This is Part II of a study investigating the disinfection of swimming pools. Part I appeared in March, 1970. The results show that the sanitation of swimming pools can be improved, and that free available chlorine is a better disinfecting agent than combined chlorine. Other findings are presented. THE DISINFECTION OF SWIMMING POOL WATER PART II. A FIELD STUDY OF THE DISINFECTION OF PUBLIC SWIMMING POOLS A. P. Black, Ph.D.; M. A. Keirn, M.S.; J. J. Smith, Jr., B.S.; G. M. Dykes, Jr., B.S.C.E.; and F. E. Harlan, M.S.P.E. THERE has been a rapid increase in of 1968-four of the authors traveled the number of public swimming pools over 2,200 miles sampling 193 pools, constructed in this country in recent ranging in size from 11,000 gallons to years, and their proper disinfection and over 600,000 gallons, located along the operation is becoming an increasingly Atlantic and Gulf coasts of Florida. important public health problem. The They included the two Hall of Fame results of a recent study of 193 typically pools at Fort Lauderdale, and all read- operated public pools indicate the need ers of this paper will be glad to know for the promulgation and enforcement that both met all of the standards used by state or local health departments of for the study. adequate codes of practice covering all aspects of pool operation, and, hopefully, Distribution by Pool Size of minimum qualifications for their operators. In the preparation or revi- Of the 193 pools, 7 had a capacity sion of these codes, it is extremely im- under 20,000 gallons and 7 were above portant that critical terms be exactly 300,000 gallons; 52 were between defined. Specifically, for each disin- 20,000 and 40,000 gallons; 52 between fectant, the type of residual required 40,000 and 60,000 gallons; 23 between should be clearly stated, and also the 60,000 and 80,000 gallons; 13 between method or methods approved for its 80,000 and 100,000 gallons; and 39 determination. were between 100,000 and 300,000 The objective of this study was to gallons. sample many different types of public Distribution by Pool Use swimming pools in order to get a sta- tistically sound evaluation of the safety, Of the 193 pools, 108 were located at operational practices, and maintenance hotels or motels along Florida's "Gold problems encountered in typically oper- Coast," including a great many of the ated pools. During the study, which most beautiful establishments in this was conducted in two parts-one in Au- highly tourist-oriented area; 41 were gust of 1967 and the other in August located at large apartments or condo- 740 VOL. 60, NO. 4, A.J.P.H. DISINFECTION OF SWIMMING POOLS miniums; 26 were municipal pools; 11 1. Very slight haziness observable in deep wvere YMCA or YWCA pools; and 7 water 2. Main drain not clearly visible were located at country clubs. 3. Main drain visible only as a dark spot, water milky Distribution by Method of Disinfection 4. Unable to see main drain. Of the 193 pools, 88 were disinfected A Beckman Model N battery-oper- with chlorine gas; 49 with sodium ated pH meter was used to measure pH. hypochlorite; 26 with calcium hypo- Free available chlorine and total chlorine chlorite; and 28 with cyanuric acid- residuals were measured by am- stabilized chlorine. In one pool, no treat- perometric titration and also with an ment of any kind was being used. orthotolidine test kit, both at pool water temperature and, in the 1968 study, on Distribution by Filter Type samples chilled to approximately 10 C. Additional parameters used in the 1968 Of the 193 pools, 56 had sand fil- study were alkalinity and cyanuric acid ters; 49 pressure diatomite filters; 76 level. Cyanuric acid was determined vacuum diatomite filters; 8 had cart- turbidimetrically using a commercial* ridge filters; 2 had anthracite filters test kit. Total alkalinity was measured and 2 were flow-through pools. with a commercial test kit employing a The only significant difference be- 25 ml sample. tween the two studies was that fewer motel pools and more apartment pools were used on the 1968 trip. Relative dis- Bacteriological Parameters Used tribution of capacity and type of disin- Bacteriological parameters used were fection were the same. Two anthrafilt coliform density-both by the multiple pools were tested in 1967 and two flow- tube technique and membrane filtra- through type pools in 1968. tion-fecal streptococci, total staphylo- cocci, Pseudomonas aeruginosa, and 48- Materials and Methods hour standard plate count. Two samples The following parameters were eval- were taken from each pool. A 100 ml uated or recorded for the 193 pools: sample was taken in a bottle containing sodium thiosulfate and sent to a board 1. Indicator organisms and bacteriological of health laboratory for coliform de- quality termination by membrane filtration. 