Background Serious organic pollution in aquatic environments threatens the quality of drinking water. Long-term low-dose exposure to multiple organic pollutants in drinking water poses potential hazards to human health.
Objective This study investigates the pollution of 69 organic compounds in four categories including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and phthalate esters (PAEs) in finished water from a large drinking water treatment plant in a southern city at the estuary of the Yangtze River, and evaluate potential health risk of exposure to mixtures of organic pollutants.
Methods Finished water samples from selected large drinking water treatment plant were collected. Solid-phase extraction and gas chromatography-mass spectrometry (GC-MS) were used to enrich and quantify the levels of organic pollutants in water samples, including PCBs, PAHs, OCPs, and PAEs. Non-carcinogenic and carcinogenic risks of exposure to individual organic compounds and mixtures were evaluated by health risk assessment method recommended by U.S. Environmental Protection Agency (EPA).
Results In the finished water samples, 6 PAEs, 6 PAHs, 5 OCPs, and 1 PCB were detected. The total concentration was 477.28 ng·L-1, the concentrations of individual chemicals were in the range of 0.02-278.21 ng·L-1, and the concentrations of the four categories of chemicals were ranked as follows: PAEs>OCPs>PAHs>PCBs. This study assessed the non-carcinogenic risks of 11 detected chemicals in three categories. Under the central tendency exposure (CTE) and reasonable maximum exposure (RME) scenarios, the non-carcinogenic risks of exposure to mixtures of organic pollutants in each age group were at the levels of 10-5 and 10-4, respectively, both much lower than 1.0, indicating an acceptable risk level. The carcinogenic risk assessment was performed on 6 detected organic substances, including 2, 3', 4, 4', 5, 5'-hexachlorobiphenyl (PCB167), chrysene (Chy), naphthalene (Nap), p, p'-dichlorodiphenyl dichloroethane (TDE), β-benzenehexachloride (β-BHC), and bis(2-ethylhexyl) phthalate (DEHP). Under the CTE scenario, the lifetime carcinogenic risk of exposure to mixtures of organic pollutants (7.11×10-7) was below the negligible risk level (< 10-6) recommended by U.S. EPA. Under the RME scenario, the lifetime carcinogenic risk (2.18×10-6) was at the acceptable risk level (10-6-10-4); the lifetime carcinogenic risk of β-BHC (1.67×10-6) was the highest among the 6 chemicals, accounting for 76.34% of the total lifetime carcinogenic risk. Moreover, oral ingestion and dermal contact were the two main exposure routes for the estimated carcinogenic risks of selected organic substances.
Conclusion Organic pollution exists in the finished water in the selected water plant, and the detected chemicals do not exceed the limits in U.S. EPA and China's drinking water quality standards. The lifetime carcinogenic risk of exposure to mixtures of organic pollutants in the finished water exceed the negligible risk level, and β-BHC is the major contributor. Although the carcinogenic risk is at the acceptable risk level, the potential carcinogenic risk from life-long exposure to the finished water should not be neglected.
DownLoad: