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Visit the National Academies Press online, the authoritative source for all books from the National Academy of Sciences , the National Academy of Engineering , the Institute of Medicine , and the National Research Council : Download hundreds of free books in PDF Read thousands of books online for free Explore our innovative research tools – try the “Research Dashboard ” now! Sign up to be notified when new books are published Purchase printed books and selected PDF files Thank you for downloading this PDF. If you have comments, questions or just want more information about the books published by the National Academies Press, you may contact our customer service department toll- free at 888-624-8373, visit us online , or send an email to [email protected] . This book plus thousands more are available at http://www.nap.edu . Copyright © National Academy of Sciences. All rights reserved. Unless otherwise indicated, all materials in this PDF File are copyrighted by the National Academy of Sciences. Distribution, posting, or copying is strictly prohibited without written permission of the National Academies Press. Request reprint permission for this book . ISBN: 0-309-55400-4, 948 pages, 6 x 9, (1977) This PDF is available from the National Academies Press at: http://www.nap.edu/catalog/1780.html http://www.nap.edu/catalog/1780.html We ship printed books within 1 business day; personal PDFs are available immediately. Drinking Water and Health, Volume 1 Safe Drinking Water Committee, National Research Council
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  • Visit the National Academies Press online, the authoritative source for all books from the National Academy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National Research Council: • Download hundreds of free books in PDF • Read thousands of books online for free • Explore our innovative research tools – try the “Research Dashboard” now! • Sign up to be notified when new books are published • Purchase printed books and selected PDF files

    Thank you for downloading this PDF. If you have comments, questions or just want more information about the books published by the National Academies Press, you may contact our customer service department toll-free at 888-624-8373, visit us online, or send an email to [email protected]. This book plus thousands more are available at http://www.nap.edu. Copyright © National Academy of Sciences. All rights reserved. Unless otherwise indicated, all materials in this PDF File are copyrighted by the National Academy of Sciences. Distribution, posting, or copying is strictly prohibited without written permission of the National Academies Press. Request reprint permission for this book.

    ISBN: 0-309-55400-4, 948 pages, 6 x 9, (1977)

    This PDF is available from the National Academies Press at:http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

    We ship printed books within 1 business day; personal PDFs are available immediately.

    Drinking Water and Health, Volume 1

    Safe Drinking Water Committee, National Research Council

    http://www.nap.edu/catalog/1780.htmlhttp://www.nap.eduhttp://www.nas.edu/nashttp://www.nae.eduhttp://www.iom.eduhttp://www.nationalacademies.org/nrc/http://lab.nap.edu/nap-cgi/dashboard.cgi?isbn=0309068371&act=dashboardhttp://www.nap.edu/agent.htmlhttp://www.nap.edumailto:[email protected]://www.nap.eduhttp://www.nap.edu/v3/makepage.phtml?val1=reprinthttp://www.nap.edu/catalog/1780.html

  • Drinking Water andHealth

    Safe Drinking Water CommitteeAdvisory Center on Toxicology

    Assembly of Life SciencesNational Research Council

    NATIONAL ACADEMY OF SCIENCESWashington, D.C. 1977

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • NOTICE: The project that is the subject of this report was approved by the Governing Board of theNational Research Council, whose members are drawn from the Councils of the National Academyof Sciences, the National Academy of Engineering, and the Institute of Medicine. The members ofthe Committee responsible for the report were chosen for their special competences and with regardfor appropriate balance.

    This report has been reviewed by a group other than the authors according to proceduresapproved by a Report Review Committee consisting of members of the National Academy of Sci-ences, The National Academy of Engineering and the Institute of Medicine.At the request of and funded by the U.S. Enviornmental Protection Agency Contract no. 68-01-3139

    Library of Congress Catalog Card Number: 77-089284International Standard Book Number: 0-309-02619-9Available fromPrinting and Publishing OfficeNational Academy of Sciences2101 Constitution Ave.Washington, D.C. 20418

    Printed in the United States of AmericaFirst Printing, November 1977Second Printing, July 1980Third Printing, September 1982Fourth Printing, July 1983Fifth Printing, October 1984Sixth Printing, September 1985Seventh Printing, January 1987Eighth Printing, May 1988

    ii

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • Contents

    Preface v

    Historical Note 1

    I Approach to the Study 9

    II Chemical Containmants: Safety and Risk Assessment 19

    III Microbiology of Drinking Water 63

    IV Solid Particles in Suspension 135

    V Inorganic Solutes 205

    VI Organic Solutes 489

    VII Radioactivity in Drinking Water 857

    Appendixes

    A Legislation and Terms of Reference of the Study 905

    B List of Participants 911

    C Executive Summary 917

    CONTENTS iii

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • CONTENTS iv

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • Preface

    This volume presents the findings of a study of the potentially harmfuleffects that impurities in water may have on the health of those who drink it. Thestudy was conducted by the Committee on Safe Drinking Water of the NationalResearch Council, supported by a contract between the Environmental ProtectionAgency and the National Academy of Sciences.

