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Genetic Engineering in Agriculture

and the Environment

Assessing risks and benefits

Maurizio G. Paoletti and David Pimentel

'WOrldWide, almost 90% of . . the human food supply is . provided by only 15 crop species and 8 livestock species, small numqers when compared with the .estirriated

10-30 million species in

.habiting our biosphere (Paoletti and

Pimcrntel 1992). Introducing genes

from various organisms into crops and livestock has long been regarded

·as a promising way to

ensure the productivity of agricul ture and forestry (Beringer et al.

1992, Gasser and Fraley 1989, Har

Jander 1989, Jensen 1988, Lehrman

1992). Then, too, the substitution or

addition of diverse genes into agri cultural and forestry species may, as

Raven (1992) has suggested, be a

,wa y to use the undiscovered re sources of biodiversity in the service social and economic development. . Genetic engineering technology dramatically reduced the time required for the development of new commercial varieties of crops. Some investigators have suggested that the use of genetic markers could reduce the usual 1

0-15 -year breeding cycles

to only

2-3 years (Kidd 1994). Ge

netic engineering is rapidly replacing traditional plant breeding programs and has become the mainstay of ag-

Maurizio G. Paoletti is a professor in

the Department of Biology, Padova Uni versity, Via Treste 75, Padova, Italy.

David Pimentel is a professor in

the Department of Entomology and Section of Ecology and Systematics, Cornell

University, Ithaca,

NY 14853. © 1996

American Institute of Biological Sci

ences.

October 1996

Genetic engineering is

rapidly replacing traditional plant breeding programs and has become the mainstay of agricultural crop improvement ricultural crop improvement. Since

1986, 2053 field trials have led to

the release of transgenic plants into natural around the world (Krattiger and Rosemarin 1994).

Recent advances in

the genetic engi neering of plants, animals, and mi croorganisms, including viruses, are encouraging and show promise for further development (Fessenden

McDonald 1992, Gasser and Fraley

1989, Mellon and Rissler 1995,

Meeusen and Warren 1989, Moffat

1986). Meanwhile, research efforts

are increasing at university, indus try, and government laboratories. In addition to the perceived ben efits of genetic engineering for the industrialized nations, proponents advocate the use of genetic engineer ing to improve agriculture in devel oping countries. This strategy might help these countries bypass expen sive, high-input crop production and move their traditional agriculture toward low-input sustainable prac-tices (Odum 1989).

Many scientists, however, have

expressed concern regarding the pos sible environmental risks of geneti cally engineered organisms (Buttel

1995, Buttel et al. 1985, Colwell et

al.

1985, Mellon 1988, Pimentel et

al.

1989, Simberloff 1986, Vitousek

1985, Wrubel et al. 1992). Many

have asserted that the release of ge netically engineered organisms might adversely affect both tropical and temperate biodiversity (Altieri and

Merrick 1988, Cook et al. 1991,

Hanson et al. 1991, Paoletti and

Pimentel 1992, Pimentel et al. 1992,

Wolf 1985).

If, as expected, the US govern

ment deregulates testing, leaving it entirely to the discretion of those with economic interests in genetic engineering, the release of geneti cally engineered organisms before their safety has been ascertained will be a danger. Some proponents of genetic engineering support deregu lation of biotechnology. However, will reducing regulations, as sug gested by Miller (1994), reduce the risks of genetic engineering?

In this article we assess the cur

rent status of the genetic engineering of plants, animals, and microorgan isms used in agriculture. We also analyze the benefits and risks this promising technology might have for the future of sustainable agriculture and the environment.

Risks and benefits

Although genetic engineering can

improve the control of pest insects,

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plant pathogens, and weeds, there are risks associated with it.

Insect

pest control. The gene for the

Bt toxin, the bacterium Bacil

lus thuringiensis, has been introduced into more than 50 plant crops (Adang

1991, Beegle and Yamamoto 1992,

Gelernter 1990, Skot et al. 1990).

Plants expressing this gene demon

strate effective control of such pests as caterpillars and beetles. In addi tion, engineered Bt has been ap proved for use as a conventional insecticide (Lereclus et al. 1995).

