Concerns and Postulated Environmental Risks of Biotechnology............................ 22

Chapter 8 Scientific Issues: Risk Assessment

and Risk Management

Photo credit: Grant Heilman, Inc.

Contents

Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .. (225)

RISK ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .. (225)

Concerns and Postulated Environmental Risks of Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Major Risk Assessment Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Biotechnology Ecological Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Applicability of Diverse Bodies of Knowledge to Assessments of Large-Scale

Commercial Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 Commercial Release Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 RISK MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .. (247)

Design of Science-Based Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Generic v. Case-by-Case Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (247)

Relative Risks Compared to Traditional Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Cost-Benefit Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Small-Scale v. Large-Scale Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 SCIENTIFIC METHODS OF MANAGING RISK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. (249)

Promoters Turned On or Off by Specific Stimuli . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

249 Suicide Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Prevention of Gene Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Combinations of Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... (250)

AGRONOMIC METHODS OF MANAGING RISK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . (250)

Physical Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Spatial Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Temporal Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 SUMMARY POINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... (251)

CHAPTER PREFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252

Boxes

Box Page 8-A. Ecological Risk Assessment Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

8-B. Learning by Doing: Successive Field Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

8-C. Monitoring Microorganisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

8-D. Relevant Research Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

Figures

Figure Page

8-1. Alternative Risk Analysis Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

8-2. Risk Assessment Framework for Environmental Introductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232

Table

Table Page

8-1. Comparison of Traditional and Developing Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

given crop species, only a small number of the wild

relative species that are reproductively compatible are

actually likely to present serious weed problems; how-

ever, it is theoretically possible for a plant to become a

weed in a novel environment (43).

One specific concern posed frequently by some en-

vironmentalists, among others (32), is that genes for her-

bicide tolerance might be transferred from crop plants to

weeds. If this were to occur, natural selection could favor

the trait in weedy neighbors of crops treated with the

herbicide. With any use of herbicides, furthermore, in-

creased selection pressure is put on wild species for any

herbicide tolerance traits they might already possess. Such

developments might lead eventually to increased use of

chemical herbicides. A fundamental debate has arisen

between industry scientists who maintain that crops can

be genetically engineered to be tolerant of particularly

‘‘environmentally friendly’herbicides and some envi-

ronmentalists who say.essentially, that no new tech-

nology should be used to favor continued use of chemicals

in the environment.

Concerns About Microorganisms

In part because they are invisible and relatively “un-

knowable, ”microorganisms tend to elicit more concerns

on the part of the public than do plants. Parameters of

concern related to genetically engineered microorganisms

include the possibility of gene transfer and recombination.

the possibility of movement into new environments, and

the possibility of infection of nontarget organisms. Ques-

tions asked include: Will genetically engineered microor-

ganisms give rise to biological risks for humans or other

species? Will they give rise to environmental problems’?

Do we have the technical understanding to evaluate and

predict any such problems’?

Whether bacteria, fungi. viruses, or baculoviruscs, mi-

croorganisms suffer from a bad reputation at the broadest

level of public perception: they are. after all often equated

with“germs.” One specific concern raised with regard

to genetically engineered organisms is the possibility of

genetic material from such organisms being transferred

to human gut bacteria. The risk of infection of humans.

or other deleterious effects, is clearly going to be ex-

amined for planned introductions of microorganisms. For

example. among the questions raised by Monterey County

staff considering the Advanced Genetic Sciences (AGS)

proposal to field test Frostban R was whether or not the

Pseudomonas fluorescens could ‘ ‘sensitize or aggravate

existing health conditions among sensitive human pop-

ulatitons living near the proposed test site’ (66).To assess risk of problematic infection of humans by genetically engineered organisms. information must be available on exposure level. This hinges on such factors as bioavailability or likelihood of absorption into cells or tissues, specificity, and level of interaction possible of the microorganisms or their chemical products with nontarget (human) tissues; and potential of the micro-organisms for colonization or infectivity. The degree of pathogenicity must be considered as well. Some relevant factors include virulence. Possession of toxins, host range,and relative susceptibility. Generally. risk assessment will factor in predictability of the behavior of the recom-binant DNA identified microorganisms based on their parent organisms, as well as knowledge of specific re-combinant techniques used (40).Scientists’ concerns focus less on pathogenicity and more on the possible impacts of genctically engineered microorganisms on the environment. Suggested impacts include possible influences on: indigenous population size.diversity of species. the ecological community. natural cycles, and evolution of the introduced organisms (76).Microbial environments are complex. By one estimate some 109 microorganisms, representing a variety of tax-onomic groups, inhabit one gram of - soil. Uncetanties exist as to possible consequences of sudden introductions on balanced microbial ecosystems (46). Microbial di-versity in the soil is high (88). This limits the niches available to introduced mirorganisms (86). While in-troduced microorganisms may thus compete poorly. they may persist in low-density populations. A key issue is whether or nor an unexpected later resurgent bloom or population expansion from a low-density population can be reasonably envisioned (84).Since microorganisms can and do change location.questions of dispersal—and possible subsequent repro-duction in nontargeted ecological sites—also are raised.The ability of a particular strain to transfer genes to other specics will affect the likelihood of other microorganisms being affected in new.nontarget areas. All questions bearing on survival, multiplicaton, and dispersal of ge-netically enginered microoganisms: on possible ex-change of genes between introduced and indigenous microorganisms: and ultimately on issues of environ-mental and public safety,are engaging attention of ac-ademic and industrial scientists,the public, and governmental regulators alike (22).Views Held in the Scientific Community Particularly in the early days. the issue of planned introductions of genetically engineered organisms sparked

a range of views on safety even among scientists (50). In the mid-eighties, microbiologist Winston Brill argued

that. for centuries, traditional breeding has altered ani-mals and plants without negative consequence: and that

microorganisms, including pathogenic species, have been added to the soil in hopes 0ft beneficial impacts. also without negative consequences (7). His conclusion that these observations alone formcd a basis for risk assess-ments of’ organsms that have had one or a few genes added drew fire from a group of ecologists ( lo). These

critics pointed out that mutations that increase an organ-isms niche range can be ecologically significant. and

that some ramifications of an organism’s impact on the

environment are not predictable from knowledge of its

introduced genes alone.Casc-by-case quantitative risk assessment for deliberate release was recommended.

In 1987, Science published side-by-side articles by Frances Shw-pies (75) and Bernard Davis ( 15). Sharples.

an ecologist.reaffirmed the need for casc-by-case as-sessments, given the complexity of any organism’s in-teractions with the environment. Molecular biologist Davis suggested that the experience of ecologists with intro-ductions of higher organisms is less pertinent to risk assessment of engineered microorganisms than are the insights of fields mom concerned with the specific prop-

erties of those microorganisms: population genetics. bac-terial physiology. epidemiology. and the study of pathogenesis.

The range of possible views on safty runs from “zero risk’ to catastrophic risk’; those who presume " small-

risk, pending research occupy the middle of the spec-trum. In the mid-eighties, molecular biologists tended to stress the relavance of the safty record of laboratory

biotechnology and graviated toward the ‘‘zero-risk” end of the spectrum. Ecologists, who tended to stress the

complexities of the natural environment. were less san-guine about potential risks. but stopped short of the cat astrohic-risk position taken by certain envronmentalists.

An important distinction exists between ecologists and

evironmentaists. The former are:

q

Principles of Risk Assessment—’ ’Risk” can be de-fined as the potential for negative or adverse consequent to arise from an activity or an event (23). Risk also can be defined as the probability of an event occurring mul-tiplied by the cost of its occurrence (44). Risk assessment can be viewed as ‘‘the process of obtaining quantitative or qualitative measures of risk levels. including estimates of possible health effects and other consequences as well as the degree of uncertainty in those estimates’ (23).

Risk assessment simply is an analytical tool that pulls together a great deal of diverse data in order to estimate a potential risk from an event or a process (81). Often, historical data on possible adverse consequences are dif-ficult or impossible to obtain, making risk assessment ‘‘an inexact process that attempts to characterize and quantify uncertainty, but never completely eliminates it. ”Nonetheless, despite the limitations and challenges, use of risk assessment principles makes it possible to orga-nize and interpret knowledge so as to improve the pre-diction of possible outcomes and ultimately to manage risk (23).

