Cancer and non-cancer risk assessment of trihalomethanes in urban drinking water supplies of Pakistan.

This study aims at monitoring and risk assessment of trihalomethanes (THMs) such as chloroform, bromodichloromethane, dibromochloromethane and bromoform, in the drinking water supplies of Rawalpindi and Islamabad. THMs were monitored at twenty locations in these twin cities using solid phase micro extraction-gas chromatography (SPME-GC). Total concentration of THMs was ranged between 21 and 373μg/L, whereas both cities had an average total THMs concentration of 142 and 260μg/L, respectively. Chloroform was found as one the major contributor to the THMs concentration (>85%). The occurrence of THMs followed the given order: chloroform, bromodichloromethane>dibromochloromethane>bromoform. Lifetime cancer risk assessment of THMs was carried out using prediction models via different exposure routes (ingestion, inhalation and dermal). An average lifetime cancer risk was found to be 0.74×10(-4) and 1.24×10(-4) for Rawalpindi and Islamabad, respectively. The number of expected cancer cases per year could reach two cases for each city. Hazard index values were found below unity for both the cities implying that there would be no considerable non-cancer risk. Oral ingestion was found to be one of the main routes of exposure for both types of risk which was followed by inhalation and dermal routes.