Although in field trials, Bt toxin

expressing cotton can effectively re pel caterpillars, a thorough assess ment of the effects on nontarget organisms has not been made (Wil son et al. 1992). However, several lepidopteran species have been re ported to develop resistance to Bt toxin in both field and laboratory (Lambert and Peferoen 1992,

Stone et al. 1991, Tabashnik et al.

1992). This finding suggests that

ritajor resistance problems are likely to develop if the Bt toxin is widely introduced into major crops such as corn, cotton, and wheat. However, because an abundance of Bt species and genetic lines live in soil, some alternative forms of Bt toxin exist that can be used if resistance devel ops to the form that is currently used (Lambert and Peferoen 1991, Mar tin and Travers 1989).

The environmental consequences

of the massive use of Bt toxin in cotton and other major crops remain unknown. There are questions about the toxin's potential interaction with other organisms in the environment (Jepson et al. 1994).

Roush et al. 1 developed a promis

ing model to evaluate the advantage of reducing pest resistance to Bt engineered plants by having Bt ex pressed only when and where needed. Bt toxins also might be expressed only moderately, so that not all sus ceptible individuals would be killed by the engineered plant. An addi tional step would involve the use of mixtures of Bt toxins within each plant. In ecological studies, the de velopment of resistance was delayed lR. T. Roush, M. Burgess, and W. McGaughey, .1993, unpublished manuscript. Cornell Uni versity, Ithaca, NY. 666
Table 1. Summary of field trial approvals granted by trait (OEeD database IX

1993). The

total number of approvals with trait characters is greater than the number of individual approvals recorded because a number of approvals have been granted for releases in which more than one trait has been introduced into a crop host. Approvals granted Minimal estimate of sites approved

Trait Number % of total Number % of total

Herbicide tolerance 489 38.9

Disease resistance 35 2.8

Virus resistance 115 9.1

Insect resistance 89 7.1

Use of markers 382 30.4

Quality traits 72 5.7

Flower color 5 0.4

Research studies 18 1.4

Male sterility 39 3.1

Resistance to stress 9 0.7

Heavy metal tolerance 3 0.2

Other 1 0.1

Total releases .

1257 100.0

when a pest population was exposed to more than one toxin at a time (Hofte and Whiteley 1989, Pimentel and Bellotti 1976) and/or when un treated refuges were provided to con serve nonresistant genotypes. 2

In addition, some viruses can be

genetically engineered to have en hanced pathogenicity for insect con trol and not persist in the environ ment (Tomalski and Miller 1991,

Wood and Granados 1991). These

latter pathogens have great potential for pest control. Engineered viruses have been experimentally released in

Britain (Bishop et al. 1988) and in

the United States at Geneva, New York, 3 for insect pest control. Thus far, the results appear encouraging.

Plant pathogen control. In 1988 a

genetically engineered bacterial strain, K1026, of Agrobacterium radiobacter (Jones and Kerr 1989) was released commercially to con trol crown gall (Agrobacterium tumefaciens) disease of stone fruit trees (e.g., peach, cherry, and al mond) in Australia (Kerr 1991). This recombinant organism was the first to be released for commercial use in agriculture for disease control, and so far it has proven highly effective.

Although

an estimated 1.5 mil lion fungi species exist, little has been done to genetically modify fungi

2See footnote 1.

3H.A. Wood, 1992, personal commimication.

Boyce

Thompson Institute, Cornell Univer

sity, Ithaca, NY.

