CHLORINE CONCENTRATION AND BACTERIAL
PRESENCE BETWEEN POOL CLEANINGS.
Samuel Hernandez and Robert McLaughlin. Department of Biological
Sciences, Saddleback College, Mission Viejo, CA, 92692.
Abstract
Background
Water is among one of the most valuable resources on earth. It is essential for life on
earth as we know it. For humans alone it is required to sustain life, develop agriculture,
and even provide the popular recreational activity of swimming. The prevalent use and
dependence on water in society today also has the effect of increasing our risk of
exposure to waterborne illnesses. A study by Elizabeth Hilborn found that in the 20092010 year, 33 cases of water-associated outbreaks were reported to the CDC. These
outbreaks comprised more than 1000 cases of illness, almost 100 hospitalizations, and
even death (3). To reduce this risk, regulations are in place to ensure water supplies are
disinfected and kept sanitary up until use or consumption. One such regulation is the
chlorination of water for use in swimming pools.
Chlorine is (the most common) currently the disinfectant of choice among recreational
swimming pools. A study by Rice, Clark, and Johnson in 1998 found that only a 1.1 mg/l
of concentrated chlorine, the average concentration in municipal water supplies, could
deactivate E. coli in a matter of minutes (4). Chlorine works by first forming
hypochlorous acid (HOCl). The hypochlorous acid then attacks lipids in the cell wall and
enzymes inside the cell, denaturing them and rendering them inoperable in the organism.
According to the CDC, current standards require chlorine concentrations to be between 13 mg/l and have a pH somewhere between 7 and 8 (5). Chlorine must also be regularly
added into the system, as organic contaminants or sunlight can extract free chlorine out of
the system, rendering it useless for disinfection.
Despite standardized regulations for recreational water disinfection, many public
waters(facilities) are not maintained appropriately. According to a collection of studies
reported by the CDC in the Morbidity and Mortality Weekly Report in 2008, 15 state and
local agencies across the US inspected 120,020 swimming pools. Of those inspected,
over 12 thousand had a violation due to inadequate disinfectant, and another 13,532 pools
had to be closed due to serious violations that threatened public health (1). A 2012 study
in Atlanta, Georgia of 161 swimming pool backwash filter samples found that 58% had
samples of nucleic acids belonging to E. coli, which strongly suggests fecal
contamination by swimmers (1).
Chlorine concentrations will be examined over time between one pool cleaning cycle,
and water samples will be collected over the period of time to test for the presence of E.
coli bacteria. Based on past research, it is predicted that as chlorine concentration in pool
water decreases, bacterial presence will increase.
Materials and methods
The Solana community pool in Rancho Santa Margarita, California was chosen to be
the collection site twelve water samples over a 24-hour period between pool cleanings on
November 24, 2013 and November 25, 2013. Sets of three 50 ml samples were collected
at 4 times of day: 9:00 AM, 3:00 PM, 9:00 PM, and 7:00 AM the next day, with each
sample coming from a different site in the pool (North, South and East). The samples
were tested for chlorine concentration using SenSafe Chlorine Test Strips. Lactose broths
were prepared in triple strength (36 tubes) and single strength (72 tubes) and autoclaved
to ensure sterility of equipment. Using aseptic technique, the following volumes of
sample were instilled into a lactose broth tube: 10 ml in each triple strength tube, 1 ml in
36 single strength tubes, and 0.1 ml in the other 36 single strength tubes. The lactose
tubes were stored in an incubator for 4 days at 37 oC. After 4 days, the samples were
removed from the incubator and examined for color change from green to yellow, which
would indicate a change in pH secondary to fermentation, and gas production.
Result
Chlorine concentration was found to decrease over time (figure 1). Statistical analysis
by ANOVA found statistical significance. The bonferroni correction found this
significance to be when comparing between sample 1 to samples 2 through 4, while no
significant difference was found to exist between samples 2(two, not 2… for the rest as
well), 3, and 4. Presumptive testing with the lactose broth solutions had one sample
belonging to group 4 turn yellow, suggesting pH change by fermentation. Gas production
however, was not observed in that or any other tube. The absence of fermentation and gas
production together strongly suggests that no E. coli was cultured in the lactose broths,
and the test was negative for E. coli.
