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National Research Council (US) Committee on Scientific Evaluation of the Introduction of Genetically Modified Microorganisms and Plants into the Environment. Field Testing Genetically Modified Organisms: Framework for Decisions. Washington (DC): National Academies Press (US); 1989.
Field Testing Genetically Modified Organisms: Framework for Decisions.
Show detailsIn late 1988, the Biotechnology Science Coordinating Committee (BSCC), representing the U.S. Department of Agriculture, Environmental Protection Agency, National Institutes of Health, National Science Foundation, and Food and Drug Administration, asked the National Academy of Sciences-National Research Council (NRC) to evaluate scientific information pertinent to making decisions about the introduction of genetically modified microorganisms and plants into the environment. The NRC was asked to use this analysis to identify criteria for defining risk categories and to recommend ways to assess the potential risks associated with introducing these modified organisms. A steering committee was formed under the Board on Biology of the NRC's Commission on Life Sciences to prepare a report responding to the BSCC request. The steering committee, with overall responsibility for preparing the report, was augmented by two subcommittees of experts, one for microorganisms and the other for plants.
The committee considered the foci of its work to be:
- plants and microorganisms, but not animals;
- introductions under field-test conditions typical of those currently being proposed, but not large-scale commercial applications and the scientific, economic, ethical, and societal issues associated with large-scale applications;
- environmental effects excluding human health effects;
- scientific issues primarily, not regulatory policy matters;
- field-test conditions only in the conterminous United States in recognition that domesticated and wild species are different in other countries and areas of the world;
- general procedures for determining categories of risk for introductions, not recommendations for specific cases.
The steering committee and subcommittees adopted the fundamental principle enunciated in the document “Introduction of Recombinant DNA-Engineered Organisms into the Environment: Key Issues” (NAS, 1987) that safety assessment of a recombinant DNA-modified organism “should be based on the nature of the organism and the environment into which it will be introduced, not on the method by which it was modified.” The principle that evaluation should be of the product and not the process by which the product is obtained is reemphasized in Chapter 2 of this report. The discussion also points out that although genetic modification by molecular methods may be more powerful and capable of producing a wider range of phenotypes, “no conceptual distinction exists between genetic modification of plants and microorganisms by classical methods or by molecular methods that modify DNA and transfer genes.”
The section of the report on plants (Chapter 3, Chapter 4, Chapter 5 and Chapter 6) discusses the relevant biological properties of genetically modified plants. It also describes past experience with genetic modification and introductions of plants modified by classical and by molecular genetic methods. The major environmental issue of potential weediness receives special attention in the report.
The section of the report on microorganisms (Chapter 7, Chapter 8, Chapter 9, Chapter 10 and Chapter 11) discusses the properties of the genetic modification, phenotypic properties of the source organism and its genetically modified derivatives, and properties of the environment with respect to the organisms that may be released into it.
Investigators modifying microorganisms for environmental introduction should assess the influence of genetic alteration on the organism's phenotype and the mobility of the altered trait. It is highly unlikely that moving one or a few genes from a known pathogen to an unrelated nonpathogen will confer pathogenicity on the recipient. If the recipient is itself a pathogen, increased virulence for particular hosts may result. If modifications of this latter type are contemplated, special attention must be paid to them. In some cases persistence is not desirable and uncertainty exists about the microorganism's effects on the immediate environment. When assessing risk in these cases, the most relevant phenotypic properties relate to the persistence of the microorganism and its genetic modification. Evaluation of phenotypic properties raises questions about the fitness of the genetically modified microorganism, the potential for gene transfer from the introduced microorganism, the tolerance of the introduced microorganism to physicochemical stresses, its competitiveness, the range of substrates available to it and, if applicable, the pathogenicity, virulence, and host range of the introduced microorganism.
The report discusses the long history of utility and safety in the use of plants and microorganisms. Society has benefited greatly from the use of genetically modified microorganisms and plants, and field testing is essential if we are to increase our knowledge about the relative safety or risk of large-scale use of genetically modified organisms and to determine the potential utility of the modified organisms.
Other major scientific conclusions are as follows:
PLANTS
- 1.
Plants modified by classical genetic methods are judged safe for field testing on the basis of experience with hundreds of millions of genotypes field-tested over decades. They are, in the terms used by the plant subcommittee, “manageable by accepted standards.” The committee emphasizes that the current means for making decisions about the introductions of classically bred plants are entirely appropriate and no additional oversight is needed or suggested in this report.
- 2.
