| Chlorination is the most prevalent disinfection for drinking water, including some strong oxidants such as liquid chlorine, chlorine, chlorine dioxide and sodium hypochlorite. Chlorination can effectively control the incidence of water-borne diseases, so it’s one of the most significant public health advances of the20th century. However, chemical disinfection can form disinfection by-products (DBPs) which have the adverse effect on health. Formation of DBPs in drinking water is inevitable when using chemical disinfectants. Toxicology studies show that some DBPs exhibit cytotoxicity, genotoxicity, mutagenicity, carcinogenicity and reproductive and developmental toxicity. Although population-based epidemiological studies suggest that DBPs are associated with an increased risk of bladder cancer and colon cancer as well as premature birth and stillbirth. Therefore, the impacts of DBPs on human health have been concerned.Given the potential health risks associated with DBPs, our country has regulated trihalomethanes (THMs), haloacetic acids (HAAs) and some other DBPs showed strong toxic effect. However, with the conformation for stronger toxic effects of emerging DBPs, the original DBPs detection methods have been unable to meet the needs of detection and exposure assessment. More importantly, the detection method for THMs and HAAs, given by China’s current drinking water standard (GB/T5750.10-2006), has the high detection limit and can only detect the four THMs and two HAAs. Besides, these methods cannot synchronously detect the unregulated DBPs (URDBPs) such as iodine-containing DBPs (I-DBPs), nitrogen-containing DBPs (N-DBPs). Therefore, it’s extremely important for establishing a detection method which can synchronously determine IF, THMs and IAA, HAAs as well as other N-DBPs, understanding the exposure levels of DBPs and accurately assessing their health risks.Factors impacting the formation of DBPs include characteristics of raw water, treatment processes, type and concentration of disinfectants and precursors, contact time between disinfectants and water. Studies about DBPs are mostly limited to laboratory simulation while field conditions are more complex and few studies are about large-scale water supply in field conditions. However, the rule of DBPs formation in field conditions and their changes with water characteristics is the premise and basis for promoting treatment processes and controlling DBPs.Shanghai is situated on the east coast of China at the mouth of the Yangtze River and belongs to the alluvial plain. Every year’s November to next April is the period of seawater intrusion and low water periods. Therefore, raw water will have a large amount of halogen compounds because of seawater intrusion, which may influence the formation of DBPs inevitably in the water treatment processes. However, few studies pay attention to the effect of seawater intrusion on the DBPs formation and corresponding health risk.Based on the facts mentioned above, our study aims to establish the detection methods which can synchronously determine IF and four THMs as well as IAA and nine HAAs, develop a modified method to detect haloacetonitriles (HANs), haloketones (HKs) and trihalonitromethane (TCNM), investigate the concentration and formation rule of DBPs in raw water, treatment processes, finished water and drinking water in distribution system from water plants in Jiangsu province, explore the DBPs levels in different treatment processes of two water plants in Shanghai during the seawater intrusion period and regular time and give the cancer and non-cancer risk of Shanghai residents.Part one The optimization and establishment of detection methods for THM5, HAA10, HANs, HKs and TCNMAn optimized method is presented using liquid-liquid extraction and derivatization for the extraction of iodoacetic acid (IAA) and other haloacetic acids (HAA9) and direct extraction of iodoform (IF) and other trihalomethanes (THM4) from drinking water, followed by detection by gas chromatography with electron capture detection (GC-ECD). A Doehlert experimental design was performed to determine the optimum conditions for the five most significant factors in the derivatization step:namely, the volume and concentration of acidic methanol (optimized values=15%,1mL), the volume and concentration of Na2SO4solution (129g/L,8.5mL), and the volume of saturated NaHCO3solution (1mL). Also, derivatization time and temperature were optimized by a two-variable Doehlert design, resulting in the following optimized parameters:an extraction time of11minutes for IF and THM4and14minutes for