Risk assessment has been defined as a five-stage proc-ess:

1. 2. 3. 4. 5Risk identification— defining the nature of the risk, source, mechanism of action, and possible adverse consequences;

Risk-source chracterization—characterizing the source of potential risk; Exposureassessment— assesing the intensity. fre-quency and duration of human or environmental exposures to risk agents;

Dose-response assessment— assessing the relation-ship between dose of the risk agent and health or environmental consequences; and

Risk estimation— intergrating a risk-source char-acterization with an assessment of exposure and dose-response,leading to overt measures of the level of the health, safety or environmental risk involved (59, 92).

Clearly these stages can be adapted to fit a variety of kinds of risks, and the entire process can take several different forms. (See figure 8-1. )

The choice of an approach to risk assessment depends in large part on the extent and quality of available knowl-edge, degree of expected precision, and importance at-tached to outcomes at a low probability. Where the knowledge base is large and little uncertainty exists, a risk or hazard may be described quite readily and a more precise “deterministic consequence analysis” might even

be performed. On the other hand, when less knowledge is available and the level of uncertainty is high. a qual-itative risk screening may be all that is possible. perhaps leading to a more quantitative‘probabilistic risk as-sessment.

A much-used framework to assess risk is that devel-oped for the evaluation of health effects associated with chemicals in the environment. This was endorsed by a National Academy of Science report (67) and refined at the Environmental Protection Agency (EPA). This chem-ical risk-assessment framework sometimes has been adapted for evaluation of planned introductions of re-combinant DNA-modified organisms into the environ-ment (13. 16. 30).

The National Research Council (NRC) and the Eco-logical Society of America (ESA) (69, 85) developed in 1989 risk assessment frameworks designed for recom-binant DNA-modified organisms. But they were quite different from the chemical approach. The NRC proce-dure takes account of the degree of “familiarity”of a planned introduction; the ESA uses a risk attributes cat-egorization; both lead towards the determintaion of an appropriate level of concern. While differing somewhat in perspective. the two approaches nonetheless resemble each other in basic conclusions and therefore together provide a solid framework for risk assessment of planned introductions. Clearly, choice of framework for risk as-sessment will influence the kinds of data required for evaluation and for permit applications (50). The two re-ports described below have had significant impact on the recent framing of discussions about planned introduc-tions. Even proponents of chemical risk-assessment pro-cedures point out that these procedures can be used to determine whether or not a particular organism should be evaluated intensively using an analogue of a chemical risk assessment (81).

National Research Council Report Background—In late 1989, the National Research Council published Field Testing Genetically Modified Organisms: Framework for Decisions. This was re-quested by the Biotechnology Science Coordinating Committee (BSCC) on behalf of its member regulatory agencies. The report covered:

q plants and microorganisms,

q field-test introductions (but not large-scale com-mercial applications and related issues), q environmental (but not human health) effects,

Figure 8-l—Alternative Risk Analysis Approaches

Precision of ananalysis

Probabilistic risk assessment

Consequence

analysis with confidence bounds

Hazard Qualitative description risk screening

I >Level of Uncertainty

SOURCE: J. Fiksel and V.T. Covello, “The Suitability and Applicability of Risk Assessment M ethods for Environmental Applications of Biotechnology” in Biotechnology Risk Assessment: Issues and Methods for Environmental Introductions (New York, NY: Pergamon Press, 1986), pp 1–34-

scientific issues principally (but not regulatory policy).

field test conditions in the conterminous United States,

and

general procedures for determining categories (not

specific case recommendations ).

fundamental principle underlying the study. and first

introduced in an earlier National Academy of Science

document (68), is that safety assessments of a recom-

binant organism ”should be based on the nature of the

organism and the environment into which it will be in-

troduced, not on the method by which it was modified.

A related point is that ‘‘no conceptual distinction exists

between genetic modification of plants and microorgan-

isms by classical methods or by molecular methods that

modify DNA and transfer genes.

Topics analyzed for the 1989 report include: relevant

biological characteristics of genetically modified plants;

experience with genetic modification and introductions

of plants modified ‘ ‘traditionally” and by molecular ge-

netic techniques; potential weediness: the features of the

genetic modification in microorganisms; phenotypic

characteristics of the parent organism and of its geneti-

cally modified derivatives: and relevant features of the

environment into which the organism will be introduced.

Findings-The report recommends that the impacts

of’ genetic modification on the phenotype of the organism

and the mobility of the altered gene be assessed. In some

cases. when persistence of’ the modified orgtanism is not

wanted or when uncertainty exists as to effects on the

immediate environment. risk assessment should empha-

size the phenotypic properties relating to the persistence of the organism and its modification. Questions to be considered include: fitness of the genetically modified organism; its tolerance to physicochemical stresses; its competitiveness range of available substrates; and. if applicable. pathogenicity, virulencc. and host range. The report describes the long historry of safety in the useful employment of’ plants and microorganisms. and under-scores the need for field tests to increase the capability to assess any risks of large-scale introductions.Specific scientific conclusionss of the report pertaining to plants include:1.2.3.4.5.6.,The current means for making evaluations of in-troductions of traditionally bred plants are appro-priate (on the basis of experience with field tests of hundreds of millions of genotypes over decades).Crops altered by molecular and cellular techniques should pose risks no different from those posed by crops modified by traditional genetic methods for similar traits.The potential for enhanced weediness is the prin-cipal risk to the environment seen from introduc-tions of genetically moditied plants. although the likelihood of this occurring is low.Confinement by biological. chemical spatial,physical. environmental and temporal means is the principal means of maintaining the safety of field introductions of classically modified plants.Experimental plants grown in field confinement rarely if ever escape to cause problems in the environment.Established confinement options are equally appli-cable to field introductions of plants modified with

——

230 . A New Technological Era for American Agriculture molecular or cellular methods and to plants mod-

ified with classical genetic methods.

Conclusions concerning microorganisms included:

1. Many molecular techniques make possible genetic

changes in microbial strains that can be fully char-

acterized.

2. The molecular techniques are powerful in their ca-

pability to isolate genes and transfer them across

biological barriers.

3. Field experience has given rise to a great deal of

information about some microorganisms; nonethe-

less, less information exists on microbial ecology

and less experience with planned introductions of

genetically modified microorganisms than there is

for plants. No adverse effects have been noted from

microbial introductions to date; a field test should

g O forward when sufficient information is available

for its safety evaluation.

4. The probability of adverse effects can be minimized

or eliminated by appropriate means of confining

the microorganism to the environment into which

it was introduced; one example would be the use

of “suicide genes.

The framework for evaluating risk developed in the report is structured around the following questions:

1. 2. 3.Are we familiar with the properties of the or-ganism and the environment into which it may be introduced?

Can we confine or control the organism effec-tively?

What are the probable effects on the environ-ment should the introduced organism or a ge-netic trait persist longer than intended or spread to nontarget environments? (69)

The familiarity criterion is key to this report and has reappeared consistently in risk assessment discussions since. Familiarity means having sufficient information on which to base a reasonable assessment of safety or risk. Thus, as our information base increases, so does the scope of “familiarity.”When the familiarity criterion is not met. the possibility of confining or controlling the organism and the potential consequences of failing to control it must be evaluated.

The report is intended to provide a basis for a “flex-ible, scientifically based. decisionrnaking process. The classification of an introduced organism into a particular risk category is made possible by the framework for evaluating field tests (69).

The 1989 NRC report is often cited and has provided a conceptual framework for many approaches to risk assessment of planned introductions of genetically en-gineered organisms into the environment. Its level of detail made it more palatable to technical audiences than the 1987 pamphlet, which was at times criticized for making assertions without documentation ( 11, 50). The Ecological Society of America Report

Another seminal assessment was published in 1989, The Planned Introduction of Genetically Engineered Or-ganisms: Ecological Consideratons and Recommenda-tions (85). This report was prepared for the Public Affairs Committee of the Ecological Society of America (ESA) and also has been broadly disseminated and cited. Dr. James Tiedje chaired a workshop committee in April 1988, examining ecological aspects of planned environ-mental introductions of genetically engineered organ-isms. The Workshop Committee’s initial draft was reviewed at great length by the ESA Public Affairs Com-mittee, the ESA Executive Committee, and other ecol-ogists. The report

supports the use of advanced biotechnology for the de-velopment of environmentally sound products. and states that the phenotype of a transgenic organism, not the proc-ess used to produce it, is the appropriate focus of regu-latory oversight. Ecological risk assessment of proposed introductions must consider the characteristics of the en-gineered trait, the parent organism, and the environment that will receive the introduced organism (85).