2. Level and forms of chlorine 3. Precision and accuracy of the orthotoli- This provided a check on results ob- dine test tained by the Earle B. Phelps Sanitary 4. pH and water temperature Engineering Laboratory of the Univer- 5. Turbidity (see below) sity of Florida, which made the other 6. Type of filter 7. Type of pool surface bacteriological determinations. 8. Type of algae. if present During the 1967 study, a 300 ml 9. Pool capacity, circulation and bather load composite sample from the shallow end 10. Pool operation in general. of each pool was collected for the bulk In addition to the above, a record of the determinations in a Roux bottle wvas made of weather conditions at the sterilized between samples in a strong time each sample was collected. hypochlorite solution, then rinsed Turbidity of pool water was rated thoroughly in pool water. This bottle on the following arbitrary scale: was attached to a special rod and pulled 0. No visible turbidity, pool water sparkling, * Manufactured by the Hach Chemical Co., main drain outline sharp P. 0. Box 907, Ames, Iowa 50011 APRIL, 1970 741 around the shallow end of the pool at a depth of approximately 18 inches. A c" cr, ON " T 300 ml portion was decanted into a cl Cl4 cl cli r- sterile BOD bottle containing thiosul- 0 0 Al fate. This procedure was simplified in 04- csi c cq I t - 0 the 1968 study by the use of sterilized 6 BOD bottles pulled through the water biD in the above manner. Samples were sent to the university laboratory each night S by bus and were processed within 24 CL a) hours. 0 ,-- cl LO c0 H - z The confirmed multiple tube test for 0 S ._~ H coliforms and MPN for fecal strepto- 0 O>4-- 0) ocq in o cs,t cocci were run by techniques from the 0 CZ 12th edition of Standard Methods for 0 the Examination of Water and Waste- 0 0t O O water, and 48-hour plate counts were 0 run on tryptone glucose yeast extract S agar at 350 C. Staphylococci were S 0 04 enumerated by membrane filtration of 0 C) C- - h- - co o - 100 ml of sample and incubation on 0 6 m-Staphylococcus broth (Difco). Pseudo- CL S monas aeruginosa was determined by 0 w. the most probable number method, de- c scribed by Favero, Drake, and Randall,' 0 .E using asparagine enrichment broth fol- S a 0 lowed by confirmation in acetamide S broth. S 0 u r. ;'- t I t co co cO Cl Results 0 0 :-4 0 0- Bacteriological Quality of Pool Water 0 0 cn S o Table 1 summarizes the bacteriolog- tn - U.n Cl , C ical results from all pools. Die-off studies S 0 0- '_4 showed that in many instances plate C- 0 -0-4 't, ~ ~~ ~ ~ ~ counts would tend to increase and num- c 0' bers of staphylococci and fecal strepto- E 4 6 0 CC_ E cocci to decrease, on standing for 24 2 LrD hours. Pseudomonas aeruginosa and Cl) Escherichia coli did not show significant LO fluctuations when tested. Therefore, plate 0 (10 _-C) couInt, staphylococci, and fecal strepto- S r- 0 cocci data can only be used for com- 0 - parison between groups in this study. C:4 r. 0 Coliforms and membrane filter results, J AlV however, appear to be valid as maximum storage time allowable for membrane IL- _0 ce- filter tests is 30 hours, and samples were C.; run well within this time limit. .7 Al a With respect to the presence of coli- 742 VOL. 60, NO. 4, A.J.P.H. DISINFECTION OF SWIMMING POOLS forms and to plate couInts, the APHA filters, even though the latter group con- recommends the following:2 tained 0.3 mg/l free available chlorine. 