IAA and HAA9; mass of anhydrous Na2SO4of4g for IF and THM4and16g for IAA and HAA9; derivatization time of160min and temperature at40℃. Under optimal conditions, the optimized procedure achieves excellent linearity (R2ranges0.9990-0.9998), low detection limits (0.0008-0.2μg/L), low quantification limits (0.008-0.4μg/L), and good recovery (86.6%-106.3%). Intra-and inter-day precision were less than8.9%and8.8%, respectively. The method was validated by applying it to the analysis of raw, flocculated, settled, and finished waters collected from a water treatment plant in China.Based on the EPA551.1, we establish a liquid-liquid extraction and gas chromatography with electron capture detector (LLE-GC-ECD) method for HANs, HKs and TCNM. The results of quality control shows that there’s no disturbance near the targets in blank control, the relative standard deviation (RSD) is between1.4%to2.7%, the recovery is the range of74.3%to101.8%, the detection limit of trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN),1,1-dichloropropane (1,1-DCP),1,1,1-trichloropropane (1,1,1-TCP) and TCNM is20,9.2,9.2,40,80,9.2,20and40ng/L, respectively. The results indicate the method is accurate and meet the need of determination.Part two The formation and variation of THM5, HAA10, N-DBPs and HKs in treatment processes of water plantsOur study choose two places, one is the water plants using Qingcaosha reservoir in Shanghai as the raw water, which has the better water quality, and another one is the water plant in Jiangsu province because of the serious pollution of its raw water. We investigate the impact of treatment processes on the DBPs formation. Besides, considering the fact that Qingcaosha reservoir is influenced by sea water intrusion every year, we compare the DBPs formation during different periods-seawater intrusion period and regular time-in two water plants from Shanghai.1. Investigation of DBPs formation and pollution status in different treatment processes and pipe water from a water plant in Jiangsu province.In order to investigate the DBPs formation and pollution status in different treatment processes and pipe water of a water plant in Jiangsu province.24water samples were collected from raw water, points for adding chlorine, finished water and pipe water in July,2011. THM4, HA A6, HANs, TCNM, HKs, IF and IAA were detected by GC-ECD after liquid-liquid extraction; Nitrosamines(NAms) were detected by gas chromatography with mass spectrometer(GC-MS) after solid-phase extraction. The results showed that most DBPs were founded in water treatment processes except for dibromochloromethane, chloroform and N-nitrosodimethylamine detected in raw water(0.61、1.64μg/L and3.06ng/L). Pre-chlorination could form HAA6,HKs, HANs and NAms(5.01、0.66.0.57μg/L and98.09ng/L). Chlorination and post-chlorination led to dramatically increase in the levels of THM4, HAA6(70.31and43.71μg/L) and other DBPs, but without increase in NAms. Finished water demonstrated that bormodichloromethane (34.12μg/L) and trichloroacetic acid (13.45μg/L) ranked first in concentration of THM4(70.31μg/L) and HAA5(43.71μg/L), respectively; Levels of HANs, HKs, CPs and two NAms were14.96、2.32、0.96μg/L and21.22、69.43ng/L; IAA, IF and other six NAms were not detected in all water samples. Proportion of bromide-containing DBPs ranges from ND to70.99%[49.91/70.31(μg/L)]. Bromide-containing DBPs were dominant in THM4class and ranged from27.11%[0.61/2.25(μg/L)] to70.99%[49.91/70.31(μg/L)]. NAms were formed after the first chlorination, few changes happened after then. This result suggested that pre-chorine was easily formed NAms. CPs were formed after the chlorination which indicated they required a longer time to finish reaction. Each substance of THM4and HAA6was in line with current national standard, but total THM4didn’t meet its standard. Levels of N-nitrosodimethylamine and N-nitrosodipropylamine were much higher than limit values of American and Canada area. The results indicated that levels of DBPs in this water plant are relative high, especially for bromide-containing DBPs and nitrogen-containing DBPs. Measures need to be taken for DBPs control.2. DBPs formation in different treatment processes from two water plants during seawater intrusion period and regular time in ShanghaiIn order to explore the DBPs variation in different treatment processes from two water plants during seawater intrusion period and regular time in Shanghai, the water samples were collected in raw water, water from treatment processes and finished water in two water plants, and detected by GC-ECD. The DBPs for detection included