Journal: Indoor Air
Dynamic real-time monitoring of chloroform in an indoor swimming pool air using open-path Fourier transform infrared spectroscopy
Ming-Jen Chen1, Jing-Min Duh2, Ruei-Hao Shie3, Jui-Hung Weng4, Hui-Tsung Hsu5*
1 Department of Occupational Safety and Hygiene, Fooyin University, 151 Chin-Hsueh Road, Ta-Liao Hsiang, Kaohsiung 831, Taiwan
E-mail: [email protected]
2 Advanced Monitoring and Analytical Department, Energy and Environmental Research Laboratories, Industrial Technology Research Institute, Hsinchu 300, Taiwan
E-mail: [email protected]
3 Advanced Monitoring and Analytical Department, Energy and Environmental Research Laboratories, Industrial Technology Research Institute, Hsinchu 300, Taiwan
E-mail: [email protected]
4 Department of Public Health, China Medical University, No. 91, Hsueh-Shih Road, Taichung 404, Taiwan
Email: [email protected]
5 Department of Health Risk Management, China Medical University, No. 91, Hsueh-Shih Road, Taichung 404, Taiwan
E-mail: [email protected]
---* Corresponding author: Hui-Tsung Hsu, Ph.D.
Department of Health Risk Management China Medical University
91 Hsueh-Shih Road Taichung 404, Taiwan
Tel.: +886-4-22053366 ext. 6502; fax: +886-4-22070429.
Abbreviations and definitions:
OP-FTIR: open-path Fourier-transform infrared spectroscopy DBPs: disinfection by-products
IARC: International Agency for Research on Cancer THMs: trihalomethanes
Acknowledgments
This study was supported by a grant (NSC101-2221-E-039-008) from the Ministry of Science and Technology, Taiwan.
Role of funding source
The sponsor was not involved in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.
Declaration of competing financial interests
Abstract
This study used open-path Fourier-transform infrared (OP-FTIR) spectroscopy to continuously assess the variation in chloroform concentrations in the air of an indoor swimming pool. Variables affecting the concentrations of chloroform in air were also monitored. The results showed that chloroform concentrations in air varied significantly during the time of operation of the swimming pool, and that there were two peaks in chloroform concentration during the time of operation of the pool. The highest concentration was at 17:30, which is coincident with the time with the highest number of swimmers in the pool in a day. The swimmer load was one of the most important factors influencing the chloroform concentration in the air. When the number of swimmers surpassed 40, the concentrations of chloroform were on average 4.4 times higher than the concentration measured without swimmers in the pool. According to the results of this study, we suggest that those who swim regularly should avoid times with highest number of swimmers, in order to decrease the risk of exposure to high concentrations of chloroform. It is also recommended that an automatic mechanical ventilation system is installed in order to increase the ventilation rate during times of high swimmer load.
Keywords: OP-FTIR; Swimming pool; Chloroform; Real-time monitoring; Disinfection by-products; Exposure assessment.
Practical Implications
In this paper, we present real-time monitoring of the variations of chloroform concentrations in the air of an indoor swimming pool in Taiwan by using OP-FTIR spectroscopy for the first time. This study shows that chloroform concentrations in the swimming pool air are largely related to the number of swimmers in the pool. Considering the adverse health effects of exposure to chloroform, the results of this study suggest that those who swim regularly should avoid times with highest number of swimmers, and that the installation of an automatic mechanical ventilation system is advisable for decreasing the volatile chloroform concentration.
1. Introduction
It is widely known that swimming pool water requires disinfection, most commonly with chlorine, in order to prevent infections in swimmers caused by microbial pathogens (Bessonneau et al., 2011; Florentin et al., 2011; Li and Blatchley III, 2007). However, swimmers can introduce various types of organic and nitrogen compounds (LaKind et al., 2010; Jacobs et al., 2007), derived from sweat, saliva, urine, mucus, hair, lotion, creatinine, and amino acids (Caro and Gallego, 2007; Li and Blatchley III, 2007), that can react with the disinfectants to form disinfection by-products (DBPs) (Nazir and Khan, 2006). More than 600 DBPs can be formed during the disinfection process (Richardson et al., 2007), being trihalomethanes (THMs), haloacetic acid, and inorganic chloramines the most commonly identified ones (Simard et al., 2013).
