Risk Assessment Of Disinfection By-products In The Beijiang River And The Pearl River, Guangzhou

In order to identify the disinfection byproducts(DBPs) precursor and to investigate the risk of trihalomethane formation potential(THMFP) in finished waters, thus, 70 surface water samples collected in November 2013 and 114 samples collected in April and 70 samples in July 2014 from different locations in the Beijiang River and the Pearl River was chlorinated using Uniform Formation Condition(UFC) method for determining their THM Formation Potential(THMFP). Twelve kinds of DBPs, including chloroform(CF), bromodichloromethane(BDCM), dibromochloromethane(DBCM), bromoform(BF), trichloroacetonitrile(TCAN), dichloroacetonitrile(DCAN), bromochloroacetonitrile(BCAN), dibromoacetonitrile(DBAN), 1,1-dichloropropanon(1,1-DCP), 1,1,1-trichloropropanon(1,1,1-TCP), trichloronitromethane(TCNM) and chloral hydrate(CH)were quantified using gas chromatography with an electon capture detector(GC-ECD). Fluorescence intensity of five dissolved organic matter(DOM) was calculated using fluorescent regional integration(FRI) method. Linear correlation between twelve kinds of DBPs, DOC, UV254(absorbance at 254 nm wavelength), and fluorescence intensity was carried out using SPSS(version 19.0) and Origin(version 8.0) data analysis software to indentify the souce of DBPs. Finally, based on the tested THMFP, the cancer risk and non-cancer risk assessment of THMs were estimated using USEPA risk assessment model while dominant factors responding for total risk potential are estimated using sensitivity analysis. The conclusions were shown as followed:(1) No better direct linear correlation between DOC, UV254 and twelf kinds of DBPs was found, but the equation between DOC, UV254 and DBPs was carried out as DOC=22.31×THMs+2.90×TCP+0.538×DCAN+0.12×CH+21.45(R2=0.685); UV254=4.76×THMs+2.40×HANs +0.20×TCP +0.01×CH+0.028(R2=0.593) when using multiple linear relationship analysis method. DOC and UV254 were suitable for the surrogate for identifying risk of DBPs(2) Fluorescence intensity of each sorts of DOM fluorescence regions showed corresponding linear correlation with different DBPFP during risk identification. tyrosine-like matter was source of TCNM(P < 0.01), Aromaticity-like protein and fulvic acid-like matter were source of HANs(P < 0.01), fulvic acid-like matter was source of HKs(p < 0.05) while tryptophan-like mater, protein-like matter and fulvic acid-like matter were source of CH(p < 0.05).(3)Among four THM species, chloroform(CF) formation potential was the highest(accounts for 96.17% of total THMs) ranging from 101.92 ~ 2590.85 μg?L-1, followed by bromodichloromethane(BDCM), dibromochloromethane(DBCM) and bromoform(BF). Cancer and non-cancer risk from ingesting THMs was estimated. The result indicates that the average cancer risk of THMs is 2.91×10-4 for male and 3.30×10-4 for female in the two rivers, respectively, exceeding the minimum or negligible risk level defined by the USEPA(1.0×10-6). Cancer risk of BDCM ranging from 2.50×10-5 to 6.37×10-4 was approximately twice as that of CF in Beijing River. BDCM plays an important role of total risk in the Beijiang River while CF plays an important role of total risk in the Pearl River, Guangzhou. Sensitivity analysis shows that CF plays an important role for estimation of total risk potential. The non-cancer risk of THMs level ranging from 2.03×10-5 to 1.00×10-5 is not more than 1.0×10-5, the minimum or negligible non-cancer risk level defined by the USEPA.