【期刊】干旱地区灌溉活动影响下地表水及地下水中全氟化合物的分布
图文摘要 | Graphical Abstract
导读 | Introduction
全氟化合物（PFASs）污染是当今环境面临的重要问题，尽管已采取一些管制措施限制PFASs的使用，但一些发展中国家仍然支持氟化学工业。由于其持久性，PFASs在环境中仍无处不在。干旱/半干旱地区由于高蒸发量和密集灌溉活动，地表水和地下水之间交换作用频繁，影响了PFASs的迁移和转化，威胁饮用水安全。本研究分析了从我国典型干旱区河套灌区采集的地表水、地下水、土壤及含水层固体样品中的传统PFASs及潜在前驱体，以探索PFASs在地表和地面之间的分布和转化规律，更好地了解干旱地区农业灌溉活动和湖泊入渗对地下水PFASs的影响，为饮用水水质监测和保护提供理论依据。
Per- and polyfluoroalkyl substances (PFASs) pollution is an environmental issue of great public concern, although some regulatory measures have been taken to limit the use of legacy PFASs, some developing countries still support the local fluorochemical industry. As a result, PFASs remain ubiquitous in the environment including groundwater. Frequent exchange of surface water and groundwater occurs in arid/semi-arid areas due to high evaporation and intensive irrigation activities, affecting the migration and transformation of per- and polyfluoroalkyl substances (PFASs) and threatening drinking water safety. This study analyzed legacy PFASs and potential precursors in surface water, groundwater, soil, and aquifer solid samples collected from a typical arid area, the Hetao Irrigation District of Northern China, to explore PFASs distribution and transformation between surface and ground. This study is intended to better understand the influence of agricultural irrigation activities and lake infiltration on groundwater PFASs in arid regions, which can be used to inform drinking water quality monitoring and protection.
一、PFAS多介质赋存特征
PFASs in surface water, groundwater, and soil
20种PFAS分析结果显示（图1）：地表水PFASs总浓度范围为29 ~ 232 ng/L，其中PFBA的贡献率最高，达到39 %。ΣPFASs浓度随季节变化而变化，枯水期地表水样品的浓度更高，但组成基本相同。与其他研究相比，乌梁素海下游排水系统和湖区内PFOA浓度相对较高，而 PFOS浓度处于较低水平。地下水样品中PFASs总浓度为2 ~ 77 ng/L，与地表水相似，PFBA在地下水中的贡献最高。乌梁素海西侧地下水中PFASs含量显著高于上游地下水，这与地表水中PFASs的空间分布一致。PFASs在土柱样品中的总浓度范围为0.09 ~ 0.58 ng/g，含水层砂样PFASs含量低于含粘土。
Total concentration of PFASs in surface water samples ranged from 29-232 ng/L, among which the highest contribution of 39 % for PFBA (Fig.1). ΣPFASs concentrations varied in different seasons, with higher concentrations in surface water sampled in April. Nevertheless, the compositions of PFASs were similar. The PFOA concentration in downstream of the drainage system and the Ulansuhai Lake were relatively higher compared to other studies. In contrast, the PFOS concentration in water samples was at a low level. Total concentration of PFASs in groundwater samples ranged from 2-77 ng/L. Similar to surface water, the contribution of PFBA in groundwater was the highest. The PFASs contents in groundwater from the west side of the Ulansuhai Lake was significantly higher than that in upstream groundwater, which was consistent with the spatial distribution of PFASs in surface water. Total concentrations of PFASs in the soil column samples ranged from 0.09 to 0.58 ng/g. The sandy samples in the aquifer had lower PFASs content compared with clay samples.
