byproducts will actually stay on the corn-fields of origin, and Rosi-Marshall has noted that whenever heavy rainfall/thunderstorms occur can be transported even further downstream faster, widening the distribution beyond what might be predicted in the early 2000's estimates. And apart from corn husks, which may simply washes downstream, pollen itself arising from genetically modified corn can reach 60 m away from source fields simply do to normal wind transport. And once distributed to adjacent fields, which may run off into different stream systems and bodies of water wind blown pollen and debris can then leapfrog over their normal zone of runoff for that particular cornfield, infiltrating other freshwater systems further away. And this effect is more pronounced during heavy rains, and other storms. The ultimate impact being unknown, but whatever the impact is it will cover a larger stretch of territory than was previously believed. Once downstream, rates of decomposition for the corn byproducts might be effected, and certain aquatic ecosystems could be excessively saturated with unbalancing nutrients. This the elimination of certain species, while creating a strain upon the food chain also has the potential to allow overgrowth for some other species. In the Midwest, it is not comparatively difficult in agricultural areas defined ponds, small bodies of water completely overtaken by algal forms due to nutrient imbalance deriving from excess nitrogen. This then, can choke out and insect species. Since the BT products do appear to maintain a high rate of fidelity in terms of their target phylum, (arthropods) it seems a reasonable extrapolation that damage to the insect population could allow overgrowth in another area of the freshwater ecosystem. The detritus can be consumed, broken down by physical forces and microscopic vectors. The more forces that interact with corn leavings, including pollen and husk remnants simply provides more avenues for the widespread dissemination of the BT proteins not only over a wider geographic area, but distributed in ways that could affect even more insect life. While the levels of BT the researchers did detect does not provide clear evidence of inescapable toxicity to non-target insects, another potential danger is a cumulative risk. Would it not be possible for decade after decade of BT deposition to build up within soil, within small bodies of fresh water, and within algae – which a wide variety of invertebrates are likely to depend upon, who have no association or interest in cornfields. Trichopterans for instance, are opportunistic with respect to feeding strategies and are very likely to consume a wide range of detritus resulting from many different sources. These organisms are filter feeders, and have been known to build their own nets that they might secure particulate items from the flowing water supply as their food source. Corn pollen is within the particulate range of material captured by their artifice. And those that scrape biofilm off of underwater surfaces are also subject to contamination. Nor can we be certain that such contamination may not accumulate within hard surfaces, and persistent plant forms within freshwater locales. Rosi-Marshall has found that corn byproducts and the detritus can adhere to the benthic algal biofilms, and a larger growths of algae, for better or worse. Should a storm system propel BT corn byproducts into some isolated pond, there is every possibility that it may linger until it has a chance to react with something, perhaps a non-target insect's digestive tract? Presently, the studies of butterfly larva do not find enough pollen consumption to pose a clear toxicity risk. But it is not unthinkable that such a danger exists for other insects, perhaps one which investigators have not thought to examine. And at present there appears to be uncertainty regarding whether or not, and the extent to which BT detritus may remain in the environment, or continuously build up over time, and in what medium. But it is already known that leaf devouring trichopterans do experience reduced growth rates, and presumed fitness when their leaf litter food supply contains BT. While they are smaller, their mortality does not appear to be affected at present. But a long term decrease in growth could injure this species in the long run. Even if the same number of individuals is present in the short term, anything that might feed upon them in turn would be impacted by the decline in their rate of growth. 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