Disinfection by-products in indoor swimming pools: A critical review to prioritize commonly occurring species and influencing factors

Abstract

Despite the reported occurrence of several disinfection by-products (DBPs) in swimming pools, it is challenging to identify important DBP species due to strewn and conflicting information about their occurrence and importance in the literature. There is a need to provide clear direction and decisive information to support regulators' and pool facilities' efforts to control DBPs. In this review, alongside providing detailed occurrence data, we have developed a novel prioritization approach to classify DBPs as Tier-1 (critical priority), Tier-2 (medium priority), and Tier-3 (low-priority) DBPs in chlorinated indoor swimming pools (ISPs). After compiling an exhaustive database of published literature on chlorinated ISPs, DBP species were evaluated on a defined scoring system based on their occurrence (concentration levels and reported frequency) and toxicity. The normalized aggregated scores from these criteria were used to prioritize the DBPs. The DBPs identified as Tier-1 species with the highest occurrence and potential toxicity include Trichloromethane (TCM), Trichloroacetic acid (TCAA), and Dichloroacetic acid (DCAA). Respectively, ten DBP species were identified in Tier-2 and fifteen in Tier-3. Implications of the prioritization results for regulatory agencies, pool facilities, and researchers have been provided. Furthermore, a comparative analysis of the available studies, that described the correlation of water quality and pool operational factors with Tier-1 DBPs, was carried out. The identified critical factors include the number of swimmers, free residual chlorine, disinfection methods, total organic carbon (TOC), and temperature. These factors can be used to control the formation of DBPs and reduce the associated risk, especially for Tier-1 species.