图1 地下水、地表水和土壤样品中的PFASs组成
Fig. 1 The average concentration fraction of different classes of PFASs in groundwater (n = 43), surface water (n = 43), and soil samples (n = 12)
二、PFASs空间分布
Spatial and vertical distribution of PFASs
在灌溉系统的影响下，河套灌区地表水PFASs的含量和组成表现出显著的空间变异性（图2）。地表水中PFASs含量呈现由引水到排水、最终到湖泊水体增加的趋势。地下水中PFASs含量受地表水补给影响较大，在水平空间分布上，PFASs浓度呈现出湖水补给区>灌溉水补给区>无补给区域的特征。垂直分布上，地下水样品中PFASs随井深增加显著降低。土壤样品中长链PFASs的相对比例显著高于地下水样品，地表水和土壤样品中PFOA和PFHpA的相对比例也高于地下水样品。这些结果表明，深部含水层地下水受地表的影响较小，使用深层水是保证饮用水安全的首选方案。
The PFASs levels in surface water samples showed an increasing trend from diversion water to drainage water and eventually to the lake water (Fig.2). The PFASs levels in groundwater were strongly influenced by surface water. In terms of horizontal spatial distribution, the concentration of PFASs showed the characteristics of lake water recharge area > irrigation water recharge area > non-recharge area. In terms of horizontal spatial distribution, PFASs in groundwater samples decreased significantly as the depth increased from 5 m to > 90 m. The relative proportion of long-chain PFASs (Perfluorocarbon chain length > 8) in soil samples were significantly higher than in groundwater samples, and the relative proportion of PFOA and PFHpA in surface water and soil samples were also higher than in groundwater samples. These results suggest that groundwater in deep aquifers is less influenced by surface water, and the use of deep water is a preferred option to ensure drinking water safety.
图2 不同地区地表水(b)和地下水(c)中PFASs的浓度和组成
Fig. 2 Concentration and composition of PFASs in surface water (b) and groundwater samples (c) collected from different areas (a)
三、氧化法估算PFCA前驱体
Estimation of PFCA-precursors concentrations by TOP assay
氧化处理后地表水、地下水和土壤样品中PFCAs浓度增加分别为2-18 ng/L、1-15 ng/L和0.01-0.13 ng/g（图3）。对比地表水和地下水样，氧化后地下水以PFBA增加为主，而地表水中PFOA的增加相对较高。通过贝叶斯推断结果显示来自FT和ECF制造源的前驱体在地表水样品中的比例与地下水相似（图4），但地表水样品中以长链前驱体为主。与传统PFAS的分布特征不同，PFCA前驱体在地表及地下水中的空间分布格局较为均匀，说明研究区水体PFCA前驱体的来源相似，大气沉降可能是主要来源。
The increased concentrations of PFCAs after TOP treatment (ΔPFCAs) in surface water, groundwater and soil samples were 2-18 ng/L, 1-15 ng/L and 0.01-0.13 ng/g. Comparing the ΔPFCAs in surface water and groundwater samples. The TOP results showed that ΔPFCAs in groundwater samples were mainly dominated by PFBA, but the increase in PFOA was relatively higher in surface water. The PFCA-precursors with different chain length from two manufacturing sources were identified by Bayesian inference, results show that the spatial distribution pattern of PFCA-precursors in water is homogeneous, which is different from the multi-media distribution characteristics of the target PFASs discussed above，indicating that the sources of the PFCA-precursors in surface water and groundwater in the study area were similar. Atmospheric deposition may be the primary source.
图3 地表水(A)，地下水(B)和土壤(C)样品中氧化产生的PFCAs
Fig. 3 Range of concentrations of PFCAs generated upon oxidation (ΔPFCAs) in (A) surface water, (B) groundwater and (C) soil samples
图4 基于TOP测定结果，使用贝叶斯推断估算可氧化PFAS前驱体的浓度
Fig. 4 Inferred concentrations of oxidizable precursors using Bayesian inference based on the results of TOP assay
四、灌溉和湖泊排泄对地下水PFASs的影响及健康风险评估
Effects of irrigation and lake recharge on groundwater PFAS and health risk assessment
河套灌区作为中国三大灌区之一，需要通过灌溉系统引水大量满足农业用水需求。然而，在当地灌溉渠中检测到包括PFASs在内的各种污染物，导致农业灌溉活动成为向地下环境输送污染物的重要来源。根据灌渠中测量到的PFASs平均浓度和每年的农业灌溉用水量，我们估计PFASs通过灌溉从地表水渗入地下水的通量高达52 kg/y。此外，根据水平衡方程可估算出PFASs从湖水向地下水的排放量达9.39±0.66 kg/y。尽管人类通过饮用地下水暴露于PFASs的风险仍较低，但研究区地下水排放主要以蒸发为主，且PFASs将会在地下环境中积累，长期风险仍不容忽视。
As one of the top three largest irrigation areas in China, a large amount of water needs to be diverted through the irrigation system to meet the agricultural demand of the Hetao Irrigation District, with an average annual agricultural irrigation water consumption of 4.5 billion. However, various contaminants including PFASs have been detected in local irrigation canals, leading to agricultural irrigation activities becoming a significant source of contaminant transport to the subsurface environment. Based on the average PFASs concentration measured in irrigation canals and the annual agricultural irrigation water consumption, we estimated the flux of PFASs infiltrated from surface water to groundwater through irrigation up to 52 kg/y. Furthermore, the discharge of PFASs from lake water to groundwater up to 9.39±0.66 kg/y.
