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颗粒物是环境污染与控制相关研究的重要对象[1]。尽管给水处理工艺通常能够保证出厂水的水质达标,但出厂水经过管网到达用户端的输配过程中难以避免发生水质变化[2]。其中,管网疏松沉积物再悬浮引发自来水变色(如“黄水”)是全世界自来水投诉中最常见的问题[3]。然而,管网疏松沉积物的结构特征及其潜在健康危害目前尚不明确。
管网疏松沉积物来源复杂,包括出厂水中的残余物质和管道的腐蚀产物等。由于给水管网中广泛使用铁质管材和管件,管网铁腐蚀产物释放是导致用户龙头“黄水”的主要原因[4-7]。ZHUANG等[8]利用合成的铁颗粒物实验首次提出,铁颗粒物导致的“黄水”不仅是感官性状问题,且铁颗粒物可通过2种机制产生潜在毒性:1)铁颗粒物(主要是针铁矿)与微量有机污染物通过特定的共价键结合方式强化电子转移,产生活性氧物种(reactive oxygen species,ROS)而增强细胞损伤[8-9];2)微量有机污染物能够显著提升铁颗粒物的比表面积,从而增强其对水中污染物的富集能力[10]。实际管网条件下生成的疏松沉积物组成往往非常复杂,以往对于“黄水”带来的风险都是基于管网的水质和水力条件进行评价和预测[11],然而“黄水”可能引发的毒性风险至今尚无评价标准[12-13]。水质的评价不能仅以饮用水标准限值为判据, 更为重要的是以水质安全风险的综合控制为依据[14]。因此,“黄水”中沉积物颗粒的风险亟需受到重视。
本研究在北方某城市频繁发生“黄水”的区域采集了管网疏松沉积物,对样品的表面形貌、元素组成、表面电位和粒径等结构特征进行了表征,利用人体健康肝脏细胞对样品的细胞毒性进行了测试,并开展了疏松沉积物的细胞毒性与其结构特征之间的相关性分析,初步明确了给水管网疏松沉积物的风险因素。
给水管网疏松沉积物的结构特征及其风险识别
Structure characteristics and health risk of loose deposits in drinking water distribution system
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摘要: 自来水变色问题通常被视为感官问题,而导致自来水变色的管网疏松沉积物的结构特征及其潜在危害尚不明确。采集了我国北方某城市频繁发生自来水“黄水”的7个小区管网中的疏松沉积物,并进行了分析。结果表明:所有疏松沉积物样品中含量最高的金属元素都是铁元素、主要晶体成分是铁氧化物,样品颗粒微观形貌大多具有锋利的针刺状结构;样品zeta电位范围为−15~20 mV、平均粒径范围为500~4 000 nm、粗糙度范围为0.25~7.81 nm。体外细胞毒性实验结果显示,沉积物可产生一定的细胞毒性(样品浓度100 mg·L−1时人体健康肝脏细胞存活率为86.61%~99.71%)。通过主成分分析发现,疏松沉积物毒性与粗糙度的相关性比与粒度的高,表明形貌对样品毒性的影响比粒径更大;γ-FeOOH是与疏松沉积物毒性相关性最显著的晶体组分,其对毒性的贡献可能是通过增加颗粒表面锋利程度造成的,余氯不足时可能会因铁释放加剧和γ-FeOOH含量增大造成更高的毒性风险。本研究结果可为全面认识给水管网疏松沉积物的风险提供参考。Abstract: Discoloration of tap water caused by loose deposits is usually regarded as a sensory problem, but structural characteristics and health risk of the loose deposits are not clear. In this study, we collected loose deposits from the residential areas from the section where frequently occurs “yellow water” in a northern city in China. Characterization results showed that in loose deposit samples, the highest metal element was iron and the main crystal component was iron oxide. The morphology of the samples contained sharp fiber-like structures. The zeta potentials of the samples were −15~20 mV, the average sizes were 500~4 000 nm, and the roughness values were 0.25~7.81 nm. The samples had certain toxicity to health human liver cells (the cell viability was 86.61%~99.71% under loose deposits 100 mg·L−1). Principal component analysis showed that roughness had the highest correlation with toxicity, which indicated that morphology had greater influence on sample toxicity than size. Among crystal components, γ-FeOOH had the highest correlation with toxicity, and its contribution to toxicity may due to sharpness increase. When the residual chlorine is insufficient, it will lead to higher toxicity risk due to the increase of iron release and γ-FeOOH content. Therefore, iron particles have great effects on the toxicity of loose deposits. This study provides an important basis for the comprehensive understanding on the risk of loose deposits in drinking water distribution system.