Like the NRC report, the ESA report emphasizes prod-uct, rather than process, as the appropriate focus of eval-uation and regulation. Thus, ‘‘genetically engineered organisms should be evaluated and regulated according to their biological properties (phenotypes), rather than according to the genetic techniques used to produce them”

(85). Yet the report acknowledges the potential for nov-elty and consequent likelihood of evaluation inherent in the new techniques. The report acknowledges, however, that ‘‘because many novel combinations of properties can be achieved only by molecular and cellular tech-niques, products of these techniques may often be sub-jected to greater scrutiny than the products of traditional techniques.Moreover, it recognizes that even precise genetic characterization of transgenic organisms does not necessarily allow scientists to predict all ecologically im-portant expressions of phenotype in the environment. The ESA report emphasizes the importance of consid-ering a variety of ecological factors in ecological rami-fications of planned introductions. Among these are

survival, reproduction,interactions with other organ-

isms, and effects on ecosystem function and dynamics.

Potential undesirable impacts must he weighed in eval-

uations. While explicitly calling attention to the com-

plexities of ecological risk assessment, the report supports

the position that “ecological oversight of planned intro-

ductions should be directed at promoting effectiveness

while guarding against potential problems. Thus, the

authors observe that most cases will present a minimal

risk to the environment and provide a set of specific

scientific criteria for ‘‘sealing the level of oversight to

individual cases. The four categories of criteria included:

1. attributes of genetic alteration,

2. attributes of the parent organism,

3. phenotypic attributes of the engineered organism

in comparison with the parent organism. and

4. attributes of the environment.

Specific attributes are grouped according to level of risk

presented and corresponding level of scientific risk as-

sessment needed. Coming as it did from a group of ecol-

ogists, the ESA report is often cited as a touchstone for

those wishing to balance the positive potential of bio-

technology with a sensitivity to the environmental con-

sequences of actions.

Biotechnology Ecological Risk Assessment

Introduction

A central goal of ecological risk assessment of planned

introductions of recombinant DNA-modified organisms

is to ‘‘make a reasonably accurate prerelease prediction

of the behavior an organism is likely to exhibit in its new

ecological context and given its particular genetic mod-

ification, and to be able to detect and avert potential

problems before they occur” (76).

Most scientists seem to concur that the focus of risk

assessment should be on a particular organism, with its

characteristics (genetically modified or not) and the genes

that code for them, in a particular environment. Exper-

imental protocols for ecological risk assessments need to

be refined to screen out potentially problematic intro-

ductions before release (l4).

While scholars argue as to which risk assessment model

would best apply to environmental introductions of re-

combinant DNA-modified organisms, all agree that the

complexity of ecological factors renders biotechnology

risk assessment particularly challenging. Living organ-

isms can change locution, reproduce, and perhaps ex-

change genes. Once released into the environment. they will interact in a dynamic fashion with other species.They are indeed different from chemicals.Ecological risk assessment is a still young methodol-ogy, and not standardized. Some argue that directly rel-evant data are scarce enough, and ecological phenomena are sufficiently complex that resasoned qualitative judg-ments are more feasible than more precise quantitative assessments. In practice, expert review panels using good scientific judgment and common sense. along with guide-lines of points to consider, achieve qualitative assess-ments of the riskiness of various combinations of factors.As experience is gained. codification of the principles of review should evolve for application to future cases.Augmentation of” human judgment with knowledge sys-tem technology has been suggested as a means of facil-itating the process (24, 66).One way of conceptuall y applying risk assessment pro-cedures to planned introduction of recombinant DNA-modified organisms into the environment is to match the three classic risk assessment stages (A. risk-source char-acterization: b. exposure assessment: and c. dose-re-sponse assessment) with the five stages involved in planned introductions. (See figure 8-2. ) Information about stage one. formation of a recombinant DNA-modifiedd organ-ism. and stage two,its deliberate release or accidental escape into the environment contributes to risk-source characterization. Exposure assessment would take into account data on stage three. proliferation of the organ-isms, including dispersal and possible exchange of ge-netic material, as well as stage tour. their establishment in an ecosystem.Stage five, human and ecological ef-fects, relate quite directly to dose-response assessment (23).Another way of looking at risk assessment of planned introductions is to consider the defination of ”risk” as the product of’ ‘‘exposure’ and “hazard.” Exposure is related to the possibility of escape of the arganism, its survial. reproduction. and spretd. as well as to the gene transferred and the vector, if present. Assessment of the hazard, or potential environmental impact. depends on the ultimate fate of the introduced organism-whether it becomes extinct. establishes a balance with indigenous species. or overruns the recipient environment (53).Specific objectives of ecological risk assessment for plants. for example. include:1. determination of the potential for crops to persist and spread in a variety of habitats,2. discovery of the range of species that can cross-pollinate with various transgenic crops.

Box 8-A—Ecological Risk Assessment Questions

Field observations

Field experiments Contained experiments Persistence

What is the survival of the

What is the fate of seeds sown into How is pollen viability affected in vegetative parts of the plant under

a range of plant communities,transgenic plants?a range of climatic conditions, on

including other arable crops, forage How is seed dormancy affected?soils of different kinds with different

crops, permanent grasslands, and categories of drainage?

natural habitats?How do transgenic plants perform How is perennation affected by the

What is the fate of transplanted in competition experiments with crop plants and with selected introduced genes?

seedlings in different habitats?native plants?What factors influence plant

What is the fate of transplanted mortality outside arable fields and

mature plants (or rootstock) in how are these influenced by the

different vegetation types?novel genes?

How long does experimentally What is the nature of seed

planted seed remain dormant but dormancy under different

viable in a range of soil types?environmental conditions, and how

does the introduced genetic

change influence triggering,

duration, and hardiness during

dormancy?

Spread of the vegetative plant What is the seed production of the

What is the vegetative growth rate Is seed size or morphology plant when grown in a crop and in

on different substrates and with different in transgenic plants, and natural vegetation?

different competing species?how might this affect seed Is seed production limited by the

Is the thinning rule (i.e., density-dispersal?rate of pollination?

dependent plant mortality) similar Do transgenic plants present What is the germination rate of

for transgenic and nontransgenic greater risks of spread by seeds in soil?

plants?vegetative fragments?What is the mortality of seeds and

What kind of compensatory growth seedlings in arable soils and

is exhibited (e.g., gap-filling)?beneath native vegetation?

What is the phenology of seedling

emergence and growth?

What are the natural enemies of

the seedlings?

What is the role of vertebrate and

invertebrate herbivores in crop and

noncrop habitats?

What is the mechanism of seed

dispersal?

How far are seeds dispersed and

how does this vary with

environmental conditions?

Do the seeds produced by plants

grown outside arable fields give

rise to a second generation of

plants?(continued on next page)

234 q A New Technological Era for American Agriculture

Box 8-A—Ecological Risk Assessment Questions—Conthuecf Field observations Field experiments Contained experiments If the plant were to prove invasive,

at what rate would it spread and

which habitats would it occupy?

Which plant species (if any) are

displaced when (and if) the plant is

established in natural habitats?

Which plant species are responsi-

ble for the competitive suppression

of the plant in different natural hab-

itats?

Horizontal gene transfer through

pollen

How much pollen is produced?What is the fate of labeled pollen?Which plant species allow pollen What is the phenology of pollen How much pollen reaches the stig-germination on their stigmas?

production and what is the phenol-mas of other wild plants under dif-How is pollen dispersal affected in ogy of stigma receptivity of other ferent conditions?transgenic plants?

plant species growing in the neigh-Which insects carry the pollen?Which plant species form viable, borhood of crops (i.e., within 500-

How far away from the crop can an hybrid seed and at what rate is this 1,000 m)?

individual, potted crop plant be pol-seed produced?

Over what distance is pollen dis-Iinated and how does the rate of What is the germination rate of hy-persed under different meteorologi-pollination fall off with distance un-brid seed?

cal conditions?der a range of habitat conditions?

What phenotypes are exhibited by Which is the pollen deposited, on What plants make the most effi-hybrid individuals?

which species, and in what num-bers?cient ‘pollen barriers’ for the con-What is the performance of hybrid struction of guard rows; is it

Where is the pollen deposited, on

plants in competition experiments nontransgenic members of the with crop plants and with selected

which species, and in what num-same species or plants that form native plants?

bers?physical barriers to pollen flow or to

insect flight?What is the nature of perennation What is the geographic distribution and vegetative dormancy in hybrid

of closely related wild plants in the and transgenic plants?

vicinity of centres of crop cultivation

and what is their small-scale (100’s

m) distribution as weeds within ara-

ble fields and on land adjoining

field foundaries?