The most prevalent DBPs are THMs consisting of chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), and bromoform (CHBr3). Chloroform, whose adverse effects have been studied extensively, is the most common THM in swimming pool waters (Richardson et al., 2010). Chloroform is classified as a class 2B carcinogen by the International Agency for Research on Cancer (IARC) based on evidences obtained from animal experiments, and can cause cytotoxicity in liver, kidney, and nasal epithelium (USEPA, 2001). Epidemiological studies have reported positive associations between
exposure to THMs and several cancers, including bladder (Villanueva et al., 2014; Cantor, 2010), colon (King et al., 2000), and rectal cancers (Bove et al., 2007). Moreover, some studies have indicated that exposure to THMs can have effects on reproductive health, such as intrauterine growth retardation, low birth weight, preterm birth, congenital malfunctions, stillbirth, and small for gestational age (SGA) neonates (Nieuwenhuijsen et al., 2000; Graves et al., 2001; Bove et al., 2002; Huang and Jaakkola, 2012; Levallois et al., 2012). Although most of the aforementioned studies on the effects of exposure to THMs on health analyzed household water use activities (e.g., consumption or showering) instead of analyzing the effects of swimming pool attendance (Catto et al., 2012), the potential health risks related to chemical exposures in swimming pools is still a public health concern.
Erdinger et al. (2004) and Lévesque et al. (1994) indicated that swimmers are exposed to chloroform primarily through inhalation. For this reason, in a previous study, we developed a two-layer model to simulate the exposure concentrations of chloroform in the boundary layer above the water surface, and the average concentrations of chloroform in the indoor swimming pool air. The results of the simulation showed that the major route of chloroform exposure for swimmers is inhalation during swimming (Chen et al., 2011). However, Lindstrom et al. (1997) estimated that the dermal exposure route accounts for about 80% of the chloroform
concentration in swimmers’ blood. Catto et al. (2012) suggested that the contribution of each exposure route depends on the environmental concentrations and on the ratio between air and water levels.
Considering that chloroform is a highly volatile DBP that can escape into the gas phase in the swimming pool environment (Catto et al., 2012; Dyck et al., 2011), monitoring the level of chloroform in indoor swimming pool air is an important step to understand the level of exposure to DBPs in indoor swimming pool environments. Concentration of chloroform in indoor swimming pool air has been investigated extensively. In situ measurements of the concentration of chloroform in air have shown a relatively large variation. The levels of chloroform in environmental air samples taken from 12 indoor swimming pools in Italy varied widely from 16 to 853 g/m3 (Aggazzotti et al., 1995). Air samples taken at the same indoor swimming pool in Germany at three different times showed chloroform concentrations from 85 to 235 g/m3 (Erdinger et al., 2004). Caro and Gallego (2008) performed an environmental monitoring of THMs in ambient air at an indoor swimming pool in Spain, and their analyses revealed that chloroform concentrations ranged from 92 to 340 g/m3. Catto et al. (2012) took four air samples per day during a five consecutive days sampling program from two different indoor swimming pools in Quebec City, Canada. Their analyses indicated large within-day variations of total THMs levels in air. The
chloroform concentrations in pool A ranged from 46.4 to 306.7 g/m3, and in pool B from 33.6 to 177.7 g/m3.
All the aforementioned studies used traditional analytical methods, such as collecting samples with adsorbent cartridges or containers (e.g. canisters) and subsequently transporting them to a laboratory for gas chromatography-mass spectrometry (GC-MS) analysis (Aggazzotti et al., 1995; Caro and Gallego, 2008), or measuring the chloroform concentration in ambient air with an electron capture detector (GC-ECD) (Erdinger et al., 2004; Catto et al., 2012). However, these methods give only a time-averaged response, and do not provide information about temporal variations in concentration, which makes the wide variation in chloroform concentrations of indoor swimming pool air at different times difficult to explain.
In this study, we used open-path Fourier-transform infrared (OP-FTIR) spectroscopy, which is a real-time monitoring instrument, to continuously assess the variation of chloroform concentrations in indoor swimming pool air. OP-FTIR spectroscopy is a well-established technique for monitoring air pollutants that does not require the collection of samples and allows the integrated measurement of the chemical composition of the atmosphere in a particular area (Briz et al., 2007). To the best of our knowledge, concentrations of DBPs in the air of indoor swimming pools have never been studied in real time. Therefore, the results of this study can be used to
more thoroughly evaluate the actual exposure of swimmers and employees at the swimming pool, including lifeguards and swim instructors, at different times throughout the day.
