A red water phenomenon occurred in several communities few days after the change of water source in Beijing, China in 2008. In this study, the origin of this problem, the mechanism of iron release and various control measures were investigated. The results indicated that a significant increase in sulphate concentration as a result of the new water source was the cause of the red water phenomenon. The mechanism of iron release was found that the high-concentration sulphate in the new water source disrupted the stable shell of scale on the inner pipe and led to the release of iron compounds. Experiments showed that the iron release rate in the new source water within pipe section was over 11-fold higher than that occurring within the local source water. The recovery of tap water quality lasted several months despite ameliora- tive measures being implemented, including adding phosphate, reducing the overall proportion of the new water source, elevating the pH and alkalinity, and utilizing free chlorine as a disinfectant instead of chloramine. Adding phosphate was more effective and more practical than the other measures. The iron release rate was decreased after the addition of 1.5 mg. L-1 orthophosphate- P, tripolyphosphate-P and hexametaphosphate-P by 68%, 83% and 87%, respectively. Elevating the pH and alkalinity also reduced the iron release rate by 50%. However, the iron release rate did not decreased after replacing chloramine by 0.5-0.8 mg. L-1 of free chlorine as disinfectant. 相似文献
This is the first study regarding the pharmacokinetics of [14C]-atrazine conducted with rhesus monkeys. The animals received one dose (0.25 mg) intravenously (IV) or three doses (1, 10, or 100 mg) orally. Plasma, urine, and feces were collected at defined times up to 7 days post-dosing. Sample radioactivity was measured to determine the mass equivalent. IV administered [14C]-atrazine disappeared rapidly from blood, with an elimination half-life of about 5.5 ± 1.1 h. The pharmacokinetic profiles of [14C]-atrazine following oral administration at the three dose levels show that kinetic parameters such as AUC and Cmax are linearly correlated with the dose. Seven days after dosing, urinary and fecal excretion of [14C]-atrazine reached 99% of total administered dose in the IV group and 91–95% in the three oral dose groups. In the IV-administered monkeys, approximately 85% of the dose was excreted in urine and 12% in feces. In three oral dose groups, urinary and fecal radioactivity recoveries approximated 57% and 21%, 58% and 25%, and 53% and 35%, respectively. More than 50% of the total urinary excreted radioactivity was found within the first 24 h after dosing. In conclusion, the principal elimination of [14C]-atrazine, IV and orally administered, is via urine. The oral bioavailability was 60% or higher. There was a significant linear correlation between administered oral dose and plasma concentration. Overall oral dose accountability ranged from 91% to 95%. Data generated may be useful in the risk assessment of human exposure to environmental atrazine contamination. 相似文献
To understand how extraction of different energy sources impacts water resources requires assessment of how water chemistry has changed in comparison with the background values of pristine streams. With such understanding, we can develop better water quality standards and ecological interpretations. However, determination of pristine background chemistry is difficult in areas with heavy human impact. To learn to do this, we compiled a master dataset of sulfate and barium concentrations ([SO4], [Ba]) in Pennsylvania (PA, USA) streams from publically available sources. These elements were chosen because they can represent contamination related to oil/gas and coal, respectively. We applied changepoint analysis (i.e., likelihood ratio test) to identify pristine streams, which we defined as streams with a low variability in concentrations as measured over years. From these pristine streams, we estimated the baseline concentrations for major bedrock types in PA. Overall, we found that 48,471 data values are available for [SO4] from 1904 to 2014 and 3243 data for [Ba] from 1963 to 2014. Statewide [SO4] baseline was estimated to be 15.8 ± 9.6 mg/L, but values range from 12.4 to 26.7 mg/L for different bedrock types. The statewide [Ba] baseline is 27.7 ± 10.6 µg/L and values range from 25.8 to 38.7 µg/L. Results show that most increases in [SO4] from the baseline occurred in areas with intensive coal mining activities, confirming previous studies. Sulfate inputs from acid rain were also documented. Slight increases in [Ba] since 2007 and higher [Ba] in areas with higher densities of gas wells when compared to other areas could document impacts from shale gas development, the prevalence of basin brines, or decreases in acid rain and its coupled effects on [Ba] related to barite solubility. The largest impacts on PA stream [Ba] and [SO4] are related to releases from coal mining or burning rather than oil and gas development.
