【作者】 林加奖；

【导师】 徐建明；

【作者基本信息】 浙江大学 ， 土壤学， 2013， 博士

【摘要】 五氯酚(Pentachlorophenol,PCP)是环境中普遍存在的一类持久性有机污染物,在我国曾被大量用于杀灭钉螺以控制血吸虫病传播。由于其性质稳定、难以降解,严重危害着土壤的生产力、生态功能、农产品质量和人类健康。因此,有关PCP在土壤中的环境行为及其修复技术已经成为土壤学、环境科学等相关学科领域的热点。水稻田是世界上最大的人工湿地。由于稻田管理的需求,水稻土中氧化还原波动控制了微生物群落结构的功能以及短期的生物地球化学过程。本文以PCP为目标污染物,研究其在不同土壤、特别是水稻土土-水界面的特异消减行为,主要包括土壤类型(包括旱地土壤、水稻土)、氧化还原状态(含水量差异)、淹水水稻土剖面(毫米级微域),外源电子供体与受体对土壤剖面PCP消减及微生物群落结构的影响。主要研究结果如下：(1)好氧、厌氧条件下PCP在土壤中的消减动态变化。选择黄斑田、红壤、潮土和黑土4种性质差异较大的土壤进行60%最大田间持水量(WHC)和淹水培养,研究两种培养条件下PCP消减的差异。结果表明在3种旱地土壤中PCP的消减为60%WHC高于淹水培养,而水稻土黄斑田则相反。通过一级动力学方程对两种条件下PCP消减进行拟合发现,在两种条件下,黄斑田与黑土中PCP的消减均符合一级动力学方程。虽然黄斑田与黑土的理化性质较其它两种土壤更为相近,并且两种土壤培养终点PCP消减率相似,但过程却明显不同。最后,采用[C1-]/△[PCP]摩尔比表示PCP脱氯效率,结果显示,淹水条件下,[Cl-]/△[PCP]为黄斑田(4.86)>黑土(2.68)>潮土(0.29)≈红壤(0.22)；好氧条件下则为黄斑田(4.93)>潮土(4.87)>黑土(4.60)>红壤(1.53)。(2)电子受体对淹水土壤PCP消减行为的影响。土壤在淹水处理下分别添力口FeCl3.NaN03和Na2SO4,研究Fe(Ⅳ)、N03-、SO42等电子受体对黄斑田、红壤、潮土和黑土4种土壤中PCP消减的影响。发现外源电子受体明显抑制了黄斑田和黑土中PCP消减以及脱氯作用,且Fe(Ⅲ)和S042-对黄斑田,Fe(Ⅲ)和N03-对黑土中PCP消减的抑制达到了显著水平(p<0.05)。在120d培养时间内,黄斑田的氧化还原电位从220mV降低到-4mV,而黑土的氧化还原电位从180mV降低到-50mV,可见仅黄斑田与黑土中形成强还原环境,电子受体对PCP消减的抑制作用仅发生在PCP还原脱氯环境中。这种抑制作用可能由两方面造成,一是外源氧化剂与PCP同作为电子受体的竞争作用,二是其氧化性提高了环境初始Eh及减缓了Eh下降速度。此外,四种土壤之间的PCP消减存在较大差异,说明土壤自身理化性质决定其能否在15mm土层内形成强还原环境。(3)PCP在土壤剖面中毫米级深度梯度尺度下的消减规律。根据PCP在三种受试水稻土剖面上不同深度土层(毫米级)的消减状况差异,可将土壤剖面分为上、下两个层次,PCP消减在上层中随土壤深度的增加而递减,而在下层中随土壤深度的增加则变异不大。然而,不同类型的土壤,其上层深度存在差异,黄斑田、红壤性水稻土和砖红壤性水稻土分别为0-15mm、0-25mm和0-30mm, PCP消减分别为40-93%、42-88%及16-100%。在下层土壤中仅红壤中PCP发生显著消减(p<0.05),黄斑田中较为微弱,而砖红壤中基本保持不变。下层土壤中PCP消减与电子供体/受体(DOC、Fe(Ⅱ)、Fe(Ⅲ)和8042-)呈显著相关关系(p<0.05),而上层土壤则不然。说明上层土壤氧化还原环境较为复杂,包括好氧环境和兼氧环境,而下层土壤则为严格厌氧环境,电子受体(Fe(Ⅲ)和8O42-)的还原会与PCP还原存在对电子供体的竞争作用。总之,从毫米级深度尺度研究土壤环境的生物地球化学过程,可以更清楚了解有机污染物的迁移转化机制。(4)基于外源添加不同作物秸秆(水稻、小麦、油菜和紫云英)的形式研究了外源电子供体对土壤剖面中PCP消减行为的影响作用。研究0-10mm、10-20mm、20-30mm和30-50mm土壤剖面内PCP消减的动态变化。添加秸秆可有效促进PCP在土壤剖面中的消减。研究表明所有添加秸秆处理土壤中PCP基本在60d内降解完全,而对照处理中仍有大量PCP残留。在黄斑田和红壤中均检测到PCP的代谢产物3,4,5-TCP和2,3,4,6-TeCP,而砖红壤中仅在培养早期的一些处理中检出微量中间产物。两种土壤中3,4,5-TCP的转化随着培养时间延长表现出极大差异,在黄斑田小麦添加处理以及红壤的水稻、小麦和紫云英添加处理中,3,4,5-TCP被进一步降解。以上结果说明秸秆分解释放的外源有机碳作为电子供体对PCP消减的促进作用因土壤性质及秸秆类型不同存在差异。(5)基于PLFAs技术,研究了PCP胁迫、电子受体和电子供体的添加对黄斑田土壤剖面中微生物量和微生物群落结构的影响及其与PCP消减的相关关系。PLFA主成分分析结果表明,在培养试验中,土层深度是影响微生物群落结构变异的首要因子,而外源电子供体和受体添加占次要位置。PLFA总量在0-10mm土层最高并随土层深度的增加有降低的趋势。真菌、好氧菌、蓝细菌、环丙烷脂肪酸前体脂肪酸、革兰氏阴性菌、饱和脂酸和单不饱和脂肪酸均在0-10mm土层最高,但随土层深度增加而降低,而细菌、放线菌、厌氧菌、革兰氏阳性菌、硫酸盐还原菌、异构和反异构则相反。土壤中添加秸秆可使这些特征脂肪酸剖面梯度差异变小甚至消失。然而,与其它任一处理相比,添加秸秆处理S/M值随土层深度增加而递增。PCP残留量与代表革兰氏阳性菌的i14:0呈极显著负相关(p<0.01),3,4,5-TCP含量与代表硫酸盐还原菌、放线菌的16:0(10Me)和17:0(10Me)、以及代表厌氧菌的cy17:0和cy19:0均呈极显著负相关(p<0.01)。更多还原

