Probabilistic approach for health hazard assessment of trihalomethanes through successive showering events

Trihalomethanes (THMs) are common disinfection by-products in chlorinated tap waters. They can cause various cancers and non-cancer health hazards. Ingestion, dermal contact, and inhalation are the three exposure routes considered in the THM hazard or risk assessments. Among these, inhalation hazard is generally calculated by assuming the initial concentration as zero. This assumption fails to address the case of continuous or successive showers that can happen in shared showering facilities such as student hostels or gymnasiums. In the present study, the leftover THM concentration from the previous bath was considered to assess the chronic daily intakes (CDI) and hazard index (HI) for successive showers. For this, tap water of a university campus was analyzed to understand the extent of THM exposure at consumer points and the result obtained was used for the hazard assessment. Total THM concentrations varied from 0.51 to 68.9 mu g L-1. To address the variability of the model input parameters, 50,000 iterations of Monte Carlo simulation were carried out. Maximum HI values of 7.94E - 02 +/- 3.63E - 02, and 6.69E - 02 +/- 3.08E-02 were observed for the 1(st) shower for females and males, respectively. This value increased exponentially up to the 5(th) shower and thereafter, the value was constant. The methodology followed in the present study successfully determines the risk and hazard of THMs through successive showers.