1. Not more than 15 per cent of samples A comparison of pools having 0.3 examiinled shall showv the presence of con- mg/l free available chlorine, measured firmiied coliforms in any of five 10 ml portions. by amperometric titration, with those 2. Not more than 15 per cent of the samples having 0.3 mg/l total chlorine but less examiiined shall contain 1.0 coliform organisms than 0.3 mg/l of free available chlorinie, per 50 ml when the memhibrane filter test is used. showed that free available chlorine is 3. Not more than 15 per cent of the samples much more effective than combined examiiined shall contain over 200 bacteria per chlorine. Fewer isolates of all indicator milliliter. organisms were found in pools in which the principal disinfectant species was Of the 193 pools reported on, 123 or free available chlorine than in pools 65 per cent contained no coliforms by where the major portion of the total multiple tube and were satisfactory by chlorine residual was combined. High membrane filtration. Plate count data plate counts also occurred more fre- were not judged sufficiently reliable to quently in the latter. Pools having 0.3 be considered as a criterion for compari- mg/I of total chlorine but less than 0.3 son with other studies. However, com- mg/l free available chlorine, however, parison of plate count data among cate- showed better bacteriology than those gories within this study would be valid. pools with 0.3 mg/l free available Of the 55 pools containing at least 0.3 chlorine but less than 0.3 mg/l free mg/l of free available chlorine, 45 or chlorine at pool pH. 82 per cent contained no coliforms The last three groups of pools-hav- whereas, of the 44 pools containing 0.3 ing low chlorine residuals, no residuals, mg/I or less of total chlorine, only 21 or stabilized chlorine residuals with no or 48 per cent were coliform-free. Of free available chlorine-showed, as ex- the 28 pools containing chlorine re- pected, a high frequency of occurrence siduals stabilized with cyanuric acid, 18 of coliforms and Pseudomonas aerugi- or 64 per cent were coliform-free. The nosa. Except for the low numbers of explanation of the difference between staphylococci found in stabilized chlo- 1967 and 1968 bacteriological data for rine-disinfected pools, these organisms the latter group is believed to be that were much more numerous in the pools only one pool in the 1967 study had with low residuals than where free greater than 0.3 mg/I free available available chlorine was present. High chlorinie wlhile 8 of the 15 studied in plate counits were also encountered more 1968 had at least this much free avail- frequently in these three groups than able chlorine, and all but one of these in the pools with 0.3 mg/l free avail- containe(d 1.0 mg/l or more. able chlorine. A calculatioin of free chlorine at. pool p/I. to be definied later, was made for Physical Parameters the 55 pools containingr 0.3 mg/I or An attempt was made to relate the -reater free a-ailable chloriine. Forty- presence or absence of algae to the type five of these lhad 0.3 mg/l or greater of pool surface and to the type of fil- free chlorinie at pool pIh. Of these 45, ter being used. No significant differ- only 6 had either colifornms or unsatis- ence was found in the incidence of factory membrane filters, wlhereas 4 of algal growths as between pools with the 10 pools Inot having 0.3 mg/l of paiinted surfaces and those coated witl free chlorine at pool pHi slhowed either marbleite plaster. Although the imlci- coliforms or unsatisfactorv membrane deuice of algal growths in pools equipped APRIL, 1970 743 with vacuum diatomite filters appeared 1. Free Chlorine in Aqueous Solu- to be somewhat less than in pools using tion-The reaction of chlorine gas with either pressure diatomite or sand filters, water to form free chlorine can be repre- the relationship was not significant at sented as follows: the 95 per cent probability level. Cl2 +H2OHOCl +H + C1- An attempt was made to relate clarity That form of chlorine represented as of pool water to the type of filter being HOCl (hypochlorous acid) is free chlo- used. While the percentage of pools with rine as found in swimming pools, and brilliant, turbidity-free water was a is more powerful both chemically and little greater in the case of pools with as a bactericide and algicide than any vacuum diatomite filters than those other form of the element. having either sand or pressure diatomite 2. Free Available Chlorine at Pool filters, the data do not definitely indi- pII-The dissociation of HOCI at values cate that one type of filter outperforms above pH 5.0 in aqueous solution estab- another as far as water clarity is con- lishes an equilibrium with hydrogen and cerned. It is believed that individual at- hypochlorite ions so that two species of tention by careful and conscientious chlorine, HOCI and OC1-, are present. operators is the most important single The relative amount of