The aim of this work was, thus, to establish a comprehensive monitoring program for real-time measuring of chloroform concentrations in the air of an indoor swimming pool. In addition, considering that many studies have indicated that DBP concentrations in air at indoor swimming pools can vary due to many parameters, such as the number of swimmers and non-swimming visitors, the concentration of chloroform in pool water, water pH, air temperature, water temperature, and the concentration of free chlorine in water (Jacobs et al., 2007; Carbonnelle et al., 2008; Hsu et al., 2009; Catto et al., 2012), the parameters that affect the chloroform concentration in air were simultaneously measured in this study, and the degree of influence of each parameter on the levels of chloroform in air are discussed.
2. Materials and methods
2.1 Indoor swimming pool in this study
This study was carried out in a public indoor swimming pool located in Hsin-Chu city, Taiwan. The pool was 50 m in length, 22 m in width, and 1.3 m in depth. The size of the indoor swimming pool building is 60 m (length) 32 m (width) 16 m (height) (Fig. 1a). This swimming pool is not equipped with a mechanical
ventilation system, but it is ventilated naturally through the windows on three walls of the building (sides A, C, and D) and the open door on side B, as shown in Fig. 1. The total window area that can be opened on side A is 90 m2, and 57.5 m2 both on side C and side D. The configuration of the windows on each wall is presented in Fig. 1. As a consequence of the relatively hot temperatures (29.2-31.0ºC, Table 2) in the indoor swimming pool building during the sampling campaign, all the windows were opened during the sampling period. The opening hours of this pool are from 5:00 to 22:00, and it is closed from 22:00 to 5:00. Sodium hypochlorite was used as disinfectant in this pool. In Taiwan, all the public swimming pools are legally required to check the pH and chemical quality of water at least four times a day. The current standard for active chlorine is 13 mg/L and combined chlorine is < 1 mg/L.
2.2 Field sampling and laboratory analysis
This study used the FACE-OP300 Open-Path Remote Sensing FTIR Gas Monitor (Taipei, Taiwan), which is an on-line air quality-monitoring system, to detect the chloroform concentrations in the indoor swimming pool air. The OP-FTIR instrument was installed at the swimming pool on September 6, 2012, and recorded measurements every 5 minutes throughout the data collection period from September 6, 2012, to September 12, 2012 (Table 1). The OP-FTIR spectrometer was aligned
and steady on a 135 cm-high tripod, and used a remote retro-reflector to reflect an infrared beam back to the receiver, as shown in Fig. 1. Therefore, chloroform concentration in the swimming pool air was monitored at a height of approximately 150 cm above the water surface. The OP-FTIR spectrometer contained a mercury-cadmium-telluride detector with a resolution of 1 cm−1, and detected molecules whose infrared spectra ranged from 500 cm-1 to 4500 cm-1. The total time to take a spectrum was 5 min, and a total of 64 interferograms, which were used to calculate path-average concentrations and path-average concentrations, were integrated for each spectrum. The 5-min average concentrations of chloroform were continuously measured at a path length of about 65 m. The gaseous pollutants were identified and quantified using IR-View analysis software and the U.S. Environmental Protection Agency quantitative reference spectra library (USEPA, 1999).
Prior to the measurement of chloroform concentrations in the indoor swimming pool air, the OP-FTIR spectrometer system was calibrated using a specially designed gas calibration cell placed directly in the path of the infrared beam. A homogeneous gas concentration was generated in the cell by injecting a known concentration of a National Institute of Standards and Technology traceable calibration gas (0.5% sulfur hexafluoride (SF6) in N2) into the cell, and subsequently, the concentration measured through the cell by the OP-FTIR spectrometer was compared with the reference
concentration in the cell. The results showed that the measured concentration differed by less than 10% from the reference concentration. In addition, the OP-FTIR spectrometer was calibrated using a laboratory optical bench for defining a background transmission spectrum, and the wavelength calibration was performed with a low-pressure mercury lamp.
Furthermore, chloroform and free chlorine concentrations in water, water pH, water temperature, and air temperature, were measured once every hour during the time of operation of the pool, acquiring a total of 70 measurements for each of these parameters. Swimming pool water samples were collected for chloroform concentration analysis at about 20 cm below the water surface, which is the average level of human body exposure. The samples were sealed in volatile organic analysis (VOA) vials with silicone-faced septa, and were treated with sodium thiosulfate in order to neutralize chloride and stop THMs formation. The sampling process followed the Taiwan Environmental Protection Agency criteria (TWEPA, 2005) for sampling drinking water for volatile organic compounds (VOCs). Water samples were analyzed using a purge and trap system (SOLATek72), directly coupled to a GC-MS instrument (Agilent 6890N-Agilent 5973 Network, Santa Clara, California, USA). Quality control samples were tested during the analyses, showing that the relative deviation of duplicates was within 20%. The recovery of laboratory control standards
was from 90-110%. Free chlorine was determined on site using a Pocket Colorimeter II (Hach, Colorado, USA), and pH and temperature of water were measured using a D-51 handheld Water Quality Meter (HORIBA Scientific, Kyoto, Japan).