总结 | Conclusions
乌梁素海通过多级灌溉系统富集了河套灌区地表水中的PFASs，高PFASs含量的湖水渗漏对周围地下水产生了影响，灌溉活动向地下环境排放PFASs年通量高达52 kg。当地表水携带PFASs通过沉积物和含水层渗透时，长链PFASs倾向于在固相颗粒中富集，而短链PFASs倾向于在地下水中富集。在PFCA前驱体样品中也观察到类似的分布模式，表明长链前驱体在通过包气带时也更容易被吸附。
PFASs in surface water of the Hetao Irrigation District were enriched in Ulansuhai Lake through a multilevel irrigation system, and the higher PFASs content lake water affected the surrounding groundwater through seepage, PFASs infiltrated from surface water to groundwater through irrigation up to 52 kg/y. When surface water carries PFASs permeating through sediments and aquifers, whereas short-chain PFASs tend to enriched in groundwater. A similar pattern was observed for the PFCA-precursors, suggesting that long-chain precursors are more likely to be adsorbed as they pass through the vadose zone.
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https://www.sciencedirect.com/science/article/pii/S0048969722067936?via%3Dihub
本文内容来自ELSEVIER旗舰期刊Sci Total Environ第858卷发表的论文：
Mao R.Y., Lu Y.L., Zhang M., Wang C., Sun B., Shi Y.J., Song S., Wang P., Yuan J.J., Zhao J.X., 2023. Distribution of legacy and novel per- and polyfluoroalkyl substances in surface and groundwater affected by irrigation in an arid region. Sci Total Environ 858, 159693.
DOI: http://dx.doi.org/10.1016/j.scitotenv.2022.159693
第一作者：毛若愚 博士
中国科学院生态环境研究中心
中国科学院生态环境研究中心博士生在读，主要研究方向为持有性有机污染物环境行为、地下水环境中全氟化合物迁移特征与风险分析。以第一作者或共同作者在Science of the Total Environment、Environmental Pollution等国际期刊发表论文2篇。
通讯作者：吕永龙 教授
厦门大学环境与生态学院
中国科学院生态环境研究中心
厦门大学环境与生态学院讲席教授，中国科学院特聘研究员，博士生导师。发展中国家科学院(TWAS)院士，欧洲科学院(Academia Europaea)院士，俄罗斯科学院(RAS)外籍院士。现任联合国秘书长任命的“联合国可持续发展技术促进机制(TFM)10人组”成员，太平洋科学协会(PSA)主席，国际环境问题科学委员会(SCOPE)前主席、联合国环境规划署(UNEP)国际专家组成员等。Science Advances副主编，Ecosystem Health and Sustainability创刊主编。主要从事环境地理学、可持续生态学、环境生态学研究。在国内外核心刊物上发表论文360多篇，其中Science、Nature、Science Advances、PNAS、Nature Communications等国际高水平学术期刊收录250多篇，出版中英文专著17部。生态学领域高被引科学家。
近2年发表在Sci Total Environ上的论文：
1.Wang et al., 2022. Contamination, transport, and ecological risks of pharmaceuticals and personal care products in a large irrigation region. Sci Total Environ 851, 158179.
2.Khan et al., 2022. Heavy metals contamination, potential pathways and risks along the Indus Drainage System of Pakistan. Sci Total Environ 809, 151994.
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