【Abstract】 Pentachlorophenol (PCP) is a ubiquitous, and highly persistent organic environmental pollutant. In China, the primary purpose for using PCP and its sodium salt (Na-PCP) is to kill the schistosome intermediate of host snails. PCP tends to accumulate in soils because of its slow rate of degradation. Soil contamination with PCP poses a great threat to the productivity and ecological functioning of soil, of food quality and human health. Therefore the behavior of PCP in the environment and remediation technologies have received increasing investigation. Paddy soils comprise the largest anthropogenic wetlands on earth. Redox potential fluctuations due to paddy soil management controls microbial community structure and function and thus short-term biogeochemical processes.PCP was selected as the target compound in this study. The behavior of PCP dissipation at the water-soil interface, the influence of redox potential, electron donors, electron acceptors, the aerobic-anaerobic gradient in soil profiles, and the response of microbes were studied. The main experiments and results were as follows:(1) The potential for dissipation of pentachlorophenol (PCP) was investigated in soils from four different sites in China. These were a silt clay Umbraqualf (Soil1), a silt clay Plinthudult (Soil2), a silt loam Haplustalf (Soil3) and a silt clay loam Argiustoll (Soil4) which were either flooded, to produce anaerobic conditions, or incubated aerobically at60%water-holding capacity (WHC). The molar ratio of [Cl-]/△[PCP] for PCP is5. Changes in the molar ratio indicated that the dissipation of PCP in different soils was caused by other processes (e.g. irreversible sorption by soil particles) in addition to dechlorination. The molar ratio [Cl-]/△[PCP] was:Soil1(4.86)> Soil4(2.68)> Soil3(0.29)=Soil2(0.22) under flooded conditions, and Soil1(4.93)> Soil3(4.87)> Soil4(4.60)> Soil2(1.53) at60%WHC.(2) Ionic oxidants (Fe(III), sulphate and nitrate) were applied to study their effects on the fate of PCP under flooded conditions. Dissipation of PCP was significantly inhibited by addition of Fe(III)(as FeCl313.5g kg-1), while addition of sulphate (as Na2SO4,2.8g kg-1) and nitrate (as NaNO3,1.7g kg-1) had different effects, depending upon the soil type. Extractable Fe(Ⅱ), sulfate and nitrate concentrations were determined to investigate interactions of redox reactions involved in the PCP dissipation. Sulfate reduction occurred in Soil1and Soil4under flooded conditions. Similarly, the redox potential decreased significantly in Soil1and Soil4, and the dissipation of PCP in the two soils was statistically significant (about96%and98%, respectively) at the end of the flooded incubation (120days). By120days of incubation, the redox potential decreased from220mV to-4mV and180mV to-50mV in soils1and4respectively. The added oxidants inhibited the dechlorination process of PCP.