Chloroform Formation from Swimming Pool Disinfection:
A Significant Source of Atmospheric Chloroform in Phoenix?
by
Christy J. Rose
A Thesis Presented in Partial Fulfillment
of the Requirements for the Degree
Master of Science
Approved November 2014 by the
Graduate Supervisory Committee:
Pierre Herckes, Chair
Matthew Fraser
Mark Hayes
Paul Westerhoff
ARIZONA STATE UNIVERSITY
December 2014
ABSTRACT
Chloroform (CHCl3) is an important atmospheric pollutant by its direct health
effects as well as by its contribution to photochemical smog formation. Chloroform
outgassing from swimming pools is not typically considered a source of atmospheric
CHCl3 because swimming pools are scarce compared to other sources. However, large
urban areas in hot climates such as Phoenix, AZ contain a substantial amount of
swimming pools, potentially resulting in significant atmospheric fluxes. In this study,
CHCl3 formation potential (FP) from disinfection of swimming pools in Phoenix was
investigated through laboratory experiments and annual CHCl3 emission fluxes from
swimming pools were estimated based on the experimental data.
Swimming pool water (collected in June 2014 in Phoenix) and model
contaminants (Pharmaceuticals and Personal Care Products (PPCPs), Endocrine
Disrupting Compounds (EDCs), artificial sweeteners, and artificial human waste
products) were chlorinated in controlled laboratory experiments. The CHCl3 production
during chlorination was determined using Gas Chromatography-Mass Spectrometry (GCMS) following solid-phase microextraction (SPME). Upon chlorination, all swimming
pool water samples and contaminants produced measureable amounts of chloroform.
Chlorination of swimming pool water produced 0.005-0.134 mol CHCl3/mol C and
0.004-0.062 mol CHCl3/mol Cl2 consumed. Chlorination of model contaminants
produced 0.004-0.323 mol CHCl3/mol C and 0.001-0.247 mol CHCl3/mol Cl2 consumed.
These numbers are comparable and indicate that the model contaminants react similarly
to swimming pool water during chlorination. The CHCl3 flux from swimming pools in
Phoenix was estimated at approximately 3.9-4.3 Gg/yr and was found to be largely
i
dependent on water temperature and wind speed while air temperature had little effect.
This preliminary estimate is orders of magnitude larger than previous estimates of
anthropogenic emissions in Phoenix suggesting that swimming pools might be a
significant source of atmospheric CHCl3 locally.
ii
For my Family
iii
ACKNOWLEDGMENTS
This material is based upon work supported by the National Science Foundation under
grant number BCS-1026865, Central Arizona Phoenix Long-Term Ecological Research
(CAP LTER). I would like to thank my advisor, Dr. Pierre Herckes and my committee
members, Dr. Matthew Fraser, Dr. Mark Hayes, and Dr. Paul Westerhoff for their
guidance in completing this work. I am indebted to the Herckes group, especially Aurelie
Marcotte, Denise Napolitano, Joana Sipe, and Jinwei Zhang, for their assistance in
sample collection, instrument troubleshooting, and endless encouragement. I also thank
Natalia Fischer, David Hanigan, Heather Stancl and other members of the Westerhoff
group for their help in analyzing water quality parameters.
iv
TABLE OF CONTENTS
Page
LIST OF TABLES ........................................................................................................ vii
LIST OF FIGURES ...................................................................................................... viii
CHAPTER
1
INTRODUCTION................. ............................................................................... 1
1.1 Project Motivation and Overview .................................................... 1
1.2 Water Disinfection and DBPs ......................................................... 2
1.3 Organic Contaminants in Swimming Pools ..................................... 3
1.4 Swimming Pool Disinfection and Water Chemistry ......................... 4
1.5 Health Risks of Exposure to DBPs in Swimming Pools ................... 6
1.6 Atmospheric CHCl3: Sources and Sinks .......................................... 8
1.7 Ambient CHCl3 in Phoenix ............................................................10
1.8 Investigations of CHCl3 Formation ................................................11
2
METHODOLOGY...............................................................................................13
2.1 Reagents .......................................................................................13
2.2 Sample Collection and Characterization .........................................13
2.3 Chlorination of Swimming Pool Water...........................................14
2.4 Chlorination of Swimming Pool Contaminants ...............................15
2.5 Extraction and GC-MS Analysis ....................................................16
3
RESULTS AND DISCUSSION ..........................................................................18
3.1 Swimming Pool Water Parameters .................................................18
3.2 Confirmation of Reaction Duration and Methods............................20
v
CHAPTER
Page
3.3 CHCl3 Formation from Chlorination of Swimming Pool Water
Samples ......................................................................................22
3.4 CHCl3 Formation from Chlorination of Swimming Pool
Contaminants ..............................................................................24
3.5 CHCl3 Flux ...................................................................................26
4
SUMMARY AND OUTLOOK............................................................................33
REFERENCES....... ........................................................................................................36
vi
LIST OF TABLES
Table
Page
3.1: Water Quality Parameters of Collected Swimming Pool Samples aWang et al.,
2013 bWesterhoff et al., 2005. cYoon et al., 2006. dLee and Westerhoff, 2007.
e
Pehlivanoglu-Mantas and Sedlak, 2008. fCDC.gov gSalter and Langhus, 2007.
h
Aiking et al., 1994. iWeaver et al., 2009 jWeng and Blatchley, 2011. ............. 18
3.2: Statistics of Swimming Pools in Phoenix (Forrest and Williams, 2010) ............ 29
vii
LIST OF FIGURES
Figure
Page
1.1: 2012 Average Annual Ambient CHCl3 Concentrations (EPA Air Toxics Data,
2012) ............................................................................................................. 10
2.1: Schematic of Reaction Vial with Cl2 and CHCl3 Sampling Set-Up .................... 15
2.2: Temperature Program for GC-MS Analysis of CHCl3. ...................................... 17
3.1: Kinetics of CHCl3 Formation From Chlorination of Resorcinol (●) and
Oxybenzone (●) in This Study. Chlorination of Resorcinol by Chaidou et al.
(1999) (—) and Oxybenzone by Duirk et al. (2013) (—) Show Comparable
Completion Timing ........................................................................................ 21
3.2: CHCl3 amd Cl2 Concentrations During Chlorination of Oxybenzone ................. 22
3.3: Molar Yield of CHCl3 per mol C from Chlorination of Collected Swimming Pool
Water. Error Bars Indicate the Standard Deviation of Triplicate Experiments.
Shaded Region indicates 0.01 mol CHCl3/mol C as Measured by Lee et al.
