Comparative Mammalian Cell Cytotoxicity of Water Concentrates from Disinfected Recreational Pools

Disinfection of recreational pools is essential to prevent outbreaks of infectious disease. Despite the health benefits of swimming, recent research demonstrated an association between the application of disinfectants to recreational pods and adverse health outcomes. Pool waters are extreme cases of disinfection that differ in important respects from disinfected drinking waters. Pool waters are continuously exposed to disinfectants over average residence times extending to months. Disinfection byproduct (DBP) precursors in pools include natural humic substances deriving from the tap water source plus inputs from bathers through urine, sweat, hair, skin, and consumer products including sunscreens and cosmetics. This study presents a systematic, chronic in vitro mammalian cell cytotoxicity analysis of different recreational waters with varied environmental conditions that were derived front a common tap water source. Recreational waters were significantly more toxic than their tap water source. Because trihalomethane concentrations are similar between tap waters and pool waters, using trihalomethanes to monitor exposure in epidemiological studies may not be the best metric. Of primary importance for cytotoxicity were illumination conditions. Pools subjected to a combination of ultraviolet light and free chlorine disinfection indoors, or outdoor sunlight exposure exhibited lower cytotoxicity than their indoor counterparts disinfected with free chlorine. Temperature and total organic carbon content, as an indirect measure of DBP precursors, were less important. Previous research on the same samples demonstrated the genotoxicity of an indoor pool disinfected with bromochlorodimethylhydantoin; the cytotoxicity of this sample was confirmed in the present study. While the association of reduced toxicity with illumination indicates that the agents responsible are photolabile, their identity is unclear. As a broad measure of adverse biological responses, cytotoxicity may be a useful metric to gauge the health impacts of alterations in pool operating conditions.