A general review of chemical sterilization in space research.
The unsolved problems in the biology and the chemistry of chemical sterilization are legion. This discussion of them emphasizes some interesting areas for useful research. Studies in molecular biology and cancer chemotherapy have produced information which has important implications in chemical sterilization, particularly with the alkylating and the oxidizing agents. Many of these problems must be solved soon if chemical sterilization is to play the role it should in space research by providing means for effectively controlling the rate and extent of mingling of the forms of terrestrial life with those of extraterrestrial life. In space research in the United States, recent work on chemical sterilization has laid heavy emphasis on the identification and exploration of principles of engineering sciences which control sterilization effectiveness. These principles are reviewed and their significance in chemical sterilization is discussed in terms of the engineering factors involved. Among these factors are: consequence of sterilant polymerization or reaction with the object to be sterilized; criteria for chemical sterilization process effectiveness; depletion of the concentration of the sterilant by evaporation or chemical reaction, including polymerization; obstacles to the diffusion or convection of the sterilizing chemical to the immediate vicinity of the microorganisms to be destroyed; protection of the microorganisms from direct contact with the sterilant; phase behavior of the sterilant in the environment of the sterilization process; presence of water or water vapor; the nature, sources and numbers of microorganisms which survive standard chemical sterilization processes; and the length of exposure required to sterilize at each temperature. The significance of chemical sterilization to space science has been well reviewed at the previous COSPAR symposia. Because several thorough reviews of the empirical knowledge concerning the effects of chemical agents on microorganisms have been published recently, this information is not discussed again for chemical sterilants other than the alkylating agents and several of the oxidizing agents. This lack of emphasis indicates only that these other chemicals have not been applied to a large extent in space research to date and that discussions of their sterilizing properties are readily available in other recent reviews. In the future, interest in many of these other chemical sterilants will increase as the variety of devices to be sterilized and the variety of functions which sterilized devices are expected to perform increase.