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CHAPTER 24 'BACK CONTAMINATION" AND QUARANTINE PROBLEMS AND PERSPECTIVES A. H. BROWN The possibility and consequences of transferring to the Earth organisms that are indigenous to another planet or to the Earth's Moon have not been a focal point of discussion by this Study. Nevertheless, the participants have been variously concerned about such a contingency. If exotic life forms are introduced into our own biosphere, would they survive, propagate, infect terrestrial organisms, or bring harm directly or indirectly to our ecosphere? If there is a real danger of this so-called "back contamination" we should evaluate the seriousness of the threat and assess the means we ought to em- ploy in our own protection. This general topic was the subject of a two-day conference on the Potential Hazards of Back Contamination which was held during the period of this Study but drew on specialists outside the ranks of the regular Study participants. The report of the conference on Potential Hazards of Back Contamination from the Planets (Space Science Board, 19 Feb. 1965) should be consulted for more detailed arguments, but the conclusions are summarized here as they have some bearing on the general topic of the Summer Study. The problem is not one of great urgency in the case of Martian round trip missions, as they will not be feasible for one or two decades. In the case of lunar missions, whatever risk may be involved is of immediate concern. 443

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444 MARTIAN LANDINGS: MANNED The existence of life on the Moon or on some planets cannot rationally be precluded. At present it seems quite impossible to estimate reliably the probability of life existing on any of several possible sites (the Moon, the Venus cloud layer, the Martian surface, possibly others). Thus some chance, however small, of back contamination must be presumed. There are various lines of reasoning which argue either for or against the seriousness of back contamination. The danger of direct infection of man with resulting disease manifestations is unlikely but possible. The harmful infection of terrestrial plants or animals other than man is far more likely. The introduction of non-pathogenic organisms seems more probable than that of agents that could cause disease. These might or might not proliferate but, if they should do so, they might bring about severely adverse effects on our environment by any of several mechanisms. Again, the chance seems remote but the possibility exists, nonetheless. In our ecosystem, where the biota has very great diversity, engendered over billions of years of evolution, clearly, no living agent has brought about a biological catastrophe of such proportions that terrestrial life was eliminated. It is true that many species (and for that matter even entire phyla) have evolved, flourished, then declined and disappeared in the long history of life on this Earth. In a few instances the decline can be ascribed to a specific, harmful, biological agent—either a pathogen, predator, or agent that altered the environment in some critical fashion. By and large, however, organisms have not developed the potency to inflict catastrophic harm on the rest of the biota, perhaps because the harmful has evolved along with the susceptible and evolution has provided for defense as well as for vulnerability. If a truly exotic organism were to be introduced, what are the chances that it would prove harmful? What are the chances that existing defenses would not suffice to keep it in check? What are the chances that its introduction would have disastrous consequences? Patently we have no way to supply precise estimates, but in a qualitative sense we know that an exotic species—if it can be harmful at all—will not likely be checked effectively by defense mechanisms built by evolution into our terrestrial species. Also, if a biological disaster is possible from back contamination, the chances of it becoming of catastrophic proportions seem enormously greater because the causal agent is so foreign to our living world. While the risks cannot be calculated, concern is based not on irrational fear of the unknown, but on appreciation of how very serious the consequences may be. It is this awareness that prevents us from dis- missing the danger as trivial, just because the risk of disaster from back contamination—even though we cannot compute it—must surely be very small. It was the well-considered, unanimous judgment of the participants at the Conference on Potential Hazards of Back Contamination that the

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"Back Contamination" and Quarantine Problems 445 United States should take leadership in the study and implementation of protective measures against back contamination. Specific protective measures would include retention of returned samples behind absolute bacteriological barriers where they should be examined under conditions of rigid biological and chemical isolation. Tests should be made on returned samples to reveal any living components and to de- termine the pathogenicity to plants, animals, and man, of returned sample material. Only after thorough testing should the samples be certified as safe to distribute to other scientific laboratories. The preparation for lunar and planetary roundtrip missions should in- clude the development of techniques for minimizing contamination of astronauts and equipment while on the lunar or planetary surface. Astro- nauts should be trained in procedures to reduce inadvertent transfer of material and the effectiveness of such procedures should be tested on Earth in a "dry run" with non-pathogenic, tracer organisms. Upon return from the mission, spacecraft, astronauts, and all persons who come in contact with them should be received into an isolation en- vironment and remain there for a period of strict quarantine which was recommended provisionally as three weesks in the case of a Martian mis- sion. The spacecraft, suits, and other equipment should not be decon- taminated until study of the returned samples indicate they may be certified as biologically safe. It seems imperative that a continuing committee or other agency be established to develop plans for quarantine, for detailed operational pro- cedures of sample collection, handling, and study, for utilizing the experi- ence of persons and organizations who have carried out relevant research, and to insure that we do our best to reduce the dangers of back con- tamination without impairing unnecessarily the primary operational re- sponsibility of NASA for the exploration of space.

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