Tam Y S, Elefsiniotis P
Watercare Services Ltd., Auckland, New Zealand.
J Environ Sci Health A Tox Hazard Subst Environ Eng. 2009 Oct;44(12):1251-60. doi: 10.1080/10934520903140009.
This study explored the potential of lead and copper leaching from brass plumbing in the Auckland region of New Zealand. A five-month field investigation, at six representative locations, indicated that Auckland's water can be characterized as soft and potentially corrosive, having low alkalinity and hardness levels and a moderately alkaline pH. More than 90% of the unflushed samples contained lead above the maximum acceptable value (MAV) of 10 microg/L (New Zealand Standards). In contrast, the copper level of unflushed samples remained consistently below the corresponding MAV of 2 mg/L. Flushing however reduced sharply metal concentrations, with lead values well below the MAV limit. Generally, metal leaching patterns showed a limited degree of correlation with the variations in temperature, dissolved oxygen and free chlorine residual at all sampling locations. Furthermore, a series of bench-scale experiments was conducted to evaluate the effectiveness of pH and alkalinity adjustment, as well as orthophosphate addition as corrosion control tools regarding lead and copper dissolution. Results demonstrated that lead and copper leaching was predominant during the first 24 hr of stagnation, but reached an equilibrium state afterwards. Since the soluble fraction of both metals was small (12% for lead, 29% for copper), it is apparent that the non-soluble compounds play a predominant role in the dissolution process. The degree of leaching however was largely affected by the variations in pH and alkalinity. At pH around neutrality, an increase in alkalinity promoted metal dissolution, while at pH 9.0 the effect of alkalinity on leaching was marginal. Lastly, addition of orthophosphate as a corrosion inhibitor was more effective at pH 7.5 or higher, resulting in approximately 70% reduction in both lead and copper concentrations.
本研究探讨了新西兰奥克兰地区黄铜管道中铅和铜的浸出潜力。在六个具有代表性的地点进行了为期五个月的现场调查，结果表明，奥克兰的水具有水质软且有潜在腐蚀性的特点，碱度和硬度较低，pH值呈中等碱性。超过90%的未冲洗样本中铅含量高于10微克/升的最大可接受值（MAV，新西兰标准）。相比之下，未冲洗样本中的铜含量一直低于相应的2毫克/升的MAV。然而，冲洗后金属浓度急剧下降，铅含量远低于MAV限值。一般来说，所有采样地点的金属浸出模式与温度、溶解氧和游离氯残留量的变化之间的相关性有限。此外，还进行了一系列实验室规模的实验，以评估调节pH值和碱度以及添加正磷酸盐作为控制铅和铜溶解的腐蚀控制工具的有效性。结果表明，铅和铜的浸出在停滞的最初24小时内占主导地位，但之后达到平衡状态。由于两种金属的可溶部分都很小（铅为12%，铜为29%），显然不溶性化合物在溶解过程中起主要作用。然而，浸出程度在很大程度上受pH值和碱度变化的影响。在pH值接近中性时，碱度的增加会促进金属溶解，而在pH值为9.0时，碱度对浸出的影响很小。最后，添加正磷酸盐作为缓蚀剂在pH值为7.5或更高时更有效，可使铅和铜的浓度降低约70%。