five THMs, ten HAAs, four HANs, two HKs and TCNM. The results showed that seawater intrusion period had the higher concentration of DBPs, excluding HKs and TCNM in A Water Treatment Plant (AWTP), compared to regular time. THMs and HAAs were also two dominate DBPs. HAAs ranked first in AWTP while THMs was first in BWTP. During seawater intrusion period, the percentage of THMs and HAAs in total DBPs detected in AWTP was40.9%and46.3%while47.6%and43.7%in BWTP. During regular time, the percentage of THMs and HAAs in total DBPs detected in AWTP was29.6%and46.7%while61.5%and21.1%in BWTP. Other DBPs had the low level and the concentration of TCNM and IAA was less than1.0μg/L. During seawater intrusion period, BCAN had the highest levels among HANs in two WTPs. In regular time, for HANs, DCAN and BCAN had higher concentration in AWTP while BCAN and DBAN levels were higher in BWTP. For HKs, AWTP had highest concentration of1,1,1-TCP while1,1-DCP and1,1,1-TCP in BWTP had the almost equal levels. IF was not detected in all water samples. Active charcoal and pre-ozonization could reduce the DBPs levels. DBPs levels could reduce12.0%-36.1%after pre-ozonization and the reduction percentage of THMs, HAAs and HANs was36.1%,26.0%and23.8%, respectively. Active charcoal could reduce HAAs, IAA, HANs, HKs and TCNM effectively. Pre-chlorination in AWTP could increase concentration of DBPs dramatically. The results suggested that seawater intrusion could affect the DBPs formation dramatically and could change the effect of treatment processes on the DBPs formation. Different pre-oxidation had the different effect on DBPs formation and pre-ozonization had the better effect. Traditional treatment processes, such as sedimentation and sand filtration, gave a bad effect on the decrease of DBPs while advanced processes gave the different effect on different DBPs.Part three Carcinogenic and non-carcinogenic risk assessment after exposing the DBPs in drinking water for Shanghai residents during seawater intrusion period and regular timeIn order to investigate the carcinogenic and non-carcinogenic risk after expose the DBPs in drinking water for Shanghai residents during seawater intrusion period and regular time, the risk of DBPs by oral, dermal and inhalation was assessed. The results indicated that carcinogenic and non-carcinogenic risk through oral, dermal and inhalation exposure pathway was affected by DBPs level in drinking water and seawater intrusion. Both two risk assessment showed female was greater than male, AWTP was greater than BWTP, seawater water period was greater than regular time. For exposure pathway, the risk through inhalation was highest and the second one was dermal pathway. BDCM and CDBM were two dominant DBPs and also had the highest carcinogenic risk. Low-dose and long-term exposure of DBPs had the carcinogenic risk and other adverse effect. In order to decrease the potential health hazard, some measure should be taken to control the DBPs formation, for example, promoting the treatment processes and decreasing the organic pollution.The main findings of these three parts are summarized as follows:(1) The methods optimized in this study have tow detection limit, high sentivity and short analysis time and achieve the synchronous detection of IF, THM4and IAA, HAA9;(2) A GC-ECD method for HANs, HKs and TCNM in drinking water is established, which achieves the rapid analysis of volatile and unregulated N-DBPs and HKs;(3) The THMs, HAAs, HANs, HKs, TCNM and NAms of raw water, different treatment process, finished water and distribution system from water plant in Jiangsu province were analyzed. The results shows the types and levels of DBPs in different treatment processes, and variation tendency of DBPs in distribution system;(4) The THMs, HAAs, HANs, HKs and TCNM of raw water, different treatment process and finished water from two water plants in Shanghai were continuous detected from December,2011to August,2012. The resuts give the change rules of DBPs during seawater intrusion period and regular time, and shows the effect of different treatment processes on DBPs formation;(5) Assess the carcinogenic and non-carcinogenic risk of Shanghai residents who exposed four THMs, DCAA and TCAA in drinking water through oral, dermal and inhalation pathways and the results suggest that risk of seawater water intrusion period is higher than regular time, females higher than males, and CDBM and DBCM have highest risk by oral pathway. Besides, the risks of three pathways rank as follows:inhalation> oral> dermal. |
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