What natural habitats are found

within 1,000 m of arable fields, in

those areas where the crops are

grown, and what flora is supported

by these habitats?

SOURCE: Michael J. Crawley, “The Ecology of Genetically Engineered Organisms: Assessing the Environmental Risks,” Intor-duction of Genetically Modified Organisms into the Environment, Harold A. Mooney and Giorgio Bernardi (eds.) (New York, NY: John Wiley and Sons, 1990).

Achieving predictive capabilities in extrapolating from

field tests to large-scale introductions is an additional

goal. Along with further research, data from field tests

and research then can feed into the design of future field

tests and large-scale introductions. our scientific under-

standing pertinent to ecological risk assessment should

increase exponentially over the next few years.

This explosion of knowledge not only can improve

safety but also the effectiveness of introduced organisms

in various habitats. There seems to be general agreement,

even among ecologists and environmentalists, that most

biotechnology products will not be harmful. However,

because uncertainty does exist, for instance, as to which

applications might be harmful. reasonable caution and

willingness to assess risk are appropriate (76).

Risk assessment prior to introductions is a reasonable

and necessary step, consensus dictates. More research

can sharpen our powers of prediction and build on an

.

already sol id foundation of information. Eventually, cri-teria can be developed to match individual cases with

appropriate risk categories. In the meantime, as a broader

knowledge base is being built, the safety of each intro-

duction needs to be judged, basically, on a case-by-case

basis (51). Understanding gained from case studies and

other relevant research can be employed in the current

transition to risk assessments of large-scale introductions.

Applicability of Diverse Bodies of Knowledge

to Assessments of Large-Scale Commercial

Release

Introduction

In all approaches to risk assessment, the key question

is predictability. Do we have sufficient information to

make a reasonable prediction as to what will occur for

a particular release’? Can we in fact legitimately draw on

knowledge gained from agricultural experience, labora-

tory tests, past field tests of recombinant DNA-modified

organisms, and accumulated knowledge of genetics, mi-

crobiology, molecular biologics, and ecology? Are the

characteristics of any individual large-scale release fa-

miliar enough that we can bring such knowledge to bear

on the risk assessment’?

Species Introductions

Those interested in the evaluation of risks from bio-

technology sometimes turn to the experience base with

introduced ‘‘exotics,species accidentally or deliber-

ately released in a completely new environment. Dutch

elm disease is often-cited as a consequence of the acci-dental introduction of a fungus; kudzu vine. running ram-pant in the South after being brought in as a roadside ground cover, is pointed to as a deliberate introduction gone awry.One viewpoint holds that species invasions may be useful analogues of planned introductions of genetically engineered species, i.e.,an invasion is an invasion. Thus.experience with analyses of key properties of ‘successful invaders,as well as of vulnerable environments. the-oretically can be brought to bear in evaluating planned introductions (63).Most scientists agree, however, that invasions by ex-otics have limited applicability to planned introductions of genetically modified species. For example, introduced exotic plants that have caused problems come with many traits that enhance weediness; whereas genetically mod-ified plants, by contrast.are modified in only a few characteristics (69). The distinction between the intro-duction of modified genotypes of crop organisms and the introductions of totally new exotics-whether or not they are genetically engineered—is, in fact, generally re-garded as an important one (14). Even so. lessons learned as to the ecological parameters of ‘‘invading species’and recipient environments may be useful in categorizing degrees of risk for a specific planned introduction of a recombinant DNA-modified organism. For example,comparisons can be made between the characteristics of such an organism and the characteristics often found in very successful invading species. Habitat characteristics can also be compared to help assess site for vulnerability or resistance to invasion (63).Agriculture Perhaps the oldest analogue to planned introductions of genetically modified species is agriculture itself. For much of human history, new forms of crops and do-mesticated animals have been introduced to the environ-ment. Major crops have been bred by the millions for centuries; all these field tests and commercial releases provide a substantial experience base. Throughout this vast experience, no significant harm to human or animal health has occurred due to these introductions per se, nor have major crop plants become bad weeds. Normal se-lection procedures have eliminated plants with problems.Furthermore, “recalls”of crop varieties are common under the laws of supply and demand. In short, no ev-idence exists in the United States that plant breeding leads to ecological problems (6).The NRC report’s call for q ’familiarity” as a criterion for risk assessment makes drawing on the experience base

236 q A New Technological Era for American Agriculture

Photo credit: Monsanto Genetically engineered tomato plants are shown being

planted by researchers at a Monsanto-leased farm in

Jersey County, IL.

co.

of agriculture logical for most planned introductions of genetically modified agricultural organisms. A specific example of how the agricultural experience can be ap-plied to biotechnology risk assessment is the 80 years of usage of Bt (Bacillus thuringiensis with its toxin) as a natural insecticide; its history of safe use is often regarded as evidence that transferring the gene for a Bt toxin would be environmentally safe (6). The 100-year experience base with vaccines, rhizobial bacteria, and other biolog-ical controls provides information applicable to large-scale microbial introductions (20, 29, 62, 90). As a final example, corn breeders have significantly changed the corn genome and have conducted planned introductions into the environment of these modifications for the past 70 years, without negative ecological experience. Breed-ers have gained experience in protecting the purity of these genomes, calculating the likelihood that the mod-ifications will spread to other plants, deploying the mod-ified genomes,and maximizing their strengths and minimizing their weaknesses ( 18).

Although there are limitations to the analogy between seed purity and gene transfer to weeds (notably, the risks associated with weed genes contaminating seed for plant-ing crops are quite different from those associated with engineered genes getting into a weed population), this analogy does represent a useful starting point for risk assessment in controlled release.

Although some observers emphasize the novelty of gene combinations that can be brought about through biotechnology, a key difference between traditional crop breeding and the“new biotechnology” is that changes in genomes are more precise using biotechnology. With genetic engineering, one gene is moved at a time; by contrast, huge numbers of genes are recombined in crosses that lead to new plant varieties. It is nonetheless true that ecological effects of a changed phenotype sometimes may not be predictable even with precise changes in genotype (85).

Certainly, risk assessments are needed of individual cases involving particular genes. For example, forage crops such as alfalfa, which are not so dependent on cultivation practices,may have higher—and perhaps problematic—survival capabilities outside of the farm than others (6).

Two of the chief concerns about planned introduction of genetically modified species have no analogs in tra-ditional agriculture. With the exception of some intro-duced crops that become weeds in tropical countries, crop plants have not invaded natural habitats. Furthermore. no obvious problems have arisen due to transfer of genes from traditionally bred crops to wild plants ( 14). Laboratory Testing

Results of laboratory tests have been drawn on by those interested in risk assessment of genetically engineered microorganisms in particular. Various studies of micro-bial genetics, as well as use of soil microcosms (or lab-oratory model ecosystems) that mimick the natural environment, have provided useful information.

A great many reported laboratory tests involve inves-tigations of mechanisms and likelihoods of gene transfer. For example, transformation (the uptake of naked DNA into a competent or receptive cell) is a form of gene transfer well understood in the laboratory, but not well described in natural settings. Laboratory records on trans-duction (the transfer of genes between bacterial strains by virus particles) have led to theoretical models pre-dicting the possibility and frequency of transduction from an introduced genetically modified microorganism to a natural species. Another mechanism of horizontal gene transfer studied in the laboratory is conjugation, the pro-cess of genetic exchange between bacterial cells. Finally, transposition, the process by which mobile genetic se-quences change positions within a genome can be as-sociated with gene transfer.

Soil microcosms, even with sterile soil, are a feasible way of assessing what kind of gene transfer mechanisms can occur in nature; they are therefore a useful tool in risk assessment (38, 70). Research has now been done using more realistic soil microcosms, with the objective of learning more about the impact of conjugation on

introduced genetically modified microorganisms. For ex-

ample, some experiments have been done using non-

sterile soils, in an attempt to produce a closer analogue

to nature.

Another set of questions that laboratory tests can help

address is related to population biology. Relative fitness

of genetically modified microorganisms in the labora-

tory, for example, pertains directly to establishment and

possible spread of introduced organisms in an environ-

ment; some information toward quantitative risk assess-

ments can be gained from contained laboratory testing

in chemostats (44). Laboratory tests also can help illu-

minate the role played by various soil environments in

successful introductions (93).