Finally, the number of swimmers in the pool and the number of non-swimming visitors poolside were counted every 15 minutes, collecting a total of 276 datasets.
2.3 Statistical analysis
Data analysis was carried out using the SPSS (Statistical Package for the Social Sciences) software, version 12.0. Since concentrations of chloroform in air or in water did not follow a normal distribution but followed a log-normal distribution (Kolmogorov-Smirnov test), the data were log transformed prior to analysis. Linear regression was used to analyze the relationships between: 1) log-transformed chloroform concentrations in air and log-transformed chloroform concentrations in water; 2) log-transformed chloroform concentrations in air and number of people in the swimming pool; and 3) log-transformed chloroform concentrations in air and number of non-swimming visitors in the swimming pool.
3. Results and Discussion
swimming pool air
In this study, the OP-FTIR instrument obtained data on the chloroform concentration in the swimming pool approximately every five minutes, which equates to twelve readings per hour, 288 readings per day, and a total of 2,016 readings during the week of sampling. However, for unknown reasons, the data log contained missing values approximately from 9:36 to 13:25 on the second day of sampling (9/7) and during some other times, which resulted in an actual total of 1,822 concentration values for this study (as shown, arranged by sampling date, in Table 1).
The chloroform concentration in the indoor air ranged from 13 to 182 g/m3 during the week of monitoring. In order to explain the regular changes in chloroform concentrations observed in the indoor pool air each day, we averaged the values every fifteen minutes, to make them comparable with the number of swimmers and non-swimming visitors in the pool that were counted every fifteen minutes, and created a vertical asymmetric error bar chart using the 96 fifteen-minute data points for each 24 hours (Fig. 2).
As shown in Fig. 2, chloroform concentrations in the indoor pool air had two peaks. From the opening hour of the pool at 05:00 until approximately 08:00, the chloroform concentration in the air slowly increased from 22 g/m3 to 72 g/m3. After 08:00, the concentration slowly decreased until approximately 12:30, when it
reached the background concentration level (about 22 g/m3). The concentration subsequently rose again, reaching a peak of 92 g/m3 at around 17:30, which is approximately 20 g/m3 higher than the average morning peak. After this second peak, the concentration began to decrease once again until 22:00, when the chloroform in the air returned to background concentration levels. This value was maintained until 05:00 the next morning, when the pool was opened again and another cycle began.
During our 24-hour surveillance, we observed that the concentration of chloroform in the indoor swimming pool air maintained steady levels (average value of 22.3 g/m3, standard deviation of 2.6-20.1 g/m3) after the pool was closed (22:00-05:00), which contrasts with opening hours (average value of 45.2 g/m3, standard deviation of 3.6-58.2 g/m3). These results show that the indoor swimming pool was influenced by factors that caused more intense fluctuations in the chloroform concentration in the air during opening hours.
A limitation of this study is associated with the fact that the OP-FTIR spectrometer measured the chloroform concentrations at a height of 150 cm above the water surface of the swimming pool because the machine was installed on a 135 cm-high tripod. However, a concentration gradient exists in the air above the water surface (Catto et al., 2012; Chen et al., 2011, Hsu et al., 2009), which may cause
much higher chloroform concentrations at the swimmers’ breathing zone than those measured at a height of 150 cm above the water surface. Therefore, the results of this study may not be directly linked to the exposure levels of swimmers, but the two layers model developed by Hsu et al. (2009), which is capable of estimating the concentration in the boundary layer adjacent to the water surface, can be used to calculate the chloroform concentration at the swimmers’ breathing zone.
3.2 Association of environmental factors with variations of chloroform concentrations in indoor swimming pool air
Every day during opening hours (05:00 to 22:00), we collected information about environmental factors that can affect the variation of chloroform concentrations in air, including water pH, water and air temperatures, and free chlorine and chloroform concentrations in water (Table 2). Moreover, the coefficient of variation (CV) of these parameters was calculated using the standard deviation of each variable divided by the average value, multiplied by 100%. A high CV indicates large variation of that variable, whereas low CV indicates small variation.