    Several factors combined to place an unusually heavy burden on all thosewho participated in this effort. At the outset, the purpose, scope, and duration ofthe study were defined in the Safe Drinking Water Act of 1974 in such a way asto require the Administrator of the Environmental Protection Agency not only toarrange for the study to be performed, but to make prompt use of the findings asthe scientific basis for revision or ratification of the Interim Primary DrinkingWater Regulations that were promulgated under the Act. These requirements, ofnecessity, imposed a severe restriction on the time available to the participants. Itwas also apparent that the application of modern methods of analysis had greatlyexpanded and diversified our knowledge of the occurrence of trace impurities inwater and was continuing to do so much more rapidly than the rate ofaccumulation of information about their toxicity. This necessitated a careful andlaborious scrutiny of a large and diverse segment of the scientific literature.Furthermore, the central effort of the study, namely, assessment of the long-termbiological effects of ingesting the variety of different materials that are present intrace amounts in drinking water, made severe demands on our ability to apply the

    PREFACE v

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • contemporary knowledge of toxicology and epidemiology to quantitativeestimation of the risks to public health in terms that would be useful in framingregulations. In recognition of these limitations, it was concluded that the intent ofCongress and the possibilities inherent in the body of scientific knowledge onwhich we could draw could best be reconciled in terms of the interpretation of thescope of the study given in Appendix A.

    To carry out the work of the study, the principal subdivisions of the subjectmatter were assigned to subcommittees, each of which was chaired by a memberof the Safe Drinking Water Committee, which, in turn, was responsible for thegeneral direction of the study (see Appendix B). We are most grateful to all thosemembers of the scientific community who served on these committees, meetingas frequently as the task required, and whose written contributions form the basisfor this report.

    It is a pleasure also to express, on behalf of the entire study group, a specialnote of thanks to the staff: Dr. Riley D. Housewright, Mr. J. P. T. Pearman, Dr.Robert Golden, Mrs. Susan Chen, and Mr. Ralph C. Wands, whose informed andtireless efforts ably supported the committees, not only in the planning andconduct of the study, but also by procuring the various bibliographic andconsulting services that proved to be required. In this connection we are gratefulto the International Agency for Research on Cancer for helping to assess thepotential carcinogenicity of organic compounds found in drinking water; and toMs. Libbey Smith, Ms. Judith L. Mullaney, Ms. Florence Carleton, Dr. PenelopeCrisp, and Dr. Lana Skirboll, all of whom assisted in an extensive search of thescientific literature.

    We acknowledge with gratitude the assistance of all those outsideconsultants who supplied information for our consideration, and the help of manymembers of the staff of the Environmental Protection Agency, especially Dr.Edgar A. Jeffrey and his successor, Dr. Joseph Cotruvo, and Dr. Robert Tardiffand Mr. Lee McCabe, who helped to place at our disposal the informationavailable within that agency.

    Organization of meetings and the labor of preparing manuscripts was madeeasier by the dedicated secretarial services of Mrs. Delores Banks, Ms. HelenHarvin, Mrs. Merle Morgan, and Ms. Carol Fisher.

    Last, but not least, we thank the members of the public who took the troubleto submit suggestions for our consideration and expressed to us their views andconcerns at our public meetings.

    GERARD A. ROHLICH, CHAIRMANSAFE DRINKING WATER COMMITTEE

    PREFACE vi

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • vii

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    Health

    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • viii

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • Historical Note

    As noted by Baker (1949), the quest for pure water began in prehistorictimes. Recorded knowledge of water treatment is found in Sanskrit medical loreand in Egyptian inscriptions. Pictures of apparatus to clarify liquids (both waterand wine) have been found on Egyptian walls dating back to the fifteenth centuryB.C. Boiling of water, the use of wick siphons, filtration through porous vessels,and even filtration with sand and gravel, as means to purify water, are methodsthat have been prescribed for thousands of years. In his writings on publichygiene, Hippocrates (460-354 B.C.) directed attention principally to theimportance of water in the maintenance of health, but he also prescribed that rainwater should be boiled and strained. The cloth bag that he recommended forstraining became known in later times as "Hippocrates' sleeve."

    Public water supplies, already developed in ancient times, assumed addedimportance with the progressive increase in urbanization. But though they wereclearly beneficial in distributing water of uniform quality, large numbers ofpeople ran the risk of suffering adverse effects when the water was unsafe todrink.

    The first clear proof that public water supplies could be a source of infectionfor humans was based on careful epidemiological studies of cholera in the city ofLondon by Dr. John Snow in 1854 (Snow, 1855). Although Snow's study of thecontaminated Broad Street pump is the most famous, his definitive workconcerned the spread of cholera through water supplied by the Southwark andVauxhall Company and the

    HISTORICAL NOTE 1

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • Lambeth Company. The former obtained its water from the Thames at Battersea,in the middle of London in an area almost certainly polluted with sewage,whereas the Lambeth Company obtained its water considerably upstream on theThames, above the major sources of pollution. In one particular area served bythese two companies, containing about 300,000 residents, the pipes of bothcompanies were laid in the streets, and houses were connected to one or the othersources of supply. Snow's examination of the statistics of cholera deaths gavestriking results. Those houses served by the Lambeth Company had a lowincidence of cholera, lower than the average for the population of London as awhole, whereas those served by the Southwark and Vauxhall Company had a veryhigh incidence. As the socioeconomic conditions, climate, soil, and all otherfactors were identical for the populations served by the two companies, Snowconcluded that the water supply was transmitting the cholera agent. Snow'sstudy, a classic in the field of epidemiology, is even more impressive when it isrealized that at the time he was working, the germ theory of disease had not yetbeen established.

    During the seventeenth to the early nineteenth centuries, a number ofimprovements in water supply were made, most of them related to improvementsin filtration to remove the turbidity of waters. During this same period, the germtheory of disease became firmly established as a result of research by LouisPasteur, Robert Koch, and others, and in 1884 Koch isolated the causal agent ofcholera, Vibrio cholera.