(2007). ........................................................................................................... 23
3.4: Molar Yield of CHCl3 per mol Cl2 Consumed from Chlorination of Collected
Swimming Pool Water. Error Bars indicate the Standard Deviation of Triplicate
Experiments. Shaded Region Indicates 0.039 mol CHCl3/mol Cl2 as Measured
by Weng and Blatchley (2011). ..................................................................... 23
3.5: Molar Yield of CHCl3 per mol C in Precursor from Chlorination of Suspected
Swimming Pool Contaminants. Error Bars Indicate the Standard Deviation of
Triplicate Experiments. *Error Bars Indicate Standard Deviation of Two
viii
Figure
Page
Measurements. Shaded Region Indicates Maximum of 0.134 mol CHCl3/mol C
Found from Chlorination of Swimming Pools Samples in This Study. ............. 24
3.6: Molar Yield of CHCl3 per mol Cl2 Consumed from Chlorination of Suspected
Swimming Pool Contaminants. Error Bars Indicate the Standard Deviation of
Triplicate Experiments. *Error Bars Indicate Standard Deviation of Two
Measurements. Shaded Region Indicates Maximum of 0.061 mol CHCl3/mol Cl2
Found from Chlorination of Swimming Pools Samples in This Study. ............. 25
3.7: Daily, Monthly, and Annual CHCl3 Flux from Swimming Pools in Phoenix
Calculated with Wind Speed and Air Temperature Data for 2013 While Holding
Water Temperature Constant. ......................................................................... 29
3.8: Daily, Monthly, and Annual CHCl3 Flux from Swimming Pools in Phoenix
Calculated with Average Annual Wind Speed, Varying Air Temperature and
Water Temperature for 2013. .......................................................................... 30
3.9: Swimming Pool Emissions of CHCl3 in Phoenix compared to estimated natural
and anthropogenic emission estimates.. ........................................................... 31
ix
CHAPTER 1
INTRODUCTION
1.1 Project Motivation and Overview
Chloroform (CHCl3) is a well documented disinfection by-product (DBP) of
water chlorination (Richardson et al., 2010). Within the scope of atmospheric pollution,
CHCl3 is of importance due to its direct health effects as well as its contribution to
photochemical smog formation. Natural sources of CHCl3 such as vegetation, soil and
ocean processes account for 90% of global CHCl3 emissions (Khalil and Rasmussen,
1999); however, most human exposure occurs in urban settings. Locally, major sources
of CHCl3 in the urban atmosphere are industrial operations such as pharmaceutical and
refrigerant manufacturing as well as landfill processing. Chloroform outgassing from
swimming pools is not typically considered a source of atmospheric CHCl3 because
swimming pools are scarce compared to other sources. However, urban areas in hot
climates such as Phoenix generally contain a substantial number of swimming pools per
capita. Arizona ranks fourth in the nation for total number of swimming pools and second
in swimming pools per capita with 4.8 swimming pools per 100 people (P.K. Data,
2013). The temperate regions of Arizona limit swimming pools to the central desert
region whereas swimming pools in other states are generally distributed throughout the
state. Additionally, states with more swimming pools than Arizona benefit from coastal
breezes that help clear the air of pollutants. It is possible that the numerous chloroformemitting pools within a valley such as Phoenix are as a sum responsible for a substantial
portion of the atmospheric chloroform in urban air. This study investigated CHCl3
formation potential (FP) from chlorination of swimming pool water collected in Phoenix,
1
AZ and suspected swimming pool contaminants to determine maximum CHCl3
production. FP was used to estimate CHCl3 flux from swimming pools in Phoenix to
determine total annual emissions.
1.2 Water Disinfection and DBPs
Disinfectants are necessary to inactivate biological contaminants in water such as
algae, viruses and bacteria. The most common chemical disinfection methods include
treatment with chlorine and chloramines. Chlorine is a very effective disinfectant and is
therefore used in heavily contaminated waste waters. If wastewater is intended for return
to consumers as non-potable irrigation water, as is increasingly common in light of water
conservation efforts, further purification such as filtration or adsorption with activated
carbon is required (Redman et al., 2001). Chloramination is preferred in drinking water
disinfection because it tends to produce less odor and taste-causing byproducts
(Boorman, 1999). Chlorination and bromination are the most common disinfectants used
in swimming pools. Disinfectants work by oxidizing the cell membranes of biological
contaminants. Because of these strong oxidative properties, organic contaminants are also
oxidized resulting in DBPs; however these DBPs are not generally removed from the
water.
DBPs were first recognized in 1974 by Rook et al. and public interest soon
followed. Despite a strong interest in understanding and extensive investigation of DBP
production, much is still unknown. The major contribution to this gap in knowledge is the
large variability in precursors resulting in a seemingly infinite number of DBP species
and therefore a tedious process in identifying and characterizing these DBPs. Several
2
classes of disinfection byproducts have been reported. Chlorination of drinking water has
been found to produce trihalomethanes (THMs), haloacetic acids (HAAs),
haloacetonitriles (HANs) and haloketones while ozonation has been found to produce
aldehydes and brominated compounds (Boorman, 1999). Over 500 DBPs have been
detected in chlorinated waters, but 50% of organic halide mass remains uncharacterized.
Other studies have identified several hundred DBPs in swimming pools alone (Kim et al.,
2002; Zweiner et al., 2007; Richardson et al., 2010).
1.3 Organic Contaminants in Swimming Pools
Organic contaminants commonly found in swimming pools are similar to those
found in waste water and surface water. These include human waste products such as
sweat and urine, Pharmaceuticals and Personal Care Products (PPCPs) such as lotions
and perfumes, and Endocrine Disrupting Compounds (EDCs) such as synthetic hormones
from oral contraceptives.
PPCPs and EDCs are of particular interest because of their ability to affect
ecosystem health and their potential to mimic or block hormones. Medicinal metabolites
such as 1,7-dimethylxanthine (caffeine metabolite) and 17α-ethinylestradiol (oral
contraceptive metabolite) are excreted and flushed down the toilet which must then be
treated at waste water treatment plants. Items such as sunscreen, lotions and perfumes are
released into the freshwater supply during swimming or bathing. Although several studies
have shown that these contaminants pose no immediate human health risks, long-term
effects are not known (Christensen, 1998; Schulman et al., 2002; Webb et al., 2003).
Swimming pools are different from surface water in that the water is continuously cycled
3
and rarely replenished, causing a build-up of contaminants. DEET, an insect repellant,
and caffeine were found in swimming pools at concentrations of 100~2100 ng/L and
50~500 ng/L, respectively (Weng et al., 2014), compared to 2~20 ng/L in various
Arizona ground and surface waters (Chiu and Westerhoff, 2010).
Ongoing efforts to reduce occurrences of contaminants and DBPs in swimming
pools focus on preventing introduction of precursors into waters. Public pools often
require swimmers to shower before entering the pool to remove body care products such
as lotions and perfumes as well as body oils and sweat. Additionally, the Center for
Disease Control (CDC) recommends showering with soap before engaging in water
activities to reduce introduction of recreational water illness (RWI)-causing pathogens
that can survive several days even in well-maintained waters, such as Cryptosporidium,
Giardia, Shigella, norovirus, and E. coli (Castor and Beach, 2004).
