[Air pollution in two waterpipe-serving premises and associated health risks]

Objective　In recent years, the number of waterpipe (shisha) bars has rapidly increased, particularly in urban areas of Japan, with increasing use among young people. While there is a widespread misconception that waterpipes are harmless because the smoke passes through water, cases of acute carbon monoxide (CO) poisoning caused by incomplete combustion of charcoal have been reported. This study aimed to measure the concentrations of CO, carbon dioxide (CO₂), and fine particulate matter (PM_2.5) in indoor air during waterpipe use to clarify the actual state of air pollution.Methods　Measurements were conducted at two establishments: a restaurant offering waterpipes (Store T1) and a shisha bar (Store T2). Concentrations of CO, CO₂, and PM_2.5 were recorded at 5-second intervals using a carbon monoxide detector, carbon dioxide monitor, and digital dust monitor, respectively. At Store T1, measurements were taken at two locations across from and next to the user during the use of a single waterpipe. At Store T2, measurements were taken at two locations, across from the user and at the counter, during the simultaneous use of two waterpipes. In addition, for employees at Store T2, exhaled CO concentrations were measured three times before and after providing waterpipes to customers.Results　During waterpipe use, the concentrations of CO, CO₂, and PM_2.5 increased significantly at both establishments, indicating pollution of the indoor air environment. Notably, the CO concentration reached 177 ppm, and even at adjacent tables, levels of 49 ppm were observed. This suggests that even patrons and employees who do not directly use waterpipes may be at risk of developing acute carbon monoxide poisoning. Furthermore, the exhaled CO concentration of shisha bar employees increased from 3 ppm (non-smokers) before waterpipe service to 21 ppm (moderately addicted smokers), indicating a potential health risk from occupational exposure.Conclusion　It was confirmed that the use of waterpipes (shisha) increased the concentrations of CO, CO₂, and PM_2.5, resulting in air pollution. In addition, the marked increase in exhaled carbon monoxide levels in employees after waterpipe use, reaching levels comparable to those of frequent smokers, indicates a substantial risk of occupational exposure. These findings highlight the need to provide accurate risk information to both waterpipe users and employees, as well as to establish appropriate regulatory measures for waterpipe-serving establishments from a public health perspective.