Chemical Hazards in Swimming Pools
Swimming pools are used for a number of different purposes: There are hot tubs and spa pools for relaxation 
therapy, exercise pools, public pools (in hotels or resorts), pools for schools and competitions and also pools used in our own backyards. They are installed and designed for a variety of different locations and climates - whether indoor or outdoor; recreational or competitive etc. In order to assure the health and safety of pool users, disinfection with high levels of disinfectant doses are applied for inhibiting pathogen activities (e.g. maintaining 1-3 mg/L of free chlorine in water). As a result, there is a greater accumulation of chemical hazardous content in pool waters than there is in drinking water. This poses particular health risks to competitive swimmers who are exposed to chemicals in pool waters at higher frequencies and for longer contact hours. It is necessary, therefore, to address these issues in order to minimize the adverse health consequences alongside the potential health benefits.
Table of Contents
- Chemical Hazards in Swimming Pools
Sources
Source water derived chemicals
If water is supplied from a municipal drinking water plant, the organic or inorganic chemicals in water, such as disinfection by-products (DBPs), are the important sources. The mineral materials should be especially considered for hot tubs and spa pools. The high bromide and iodide contents are also important to form brominated and iodinated DBPs with higher adverse effects when seawater sources are used.
Bather derived chemicals
These chemicals are mostly nitrogenous compounds and contained in sweat, urine and the eluate from the skin. They are primarily in the form of urea, ammonia, amino acids and creatinine. Only limited information is available on the distributions and concentrations of body fluids and excreta in swimming pools. More characteristics about cosmetics, suntan lotions and soap residues etc. in swimming pools are important issues to be assessed.
Management derived chemicals
Many kinds of chemicals are applied to kill or inactivate the pathogens in swimming pools, which generally include the disinfectants, their corresponding by-products and pH correction solutions. Chlorine based disinfectants are the most widely used disinfectants because of their residual properties; chlorine dioxide, ozone and ultraviolet are also commonly applied in pool water disinfections. However, the original forms and also the derived forms can cause direct effects such as eye or respiratory irritation and many other indirect effects. According to the different disinfection treatments, acidic or alkaline chemicals are used for pH adjustment, such as sodium carbonate and sodium hydrogen sulfate, and there should be no apparent adverse health effects if chemicals are dosed correctly.
Disinfection by-products formation
The precursors in water can react with disinfectants to form various kinds of DBPs, which commonly include inorganic (e.g. bromate (BrO3-), chlorite (ClO2-) and chlorate (ClO3-)) and organic DBPs (e.g. trihalomethanes (THMs), haloacetic acids (HAAs) and nitrosamines). Their concentrations can vary depending on the types and contents of precursors, types and doses of disinfectants, residual concentrations, water temperature and pH values, etc.
- The mean concentrations of chlorate measured in pools could be as high as 30.92 mg/L, and the highest mean levels of chlorite and bromate are 2.53 mg/L and 0.51 mg/L, respectively (Michalski and Mathews, 2007).
- THMs show the greatest quantities and HAAs are the second majority in swimming pool water. The chlorinated THMs (e.g. chloroform) and HAAs (e.g. dichloroacetic acid and trichloroacetic acid) are the most abundant species due to the widely uses of chlorine based disinfectants. The total THM levels in pool waters range from 0.2 μg/L to 360 μg/L in indoor pools (Chu and Nieuwenhuijsen, 2002; Thacker and Nitnaware, 2003; Lee et al., 2009) and from 34 μg/L to 1287 μg/L in beachfront pools (Beech et al., 1980). The non-volatile HAAs can accumulate and reach up to approximate 300 μg/L in outdoor pools (based on an unpublished data in Taiwan). If the source water has higher bromide or iodide concentrations (e.g. seawater source), the brominated or iodinated DBPs will be generated, and the bromate by-products will also be found in ozone treated pool water.
- The bather derived substances and personal used chemicals can react with disinfectants to form nitrogenous DBPs with higher toxicities (e.g. nitrosamines and haloacetonitrile). The N-nitrosodimethylamine (NDMA) concentrations in pool waters can reach up to 303 ng/L median in indoor hot tubs, which is 10-fold greater than the 32 ng/L median in indoor pools and 60-fold greater than the 5.3 ng/L median in outdoor pools (Walse and Mitch, 2008).
- Data on the distributions and characteristics of DBPs in swimming pools are relatively limited and have to be collected for further study because of the expectable accumulation to levels greater than those observed in drinking water.
Exposures
The chemicals applied or generated in the pool waters can get into users’ or swimmers’ body through different routes and their exposure amounts are affected by various factors. For providing additional reassurance for the health protection in swimming pools, the guideline values in the WHO Guidelines for Drinking-water Quality (WHO, 2006b) can be used to screen and diminish the potential risks based on the tolerable risks over a lifetime.
Direct ingestion
The amounts of water ingestion mainly depend upon the age, gender, skill and type of activities for swimmers. The less skilled, children or male swimmers may have higher intakes.
Inhalation
VOC or aerosolized substances are the commonly inhaled chemicals by swimmers. The exposures are significantly associated with the time and intensity of efforts during swimming, and the concentrations of the volatile substances in inhaled air are largely diluted in outdoor pools.
Dermal contact
Chemicals in pools will extensively contact with human skin and be absorbed into the body across the stratum corneum. Some substances may directly cross through the eyes and mucous membranes. The uptake is a function of the lipophilic/hydrophilic property of chemical, the temperature and the period of contact with the water.
Disinfection Methods
The disinfectants used in swimming pools are similar to those used in drinking water treatments in order to kill or inactivate pathogens and other microorganisms. Many types of disinfectants are applied for pools and the chlorine based disinfectants are the most widely used.