(3) A soil microcosm was designed to mimic the soil-water interface of three typical Chinese paddy soils, Umbraqualf (Soil1), Plinthudult (Soil2), Tropudult (Soil3). Vertical variations in the dissipation potential of pentachlorophenol (PCP) were investigated at the mm-scale in an unplanted, flooded, paddy soil. The depth of soil profiles where PCP dissipation occurred was different due to different soil characteristics. They were0to15mm,0to25mm and0to30mm with the PCP dissipation of40-93%,42-88%and16-100%for Soil1, Soil2and Soil3respectively. The dissipation rate of PCP decreased with increasing soil depth. Pentachlorophenol was significantly (p<0.05) dissipated within the10to50mm depth in Soil2, while dissipation in Soil1was weak, and did not occur in Soil3, where the PCP concentration remained constant until the end of the120day incubation. The PCP dissipation in the surface layer may have been caused by leaching, photolysis, diffusion and biodegradation, and controlled by complex factors including both soil chemical properties and environmental conditions (e.g. temperature and moisture). The vertical profiles of Fe(II) and SO42-indicated that the high SO42-concentration inhibited the dissipation of PCP and the reduction of Fe(III), and the reduction of Fe (III) also competed for electron donors with PCP. The PCP significantly inhibited the reduction of Fe(III) and SO42-and the production of NH4+. In addition, the anions in flooded soils were highly mobile in the soil profiles. (4) The effect of different crop residue additions, wheat(Triticum aestivum), rice (Oryza sativa), rape (Brassica campestris L.) and Chinese milk vetch(Astragalus sinicus) on PCP dissipation under greenhouse incubation conditions were investigated in three typical Chinese paddy soils. These were an Umbraqualf (Soil1), a Plinthudult (Soil2) and a Tropudult (Soil3). Crop residue addition rapidly increased PCP dissipation in soil profiles. PCP was dissipated completely in all crop residues addition treatments at60days incubation. The distribution of electron donors and acceptors in soil profiles was also influenced by crop residues. The distribution of electron donors and acceptors clearly differed, as indicated by Principle Component Analysis (PCA) of their concentrations in the soil profiles. The metabolites3,4,5-trichlorophenol (3,4,5-TCP) and2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) were produced during PCP dissipation in soils1and2.(5)The changes in microbial community structure were investigated in crop residues (wheat, rice, rape and Chinese milk vetch) and electron acceptors (NO3-, SO42-), in amended soils under greenhouse conditions.In all treatments, the highest concentration of total PLFAs was in the0-10mm depth. Compared with the control treatment, there were significant changes between the PLFA patterns in soils amended with crop residues and electron acceptors as indicated by Principal Component Analysis (PCA) of the PLFA signatures. The i14:0, which can represent gram-positive bacteria, had remarkable relationships with PCP dissipation (p<0.01).3,4,5-TCP was negatively related (p<0.01) to16:0(10Me),17:0(10Me), cyl7:0and cyl9:0, which represent actinomyces and anaerobic bacteria respectively. In addition,16:0(10Me) is also the signature PLFA of sulfate-reducing bacteria.更多还原