Influence of mature compost amendment on total

and bioavailable polycyclic aromatic hydrocarbons

in contaminated soils

Guozhong Wu a, b, Cedric Kechavarzi b, Xingang Li a, c, Hong

Sui a, c, Simon J.T. Pollard b, Frédéric Coulon a, b, *

a School of Chemical Engineering and Technology, Tianjin

University, Tianjin 300072, China

b Department of Environmental Science and Technology, Cranfield

University, Cranfield MK43 0AL, UK

c National Engineering Research Centre for Distillation

Technology, Tianjin 300072, China

* Corresponding author:

E-mail: f.coulon@cranfield.ac.uk

Phone: +44 1234 754 981

Fax: +44 1234 754 036 

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Abstract

A laboratory microcosm study was carried out to assess

the influence of compost amendment on the degradation and

bioavailability of PAHs in contaminated soils. Three

soils, contaminated with diesel, coal ash and coal tar,

respectively, were amended with two composts made from

contrasting feedstock (green waste and predominantly meat

waste) at two different rates (250 and 750 t ha-1) and

incubated for 8 months. During this period the treatments

were sampled for PAH analysis after 0, 3, 6 and 8 months.

Total and bioavailable fractions were obtained by

sequential ultrasonic solvent extraction and

hydroxypropy-β-cyclodextrin (HPCD) extraction,

respectively, and PAHs were identified and quantified by

GC-MS. Bioavailability decrease due to sorption was only

observed at the first 3 months in the diesel spiked soil.

After 8 months, compost addition resulted in over 90%

loss of total PAHs irrespective of soil types. Desorption

and degradation contributed to 30 and 70%, respectively,

of the PAH loss in the spiked soil, while PAH loss in the

other two soils resulted from 40% enhanced desorption and2

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60% enhanced degradation. Compost type and application

rates had little influence on PAH bioavailability, but

higher PAH removal was observed at higher initial

concentration during the early stage of incubation. The

bioavailable fraction of PAH was inversely correlated to

the number of benzene rings and the octanol-water

partition coefficient. Further degradation was not likely

after 8-month although over 30% of the residual PAHs were

bioavailable, which highlighted the application of

bioavailability concept during remediation activities.

Keywords: Bioavailability, Compost, PAHs, Degradation,

Desorption

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1. Introduction

Composting capacity in the UK has recently seen a rapid

annual expansion of about 25% as a result of the

implementation of the EU Landfill Directive 99/31/EC and

Waste Strategy for England . This requires the UK to

divert large quantities of organic wastes from landfill,

including most biodegradable organic fractions of

municipal solid waste, food and kitchen waste and wood

waste . As a result, the possibility of using compost as

an amendment to return degraded or contaminated land to

productive use has received increasing attention (Puglisi

et al., 2007; Lord et al 2007; Tejada et al, 2008;

Gandolfi et al, 2010). Addition of compost is beneficial

to soil in terms of physical properties, nutrient

availability and microbial activity and it can help

sustain plant growth (Wanas and Omran, 2006; Tejada et

al, 2008; Gandolfi et al, 2010) There have been several

trials in the UK aimed at establishing biomass crops on

neglected land using compost (Paulson et al, 2003; Lord

et al, 2007). High compost application rates (between 250

and 750 t ha-1) were used to overcome the nutrient 4

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deficiency, the phytotoxicity of the contaminants and the

poor soil physical conditions. However, the

sustainability and viability of such practice will depend

on its impact on the long-term management of risk from

contaminants and notably on the influence of compost on

the fate of organic contaminants. The main concern of

using such large amounts of compost is that mixing

compost with contaminated soil may result in a far

greater quantity of contaminated material. This

uncertainty and the relative paucity of information on

the toxicity, distribution and bioavailability of such

contaminants in compost amended soils may therefore

result in the derivation of overly stringent soil

assessment criteria with concomitant remediation cost

implications .

Several studies have demonstrated the efficiency of

bioremediation by means of compost amendment, however our

understanding of the effects of compost on the

bioavailability of organic contaminants such as PAHs is

still limited. Puglisi et al. found that the addition of

green compost to soils spiked with phenanthrene increased5

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phenanthrene sequestration thus reducing its

bioavailability; but in the meantime the degradation was

enhanced due to the native microorganisms present in the

compost. However, it remains unclear to which extent

these two processes influence the phenanthrene

bioavailability. Moreover, there is a need to investigate

authentic contaminated soils where the fate and transport

of complex mixture of PAHs are controlled by a number of

factors such as ageing time, mineral and organic matter

content, aqueous solubility, polarity, hydrophobicity,

lipophilicity and molecular structure of contaminants .

