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Researchers: Wei Wang, Yichao Qian, Jessica M. Boyd, Minghuo Wu, Steve E. Hrudey, Jinhua Li, Birget Moe, Claire F. McGuigan, Shengwen Shen and Xing-Fang Li, University of Alberta (Edmonton, Alberta, Canada), and Haiying Du, Jilin University (Changchun, Jilin Province, China)

Swimming is a favorite summer pastime for many, and swimming pools are frequent destination for this activity. Of course, keeping the water in swimming pools clean means the use of disinfectants, and researchers at the University of Alberta in Canada published some insightful findings in this area. Wei Wang and coworkers in the university’s Division of Analytical and Environmental Toxicology conducted a study using the SCIEX Triple Quad™ LC-MS/MS System to quantify the presence of halobenzoquinones (HBQs), a class of disinfection byproducts (DBPs) of health relevance, in swimming pools.

Halobenzoquinones and their significance

It is essential for drinking water to undergo a disinfection process to inactivate pathogenic microbes and prevent waterborne diseases. Common disinfection processes include chlorination, chloramination, ozonation and UV. While these processes function effectively to remove microbial risks, these disinfecting agents can also react with the natural organic matter that might be present in the water, resulting in the creation of DBPs.

There are numerous types of DBPs that can be formed, depending on the composition of the organic matter in the water and the treatment process used, and significant scientific research has focused on identifying and understanding DBPs that are toxicologically significant. HBQs are 1 of 5 DBP classes that are predicted to have toxicological importance. A study published by Haiying Du (currently at Jilin University in China), Jinhua Li and other coworkers at the University of Alberta evaluated the cytotoxicity of 4 HBQ compounds.¹ The research team identified that HBQs are, in fact, cytotoxic to T24 bladder cancer cells, with cytotoxicity impacted by oxidative stress. The comprehensive study produced significant results for identifying the toxicological significance of HBQ compounds as well as beginning to formulate the cellular mechanism of that toxicity.

Swimming pools and halobenzoquinones: the connection

The formation of assorted disinfection byproducts in swimming pools is a complex chemical process. Swimming pools usually contain significantly more organic matter than regular tap water (consider cosmetics, lotions and sunscreens) and may also contain other contaminants (such as urine or sweat) among a variety of other residues. Swimming pools commonly use chlorine as the primary means of disinfection, and the chlorine dose applied in swimming pools is usually higher than the residual chlorine in regular tap water to control waterborne disease. UV irradiation may also be used as a secondary disinfection treatment. So, the variety of DBPs that could be present in swimming pools can be vast.

Study overview

Wang and coworkers sought to identify and quantify assorted HBQ compounds in swimming pools with a goal to better understand how those compounds are formed as well as the potential human health risks associated with exposure to these HBQ compounds.² The team utilized solid-phase extraction (SPE) to extract HBQ residues from swimming pool water samples, with additional washes to remove excess salinity or other matrix residues. Samples were analyzed using LC-MS/MS, with LC separation performed using a Phenomenex Luna C18(2) column and MS analysis using a SCIEX Triple Quad LC-MS/MS System using negative electrospray ionization (ESI) mode and with multiple reaction monitoring (MRM).

Several sample types were evaluated in the study, including:

• Swimming pool water treated with chlorine or chlorine plus UV irradiation
• Diluted urine samples (to identify HBQ compounds that might form directly from urine)
• Water containing personal care products (to identify HBQ compounds that might form directly from assorted lotions and sunscreens)
• Tap water (to evaluate 8 HBQ compounds for the study)

Results and findings of the study

Of all HBQ compounds studied by Wang and coworkers, 2,6-DCBQ (2,6-dichloro-1,4-benzoquinone) had the most elevated concentration in pool water relative to tap water (increased by a factor ranging from 5- to 100-fold), and 3 other HBQ compounds were detected in the pool water but not detected in the tap water. The team then investigated the factors that led to the increase of these HBQ compounds in the pool water, looking into the effects of water temperature and chlorine dose. The results showed that higher water temperatures and increased chlorine content both contributed to an increase in the presence of HBQ residues, particularly 2,6-DCBQ.

The team followed up with an investigation of what caused the increased concentration of HBQs in the swimming pool water, evaluating whether the formation occurred from biological fluids (e.g., urine) or from personal care products (e.g., sunscreens and lotions). The results showed that lotions and sunscreens introduced by swimmers could increase the concentration of HBQs in the swimming pool water, but it is dependent on the type of lotion or sunscreen present (most likely due to differences in formulations and active ingredients in different products). Urine did not seem to serve as a precursor to the formation of HBQs.

Conclusions

Both these studies used a SCIEX Triple Quad LC-MS/MS System to identify and quantify HBQ compounds in swimming pools, showed that multiple HBQ residues of toxicological significance do form in swimming pools as a result of the reaction between the disinfection agents used in the pool and the organic residues introduced by swimmers. What is the relevance of all of this? Epidemiological studies have indicated a potential association of consumption of chlorinated water with an increased risk of bladder cancer. The results showing the cytotoxicity induced by HBQs at micromolar concentrations to T24 bladder cancer cells could potentially be the first steps in understanding the toxicity of these compounds. While cytotoxicity testing is done at micromolar concentrations, HBQs in treated water are at ng/L levels. The effects of long-term exposure to the trace HBQs are unclear. Therefore, additional research is certainly warranted.

In the meantime, enjoy your time at the pool this summer, but take a shower before jumping into the pool. The mass spectrometer can tell. Keep the swimming pool clean for your health!

References:

¹ Du, H.; Li, J.; Moe, B.; McGuigan, C.F.; Shen, S.; Li, X-F. Cytotoxicity and Oxidative Damage Induced by Halobenzoquinones to T24 Bladder Cancer Cells. Environ Sci Technol. 2013, 47 (6), 2823–2830. https://doi.org/10.1021/es303762p

² Wang, W.; Qian, Y.; Boyd, J.M; Wu, M.; Hrudey, S.E.; Li, X-F. Halobenzoquinones in Swimming Pool Waters and Their Formation from Personal Care Products. Environ. Sci. Technol. 2013, 47 (7), 3275–3282. https://doi.org/10.1021/es304938x

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