Sample
collection
Chlorine
concentration
(ppm)
Fermentation/Gas
Production
Fermentation/Gas
Production
Fermentation/Gas
Production
10 ml tubes
1.0 ml tubes
0.1 ml tubes
MPN
9:00 AM
1.40
0
0
0
< 0.5
3:00 PM
0.73
0
0
0
< 0.5
9:00 PM
0.47
0
0
0
< 0.5
7:00 AM
0.43
0
0
0
< 0.5
Table 1. Chlorine concentrations demonstrating a decline in chlorine concentration
over time. No tubes demonstrated any form of fermentation and gas production
1.80
Chlorine Concentration (mg/l)
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0
200
400
600
800
1000
Time (min)
1200
1400
1600
Figure 1. Decline in chlorine concentrations over time
Discussion
The initial drop in chlorine concentration was statistically significant, dropping below
the 1.0 mg/l line that is the current standard in pool disinfection by chlorination. Based on
prior research, this suggests it is possible that E. coli ( I just italicized it )bacteria could
colonize and grow in the pool water. The presumptive test produced one test tube with a
color change to yellow due to pH change secondary to bacterial fermentation. The
bacteria in this tube did not produce any gas, making the presumptive test negative for E.
coli. Based on the results obtained, it does not support that as concentration decreases,
bacterial presence increases.
References Cited
CDC. Violations Identified from Routine Swimming Pool Inspections --- Selected States
and Counties, United States, 2008. Morbidity and Mortality Weekly Report. May 21,
2010. 2013 Dec. 59(19);582-587.
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5919a2.htm
CDC. Microbes in Pool Filter Backwash as Evidence of the Need for Improved Swimmer
Hygiene — Metro-Atlanta, Georgia, 2012. Morbidity and Mortality Weekly Report,
May 17, 2013. 2013 Dec. 62(19);385-388.
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6219a3.htm?s_cid=mm6219a3_w
Hilborn, Elizabeth D., D.V.M. 2013, Surveillance for Waterborne Disease Outbreaks
Associated with Drinking Water and Other Non-recreational Water - United States,
2009-2010. Atlanta: U.S. Center for Disease Control, 2013.
Rice EW, Clark RM, Johnson CH. Chlorine Inactivation of Escherichia coliO157:H7.
Emerg Infect Dis [serial on the Internet]. 1999, Jun. 2013 Dec.
http://wwwnc.cdc.gov/eid/article/5/3/99-0322.htm
http://www.cdc.gov/safewater/publications_pages/chlorineresidual.pdf
Delete
Replace
Move
The paper was well written, there are very few correction I found, the only thing is if you
are citing the source at the end of the sentence, it is overkill to also cite it at the
beginning. You should be able to just start a sentence, the reader will know its from that
article.
Also, there is different spacing in your paper, its on 1.0 and 1.15, I’m changing it to 1.0
all around.
Furthermore, the Methods, results, into… should be in the center of the page according to
Teh.
Lastly, you don’t need to number your sources. Just indent the ones after the first line. Is
the last one officially cited?
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s): Samuel Hernandez and Robert McLaughlin
Title CHLORINE CONCENTRATION AND BACTERIAL PRESENCE BETWEEN POOL
CLEANINGS.
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the
paper.
This paper was about chlorine concentrations in pools and how effective cleaning is. Many
pools are not cleaned properly, so they collected data at a pool to see how much chlorine
was found in the pool between cleaning it, and they found E. coli in the pool, and there was
an insufficient amount of chlorine to clean the pool after the first sample of data.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important
to our current state of knowledge.
There were no grammatical errors that I caught, the paper was well written. The methods
were clear to me, and I could follow everything you said.
Weaknesses found were minor with formatting. The references were not done correctly,
and the into, methods, results and discussion needed to be centered on the page.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors,
grammatical errors, and minor textual problems. It's not the reviewer's job to copy Edit the paper,
mark the manuscript.
X This paper was a final version
This paper was a rough draft
The paper was well written, there are very few correction I found, the only thing is if you
are citing the source at the end of the sentence, it is overkill to also cite it at the beginning.
You should be able to just start a sentence, the reader will know its from that article.
Also, there is different spacing in your paper, its on 1.0 and 1.15, I’m changing it to 1.0 all
around.
Furthermore, the Methods, results, into… should be in the center of the page according to
Teh.
Lastly, you don’t need to number your sources. Just indent the ones after the first line. Is the
last one officially cited?
Recommendation
 This paper should be published as is
 This paper should be published with revision
 This paper should not be published