Crops modified by molecular and cellular methods should pose risks no different from those modified by classical genetic methods for similar traits. As the molecular methods are more specific, users of these methods will be more certain about the traits they introduce into the plants. Traits that are unfamiliar in a specific plant will require careful evaluation in small-scale field tests where plants exhibiting undesirable phenotypes can be destroyed.
- 3.
At this time, the potential for enhanced weediness is the major environmental risk perceived for introductions of genetically modified plants. The likelihood of enhanced weediness is low for genetically modified, highly domesticated crop plants, on the basis of our knowledge of their morphology, reproductive systems, growth requirements, and unsuitability for self-perpetuation without human intervention.
- 4.
Confinement is the primary condition for ensuring safety of field introductions of classically modified plants.
- 5.
Depending on the crop species, proven confinement options include biological, chemical, physical, spatial, environmental, and temporal isolation, as well as size of field plot.
- 6.
Plants grown within field confinement for experimental purposes rarely, if ever, escape to cause problems in the natural ecosystem.
- 7.
Established confinement options are as applicable to field introductions of plants modified by molecular and cellular methods as to introductions of plants modified by classical genetic methods.
MICROORGANISMS
- 1.
The precision of many of the molecular methods allows scientists to make genetic modifications in microbial strains that can be fully characterized, in some cases to the determination of specific alterations of bases in the DNA nucleotide sequence.
- 2.
The molecular methods have great power because they enable scientists to isolate genes and to transfer them across biological barriers.
- 3.
Although field experience provides considerable information about some microorganisms—for example, rhizobia, mycorrhizae, and many plant pathogens and biocontrol agents—in general, information regarding the ecology of microorganisms and experience with planned environmental introductions of genetically modified microorganisms is limited compared with that regarding plants. However, no adverse effects have developed from introductions of genetically modified microorganisms. Ecological uncertainties can be addressed scientifically with respect to genetic and phenotypic characterization of the microorganisms as well as by consideration of environmental attributes such as nutrient availability. Field tests of genetically modified organisms can go forward when sufficient information exists to permit evaluation of the relative safety of the test.
- .4.
The likelihood of possible adverse effects can be minimized or eliminated by appropriate measures to confine the introduced microorganism to the target environment, for example, by introducing “suicide” genes, as they become practicable, into the organisms.
FRAMEWORK
The committee developed a framework for the evaluation of risk based on criteria that are summarized below and detailed in Chapter 6 and Chapter 11.
- Are we familiar with the properties of the organism and the environment into which it may be introduced?
- Can we confine or control the organism effectively?
- What are the probable effects on the environment should the introduced organism or a genetic trait persist longer than intended or spread to nontarget environments?
When the familiarity standard for a plant or microorganism has been satisfied such that reasonable assurance exists that the organism and the other conditions of an introduction are essentially similar to known introductions, and when these have proven to present negligible risk, the introduction is assumed to be suitable for field testing according to established practice.
The familiarity criterion is central to the suggested framework of evaluation. Its use permits decision-makers to draw on past experience with the introduction of plants and microorganisms into the environment, and it provides future flexibility. As field tests are performed, information will continue to accumulate about the organisms, their phenotypic expression, and their interactions with the environment. Eventually, as our knowledge increases, entire classes of introductions may become familiar enough to require minimal oversight.
Familiar does not necessarily mean safe. Rather, to be familiar with the elements of an introduction means to have enough information to be able to judge the introduction's safety or risk.
When knowledge of the type of modification, the species being modified, or the target environment is insufficient to meet the familiarity criteria, the proposed introduction must be evaluated with respect to the ability to confine or control the introduced organism and to the potential effects of a failure to confine or control it. The results of these latter evaluations will define the relative safety or risk of a proposed introduction.
The frameworks for microorganisms and plants differ in nomenclature and in emphasis on particular issues, mainly because of differences in life cycles, mechanisms of gene transfer, dispersal and containment or control procedures, persistence, and environmental factors. Fewer proposed field tests of microorganisms than plants may meet the familiarity criterion because the data base, from a history of planned introductions, is more limited at this time. Means to confine plants are well established and can be relatively simple, whereas means to control microorganisms appear to be more difficult. As a consequence, the subcommittee on microbiology suggests in its framework a close link between considerations of control and possible effects. The plant subcommittee's framework shows a distinct separation between considerations of confinement and of environmental effects.
We believe that our evaluation of the scientific issues and our proposed frameworks provide the responsible government agencies with the foundation for a flexible, scientifically based, decision-making process. Use of the frameworks for evaluation of field tests permits the classification of an introduced organism into a risk category.
- Executive Summary - Field Testing Genetically Modified OrganismsExecutive Summary - Field Testing Genetically Modified Organisms
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