each species is factor (and the one most frequently dependent upon pH, the absence of am- lacking) in maintaining a clear, clean monia, and of other environmental de- pool. bris. The following equation represents Pool pH the dissociation: HOCIHI+ 0+C1- The Florida Code requires that pool Free chlorine Available chlorine pH be maintained within the range pH The meaning of the word "available" 7.2-8.0. The APHA2 recommends that must be made clear. The hypochlorite the upper limit be extended to pH 8.2. ion, OC1-, has little or no bactericidal The results of our study seem to indi- activity but it serves as a reservoir or cate clearly that most pool operators are bank from which more free chlorine, either not aware of these limiting and HOCI, may be formed as that initially permissible values or that they make present is removed by pool water little or no attempt to follow them. Of demand. the 193 pools studied, 51 per cent con- 3. Combined or "Stabilized" Chlorine tained water with pH values either be- low 7.2 or above 8.2. Specifically, 83 -This is the form which chlorine as- had pH values below pH 7.2 and 16 sumes in the presence of such materials had pH values above pH 8.2. as ammonia or its salts, cyanuric acid, sulfamic acid or urea. The relative Orfhotolidine Measurements amount of combined or "stabilized" Misleading chlorine and the forms it can take are The standard OT test as performed dependent on pH, temperature, and the by pool operators gives results which concentrations of both HOCI and the are both erroneous and misleading. stabilizing material. The reaction with Orthotolidine produces a yellow color NH3 is as follows: when oxidized at pH values lower than NH3 +HOCL:±NH2Cl +H20 1.8 by chlorine, chloramine, nitrites, The product is called monochloramine, and the higher oxidation states of iron which is probably the most common and manganese. Before we discuss the form of combined or stabilized chlorine reactions involved, perhaps some defini- found in pools. However, its kill time is tion of terms would be helpful. only about one-thirtieth that of hypo- 744 VOL. 60, NO. 4, A.J.P.H. DISINFECTION OF SWIMMING POOLS chlorous acid3 which is much too slow free available chlorine is determined by for swimming pool disinfection. titration with phenylarseneoxide at pH According to Zettler and Solsor,4 free 7.0. Platinum electrodes measure the chlorine is produced in water by the drop in current as the reaction proceeds. general reaction: The end point is reached when no fur- ACI+H20.AH+HOC1 ther decrease in current occurs upon addition of a small amount of phenyl- where A represents the negative part of arseneoxide. After the free available the molecule to which the positive chlo- chlorine is titrated, the pH is lowered rine is originally attached (in the above to 4.0 and excess iodide added. Com- case NH2). This may be Cl--Cl+ as in bined chlorine present will oxidize chlorine gas, NAO-Cl+, chloramide iodide to iodine and the free halogen (cyanuric acid) or chlorimide. The is titrated with phenylarseneoxide, amount of free chlorine released when thereby measuring the amount of com- ACI is added to water depends on the bined or "stabilized" chlorine present. rate and degree of hydrolysis of ACI Table 2 and Figure 1 show the per- and the amount of AH present. In the centage of HOCI (free chlorine) and case of chloramine and other N-chloro- OC1- (hypochlorite ion or available inorganic compounds the rate of hydrol- chlorine) present at pH values from 4-9, ysis is so low that very little HOCI is for a total chlorine residual of 1.0 ppm. formed, hence the weak disinfecting Table 2 gives the data for the usual powers exhibited. The chloramides, in pool pH values. It shows that, at a pool rate and degree of hydrolysis, fall be- pH of 7, about three-fourths of the re- tween the complete hydrolysis of chlo- sidual present is "free chlorine" or rine gas and hypochlorite, and the inac- HOCI. However, at pH 8, less than one- tivity of chloramine. fourth is "free chlorine" and a little The pool operator is primarily in- more than three-fourths is relatively in- terested in the level of free available active "available chlorine." No method chlorine in the pool. The method of dif- is available for measuring free chlorine ferentiating free available chlorine and at pool pH which is actually what we combined chlorine by the standard wish to know and