Leung Chi-Man, Jiao Jiu Jimmy
Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
Water Res. 2006 Feb;40(4):753-67. doi: 10.1016/j.watres.2005.12.016. Epub 2006 Jan 31.
The lower slope of the Mid-Levels area, Hong Kong, is one the most heavily urbanized coastal areas in the world. A comprehensive groundwater heavy metal and trace element study was conducted in the Mid-Levels area aiming to investigate the impacts of urbanization on the aqueous distributions of these chemicals. Groundwater samples were collected in the upper natural slopes and the lower highly urbanized spaces in the area in different seasons, and analyzed for heavy metal and trace element contents. Compared to the results from natural slopes, groundwater samples in the developed spaces did not exhibit significant elevated levels in Zn, Cr, Cu, Cd, Pb and Fe, which are commonly found in stormwater. On the other hand, the samples were found to have elevated contents in Mn, V, Co and Mo, minor stormwater-related heavy metals, suggesting that stormwater drains may be leaking to some extent. However, the results suggested that the vadose zone could remove many of the heavy metals, protecting groundwater from being contaminated seriously. Statistical analysis suggested that a certain amount of Mn and Co was likely to be re-mobilized from natural soils due to the changes in local redox conditions, while Mn, V, Co and Mo may also be derived from steel corrosion as a result of prolonged submergence. Besides, the average B concentration in the developed spaces was about eight times higher than that in the natural slopes, indicating the presence of sewage. The mean Se concentration in the developed spaces was about 100 times higher than that in the natural slopes. About 40% of samples in the developed spaces contained Se level higher than the drinking water guideline value proposed by the World Health Organization. Se was found to be positively correlated with B and SO4(2-) (R = 0.534 and 0.631, respectively), suggesting that Se may also be related to leakage from sewage pipes. Part of the Sr may come from leakage of flushing water and/or sewage as Sr was strongly correlated with Cl- (R = 0.929). According to the measured results, deep groundwater samples collected from piezometers (> 10 m in depth) in the urbanized spaces appeared to be virtually free from any anthropogenic contaminations. This study may shed important light on the identification and evaluation of leakage from service pipes in a particular area based on aqueous distributions of heavy metals and trace elements. Moreover, the above findings may be instructional for other coastal cities with a similar level of urban development to understand the potential threats to their groundwater resources.
香港半山地区的较低斜坡是世界上城市化程度最高的沿海地区之一。在半山地区开展了一项全面的地下水重金属和微量元素研究，旨在调查城市化对这些化学物质在水体中分布的影响。在该地区不同季节的上部自然斜坡和下部高度城市化区域采集了地下水样本，并分析了重金属和微量元素含量。与自然斜坡的结果相比，城市化区域的地下水样本中锌、铬、铜、镉、铅和铁（这些常见于雨水中）的含量并未显著升高。另一方面，样本中锰、钒、钴和钼（与雨水相关的微量重金属）的含量有所升高，这表明雨水排水管道可能在一定程度上存在渗漏。然而，结果表明包气带可以去除许多重金属，保护地下水不被严重污染。统计分析表明，由于当地氧化还原条件的变化，一定量的锰和钴可能从天然土壤中重新活化，而锰、钒、钴和钼也可能是由于长期淹没导致钢铁腐蚀产生的。此外，城市化区域的平均硼浓度约为自然斜坡的八倍，表明存在污水。城市化区域的平均硒浓度约为自然斜坡的100倍。城市化区域约40%的样本中硒含量高于世界卫生组织提出的饮用水指导值。发现硒与硼和硫酸根离子呈正相关（相关系数分别为0.534和0.631），这表明硒可能也与污水管道渗漏有关。部分锶可能来自冲洗水和/或污水的渗漏，因为锶与氯离子强烈相关（相关系数为0.929）。根据测量结果，从城市化区域的测压管（深度大于10米）采集的深层地下水样本似乎几乎没有受到任何人为污染。这项研究可能为基于重金属和微量元素的水体分布来识别和评估特定区域服务管道的渗漏提供重要线索。此外，上述发现可能对其他具有类似城市发展水平的沿海城市了解其地下水资源面临的潜在威胁具有指导意义。