DBP removal from swimming pools generally occurs only through outgassing of
volatile compounds at the surface. Swimming pool water is not well-mixed in unused
pools; therefore conditions vary in vertical profiles due to temperature gradients and UV
penetration in addition to out-gassing at the surface (Lian et al., 2014). Turbulence from
splashing can bring more DBPs to the water’s surface causing an increase in outgassing
of DBPs and therefore increased exposure rates in swimmers (Aggazzotti et al., 1995).
1.4 Swimming Pool Disinfection and Water Chemistry
Chlorination is the most common type of swimming pool disinfection because it
is the cheapest and most effective method. When chlorine gas is used, Cl2 hydrolyzes in
4
water to form hypochlorous acid (HOCl) (Equation 1.1) which then dissociates to
hypochlorite (OCl-) (Equation 1.2).
Cl2 (g) + H2O (l) ↔ HOCl (aq) + HCl (aq)
pKeq=-4.60
Equation 1.1
HOCl ↔ OCl- (aq) + H+ (aq)
pKa=7.54
Equation 1.2
Hypochlorous acid is more often added directly to pools as aqueous sodium hypochlorite
(NaOCl), commonly referred to as liquid chlorine or bleach, or solid calcium
hypochlorite (Ca(OCl)2) via tablets. Speciation of hypochlorous acid is largely pH
dependent. Below pH ~5, hypochlorous acid exists primarily as hypochlorite. Between
pH 5 and pH 8, HOCl and OCl- exist in similar concentrations and above pH 8,
hypochlorous acid exists primarily as the protonated form. Hypochlorite, referred to as
active chlorine, is the reactive species responsible for disinfection whereas HOCl,
referred to as available chlorine, is known to have no bactericidal properties but rather
serves as a reservoir to replace OCl- as it is consumed (Black et al., 1970). Rate of
formation of DBPs has been found to be largely pH dependent due to this speciation. The
recommended range for pH in swimming pools is 7.2-7.8. Within this range, chlorine is
most effective as a disinfectant without irritating eyes and nasal linings (CDC.gov).
Chlorine is measured as chlorine residual, which is expressed in two forms: free
and total chlorine. Free chlorine is a measure of the disinfection power of the chlorine in
water and includes both OCl- and HOCl. Because chlorine exists in several forms,
representation is standardized as mg/L Cl2 and refers to all available forms of reactive
chlorine. Hypochlorous acid, OCl- and Cl2 are considered available forms while chloride
ion (Cl-) is not reactive and therefore is not considered available chlorine. Combined
chlorine is a measure of the concentration of chlorine present in non-reactive compounds
5
such as DBPs. Total chlorine refers to the sum of free and combined chlorine in the
sample.
Spectrophotometric measurement of free and total chlorine using N,N-diethyl-pphenylenediamine (DPD) as an indicator is well-outlined in EPA Method 334.0
(Wendelken et al., 2009) and is similarly used in waste water, drinking water, and
swimming pool water testing (Moore et al., 1984). Free chlorine reacts with DPD to form
a magenta solution. In the case of total chlorine, potassium iodide is added to liberate any
combined chlorine to form free chlorine that then can then react with DPD.
Several other chemicals are also added to swimming pool water to maintain
adequate water chemistry. Bicarbonate buffer is added to maintain pH during heavy use.
Cyanuric acid is added as a stabilizer to protect chlorine from UV degradation. Algaecide
is added to treat or prevent algae growth. Copper-containing algaecides are most effective
but can cause staining in pools and are only used in cases of heavy algae growth. Alkyl
dimethyl benzyl ammonium chlorine, commonly called quat algaecide (referring to the
quaternary ammonium functional group) is cheaper and does not stain pools and therefore
is the most commonly used algaecide (Rowhani and Lagalante, 2007).
1.5 Health Risks of Exposure to DBPs in Swimming Pools
Although swimming is often applauded as a low-impact fitness activity and fun
pastime, exposure to DBPs in swimming pool water can pose various health risks. The
most common complaint from swimmers is of irritation to mucus membranes in the eyes
and nose. This irritation is caused by exposure to chloramines, which are responsible for
the distinctive “chlorine” smell of pools (Hery et al., 1995). Prolonged breathing of
6
indoor swimming pool air can also cause irritation in lungs and is blamed for adolescent
and occupational asthma symptoms (Font-Ribera et al., 2009; Jacobs et al., 2007;
Thickett et al., 2002). Chloramines are formed by chlorination of nitrogen-containing
compounds which are often introduced to the pool as biological waste products such as
sweat and urine.
Chloroform as a DBP is of particular interest because of its known carcinogenic
properties. A positive correlation has been found between bladder cancer mortality rates
and CHCl3 concentrations in drinking water (Cantor et al., 1978; Hogan et al., 1979).
High doses of CHCl3 inhalation have also been found to induce liver cancer in mice
(Larson et al., 1996). Cancer risk from dermal exposure to CHCl3 while swimming was
found to be substantially higher than gastrointestinal or dermal exposure to CHCl3 in tap
water (Panyakapo et al., 2008).
Inhalation and dermal exposure to CHCl3-containing waters such as when
swimming leads to higher blood levels than does oral exposure such as drinking
chlorinated water (Aggazzotti et al., 1993; Weisel and Jo, 1996; Kuo et al., 1998). In
adults, CHCl3 in exhaled air was found to be 6.8 times higher after 40 minutes of indoor
swimming (Kogevinas et al., 2010). Elevated CHCl3 concentrations in blood plasma and
exhaled air were detected up to 10 hours after exposure (Aggazzotti et al., 1990). These
symptoms are thought to be exacerbated in indoor swimming pools compared to outdoor
pools due to a build-up of volatile chemicals in indoor pool air despite required
ventilation (Aiking et al., 1994). In outdoor swimming pools, these volatile chemicals are
readily dissipated from the surface of the water by wind, resulting in decreased exposure.
Chloroform concentrations in blood and urine were found to be lower when swimming in
7
outdoor pools compared to indoor pools (Aiking et al., 1994). However, this dissipation
can potentially result in elevated atmospheric concentrations.
1.6 Atmospheric CHCl3: Sources and Sinks
Atmospheric CHCl3 is important as a main transporter of chlorine through the
troposphere, however global budgets show large missing sources (Rhew et al., 2008a).
Total CHCl3 flux through the environment is estimated to be 660±220 Gg∙yr -1 of which
approximately 90% is from natural sources (McCulloch, 2003). The largest natural
sources of CHCl3 are from biological processing in ocean water and soil. Ocean algae
and seaweed have been reported to produce CHCl3 in measureable concentrations
(McCulloch, 2003; McConnell and Fenical, 1997; Nightingale et al., 1995). Emissions
from soil were found to much smaller in dry soils such as in deserts than moist soils such
as in rain forests or summer tundra (Rhew et al., 2008b).
