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ABSTRACT :In this essay i had mentioned different potential health effects of genetically modified food crops like their allergenicity,antibiotic resistance,heavy metal contamination,poisonous GM foods,adverse effects on non target species and some more important effects of GM crops on human population.
INTRODUCTION:Genetically modified food crops have the potential to eliminate hunger and starvation in millions of people,especially in highly populated countries like india and china.These plants contains greater amount of nutrients such as proteins,vitamins and they are more resistant to pests and droughts when compared to conventional food crops.But there are some concerns about the safety of genetically modified food crops.The main concerns of genetically modified food crops regarding to food safety are:
1.presence of Allergenic substances in GM food crops.
2.presence of antibiotic resistant genes in GM food crops.
3.presence of toxic heavy metals in GM food crops
4.GM food crops sometimes less nutritious than conventional crops.
POTENTIAL HEALTH EFFECTS OF GENETICALLY MODIFIED FOODS:
1.Possibility of Allergenicity: Food allergies can be reffered to as "individualistic adverse reactions" to foods.Food related allergies are individualistic because they effect only a few people in thepopulatio
-n.These food allergies are of two types:
Immunoglobulin E i.e. IgE anti body - mediated food allergies among adults being approximately 2% and nearly 5% in children(Lehrer,1999a,1999b,Ladics and Dong,2002).The main important thing to note that is consumption of conventional foods can trigger allergic reaction.In 1996, a major con-cern for consumption of genetically modified crops materialised when studies demonstrated that Brazil-nut gene spliced in to soybeans could induce potentially fatal allergies in humans allergic to Brazil-nuts(Nordlee et al.,1996).Actually this Brazil-nut gene was inserted in to soybean plants to
enhance their protein content for animal feed.In an in vitro test and a skin prick test,the transgenic soybeans reacted with immuno-globulin E (IgE), a class of antibody molecules involved in allergic re-actions,of individuals with Brazil-nut allergy in a way that indicated that these individuals would Have an adverse,perhaps even fatal,reactions to transgenic soybeans(Nordlee et al.,1996).In sept e-mber 2000,a variety of transgenic corn,called starlink,prohibited for human consumption.Actually this transgenic corn species was produced by Aventis corporation and it was approved by federal agencies in 1998 for animal feed.This corn has been genetically modified in a way that makes it hard-er to break down in the human gastro intestinal tract,agencies have refused to approve it for huma-n use(Kaufman,2000).It is postulated that the ability of a protein to withstand heat and gastric juices is an indicator that it will cause an allergic reaction(Taylor and Lehrer,1996.,Lehrer,1999a).Peanuts which show the above characterstics can cause fatal allergic reactions and so do other foodsthat are known to be allergnic.People,however,would have to be exposed to the special starlink protein,known as Cry9C,many times over an extended period to develop an allergy to it(Taylor andLehrer,1996).The Cry9C protein accounts for only .013% of the corn grain,where as most allergenic proteins account for 1-40% of the food ingredients in which they offer(Taylor and Lehre,1996).This Star link corn contains a gene from the bacterium Bacillus thuringiensis.,that gene,known as Bt,makes the plant toxic to insects pests.The National research council of U.S.A(2000A,2000b) recently recommended additional research on the allergy issue and singled out the Cry9C protein as needing special attention.The Cry9C protein takes atleast 30 min to break down in gastric juices, about 4times as long as proteins in other Bt corn varities (Associatedpress,2000) .Monsanto company inserted Bt gene that produces insect toxin into this Bt corn and this corn has high yield of the crop.This corn has environmental and human health benefits.By using this plants farmers reduced their insecticide use.The important concerns about Bt crops are that the Bt gene will become established in wild relatives as Bt crops.Resistance would develop because insect pests feeding on Bt crops are exposed to toxins continuosly and they are likely to develop resistance from mutations.And also,where Bt crops are grown near wild relatives,it is highly likely that the Bt gene will transfer to the wild populations as result of movement of pollen from the Bt crop to its unmodified relatives.Some of the resultant plants may produce enough Bt toward off insects that normally feed on them,and this may cause harmful results to the ecosystem(Rissler,1997).
