Physiologically based kinetic model for assessing intermittent chronic internal exposure to chemicals: Application for disinfection by-products in swimming pool water

Chronic exposure to disinfection by-products (DBPs) via swimming in chlorinated pools can damage the genetic material and even cause cancers in humans. To assess the intermittent chronic internal exposure to DBPs in swimming pool water, a physiologically based kinetic (PBK) modeling framework was introduced to simulate daily average internal exposure doses of DBPs that can be linked to the corresponding daily average external doses. Biotransfer factor (BTF), i.e., the steady-state concentration ratio between human bodies and swimming pool water, was applied to measure the bioaccumulation potential of chemicals in organs and tissues. The results simulated for the four selected trihalomethanes (THMs) (i.e., chloroform, bromoform, dibromochloromethane, and bromodichloromethane) showed that lungs had the highest simulated BTF among human organs and tissues, with the inhalation route showing the maximum contribution to the overall external dose. In addition, route-specific analysis indicated that chronic internal exposure doses of THMs via oral and dermal routes were negligible compared to the inhalation route. Theoretical simulation using the dissipation coefficient of THMs in the air can help optimize the design and operation of swimming pools to substantially reduce chronic internal exposure doses of THMs. The simulated results for time-dependent chloroform concentration in human blood agreed with the reported data and can be further improved once more information about the THM concentrations in breathing zones of swimmers is obtained, indicating that the proposed model can be used as a practical tool to assess intermittent chronic internal exposure of THMs in swimming pool water. In future studies, human exposure to THMs via other pathways (e.g., drinking water, showering, and bathing) can be incorporated into the proposed model to comprehensively evaluate the internal exposure doses of THMs in humans.