A regional-scale assessment of micro-organic contaminants in shallow groundwater in the Pearl River Delta, China

Industrialization and urban expansion can result in the contamination of shallow groundwater by micro-organics (MO) in the Pearl River Delta (PRD), China. This study provides a regional scale assessment of MO contaminants in shallow groundwater in the PRD, investigating the occurrence and distribution of different compound groups, highlighting the relationship between MOs and aquifers, and between MOs and land-use. The main influence of the vadose zone and regional socioeconomic development on each relationship is also analyzed. Twenty-one compounds were detected, with naphthalene, acetophenone, 2-methylnaphthalene and chloroform recording the highest frequencies (1.4–3.1%), 2-methylphenol (328 μg/L), 1,3,5-trimethylbenzene (59 μg/L) and 2,4-dimethylphenol (53.4 μg/L) recorded the highest concentrations. Due to differences in lithology and thickness of the vadose zone over different aquifer groups, notable differences in MOs were recorded between aquifer groups. Twenty-one compounds were also detected with the highest concentrations in Granular aquifers; Karst aquifers recorded the lowest concentration and fewest number of compounds. Different land-use types have also resulted in notable differences in MO contamination, particularly for natural land-use types and urban-industrial types. Natural land recorded both the smallest number of compounds and the lowest concentrations; urban and industrial land-use type had 14 compounds not recorded in other land-use types. Principal component analysis results indicated that urbanization and industrialization in the PRD region were the main driving mechanisms of groundwater MO contamination (via discharges of untreated wastewater). This finding was also verified by the strong positive relationships between waste water levels, discharge volume and, chloride concentrations and MO of the shallow groundwater in the PRD.工业化与城市扩张可导致中国珠江三角洲（Pearl River Delta, PRD）地区浅层地下水受到有机微污染物（micro-organics, MO）的污染。本研究针对该区域浅层地下水中的有机微污染物开展区域尺度评估，对各类化合物组的赋存状态与分布特征进行调查，重点阐明有机微污染物与含水层、以及有机微污染物与土地利用类型之间的关联，同时分析了包气带与区域社会经济发展对上述关联的主要影响。本次检测共检出21种化合物，其中萘、苯乙酮、2-甲基萘与三氯甲烷的检出频率最高，介于1.4%~3.1%之间；2-甲基苯酚（328 μg/L）、1,3,5-三甲基苯（59 μg/L）以及2,4-二甲基苯酚（53.4 μg/L）的浓度峰值最高。由于不同含水层组的包气带岩性与厚度存在差异，各含水层组间的有机微污染物含量呈现显著差异。颗粒含水层中检出的该21种化合物浓度最高，而岩溶含水层的污染物浓度最低、检出化合物数量最少。不同土地利用类型同样会导致有机微污染物污染程度出现显著差异，其中以自然用地与城市-工业用地的差异最为突出。自然用地的检出化合物数量与污染物浓度均为最低；城市与工业用地中则存在14种其他土地利用类型未检出的化合物。主成分分析结果显示，珠江三角洲地区的城市化与工业化是浅层地下水中有机微污染物污染的主要驱动因素，其污染途径为未经处理的废水排放。该结论也得到了验证——珠江三角洲地区废水水位、排放量与氯化物浓度和浅层地下水中有机微污染物含量之间存在显著正相关关系。