Of course, constraints exist on the applicability of lab-

oratory tests, having to do with feasibility and with the

impossibility of reproducing the full complexity of a nat-

ural environment. Some important parameters relevant

to introductions are, for example, the relative fitness of

the introduced recombinant DNA-modified organism in

the new environment with its multiple dimensions of

biological, chemical, and physical features, including

competition with other microorganisms; microbial pop-

ulation density, which may vary over time and space;

population dynamics; and availability of habitats (5). The

dynamic complexity of many such features makes it im-

possible for a laboratory test to mimic reality completely.

Work is beginning on testing for effects such as patho-

genicity or toxicity in more realistic multispecies systems

or microcosms (26).

Perhaps the principal lessons learned from laboratory

research have to do with the potential to work creatively

with soil microcosms. The more realistic the soil micro-

cosm used, the higher the predictive value of the labo-

ratory tests is likely to be, particularly where extrapolation

from the laboratory to the field is relatively well under-

stood. It has been suggested that mesocosms (larger con-

tained walk-in chambers, the environmental parameters

of which can be controlled) could provide more realistic

complexity than soil microcosms. This added realism

might improve risk assessment (93).

Small-Scale Field Tests

Field tests of conventionally produced crop varieties

represent part of a step-wise progression toward full-scale

commercialization; the same is true of field tests of re-

combinant DNA-modified organisms. Initially. new va-

rieties are assessed in a laboratory or greenhouse; then

they are observed in small-scale field plots where they

are evaluated according to various protocols, statistical Photo credit: Monsanto Co.Researchers begin test of tomato plants carrying the Bt toxin gene in test plant.procedures, and analytical methods. Large-scale tests and commercialization complete the process. Each stage pro-vides information for the next stage (53 ). For the most part. principles and procedures useful in small-scale field tests are also relevant at the large-scale test and com-mercialization stages as well (36). Field testing and mon-itoring constitute ‘‘real world empirical methods’ that are important components of risk assessment (23).Small-scale field tests can be used to elucidate char-acteristics that will be factored into risk assessments of possible large-scale planned introductions. For example,survival and spread of particular recombinant bacteria in a particular soil environment, as well as efficacy of func-tion and stability of an introduced gene. can be estimated in field tests ( 1, 3, 47). Field tests also can be used to assess ‘‘invasiveness’of transgenic crops (73). Data from field tests can be integrated into quantitative pre-dictive models of gene flow and gene spread (39).Field tests also provide agronomically significant in-formation, including data on the expression or perfor-mance of the introduced gene and on the overall growth and vigor of the genetically modified plant (64). For example, 1990 field tests of insect-resistant cotton plants have allowed such agronomic traits as yield, fiber length,fiber strength, fiber quality, seed composition, and qual-ity to be evaluated by Monsanto, which is planning for commercial introduction in 1994 or 1995 ( 28).Well-designed, well-monitored field tests of increas-ing scale and complexity also should allow undesirable impacts to be observed while there is still an opportunity to correct them (43). A ‘‘stepwise progression in test

A step-by-step progression from individ-

ual field tests through multisite field tests to large-scale

testing to commercialization is being followed for re-

combinant DNA-modified organisms as it has been for

conventionally produced organisms. without problems.

Research still needs to be done to identify important

distinctions between small-scale and large-scale tests; this

should improve experimental design and efficiency (53).

Deliberations on Field Tests and on

Large-Scale Release

Over the past several years. field tests have made im-

portant contributions to risk assessments for large-scale

release of- DNA-modfied organisms. The data from field

tests provide the most directly relevant basis for predic-

Box 8-B—Learning by Doing: Successive Field Releases

Crop Genetics International (CGI) is a company that has used a “stepwise progression in test design” as it has moved from an initial field test to later tests. The focus was the delivery of biopesticidal gene products by

endophytic bacteria inoculated into seeds. First tested was a bacterial endophyte (Clavibacter xyli subsp. cynodontis)

genetically modified to produce low levels of the delta-endotoxin of Bacillus thuringiensis (Bt) subsp. kurstaki, and inoculated into corn seed. CGI developed a strategy for multiple risk assessment studies of field releases. The

focus of the field release studies was twofold: performance of plants grown from endophyte-inoculated seed; and persistence and spread of the genetically modified strain under different environmental conditions. The first two releases were used to develop a profile of the recombinant strain’s behavior in the environment. In 1989, the test design was extended to multiple sites in four States to examine its behavior overdiversified environmental conditions. This was the first release to take place in multiple States of a viable microorganism genetically modified to produce

a biopesticide. In 1990, a new recombinant strain selected for its activity against the target pest (European corn

borer) was incorporated readily into the well-established testing procedures and program, with the objective of

determining efficiency. As the study progressed between 1988 and 1990, by agreement with regulators, levels of containment were gradually lowered as data on safety were obtained. In fact, the early tests were specifically designed to address risk assessment issues such that future small-scale introductions could be made with less rigid containment and such that containment requirements could be eliminated in large-scale field tests. Efficacy studies now can be done under reduced containment requirements. Multiple-site field testing of the improved strains

is the next logical step toward large-scale tests and commercialization. Stepwise progression of tests is a rational strategy from a company’s point of view, as well as from a regulator’s point of view.

SOURCE: Stanley J. Kostka, “The Design and Execution of Successive Field Releases of Genetically Engineered Microorgan-isms,” Biologicd Monitoring of Genetically Engineered Plants and Microbes, D.R. MacKenzie and Suzanne C. Henry

(eds.) (International Symposium on the Biosafety Results of Field Tests of Genetically Modified Plants and Microor-

ganisms, Kiawah Island, SC, Nov. 27-30, 1990) (Bethesda, MD: Agriculture Research Institute, 1991), pp. 167-176.

(ion as to the safety of large-scale release, particularly in cases where a small-scale field test is itself scaled-up to a large-scale introduction. Equally important, scien-tists in many disciplines have been gaining practice through field testing in the process of risk assessment. Now that applications for large-scale release are imminent, re-searchers familiar with comparable evaluations at a small-scale can begin to integrate their experience and apply it to the new assessment task at hand.

Several recent conferences have helped to define ap-proaches to the risk assessment of large-scale introduc-tions. Commonalities arc emerging, suggesting that a state of readiness for large- scale introductions is in fact being reached.

Several biological principles with implications for as-sessment of large-scale introductions emerged from the International Symposium on the Biosafety Results of Field Tests of Genetically Modified Plants and Microorgan-isms (November 27–30, 1990. Kiawah Island. South Carolina). For example:

q q q q q The integration of genes into the chromosomes of recombinant DNA-modified organisms has proven to be predictably stable.

Gene transfer frequencies of recombinant DNA-modified organisms are consistent with patterns re-corded for natural populations.

The frequencies of transposon relocations in recom-binant DNA-modified organisms are consistent with those of natural populations.

Some microorganism detection methods are ex-tremely sensitive. and this contributes to better un-derstanding of- the fate of a microorganism in the environment.

Background microbial populations have been char-acterized as complex.and thus the release of ge-netically modified microbes may be insignificant by comparison..

The symposium also highlighted the strong foundation of conventional knowledge in crop improvement, micro-bial testing. and food processing that is available to sup-port safe commercialization of biotechnology products. Research needs cited included: detection methods, sam-pling methodologies.monitoring protocols and modeling techniques, and empirical data for improved design and evaluation of experiments (53).

A workshop on transgenic plants conducted by the Maryland Biotechnology Institute and the USEPA Office of Pesticide Programs (June 18–20, 1990) evaluated the human and environmentall impacts that could result from the‘‘widespread. full scale”use of plants genetically modified to produce a pesticidal substance. Workgroups discussed: 1) studies and information needed for assess-ment;

2)

scientific rationale for determining the occa-sional need for specialized studies; and 3) availability and test protocols for developing risk assessment infor-mation.

The consensus of all groups was that such transgenic plants posed concerns and possible effects that are not unique, and risk assessment issues can be addressed through readily obtainable information on possible effects of the plant or of the pesticidal substance (89).

The USDA-sponsored‘‘Workshop on Safeguards for Planned Introductions of Transgenic oilsecd Crucifers’(October 9, 1990, Cornell University’) was held to iden-tify agricultural biosafety issues relevant to oilsecd rape (or canola) as soon as possible. Unlike most crops, oil-seed rape has weedy relations in North America. The

potential for. and possible results of, gene transfer

240 q A New Technological Era for American Agriculture

Commercial Release Issues

A variety of issues relevant to planned introductions

of recombinant DNA-modified organisms are receiving heightened attention as large-scale commercial releases become imminent. Principal concerns focus on the fitness

of the engineered organism (defined as overall genetic contribution to future generations, usually quantified as number of offspring produced) and its potential to be-come established as a weed or a pest, the stability of the engineered gene, the potential for gene transfer, and im-pact on other organisms and the environment. Basically, these concerns are the same ones raised with regard to small-scale field tests of genetically engineered organ-isms. Large-scale agricultural uses involve large numbers

of organisms that are usually less contained than their less numerous counterparts in field trials.