which determines the orthotolidine test is to cool the test sam- rate of bacterial kill. ple to 10 C, add orthotolidine solution, As stated earlier, free available chlo- and read the flash color within five sec- rine is determined amperometrically at onds as free available chlorine. A sec- pH 7.0. The following equation repre- ond sample is treated at pool tempera- sents the species of chlorine at this pH: ture and allowed to react five minutes HOCI±H++OC1l after orthotolidine is added, then read. 72.5% 27.5% The difference between the two deter- minations is combined chlorine. During this survey, however, we found no pool Table 2-Effect of pH on forms of operators and only one sanitarian who chlorine5 measured chlorine residuals in the above pH % C12 % HOCI %oC1- manner. Most merely read the flash and five minute residuals at pool water 4 0.5 99.5 0 temperature, which leads to inaccurate 5 0 99.5 0.5 results. 6 0 96.5 3.5 A second, more accurate method of 7 0 72.5 27.5 8 0 21.5 78.5 measuring free available chlorine is by 9 0 1.0 99.0 means of an amperometric titrator. The APRIL, 1970 745 Figure 1-Effect of pH on per cent HOCI from the pool pH and the residual de- for any free available chlorine residual termined by titration; however, most operators are not fortunate enough to have a titrator and must rely on the orthotolidine test kit. The same free available chlorine is, supposedly, meas- 7 ured by orthotolidine, but one signifi- cant difference exists, namely, the pH of the sample is lowered to below 1.8 when orthotolidine is added. At this pH, and at pool temperature, most of the combined or "stabilized" chlorine 0 10 20 30 40 50 60 70 80 90 100 will be measured as free available chlo- % HOCI rine, indicating a higher than actual level of active disinfectant. The rate of As one titrates the HOCI, the equi- the reaction with orthotolidine is, there- librium shifts to the left and continues fore, a function of temperature, pH, and to do so until all the HOCI and OCl- concentration. are titrated. The final reading is the In order to evaluate the discrepan- sum of both the powerful disinfectant, cies between residuals determined with HOCI and OC1-, which is bactericidally orthotolidine and those determined ineffective. This measurment is free amperometrically, both tests were car- available chlorine. ried out at each pool. Of the 110 pools Let us assume that a pool whose pH disinfected with chlorine or hypochlo- is 7.5 shows a free available chlorine rite and which had measurable residual residual of 1.0 ppm. Reference to Table by both methods, residuals measured by 3 shows that actually only 0.47 ppm of orthotolidine were almost uniformly this is free chlorine and the other 0.53 significantly higher than those measured ppm is available chlorine, and the pool by amperometric titration. This can be with a measured 1.0 ppm residual seen when the deviations are plotted in barely meets the 0.4 ppm APHA2 cri- Figure 2 as orthotolidine residual minus terion. amperometric residual versus the com- Therefore, to convert any measured free available chlorine residual to the Table 3-Amount of free available chlo- equivalent amount of free chlorine at rine required to provide 0.40 ppm free pool pH, one merely multiplies the chlorine at pool pH measured residual by the percentage shown in column 2 (Table 3) for the Percentage Free avail- pool pH and divides the result by 100. of free able chlorine available required For example, to convert 0.45 ppm of pH of chlorine to provide free available chlorine, as determined pool present Conversion 0.4 ppm either by the amperometric titrator or water as HOCI factor free chlorine the OT test performed at about 10 C, 7.2 62.3 1.60 0.64 pool pH 7.6: 7.3 57.2 1.77 0.70 4 7.4 52.1 1.94 0.77 0.45 x =0.19 ppm truie free chlorine at 7.5 47.0 2.14 0.85 pH 7.6. 