Contents
Preface
PART I SOIL
Chapter 1 The forms and availability of PAHs in soil3
1.1 The forms of PAHs in soil3
1.1.1 Fractionation methods of PAH residues in soil4
1.1.2 Desorbing fraction of PAHs in soil5
1.1.3 Non-desorbing fraction of PAHs in soil7
1.1.4 Bound residues of PAHs in soil10
1.2 The availability of PAHs in soil12
1.2.1 Available fractions of PAHs in soils as a function of aging time13
1.2.2 Microbial degradation of available fractions of PAHs in soils15
1.2.3 Transformation of available fraction of PAHs to bound residue in soils17
1.2.4 Butanol-extraction technique for predicting the availability of PAHs in soil18
1.2.5 Phytoavailability of bound-PAH residues in soils18
Chapter 2 Gradient distribution of PAHs in rhizosphere soil24
2.1 Gradient distribution of PAHs in rhizosphere soil: a greenhouse experiment25
2.1.1 Gradient distribution of phenanthrene and pyrene in rhizosphere26
2.1.2 Gradient distribution of root exudates in rhizosphere27
2.1.3 The correlations of PAH concentration gradient with the conc entration gradient of root exudates in rhizosphere30
2.2 In situ gradient distribution of PAHs in rhizosphere soil: a field study33
2.2.1 In situ gradient distribution of PAHs in rhizosphere soil34
2.2.2 Rhizosphere effects on PAH distribution in soil37
2.3 Rhizospheric gradient distribution of bound-PAH residues in soils40
2.3.1 Gradient distribution of bound-PAH residues in rhizosphere41
2.3.2 Mechanism of rhizospheric gradient distribution of bound-PAH residues in soils46
Chapter 3 Partition of PAHs among soil， water and plant root48
3.1 Sorption of PAHs by soils with heavy metal co-contaminants49
3.1.1 Sorption isotherms of phenanthrene by soils50
3.1.2 Sorption of phenanthrene by heavy metal-contaminated soils52
3.1.3 Mechanisms of the heavy metal enhanced-sorption of phenanthrene by soils53
3.2 Dissolved organic matter （DOM） influences the partition of PAHs between soil and water57
3.2.1 Effect of inherent DOM on phenanthrene sorption by soils59
3.2.2 Effect of exotic DOM on phenanthrene sorption by soils63
3.3 Partition of polycyclic aromatic hydrocarbons between plant root and water67
3.3.1 Partition of phenanthrene between roots and water68
3.3.2 Estimation of partition coefficient of phenanthrene between root and water using a composition model70
3.3.3 Partition of phenanthrene between root cell walls and water71
Chapter 4 Impact of root exudates on the sorption， desorption and availability of PAHs in soil73
4.1 Impact of PAHs on root exudate release in rhizosphere73
4.1.1 Impact of PAH contamination levels on root exudation in rhizosphere74
4.1.2 Distribution of root exudates in different layers of rhizosphere soil77
4.2 Impact of root exudates on PAH sorption by soils77
4.2.1 Root exudate component-influenced sorption of PAH by soil78
4.2.2 Mechanism discussions80
4.3 Impact of root exudates on PAH desorption from soils83
4.3.1 Desorption of PAHs from soils as a function of root exudate concentration84
4.3.2 PAH desorption by root exudates in different soils86
4.3.3 Effects of soil aging on PAH desorption by root exudates from soil87
4.3.4 Desorption of different PAHs by root exudates in soil88
4.3.5 Impact of root exudate components on PAH desorption in soil89
4.3.6 Dissolved organic matter in soils with the addition of root exudates90
4.4 Impact of root exudates on PAH availabilities in soils92
4.4.1 Impact of root exudates on n-butanol-extractable pyrene in soil93
4.4.2 Impact of root exudate components on the n-butanol-extractable pyrene in soil95
4.4.3 Mechanisms by which root exudate and its components influence PAH availa-bility in soil98
Chapter 5 Low-molecular-weight organic acids （LMWOAs） influence the transport and fate of PAHs in soil101
5.1 LMWOAs-influence the PAH sorption by different soil particle size fractions102
5.1.1 Fractionation protocol of different soil particle size fractions103
5.1.2 PAH sorption by different soil particle size fractions106
5.1.3 Effects of LMWOAs on PAH sorption by different soil particle size fractions108
5.1.4 Mechanisms of LMWOA-influenced PAH sorption by different soil particle size fractions109
5.2 LMWOAs enhance the PAH desorption from soil114
5.2.1 LMWOA-enhanced desorption of PAH from PAH-spiked soil115
5.2.2 LMWOA-enhanced desorption of PAHs from soils collected from a PAH- contaminated site118
5.2.3 Mechanisms of LMWOA-enhanced desorption of PAHs from soils124
5.3 Impact of LMWOAs on the availability of PAHs in soil127
5.3.1 Impact of LMWOAs on the butanol-extractable PAHs in soils128
5.3.2 Mechanism discussions132
5.4 Elution of soil PAHs using LMWOAs133
5.4.1 Elution of PAHs in soil columns by LMWOAs135
5.4.2 Distributions of PAHs in soil columns136
5.4.3 Butanol-extractable and nonextractable PAHs in soil
內容試閱：
PART I SOIL
Chapter 1 The forms and availability of PAHs in soil
Soil is considered to be one of the most important natural resources for human beings. However， organic pollutants occur frequently within the soil environment as a result of air deposition， sewage irrigation， and industrial accidents （Gao et al.， 2009）. This organic pollution triggered by human activities has been a long-term environmental problem in past decades （Führ and Mittelstaedt， 1980; Kipopoulou et al.， 1999; Gao et al.， 2007）. Because of the health hazards of these organic contaminants， knowledge on their transport and fate in the soil environment is of crucial importance in dealing with contaminated sites.