685 41.7 56 3.4 144 8.8 134 8.2 442 26.9

81 4.9 7 0.4

19 1.2

61 3.7 9 0.5 3 0.2 1

0.1

1642 100

for agricultural use in plant patho gen control (Hawksworth and

Mound 1991, May 1991). Hynes

(1986) and Yoder et al. (1986) devel oped modified

Aspergillus nidulans

and Helminthosporium maydis, and

Staples et al. (1988) transformed an

entomophagous fungus, Metar hyzium anisopliae, with a plasmid containing a gene for resistance to benomyl, a broad-scale fungicide (Staples et al. 1988). This product will help protect plants because heavy applications of fungicide can be used on the crop without reducing the effectiveness of the entomophagus fungus. To protect chestnuts against chestnut blight, hypovirulent modi fied strains of Cryphonectria para sitica have been developed (Polashock et al. 1994). Fusarium graminearum has been modified to inhibit synthe sis of trichothene toxins and reduce diseases in some plant hosts. Em ploying genetic engineering to in crease host plant resistance to patho genic fungi is another promising goal.

Some genes derived

from plant

RNA viruses confer virus resistance

in transgenic crop plants. A squash recently developed by Asgrow Seed

Company has been approved for

commercialization in the United

States. Also, approximately 5% of

tobacco cultivated in China has been modified to be resistant to Tobacco

Mosaic Virus (TMV). Engineered

tobacco with double resistance to

TMV and CMV (Cauliflower Mo

saic Virus) is now under trial (Krattiger 1994). Approximately 8%

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able 2. Annual field trial approvals granted-by crop (OECD database IX 1993).

Numbers granted each year

1986 1987 1988 1989 1990 1991 1992 Total

Ifalfa

llegheny pple ,Asparagus

Canol a

,cantaloupe

Carnation

hicory > hrysanthemum Corn 'Cotton

Cucumber

'1flax

Kiwi fruit

lLettuce

Melon

Papaya

Petunia'

Poplar

Potato

Rice I

SoybJan

Suga,rbeet

Sunflower

Tobacco

Tomato

Walnut

""Others

Total

1 1 2 3 3 1 9 1 1 5 1 1 8 7 12 1 37
of approved field trials (Table 1) are 'transgenic virus-resistant plants (AIBS 1995). Although the use of viral genes for resistance in plants to virus pathogens has potential ben efits, there are some risks. Recombi nation between an infecting plant ;RNA virus and a viral RNA inside the engineered plant could produce a new pathogen, and a potential ,Synergism and other interactions could lead to new, more severe dis ease problems (AIBS 1995).

Today, from 75% to 100% of

agricultural crops contain some de gree of host plant resistance 4 ( Oldfield 1984). Most of these resis tant traits in crops were added by classical plant breeding, and they provide enormous benefits to agri culture. Some proponents of genetic engi neering technology suggest that the introduction of foreign crops into the United States is a good model for

4A. Kelman, 1980, personal communication.

University

of Wisconsin, Madison, WI.

October 1996

7 15 5 1 5 2 12 4 1 9 7 1 69
4 1 41
7 1 2 9 1 6 1 1 2 21
2 5 7 8 20 14 1 154
3 1 54
3 1 1 2 23
9 1 13 1 1 1 1 38
1 5 2 9 1 19 18 1 209
6 21 1 1 1 1 1

175 290

4 14 1 1 1 2 3 5 1 3

40 65

14 37
3

24 49

1 1 1 2 4 1 1 2 6

52 133

1 4

26 40

4 13

10 28

1 2

13 72

18 72

2 3

399 878

predicting potential effects of intro duced genetic material from foreign plant types (NAS 1987a). If so, then there is reason for concern because

128 species

of intentionally intro duced crops have become serious weeds, like

Johnson grass (Pimentel

et al. 1989). Weed control and herbicide resis tance. Weeds are a major pest prob lem in agriculture, and both herbi cides and several nonchemical technologies are used to control them. For example, approximately

275 million kg of herbicides are ap

plied to US agricultural crops each year (Pimentel et al. in press). In addition to controlling some weeds, herbicides can also damage crops and increase some insect and plant pathogen pests in the agroecosystem (Pimentel 1995, Pimentel et al. 1992).

The use of herbicide-resistant

crops makes possible the heavy use of herbicides without damage to the crop. At present, breeding crops for herbicide resistance dominates (41 %) the field trials of genetically engineered organisms (Tables 1 and

2; Mannion 1995). This emphasis

on herbicide resistance is indicated by recent data on field test permits in the United States (APHIS 1996), which include

207 issued permits for

test releases of herbicide-tolerant crops. The crops are tolerant to her bicidal chemicals such as glyphosate, phosphinothricin, sulfonylurea, bromoxynil, and 2,4-D.