Fitness and Potential to Become Established

For a species to become established in a natural com-munity, its relative fitness must be such that it competes successfully with other species. The lack of weediness on the part of most major crops illustrates a direct contrast between domestication and what is useful for survival in the wild ( 14. 43). Many traits necessary for successful weediness either have never existed in or have been de-liberately bred out of crop plants to maximize produc-tivity in a cultivated setting. One analysis showed that serious weeds tend to have on average 10 to 11 ‘‘weedy characteristics’;crop plants have on average only 5 of these characteristics (42). Thus, the chances of any crop plant simultaneously undergoing five to six relevant gene changes to become a weed are vanishingly small (37).

Features of organisms that ecologists identify with weediness include broad ecological tolerance, ability to exploit an under-utilized resource. or ‘‘readaptation’

to a new habitat to which the organism is well-suited and

in which controlling biological agents do not exist (76). Other characteristics that help to make a plant thrive as

a weed include the following:

q q

q q q q q q q rapid growth to a flowering stage,

continuous seed production as long as growing

conditions allow,

high seed output.

long-lived seed,

pollination by wind or unspecialized insects,

high competitive ability,

broad environmental tolerance,

seed dispersal over short and long distances, and

vegetative persistence and propagation.

The probability of successful establishment of a re-

combinant DNA-modified organism as compared to its

unmodified counterpart will naturally be dependent on

the nature and phenotypic expression of the specific gen-

otypic modification made, along with the rest of the

organism’s phenotype, in relation to these ecological cri-

teria. Different kinds of engineered genes will vary in

the degree and nature of their impact on the phenotype

of the engineered organism. Also, engineered genes may

vary in terms of the conditions under which they will be

expressed. For example, if a gene is only induced to be

expressed under specialized conditions, then its pheno-

typic impact will be negligible the rest of the time.

It has been well established from studies of induced

mutations that most dramatic phenotypic changes in an

organism result in reduced fitness (2, 14). Engineered

genes that affect the growth, resource allocation, or some

other aspect of an organism may convey added economic

value, but may also produce a maladapted plant that is

unlikely to survive outside of cultivation. On the other

hand. genes that have relatively little effect on the overall

phenotype, such as genes induced only on certain oc-

casions for disease or pest resistance, might confer a real

fitness advantage, even in natural populations. It is gen-

erally assumed that genes for disease resistance present

a physiological cost that reduces fitness in the absence

of disease, although the importance of that cost has been

challenged (7 I ). However, sometimes if the gene is not

expressed, such costs go down, contributing to its po-

tential long-term persistence.

Assessments of the risks of introduced organisms be-

coming pests must take these factors into account as well

as others. For example, introducing a character into an

organism whose ecological properties are otherwise well-

known, or taking a particular property associated with

terrestrial bacteria and introducing it into another terres-

trial bacterium, enables some prediction of how that char-

acter might respond in that target ecological setting. Thus,

in assessing the potential risk associated with a particular

phenotypic modification, the target environment should

be considered.

If a species became established as a pest, existing

communities would be disrupted; fortunately, the like-

lihood of either a genetically modified plant or a micro-

organism becoming a pest is relatively low. Most crop

varieties produced through conventional means do not

become pests (6). Experiments to date indicate that ge-

netically modified microorganisms in some cases may

not persist at significant levels (3) and therefore may

often be unlikely to proliferate and disrupt existing com

munities composed of vast numbers and numerous spe-

cies of microorganisms (19. 86). So for all organisms

modified in any way. emphases in risk assessment of

microorganisms should be placed on the specific product.

Until more is known about consequences of large-scale

use of genetically modified plants. a deliberate approach

rather than complacency seems warranted.

Gene Stability

The stability of an engineered gene is important to risk

assessments of planned introductions of recombinant DNA-

modified organisms. A gene that has become a stable

component of the transgenic organism is more predictable

in its function, expression.and possible mobility than

one that has not. one aspect of gene stability is persis-

tence. An engineered gene construct usually consists of

several components,all of which must be present and

intact for the gene to function. In addition to the structural

gene that codes for the desired gene product. a promoter

gene is needed for it to be expressed—to be turned ‘‘on’

or ‘‘off. Such constructs maybe broken apart by natural

genetic recombination. A promoter separated from its .structural gene is useless; the structural gene without the

promoter remains unexpressed.

The stability of a particular gene also may be directly

influenced by the vector used to introduce it into the

engineered organism.Bacterial plasmids or DNA-car-

rying bodies, are potentially the most mobile of the vec-

tors used to insert genes. Plasmids function by inserting

themselves into the bacterial chromosome. carrying an

engineered gene along with them. Insertion sites for such

plasm ids are nonrandom; they are specific sequences that

could be recognized by other plasmids, which may pick

up the inserted gene and carry it along to another organ-

ism. on the other hand, it also is often true that insertion

of a particular plasmid will immunize the cell against

insertion of similar plasmids.

Genes directly inserted into chromosomes are more

stable than genes carried by plasmids. However, chro-

mosomes are complex structures, and the manner in which

particular genes express or recombine is determined by

their relative positions on chromosomes. An engineered

gene inserted in some parts of the chromosome may be

more exposed to recombination than genes on other parts

of the chromosome. The relative stability of an engi-

neered gene in a plant species can be increased by in-

serting it into portions of chromosomes subject to lower

levels of recombination.To summarize. a gene’s stability depends on the nature of the gene itself and on the means of introducing it into the recipient organism.Either of these can be manipu-lated deliberately to increase stability.Gene Transfer Another appropriate focus for risk asessments of planned introduction of recombinant DNA-modified organisms is the possibility) that novel genes may become incorporated into related wild species. Such transfers, it is argued, might lead to harmful bacteria or weeds with an " improved"characteristic such as resistance to pest attack: this might make them more difficult to control. Three key questions to be considered are: What is the probability that a gene will move from an agricultural organism to wild species’?What can be done to lower the probability? What would be the consequences of such gene transfer on agricultural and natural communities

On the bright side, a number of recently developed techniques exist that can greatly facilitate studies of bac-terial interactions in natural substrates (48), including flow cytometry (a technique that involves the use of laser-activated fluorescence of stained particles) and poly-merase chain reaction (PCR) (65), involving the ampli-fication of a particular gene contained at low concentration in soil to sufficiently high concentrations that it can be detected by standard DNA analysis. PCR can be used to monitor the movements of introduced genes in natural substrates (79). This allows the population dynamics of the engineered organism to be more closely monitored, the transmission of the engineered gene to background organisms to be quantified, and potential risks to be eval-uated. Also, the introduced population can be “tagged’with a specific but nonfunctional DNA sequence such that the growth or decline of that population in the soil can be monitored independently of the engineered gene(s). Actual probabilities of gene transfer of various kinds among microorganisms are still being researched. Al-though differing opinions certainly exist, one school of thought is that the order of magnitude of microorganisms present in the natural community, and the probable fre-quency with which they exchange genes, renders the potential impact of most recombinant genes being trans-ferred relatively low.

For higher organisms. vector-mediated transfer of en-gineered genes is not a major concern. For example, a widely used vector for dicotyledormus plants, Agrobac-terium tumefaciens (crown gall virus) can be readily screened out of transformed organisms before they are released. Furthermore. for many important crop species, notably cereal crops,vectors for gene transfer are not used: rather ballistic incorporation of genetic material into tissue-cultured cells (using ‘“gene guns’ ) is the method currently in development. Using this method there is no chance of vector-mediated gene transfer. This leaves gene transfer through hybridization of crops and reproduc-tively compatible (i. e.,closely related) weeds as a possibility.