The results of this study showed very few fluctuations in water pH (7.2-7.6), water temperature (29.2-32.0C), and air temperature (29.8-33.0C), which resulted in extremely small CV values for these variables (1.2, 1.3, and 2.3%, respectively). On
the contrary, the CV value of the chloroform concentration in air at the indoor swimming pool was 65%, which indicates that water pH, water temperature, and air temperature did not contribute significantly to the variation of chloroform concentrations in air. Nevertheless, the free chlorine concentration in water (average value of 0.70.3 ppm, range from 0.3 ppm to 1.2 ppm) and the chloroform concentration in water (average value of 71.311.0 g/L, range from 48.3 g/L to 92.5 g/L) showed moderate variations during the sampling period, and their CV values were 37% and 18%, respectively. It indicated that chlorine and chloroform concentrations in water may contribute to change chloroform concentrations in air.
Bessonneau et al. (2011) took samples from 15 indoor swimming pools in France, and showed that THM concentrations in water and in air were correlated. The results of their study showed that the variation in THM concentration in water can account for approximately 20% of the variation in THM concentration in air during summer, and that the regression coefficient of determination (r2) between both variables was 0.30 during winter. The compilation of year-round data indicated that variations in THM concentration in water could account for approximately 19% of the variation in THM concentration in air. In our study, regression analysis of the chloroform concentration in water and in air showed that r2 was 0.16 (Fig. 3), which is close to the results of Bessonneau et al. (2011).
Presently, few European countries have standards for total trihalomethanes (tTHMs) in swimming pool water: Denmark’s highest permissible concentration is 25g/L (Jackson and Rule, 2002); Germany has stricter standards, allowing only 20g/L; and Belgium’s maximum permissible concentration is 100g/L (Simard et al., 2013). By comparison with these standards, 100% of the chloroform levels in the swimming pool water analyzed in this study were higher than Denmark’s standard (25g/L), suggesting that the studied swimming pool had high exposure to THMs.
3.3 Association of occupant activities with variations of chloroform concentrations in indoor swimming pool air and water
In contrast with modest variations of water pH level, and water and air temperatures, variations in the number of swimmers and non-swimmers were much greater, showing CV values of 74% and 60%, respectively (see Table 2). The scatter plot presented in Fig. 4(a) shows a high correlation between the concentration of chloroform in the air of the indoor swimming pool and the number of swimmers (r2 = 0.3909; p < 0.001). As the number of swimmers increases, their swimming stirs the water, which favors the volatilization of chloroform and increases its concentration in the air. This correlation is also evident in Fig. 2, in which the peaks in the number of swimmers at 07:45 (20.2 swimmers in the pool) and at 17:30 (39.2 swimmers) are
coincident with peaks in chloroform concentration in the air, and the fluctuation pattern of the number of swimmers in the pool is very similar to the changes in chloroform concentrations in the air.
These observations are consistent with the results of several other studies. For example, Kristensen et al. (2010) found that the concentration of THMs in the water of a swimming pool and its operational status were correlated. These authors pointed out that swimming activities throughout the day, including hitting the surface of the water and stirring the water, can facilitate the volatilization of THMs, which causes lower concentrations of volatile DBPs in the water during the day than at night. Their results showed that under the influence of volatilization, daytime concentration of THMs in the air of the indoor swimming pool was much higher than at night. In addition, Weng et al. (2011a) conducted a study on trichloramine (NCl3), another type of volatile DBP, in indoor swimming pools. Their sampling results showed that every day from 16:00 to 22:00, coinciding with the highest number of swimmers, the concentration of NCl3 in the air was higher; i.e., the number of swimmers and the concentration of volatile DBPs in the air were highly correlated. A statistical analysis of British indoor swimming pools by Chu and Nieuwenhuijsen (2002) showed that the number of swimmers is the most important impact factor for the concentration of THMs in swimming pool air.
Fig. 4(b) shows a scatter plot of the number of non-swimming visitors in the swimming pool and the concentration of chloroform in the air. The number of non-swimming visitors can account for approximately 10% of the variation in the concentration of chloroform in the air. The results of our previous study suggested that the number of non-swimming visitors can induce turbulence and dispersion of chloroform in indoor swimming pool air; that is, as the number of non-swimming visitors increases, the entrainment and mixing of chloroform from the surface of the pool water into the indoor swimming ambient atmosphere increases (Hsu et al., 2009). However, in the present study, the effect of the number of non-swimming visitors was less than that of the number of swimmers in the pool because the average number of non-swimming visitors was approximately ¼ of the average number of swimmers (4.2 vs 15.9). This indicates that the number of swimmers in the pool is the main impact factor for the concentration of volatile chloroform in the air.
