【作者】 赵丽霞；

【导师】 祝凌燕；

【作者基本信息】 南开大学 ， 环境科学， 2013， 博士

【摘要】 全氟化合物(Perfluoroalkyl Substances,PFASs)以其优良的热稳定性、化学稳定性、高表面活性及疏水疏油性能,被广泛应用于工业生产和生活消费领域。由于大规模的使用,目前PFASs已经成为全球性的环境污染物,在不同的环境介质、野生动物及人体内均检测到不同浓度的PFASs。2009年5月斯德哥尔摩公约(POPs公约)第四次缔约方大会将全氟辛烷磺酸(Perfluorooctane sulfonate,PFOS)及其盐类(PFOSA)和全氟辛基磺酰氟(PFOSF)列入新增POPs名单中。由于全氟化合物的低挥发性和高水溶性,水环境是全氟化合物存在的一个重要场所。一些研究表明,沉积物和深海是PFASs在环境中两个主要的汇。目前,尽管有关水体中PFASs的报道较多,但绝大多数是关于水、沉积物或水生生物的监测数据,少数关于PFASs在沉积物上吸附的研究也仅限于PFOS等几种PFAS。而关于PFASs在沉积物上吸附解吸的系统研究明显不足,对于PFASs在沉积物上的分配行为和微观机制尚不清楚。针对目前的研究现状,研究了一系列PFASs在不同粒径沉积物上的分配、不同种类的腐殖质上的吸附和解吸行为,以及在不同土壤样品中的锁定行为和生物有效性,揭示PFASs在沉积物/土壤中分配和锁定的内在机制,为PFASs的生态风险评价、污染控制和制定环境质量标准等提供科学依据。本论文的主要研究内容和结论如下：1.选取组成和性质不同的两种沉积物,以3种全氟烷基磺酸(PFSAs)和6种全氟烷基羧酸(PFCAs)为目标污染物,根据沉积物的粒径和密度不同采用湿筛分法将每种沉积物分为8个组分,通过比较这一系列PFASs在这些组分上的分配和解吸情况,考察PFASs的性质、沉积物的组成和结构对PFASs在沉积物上分配的影响。结果表明,尽管两种沉积物(S1和S2)中轻组分的质量仅占全部沉积物质量的17.8和22.3%,但其较高的有机质含量使得其中PFAS的含量远高于重组分。说明疏水作用是控制PFASs在沉积物中分配的主要作用,其他作用(如静电作用、氢键)对短链PFASs在沉积物上的分配有较大影响。碳链长度和官能团都会影响PFASs在沉积物各粒径中的分配和解吸。随着碳链长度的增加,PFAS在沉积物各粒径中的浓度逐渐增加,解吸能力逐渐降低；相同碳链长度的PFSA比PFCA更容易吸附在沉积物上,同时更不容易从沉积物上解吸下来。C5-C12PFCAs的LogKo。值为1.70-3.80,C4-C8PFSAs为1.75-2.97。短碳链PFASs容易在水体中发生长距离迁移,而长碳链PFASs容易吸附到沉积物上,也就是说沉积物是长碳链PFASs在环境中一个重要的汇。因此PFASs在沉积物中的生物可利用性也随着碳链长度的增加而降低。2.利用化学方法从一种泥炭土中顺序提取三种不同腐殖质(腐殖酸HAl、HA2和胡敏素HM),研究比较PFHxS和PFOS在这三种腐殖质上的吸附解吸行为和溶液pH值对吸附的影响,考察有机质的异质性及其性质对全氟化合物吸附的影响,探讨腐殖质对全氟化合物吸附行为的内在机制。吸附动力学和热力学实验表明,PFHxS和PFOS在三种吸附剂上的吸附量均符合以下顺序：HA1<HA2<HM,这和三种吸附剂的疏水性一致。在同一种吸附剂上,PFOS的吸附量明显高于PFHxS,说明吸附主要是通过腐殖质和PFSAs碳链之间的疏水作用完成。由于PFHxS和PFOS具有较高的水溶性,腐殖质对两者的吸附能力远低于一般的疏水性有机污染物,比如苯并[a]芘、菲和林丹。PFHxS和PFOS的logKoc值随着腐殖质中脂肪碳含量的升高而增大,而随着芳香碳含量的升高而减小,说明腐殖质中脂肪族成分对PFSAs的吸附起着重要作用。解吸实验表明,PFHxS在腐殖质上具有明显的解吸滞后现象,而PFOS的解吸滞后现象却不明显。这可能是因为PFHxS的分子尺寸小于PFOS,因此PFHxS更容易进入到腐殖质内部的微孔中,而PFHxS分子一旦进入微孔,它便和腐殖质内部的特殊点位结合导致腐殖质结构发生变化,从而引起吸附的不可逆性。pH值对PFHxS和PFOS在HSs上的吸附有重要影响,随着溶液pH值的升高,PFHxS和PFOS在腐殖质上的吸附量逐渐减少。在一般的环境条件(pH5-8)下,疏水作用在吸附中起主要作用,而在较低pH值下静电作用和氢键作用对吸附有较大影响。3.选取环境中常见的8种PFCAs和3种PFSAs同系物为研究对象,研究其在3种泥炭土和一种普通农田土壤中自由态和结合态(富里酸、胡敏酸和胡敏素上)的分配和老化行为,同时使用NaN3作为抑菌剂设立添加抑菌剂的微生物抑制对照组,考察土壤中微生物对PFASs的生物降解情况;并以赤子爱胜蚓为受试生物,进行生物富集实验,考查老化过程对土壤中PFASs自由态和结合态的分布和生物可利用性的影响。结果表明：PFASs在普通农田土壤中主要以自由态存在,而在泥炭土中主要以结合态存在,说明PFASs在土壤中的锁定主要是由土壤有机质引起的。蚯蚓对土壤中长碳链的PFCAs和PFSAs有明显的富集效应,相同碳链长度的PFSAs比PFCAs容易在蚯蚓体内富集,土壤锁定行为会导致PFASs生物有效性降低,老化过程显著降低土壤中PFASs,尤其是高碳链PFCAs的生物有效性。经过40天的老化,未添加抑菌剂的农田土壤中自由态PFASs的浓度降低更多,表明土壤中的微生物群落活动可能促进了PFASs的矿化,对PFASs有一定的降解作用。此结论需要进一步的研究加以验证。更多还原

【Abstract】 Perfluoroalkyl substances (PFASs) are widely used in numerous industrial and commercial applications due to their unique physicochemical properties, such as thermal and acid resistance, high surface activity, both hydro-and lipophobicity. As a result of the high demand and wide application, PFASs have been detected in water, sediment, soil, wildlife and humans all over the world. In May2009, perfluorooctane sulfonate (PFOS), its salts and perfluorooctane sulfonyl fluoride were added to Annex B of the Stockholm Convention on persistent organic