Estimating airborne trichloramine levels in indoor swimming pools using the well-mixed box model

Abstract

Exposure to airborne disinfection by-products, especially trichloramine (TCA), could cause various occupational health effects in indoor swimming pools. However, TCA concentration measurements involve specialized analysis conducted in specific laboratories, which can result in significant costs and time constraints. As an alternative, modeling techniques for estimating exposures are promising in addressing these challenges. This study aims to predict airborne TCA concentrations in indoor swimming pools using a mathematical model, the well-mixed box model, found in the IHMOD tool, freely available on the American Industrial Hygiene Association website. The model’s predictions are compared with TCA concentrations measured during various bather load scenarios. The research involved conducting 2-hr successive workplace measurements over 16- to 18-hr periods in four indoor swimming pools in Quebec, Canada. TCA concentrations were estimated using the well-mixed box model, assuming a homogeneous mixing of air within the swimming pool environment. A novel approach was developed to estimate the TCA generation rate from swimming pool water, incorporating the number of swimmers in the model. Average measured concentrations of TCA were 0.24, 0.26, 0.14, and 0.34 mg/m³ for swimming pools 1, 2, 3, and 4, respectively. The ratio of these measured average concentrations to their corresponding predicted values ranged from 0.51 to 1.30, 0.67 to 1.04, 0.57 to 1.14, and 0.68 to 1.49 for the respective swimming pools. In a worst-case scenario simulating the swimming pool at full capacity (maximum bathers allowed), TCA concentrations were estimated as 0.23, 0.36, 0.14, and 0.37 mg/m³ for swimming pools 1, 2, 3, and 4. Recalculated concentrations by adjusting the number of swimmers so as not to exceed the recommended occupational limit concentration of 0.35 mg/m³ gives a maximum number of swimmers of 63 and 335 instead of currently 80 and 424 for swimming pools 2 and 4, respectively. Similarly, for swimming pools 1 and 3, the maximum number of swimmers could be 173 and 398 (instead of the current 160 and 225, respectively). These results demonstrated that the model could be used to estimate and anticipate airborne TCA levels in indoor swimming pools across various scenarios.

Keywords:

• Disinfection by products
• mass emission rate
• modeling
• NCl₃
• swimmer
• worker exposure

Acknowledgments

The authors extend their sincere appreciation to Mr. Daniel Drolet for his invaluable support and essential collaboration in this research. We extend our appreciation to the research team members for their support in the analysis process. We express our sincere appreciation to the reviewers for their valuable and constructive comments that have strengthened the quality of this work.

Data availability

The corresponding author can provide the data supporting the findings of this study upon reasonable request.

Disclosure statement of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The authors confirm no conflicts of interest associated with this publication.

Disclaimer

Furthermore, the views and opinions expressed in this paper are solely those of the authors and do not necessarily reflect the official policy or position of this funding institute or any other organization.

Additional information

Funding

We would like to acknowledge the financial support provided by the “Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST)” for the project titled “Développement de stratégies visant à contrôler le niveau de contamination des piscines par les sous-produits de désinfection” (Project Numbers N/Dossier 2015-00102).