    Importance of Water FiltrationIn 1892, a study of cholera by Koch in the German cities of Hamburg and

    Altona provided some of the best evidence of the importance of water filtrationfor protection against this disease (Koch, 1894). The cities of Hamburg andAltona both received their drinking water from the Elbe River, but Altona usedfiltration, since its water was taken from the Elbe below the city of Hamburg andhence was more grossly contaminated. Hamburg and Altona are contiguouscities, and in some places the border between the two follows a contorted course.Koch traced the incidence of cholera in the 1892 epidemic through these twocities, with special attention directed to the contiguous areas. In such areas it wasassumed that climate, soil, and other factors would be identical, the principalvariable being the source of water. The results of this study were dear-cut:Altona, even with an inferior water source, had a markedly lower incidence ofcholera than Hamburg. Since by this time it was well established that cholera wascaused by intestinal bacteria excreted in

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  • large numbers in the feces, it was concluded that the role of filtration was toremove the contaminating bacteria from the water.

    In the United States, cholera was not a problem after the mid-nineteenthcentury; the waterborne disease of particular concern was typhoid fever. InEngland, William Budd had shown by the mid-nineteenth century that typhoidfever was a contagious disease, and the causal agent was isolated and identifiedby Eberth in 1880 and Gaffky in 1884 (Wilson and Miles, 1957). Although thecausal agent, now called Salmonella typhi, is transmitted in a variety of ways, oneof the most significant is by drinking water.

    Experiments on water filtration were carried out in the United States duringthe late 1880's and early 1890's, notably by the Massachusetts State Board ofHealth experiment station established in 1887 at the city of Lawrence. At thisstation the treatment of water as well as sewage was considered by aninterdisciplinary group that included engineers, chemists, and biologists. A leaderin this work was W. T. Sedgwick, a professor at the Massachusetts Institute ofTechnology (MIT), and MIT's influence on water-supply research remainedstrong throughout the first quarter of the twentieth century. Much of the historyof this work has been reviewed by Whipple (1921) and in the two editions ofHazen's book (1907, 1914); the technical aspects are discussed and clearlyillustrated by Johnson (1913). One important technological advance that madewater filtration adaptable even to rather turbid sources of water was the use ofchemical-coagulation filtration processes, patented about 1884 by the brothers J.W. and I. S. Hyatt.

    While the Lawerence experiments were going on, an epidemic of typhoidswept through the city, hitting especially hard at those parts that were using theMerrimac River as its water supply. As a result, the city of Lawrence built a sandfilter, and its use led a marked reduction in the typhoid fever incidence. Asreported by Hazen (1907), the death rate from typhoid fever in Lawrence dropped79% when the 5-yr periods before and after the introduction of the filter werecompared. Of additional interest was a reduction in the general death rate (allcauses) of 10%, from 22.4 to 19.9 per 1,000 living.

    Another major series of filtration experiments were made in 1895-1897 atLouisville, Ky., where the source of water was the muddy and polluted OhioRiver. These experiments were successful, and from an engineering point of viewwere of importance because they showed that it was possible to treat sourcewaters of a rather poor quality (the Merrimac River at Lawrence may have beenpolluted, but at least it was a clear water, making filtration rather easier.) Thesuccess of the Louisville experiments and the other studies led to rapidestablishment of filters as a

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  • means of water purification; by 1907 Hazen could list 33 cities in the UnitedStates, some of comparatively large size, which were using mechanical filters,and 13 cities that were using slow sand filters. As discussed by Hazen, filtrationled to an elimination of turbidity and color from the water, and to a removal ofabout 99% of the bacteria present. At that time these conditions were consideredas a standard by which the quality of a treated water should be judged. As Hazenstates: "There is no final reason for such standards. They have been adopted byconsent because they represent a purification that is reasonably satisfactory andthat can be reached at a cost which is not burdensome to those who have to payfor it . . .. There is no evidence that the germs (characteristic of sewage pollution)so left in the water are in any way injurious. Certainly if injurious influence isexercised it is too small to be determined or measured by any methods now at ourdisposal." This last statement is of considerable importance when considered inthe light of the important advance in water purification practice yet to come,chlorination.

    An excellent overview of the relationship between water quality and typhoidfever incidence was published at about this time by Fuertes (1897). He gatheredtyphoid fever statistics for a large number of cities in North America and Europeand grouped the data by type of source water and water treatment.

    Chlorination, The Most Significant Advance in WaterTreatment

    Although a reading of Hazen's 1907 book might lead one to conclude thatexcellent water quality had been well established by filtration, the most importanttechnological advance in water treatment was yet to come. The introduction ofchlorination after 1908 provided a cheap, reproducible method of ensuring thebacteriological quality of water. Chlorination has come down to us today as oneof the major factors ensuring safety of our drinking water.

    Calcium hypochlorite was manufactured industrially for use as a bleachingpowder and was used in paper mills and textile industries. It was a cheapchemical, and hence readily adaptable to use on the large scale necessary fordrinking water. The first practical demonstration in the United States of its use inwater supply was at the filter plant of the Chicago Stock Yards, where it wasintroduced by Johnson in the fall of 1908 (Johnson, 1913).