pollutants by the Fourth Conference of Parties.Due to the low volatility and high solubility of PFASs, aquatic environment is an important sink for PFASs. Some studies suggested the only environmental sinks for PFASs were sediment burial and transport to the deep oceans. Although there are many studies about PFASs in water, most of them reported the pollution level of PFASs in water, sediment and aquatic biota. There are a few studies about sorption of PFASs on sediment, while most of them focused on PFOS, little has been done to other PFASs. Systematic studies about sorption and desorption behaviors of PFASs on sediment are obviously insufficient. It remains unclear how PFASs are distributed in sediment and the distribution mechanism.This study provides particle-scale understanding of perfluoroalkyl substances (PFASs) distribution in two sediments with different compositions and properties. Three perfluoroalkane sulfonates (PFSAs) and six perfluoroalkyl carboxylates (PFCAs) were selected as target compounds. Wet sieving was performed to separate each sediment into eight fractions according to particle size and density. The partitioning and desorption behaviors of PFASs in each fraction of the two sediments were compared. The study aimed to illustrate the impacts of the properties of PFASs and the compositions and structure of sediments on sorption. Even though lower density carbonaceous fractions contributed only17.8%and22.3%of the total sediment mass, they displayed stronger affinity to PFASs with much higher PFAS concentrations than in the heavy fractions. Hydrophobic interaction predominated the partition of longer chain PFASs while electrostatic interaction could affect the sorption of short chain PFASs in sediment fractions. Both the length of the perfluorocarbon chain and the functionality of the head group affected the distribution and desorption of the anionic PFAS surfactants in the sediment fractions. The individual PFAS concentrations increased with increasing perfluorocarbon chain length, and the concentrations of PFSAs in the same sediment fraction were higher than PFCAs with the same chain length. Desorption experiments indicated desorption became difficult as the chain length increased, and PFSAs were harder to be desorbed than the corresponding PFCAs. LogKoc was in the range of1.70-3.80for C5-C12PFCAs and1.75-2.97for C4-C8PFSAs. Short-chain PFASs displayed a higher potential for aqueous long-range transport, while sediment could act as a sink for long-chain PFASs. The results suggest that the bioavailability of PFASs in sediment decreases with increasing the carbon chain length.To better understand the sorption mechanisms of PFSAs on soils/sediments, different fractions of humic substances (HSs), including two humic acids (HAs), and humin (HM) were sequentially extracted from a single peat soil. The sorption of the two typical PFSAs, including perfluorohexane