Several anthropogenic sources of CHCl3 are known. Anaerobic decomposition
such as in landfills and feedlot waste has been reported to produce significant amounts of
CHCl3 (Aucott et al., 1999). Pharmaceutical manufacturing and disposal are also known
to utilize large amounts of CHCl3 as solvent. However, paper mills are by far the largest
source of anthropogenic CHCl3 emissions as CHCl3 is a known by-product of chemical
decomposition of wood pulp and bleaching of paper with chlorine. In 1990, paper
manufacturing and pulp processing plants were responsible for release of 9.97 Gg CHCl3
to the environment in the United States or 90% of all reported CHCl3 releases (Aucott et
al., 1999). Human exposure to CHCl3 primarily occurs in urban settings from
anthropogenic sources. Potable water is a main source of exposure through drinking and
8
showering in water containing CHCl3 (Aucott et al., 1999; Kuo et al., 1998; Richardson
et al., 2007). Drinking water and waste water treatment plants generated an estimate 2
Gg/yr (Aucott et al., 1999). Use of bleach and other chlorine-containing cleaners also
introduces exposure potential. CHCl3 concentrations were found to exceed 1 mg/L in
washwater of residential washing machines during laundering with bleach (Shepherd et
al., 1996).
Industrial emissions of several toxic chemicals are monitored by the
Environmental Protection Agency (EPA) via the Toxic Release Inventory (TRI) Program.
Under this program, facilities are required to report annual disposal management or
release to the environment of certain toxic chemicals if the facility is in a specified
industry such as manufacturing or mining, employs 10 or more full- time employees, and
manufactures or process more than 25,000 lbs of a TRI-listed chemical or otherwise uses
more than 10,000 lbs of a TRI-listed chemical each year (EPA TRI Program, 2014). This
data can be used to provide a rough estimate for anthropogenic emissions but is limited in
that it only contains larger point sources.
Chloroform readily hydrolyzes in water; however the high volatility of CHCl3
leads to transport into the gas phase at a faster rate than hydrolysis occurs (McCulloch,
2003). Therefore, water is not considered to be an acceptable CHCl3 sink. Recent studies
report possible sinks in soils and plants through unexplained uptakes (Liu, 2006; Wang et
al., 2007). Atmospheric removal of CHCl3 is the main removal pathway from the
environment and occurs through oxidation by hydroxyl radical (OH•) (McCulloch, 2003)
9
1.7 Ambient CHCl3 in Phoenix
Figure 1.1 shows annual average ambient CHCl3 concentrations for several cities
in the United States from 2012. Seattle, WA and Cedar Rapids, IA show the highest
concentrations of CHCl3 followed by Tulsa, OK and Phoenix, AZ. Based upon TRI data,
CHCl3 sources can be identified in Seattle, Cedar Rapids and Tulsa but not in Phoenix.
The large paper mill industry in Washington surrounding Seattle leads to high emissions
of CHCl3. A large number of pharmaceutical companies in Cedar Rapids report use of
CHCl3. In Tulsa, CHCl3 several oil refineries report production of CHCl3. However, no
CHCl3 use in Phoenix has been reported to TRI since 1999. Therefore, a disparity exists
between ambient CHCl3 concentrations in Phoenix and recognized emission sources. It is
important to note that emission of CHCl3 does not always correlate directly to ambient
concentrations. For example, presence of oil refineries throughout Texas is not consistent
with high ambient CHCl3 concentrations, possibly due to meteorological factors such as
Figure 1.1: 2012 Average Annual Ambient CHCl3 Concentrations
(EPA Air Toxics Data, 2012)
10
coastal breeze clearing the air. However, anthropogenic influences are a good indicator
for presence of CHCl3 and other pollutants. Urban areas typically see air toxic
concentrations well above the one in one million cancer risk level. A 2005 study found
that average annual CHCl3 ambient concentrations in Phoenix were exceptionally high
(>75th percentile) despite a lack of reported sources (Hafner and O’Brien, 2006). The
Motorola, Inc. Superfund Site in Phoenix is an area with known chemical contamination
and CHCl3 emission from this site was investigated (North Indian Bend Wash, 2005).
Modeling estimates report 3.94 kg/yr CHCl3 is released from the superfund site and is
expected to decrease as cleanup for the site continues. Additionally, likely local
emissions sources including semiconductor manufacturing, have abandoned the use of
CHCl3 as a solvent in recent years.
Although previous studies provide estimates on anthropogenic CHCl3 emissions,
natural sources are not well characterized in Phoenix. Studies of natural CHCl3 emissions
in the desert regions of southern California can provide reasonable comparisons to
Phoenix desert emissions. Chloroform emission in dry dessert shrubland was found to be
6.6 nmol∙m-2∙day-1 (Rhew et al., 2008a). This estimate is possibly high for Phoenix
because desert plants are sparser in Arizona than in California.
1.8 Investigations of CHCl3 Formation
Although a mechanism for formation of CHCl3 is still not known, other aspects of
CHCl3 formation have been well-studied. Chloroform rate constants from chlorination of
resorcinol change non-linearly with pH, and occur as a minimum at pH ~6 with a
maximum at pH~8 (Gallard and von Gunten, 2002a). Additionally, CHCl3 formation in
11
swimming pools has been shown to be closely related to bather load due to introduction
of precursors. One study showed diurnal variations in CHCl3 during daily heavy
swimming pool use (Weng and Blatchley, 2011). Chloroform formation is often express
as formation potential (FP) which describes the maximum formation of a product without
regard to rate of formation. This value is determined to be the concentration of product
after all reactions have reached equilibrium.
12
CHAPTER 2
METHODOLOGY
2.1 Reagents
All glassware was washed and solvent rinsed with isopropanol (Optima grade,
Fisher Scientific; Fairlawn, NJ) and baked at 450 °C for 12 hours and stored in aluminum
foil to keep them clean until used. Chloroform (99.8% purity) was purchased from
Mallinckrodt Chemicals (St. Louis, MO) and deuterated chloroform (99.96% purity) was
purchased from Cambridge Isotope Labs (Tewksbury, MA). Sodium hypochlorite (1012% active chlorine) and all other reagents (≥98% purity) were purchased from Sigma
Aldrich (St. Louis, MO). All water used was 18.2 MΩ∙cm from a Millipore water
filtration system (EMD Millipore; Billerica, MA). Stock buffer solution was made using
monohydrogen sodium phosphate (HNa2PO4) and dihydrogen sodium phosphate
(H2NaPO4) and pH was adjusted to 7.2 using 10 N sulfuric acid (H2SO4) and 3 M sodium
hydroxide (NaOH).