The term ‘bioavailability’ refers to the fraction of a

chemical in a soil that can be taken up, or transformed,

by living organisms or the degree to which a compound is

free to move into or onto an organism . The

bioavailability of contaminants has significant

implications for the risk assessment and remediation of

contaminated media . If it can be demonstrated that

greater levels of contamination can be left in soil

without additional risk, lower costs and smaller

remediation volumes may be realised and an opportunity 6

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for less intrusive remedial approaches exists . This

implies that a contaminated site where the bioavailable

concentrations of the chemicals of concern are below the

relevant regulatory concentrations may be deemed to

present an acceptable risk even though their total

concentrations exceed the target values in soils.

However, most of the current models used for assessing

human health risk posed by contaminated land defined the

end-point of remedial activities based only on the

chemical concentration likely to pose significant risk

and do not account for bioavailability. This is largely

due to the uncertainties and complexity of assessing the

bioavailability of complex hydrocarbon mixtures and a

lack of substantive bioavailability data . These

identified gaps highlight the need for further research

investigating the interrelationships between hydrocarbon

bioavailability, toxicity and mass transport in

contaminated soils.

In this study, we characterised the influence of large

amount of compost addition on the bioavailability of 16

PAHs from spiked and authentic contaminated soils with 7

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PAH concentration ranging from 4 to 211 mg kg-1. The main

objectives were to (i) identify the changes in total and

bioavailable PAH concentrations after compost addition;

(ii) quantify the contribution of degradation and

desorption to bioavailability change; and (iii) compare

the behaviour of individual PAH in terms of

bioavailability.

2. Materials and methods

2.1. Chemicals

All reagents were purchased from Sigma-Aldrich (UK) and

all solvents were HPLC grade. QTM standard PAH mix in

dichloromethane (DCM) was used for quantification of 2-

bromonaphthalene (BNap) and the following fifteen US EPA

Priority PAHs : acenaphthene (Ace), acenaphthylene (Acy),

naphthalene (Nap), anthracene (Ant), phenanthrene (Phe),

fluorine (Flu), fluoranthene (FL), chrysene (Chr),

pyrene(Pyr), benzo[a]anthracene (BaA),

benzo[b]fluoranthene (BbF), benzo[ghi]perylene (BgP),

benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (DbA) an

dindeno[1,2,3-cd]pyrene (InP). Deuterated PAH standard 8

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mixture containing naphthalene-d8, anthracene–d10,

chrysene-d12 and perylene-d12 in DCM was used as internal

standard and added to extracts at 0.5 µg mL-1.

2.2. Soils and composts

Three soils and two types of compost were used. A sandy

loam soil (Soil A) was initially spiked with diesel at

12.5 g kg-1 and then stored outside, covered with

tarpaulin and left to age for 3 yr by mixing periodically

to keep it aerated. The two other soils (Soils B and C),

historically contaminated with coal tar and coal ash,

respectively, were collected from brownfield sites in

County Durham, UK. The two composts applied were green

waste compost (Compost A) and Compost B composed of

approximately half green waste and half catering meat

waste (hereafter referred to as green and meat composts,

respectively). Both were certified PAS100 which is the

British Standards Institution's publicly available

specification for compost material . For each soil and

compost, the physicochemical properties including pH,

moisture, loss on ignition (LOI), total carbon (TC), 9

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organic carbon of soil (% Org C), available phosphorus

(AP), total phosphorus (TP), total nitrogen (TN) and

particle size distribution were determined on triplicate

samples using standard methods .

2.3. Incubation process

The soils and composts were screened through a 19.5 and

12.5 mm sieve, respectively, to remove large stones and

debris. Each soil was amended in duplicate with two rates

of compost equivalent to field application rates of 250

and 750 t ha-1 with an incorporation depth of 30 cm and

similar to the application rates used in field trials by

. Soils without compost were prepared to provide

unamended controls. The amended soils and unamended

controls were packed into cylindrical cores (1.29 L, Fig.

SM-1 in Supplementary Material (SM)). The samples were

stored at room temperature on plant pot saucers and

covered with parafilm with small holes to reduce

evaporation. To ensure the soils were kept at the same

moisture content, water was added at 7-d intervals to

saturate the first few cm of the soils which drained to 10

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the field capacity without leaching. Subsamples (10 g)

were collected from the upper part of each cylinder

directly at the onset of the experiment (T0), and after 3

(T3), 6 (T6) and 8 (T8) months. The sampled soils were

ground using a mortar, screened through a 1 mm sieve and

stored at 4 °C before analysis.