Actually,food allergens share several common properties.They are proteins or glycoproteinWith acidic isoelectric points and are usually in the molecular range of 10,000 to 80,000Da(Lehrer,1999b).Most characterized food allergens are stable to digestion andprocessing,and many of the major allergens are generally proteins that are present inlargeamountsin allergenic foods(Lehrer,1999b).
The symptoms of food allergies towards people range from mild effects to sudden death,may likely be affected by exposure to foreign proteins introduced in to foods by genetic engineering.The novel proteins can be introduced into the food supply by genetically modified foods From organisms that are never consumed as foods.Some proteins could be allergnic.It is a difficult task to predict whether a particular protein will be a food allergen if consumed by humans.The reliable method to determine whether a protein in food will be an allergen is through consumption of the engineered food .Therefore,incorporating genes that produce novel proteins into crops by genetic engineering,especially from non-food sources,might pose a health risk(Union of concerned scientists,2000.,Lachman,1999).
Certain measures can be taken to reduce the possibilities that a newly introduced protein will be an allergen.The protein structure can be compared to the structures of allergenic proteins,and if a similarity is found and if sera from sensitive individuals are available,an analysis of possible cross-section can be performed.If similarities exists,then that engineered crop is not fit for consumption and further genetic modification is necessary.The allergenicity of proteins assessment from unlnown protein sources continues to be a challenge to the food industry.According to the Taylor and Lehrer(1996),there is no cause for concern about allergenic potential of proteins introduced into plants from sources with no amino acid sequence similarities to known food allergens,or that are rapidly digested,or are expressed at low levels compared to the expression of major allergens.
The world health organization(WHO) and the Food and Agriculture organization of the United Nations(FAO) (FAO/WHO,2001) and Lehrer (1999a) have recently described a hierarchial approach to evaluate the allergenicity of genetically modified foods or crops.The three main approaches that can be utilised to identify allergen sources include(1) amino acid sequence characterization-that method would increase the number of allergenic sequences in the data bank.,(2)identification of the amino acid sequences that define allergenic epitopes to develop more precise sequence -screening criteria., and (3)Development of an animal model(s) that can recognise food allergens in a manner similar to that which occurs in human disease.Widely accepted animal models are not currently available to identify potential allergens.,however,some progress has been made in this area by using rodents and other species (Kimber and Dearman,2001).Other factors indetermining potential allergenicity of modified gene products include molecular mass (the molecular mass of most known allergens is between 10,000 and 40,000 Da),heat and processing stability (labile allergens in foods that are ingested after cooking or undergo other processing before consumption are of less concern),pH and gastric juices (most allergens are resistant to gastric acidity and to digestive proteases), and prevalence in foods (for example,new proteins expressed in non edible portions of plants are not a concern interms of food allergen).There is a good correlation between the resistance of proteins to proteolytic digestion and their allergic potential(Astwood et al.,1996).The issue of labelling is also important.Genetically modified food should be labelled to make people aware of what they are buying,and individuals who have allergies should read the labels and not buy foods they think may be harmful to them(Miller,1999).Presently, there are no in vitro and animal models that have been validated for the identification of protein allergens(Ladics and Dong,2002).Recently various animal species have been used to study the allergenic potential of genetically modified foods.The animal tested included Balb/c mice (Kimber and Dearman,2002).In above studies allergenic responses were noted with considerable success,although the responses were not observed in 100% of the animals.It is hoped that reliable In vitro and in vivo models would be available in the next few years.
2.Possibility of Antibiotic Resistance:The ability of an organism to be unaffected by the antibiotic is called antibiotic resistance and occurs naturally by evolution.During the process of genetic engineering it often involves the use of genes for antibiotic resistance as "selectable markers".Actually , the markers help in selection of cells that have incorporated foreign genes.There are some concerns that these genes might unexpectedly recombine with pathogenic bacteria in the environment or with naturally occurring bacteria in the gastrointestinal tract of mammals who consume genetically modified food ,contributing to the growing public health risk associated with antibiotic resistance for infections that cannot be treated with traditional antibiotics.
Antibiotic resistance genes presence in foods might produce harmful effects.First,Consumption of these genetically modified foods might reduce the effectiveness of antibiotics to fight bacterial diseases.,antibiotic resistance genes produce enzymes that degrade antibiotics.Second, antibiotic resistance genes might be transferred to human or animal pathogens, making them resistant to antibiotics.