2.2 Sample Collection and Characterization
Swimming pool samples were collected in June 2014 from outdoor pools
throughout the Phoenix metro area. Samples were collected at approximately 30-40 cm
below the water’s surface into 1 L high-density polyethylene (HDPE) bottles that had
been cleaned and solvent-rinsed with isopropanol. Samples were immediately stored
under refrigeration at 4°C. Prior to use, all pool samples were filtered with pre-baked
quartz fiber filters (0.7 μm, Whatman, Piscataway, NJ). Sample pH was measured using
an Accumet (Hudson, MA) AP62 portable pH meter calibrated with pH 4, 7 and 10
13
buffers. UV absorbance at 254 nm was performed with a Shimadzu (Columbia, MD)
PharmaSpec UV-1700 UV-Vis Spectrophotometer in photometric mode. Chlorine
residual was measured spectrophotometrically as free and total chlorine according to
EPA Method 344 (Wendelken et al., 2009) using commercially prepared DPD reagent
pillows (Hach, Loveland, CO). Absorbance of DPD was measured at 514.6 nm using a
handheld Vernier (Beaverton, OR) LabQuest with SpectroVis Plus attachment.
Conductivity was measured using a VWR (Radnor, PA) Model 2052 digital conductivity
meter. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were
measured by Natalia Fischer of the Westerhoff group (ASU) using a Shimadzu Total
Organic Carbon (TOC)-VCSH after acidifying and purging with carbon-free oxygen.
Dissolved organic nitrogen (DON) was calculated as the difference between TDN and
dissolved inorganic nitrogen (TDN) (ammonia, nitrate, and nitrite). Ammonia, nitrate,
and nitrite measurements were performed spectrophotometrically using commercially
prepared Hach reagent sets with absorbance measured in a Hach DR 5000
spectrophotometer. Bromide was measured using a Dionex (Sunnyvale, CA) DX-120 ion
chromatograph (IC) system by Heather Stancl of the Westerhoff group (ASU).
2.3 Chlorination of Swimming Pool Water
Pool samples were mixed with 1 M phosphate buffer at pH 7.2 to achieve a 0.5 M
phosphate buffer solution. Previously measured DOC was used to determine chlorine
demand of pool water and chlorine (NaOCl, 10-15% active chlorine) was added at 100x
excess. Deuterated chloroform (CDCl3) was added as an internal standard, free and total
chlorine were measured, and pH was recorded. The sample solution was transferred to an
14
amber glass reaction vial and capped with a polytetrafluoroethylene (PTFE) septum cap
within 30 seconds of addition of chlorine. Initial CHCl3 concentration was measured. The
septum allowed liquid sample retrieval via syringe and headspace extraction while
maintaining a gastight system. Reactions were stored at constant room temperature (22
°C) for at least 85 hours. Then final concentrations of CHCl3, chlorine residual and pH
were measured. Figure 2.1 shows a schematic of the reaction vial and sampling set-up.
Figure 2.1: Schematic of Reaction Vial with Cl2 and CHCl3 Sampling Set-Up.
2.4 Chlorination of Swimming Pool Contaminants
Chlorination of various precursors (PPCPs, EDCs, artificial sweeteners, and
artificial human waste products) in simulated swimming pool water were investigated to
determine possible contributions to CHCl3 FP. Precursors were chosen because of known
or suspected occurrence in swimming pool water or detection in Arizona surface water
(Chiu and Westerhoff, 2010). Reactions were performed in 0.5 M phosphate buffer at pH
7.2. Precursors were dissolved in dimethylsulfoxide (DMSO) then added at ~1 mg/L.
15
Precursor concentrations in this study were chosen at higher concentrations than those
found in surface water due to instrument sensitivity. Chlorine was added at 100x excess
and CDCl3 was added as an internal standard. A reaction blank using DMSO was also
performed. Free and total chlorine was measured, pH was recorded, and the reaction
solution was placed in an amber glass reaction vial then capped within 30 sections of
chlorine addition. Reactions were stored at 22 °C. Final CHCl3 concentration, chlorine
residual and pH were measured after at least 85 hours.
2.5 Extraction and GC-MS Analysis
Chloroform was extracted by 15 minute headspace extraction via solid phase
microextraction (SPME) using a 100 μm film-coated polydimethylsiloxane (PDMS) fiber
assembly with manual holder (Supelco, Bellefonte, PA). After extraction, an Agilent
(Santa Clara, CA) 6890N Gas Chromatograph (GC) coupled with Agilent MSD 5973
Mass Spectrometer (MS) in electron impact (EI) ionization mode was used to isolate and
determine CHCl3. Separation was performed with a SPB-1 fused silica capillary column
(30 m x 0.25 mm x 0.25 μm, Supelco) with helium as the carrier gas at 1.2 mL/min after
splitless injection at inlet temperature 230 °C. The total analysis run time was 5 minutes,
with constant temperature of 40 °C for 2 min then temperature ramp at a rate of 20
°C/min until 100 °C was achieved. Figure 2.2 shows a graphical representation of the
temperature program. Chloroform elution occurred at approximately 2 minutes with
additional temperature ramp to remove impurities on SPME fiber. Deuterated chloroform
was added to all samples as an internal standard to determine instrument response and
calculate CHCl3 concentration. Mass-to-charge ratios of 83 and 84 give the strongest
16
signals for CHCl3 and CDCl3, respectively. A ratio of peak areas for m/z=83 and 84 was
used to form a calibration curve.
temperature (°C)
120
100
80
60
40
20
0
1
2
3
time (min)
4
Figure 2.2: Temperature Program for GC-MS Analysis of CHCl3.
17
5
CHAPTER 3
RESULTS AND DISCUSSION
3.1 Swimming Pool Water Parameters
Table 3.1 shows the water quality parameters of collected pool samples. Pools
were categorized into three types: private, community, and public pools. These categories
can be used to describe bather load of the swimming pool to estimate the rate at which
contaminants are introduced into a pool. Private pools have tens of bathers per season,
and might not be used daily. Community pools such as those in apartment complexes or
country clubs may have hundreds of bathers per season, while public pools might see as
many as 1000 bathers per season.
DOC was measured to determine total organic contaminants in the water. All
pools except pool 6 contained DOC concentrations above the expected 2-13 mg/L DOC
for swimming pools (Zweiner et al., 2007; Kanan and Karanfil, 2011; Wang et al., 2013).
This might be attributed to potentially high use of alkyl-containing algaecides during
summer months. Haboobs in Phoenix kick up iron-rich dust which is then deposited
throughout the city, including into outdoor swimming pools. Iron is known to promote
DOC
SUV254
DON
(mg/L) (L∙mg-1∙m-1) (mg/L)
free Cl2 total Cl2 Conductivity
(mg/L) (mg/L)
(mS/cm)
pool type
1
private
41
0.07
52
7.50
0.03
0.15
2.01
4.04
2
private
49
0.06
62
7.32
8.7
9.2
2.37
0.11
3
community
69
0.10
80
7.47
19.6
25.7
2.19
6.85
4
community
138
0.06
195
7.27
8.3
9.4
3.81
1.47
5
community
92
0.03
118
7.08
3.0
3.4
3.41
0.74
6
public
2.1
0.75
10
15
4.72
0.07
expected:
2-13
a
1-6
b,c,d
2-14
pH
CHCl3
(μM)
pool #
7.16
e
7.2-7.8
15
f
1-3
g
h
0.15-0.21h,i,j
<3
a
Table 3.1: Water Quality Parameters of Collected Swimming Pool Samples. Wang et al.,
2013 bWesterhoff et al., 2005. cYoon et al., 2006. dLee and Westerhoff, 2007.
e
Pehlivanoglu-Mantas and Sedlak, 2008. fCDC.gov gSalter and Langhus, 2007. hAiking et
al., 1994. iWeaver et al., 2009 jWeng and Blatchley, 2011.