2.4. PAH analysis

The total PAHs in soils was determined by sequential

ultrasonic solvent extraction . Briefly, soils (5 g) were

chemically dried with 5 g anhydrous Na2SO4 in 50 mL Teflon

centrifuge tubes. Acetone (4 mL) was added and sonicated

for 2 min at 20 °C. Acetone (6 mL) and hexane (10 mL)

were added to the samples and sonicated for 10 min,

followed by manually shaking to mix the solvent and soil.

This step was repeated twice followed by centrifugation

for 5 min at 750 rpm. After passing the supernatant

through a filter column fitted with glass receiver tube,

a sequential step series, including resuspension of the

samples in 10 mL of acetone/hexane (1:1), sonicated for

15 min at 20 °C, centrifugation for 5 min at 750 rpm, and11

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decantation into a filter column, was repeated twice. The

final extract volume was adjusted to 40 mL with a mixture

of acetone/hexane (1:1) and homogenized by manual

shaking. The silica gel column clean-up was performed by

passing the extracts through a column filled with

florisil.

Bioavailable PAHs in soil were extracted using

hydroxypropy-β-cyclodextrin (HPCD) extraction method

previously described by Oleszczuk . Aqueous HPCD solution

was prepared using deionized water to make up a

concentration of 50 mM. Soil samples (2.5 g) were weighed

into 50 mL Teflon centrifuge tubes. After adding 50 mL

of HPCD solution, the tubes were sealed and shaken on a

side-to-side shaker at room temperature at 150 rpm for 20

h. The tubes were centrifuged at 2000 rpm for 30 min and

the supernatant was discarded. After manually shaking

with deionised water, the residue soil slurry was

centrifuged again and the supernatant was then discarded.

The residual PAHs were determined by ultrasonic solvent

extraction method as described previously. The difference

between the total and the residual PAHs after HPCD 12

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extraction was assumed to be the bioavailable fraction of

PAHs.

PAHs were identified and quantified by GC-MS. Details

of GCMS operational conditions are available in the

Supplementary Material.

2.5. Statistical analysis

The ANOVA with Tukey test was performed to compare the

differences in the physicochemical properties between

soils and composts. Differences in the PAH concentration

between different treatments were compared using ANOVA by

LSD test. The difference was recognised as significant

where P < 0.05. All tests were performed using SPSS 17.0.

Similarity between the 16 target PAHs in terms of their

bioavailable and non-bioavailable concentration profiles

were identified by the hierarchical cluster analysis

using PRIMER 6.0 (Primer-E, UK).

3. Results and discussion

3.1. Soils and composts physicochemical properties

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General physicochemical properties of the soils and

composts are presented in Table 1. The textual analysis

showed that all soils were sandy loam, while Soil C had a

higher percentage of silt. The pH of the three soils were

slightly alkaline (pH value: 7.9-8.2) and within the

preferable ranges for bioremediation . The largest

differences in the physicochemical properties were

observed between Soil A and the two other soils

especially in terms of LOI, TC and % Org C, suggesting

that the PAH-coated soil solids phase may be less

important than in the two other soils due to its lower

carbon content .

According to the theoretical C: N: P ratio 100:10:1 of

a microbial cell , the N and P concentrations in the

three soils were not optimal (Table SM-2). The addition

of compost to the soils reduced the unbalanced C:N ratio.

This suggested that compost addition would change the

nutrient dynamics by reducing C:N ratio which determined

whether mineralization or immobilization dominated in the

early stages of organic matter decomposition in the soils

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3.2. Initial PAH concentrations in the unamended soils

The initial PAH concentrations before compost amendment

are reported in Table 2. PAHs were grouped as 2-ring (Nap

and BNap), 3-ring (Acy, Ace, Flu, Phe and Ant), 4-ring

(FL, Pyr, Chr and BaA), 5-ring (BbF, BaP and DbA) and 6-

ring (InP and BgP) for discussion. Results show that the

PAH content in Soil A was about one-order of magnitude

lower than that in the other two soils. The 4-ring PAHs

were the most abundant PAHs in the three soils (Table 2).

However, information on PAH distribution alone is

inadequate to predict risk because it ignores the changes

in contaminants' bioavailability which often results in

overestimating the level of cleanup needed at

contaminated sites .

Table 2 indicates that there are only slight

differences in the bioavailability of ∑16PAHs among the

three soils. PAH bioavailability decreased with an

increased number of aromatic rings and molecular weight

due to higher octanol-water partition coefficients

(logKow). In particular, the contribution of bioavailable 15

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fractions in 6-ring PAHs was 57% lower than that of 2-

ring PAHs in Soil C.