Research by Aggazzotti et al. (1998) showed that the concentration of chloroform in the air of an indoor swimming pool when the number of swimmers was 40-50 was roughly twice than when there were no swimmers. In this study, we divided the number of swimmers into groups of 41-50 and above, 31-40, 21-30, 11-20, 1-10, and 0, and we compared the number of swimmers with the mean concentration of chloroform in the indoor swimming pool air (Fig. 5). When the
number of swimmers was 41-50, the average concentration of chloroform in the air was 99 g/m3, and when the number of swimmers was 0, the average concentration of chloroform in the air was 22 g/m3, that is, a 4.4-fold difference between the two groups (C41-50/C0), which is greater than that obtained by Aggazzotti et al. (1998). In addition, the mathematical model proposed by Hsu et al. (2009) showed that when the number of swimmers was 40-50, the average concentration of chloroform in the air of an indoor swimming pool was 2.7 times the value when there were no swimmers, which is reasonably close to the data in this study, and shows that OP-FTIR real-time monitoring data can provide valuable information regarding the effect of swimmer load on the concentration of volatile chloroform in the air of an indoor swimming pool.
The statistical data of the daily number of swimmers in the pool (Table 3) show that the maximum number of swimmers in the pool was reached on day 4 (9/9), and that the larger variations of the number of swimmers occurred on days 4, 5, and 6, according to CV values. This can be one of the reasons for the large variations of chloroform concentrations in the air during these three days (see Table 1).
Although the highest concentration of chloroform in the indoor swimming pool air was measured on 9/10 (see Table 1), the highest number of swimmers was counted on 9/9 (see Table 3). Therefore, other than the number of swimmers in the pool, there
were other factors influencing the variation of the concentration of chloroform in the indoor swimming pool air. Wind is one of the factors that may have played a role in this process. Fig. 6 displays the daily wind direction and speed during the sampling period, collected at a meteorological station near the indoor swimming pool. The wind speed was about the same during the sampling period, ranging from 1.4 m/s to 1.6 m/s, but wind directions could be classified into two main groups. On 9/6 and 9/10 the prevailing wind direction was from the southeast, whereas the prevailing wind for the rest of the days was from the southwest. The presence of a large building in the southeastern side of the swimming pool building probably causes a low air-change rate when the wind blows from the southeast, which might reduce the natural ventilation of the pool. This process can explain that the highest chloroform concentration in this study was obtained on 9/10. A 400 m-long flat track and field is located on the southwest corner of the pool building. Hence, wind blowing from the southwest can easily reach the building and enhance the dilution of chloroform in the indoor swimming pool air. Considering that the average number of swimmers on 9/9 and 9/11 was higher than that on 9/10 (when the highest chloroform concentration was reached), dilution was more significant during these two days than on 9/10. These considerations indicate that ventilation is another important factor controlling the chloroform concentration in the air of indoor swimming pools that needs to be
considered.
As previous studies indicated that some substances produced by bathers, such as sweat and urine, can trigger the formation of chloroform in chlorinated swimming pool water (Judd and Bullock, 2003; Weng and Blatchley III, 2011b; Kanan and Karanfil, 2011), we compared the chloroform concentration in the water when bathers were in the pool and the chloroform concentration in the water when no bathers were in the pool during the sampling period (Fig. 7). Under a nearly stable temperature, the difference between the chloroform concentration in the water with no swimmers in the pool (average value of 73.8 13.7 g/l, range from 49.1 g/L to 92.5 g/l) and the chloroform concentration in the water with swimmers in the pool (average value of 67.4 11.2 g/L, range from 44.9 g/L to 86.5 g/L) was not significant (p > 0.05). By combining the previous studies and our findings, it can be reasonably concluded that the increase of chloroform concentrations in indoor swimming pool air associated with higher numbers of people in the swimming pool is related to the volatilization of chloroform caused by swimming activities (Hsu et al., 2009) and to the chloroform formation caused by the reaction of chlorinated water with substances produced by bathers. The additional formation of chloroform in the water may be balanced by its volatilization during swimming activities, which may explain the small variations of chloroform concentration in the pool water. However, it is difficult
to identify the individual contributions of both processes to the chloroform concentration in the air due to the lack of comprehensive in-situ kinetic measurements of the rate of chloroform formation coupled with the effects of swimming activities, which is an interesting field for further study.