18
rapid algal growth (Griffin and Kellogg, 2005), therefore algaecides are added as
preventative maintenance. Addition of alkyl-containing algaecides might result in high
DOC measurements. Pool Time (Lawrenceville, GA) preventative algaecide, advertises
20% w/w alkyl (50% C14, 40% C12 and 10% C10) dimethyl benzyl ammonium chloride as
the active ingredient. Weekly addition of 3 fl. oz. per 10,000 gallons as directed would
result in 4.15 mg/L DOC added per week. For an average swimming season of 27 weeks
(Forrest and Williams, 2010), algaecides would contribute 112 mg/L DOC per swimming
season.
SUV254 is calculated by Equation 3.1 and gives a measure of aromatic content to
help determine degree of natural organic matter. SUV254 was lower than expected which
indicates low aromaticity and high non-aromatic carbon. This is consistent with frequent
alkyl-containing algaecide use.
Equation 3.1
DON was measured to determine biological matter in pool samples. Ammonia
and nitrite were not present in any pool samples while nitrate was present in all samples
in small concentrations (<9mg/L). DON was higher than expected in all pools. This
might be due to the use of alkyl algaecides, which contain quaternary ammonium centers,
or organic stabilizers such as cyanuric acid (C3H3N3O3).
Measurements of pH in all pools were close to or within the recommended range
of 7.2-7.8 and were consistent with pH ranges found in other studies (Wang et al., 2013).
Free and total Cl2 were above the recommended values of 1-3 mg/L, respectively,
for all pools except pool 1 and 5. High Cl2 dosing is typical during seasons of high use to
eliminate the need for frequent monitoring.
19
Conductivity was measured to determine total inorganic content in pool samples.
These species include any ions in the water such as Na+, Ca2+ and Cl-. Pools 1-3 were
within the expected range of <3 mS/cm. Above this value, water chemistry becomes
difficult to maintain but swimming comfort is not affected.
Chloroform was present in all pools at the time of collection with an average 2.21
μM. Chloroform concentrations in pools 2 and 6 were similar to concentrations found in
other swimming pools (Aiking et al., 1994; Weaver et al., 2009; Weng and Blatchley et
al., 2011). All other pools were higher but still below the recommended 8 μM limit.
Bromide measurements were performed but bromide was not detected. This was
expected as bromide levels are generally very low except in brominated pools and spas.
3.2 Confirmation of Reaction Duration and Methods
Resorcinol and oxybenzone were used as model compounds to determine reaction
time to reach completion of CHCl3 production. This point was determined as the point at
which the rate of CHCl3 formation significantly decreased. Resorcinol displayed
completion within 1 hour (Figure 3.1) and is consistent with findings from previous
studies which report a range of 1 to 10 hours (Gallard and von Gunten, 2002a; Gallard
and von Gunten, 2002b; Blatchley et al., 2003; Chang et al., 2006). Oxybenzone
displayed completion after approximately 85 hours whereas previous studies have shown
that CHCl3 formation reached completion after 24 hours in a pH range of 6-8 and a 25 °C
for oxybenzone (Duirk et al., 2013). This difference might be due to pH and temperature
variations. Rate constants have been shown to decrease at higher pH and lower
20
temperatures. Therefore, CHCl3 formation was allowed to occur for 85 hours before final
measurements were taken to ensure completion of CHCl3 formation had been reached.
Resorcinol displayed a molar yield of 0.251 mol CHCl3/mol resorcinol which is
typical of other molar yields for phenolic compounds with a range of 0.01-0.3 mol
CHCl3/mol phenol (Gallard and von Gunten, 2002a). This similarity with literature data
further confirms validity of these methods.
Figure 3.2 shows an increase in CHCl3 concentration as free chlorine
concentration decreases. Consistent presence of free chlorine after 85 hours confirms that
chlorine was not a limiting factor of CHCl3 FP. Limit of quantification (LOQ) of CHCl3
was determined to be 50 nM and the limit of detection (LOD) was determined to be 20
nM.
18
16
resorcinol
CHCl3 (μM)
14
12
resorcinol, scaled
(Chaidou et al., 1999)
10
8
oxybenzone
6
4
oxybenzone, scaled
(Duirk et al., 2013)
2
0
0
20
40
60
80 100 120 140 160 180
time (hrs)
Figure 3.1: Kinetics of CHCl3 Formation from Chlorination of Resorcinol (●) and
Oxybenzone (●) in This Study. Chlorination of Resorcinol by Chaidou et al. (1999) (—)
and Oxybenzone by Duirk et al. (2013) (—) Show Comparable Completion Timing.
21
160
CHCl3 (μM)
150
10
140
130
5
120
0
free chlorine (mg Cl2/L)
15
110
0
50
100
time (hrs)
150
200
Figure 3.2: CHCl3 amd Cl2 Concentrations During Chlorination of Oxybenzone.
3.3 CHCl3 Formation from Chlorination of Swimming Pool Water Samples
Figure 3.3 shows the molar yield of CHCl3 per mole C present in the pool water.
Chlorination of pool 6 exhibited chloroform formation similar to other pools despite
containing the smallest concentration DOC, resulting in the largest molar yield at 0.134
mol CHCl3/mol C while Pools 1-5 produced less than 0.03 mol CHCl3/mol C. Molar
yield does not appear to be dependent on any of the measured water quality parameters.
A correlation is expected between DOC and CHCl3 formation as carbon should be the
limiting reactant, however this trend is not seen, suggesting the formation of other DBPs
competes with formation of CHCl3.
Figure 3.4 shows molar yield of CHCl3 per mole Cl2 consumed. Pool 6 again
showed a higher molar yield than other pools with 0.062 mol CHCl3/mol Cl2, indicating
that CHCl3 was formed while consuming less Cl2 than other pools.
22
Figure 3.3: Molar Yield of CHCl3 per mol C from Chlorination of Collected Swimming
Pool Water. Error Bars Indicate the Standard Deviation of Triplicate Experiments.
Shaded Region indicates 0.01 mol CHCl3/mol C as Measured by Lee et al. (2007).
Figure 3.4: Molar Yield of CHCl3 per mol Cl2 Consumed from Chlorination of Collected
Swimming Pool Water. Error Bars indicate the Standard Deviation of Triplicate
Experiments. Shaded Region Indicates 0.039 mol CHCl3/mol Cl2 as Measured by Weng
and Blatchley (2011).