In a few situations,

the presence of herbicide-resistant crops could reduce herbicide use, provided that farmers adopted the strategy of us ing only a postemergence herbicide (i.e., one that acts after the crop plant germinates) to control weeds rather than both pre emergence and postemergence herbicides (Wrubel et al. 1992). Another option is to use a single, broad-spectrum herbicide that breaks down relatively rapidly in stead of a persistent herbicide such as atrazine or 2,4-D (Gressel 1992,

Krimskyand Wrubel 1993).

However, in actuality the use

of herbicide-resistant crops is likely to increase herbicide use as well as pro duction costs (Rissler and Mellon

1993).

It is also likely to cause seri

ous environmental problems (Pimen tel et al. 1989, Schulz et al. 1990,

Tiedje

et al. 1989). When a single herbicide is used repeatedly on a crop, the chances of herbicide resis tance developing in weed popula tions greatly increase. Also, glypho sate, one of the herbicide substitutes that is recommended as having po tential benefits for herbicide-resis tant crops, has been reported to be toxic to some nontarget species in the soil-both to beneficial polypha gous predators, such as spiders, predatory mites, carabid beetles, and coccinellid beetles, and to detriti vores, such as earthworms and wood lice (Asteraki et al. 1992, Brust 1990,

Eijsackers 1985,

Hassan et al. 1988,

Mohamed et al. 1992, Springett and

Gray 1992)-as well as to aquatic

organisms, including fish (Henry et al.

1994,

Wan et al. 1989, WHO 1994).

Because

engineered organisms bear alien genes that could circulate in wild relatives, some concern has been expressed about genetically en gineered plants upsetting not only the agroecosystem but also other eco systems (Giampietro 1995).

For ex-

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ample, important weed species have originated by hybridization of weedy species with related crop plants, such as crosses of Brassica napus {oilseed rape} with Brassica camprestris {a weedy relative} and of Sorghum hi color {Sorghum corn} with Sorghum halepense (Johnson grass; Colwell et al. 1985, Mikkelsen et al. 1996).

However, proponents of genetic en

gineering rely on the experience with corn hybrids and other genetically altered crops that have not caused any major environmental problems {NAS 1987a}. Nonetheless, the ba sic question remains as to how to evaluate every genetically engineered organism before its release to ensure its safety for the environment. ,Assessing environmental risks

To date, more than 2000 approved

releases of genetically engineered plants have taken place worldwide in field trials without any obvious misadventures {OECD

1993, Whit

ten 1992}. However, little or no eco logical research has been devoted to determining the interaction of these plants with their environments and their effects on natural biota {Krimsky 1991}. According to

Dekker and Comstock {1992}, the

emphasis has been placed on the possible benefits rather than the po tential risks. Indeed, the misconcep tion exists that only a few ecological questions have to be investigated before the release of a genetically engineered organism {Levidow

1992,

Pimentel 1995, Pimentel et al. 1989,

Wrubel et al. 1992}. This viewpoint

may hinder sound ecological assess ments of genetically engineered or ganisms.

Monitoring protocols must be able

to identify changes in biodiversity both in soils and above ground, thus revealing whether genetically modi fied organisms have caused harm to nontarget organisms {the United

Kingdom's Environmental Protection

Act of 1990; Levidow and Tait 1992}.

Whitten {1992} proposes several es

sential characteristics that genetically engineered organisms must have if they are to be suitable for release in agriculture and the environment:

They should be environmentally safe,

have limited impact on nontarget organisms, not be present in human 668
food, not cause pest resistance, and be able to be withdrawn from the environment if ultimately required. In addition, the Commission of the

European Community {CEC 1990}

has described the various impacts that genetically modified organisms may have on an ecosystem, includ ing enhanced primary production, improved recycling of nutrients, and decomposition of organic matter.