A genetically engineered Bt corn variety from Novaritis includes an ampicillin resistance gene(Cannon,1996).Generally, ampicillin is an antibiotic that is used to treat a variety of bacterial infections in humans and animals.All European countries ,including Britian,have refused to allow the Novaritis Bt corn to be grown because of concern that the ampicillin resistance gene might be transferred from Bt corn to bacteria,making ampicillin a far less effective antibiotic against bacterial infections.In September 1998,the British Royal Society released a report on genetic engineering that recommended the termination of the use of antibiotic resistance marker genes in engineered food products.According to one prediction,alternative types of marker genes will be developed in approximately 5 year and no new transgenic crops using antibiotic resistance marker genes will appear on the market(Henney,2000).
It should be noted that organisms containing DNA encoding for antibiotic resistance proteins are common and of increasing prevalence in the environment(Society of Toxicology,2002). However,the contribution of the antibiotic of the antibiotic resistance markers in genetically modified organisms to antibiotic resistance in bacteria in the gastrointestinal(G1)tract has not been studied.,it is expected to be very small(Royal Society,1998)for several reasons-efficient destruction of the resistance gene in the human gastrointestinal tract and the very low intrinsic rate of plant microbe gene transfer.However,it should be noted that genes occur widely in nature and the antibiotics involved are not widely prescribed by physicians(Society of Toxicology,2002).In addition,recent advances in genetic engineering do not employ the use of such selection markers(Goldsbrough et al.,1996.,Koprek et al.,2000) and their use is likely to diminish.
3.Genetically Modified Foods are sometimes poisonous to Mammals:In 1999,front page headline stories in the British press disclosed Rowett institute scientist Dr.Arpad Pusztais research findings that genetically modified potatoes are poisonous to mammals.Actually these genetically modified potatoes were engineered to produce a molecule called Galanthus nivalis agglutinin(GNA).This is a natural insecticide,usually found in snow drops.The engineered potatoes were very different in chemical composition compared to ordinary potatoes and were found to damage vital organs and immune system of rats.,the most alarming discovery was the toxic effects the altered potatoes had on the stomach lining of rats(Pusztai and Ewen,1999).Stanley Ewen,a pathologist from the university of Aberdeen,indicated the damage was not due to GNA but to a component in the genetic engineering process itself,because the genetically modified potatoes produced more damage to the rats than for a control group fed ordinary potatoes with GNA added.Studies suggest it was the 35S
Cauliflower -Mosaic-virus (CaMv) promoter,a promoter spliced in to almost all genetically engineered foods and crops.The promoter could have ended up in the wrong chromosome and started swithing thewrong genes on(Anonymous,1999).This is not the only possibility,but is certainly One explanation. The Pusztai and Ewen(1999) studies were discontinued because the British government suspended his research funding.
4.Genetically modified food crops are some time less nutritious than conventional food crops:In 1999,It was shown that concentrations of phytoestrogen compounds,which are believed to protect against heart disease and cancer,were lower in genetically engineered soybeans than in traditional strains(Lappe and Bailey,1999).If we see an example,the milk from cows injected with gamma bovine growth hormone contains higher levels of fat and bacteria,and can therefore go sour faster.New proteins in foods could alter the cellular metabolism of the food producing organism in unintended and unanticipated ways.Due to this ,the food producing organism might fail to make an important vitamin or nutrient that it naturally synthesizes.therefore,it is possible that genetically modified food will lack important nutrients that are normally present in the corresponding natural,non genetically engineered food.
5.Possibility of contamination with toxic heavy metals:Municipal sludge contains plant nutrients,but it cannot be used as a fertiliser because it is contaminated with toxic heavy metals.Some genetically modified food crops are created inorder to utilize municipal sludge as fertiliser.Introduction of some genes into crop plants can remove heavy metals such as mercury or lead from the soil and concentrate them in plants.The main goal is to genetically engineer plants to localize those metals in in edible parts of plants to prevent adverse health effects from consumption of such crops.For example,in tomato,the metals would be sequestered in the roots.,in potatoes,they will be sequestered in leaves.Turning on the genes in only some parts of the plants require the use of genetic "on" and "off" switches that turn on only in certain issues,like leaves.Such products pose risks of contaminating foods with high levels of toxic metals if the on and off switches are not completely turned off in edible tissues(Cummins,2000).The important thing should be kept in mind is that the crops used in heavy metal extraction should not be consumed as human food.