sulfonate (PFHxS) and PFOS, on the HS fractions were investigated. Batch experiments including sorption kinetics, sorption and desorption isotherms were conducted. The effect of solution pH on their sorption and the possible sorption mechanisms were investigated. The sorption kinetics and isotherms showed the adsorption of PFOS on the HSs was much higher than PFHxS. For the same PFSA compound, the sorption on HSs followed the order of HM>HA2>HA1. These suggest that hydrophobic interaction plays a key role in the sorption of PFSAs on HSs. Due to the higher water solubility, the PFSA sorption capacities on the HSs are significantly weaker than the typical hydrophobic organic compounds (HOCs), such as benzo[a]phrene, phenanthrene and lindane. The sorption capacities of PFSAs on HSs were significantly related to their aliphaticity, but negatively correlated to aromatic carbons, indicating the importance of aliphatic groups in the sorption of PFSAs. As compared to PFOS, PFHxS displayed distinct desorption hysteresis, probably due to irreversible pore deformation after sorption of PFHxS. Solution pH displayed significant effect on their sorption on the HSs, and the sorption of the two PFSAs on HSs decreased with an increase in pH in the solution. Under normal environmental pH conditions (pH5-8), the sorption of PFSAs on HSs is mainly contributed by hydrophobic interaction. This is ascribed to the electrostatic interaction and hydrogen bonding at lower pH. Hydrophobic interaction might also be stronger at lower pH due to the aggregation of HSs.To further illustrate the interaction of PFASs with organic matters in soil/sediment, the influence of contact duration on the chemical extractability and degradation of PFASs in three peat soils and a farmland soil were investigated under antibacterial and non-antibacterial regimes. Three PFSAs and eight PFCAs were selected as target compounds. Earthworms were exposed to artificially PFASs contaminated soils to investigate the bioaccumulation and bioavailability of PFASs in soil. The results indicated that most of PFASs were extractable in the farmland soil while were sequestrated in the peat soils, suggesting that the sequestration of PFASs in soils was caused by soil organic matters. The accumulation of long carbon chain PFCAs and PFSAs in earthworms was obvious, and PFSAs showed stronger bioaccumulation potential than the corresponding PFCAs. The bioavailability of the PFASs in soils significantly decreased along with the sequestration and aging. Long chain PFCAs were more strongly influenced by aging than the short ones. The extractability of PFASs from the soil without NaN3was much lower than the soil with NaN3, indicating that the presence of microbes promoted the formation of a larger nonextractable residual fraction. Part of PFASs might be degraded by the microbes. Further studies are deemed to understand the funtions of the microbes.更多还原