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Key words:
- drinking water distribution system /
- loose deposits /
- yellow water /
- toxicity
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表 1 管网疏松沉积物样品的元素组成
Table 1. Elemental compositionof the loose deposits in pipe network
% 序号 C N O As Al Si S Pb Mn Fe Cu 1# 2.40 0.29 30.90 0.46 0.55 0.55 0.55 0.33 1.66 61.65 0.32 2# 4.47 0.36 31.96 0.10 1.20 1.71 0.13 0.54 0.59 57.99 0.95 3# 2.59 0.23 18.37 0.33 1.12 1.23 0.13 0.70 0.99 73.23 1.08 4# 15.17 0.30 2.50 0.03 0.28 0.10 0.00 0.21 0.66 78.82 1.94 5# 8.53 0.38 30.70 0.27 0.41 0.60 0.32 1.02 0.43 56.20 1.14 6# 5.54 0.32 33.62 0.37 0.57 0.87 0.22 0.74 0.32 56.39 1.02 7# 3.30 0.34 32.53 0.61 1.04 1.02 0.12 0.58 0.31 59.21 0.93 表 2 管网疏松沉积物样品的晶体组成
Table 2. Crystal composition of the loose deposits in pipe network
% 样品
编号Fe3O4 CaCO3 α-Fe2O3 γ-Fe2O3 δ-FeOOH α-FeOOH Fe γ-FeOOH β-FeOOH FeCO3 SiO2 1# 15 0 37 28 0 13 0 0 7 0 0 2# 3 14 3 57 0 2 1 9 3 4 3 3# 0 5 7 19 17 16 1 4 5 4 25 4# 6 34 11 13 4 5 0 11 1 1 14 5# 13 0 5 0 0 8 0 14 35 0 26 6# 9 0 9 11 0 14 0 27 8 0 21 7# 8 5 6 7 0 7 0 10 9 0 48 表 3 管网疏松沉积物性质与细胞存活率的Pearson相关系数
Table 3. Pearson correlation coefficient of structure property and cell viability
zeta电位 粗糙度 平均粒径 PV zeta电位 1 0.225 −0.851* 0.203 粗糙度 1 0.032 −0.507 平均粒径 1 −0.191 PV 1 注:*代表显著性水平为0.05。 表 4 管网疏松沉积物晶体组成与细胞存活率相关系数
Table 4. Correlation coefficient of crystal composition and cell viability
Fe3O4 CaCO3 α-Fe2O3 γ-Fe2O3 δ-FeOOH α-FeOOH Fe γ-FeOOH β-FeOOH FeCO3 SiO2 PV Fe3O4 1 −0.411 0.600 −0.364 −0.686 0.095 −0.804* 0.072 0.533 −0.859* −0.103 −0.335 CaCO3 1 −0.190 0.179 0.100 −0.589 0.067 −0.081 −0.488 0.252 −0.210 −0.097 α-Fe2O3 1 0.091 −0.159 0.381 −0.359 −0.477 −0.177 −0.372 −0.512 0.197 γ-Fe2O3 1 −0.042 −0.349 0.679 −0.359 −0.527 0.671 −0.682 0.519 δ-FeOOH 1 0.494 0.592 −0.347 −0.262 0.625 0.114 0.588 α-FeOOH 1 −0.038 0.002 0.016 −0.112 0.084 0.184 Fe 1 −0.336 −0.339 0.981** −0.235 0.738 γ-FeOOH 1 0.212 −0.344 0.270 −0.762* β-FeOOH 1 −0.417 0.293 −0.089 FeCO3 1 −0.273 0.711 SiO2 1 −0.441 RV 1 注:*代表显著性水平为0.05。 -
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