Assays of soil biota may provide

an efficient and accurate measure of the safety and environmental impact of genetically engineered organisms introduced into agroecosystems. For many years this technology has proven effective for assessing the potential environmental impact of pesticides {E'dwards and Bohlen

1992, Paoletti et al. 1991}.

Agenda for the development of

genetic engineering

Some desirable areas of development

for genetic engineering technologies that have the potential to benefit agricultural sustainability, the integ rity of the natural environment, and the health and safety of society are as follows:

Enhancing

crop resistance to pests.

Approximately 500,000 kg of pesti

cides are applied each year in US agriculture, and many nontarget spe cies beneficial to the environment are negatively affected. Genetic en gineering targeted for pest control could diminish the need for pesti cides {Pimentel et al. 1992}.

Resistance factors

and toxins that exist in nature can be used for insect pest and plant pathogen control {Pimentel 1988}. For example, more than 2000 plant species are known to possess some insecticidal activity {Crosby 1966}, and approximately

700 natural substances in bacteria,

fungi, and actinomycetes have fungi cidal activity {Marrone et al. 1988}.

Traits for resistance to different in

sect pests and diseases already exist in many cultured crops, including corn, wheat, barley, soybeans, beans, apples, grapes, pears, tobacco, to matoes, and potatoes {Russell 1978,

Smith 1989}.

Although some resistance charac

teristics have been reduced or elimi nated in commercial crops, they still can be found in related wild variet ies, which provide an enormous gene pool for the development of host plant resistance {Boulter et al. 1990}.

For example, a wild relative of to

bacco that produces a single acety lated derivative of nicotine is reported to be 1000 times more toxic to the tobacco hornworm than is cultivated tobacco (Jones et al. 1987). Trans ferring this toxic gene to nonfood crops, such as ornamental shrubs and trees, would protect them from some insect pests. In addition, thionins, proteases, lectins, and chitin binding proteins, which are often present in plants, especially in the seeds, help control some pathogens and pest insects in wild plants (Boulter et al. 1990, Czapla and Lang

1990, Garcia-Olmedo et al. 1992,

Pimentel 1988, Raikhel et al. 1993).

Indeed, developing disease-resis

tant crops that reduce the use of fungicides should receive high prior ity because fruit and vegetable crops are routinely treated with large amounts of fungicides. For example, on average each year US apple or chards receive 18 kg/ha of fungi cides, grapes receive

29 kg/ha, and

tomatoes receive 15 kg/ha (Pimentel et al. 1993). Fungicides are some times harmful to beneficial insects and toxic to earthworms and many other beneficial soil biota (Edwards and Bohlen 1992, Flexner et al. 1986,

Paoletti

et al. 1988, 1991). Thenum ber and activity of these soil biota are important in maintaining soil fertility over time because they re cycle nutrients in organic matter and aid in water percolation and soil aeration (Crossley et al. 1992). Fur thermore, the carcinogenicity of fun gicides ranks the highest of all of the pesticides applied to agriculture (NAS 1987b), accounting for ap proximately 70% of the human health problems associated with pes ticide exposure (Culliney et al. 1993,

NAS 1987b).

Improving vaccines

for livestock dis eases.

Most data in the literature

support the theoretical and practical use of genetically modified vaccines against rabies (Brochier et al. 1991,

Jenkins et al. 1991). However, the

risk of recombination between the engineered vaccine virus and other orthopoxviruses endemic in wild-

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Table 3. What is coming to market? An update on commercialization (Gene Exchange December 1994). The chart below

summarizes agency actions on commercialization of genetically engineered products.