    The use of chlorination in an urban water supply was introduced in JerseyCity, N.J., in the latter part of 1908. The circumstances surrounding the JerseyCity case are of some interest from a historical point of view and will be brieflyreviewed. Jersey City received its water from a

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  • private company that used a large reservoir at Boonton, an impoundment of theRockaway River. The water was supplied to the city unfiltered, although somesettling took place in the reservoir. Several years before 1908 the city raised thecontention that the water being supplied was not at all times pure and wholesomefor drinking, as was required by the terms of its contract with the privatecompany. At certain times of the year, the water in the reservoir became pollutedas a result of sewage influx from communities on the river above the reservoir.Rather than undergo the expense of a filtration plant, or attempt to control thesewage influx from the various communities, the private company chose tointroduce a chlorination system. The results were dramatic. A marked drop intotal bacterial count was obtained, and at a cost far lower than any otherprocedure. After many months of operation, further testimony before the courtwas held, to determine whether the company was meeting its contract, and thecourt decided that the evidence was favorable to the company. As stated by thecourt examiner: ''I do therefore find and report that this device [chlorination] iscapable of rendering the water delivered to Jersey City pure and wholesome forthe purposes for which it is intended and is effective in removing from the waterthose dangerous germs which were deemed by the decree to possibly exist thereinat certain times.''

    The dramatic effect that chlorination had on water-supply problems is wellillustrated by comparing the first and second editions of Hazen's book (1907 and1914). In the first edition, barely any mention of disinfection is made (merely aremark about ozone being too expensive), but in the second edition Hazen waxesenthusiastic about the advantages of chlorination. As he says, chlorination couldbe used "at a cost so low that it could be used in any public waterworks plantwhere it was required or advantageous . . .. When the advantages to be obtainedby this simple and inexpensive treatment became realized, as a result of thepublicity given by the Jersey City experience, the use of the process extendedwith unprecedented rapidity, until at the present (1914) the greater part of thewater supplied in cities in the United States is treated in this way or by somesubstitute and equivalent method."

    Interestingly from the point of view of the present report, the introduction ofchlorination also changed markedly the established ideas about water-qualitystandards: "The use of methods of disinfection has changed these standardsradically. By their use it has been found possible to remove most of the remainingbacteria so that the water supplied can be as easily and certainly held within one-tenth of one percent of those in the raw water, as it formerly could be held withinone percent . . . . Even today the limit has not been reached. It may be admittedthat the

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  • time will come when a still higher degree of bacterial efficiency will be required.Present conditions do not seem to demand it, but we must expect that in sometime in the future conditions will arise which will make it necessary. Whenadditional purification is required it can be furnished." (Hazen, 1914).

    The importance of Hazen's book is that Hazen was a major consultingengineer for a wide variety of water works, and was very influential inrecommending treatment methods. Chlorination was introduced at about the timethat adequate methods of bacteriological examination of water had developed,permitting an objective evaluation of the efficiency of treatment. This evaluationwas not based on the incidence of typhoid fever directly, but was based on anindirect evaluation using bacterial or coliform counts.

    Soon after chlorination was introduced, it was possible to obtain firmepidemiological evidence that cities chlorinating water had lowered incidences oftyphoid fever (G. C. Whipple, 1921). Filtration was introduced in 1906 andchlorination in 1908, and both led to marked reductions in the incidence oftyphoid fever. Another dramatic example derives from observations at Wheeling,W.Va., in 1917-1918 (Gainey and Lord, 1952). The incidence of typhoid fever inWheeling was 155-200 per 100,000 during these years. Chlorination wasintroduced in the latter part of 1918, with the result that during the first 3 monthsof 1919 only seven cases were recorded. For 3 weeks during April 1919chlorination was discontinued, with the result that the number of cases increasedto 21, or a 300% increase. Chlorination was continued thereafter, and only 11cases were recorded for the last 6 months of the year. Other examples of this sortcould be cited (Gainey and Lord, 1952).

    SummaryWe thus see that by the beginning of World War I the essential features of

    water purification techniques were known, and their worth had been wellestablished. Since that time there have been many refinements made at anengineering level, but no changes in the basic concepts. It is clear that the primemotivation for the development and introduction of purification methods has beento protect the public health, with special concern for controlling the spread oftyphoid fever. An ancillary consideration has been esthetics, showing concern forthe appearance, taste, and odor of the water.

    One point worth emphasizing is that the availability of adequate treatmentmethods has influenced the standards for drinking water. This point was impliedin the books by Hazen (1907 and 1914), but is most

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  • clearly seen in the preamble to the 1925 Federal Standards, which superseded thebrief 1914 Standards (see Standard Methods, 7th edition, 1933, p. 136, for thecomplete 1925 Standards). The following quote is relevant:

    The first step toward the establishment of standards which will insure the safetyof water supplies conforming to them is to agree upon some criterion of safety.This is necessary because "safety" in water supplies, as they are actuallyproduced, is relative and quantitative, not absolute. Thus, to state that a watersupply is 'safe' does not necessarily signify that absolutely no risk is everincurred in drinking it. What is usually meant, and all that can be asserted fromany evidence at hand, is that the danger, if any, is so small that it cannot bediscovered by available means of observation. Nevertheless, while it isimpossible to demonstrate the absolute safety of a water supply, it is wellestablished that the water supplies of many of our large cities are safe in thesense stated above, since the large populations using them continuously have, inrecent years, suffered only a minimal incidence of typhoid fever and otherpotentially waterborne infections. Whether or not these water supplies have hadany part whatsoever in the conveyance of such infections during the periodreferred to is a question that cannot be answered with full certainty; but the totalincidence of the diseases has been so low that even though the water supplies becharged with responsibility for the maximum Share Which may reasonably besuggested, the risk of infection through them is still very small compared to theordinary hazards of everyday life.