Chlorine based disinfectants
Chlorine based disinfectants are the most widely used disinfectants mainly due to their residual efficacy. They are mostly in the form of chlorine gas, sodium hypochlorite etc. For considering the health protection and minimizing the irritation at the same time, the acceptable level of free chlorine is recommended not to exceed 3 mg/L in public/semi-public pools and not to exceed 5 mg/L in public/semi-public hot tubs. Besides monitoring the residual chlorine concentrations in pool water, the levels of the by-products should also be considered. For example, dissociated cyanuric acid is required to keep at an acceptable concentration if chlorinated isocyanurates is used.
Chlorine dioxide
Chlorine dioxide is an alternative disinfectant as a result of the higher and selective oxidizing power - it breaks down to chlorite and chlorate in water. Based on the WHO health-based drinking water provisional guideline value and total daily intake level for chlorite (0.7 mg/L and 0.03 mg/kg, respectively) (WHO, 2006b), the chlorite and chlorate levels are recommended to be maintained at less than 3.0 mg/L. The maximum contaminant level (MCL) of chlorite in USEPA guidelines is set at 1.0 mg/L (USEPA, 2009).
Bromine based disinfectants
Bromine based disinfectants are primary used in the form of bromochlorodimethylhydantoin (BCDMH) and are applied with a two-part system with sodium bromide and an oxidizer. These disinfectants are often recommended for hot tubs and spa pools because chlorine dissipates at a higher temperature to cause a strong chemical smell. However, they are generally not used in outdoor pools due to the rapid exhaustion of bromine residuals in sunlight (MDHSS, 2011).
Ozone and ultraviolet
Ozone and UV radiation are also commonly used in swimming pools, but the primary drawback is that neither of them last residuals in water. Although ozone is an effective and powerful oxidizing agent, the leakage of ozone into the atmosphere can cause severe respiratory irritation for operators and swimmers, and so it needs to be properly ventilated in an operation room. The ambient ozone concentration is required to keep below the air quality guideline value (e.g. 100 μg/m3 (WHO, 2006a)), and the bromate by-product is recommended less than the 10 μg/L MCL (USEPA, 2009).
Other disinfectants
Hydrogen peroxide combined with silver and copper ions is also used in private pools.
Problems and Suggestions
Based on observations and studies relating to swimming pool water quality, much information is needed for further assessment of their potential health effects.
The current background information on pool water qualities and the factors of operation and management parameters on pool waters are not sufficient today. The association between pool water qualities and human health are also not clear. More discussions and researches are required to clarify these knowledge gaps and their correlations.
Long retention time of pool water is frequently observed in practical operations (in some cases longer than 6 months) due to the high costs of a water exchange, which results in accumulations of the contaminants and causes poor water quality. For management purposes and the protection of public health, the frequencies of pool water exchanges and pool cleans should be increased and recorded.
Swimmer numbers significantly affect the water quality, too. The limitation of the number of swimmers at peak hours according to the pool operation characteristics is needed and should be monitored and recorded.
Pool operators generally lack the knowledge of disinfection requirements and suitable methods which may result in potential risks during operation (e.g. high ozone concentrations in the air) and higher exposure of swimmers (e.g. over-dosed disinfectants or high levels of DBPs). Continuous personnel training including operation procedures and emergency response plans is necessary.
Education for swimmers and users can play an important role in ensuring the pool safety and swimmers’ health, such as the proper dress, health behaviors and a shower before swimming, etc. It should be promoted to provide appropriate and targeted information to the pool users.
In some areas, no comprehensive national regulations are applied to swimming pools and similar recreational water environments. These regulations should include the requirements for the use of certified materials and the recruitment and training of the qualified staffs, etc. Established regulations can ensure and verify the better operation and management plan to provide greater public health protection and public confidence.
References
Beech J.A., Diaz R., Ordaz C. and Palomeque B. (1980). Nitrates, chlorates and trihalomethanes in swimming pool water. American Journal of Public Health 70:79-82.
Chu H. and Nieuwenhuijsen M.J. (2002). Distribution and determinants of trihalomethane concentrations in indoor swimming pools. Occupational and Environmental Medicine 59:243-247.
Lee J., Ha K.T. and Zoh K.D. (2009). Characteristics of trihalomethane (THM) production and associated health risk assessment in swimming pool waters treated with different disinfection methods. Science of the Total Environment 407:1990-1997.
MDHSS (2011). Swimming pool and spa water chemistry. Missouri Department of Health and Senior Services, Section for Environmental Health (http://www.dhss.mo.gov/RecreationalWater/PoolSpaChem.pdf)
Michalski R. and Mathews B. (2007). Occurrence of chlorite, chlorate and bromate in disinfected swimming pool water. Polish Journal of Environmental Studies 16(2): 237-241.
Thacker N.P. and Nitnaware V. (2003). Factors influencing formation of trihalomethanes in swimming pool water. Bulletin of Environmental Contamination and Toxicology 71:633-640.
USEPA (2009). National primary drinking water regulations. U.S. Environmental Protection Agency. EPA 816-F-09-0004.
Walse S.S. and Mitch W.A. (2008). Nitrosamine carcinogens also swim in chlorinated pools. Environmental Science & Technology 42(4): 1032-1037.
WHO (2006a). Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide. Global update 2005. Summary of risk assessment. World Health Organization. WHO/SDE/PHE/OEH/06.02.
WHO (2006b). Guidelines for drinking-water quality, 3rd ed. Vol.1. Recommendations. World Health Organization.
WHO (2006c). Guidelines for safe recreational water environments. Volume 2: Swimming pools and similar environments. World Health Organization.