23
3.4 CHCl3 Formation from Chlorination of Swimming Pool Contaminants
Figure 3.5 shows molar yield of CHCl3 per mole C chlorinated for several
suspected swimming pool contaminants. A ratio of 1 would indicate complete conversion
to CHCl3. Chlorination of urea showed the highest molar yield at 0.323 mol CHCl3/mol C
and artificial sweat showed the lowest with 0.004 mol CHCl3/mol C. Molar yields for
these model compounds are comparable to those found from chlorination of swimming
pool water which indicates that these model compounds behaved similarly to swimming
pool water when chlorinated.
Nitrogen-containing compounds are thought to result in smaller molar yields because
the fast formation of chloramines shifts by-product formation from CHCl3. Previous
studies reported a complete lack of CHCl3 upon chlorination of urea with NCl3 being the
main by-product (Blatchley and Cheng, 2010). In this study, a considerable amount of
Figure 3.5: Molar Yield of CHCl3 per mol C in Precursor from Chlorination of Suspected
Swimming Pool Contaminants. Error Bars Indicate the Standard Deviation of Triplicate
Experiments. *Error Bars Indicate Standard Deviation of Two Measurements. Shaded
Region Indicates Maximum of 0.134 mol CHCl3/mol C Found from Chlorination of
Swimming Pools Samples in This Study.
24
CHCl3 was produced from chlorination of urea. In contrast, artificial urine (urea plus
creatinine) and artificial sweat (urea plus lactic acid) showed low molar yields. Other
nitrogen-containing compounds (acetaminophen, carbemazepine, DEET, primidone, and
sulfamethoxazole) do not consistently display decreased CHCl3 yields; therefore presence
or absence of nitrogen is not the main factor in determining formation potential with
these precursors.
Low production of CHCl3 per mole Cl2 consumed (Figure 3.6) indicates high
formation of combined chlorine as other DBPs. In sucralose, the low CHCl3/C molar
ratio with high CHCl3/Cl2 molar ratio indicates that less Cl2 is consumed for consumption
of carbon when compared to other compounds. This is because sucralose is chlorinated
on three carbons, and the presence of chlorine in the compound results in less chlorine
addition needed to form a CHCl3. Overall reactivity of sucralose is expected to be low
because halogenation leads to stability of sucralose, as seen by the inability for sucralose
Figure 3.6: Molar Yield of CHCl3 per mol Cl2 Consumed from Chlorination of Suspected
Swimming Pool Contaminants. Error Bars Indicate the Standard Deviation of Triplicate
Experiments. *Error Bars Indicate Standard Deviation of Two Measurements. Shaded
Region Indicates Maximum of 0.061 mol CHCl3/mol Cl2 Found from Chlorination of
Swimming Pools Samples in This Study.
25
to be digested by the human body, hence use as a zero-calorie sweetener (Roberts et al.,
2000). Previous studies have also found sucralose to be persistent in waste water after
chlorination and UV radiation (Torres et al., 2011). However, triclosan, which also
contains chlorinated carbons, exhibited opposite behavior, with high CHCl3/C ratio and
low CHCl3/Cl2 ratios.
3.5 CHCl3 flux
A simple boundary layer model is used to estimate flux of chloroform from a pool
to the atmosphere across a water-air boundary (Schwarzenbach et al., 2003). In this
model, the flux can be evaluated by considering factors affecting activity on both sides of
the boundary. Flux across an air-water boundary, Fa/w (mol∙cm-2∙s-1), is calculated by
Equation 3.2
where va/w is the overall transfer velocity (cm/s) across the air-water boundary, cw is the
concentration (M) of chloroform in the water layer, ca is the concentration (M) of
chloroform in the air-side layer, and Ka/w is the dimensionless Henry’s law constant of
chloroform. The average CHCl3 concentration found from chlorination of swimming pool
water in this study, 1.7μM, was used for cw. This value was similar to concentrations
found in swimming pools at the time of collection. Values for ca were determined from
the partial pressure above the CHCl3-pool water mixture and is dependent on air
temperature. The overall transfer velocity va/w is related to the transfer velocity
contributions from the water-side and air-side boundaries by
Equation 3.3
26
where va is the transfer velocity (cm/s) of chloroform air-side boundary and vw is the
transfer velocity (cm/s) of chloroform on the water-side boundary. The dimensionless
Henry’s law constant for chloroform is 0.1445 at 25 °C (Schwarzenbach et al., 2003).
Henry’s law constant changes with temperature and can be estimated by
Equation 3.4
Where temperature is expressed in Kelvin and c is 4600K (Gossett, 1987) and is an
experimentally determined constant. Transfer velocities on the air-side boundary are
determined by comparing molecular diffusivity ratios of different substances, which can
easily be determined by a molar mass relationship of those substances. In this case,
chloroform is compared to the well-known properties of water vapor by
Equation 3.5
where va∙water is the transfer velocity of water vapor (cm/s) and M is molecular weight.
Transfer velocity of water vapor is directly related to wind speed by
Equation 3.6
where u10 is the wind speed (m/s) at a standard height of 10 meters.
Transfer velocity on the water-side boundary is controlled by molecular
diffusivity and kinematic viscosity which are expressed through the Schmidt number, Sc.
Transfer velocity can only be calculated when Sc=600. At other Schmidt numbers,
transfer velocity can be determined through a relationship with CO2 where the transfer
velocity at Sc=600 is known:
α
Equation 3.7
27
where vw∙CO2 is the transfer velocity (cm/s) when ScCO2=600, Scw∙CHCl3 is the Schmidt
number of chloroform, and α=2/3 for u10≤5 m/s and α=1/2 for u10>5 m/s. The transfer
velocity of CO2 at 20°C when Sc=600 is found by
Equation 3.8
where u10 is the wind speed (m/s) at a height of 10 meters. The Schmidt number of
chloroform can be calculated by
Equation 3.9
where νw is the viscosity of water (cm2/s) and Dw∙CHCl3 is the molecular diffusivity (cm2/s)
of chloroform in water. Molecular diffusivity is calculated by
Equation 3.10
where M is molar mass. The transfer velocity of chloroform on the water-side boundary
can then be evaluated for different temperatures by comparing against the viscosity of
water at different temperatures.
Equation 3.11
After flux is calculated per unit area, this value is extrapolated to determine total
annual CHCl3 for all pools in Phoenix Ftot according to
Equation 3.12
28
where Fa/w is the flux across the air-water surface per unit area, aavg is the average area of
swimming pools in Phoenix and nPHX is the number of swimming pools in Phoenix
(Table 3.2).