7.6 41.9 2.37 0.95 The pool operator could easily de- 7.7 36.8 2.70 1.09 termine his free residual 1v calculation 7.8 31.7 3.14 1.26 746 VOL. 60, NO. 4, A.J.P.H. DISINFECTION OF SWIMMING POOLS Figure 2-Relationships of (OT7- three cases, no orthotolidine residual AMP±r) in mg/p to combined chlorine was found when total chlorine was present greater than 0.25 ppm (one as high as 2.0- 0.45 ppm), when measured by ampero- metric titration. Figure 3 shows the dis- tribution of the 103 total chlorine re- 1.5j1 siduals measured by both methods. If the two methods of measurement were 1.0- equivalent, the points plotted would have fallen along a line with a slope of 1.0. E It is apparent that they do not but were found to lie about a line with slope of tL 0.83±0.07 with an intercept at 0.06 *- ,* - ppm. This shows that the orthotolidine z rn v . vV e - ,. residual becomes slightly less sensitive 1.0 COMBINED CHLORINE RESIDUAL I.mq/P) 2 2.0 at high residuals than at low residuals, -Z and that it fails to pick up residuals less than 0.06 ppm, which is in the ACCEPTABLE RANGE OF DEVIATION (APHA RECOMENDATION 0.1 ppm) range of the consistent failure at resid- uals less than 0.15 ppm. A frequency -I. c- distribution of the deviation of the orthotolidine test and amperometric ti- tration method for total chlorine is given bined chlorine residual obtained by in Table 4. Only 31 per cent were within amperometric titration. The discrepancy the +0.1 ppm agreement recommended became strongly positive in cases where by the APHA. greater than 0.40 ppm of combined In 27 of the 28 pools employing chlorine was present. It was felt, after cyanuric acid stabilized chlorine, ortho- the 1967 survey, that chilling the sam- tolidine residuals were compared with ple to 340 F might reduce the strong residuals measured by amperometric interference in the orthotolidine test by titration. Eleven of these 22 pools concentrations of combined chlorine. showed no measurable free available However, tests conducted during the 1968 study show that chilling does not bring any improvement. Furthermore, Figure 3-Comparison of chlorine resid- uals determined with orthotolidine and discrepancy did not appear to be in- by amperometric titration fluenced by either pH or alkalinity. The parallel lines of Figure 2 enclose the area within which are found all measured residuals which were within +0.1 ppm of amperometric values. In this study 52.8 per cent of the measured residuals fell outside this satisfactory area. The orthotolidine test also has short- comings as a measure of total chlorine residual. The test kit usually failed to show any residual in cases where total chlorine by amperometric titration was 1.0 less than approximately 0.15 ppm. In AMP. TITR. (mg/t) APRIL. 1970 747 chlorine residual by amperometric ti- ing agent than combined chlorine. The tration. Two had free available chlorine over-all total of 35 pools showing the residuals less than 0.3 ppm and nine presence of coliforms represents 18 per showed values greater than 0.3 ppm. It cent of the total pools and is slightly is noteworthy that each of the 22 pools higher than the 15 per cent maximum showed a high free available chlorine isolation rate recommended by APHA. residual with orthotolidine "flash" test. However, the 56 pools yielding unsatis- Behavior of the titrator was sluggish factory membrane filters is much higher in measuring free available chlorine at than the maximum. Most of these iso- 9 of the 28 pools, with significant free lates were found in pools with little or available chlorine residuals. In titrating no free chlorine at pool pH. free available chlorine in the absence In this study, fecal streptococci were of cyanuric acid, the microammeter found much less frequently than coli- needle drop is sharp with incremental forms, even though Streptococcus addition of phenylarseneoxide, and the fecalis is more resistant to chlorine than end point in sharp. When cyanuric acid E. coli.3'9 Additionally, fecal strepto- was present, both in the field study and cocci were usually associated with the in the laboratory, needle response is presence of other indicator bacteria. slow and irregular and the end point Pseudomonas aeruginosa, a potential difficult to define due to needle drift. pathogen and a causative agent of ear This opens the question of whether the infection among swimmers,10 was found cyanuric acid stabilized chlorine so in alarming frequency in pools where measured is really free as HOCI and less than 0.3 mg/l free chlorine at pool OC1-, or whether it is merely bound pH was present. This organism was not loosely enough to react with the reduc- found more frequently than coliforms ing agent added. The cyanuric acid in any disinfectant group studied. level was tested in the 15 pools encoun- Staphylococci were found in a very, tered in the 1968 study. In pools show- large proportion of the pools, but were ing free available chlorine, the average found in large