Product Altered trait

I

Canola Altered oil composition-

,( oilseed rape; high lauric acid

Calgene)

Cotton Resistance

to herbicide (Calgene, bromoxymil

Rhone Poulenc)

Cotton

Resistance to insects

(Monsanto) (Bttoxin)

Cotton Resistance to herbicide

(Monsanto) glyphosate

Potato Resistance

to Colorado (Monsanto) potato beetle (Bt toxin)

Pseudomonas Toxicity to insects

fluorescens (Bttoxin) (Mycogen)

Rhizobium

meNloti Enhanced nitrogen (Research) fixation soybeln Resistance to herbicide (Monbnto) glyphosate (Upjohn) Virus resistance

Tomato Delayed ripening

-(DNA plant research)

Tomato Delayed ripening

(Calgene)

Tomato Delayed ripening

(Monsanto)

Tomato Thicker skin, altered

(Zeneca) pectin

Vaccinia virus Immunity

to rabies vaccine (Rhone Merieux) life, such as cowpox virus, still needs to be accurately investigated (Bou langer et al. 1995). The broad range of potential vaccines for control of various diseases is especially prom ising because of their low environ mental risks and excellent socioeco nomic benefits.

Drought resistance in crops. Approxi

mately 5 million liters of water are required to produce 1 ha of corn (Pimentel et al. 1995). Thus, increas- . ing drought resistance in crops would be of great benefit (Stanhill 1991).

Given

that water is vital to photo synthesis and that all crops consume enormous amounts of water, best

October 1996

Purpose Source of new genes Agency action On the market?

Expand use in California

Bay, turnip USDA approved, FDA No

soap and food oilseed rape,bacteria, virus pending, EPA not required products Control weeds Bacteria, virus USDA approved, FDA No approved, EPA pending

Control insect Bacteria USDA pending, FDA,

EPA No

pests pending

Control weed Bacteria, virus USDA, FDA,

EPA Yes

Arabidopsis approved

Control insect Bacteria USDA pending, FDA approved, No pests EPA pending Control insect Bacteria • USDA not required, FDA not Yes pests required, EPA approved

Increase yield in Bacteria USDA

not required, FDA not No alfalfa required, EPA pending Control weeds Petunia, soybean, USDA approved, FDA approved, No bacteria, viruses EPA pending Control virus Viruses USDA approved, FDA approved, No (1995) diseases EPA not required

Enhance fresh

Tomato, bacteria, virus USDA pending, FDA approved, No market value EPA not required

Enhance fresh

Tomato, bacteria, virus USDA approved, FDA approved, Yes market value EPA not required Enhance fresh Bacteria USDA approved, FDA approved, No market value EPA not required

Enhance

Tomato, bacteria, virus USDA pending, FDA approved, No processing value EPA not required Control raccoon Rabies virus USDA pending, FDA not required, No rabies epidemics

EPA not required

estimates are that water use in crop production could be reduced by ap proximately 5%.5 dertaken to adapt wild plants such as

Salicornia spp., Aster tripolium,

and Crambe maritima to salinized soils (Huiskes 1993).

Salt tolerance in crops. Traditional

agricultural systems have developed some crop varieties resistant to salin ization, for example, red rice variet ies in China (Needham 1985). The amelioration of salt intolerance is likely to help extend the usefulness of salinized agricultural areas, which worldwide are increasing by approxi mately 1 million ha per year (Umali

1993). Projects have also been un-

SW. Pfitsch, 1995, personal communication.

Hamilton College, Clinton, NY.

Nitrogen fixation in corn, wheat,

rice, and other crops. One of the ultimate aims of genetic engineering is to develop cereals able to provide their own nitrogen by bacterial sym biosis, as do leguminous plants (Pimentel et al. 1989). If this goal were achieved, it would reduce the large amount of energy used to pro duce and apply nitrogen fertilizers and would also reduce the costs of production. There is growing evi dence that this goal eventually might

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be realized through genetic engineer ing by improving inoculation processes, as was done in rice (You et al. 1992).

In addition, Rhizobium meliloti

is under US Environmental Protec tion Agency application for com mercialization (Table 3). A modi fied version of this nitrogen-fixing symbiotic organism is expected to increase alfalfa production by im proving nitrogen fixation in the crop (Bosworth et al. 1994).

