RESUMO
It is difficult for waterworks that add chlorine into finished water once to maintain sufficient residual chlorine at unfavorable points of the pipe network that supply water for large areas of coverage. Therefore, booster chlorination was employed for a long-distance water distribution system. The study was performed in H City with a water supply system serving about 400 km2 of downtown and rural areas. The purpose of this work is to obtain the distribution characteristics of disinfection by-products (DBPs) in the booster chlorination disinfection pipe network through uniformly distributed sampling analysis. The results showed that detected DBPs include trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and tribromomethane (TBM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). The concentrations of the regulated DBPs were found to be lower than the standard limits specified in the Sanitary Standard for Drinking Water (GB5749-2006). Before booster chlorination, the average concentrations of the DBPs mentioned (expressed as mean±deviation) were (8.08±3.34), (9.77±2.91), (7.38±4.82), (2.65±2.02), (2.95±3.26), (6.02±6.06), (3.13±2.48), (1.61±2.05), and (0.15±0.10) µg·L-1, while afterwards, they were increased to (10.30±4.55), (11.73±3.60), (8.23±5.22), (2.95±2.45), (3.29±3.60), (8.15±7.58), (3.31±2.61), (1.33±2.04), and (0.12±0.06) µg·L-1, respectively. Trihalomethanes (THMs) and haloacetic acids (HAAs) increased by 6.32%-26.60% and 5.32%-42.71%, respectively, after booster chlorination. In addition, raw water quality and seasonal changes had a certain impact on the occurrence of DBPs. The levels of DBPs in summer were generally higher than those in spring or autumn. According to the analysis of DBP formation potential of source water, finished water, and tap water, it was found that the risk of DBPs exceeding the standard limit may exist in the water supply system of H City; therefore, further optimization of the treatment process should be considered to ensure water quality.
RESUMO
The occurrence of 18 types of disinfection by-products (DBPs) in two waterworks and the corresponding water supply networks of H City in Zhejiang Province was determined by gas chromatography coupled with electron capture detector (GC-ECD). The correlation between DBPs and organic precursors, and health risks caused by DBPs, were discussed. Results showed that the disinfection by-products detected in drinking water in H City mainly include trihalomethanes (THMs), haloacetic acid (HAAs), haloacetonitrile (HANs) and trichloronitromethane (HNMs), with highest concentrations of THMs followed by HAAs. In the finish water of CX Waterworks and tap water supplied by CX Water works, concentrations of THMs ranged from 7.70 to 32.73µg·L-1and 9.00 to 51.42µg·L-1, respectively, and those of HAAs 3.05 to 21.30µg·L-1 and 6.00 to 26.79µg·L-1, respectively. The THMs in finished water and tap water of TH Waterworks were in the range 8.65-38.76µg·L-1 and 12.09-42.04µg·L-1, respectively, and those of HAAs were 2.42-14.79µg·L-1 and 2.80-33.40µg·L-1, respectively. The DBPs in the finished and tap water of the two waterworks were at lower levels than the limitations regulated by the Sanitary Standard for Drinking Water (GB 5749-2006). The index of dissolved organic carbon (DOC) and UV254 were adopted to describe the organic compounds, and it was found that trichloromethane (TCM) was significantly negatively correlated with DOC and UV254in tap water. Based on the EPA recommended health risk assessment model, the carcinogenic and non-carcinogenic risks of chlorine disinfection by-products in the oral intake route were calculated. It was found that the carcinogenic risks caused by the disinfection by-products in the finished water and tap water of H City were 5.94×10-6-4.76×10-5 and 5.94×10-6-5.56×10-5, respectively, while the non-carcinogenic risks were 0.91×10-2-4.20×10-2 and 1.26×10-2-4.72×10-2, respectively. The carcinogenic risk is mainly from THMs:bromodichloromethane (BDCM) contributes the highest cancer risk, and the non-carcinogenic risk is mainly from TCM.
Assuntos
Desinfetantes , Água Potável , Poluentes Químicos da Água , Purificação da Água , Desinfecção , Trialometanos , Abastecimento de ÁguaRESUMO
OBJECTIVE: To study the clinical value of coronary artery calcification score with 64-slice MDCT in the diagnosis of coronary artery disease (CAD). METHODS: 96 subjects including 49 with confirmed CAD (CAD group) and 47 asymptomatic people as control group were recruited between May 2006 and December 2006 by the department of radiology in our hospital. The selective coronary angiography was also performed in 30 subjects including 25 with CAD and 5 asymptomatic people and subsequently divided into three groups (< 50%, 50%-75% and > 75% of maximum degree of vessel occlusion). We investigated the correlation of calcification score (CS) and the maximum degree of vessel occlusion measured by coronary angiography were investigated. RESULTS: The larger CS and more numbers of regions of interest of calcification in the right coronary artery and left anterior descending artery in 96 subjects were observed. The total mean CS of CAD (462 +/- 314) was higher than that of control group (83 +/- 52) (P < 0.001). There was a moderate correlation between degree of vessel stenosis and CS for individual vessels in patients with positive calcium scan(r = 0. 445, P < 0.01). CONCLUSION: Although CS measured by MDCT is not an accurate marker of the degree of vessel stenosis in CAD, it can be applied as a screening tool for high risk CAD patients and could greatly reduce the expense on coronary angiography.