3.4 Implication for reducing the exposure to volatile chloroform in indoor swimming pools
Since there are currently no international management standards for indoor swimming pool concentrations of trihalomethane (THM), we followed the classification of THM concentrations in air by Silva et al. (2012) into low (< 36), moderate (36-136), and high (> 136 g/m3) exposure values. Using these concentrations as reference, we found that when the swimmer load was less than 26, the highest concentration of chloroform measured in air was 125 g/m3 in this study, which did not reach the high exposure level. When the swimmer load was more than 27, the chloroform concentrations in air could reach the high-exposure level (Table 4); 12.5% of the measured chloroform concentrations in air were less than 36 g/m3, 82.1% of the chloroform concentrations in air were within the range of 36-136 g/m3, and 5.4% of the data were higher than 136 g/m3. Chloroform concentrations in air higher than 136 g/m3 happened between 16:30 and 18:30. Therefore, the approach
we used in this study can provide important risk information for swimmers and swimming pool manager to understand how the chloroform concentrations vary in the indoor swimming pool with time, and when the air quality is mostly deteriorated during a normal operating day. Those who swim regularly in this particular pool should avoid times when the number of swimmers is higher than 27 to decrease health risk from exposure to high concentrations of volatile chloroform and other DBPs. Moreover, installing an automatic mechanical ventilation system, which would change the ventilation rate in the indoor swimming pool, would be advisable for reducing the volatile chloroform concentration, especially for times with high swimmer load, i.e. from 16:30 to 18:30.
4. Conclusion
The results of monitoring the pool over seven consecutive days showed regular fluctuations in the concentration of chloroform in the indoor pool air. Two peaks in the concentration of chloroform were observed during each operating day, with the highest concentration at around 17:30. The OP-FTIR monitoring data showed that chloroform concentrations in air at day and night varied significantly, which indicated that certain factors had influence on the chloroform concentrations during opening hours. Monitoring of environmental parameters and occupant activities showed that
the number of swimmers was one of the most important factors affecting the concentration of volatile chloroform in the air. As the number of swimmers increased, the concentration of chloroform in the air increased due to the volatilization of the chloroform in the water. The results of our study showed that when the number of swimmers surpassed 40, the concentration of chloroform was on average 4.4 times the concentration measured when there were no swimmers in the pool. According to the results of this study, we suggest that those who swim regularly avoid times when the number of swimmers is high, in order to decrease health risks from exposure to high concentrations of volatile chloroform and other DBPs. Moreover, installing an automatic mechanical ventilation system in the indoor swimming pool would increase the ventilation rate during times with high swimmer load, and would decrease the concentration of DBPs.
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Table 1
Monitoring periods, number of OP-FTIR readings, chloroform concentration range, and mean concentration of chloroform in air as determined by OP-FTIR spectroscopy for the studied indoor swimming pool
Date Start time End time n Range (g/m3) meanstd (g/m3) Openedb meanstd (g/m3) Closedc meanstd (g/m3) 09/06 (Thursday) 12:23 23:59 149 13-86 2615 2816 215 09/07a (Friday) 00:00 23:59 258 13-73 3314 4113 238 09/08 (Saturday) 00:00 23:59 305 13-97 3716 4216 247 09/09 (Sunday) 00:00 23:59 306 13-150 3927 4829 216 09/10 (Monday) 00:00 23:59 306 13-182 4936 6237 217 09/11 (Tuesday) 00:00 23:59 306 13-159 4025 4826 255 09/12 (Wednesday) 00:00 15:04 192 13-84 3014 3416
--a OP-FTIR was not functioning from 09:36 to 13:25 for unknown reasons. b Opened: 05:00-22:00