6.Effect of removal or Inactivation of genes:Generally,many of the health risks of genetically modified food are due to newly added genes,but the removal of genes from plants and other organisms can lead to the production of desirable or undesirable traits.Sometimes,genetic engineers may intentionally remove or inactivate genes to achieve desirable effects.Such genes,however,may also pay other roles and consideration must be given to the possibility that removal of a gene may have an unexpected detrimental effect on food quality(Union of concerned scientists,2000).If we see a example ,decaffeinated coffee can be made by genetic engineering.In decaffeinated coffee plants,genes coding for caffeine synthesis are deleted or turned off.But the removal of the caffeine gene may have an undesirable side effect.This caffeine inhibits the synthesis of aflatoxin,a potent toxin and a carcinogen,produced in certain molds.Coffee beans without caffeine gene may be subject to greater contamination by afflatoxin producing mold.This toxin may remain active through processes of food preparation ,but no experimental data have shown that decaffeinated coffee contains aflatoxin(Union of concerned scientist,2000).
7.Adverse effects on Non target species:Many environmentalists are concerned that the pesticidal gene product of the genetically modified crops might be toxic to nontarget organisms that consume it.,for example,the incorporation of Bt genes in to crop plants for insect control.The adverse health effects of Bt toxins in nontarget species have been reported(Betz et al.,2000).They show a narrow of toxicity that is limited to specific groups of insects,Lepidoptera,coleoptera,or Diptera-depending on the Bt strain.Plant species containing Bt genes have been tested to determine whether any alterations in this limited spectrum of toxicity occurs and no unexpected results were reported(Orr and Landis,1997.,Pilcher et al.,1997.,Lozzia et al .,1998).Co cern has been expressed about the potential toxicity of the Bt toxin in corn pollen to the monarch butterfly because initial laboratory studies showed increased mortality in larvae(Losey et al.,1999).However ,sears et al.(2001)believe that is unlikely that a significant risk to those butterflies exists in the field.
8. Evidence of effects in the general population: It is often claimed that there have been no ill effects from several years of GMO consumption in the US.However, there is no scientific evidence to support this statement.Indeed, one GM food product is known to have caused severe problems and health trends indicate that unidentified negative effects could be occurring:
L-tryptophan:This Gm food supplement caused many deaths and disabilities in the US,because of unidentified toxins.The company paid 2 billion pounds to over 2000 victims.
UK:Soya allergies rose by 50% over the previous year in 1999 when imports of GM soya started,according to the York Nutritional laboratory which monitors allergies.
Ireland :Doctors report a rise in soya allergies in children since the start of GM soya imports.(Dr Elizabeth Cullen,co-chair of the Irish Doctors,The Irish Times 13.3.2001)
US: Coinciding with the introduction of GMOS in food, food derived illnesses are believed to have doubled over the last seven years. (New York Times, 18.3.2001)
9.Some studies have found negative effects of GM plants:
Flavr Savr tomato:Resulted in lesions in the rats.On a scale of 1-4 ,the effects were 2-3,but described by the company as "mild".Seven of the 40 rats also died with in a fortnight.Despite concerns by US scientists ,it was approved in the USA and the UK.
GM forage maize(Chardon LL):In the company study,twice as many chickens died as those fed non-GM feed .The UK Government approved the maize.
Newcastle University research on gene transfer:This study ,commissioned by the Food Standards Agency,found that eating food containing GM soya results in the inserted genes moving out and entering the gut bacteria.
10.Outcrossing:The movement of genes from GM plants into conventional crops or related species in the wild(reffered to as "outcrossing"),as well as the mixing of crops derived from conventional seeds with those grown using GM crops,may have an indirect effect on food safety and food security.This risk is real,as was shown when traces of a maize type which was only approved for feed use appeared in maize products for human consumption in the United States of America.Several countries have adopted strategies to reduce mixing,including a clear separation of the fields within which GM crops and conventional crops are grown.
Feasibility and methods for post marketing monitoring of GM food products, for the continued surveillance of the safety of GM food products, are under discussion (WHO, 1993).
Conclusion:Genetically modified food crops are very important for ever growing world population.So these foods should be tested for all hazards before going to release into the market.