Study On Health Risk Assessment Method Of Trihalomethanes From Drinking Water In Urban Households

Trihalomethanes (THMs) is a class of primary disinfection byproducts which arepresent in drinking water widespreadly. At present, a large number of epidemiologicalstudies and animal toxicology studies have shown that THMs have carcinogeniceffects on the human body, as well as teratogenic effects, reproductive toxicity andother adverse effects. Therefore, the study aims at the human health risks via exposueto THMs in drinking water by the urban residents in China in their daily householdwater-related activities based on the cumulative health risk assessment (CRA)framework and the total exposure model (TEM).Firstly, the CRA framework and the traditional risk assessment framework werecompared and analyzed, which were both proposed by the Environmental ProtectionAgency of United States (USEPA); the concept of CRA and its application in thisstudy were demonstrated from the aspects of exposure assessment, toxicityassessment, risk characterization, uncertainty, and variability; and the improved TEMwas proposed, and the quantification methods used herein for uncertainty andvariability were also introduced; accordingly, the methods and ideas in this study wereidentified.Secondly, according to the residential apartment features in China, the Mckone’sthree-component model was improved to establish the indoor THMs concentrationestimation models respectively with and without an independent shower room basedon the mass balance equations and two-film theory, which were used to describe theevaporation process of THMs in drinking water and transfer process of THMs in air indifferent indoor compartment. The exposure estimation models and risk estimationmodels via inhalation, ingestion and skin recommended by USEPA were applied andsimplified, and the model parameters were classified and investigated. In addition, thedata were analyzed by statistical means such as distribution fitting and correlationanalysis.Thirdly, considering four kinds of typical exposure scenarios, the models ofTHMs concentration in air were solved by using MATLAB programming based onthe Runge-Kutta method, and the changes of houshold THMs concentration indifferent compartments for24hours were obtained respectively for different residential apartment features and different lifestyles. Sevaral new concepts wereestablished in exposure assessment, including population exposure characteristicmatrix, contaminant exposure level vector, and age vector; and then the exposurelevels in different water-related activities through different exposure routes forvarious sub-populations were calculated using point evaluation method throughmatrix operations, so that the variabilities and uncertainties in risk assessment couldbe distinguished, and the calculation process were also simplified.Finally, a1D-S-2D system of risk assessment and control was established.Considering the correlation between the variables, the carcinogenic risk distributionvia various exposure routes were evaluated by one-dimensional Monte Carlo (1D-MC)simulations; without considering the correlation between the variables multivariate,sensitivity analysis were carried out to determine the sensitive risk factors; and thencombining the risk calculation results and the sensitivity analysis results with variablecharacteristic analysis, quantitative scheme for risk control of drinking water THMswas proposed by using a two-dimensional Monte Carlo (2D-MC) simulation aimingat the exposure pathway associated with the highest risk level. Additionally,suggestions for risk control measures of drinking water THMs were put forwardrespectively from the angle of risk managers and exposed populations.