Objective To understand the disinfection byproducts distribution and their potential health risks by estimating the levels of trihalomethanes (THMs) and haloacetic acids (HAAs) in the finished water of the water treatment plants located in Pudong New Area, Shanghai.
Methods A total of 28 water samples were collected in March, May, and June 2012, March, May, and August 2013, and February 2014 from five water treatment plants in Pudong New Area. Concentrations of THMs and HAAs in the water samples were detected and assessed for their oral cancer and non-cancer risks using health risk assessment models.
Results The highest concentration of disinfection byproducts was chloroform (CF) (15.0 μg/L) in plant D during the wet seasons, while the lowest one was dichloroacetic acid (DCAA) (not detected, ND) in plant B during the dry seasons. For the five water treatment plants, the CF concentrations during the wet seasons were higher than those in the dry seasons, while the patterns of dibromochloromethane (DBCM) and bromoform (BF) were reversed. The ranges of DCAA and trichloroacetic acid (TCAA) concentrations was ND-3.33μg/L and 0.55-8.25μg/L, respectively. The TCAA concentrations in the wet seasons were slightly higher than those in the dry seasons, while DCAA showed little fluctuation. For oral cancer risk, DBCM ranked the first (2.90& #215;10-5) and BF the last (5.30& #215;10-7). Except for BF in the wet seasons with cancer risk levels between 5.30& #215;10-7 and 1.10& #215;10-6, the cancer risks of DBCM, BDCM, DCAA, and TCAA from five plants ranged from 2.00& #215;10-6 to 3.14& #215;10-5 and exceeded the acceptable cancer risk level of 1& #215;10-6 recommended by the U.S. Environmental Protection Agency. CF presented the highest non-cancer risk, followed by DCAA in the dry seasons. The oral cancer and non-cancer risks for the detected disinfection byproducts showed variations by time and gender:dry seasons showed higher risks than wet seasons (expect that CF in five water treatment plants and DCAA and TCAA in plant B during the wet seasons showed higher non-cancer risks than those in the dry seasons) and the risks in female were higher than those in male.
Conclusion DBCM and BDCM show the highest cancer risks, and CF and DCAA show the highest noncancer risk. The risk levels in dry seasons are higher than those in wet seasons. These findings indicate that more attention should be paid to the reduction of potential cancer and non-cancer risks of long-term exposure to disinfection byproducts and the treatment process adjustment according to seasonal variations.
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