Airborne trichloramine in indoor swimming pools in Sweden

Trichloramine is a disinfection by-product in chlorinated swimming pools. It can evaporate into the air and irritate eyes and airways among swimmers and pool workers. This study aimed to evaluate airborne concentrations of trichloramine in different types of indoor swimming pools. Altogether, 72 swimming pools across Sweden were included; 36 exercise pools, 16 instruction pools, seven adventure pools, and 13 rehabilitation pools. In total, 167 sampling sessions were performed with the majority (N = 91) conducted in public exercise pools. Repeated sampling sessions on different days were performed within all pool categories. Airborne trichloramine was measured stationary by the poolside using active sampling on quartz filters. In total, 434 air samples were collected. The geometric mean (GM) concentration of trichloramine for the exercise pools was 0.12 mg/m³ (range GM_pool: 0.02-0.29 mg/m³) and for about 30% the GM_pool exceeded the Swedish public health guideline value (0.2 mg/m³). The geometric mean for instruction pools was 0.18 mg/m³ and for adventure pools 0.20 mg/m³. Trichloramine concentrations were statistically significantly lower in rehabilitation pools (GM: 0.03 mg/m³) compared with the other pool categories. A statistically significant effect of time of the day for sampling was found for the exercise and instruction pools, with higher trichloramine levels during evenings compared with mornings and afternoons. For the rehabilitation pools, trichloramine was significantly higher during the cold season compared with the warm season. Variability in trichloramine concentrations was attributed to between-pool as well as within-pool variances. The within-pool variability encourages a repeated sampling strategy to capture the variation between different days. These findings have implications for exposure assessment in epidemiological studies as well as for indoor air quality monitoring. Trichloramine can cause acute irritative effects at elevated levels, and since trichloramine concentrations may differ depending on the time of the day it is recommended that full-day stationary measurements are supplemented with short-term samplings to capture these variations.