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Although swimming is regarded as a safe and healthy form of exercise, disinfection byproducts (DBPs) are formed in pools when chlorine or other disinfectants are used. DBPs are formed by the reaction of disinfectants with organic matter, (1-19) including natural organic matter from source water and human inputs, such as sweat, urine, pharmaceuticals, and personal-care products. Although disinfection is important to inactivate harmful pathogens, adverse health effects associated with exposure to DBPs, such as asthma and bladder cancer, have been noted in human epidemiologic studies.

Increased incidences of asthma and other respiratory effects were found in several epidemiologic studies of Olympic swimmers and pool workers, with less clear evidence for recreational adult swimmers and children. (20-25) There are also recent reports of increased ocular, respiratory, and cutaneous symptoms for swimmers and pool workers, (26-28) as well as sore throat and phlegm reported more frequently for lifeguards and swimming instructors. (29) Short-term changes in respiratory biomarkers were also reported for swimmers in a chlorinated pool. (30) In addition, an association was found between testicular hormones at adolescence and attendance at chlorinated swimming pools during childhood, with swimmers strongly associated with lower levels of serum inhibin B and total testosterone. (31) Increased bladder cancer (32-34) and genotoxic effects (35) were also reported in swimmers. A new study in rats showed effects on their health, training, and metabolic profiles when tested in a 12-week swimming training program in simulated chlorinated pools. (36)

Trichloramine, formed by the reaction of chlorine with constituents of human urine and sweat, (2, 37, 38) is suspected to be associated with asthma and other respiratory effects, but causality is not yet proven. Trichloramine has a high Henry’s law constant, so it is present at high concentrations in pool air. (39, 40) Indoor swimming pool air shows similar inflammatory effects. However, it is likely that other air contaminants (i.e., DBPs) also contribute. (41)

Trihalomethanes (THMs) were the first class of DBPs studied in pools, (5, 9) and now there are quantitative data for many other classes. (4, 42-49) Although DBPs are regulated in drinking water, only Germany has a regulation for pools, with a maximum level of 20 μg/L for total THMs. (50) France recently set a recommended limit of 100 μg/L for total THMs. (51)

The first comprehensive, broadscreen studies of DBPs in pools were published in 2007 (outdoor pools) (1) and 2010 (indoor pools). (52) These studies went beyond target analysis of a few DBPs like THMs and HAAs to comprehensively identify all DBPs detected by GC–MS. Membrane-introduction mass spectrometry (MIMS) and liquid chromatography (LC)-MS also have been used to identify volatile amines (2, 4, 53) and halophenols. (54) In 2016, a study of DBPs and mutagenicity in freshwater and seawater pools disinfected with chlorine was published in which THMs, haloacetic acids (HAAs), haloacetonitriles, haloketones, chloral and bromal hydrate, and halonitromethanes were quantified. (49)

For DBPs quantified in pools, HAA concentrations are among the highest, up to 6800 μg/L for dichloroacetic acid. (55) HAAs are not volatile and will accumulate in pool waters. Although studies on DBPs in pools have increased over the last 5 years, there are only a few studies of spas, including measurements of THMs and nitrosamines. (53, 56) Recent reviews summarize the occurrence, implications, and control of DBPs in swimming pools. (12, 57)

There is also a paucity of toxicity data for spas. Recent mammalian cell genotoxicity data for a chlorinated spa revealed significantly higher genotoxicity than the incoming tap water, but less than an unheated chlorinated pool at the same facility. (57) To the best of our knowledge, there are no reports on mutagenicity of spa water, and only three on pool water. (49, 52, 58) All found that pool waters were mutagenic, but did not evaluate source or tap water for comparison. Three studies evaluated the ability of pool and spa waters to induce DNA damage; all found these waters to be genotoxic; (59-63) one study evaluated only cytotoxicity. (64) Collectively, the genotoxicity studies demonstrated that disinfection of recreational waters by brominating agents resulted in more genotoxic waters than by chlorinating agents.

Here we report the first integrated mutagenicity and comprehensive chemistry analysis of spa water, as well as the first comprehensive study of the progression of DBP formation and accompanying mutagenicity from source water to finished water at the drinking water treatment plant, to tap water at the pool/spa facility, to the spa and swimming pool. We sampled public and private pools and spas from seven locations in the U.S. where chlorine, bromine, ozone, or ozone-chlorine was used for disinfection. Two sites were also sampled during heavily used situations following large swimming competitions (pools) or after 3 weeks of continuous use (spas). These heavily used situations were compared to clean situations, sampling 24 h following draining-cleaning-refilling-disinfection of the spas and after normal or limited use of the pools (no swimming competitions). In this way, the effect of increased human inputs or bather load (precursors) could be assessed.