    At present other considerations make it necessary [for us] to be lessconfident than was the 1925 Committee on Standards. Typhoid fever and choleraare dramatic diseases whose causal agents are transmitted by the water route.Typhoid fever statistics have provided some of the best evidence of the efficacyof treatment systems, but it should be kept in mind that other diseases, not soeasily diagnosed, might also be kept under control at the same time. The so-calledMills-Reincke theorem held that, for every death from waterborne typhoid, therewere several deaths from other diseases for which the causal agents weretransmitted by water (Shipple, 1921). At present, the incidence of typhoid fever inthe United States is so low that no useful information on the effectiveness ofrecent changes in water-purification practices can be obtained from anexamination of the statistics. During the years 1946-1970, there were 53outbreaks of waterborne infectious disease due to typhoid, but there were 297outbreaks due to other bacterial or vital agents, including 178 outbreaks ofgastroenteritis of undetermined etiology (Craun and McCabe, 1973). Of theoutbreaks, 71 percent resulted from contamination of private water systems, butmost of the illness (83%) was associated with community water systems. Duringthe period 1946-1960 there were 70 outbreaks of waterborne disease incommunities served by public utilities (Weibel et al., 1964), of which only 6 weretyphoid fever. When data

    HISTORICAL NOTE 7

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  • during this period for the number of outbreaks are examined, the incidence oftyphoid is even lower—103 cases out of a total of 19,928 (for a percentage of0.5%). Even considering that typhoid is more likely to be fatal than infectioushepatitis or gastroenteritis of unknown etiology, the Mills-Reincke theorem doesseem to have considerable merit. Thus, the rationale that has been used indevising standards for microbiological contaminants (see quotation above fromthe 1925 Standards) does not necessarily hold up on careful examination. Thecoliform standards may have ensured freedom from typhoid fever, but we do nothave the same assuredness that they have guaranteed freedom from otherinfections. Even granted that most of the outbreaks reported have occurredbecause of breakdowns in the proper functioning of water systems, the resultsshow that intestinal infections other than typhoid are common and, because oftheir often ill-defined nature, may be improperly diagnosed. Finally, only"outbreaks" find their way into public health statistics, whereas sporadic, randomcases of gastroenteritis generally go unreported. The epidemiological significanceof the present microbiological standards warrants continuing investigation tobring about further refinements in meeting the goal of maximum protection ofpublic health.

    REFERENCESBaker, M.N. 1949. The Quest for Pure Water. Am. Water Works Assoc., New York.Craun, G.F., and L. J. McCabe. 1973. Review of the causes of waterborne-disease outbreaks . J. Am.

    Water Works Assoc. 65:74.Fumes, J.H. 1897. Water and public health. John Wiley, New York.Gainey, P.L., and T.H. Lord. 1952. Microbiology of water and sewage. Prentice-Hall, Inc., New

    York.Hazen, A. 1907. Clean water and how to get it, 1st ed. John Wiley, New York.Hazen, A. 1914. Clean water and how to get it, 2d ed. John Wiley, New York.Johnson, G.A. 1913. The purification of public water supplies. U.S. Geol. Surv. Water-Supply Paper

    315.Koch, R. 1894. Professor Koch on the Bacteriological Diagnosis of Cholera, Water-filtration and

    Cholera, and the Cholera in Germany during the Winter of 1892-93. Translated by G.Duncan David Douglas, publisher, Edinburough.

    Snow, J. 1855. A reprint of two papers by John Snow, M.D., 1936. The Commonwealth Fund, NewYork.

    Weibel, S.R., F.R. Dixon, R.B. Weidner, and L.J. McCabe. 1964. Waterborne-disease outbreaks,1946-60. J. Am. Water Works Assoc. 56:947-958.

    Whipple, G.C. 1921. Fifty years of water purification. In M.P. Ravenel, ed. A Half Century of PublicHealth, pp. 161-180. American Public Health Association, New York. (Reprinted 1970 bythe Arno Press and the New York Times.)

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • I

    Approach to the Study

    INTRODUCTION

    In this chapter the general approach, principles, and criteria adopted in thestudy are discussed in outline. Considerations that entered into evaluations of theeffects on health of the various contaminants of drinking water are described,together with the reasons for selecting the subjects that were studied. Thefindings of the study are not summarized comprehensively in this section; eachsucceeding chapter includes a summary of the relevant conclusions andrecommendations. A short summary of the principal conclusions of the study isgiven in Appendix C.

    The study was undertaken by the NAS-NRC to meet the needs expressed inthe Safe Drinking Water Act (PL 93-523), which requires the EnvironmentalProtection Agency to promulgate national drinking water standards and, for thefirst time, regulations for enforcing them. The Act also directs the Administratorof the Environmental Protection Agency to arrange with the National Academyof Sciences, or other appropriate organization, to study the adverse effects onhealth attributable to contaminants in drinking water. Although the high qualityof drinking water in the United States is recognized throughout the world, the lawis an expression by the Congress of the concern of many citizens aboutmaintaining the quality of public water supplies in this country.