Sensitivity tests were performed to investigate impacts of wind speed, air
temperature, and water temperature on CHCl3 flux. To investigate this, flux was
calculated using several combinations of these factors when holding some constant and
varying others. Additionally, these factors were averaged daily, monthly, and annually to
determine if averaging these factors was representative of total annual flux. Figure 3.7
shows the CHCl3 flux calculated from swimming pools in Phoenix using wind speed and
air temperature data from 2013 while keeping water temperature constant at 29.4 °C,
which is the recommended pool water temperature for a multi-purpose pool
Estimated number of pools
average area of a pool
286,000
41.1 m2
Table 3.2: Statistics of Swimming Pools in Phoenix (Forrest and Williams, 2010)
CHCl3 flux (kg∙day-1)
350
300
250
daily flux
200
monthly flux
150
annual flux
100
50
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
Figure 3.7: Daily, Monthly, and Annual CHCl3 Flux from Swimming Pools in Phoenix
Calculated with Wind Speed and Air Temperature Data for 2013 While Holding Water
Temperature Constant.
29
(USWFA.com). Chloroform flux shows very little daily variation at 90 kg∙day-1. Days
with significantly higher CHCl3 fluxes are a result of high daily wind speeds. Averaging
of daily, monthly or annual wind speed and air temperature shows little variation in
CHCl3 fluxes.
Figure 3.8 shows CHCl3 flux from swimming pools when keeping wind speed
constant while varying air and water temperature. No reliable records for annual water
temperature variations were available. For these calculations, water temperature was
estimated by a linear increase/decrease between observed summer (28 °C) and winter (8
°C) water temperatures in an unheated swimming pool. A large increase in CHCl3 flux
can be seen as a result of increasing water temperature. Therefore, CHCl3 flux from
swimming pools in Phoenix is not driven directly by the extreme air temperatures for
which Phoenix is known, but rather indirectly through warming of swimming pool water.
However, solar irradiation might be a stronger force in warming swimming pool water.
CHCl3 flux (kg∙day-1)
100
90
80
daily flux
70
monthly flux
60
annual flux
50
40
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 3.8: Daily, Monthly, and Annual CHCl3 Flux from Swimming Pools in Phoenix
Calculated with Average Annual Wind Speed, Varying Air Temperature and Water
Temperature for 2013.
30
Flux calculated by averaging daily and monthly air and water temperature resulted in
values similar to annual CHCl3 fluxes, which indicates that using anually averaged
meterological data provides a good estimate for annual CHCl3 flux.
Summing daily CHCl3 flux produced a total annual emission rate. Depending on
variations in meteorological factors, calculations from this study indicated that swimming
pools in Phoenix might produce an estimated 3.9-4.3 Gg/yr. Figure 3.9 shows this
emission estimate from swimming pools in Phoenix compared to natural and
anthropogenic emission estimates. If Phoenix is assumed to be similar to desert shrubland
in the southern California desert, an area the size of Phoenix (2970 km2) with a flux of
6.6 nmol∙m-2∙day-1 would generate an estimated 0.854 Mg/yr as natural emissions (Rhew
et al., 2008a). Chloroform emission from swimming pools is four orders of magnitude
larger than this number. In 2011, 0.063 Gg/yr was reported as total anthropogenic
Figure 3.9: Swimming Pool Emissions of CHCl3 in Phoenix compared to estimated
natural and anthropogenic emission estimates.
31
emissions for the Phoenix metropolitan area (Hafner and O’Brien, 2006) which is two
orders of magnitude less than CHCl3 emission from swimming pools found in this study.
This suggests that CHCl3 from swimming pools might be a significant source of
atmospheric CHCl3 in Phoenix.
32
CHAPTER 4
SUMMARY AND OUTLOOK
Unexplained elevated atmospheric CHCl3 concentrations in Phoenix, AZ lead to a
necessity to evaluate unconventional sources as a supply for CHCl3 flux into the
atmosphere. This study evaluates chlorination of swimming pools as a potential source
of atmospheric CHCl3 in Phoenix. Swimming pool samples from Phoenix, AZ were
collected and characterized, and CHCl3 formation upon chlorination in a controlled
laboratory experiment was determined using Gas Chromatography-Mass Spectrometry
(GC-MS) after headspace solid phase microextraction (SPME). Measurements from this
study found CHCl3 present immediately upon collection in all pool samples at an average
concentration of 2.21 μM. Upon chlorination, CHCl3 formation occurred in all pool
samples. These samples gave molar yields of 0.005-0.134 mol CHCl3/mol C and 0.0040.062 mol CHCl3/mol Cl2 consumed. However no visible trends relating swimming pool
water parameters with formation potential of CHCl3 could be determined and therefore
predictions could not be made as to factors affecting CHCl3 formation in swimming
pools.
Model contaminants were also chlorinated in controlled laboratory experiments.
These contaminants were chosen because of their known presence in swimming pool
water or their detection in Arizona surface water from anthropogenic contamination.
Chlorination of these compounds gave molar yields of 0.004-0.323 mol CHCl3/mol C and
0.001-0.247 mol CHCl3/mol Cl2 consumed which are similar to molar yields from
33
chlorination of swimming pool water. These results did not display any trends in CHCl3
yield based on elements, functional groups, or molecular size.
Chloroform flux was calculated using Henry’s Law and a simple boundary-layer
model. Sensitivity tests were performed to investigate impact of air temperature, water
temperature, and wind speed on CHCl3 flux. These tests determined that water
temperature had the largest effect on CHCl3 flux. Wind speed showed a minor effect on
the flux and air temperature had no effect on flux values even though Phoenix is known
for its high summer temperatures. Variations in wind speed and water temperature
resulted in potential flux calculations in the range of 3.9-4.3 Gg∙yr -1. This number is
larger than previous anthropogenic source estimates and is four orders of magnitude
larger than estimated natural emissions in Phoenix. However, more work is required to
confirm initial results.
Measurements of annual variation in swimming pool water temperature would
also significantly refine flux measurements. This would aid in validating flux calculations
using a simple boundary-layer model. Water temperature was assumed as a linear
increase/decrease symmetrically about the calendar year, when annual variation of water
temperature is not known. In future work, these results might be validated through flux
measurements in sample swimming pools throughout Phoenix. Air measurements of
CHCl3 concentrations over a period of time can be taken near swimming pools to
measure CHCl3 concentrations in outdoor swimming environments. Additionally,
swimming pool water should be collected during different times of the year. These
samples were not time-resolved and significant changes in water chemistry between
seasons might affect CHCl3 formation.
34
An alternate pathway suggesting swimming pool chlorination as a source of
atmospheric CHCl3 is through outgassing of Cl2 and HOCl with CHCl3 formation in the
atmosphere above swimming pools rather than in the water. Therefore, future work
should also investigate the impacts of these pathways. Flux estimates from swimming
pools in a previous study were used to calculate possible flux of Cl2 and HOCl in
Phoenix, suggesting pools in Phoenix might outgas Cl2 and HOCl at rates of 0.1 Gg/yr
and 1 Gg/yr, respectively (Chang et al., 2001). Depending on chlorine demand and
conversion rate, this Cl2 might produce 0.2 Gg/yr CHCl3 in the atmosphere and this
HOCl might produce 1 Gg/yr CHCl3. Investigations to determine competition between
chlorine reactivity and outgassing should be performed to investigate possibility of
alternate CHCl3 formation pathways.
35
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