Exposure Assessment Of Trihalomethanes And Haloacetic Acids In S City Residents’ Daily Water Consumption

Chlorination is the most prevelant water disinfection treatment in China and plays an important rolt to ensure drinking water safety. Since its application, water disinfection was regarded as a great triumph in Public Health. Hypochlorous acid (HOCI) was formed when chlorine added to water and inactivated pathogens. However, the unwanted disinfection by-products (DBPs) were also formed. Given that nobody could survive without water, the lifelong persistent exposure to DBPs and its potential adverse health impact can’t be neglected.The formation of DBPs is inevitable in drinking water treatment. Irremovable organic matters in water will react with the residual chlorine to form DBPs in the process of water distribution. There’re mainly6types of DBPs, including trihalome thanes (THMs), haloacetic acid (HAAs), haloacetonitiles (HANs), haloketones (HKs), chloral hydrate (CH) and chloropicrin (CP). Among them, THMs and HAAs amont the most and account for more than70%DBPs in drinking water.Since its mutagenicity and potential carcinogenicity were discovered in1970’s, DBPs were paid great attention on its adverse health impact. Evidence of genetic toxicity tests was accumulated in vitro studies. Researches showed that DBPs could induce multiple organ carcinoma, malformation, reduction of birth weight and growth retardation in experimental animals. Association was found between DBPs and rectal and bladder cancer in epidemiology studies. But results from the epidemiology studies were quite inconsitent. Exposure measurement remains a great challenge in epidemolgy studies related to drinking water. Reasons were probably:(1) multiple drinking water choice provide access to different drinking water quality;(2) great variance exists in drinking water consumption among individuals;(3) factors such as season and pre-treatment of drinking water influence the concentration of DBPs.Based on above-mentioned factors, this study aimed to measure concentration of THM4and HAA6and their possible influential factors in water distribution system in S city and compare measurement in residential tap water and water distribution system. A cross-sectional survey was conducted to analyze water consumption habits among residents in S city. Monte Carlo simulation was applied to calculate THM4 and HAA6exposure and their risk of carcinogenicity in S city.Part One Spatial and Temporal Distribution of THM4and HAA6and Their Potential Influential FactorsThe Stage1Disinfectants/Disinfection By-products Rule was promulgated, including four THMs (chloroform, dichlorobromomethane, dibromochloromethane and bromoform) and five HAAs (monobromoacetic acid, dibromoacetic acid, monochloroacetic acid, dichloroacetic acid and trichloroacetic acid) by US Environmental Protection Agency (EPA). In addition, water plant must monitor bromomonochloroacetic acid if its water supply reached a scale over100,000people.We have measure on a year track for concentration of THM4and HAA6, water temperature, chlorine residual, CODMn and pH value in drinking water from a trunk pipe of Y water plant. Comparisons of THM4and HAA6concentration between residential tap water and trunk pipe water were made.Results showed that THM4and HAA6concentration display temporal variation. In summer, chlorinated-DBPs amount higher while, brominated-DBPs were higher in winter and spring. Spatial variation was found in residential tap water. THM4concentration exceeded national standard, with the highest reached97.20μg/L. The maximum concentration of THM4and HAA6in both residential tap water and truck pipe water were in the latter part of water distibution system. THM4concentration was relatively comparable between residential tap water and truck pipe water. However, HAA6concentration in residential tap water was relatively low.Part Two Water Consumption Habits and Drinking Water Choices in S CitySince the adoption of chlorinated drinking water in Shanghai in1930’s, chlorination was applied in more than98%cities in China. However, information concerning daily water consumption was scarece in China. This part aimed to obtain first-hand water consumption habits in S city and lay foundation for accurate exposure assessment for residents in S city.Results showed that drinking wate consumption was related to gender and season. Oral exposure was a major exposure route for male. Personal drinking water consumption reached high in summer. Shower time was related to gender, age and season. Female exposed most through dermal absorption than male. The juvenile had the longest shower time and the middle-aged the shortest. The average showering time is the longest in summer and shortest in winter. Housework habits was related to gender and age. Female spent much more time in washing clothes and bowls. There existed no difference between juveniles and youngs in bowls washing time. But the juveniles washed clothes for the shortes time. The middle-aged and the elder washed for the longest time.Domestic drinking water choices diversified in China, with tap water a mainstream but alternative drinking water noticeably changed. Domestic filtrated water increased and barrelled/bottled water decreased, compared with that decade ago. Domestic drinking water choices were correlated with age, education, annual income, housing condition, risk perception and belief in what kind of drinking water the cleanest. Strong correlation was found between one’s belief in what type of water the cleanest and one’s domestic drinking water choices (P<0.001) by using backward stepwise logistic regression model. However, there existed confusion about what kind of drinking water the cleanest in the general public.Part Three Exposure Assessment and Carcinogenic/Noncarcinogenic Risk of THM4and HAA6Among S City ResidentsDrinking boiled water is a prevelant habit in China. THM4and HAA6are volatile/semi-volatile compounds. Understanding the influence of boiling time on THM4and HAA.6concentration is significant in practical guidence. In addition, studies in part two revealed an increase in filtration water in S city. The comparison of THM4and HAA6concentration is helpful in exposure assessment.The integrated risk information system (IRIS) is created by US.EPA to provide reliable data used in risk assessment. We utilized drinking water consumption habits and THM4and HAA6concentration obtained from the first two parts. Monte Carlo simulation was applied to assess exposure and carcinogenic risk of THM4and HAA6.Results showed that residents in S city drink boiled water.77.75%respondents stoped heating when water was boiled in one minute.97.00%respondents stoped heating when water was boiled in five minutes. THM4concentration decreased to nearly3/4when boiled. After boiling for10minutes, none THM4was detected. There exhibited no evident change in HAA6concentration in spiked water. However, with the increase of boiling time, HAA6concentration gradually decrese. But DCAA concentration exhibited a slight increase in the first10minutes, and TCAA exhibited an evident decrease in5minutes.18.25%of respondents had the habit of cooling drinking water in refrigerator.48-hour refrigeration showed a slight decrease in THM4concentration after48hours, but HAA6concentration remains relatively stable.42℃water bath experiment showed that trihalomethane concentration was a little bit decreased while HAA6concentration remained stable.Monte Carlo simulation was applied to calculate the exposure level of THM4and HAA6. Results showed that residents in S city were mainly exposed to Br-DBPs. The middle-aged and the elder exposed a higher level of THM4and HAA6than the juveniles and young. Females exposed more from inhalation and dermal routes than males. Although individual concentration of THM4and HAA6didn’t exceed the reference dose given by US. EPA, indicating no existence of noncarcinogenic risk. However, the carcinogenic risk shouldn’t be neglected through our investigation for DBCM, the individual DBPs with the highest concentration in S city.