    The reader should not equate the size of this report or that of any of itschapters with the Committee's assessment of the magnitude of the challenge topublic health that may be due to the presence of particular

    APPROACH TO THE STUDY 9

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • constituents in drinking water in the United States. Several factors havecontributed to the length of this report: The Safe Drinking Water Act defined thescope of the study in encyclopedic terms and consequently the length of some ofthe chapters reflects the large number of topics and substances that it wasnecessary to consider. Other chapters deal with subjects that are complex andabout which there are uncertainties, conflicting opinions, and inconclusive orincomplete data. The relevant studies, assumptions, methodologies, healtheffects, and research recommendations for each group of constituents requireddetailed consideration from several points of view before balanced judgmentscould be achieved. In some cases brevity had to be sacrificed to reach thisobjective within a reasonable time.

    The primary purpose of the study was to assess the significance of theadverse effects that the constituents of drinking water may have on public health.The economic or technological feasibility of controlling the concentration ofthese constituents was outside the scope of the study.

    The health effects associated with some methods of disinfection were noted,but the relative effectiveness and potential hazards associated with the variousmethods of water disinfection were not evaluated.

    Application of analytical methods of great sensitivity has, in recent years,expanded our knowledge of the occurrence and diversity of impurities in drinkingwater. However, information about the biological results of chronic ingestion, atlow dose rates, of most of these substances is acquired slowly because thebioassays that are usually required may take two or more years to complete.Although new approaches to the problem of estimating chronic adverse healtheffects may, in the future, ease this difficulty, the current knowledge on whichthis study is based is insufficient to assess all the contaminants of drinking water.The results reported here must therefore be considered as a contribution to aneffort that should be continued.

    Besides the known constituents of drinking water, some were alsoconsidered that it would be plausible to expect to be present, even though theyhave not yet been detected in water. (Certain pesticides used in large quantitiesfall into this category.)

    In our review of water constituents, we have attempted to take into accountnot only their identities, concentrations, and toxicities, but also to consider otherquestions, such as:

    1. What reason is there for concern about the material? What risks areassociated with its presence in water?

    2. How does the material get into water?3. What sources are there other than water?

    APPROACH TO THE STUDY 10

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • 4. What contaminants need to be controlled?5. Are there special places or persons at higher than average risk?6. Are there essential nutritional requirements for this material?7. In view of the data at hand, can one say that this is a material that

    causes temporary ill effects? Permanent ill-effects? Reversibleeffects?

    8. In view of these effects—and their reversibility (or lack of it)—is itpossible to set "no-observed-adverse-health-effects" levels?

    9. For materials with special health benefits, what concentrations willmaximize these benefits, while keeping the health risk associatedwith them at an acceptably low level?

    10. What additional information is required to resolve the outstandingproblems?

    Many of the constituents of drinking water are natural materials, and enterwater from the rocks and the soil and the air. Some are the natural waste productsof men or animals. Others are artificial or synthetic materials, made and used forspecial purposes, that inadvertently find their way into water. Yet others occurnaturally, but have become more widely distributed in populated areas as a resultof industrial and agricultural activity.

    WATER CONSUMPTION

    In this study, a quantity of 2 liters per day has been taken to be the averageamount of water consumed per person. This is also the amount used by EPA tocalculate the current interim standards. Daily consumption of water is a functionof temperature, humidity, physical activity, and other factors that vary widely.The average per capita water (liquid) consumption per day as calculated from asurvey of nine different literature sources was 1.63 liters (NAS, 1974; McNalland Schlegal, 1968; Wolf, 1958; Guyton, 1968; Evans, 1941; Bourne and Kidder,1953; Walker et al., 1957; Randall, 1973; Pike and Brown, 1975). However, thelarger volume of 2 liters/day was adopted as representing the intake of themajority of water consumers. We estimate that most of those who consume morethan 2 liters per day still are afforded adequate protection, because the margin ofsafety estimated for the contaminants is sufficient to offset excess waterconsumption. Nevertheless, consideration should be given to establishing somestandards on a regional or occupational basis, to take extremes of waterconsumption into account.

    APPROACH TO THE STUDY 11

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • RISK AND SAFETY

    The hazards of ingesting chemical pollutants in drinking water have beenassessed in two general ways: with laboratory toxicity studies andepidemiological studies. The aim of studies of both types is to provideinformation about the risk to man. Risk constitutes only half of the equation; theother half is benefit to the exposed population. It is not possible to guarantee arisk-free society. The scientific methods and criteria we have used for evaluatinglong-term effects and risks in man are described in Chapter II, "ChemicalContaminants: Safety and Risk Assessment" and in the chapters concerning eachgroup of contaminants.

    Most of the experimental results on which the current knowledge of toxicityrests are based on observed effects on man and animals of doses and dose ratesthat are much larger than those that correspond to the usual concentrations ofharmful materials in drinking water. There is, consequently, great uncertainty inestimating the magnitude of the risk to health that ingestion of contaminants inwater may produce. An additional problem is to take into account the combinedeffects of two or more contaminants.

    The theoretical and experimental bases for extrapolating estimations of riskto low levels of dose have been reviewed, and some principles are proposed toguide the conduct of this and similar studies.

    MICROBIOLOGICAL CONTAMINANTS

    Outbreaks of waterborne disease are reported to the National Center forDisease Control (CDC) by state health departments. In addition, EPA obtainsinformation about additional outbreaks from state water-supply agencies. BothCDC and EPA are aware that data on waterborne outbreaks have limitations andmust be interpreted with caution. The data collected represent only a small part of alarger public health problem. The number and kind of reported outbreaks and ofsome etiologies may depend upon the interest or capabilities of a particular statehealth department or individual. They do not reflect the actual number ofoutbreaks, cases, or etiologies of disease associated with drinking water.