In higher plants, the main risk associated with gene transfer from transgenics into surrounding populations is. in fact, that of hybridization. Modified genes poten-tially could be transferred from transgenic plants and incorporated into the genome of a weedy species through introgressive hybridization, whereby genes are transmit-ted through pollen in sexual reproduction. However, working against this possibility are limited viaility of pollen, distance and physical barriers to pollination. ge-netic dissimilarities (i. e.,incompatible fertilization pro-cesses), and failure to produce viable, fertile offspring. Most crops grown on a large scale in temperate re-gions, such as corn and wheat, are grown outside of their geographic region of origin; consequently there typically are no related weed species growing in association with them. Therefore, for most crop species in the United States, pollen-mediated transfer of modified genesis only of theoretical concern. However, there are several im-portant crop species for which closely related weed spe-cies have become introduced. Specifically. many crops in the family Brassicaceae. such as canola (oil-seed rape) and radishes, have co-occurring weedy relatives (21). Sunflowers had their center of origin in the United States and have related weedy species here as well.

Most major crop species originated in what arnow regarded as developing countries. For example, corn was developed in Central America, wheat was first cultivated in the Middle East, rice in Southeast Asia. and potatoes in South America (77). Consequently, introduction of genetically engineered crops into such regions should be handled with particular attention to the probability of gene transfer into background populations.

Additional concern focuses on the potential impact of introduced genes on the genetic structure of natural pop-ulations of plants related to important crop species. These populations represent the genetic heritage of the crop and are an irreplaceable reservoir of diverse genetic variation that may be needed in future development of the crop (8). If, because of a novel gene effect, one strain or lineage became a super weed it might outcompete and therefore eliminate other lineages; genetic variation potentially useful for crop development could be lost. More generally, bio-diversity is intrinsically valued by many ( 12).

Pollen-mediated transfer of novel genes from crops into related weeds might also result in weeds becoming similar to the crop species. A number of well-known instances exist where selection pressures exerted by tra-ditional agronomic practices have caused weedy species to evolve to resemble the crop species. Such weeds can-not be eliminated by standard control practices (4). Thus, weeds are capable of a wide range of genetic adaptation even without the introduction of novel genes. Although there could clearly be problems associated with potential gene transfer from transgenic plants into weed popula-tions. there is also a large experience base in agricultural and natural populations on which to draw for predictions in this area.

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雅思大作文环境保护集团文件发布号：（9816-UATWW-MWUB-WUNN-INNUL-DQQTY-

环境保护类 一．环境问题 1.气候变化、全球变暖：climate change global warming 2.空气污染、垃圾增多：air pollution increase of rubbish / garbage 3.能源危机、缺水、森林砍伐：energy crisis water shortage deforestation 4.自然灾害、酸雨、沙尘暴、干旱、水灾： natural disasters acid rain stand storm drought flood 二．原因（根本） 人口增长工业发展人类活动Population growth industrial development long-term human activities 三．方法 1.世界方面: 全球合作达成共识制定环境保护国际准 Global cooperation reach agreement set international standard s for 2.政府方面： 环保政策鼓励低碳经济发展

Work out / make / enact environmental policy encourage low carbon economy 3.企业方面： 推出环保产品引领大众绿色消费习惯 Promote environmental products / production lead green consuming habits Environmental-friendly 4.个人: 提升环保意识倡导低碳生活方式Improve public’s green awareness encourage / advocate low carbon life style Raise Arouse Increase 5．科技： 开发可再生清洁能源投资开发节能科技 Exploit renewable clean energy invest in energy-saving technologies 你认为环保一定是政府或企业的责任吗? 范文

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雅思大作文环境保护

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雅思写作7分官方评分标准解析

Some experts believe that it is better for children to begin learning a foreign language at primary school rather than secondary school. Do the advantages of this outweigh the disadvantages? Foreign languages have increasingly gained popularity among students these years, given that the world is shrinking and each country now has a more frequent contact with the outside world. Many people[c1]argue that children should begin learning a foreign language at elementary school, instead of waiting until [c2] they enter secondary school. There are several reasons for this. Firstly, despite the fact that parents do not want to put too much pressure on their children, they also do not want them to lose at the starting line. This means, if the kids start to learn a foreign language early, their parents are relieved from the thought that their kids will have to catch up later on, which is true to some extent. On the other hand, it is scientifically proved that children tend to learn a language faster before the age of 12. As far as I know, my friends who started to learn English when they were six or seven now have a much more satisfactory English level than those who started at12 or 13. So it is wise to have foreign language course in primary school curriculum. Additionally, learning a foreign language at an earlier age can lay children a solid foundation for future studying.Rather than just learning a language itself, children learn a lot more about the learning methods. As a result, when they enter secondary school, they can explore more languages and enrich their knowledge by extensive readings.

保护环境的英语作文10篇完整版

《保护环境的英语作文》 保护环境的英语作文（一）： Now， our side of the car constant more up， the environment also increasingly worse! That the air around us there are many harmful substances。 Therefore， we want to Sue around things start to do。 For example， we can go to school by bike or walk， it can exercise。 If you have time can use less elevator， many climb stairs。 We can not only physical exercise， but also to protect our environment。 此刻，我们身边的汽车不断的多了起来，环境也越来越糟糕！以至于我们周围的空气有很多有害物质。所以，我们要苏身边的小事做起。比如，我们能够骑自行车上学或者步行，这样还能够锻炼身体。有时光的话能够少用电梯，多爬楼梯。我们不仅仅能锻炼身体，也能保护我们的环境。 保护环境的英语作文（二）： There are still many problems of environmental protection in recent years。 One of the most serious problems is the serious pollution of air，water and soil。 the polluted air does great harm to peoples health。 The polluted water causes diseases and death。 What is more， vegetation had been greatly reduced with the rapid growth of modern cities。 To protect the environment， governments of many countries have done a lot。 Legislative steps have been introduced to control air pollution，to protect the forest and sea resources and to stop any environmental pollution。 Therefore， governments are playing the most important role in the environmental protection today。 In my opinion， to protect environment， the government must take even more concrete measures。 First， it should let people fully realize the importance of environmental protection through education。 Second， much more efforts should be made to put the population planning policy into practice， because more people means more people means more pollution。Finally，those who destroy the environment intentionally should be severely punished。 We should let them know that destroying environment means destroying mankind themselves。 保护环境 目前环保还存在着许多问题。最严重的问题就是空气、水和土壤的严重污染。污染的空气对人类的健康十分有害。污染的水引起疼病，造成死亡。更有甚者，随着现代社会的迅速扩建，植被大大的减少。

环境类--雅思范文Environmental-problems

环境类--雅思范文 1. Environmental problems are too big for individual countries and individual people to address. We have reached the stage where the only way to protect the environment is to address it at an international level. To what extent do you agree or disagree? Nowadays, environmental problem has been the focus of a debate. Among these related problems, the issue of international efforts in combating environmental pollution is an extremely acute one. It is firmly believed that the benefits of large scale groups have remarkable impact on our society, especially on environment and animals aspects. First and foremost, environmental pollution is a problem that beyond national borders. This is because the destructive effects that it brought cannot be solved without the co-operation of all the countries in the world. A case in point is the occurrence of extreme weather condition, like La Nina in terms of heavy flood and drought; in addition to, global warming, acid rain that happen in many parts of the world. Due to its chronic and perpetual environment effect, it is necessary for the countries on the earth to form an association and join hands to protect our land from further environment deterioration. Another reason is that it is urgent to set up international alliance to prevent the shrinking space of animals' habitat. It is due to the fact that, local ecosystem has gradually been destroyed all over the world. For instance, Mountain Gorilla has loss its natural habitat to human beings, for being continually developing housing estate deep into the forest. Thus, the breaking down of ecosystem has pushed species closer to the brink of extinction. Hence, it is cleared that the prevention of declining the numbers of rare animals need the joint efforts from many administrative agencies in the world. In conclusion, I totally agree with the idea that international collaboration and cooperation in tackling environmental pollution is positively affects the sustainable development on earth. It is expected that environmental preservation can be greatly enhanced through cultivating environmental awareness around the people in every countries in the foreseeable future.