numbers only in pools cyanuric acid level was 58 mg/l as op- with low chlorine residuals. These data posed to 80 mg/l in those without meas- do not agree well with previous work urable free available chlorine residuals. reported in the literature,l a fact This agrees with findings of other in- probably due to die-off in shipment. It vestigators 67'8 who found that hydrol- has been shown that staphylococci are ysis was greatly suppressed by levels of present in high numbers in heavily used cyanuric acid greater than approxi- pools in the absence of coliform organ- mately 50 mg/l. These results conclusively indicate the obsolescence of the orthotolidine test for Table 4-Frequency distribution of measurement of chlorine in swimming (Ampr-OTr) in 103 pools pools for two reasons. First, it does not Deviation Nuimber of pools differentiate between free and combined chlorine, but reports a substantial per- 0 7 centage of combined chlorine as "free ± 0.01-0.05 9 available." Second, it does not meet that ± 0.06-0.10 16 criterion of APHA which recommends + 0.11-0.15 12 an accuracy of +0.1 ppm. ± 0.16-0.20 17 ± 0.21-0.25 10 Discussion ± 0.26-0.30 12 The results show again that free avail- >0.30 20 able chlorine is a much better disinfect- 748 VOL. 60. NO. 4, A.J.P.H. DISINFECTION OF SWIMMING POOLS isms, and that staphylococci are more tion, and orthotolidine, coliform den- resistant to disinfecting agents than E. sity by both multiple tube and mem- coh. brane filtration, fecal streptococci, total Staphylococci are derived from the staphylococci, and Pseudomonas aerugi- skin and mucous membranes of human nosa. beings; their presence in pool water in- 2. The study indicates that the opera- dicates the possibility of transmittance tion of public swimming pools is not as of staphylococcal infections, and also good as it should be. One hundred and that other pathogenic organisms from five of the 193 pools failed to have the the skin or mucous membranes may be residual required by the state health present. The high numbers found in the code, and 106 failed to have pH values absence of adequate or marginal chlori- within the acceptable limits. Eighteen nation provide further that large popu- per cent of the pools studied contained lations of these organisms may build up. coliforms or showed unsatisfactory A standard of 100 staphylococci per membrane filtration results. In many 100 ml in swimming pools has been pro- instances, pool operators knew little posed by Favero, et al1 This allows a more than the simple details of me- tremendous number of staphylococci to chanical operation. All too many of contact the skin of a bather immersed them had little or no conception of the in a pool. This number was only rarely significance of pH or chlorine residual, exceeded both in this study and in a or how to maintain a residual within previous study in which more heavily acceptable limits. Many monthly reports, used pools were sampled. Therefore, it to be submitted to the health depart- is felt that this criterion offers no great ment, were found filled out days in degree of safety. A more conservative advance. figure of perhaps 30 staphylococci/100 3. The standard orthotolidine test for ml of pool water would be more ra- chlorine residual, as performed by most tional. Robinton, et al.,11 showed that pool operators, yields misleading and in pools with greater than 1.0 ppm free erroneous results. At pool water tem- available chlorine no more than four perature, the flash reading of free avail- staphylococci per 100 ml were present, able chlorine residual also includes a even where loads were reasonably portion of the combined chlorine re- heavy. Keirn and Putnam3 found ap- sidual, the amount depending upon the proximately 20 staphylococci/100 cc in ratio of free and combined chlorine. pools containing free available chlorine, This interference is especially bad at but in these pools residuals averaged low free available chlorine residuals. At much lower than in those investigated present, the only foolproof way of ob- by Robinton. taining the free available chlorine re- sidual is by amperometric titration, a Summary method requiring expensive laboratory apparatus. 