    Many small outbreaks are not reported to state health departments. There isno law or regulation requiring state authorities to report all gastroenteritis cases toCDC. In 1975, CDC reported 24 waterborne disease outbreaks involving 10,879cases. No etiologic agent was found for the two largest outbreaks (Sewickley,Pa., 5,000 cases and Sellersburg,

    APPROACH TO THE STUDY 12

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    Copyright © National Academy of Sciences. All rights reserved.

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  • Ind., 1,400 cases). In fact, no etiologic agent was identified in 17 of the 24outbreaks. These 17 outbreaks accounted for 9,760 cases, or 89%, of the totalreported in 1975.

    Conclusions in the microbiology chapter, based on epidemiological data, aresubject to the limitations of the reporting system and to our limited ability toidentify etiologic agents in outbreaks known to be associated with drinkingwater.

    The microbiological contaminants selected for consideration in this reportare those for which there is epidemiological or clinical evidence of transmissionby drinking water. They include a variety of bacteria, viruses, and protozoa.Methods of detecting these contaminants of drinking water were reviewed, andthe quantitative relationships between dose levels and infectivity were examined.Because current drinking water standards place major emphasis on detection ofmicrobiological contaminants, attention was devoted to the validity and healthsignificance of microbiological standards.

    PARTICULATE CONTAMINANTS

    Finely divided solid particles of mineral and organic composition arecommonly found suspended in some drinking water, particularly those suppliesthat do not practice coagulation and filtration. To discover whether or not thelong-term ingestion of these materials in water is likely to produce adverseeffects on human health, their occurrence, composition, and properties werereviewed.

    This review indicated that many kinds of particulate matter may indirectly,through adsorption, facilitate the transport of toxic substances and pathogenicorganisms and affect the efficiency of disinfection. Particles of organiccomposition also may indirectly give rise to chlorinated compounds by reactionwith chlorine in water treatment.

    Only in the case of particles derived from asbestos minerals, however, arethere grounds for suspecting that direct effects on human health could beinvolved. Fibrous particles of asbestos minerals are known to be associated withincreased incidence of cancer, including gastrointestinal cancer, among workerswho inhale asbestos-laden air. Experiments on the inhalation of asbestos mineralfibers by animals have also demonstrated a carcinogenic effect. The particulatematter in drinking water often includes similar particles.

    Although epidemiological studies have not indicated an increase with time incancer death rates that can be ascribed to fibrous contamination of the drinkingwater, these negative findings do not exclude the

    APPROACH TO THE STUDY 13

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  • possibility that such an increase may be detected in the future, because manycancers have long induction periods.

    For these and other reasons, detailed elsewhere, it is believed to beimportant that research on the analysis of fibrous mineral particles in water, andon the toxicity of these materials when ingested, should be strongly pursued.

    INORGANIC SOLUTES

    The Interim Primary Drinking Water Regulations list maximum allowableconcentrations for six metallic elements—barium, cadmium, chromium, lead,mercury, and silver. Ten additional metals were reviewed in this study—beryllium, cobalt, copper, magnesium, manganese, molybdenum, nickel, tin,vanadium, and zinc. Sodium, which is also a metal, was considered separately,because the problems it poses are quite distinct from those associated with theother metallic substances. In addition, the effects on health of several otherinorganic constituents of drinking water were studied. These include arsenic,selenium, fluoride, nitrate, and sulfate. The relationship between water hardnessand health also received attention.

    The sources of inorganic ions in groundwater, surface water, water-treatment chemicals, and from the storage and distribution system are consideredalong with the health effects resulting from the total intake from food, air, andwater.

    ORGANIC SOLUTES

    Of the 298 volatile organic compounds so far identified in drinking water, 74were selected for detailed study along with 55 pesticides. A compound wasselected for consideration if any of the following criteria applied:

    1. Experimental evidence of toxicity in man or animals, includingcarcinogenicity, mutagenicity, and teratogenicity.

    2. Identified in drinking water at relatively high concentration.3. Molecular structure closely related to that of another compound of

    known toxicity.4. Pesticide in heavy use; potential contaminant of drinking water

    supplies.5. Listed in the Safe Drinking Water Act or National Interim Primary

    Drinking Water Regulations.

    APPROACH TO THE STUDY 14

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  • The evaluation of toxicity was based on a critical review of the scientificliterature. The available data were of variable quality and quantity and, in someinstances, inadequate for proper assessment of toxicity. In those cases wheresufficient data were available, professional judgment was used to determinewhich compounds are carcinogenic, mutagenic, teratogenic, andnoncarcinogenic.

    The limitations that are inherent in the extrapolation of high-dose animalbioassay data to low-dose human exposure and the difficulty of makingpredictions for species that may have different metabolic rates and pathways forhandling carcinogens, or different target-organ responses, are well known. Suchrisk assessment and extrapolation procedures are further compromised by thelimited information that is available concerning the mechanisms by which theseagents act (such as initiators, promoters, and modifiers) and the almost total lackof data regarding the potential synergistic and antagonistic interactions of theseagents with each other and with other environmental agents. The risk of ingestingknown or suspected carcinogens was estimated by the methods described inChapter II. These methods are based on an assumption that there is no thresholdin the dose-response relationship. The risk-estimate approach may provide uniqueadvantages for other areas of toxicologic evaluation.

