ES&T
GUEST EDITORIAL Disinfection and indicator organisms Literally, the word "disinfection" means to "free from infection." As used with processing of food, water, and sludges, disinfection is the means by which potentially harmful organisms are inactivated, but it does not necessarily imply the condition of being free from the capability to cause infection. When used in this way, the objective of disinfection is to reduce the number of pathogenic organisms present, or presumed to be present, to levels at which the risk associated with use of the food or water or the dispersal of the waste to the environment is reasonable and acceptable. Regarding threats to public health, the concepts of "reasonableness" and "acceptability" as applied to risk involve a spectrum of interactions ranging from those governed only by natural law through those that regulate relationships among people. The boundaries and limits of the latter are defined by legal procedures when the issues in question become sufficiently important to justify the costs associated with litigation. Linkages between sanitation and public health, and between gastrointestinal disease and water contaminated with fecal matter, and the associative relationship between the presence of coliform organisms in water and its potential contamination were all firmly established at the beginning of this century. Advances since then in microbiology and in statistical analysis have refined techniques for counting coliforms in water and wastewater, but have accomplished little in establishing a greater degree of significance to the count. Surrogate characteristics, such as numbers of coliform organisms, serve a useful purpose. However, care must be exercised in reaching conclusions based on false inferences relating the significant parameter and the surrogate to the hypothesis being tested. We must remind ourselves periodically of the 1963 statement of the Public Health Activities Committee of the American Society of Civil Engineers, namely that " . . . there is little if any proof that disease hazards are directly associated with large numbers of coliforms." 0013-936X/84/0916-0231A$01.50/0
Coliform organisms are not the causative agents for waterborne infections. Neither the ratio of the numbers of coliforms to pathogens nor their comparative resistance to disinfection processes is known. Since the inactivation of coliforms may be disproportional to inactivation of pathogens, it is possible that contacts subsequent to "disinfection" between sources of contamination and water supplies would fail to be detected by determination of coliforms' presence. Thus, "disinfection" processes may actually increase the risk associated with dispersal of the "disinfected" wastes by destruction of evidence regarding their origin. Since the degree of proportionality between coliform organisms and pathogens is not known, nor is their relative resistance to "disinfection," the effect of disinfecting procedures on numbers of coliforms is a measure neither of actual nor of relative disinfection. It may even be desirable to reintroduce coliform organisms or some other surrogate into the treated wastes to reestablish the degree of protection of public water supplies that was formerly afforded by their presence. Associative relationships between indicator organisms and what they indicate must continue to be subjected to scientific inquiry. The fact that such research is difficult and expensive is real. However, the difficulty and expense of conducting significant research are not acceptable reasons for acquiring and using substitute information of weak, if any, scientific validity just because that information is easy to obtain.
© 1984 American Chemical Society
Edward H. Bryan, PhD is program director/or environmental and water quality engineering in the National Science Foundation Engineering Directorate's Division of Civil and Environmental Engineering. The opinions expressed in this editorial are his own and do not represent an official position of the National Science Foundation or any other federal agency. Environ. Sci. Technol.. Vol. 18, No. 8, 1984
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