Table 2
Summary of the environmental data acquired at the indoor swimming pool during field sampling at opening hours
Parameter n Max Min Meanstd CV (%)
No. of swimmers 276 50 0 15.911.8 74 No. of non-swimmers 276 9 1 4.22.5 60 pH 70 7.6 7.2 7.50.1 1.2 Free chlorine (ppm) 70 1.2 0.3 0.70.3 37 Water temperature (C) 70 32.0 29.2 30.10.4 1.3 Air temperature (C) 70 33.0 29.8 31.30.7 2.3 [Chloroform]water (g/L) 70 92.5 48.3 67.112.2 18 [Chloroform]air (g/m3) 276 182 13.2 41.427.0 65
Table 3
Statistical data of the daily number of swimmers counted in this study from 2012/09/06 to 2012/09/12 Date Average number of counted swimmers in the pool Standard deviation CV (%) Max 9/6 16.2 10.9 66.9 37 9/7 15.4 8.1 52.7 30 9/8 19.1 9.4 49.1 41 9/9 21.3 15.1 70.8 50 9/10 16.6 11.6 69.9 44 9/11 17.5 13.3 76.0 48 9/12 11.1 7.1 64.0 27
Fig. 4
Relationship between the level of exposure and swimmer load Chloroform concentration (g/m3) Level of exposure Swimmer load
Meanstd Min Max Median
< 36 Low 5.48.2 0 24 0
36 136 Moderate 20.311.4 0 49 19
60 m 16 m 8.0 m 3.0 m (c) 2.0 m 60 m 16 m 4 m 2 m 2 m 5.5 m 4 m 4 m 4 m 3.0 m 1.5 m 2 m 1.5 m 1.5 m (b) List of symbols OP-FTIR Retro-reflector 65 m 16m 32m 60m 50m 22m
A(east)
B(west)
C(s
out
h)
D(
nor
th)
(a)Fig. 1
(a) Configuration for the monitoring of chloroform concentrations in ambient air at an indoor swimming pool in HsinChu, Taiwan; (b) Configuration of the windows on wall A; (c) Configuration of the door on wall B; (d) Configuration of the windows on walls C and D. 32 m 16 m 5.5 m 3.0 m 2.5 m 2.5 m 2.5 m 2.5 m 3.5 m 1.0 m 1.0 m 1.5 m 1.5 m (d)
Fig. 2
Effect of the number of swimmers in the pool on the chloroform concentration in the ambient air of the indoor swimming pool based on 24 hours of continuous measurement using OP-FTIR spectroscopy. Error bars indicate the standard deviation of the average concentration over 15 minute intervals.
Time (hr) 0 5 10 15 20 C hl or of or m c on ce nt ra tio n in a ir ( g /m 3 ) 0 30 60 90 120 150 180 T he n um be r of s w im m er s in th e po ol 0 10 20 30 40 50 CHCl3 (g/m3) Number of swimmers
Fig. 3
Scatter plot of chloroform concentrations in air and water. The solid line is the linear regression line of the sampling data, and the dashed lines are the 95% confidence intervals for the regression line.
Log(Chloroformwater) 1.60 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00 L og (C h lo ro fo rm ai r ) 1.0 1.2 1.4 1.6 1.8 2.0 2.2 r2 = 0.16 p < 0.001
Fig. 4
The number of people in the swimming pool
0 10 20 30 40 50 L og (c h lo ro fo rm ai r ) 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 (a) r2 = 0.39 p < 0.001
The number of non-swimming visistors in the swimming pool
0 2 4 6 8 10 12 14 16 L og (c h lo ro fo rm ai r ) 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 (b) r2 = 0.10 p < 0.001
(a) Scatter plot of Log(chloroformair) as a function of the number of swimmers in the indoor swimming pool. (b) Scatter plot of Log(chloroformair) as a function of the number of non-swimming visitors in the swimming pool.
Fig. 5
Relationship between the mean concentration of chloroform in the indoor swimming pool air and the number of swimmers.
The number of people in the swimming pool
0 1-10 11-20 21-30 31-40 41-50 M ea n c on ce nt ra ti on o f ch lo ro fo rm in a ir (g /m 3 ) 0 20 40 60 80 100 120 140
Fig. 6
Wind rose depicting the wind direction and speed during the sampling period. The circles represent the magnitude of wind speed in m/s.
0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 Wind speed (m/s) 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 9/6 9/10 9/7 9/12 9/11 9/9 9/8 0 30 60 90 120 150 180 210 240 270 300 330
Fig. 7
Relationship between the chloroform concentration in the indoor swimming pool water and the number of swimmers
The number of people in the swimming pool
0 3 6 9 12 15 18 21 24 27 30 33 36 C H C l3 in p oo l w at er ( g /L ) 0 10 20 30 40 50 60 70 80 90 100 T em pe ra tu re in p oo l w at er ( o C ) 24 26 28 30 32 34 36 38 40
CHCl3 in water with swimmers Pool water temperature