2016.12.17雅思真题大作文7分范文

Task：Some people think getting old is entirely bad. However, others think that life of the elderly in modern world is much easier than in the past. Discuss both views and give your own opinion. 思路解析： 2016年雅思收官之战的作文来了一道新题，问当今社会老年人的生活是不是很 糟糕?说是新题，因为本题以前从未原题出现过，但关于年龄的话题却不缺少。 比如2010年7月10日“年轻人是否适合担任政府要职”，2012年3月10日“老 龄化现象的原因及解决方法”，2012年3月31日“年轻人和老年人谁的价值更 高?”，2013年6月8日“政府是否应该对老年人养老提供财政支持?”，2015 年1月1日“年轻人当领导，行不行?”，2015年4月11日“老年人与年轻人 争夺工作职位，怎么办?”等等。 本题需要论证的对立观点是：年老很糟糕 vs. 当今社会年老没有那么糟糕。那 么，变老有哪些坏处呢?首先，当然是身体条件没有以前好了，甚至可能出现多 种疾病(物质层面);其次，不工作了，与人的联系少了，心里可能会感觉孤单， 甚至感觉没有价值了(精神层面);最后，变老后对社会的依赖程度更高，给社会 增加了压力(社会层面)。那么，这些问题在当今社会是不是得到了解决呢?首先， 医疗条件的改善有助于保持老年人的身体状况;互联网的出现有助于缓解老年人 的心理孤单问题;物质水平的提高也降低了老年人给社会造成的压力。如此观之， 现代社会老年人的生活的确容易多了，但我的观点是：外部条件只是改善老年人 生活的一个方面，最重要的还是老年人自己要积极调整心态，努力适应退休后的 生活，从而过一个更幸福更祥和的晚年。 Sample answer： Getting old is a natural process that nobody really likes. When you reach a certain age, your physical conditions will inevitably deteriorate, and you may suffer from various kinds of diseases. When you retire, you will feel isolated because your previous work contacts may be all gone, then you may feel useless to the world. Furthermore, when you get too old, you’ ll have to rely heavily on the support from others, either physically or emotionally, and your life will become a great pressure to your family and the whole society as well. For all these bad things about getting old, many people argue that the life of the elderly today is much easier than in the past. In the first place, medical advances nowadays have made it possible for the old people to stay sound and healthy for quite a long while even after they retire. Diseases such as diabetes, hypertension and heart attack which might have

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英语作文范文 雅思写作高分范文：环境保护 Environmental hazards are often too great for particular countries or individuals to tackle. We have arrived at a point in time where the only way to lessen environmental problems is at an international level. Environmental problems have reached such proportions that people feel international organizations must be set up to intervene in world affairs to resolve these problems. Whether this will resolve the problem is very unlikely as international organizations are just an extension of human behavior. That is, if human conflicts cannot be resolved at home, then they are unlikely to be resolved at the international level. Nevertheless, international organizations do attract attention to the growing problem of aims of the international community to resolve the issue of environmental pollution and support their cause, I do not believe it is the best or only way to protect the environment; in fact, it is only a small part of what is needed in a global initiative.

雅思小作文7分万能模板整合

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8增加：Increase / raise / rise / go up/ soar/ascend/ mount/ climb 9减少：Decrease / grow down / drop / fall/ reduce/descend/ shrink to/decline 10稳定：Remain stable / stabilize / level off/ remainunchanged 雅思小作文7分万能模板 1 It can be seen from the table that 由表格我们可以看出 2 The table shows the changes in thenumber of… over theperiod from…to… 该表格展示了从…到…数据的变化 3 The table provides some data of 该表格提供了有关…的数据 4 As can be seen clearly from thetable, 从表格中我们可以清楚地看出， 5 As can be seen from the table,great changes have taken place in...

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保护环境的英语作文10篇 保护环境的英语作文保护环境的英语作文（一）： Now , oursideofthecarconstantmoreup , theenvironmentalsoincreasinglyworse!Thattheairaroun dustherearemanyharmfulsubstances 。Therefore , wewanttoSuearoundthingsstarttodo。Forexa mple, weca n gotoscho ol bybikeo rwa lk, itc anex ercis e。Ify ouha vetime can useless el evator, m a nyclimbst airs we can noton lyphy sicalexer c ise, buta Is otoprot ect ourenv iron ment o 此刻，我们身边的汽车不断的多了起来，环境也越来越糟糕！以至于我们周围的空气有很多有害物质。所以，我们要苏身边的小事做起。比如，我们能够骑自行车上学或者步行，这样还能够锻炼身体。有时光的话能够少用电梯，多爬楼梯。我们不仅仅能锻炼身体，也能保护我们的环境。 保护环境的英语作文（二）： Th erearesti 1 lmanypro bl emsofen vir onment alpr otect o neofthe mo stseriou s problemsi stheseriou ionin rece ntyear s o spollution ofair, wat e randsoil。t hepollu ted airdoe sgre athar mtope ople，sheal th。Thepoll ut edwaterc a usesdisea sesanddeat h。whatismo re, vegeta, t ionhadbe en greatly red ucedwi thth erapi dgrow thof modern cit ies。 T o protectth eenvironme nt, governm entsofman y countrie

雅思大作文5分与7分范文各项指数对比分析

雅思大作文5分与7分范文各项指数对比分析 Let’s compare two answers to a question.The topic is as follows: International tourism has brought enormous benefit to many places. At the same time, there is concern about its impact on local inhabitants and the environment. Do the advantages of international tourism outweigh the disadvantages? A Poor Essay – The following is a band 5 essay. International tourism has brought enormous benefit to many places. At the same time, there is concern about its impact on local inhabitants and the environment. Do the disadvantages of international tourism outweigh the advantages? In my opinion advantages outweight the disadvantages. Firstly, many countries like Egypt or Tailand live from tourism Lots of people work there as a seilsmens or tourist guides. These countries without support of tourists wouldn’t be able to funtcion properly. Secondly, in countries visited by tourists are plenty of places where people just can’t pass because of rare animals or plant s. Another thing is that people like traveling and seeing new exotic places. They like lie on the beach or swim in ocean. Furthermore, tourism is now more growing industry highering tousands of people. There are makeing new places to work and to have fun. But on the other hand, people often for get that they aren’t the only beings on the planet. Many tourists are living garbage just anywhere. Some of them wan’t an exotic souvenir so they pay for illegal things like dea d or live animals or some sculpture. To sum up I think international traveling is a good thing but people must realise that there is something else besides them. They need to know that flora and fauna needs to be protected. People have to enjoy their holidays but alsow protect environment. Below is an analysis of this essay. Task Response The essay question has been copied and used as the introduction (paragraph 1). Once these 34 words are taken off the word count, the response is underlength at 194 words and so loses marks. Nevertheless, the topic is addressed and a relevant position is expressed, although there are patches – as in the third paragraph – where the development is unclear. Other ideas are more relevant but are sometimes insufficiently developed.

雅思7分作文集

Popular events like the football world cup and other international sporting occasions are essential in easing international tensions and releasing patriotic emotions in a safe way. To what extent do you agree or disagree with this opinion? The World Cup football match and the Olympics are held worldwide with great national support and expectations. As a fan of those competitions, I agree with the idea that sporting events can be necessary for international relations and national unity. In this essay, I will think about the effects of these popular sporting events. First of all, the World Cup, Olympics and other international games work for easing tensions among different nations. For example, South and North Korea have football games regularly which give two nations a chance to understand each other deeply. In the mid 1990s, a hundreds of North Korean supporters came to South Korea with the footballers and they were very excited during the sporting events. Even if it sounds ridiculous, many South Koreans were quite surprised at that moment when North Koreans shouted and cried during the match. We all realized that they were very normal sports fans even though they were occasionally very secretive. Through the sports, two divided nations could reduce their political and ideological tensions and could feel the patriotic unity. On the other hand, some sports matches can make international relations worse. For instance, football or baseball games between Korea and Japan are always big matches in two countries where full of tensions overflow. Sometimes, after the matches, the two rivals blame each other and their patriotic emotions explode in an aggressive way. Even much worse scenario is that the troubles caused by losing games affect the players directly. As far as I know, a couple of Korean players in Japan are suffered from invisible discrimination after the match between two countries. In conclusion, I think that international sporting occasions can be one of the good ways to ease tensions or to release patriotism safely. However, I believe that games can not be the fundamental ways for the sound patriotism or peaceful international relations Some people say that the Internet is making the world smaller by bringing people together. To what extent do you agree that the internet is making it easier for people to communicate with one another? In today?s world _ due to the advancement of technology new inventions are coming into existence. It is a certainty that ?necessity is a mother of invention?. _ Internet is just like a wonder box, which contains every type of information. Besides it has also proved as a very important tool to connect people with each other. In today?s modernized era nobody has sufficient time to write letters to their loved ones. Moreover it also takes longer to send or receive any information. But through an internet it is an easiest way to send massages to our loved ones. Either it can be in the form of an e- mail or by text messages from internet to cell phones. We can send and receive messages straight way. In other hand today?s youth generation mostly prefer to do chatting on () internet. Through this chatting we can write messages and straight way can get their reply. Moreover voice chatting is going to be very popular day-by-day.