As priority pollutants that are commonly found in the soil environment， polycyclic aromatic hydrocarbons （PAHs） are of major concern due to their recalcitrance and strong mutageniccarcinogenic properties （Weber and Huang， 2003; Tang et al.， 2007）. The hydrophobic characteristic and persistence of PAHs result in their accumulation and enrichment in soils. PAHs are widespread and occur at high concentrations of hundreds of mgkg in soils of many countries （Joner and Leyval， 2003; Ling et al.， 2013）. Contamination of soil with PAHs poses risks to human and ecosystem health.
When entering into soils， a significant proportion of the organic contaminants is not extractable， but is found bound to soil solids. These bound contaminant residues are less available for plant uptake （Ling et al.， 2010）. Researchers now realize that data on only the extractable or total concentrations of a given organic chemical may be of limited utility when assessing its environmental significance （Macleod and Semple， 2003）. Instead， the form and availability of these contaminants in soil are the most important indices for risk assessment.
1.1 The forms of PAHs in soil
The forms of organic contaminants in soil environments have been reported in literatures （Monteiro et al.， 1999; Northcott and Jones， 2000; Loiseau and Barriuso， 2002; Lesan and Bhandari， 2004）. Macleod and Semple （2003） observed that the extractable fraction of pyrene decreased significantly， whereas the bound residue increased with its contact time in soil. Similar results were observed by other researchers （Kohl and Rice， 1998; K?cker et al.， 2002）. However， the PAH concentrations tested in these studies were at their native concentrations in soils， which may be far lower than those at contaminated sites. In addition， only a very limited number of PAHs and soils have been investigated thus far， while the interactions between the forms of PAHs and the influences of soil properties as well as other environmental factors， such as microbial activity on PAH forms still remain unclear. Recently， we fractionated the forms of parent PAH compounds in soils （Gao et al.， 2009; Ling et al.， 2010）. The influence of aging time and microbial activities on the forms of PAHs was also investigated. Results of this work will have considerable benefits for risk assessment， food security， and development of remediation strategies for contaminated sites.
1.1.1 Fractionation methods of PAH residues in soil
A sequential extractionchemical mass balance approach described by Sabaté et al （2006） was used to fractionate the forms of parent PAH compounds in soils. PAHs in soil were separated into three fractions: a desorbing fraction， a non-desorbing fraction， and a bound residual fraction （Gao et al.， 2009; Ling et al.， 2010）.
（1） Desorbing fraction. A mild extraction technique to obtain the desorbing fraction of PAHs was adapted according to the methods described by Reid et al. （2000） and Cuypers et al. （2002）. Three grams of treated soil from each microcosm were placed in a 25 mL glass centrifuge tube， and 15 mL of the mild extraction solution were added. Mild extraction solution consisted of 70 mmolL hydroxypropyl-β- cyclodextrin （HPCD） and 0.05 g NaN3 per mL in Milli-Q water. Tubes were closed with a Teflon-liner cap， shielded from light， and shaken horizontally at 150 rmin at 25℃. At 60 h， 120 h and 240 h， tubes were centrifuged for 25 min at 2000 rmin to separate soil from aqueous solution. The supernatant was collected， and fresh mild extraction solution was added. Tubes were then shaken and centrifuged again. The supernatant was liquid-liquid extracted three times using 10 mL of dichloromethane， and the extraction efficiency was tested. Organic phases were dehydrated by percolation through Na2SO4 anhydride and combined. The solvent was firstly concentrated by rotary evaporation， then evaporated under a gentle stream of N2， and diluted with methanol to a final volume of 2 mL. After filtration through a 0.22 ?m filter， PAHs were detected by high pressure liquid chromatography （HPLC）.
（2） Non-desorbing fraction. This fraction was obtained by exhaustive extraction following mild extraction. After 240 h of mild extraction for the desorbing fraction， the pellet
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