ES&T LETTERS Editorial on disinfection Dear Sir: Edward H. Bryan's guest editorial, "Disinfection and indicator organisms," which appeared in the August 1984 issue (p. 231 A) contained a number of statements, which, while they once may have been thought to be correct, have since been overtaken by more persuasive evidence. While there is serious and valid controversy over the necessity and desirability of disinfection of wastewater effluents and, to a lesser degree, drinking waters, I wish to point out some factual inaccuracies so that these mistakes are not perpetuated. Bryan states that "Advances since [the beginning of the twentieth century] 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" (emphasis added). He also asserts the validity of a 1963 statement of a committee of ASCE that " . . . there is little if any proof that disease hazards are directly associated with large numbers of coliforms." In several of recent studies (i), a statistically significant correlation has been shown between components of the coliform group on bathing waters and the incidence of subsequent disease in swimmers in those waters. While other indicator groups have been shown to provide a better index of hazard potential, nevertheless there has been an association observed between disease cases and microbial water quality as measured by coliforms. A currently pending EPA proposal is based on the use of the cited associations for determining the acceptable level of Escherichia coli or enterococci in recreational waters (2). Bryan asserts that "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." In fact, enterotoxigenic strains of E. coli have been known since the 1960s (3), and other members of the fecal or total coliform groups may be opportunistic pathogens. Admittedly, the relative number of coliform and pathogenic or324A
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ganisms is variable, but relative resistance of various indicator microorganisms vis-à-vis various pathogens to disinfection has been extensively, although not completely, characterized and reviewed by a number of workers, including a committee of the National Academy of Sciences (4). Bryan is correct that "'disinfection' processes may actually increase the risk associated with dispersal of the 'disinfected' wastes by destruction of evidence regarding their origin" only in the sense that such disinfection, when using an indicator whose relative abundance and resistance are low relative to pathogens, may lead to a false sense of security regarding the use of the recreational or potable water resource. Absent such a change in patterns of use, any disinfection process, to the degree that it inactivates some pathogens, no matter how few, will lead to some risk reduction. The criticism is not against the concept of disinfection as such, but rather with the particular organisms and standards by which disinfection efficiency is measured. Bryan should be aware of a large body of literature (5) on the use of alternative indicator organisms, particularly for the assessment of disinfection efficiency. Parenthetically, one must note that virtually none of this work, which he appears to deem so important, has received financial support from the National Science Foundation. Environmental engineers have reason to be proud of the reduction in infectious disease that has been achieved, due in part to the disinfection of waters and wastewaters. While these processes may have been employed unnecessarily, one must be careful not to throw the baby out with the bathwater in an attempt to deal with some of the imperfections in disinfection. Charles N. Haas Illinois Institute of Technology Chicago, 111. 60616
References (1) Cabelli, V; Dufour, A. In "Municipal Wastewater Disinfection"; Venus, A. D.; Akin, E. W., Eds.; EPA: Cincinnati, Ohio, 1983. (2) Fed. Regist., May 31, 1984. (3) Sack, R. B. Annu. Rev. Microbiol. 1975, 29, 333-53.
(4) "Disinfection of Drinking Water," report prepared by the Subcommittee on Efficacy of Disinfection of the Safe Drinking Water Committee, Board on Toxicology and Environmental Health Hazards, National Research Council, 1979. (5) Cabelli, V. In "Water Pollution Microbiology"; Mitchell, R., Ed.; Wiley Interscience: New York, N.Y., 1978; Vol. 2.
Edward Bryan replies: Dr. Haas mistakenly interpreted my editorial comments as extolling alternatives to coliforms as indicator organisms and as questioning the value of disinfection for reducing the risk to human health associated with ingestion or body contact with infected water. Neither was my intent. Parallel to his caution that we not throw the baby out with the bathwater, may I suggest we not fail to see the forest for the trees? Transport of terphenyls Dear Sir: The precipitation sampler used in the project whose results were reported in "Evidence for the long-distance transport of polychlorinated terphenyls" (ES&T, August 1984, p. 625) was purchased with funds from U.S. EPA Grant R-805325 to DePaul University. The sampler was loaned to Argonne National Laboratory for this study. Thomas J. Murphy Department of Chemistry DePaul University Chicago, 111. 60604 Incineration research Dear Sir: The outlook entitled "Hazardous waste research" in the July 1984 issue (p. 222A) appears to contain a potentially serious misinterpretation of EPA's incinerator performance data. The problem occurs on p. 223A where it is stated: "Sometimes the total amount of hazardous PIC s can exceed the total of the original POHCs, Trenholm warned." The sentence caught my attention as being misleading because Andrew Trenholm's work for EPA determined instead that sometimes the amount of PICs can exceed the POHCs in the stack, but not in the original waste fed into the incinerator. Stating that PICs exceed POHCs in the waste feed gives the reader an exaggerated view of the
amount of PICs we found. The sentence, therefore, portrays incinerators as if they sometimes actually emit a larger amount of harmful material than they consume, which certainly is not the case. In most if not all units we have tested so far, some 99.99% of the "original" or feed POHCs have been destroyed, and the mass emissions of all PICs in the stack generally total less than 0.01% of the mass of original POHCs fed to the incinerators. Also, five lines above this sentence a figure of 0.07-6.5 s is given for residence time. More correctly, 0.07 should have been 0.17, but this apparent error is not as serious as the PIC item. Finally, on p. 222A, the figure titled "PIC formation" is subtitled "Incineration of 2 , 2 ' , 4 , 4 ' , 5 , 5 ' hexachlorobiphenyl in air." In studies of compound behavior under heat, with the absence of the flame environment that we usually see in large incinerators, we normally refrain from using the term incineration. Instead, we sometimes call the UDRI-type of destruction simply "thermal destruction." Donald A. Oberacker U.S. EPA, IERL Cincinnati, Ohio 45268
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