1. A field study was made of the 4. Coliforms were present in 18 per chemical and bacteriological quality of cent of the pools studied, mostly in pools the water of 193 below-ground public with inadequate chlorine residuals. pools in Florida. These pools ranged in Fecal streptococci were found much less size from 11,000 to 624,000 gallons. frequently than coliforms. Staphylococci Parameters investigated included tur- were isloated in a very large proportion bidity, type of filter, presence or ab- of the pools and were present in high sence of algae, pH, determination of numbers in pools with low chlorine re- chlorine residual by amperometric titra- siduals. Pseudomonas aeruginosa was APRIL, 1970 749 isolated with about the same frequency Covering Public Swvimming Pools. Pre- as coliforms. pared by the Joint Committee on Swim- ming Pools of the APHA in cooperation 5. The bacteriological data clearly wvith USPHS, 1964. show the importance of pH to the bac- 3. Keirn, M. A., and Putnam, H. D. The tericidal effectiveness of chlorine. Pools Resistance of Staphylococci to Halogens in which most of the free available as Related to a Swimming Pool Environ- chlorine was calculated to be 0C1- ment. Health Lab. Sc. 5:180, 1968. 4. Zettler, T. T., and Solsor, J. Q. Swimming showed much worse bacteriology than Pool Sanitizers. Soap & Chemical Special- those pools where the predominant spe- ties (Mar.) 1966, p. 51. cies was HOCI. 5. Black, A. P.; Kinman, R. N.: Thomas, 6. The authors strongly recommend W. C., Jr.; Freund, G.; and Bird, E. D. that free chlorine residuals at pool pH Use of Iodine for Disinfection. J. Am. Waterworks A. 57:1401, 1965. be included in any swimming pool code 6. Andersen, J. R. A Study of the Influence and, further, that more effective opera- of Cyanuric Acid on the Effectiveness of tion of public pools could be obtained Chlorine. Presented at NSPI Convention, by requiring licensing of operators and Chicago, 1964. complete automatic control of chlorina- 7. Fitzgerald, G. P., and Der Vartanian, M. E. Factors Influencing the Effectiveness of tion and pH adjustment. Swimming Pool Bactericides. Applied ACKNOWLEDGMENTS - The authors wish to Microbiol. 15:504, 1967. acknowledge the valuable assistance of Miss V. 8. Robinton, E. D., and Mood, E. W. An A. Morgan and Mrs. Albertha Pringley in Evaluation of the Inhibitory Influence of making the bacteriological analyses in the Cyanuric Acid Upon Swimming Pool Dis- Earle B. Phelps Laboratory in the Bioenviron- infection. A.J.P.H. 57:301, 1967. mental Engineering Department, University of 9. Stuart, R. S.. and Ortenzio, R. F. Swim- Florida. Appreciation is also expressed for ming Pool Chlorine Stabilizers. Presented bacteriological analyses made by laboratories at the 50th Midyear Meeting, Chemical of the Florida State Board of Health at Jack- Specialties Manufacturing Association, sonville and Miami, and the County Health Chicago (May 19), 1964. Department Laboratory at Sarasota. 10. Cothran, Walter W., and Hatlan. Jack B. A Study of an Outdoor Swimming Pool REFERENCES Using Iodine for Water Disinfection. Stu- dent Med. 10,4:493, 1962. 1. Favero, M. S.; Drake, C. H.; and Randall, 11. Robinton, E. D.; Mood, E. W.: and G. B. Use of Staphylococci as Indicators Elliot, L. R. A Study of the Bacterial of Swimming Pool Pollution. Pub. Health Flora in Swimming Pool Water Treated Rep. 79:61, 1964. with High Free Residual Chlorine. 2. Suggested Ordinance and Regulations A.J.P.H. 47:1101, 1957. Dr. Black is Research Professor Emeritus of Chemistry and Bioenvironmental Engineering, University of Florida, and Project Director, Iodine Demonstration Grant, City of Gainesville (P.O. Box 1329), Gainesville, Fla. 32601. Mr. Keim and Mr. Smith are Research Associates, Iodine Demonstration Grant, Gaines- ville. Mr. Dykes is Sanitary Engineer, Division of Water Supply, Florida State Board of Health, Jacksonville. Mr. Harlan is Assistant Professor of Physical Education and Swimming Coach, University of Florida, Gainesville. Work on this project was supported by Demonstration Grant WPD-19-05-67, WPD-19-06-68 awarded by the FWPCA of the Department of the Interior. The paper was presented before a Joint Session of the Conference of Local Environmental Health Administrators, the Conference of State Sanitary Engi- neers, the National Association of Sanitarians, and the Engineering and Sanitation and Laboratory Sections of the American Public Health Association at the Ninety-Sixth Annual Meeting in Detroit, Mich., November 14, 1968. 750 VOL. 60, NO. 4, A.J.P.H.
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