    The more traditional approach of combining the maximum no-observed-adverse-effect level with an uncertainty (safety) factor to calculate an acceptabledaily intake (ADI) was used for agents that were not considered to be known orsuspected carcinogens and for which there was adequate toxicity data fromprolonged ingestion studies in man or animals. Several alternative terms otherthan ADI were considered, but it was concluded that the introduction of newterms might lead to confusion and that the use of a widely recognized andgenerally acceptable term would be preferable for this report. Although the ADIhas been used previously as an internationally established standard for thetoxicological evaluation of food additives and contaminants, the concept isapplicable to other cases of exposure by ingestion. The ADI is an empiricallyderived value that reflects a particular combination of knowledge and uncertaintyconcerning the relative safety of a chemical. The uncertainty factors used tocalculate ADI values in this report represent the level of confidence that can bejustified on the basis of the animal and human toxicity data. ADI values were notcalculated for agents where the data were considered to be inadequate.

    Since the calculation of the ADI values is based on the total amount of

    APPROACH TO THE STUDY 15

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  • a chemical ingested, the ADI values calculated in tiffs report do not represent thesafe level for drinking water.

    Little or no data are available on the toxicity of many organic compoundsidentified in drinking water. There is a need to determine which of thesecompounds should be subjected to extensive toxicity testing. Some of the criteriaused for developing the order in which compounds should be tested are:

    1. The relative concentrations of the compounds and the number ofpeople likely to be exposed.

    2. The number of supplies in which they occur.3. Positive responses in in vitro mutagen screening systems.4. Positive responses in in vitro prescreening systems for potential

    carcinogens (mammalian cell transformations).5. Similarity of the chemical structure of the test compound with that of

    other compounds having defined toxic properties (i.e., structure-activity relationships).

    6. Relationships of dose from water to total body burden.

    RADIOACTIVE CONTAMINANTS

    Because the presence of ionizing radiation is one of the standard features ofthe earth's surface, the adverse effects on health that may be ascribed toradioactive contaminants of drinking water were assessed in relation to theaverage background radiation dose, from all sources, of 100 mrem per year.

    Previous estimations of the biological effects of the background radiation onhuman health were reviewed in the light of more recent scientific knowledge andused to calculate the magnitude of three kinds of adverse health effects thatradiation can produce; namely, developmental and teratogenic effects on thefetus, genetic disease, and somatic (principally carcinogenic) effects.

    When these estimates are related to the concentrations of radionuclides thatare commonly found in drinking water, it is seen that consumption of 2 liters ofwater per day contributes such a small fraction to the total radiation backgroundthat the incidence of developmental, teratogenic, and genetic disorders is notincreased enough for the change to be detectable.

    Where somatic effects are concerned, it is estimated that the radionuclides indrinking water typically account for less than 1% of the incidence of cancers thatmay be attributed to the natural background of

    APPROACH TO THE STUDY 16

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • radiation. Only certain bone-seeking radionuclides (chiefly radium), in a fewregions, reach concentrations in drinking water that are high enough to cause asignificant increase in the incidence of bone cancer.

    SUSCEPTIBLE SUBGROUPS AND OTHER CONSIDERATIONS

    Groups that are more susceptible than the normal population are consideredin the chapters on various classes of contaminants.

    This report is concerned only with water used for drinking. Although allcontaminants may cause problems when present in water used in health carefacilities, the health hazards associated with such diverse uses of water as inhumidifiers, kidney dialysis units, laundries, heating and cooling equipment, ormany special uses that require further treatment of tap water, have not beenconsidered. References and summaries of the scientific literature in this field havebeen published by DeRoos et al. (1974).

    REFERENCESBourne, G.H., and G.W. Kidder, eds. 1953. Biochemistry and Physiology of Nutrition, vol. 1.

    Academic Press, New York.DeRoos, R.L., V.R. Oviatt, A.G. DuChene, and N.J. Vick. 1974. Water use in biomedical research

    and health care facilities—A presentation of article summaries. National Institutes ofHealth, Department of Health, Education, and Welfare, Contract no. NIH-ORS-72-2111.

    Evans, C.L. ed. Starling's Principles of Human Physiology, 8th ed. Lea and Febiger, Philadelphia.Federal Register, Wednesday, December 24, 1975, vol. 40, no. 248.Guyton, A.C. 1968. Textbook of Medical Physiology, 3d ed. W.B. Saunders Co., Philadelphia.McNall, P.E., and J.C. Schlegel. 1968. Practical thermal environmental limits for young adult males

    working in hot, humid environments. ASHRAE Transactions 74:225-235.National Academy of Sciences-National Research Council. 1974. Recommended Dietary

    Allowances, 8th ed. Washington, D.C.Pike, R.L., and M. Brown. 1975. Minerals and Water in Nutrition—An Integrated Approach, 2d Ed.

    John Wiley, New York.Randall, H.T. 1973. Water, electrolytes and acid base balance. In R.S. Goodhart and M.E. Shils, eds.

    Modem Nutrition in Health and Disease. Lea and Febiger, Philadelphia.Walker, B.S., W.C. Boyd, and I. Asimov. 1957. Biochemistry and Human Metabolism, 2d ed.

    Williams & Wilkins Co., Baltimore.Wolf, A.V. 1958. Body water. Sci. Am. 99:125.

    APPROACH TO THE STUDY 17

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    ase

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    as th

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    itativ

    e ve

    rsio

    n fo

    r attr

    ibut

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    Copyright © National Academy of Sciences. All rights reserved.

    Drinking Water and Health, Volume 1http://www.nap.edu/catalog/1780.html

    http://www.nap.edu/catalog/1780.html

  • APPROACH TO THE STUDY 18

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