Development of perennial grain

crops. At present, the major cereal crops of the world are annuals. The conversion of annual grains to pe rennial grains by genetic engineering would reduce tillage and erosion and conserve water and nutrients (Jack son 1991). Such crops would decrease labor costs, improve labor allocation, and, overall, improve the sustainability of Energy efficiency in the cultivation of perennial cereal crops would be greatly superior to annual crops (Jackson 1991).

Improved botanical pesticides. Only

limited quantities of botanical pesti cides are now used in developed coun tries in place of some synthetic pesti cides.

However, in some developing

countries, including

China and In

dia, botanical pesticides such as neem are effectively used (NAS 1992). In creasing the effectiveness of neem and other available botanical pesti cides by genetic engineering would be an asset to farmers because they are relatively effective and safe.

Microorganisms to improve the re

cycling of toxic wastes. Genetic modi fications have enhanced the ability of microorganisms to digest some chemical pollutants and thereby re duce the hazards to the environment (Contreras et al. 1991, Krimsky

1991). This aspect of biotechnology

seems positive.

In prerelease testing,

the interactions of such new geneti cally engineered organisms with non target organisms in the soil commu nities and contaminated landscapes must be carefully monitored to avoid potentially deleterious side effects.

Improving

the palatability of fruits and vegetables. Recently a long-last ing, flavorful tomato was developed and introduced into the US market- 670
place (Table 3). Some consumer groups argue that this tomato should be labeled as genetically engineered so that consumers can select toma toes according to their own prefer ences (Verrall

1994). Appropriate

labeling of genetically engineered food products continues to be an important issue for many consum ers.

When food crops are genetically

engineered to make them brighter, harder, larger, or modified to have other desirable characteristics, care must be taken not to diminish their nutritional value.

Improving livestock

ruminant nutri tion. Developments in genetic engi neering technology.may improve ru minant nutrition, modifying the microbes that are involved in rumi nal fermentation. The objective will be to find suitable foreign bacterial genes that can be inserted into rumi nal bacterial organisms (Wallace 1994).

Questionable genetic

engmeermg

We believe there are some question

able uses of genetic engineering.

These uses include:

Bovine

growth hormone (BGH) in dairy cattle. Genetically engineered 'BGH increases milk production in dairy cattle by as much as 40 % (Bur ton et al. 1994). The US Food and

Drug Administration has ruled that

the presence of the hormone in milk is safe for adults and children. Yet there are concerns about the impacts of this technology on the health of both cattle and humans (Broom

1995). Using BGH in cattle increases

the chances of bacterial infections and mastitis and also reduces the reproductive cycle in treated dairy cattle (Broom 1995, Burton et al.

1994, GAO 1992).

Millstone et al. (1994) report that

increased infections in cattle will re quire treatment with antibiotics. Al though not all antibiotics appear in milk, some do.

Thus, if more antibi

otics are used, there might be a risk to humans because some residues may remain in the milk (GAO 1992). BGH treatment of cattle also raises the relevant issues of bioethics of human health and animal welfare (Broom 1995).

Human genes introduced into live

stock and crop plants. The introduc tion of human genes into livestock and crop plants is being investigated (Buttel 1988). This approach in ge netic engineering appears to be un ethical; if implemented, it is likely to raise serious questions in the public's mind about genetic engineering. Fur thermore, billions of genes are avail able for use in genetic engineering, so introducing human genes into live stock and crop plants for human consumption is not necessary.

Microbes for insect biocontrol. It is

not useful to engineer organisms that are already naturally effective bio logical control agents; hence, this use should not be a priority. For example, the nuclear polyhedrosis virus, a highly effective biocontrol agent for the cabbage looper, need not be genetically engineered. The cabbage looper can be controlled simply by placing five infected loop ers in

400 liters of water and spray

ing this concoction over a hectare of crop plants. 6

Long-term human con

sumption and various other data have demonstrated that consuming this natural virus, which is highly spe cific for cabbage looper, is unlikely to pose a risk to humans or other mammals.

Release of genetically engineered

native organisms. This option could lead to the possibility of hybridiza tion and the development of new plant races, including weeds. Just because the original organism is a native species does not mean that it will be safe after it has been geneti cally engineered. Adding or deleting a gene from a native species may significantly alter its ecology, in cluding the potential for increased pathogenicity (Pimentel et al. 1989).

The safest procedure may be to

introduce an organism from the trop ics and genetically alter it. Then, once released in the northern part of the United States or in Europe, it would have a low probability of sur viving the winters, and the possibility of its upsetting the ecosystem would be negated (Pimentel et al. 1989).

Toxic chemicals bred into food and

forage crops. Some toxicants, such

6D. Pimentel, 1991, unpublished manuscript.

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as cyanide and alkaloids, exist natu rally in crop plants at relatively low levels (Pimentel 1988). Although these toxicants might be employed in shrubs and trees for pest control, genetic engineering should not be used to add additional toxins to food or forage crops. The known risks to humans and other animals associ- , ated with these natural toxins should be avoided (Culliney et al. 1993).

Introducing genes

into crops that subsequently may become weeds.

Crawley et al. (1993)

reported that engineered oilseed rape is not more invasive than its conventional coun- , terpart. However, the evaluation of genetic engineering risks for one crop provides insufficient evidence to judge the risks for all crops (Wilson

1990). This concern is

supported by the fact that 128 species of appar ently/desirable crop plants that were intrQ'duced intentionally into the

United States have subsequently be

come weed pests (Pimentel 1995).

Conclusions

Genetic engineering technology holds

exceptional promise for improving agricultural production and keeping it environmentally sound. Potential benefits include higher productivity of crops and livestock, increased pest control and reduced pesticide use, reduced fertilizer use by enhanced nitrogen fixation, and improved con servation of soil and water resources.

Along

with the potential benefits for agriculture come some risks. In essence, the release and regulation of genetically engineered organisms into the environment should be similar to the release and regulation of exotic plant and animal species into a new environment (Pimentel et al. 1989).

Therefore, time

and effort must be devoted to laboratory and field testing before the release of geneti cally engineered organisms.

Without

caution and suitable regulation, en vironmental problems are likely to arise and the expected benefits of genetic engineering are likely to be jeopardized.

Acknowledgments

We are indebted to the following

persons for discussions, suggestions,

October 1996

and information kindly shared con cerning early drafts of the manu script:

M. J. Adang, University of

Georgia, Athens, Georgia; Roberto

Bassi, Antonia Costacurta, and

Mario Terzi, Padova University,

Padova, Italy;

Thomas H. Czapla,

Monsanto Company, St. Louis, Mis

souri; Abhey

Dendikar, University

of California, Davis, California;

Clive A. Edwards, Ohio State Uni

versity, Columbus,

Ohio; David A.

Fischhoff,

Monsanto Company, St.

Louis, Missouri; Cecil W. Forsberg,

University of Guelph, Ontario,

Canada; F. Gould, North Carolina

State University, Raleigh, North

Carolina; Heikki Hokkanen, Uni

versity of Helsinki, Finland; Sheldon

Krimsky,

Tufts University, Cam

bridge, Massachusetts; Les Levidow,

Open University at Milton Keynes,

United Kingdom; W. F. Mueller,

New Mexico State University, Las

Cruces,

New Mexico; Jane Rissler,

Union of Concerned Scientists,

Washington, DC; Michael C. Smith,

University

of Kansas, Lawrence,

Kansas; Roger Wrubel, Tufts Uni

versity, Cambridge, Massachusetts;

Thomas ZappIa, Pioneer, Des

Moines, Iowa; and at Cornell Uni

versity, Ithaca,

New York: Martin

Alexander, Thomas Eisner, Robert

Granados, D. Halseth, Robert

Plaisted, R. T. Roush, M. E. Sorrells,

Steven Tanksley, Ward Tingey,

Quintin Wheeler, Alan Wood, and

Milton Zaitlin. We especially ap

preciate the work of M. Pimentel in editing early drafts of the manu script. Two anonymous reviewers helped to improve the manuscript as well. An

Organization for Economic

Cooperation and Development grant

to M. G. Paoletti to conduct this research at University is gratefully acknowledged.

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