3.3. PAH bioavailability changes and degradation

The changes in PAH concentration following compost

addition are presented in Table 3. Less than 40%w/w of

∑16PAHs was lost in the three unamended soils over the 8-

month duration. The PAH loss in Soil A was approximately

48% higher than in other soils, probably due to the more

recalcitrant PAHs in the genuinely contaminated soils

than in the spiked soil (Table 2).

The most significant decrease in the unamended

controls was observed for the 2-ring and 3-ring PAH group

after 8 months, but little (< 20 wt%) degradation was

observed for the 6-ring PAHs. In Soil B and C, the

percentage of total PAH loss was at least 50% less than

that of the bioavailable fractions. For example, less

than 25 wt% of ∑16PAHs was lost in unamended Soil C (Table

3) although over 50 wt% of ∑16PAHs was bioavailable (Table

4) throughout the incubation process. This suggests that

bioavailability was not the limiting factor. Instead, the16

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slow biotransformation may be attributed to the high

C:N:P ratio which may potentially reduce the

biodegradative activity of PAH-degrading bacteria .

3.4. Effect of compost amendment on PAH bioavailability

and degradation

Overall, soil amendment with the two composts was

beneficial for PAH removal (Table 3). The 3-ring PAHs

were characterized by the largest decrease (> 94%) in

concentration after 8-month independent of treatments.

The smallest decrease was observed for the 6-ring PAHs,

as up to 45, 17 and 8% of their initial content was still

present in Soil A, B and C, respectively after 8 months.

The enhancement in degradation by compost addition may

be moderated by a decrease in bioavailability after

organic amendment , because compost can serve as a major

compartment for sorption which sequestrates PAHs within

the organic matrix (i.e. the lignin-cellulosic residues).

On the other hand, studies have showed that humic acid-

like compounds in the compost behaved as biosurfactants

and enhanced desorption by decreasing surface tension, 17

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forming micelles and incorporating PAHs in the micelles

cores . The sorption process drives the PAHs from

accessible compartments (e.g. aqueous phase) into less

accessible or inaccessible compartments (e.g. micro- or

nano-pores of soil organic matter) thereby increasing the

non-bioavailable fractions, while desorption process

enhances water solubility of hydrophobic molecules

therefore reducing the non-bioavailable fractions.

The contribution of sorption/desorption (non-

bioavailable concentration changes) and degradation

(difference between total concentration loss and non-

bioavailable concentration changes) to the overall PAH

loss after compost addition is shown in Fig. 1. In Soil

A, the PAH degradation and sorption changed in a biphasic

manner. During the first 3 months, compost addition was

adverse for PAH removal as the overall PAH loss in the

compost amended soils was 26 to 89% less than that in the

unamended controls (Table 3). This was attributed to the

decreased bioavailability resulting from strong sorption

(Fig. 1). Table 3 further demonstrated that the compost

addition restrained the removal of high molecular (5- and18

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6-ring) PAHs. Similar to Oleszczuk , there was initially

an increase of the PAH content adsorbed to the soils and

thereby temporarily less solvent extractable.

It is of particular interest to observe that the

addition of green compost at 250 t ha-1 had no influence

on the loss of total PAH as the decreased bioavailable

fractions were completely transformed into non-

bioavailable fractions rather than degraded. After 6

months, the PAH removal in the compost amended soils

reached 90%. Approximately 30% of the total loss was

attributed to the enhanced desorption and 70% attributed

to the enhanced degradation after compost addition (Fig.

1).

In Soil B, compost addition resulted in up to 30% PAH

loss in the first 3 months and further increased to 94%

after 8 months. Similar trends were found in Soil C but

the PAH loss was up to 76% in the first 3 months. In most

cases for Soil B and C, approximately 40% of the PAH loss

was due to desorption and 60% due to degradation (Fig.

1). An exception was observed when the composts were

applied at 250 t ha-1 where, in the first 3 months, 19

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desorption was less important and contributed only to 2-

35% of the total loss. Sorption due to compost addition

in these soils was not obviously observed, probably

because the PAHs in heavy coal tar or coal ash in the

soils were not able to overcome the mass transfer

limitations to move to the compost matrix.

In general and irrespective of soil type, further loss

of 6-ring PAHs was unapparent after 8 months although

over 30% and 10% of the total mass was bioavailable in

the unamended and amended soils, respectively (Table 4).

In contrary, the concentration of 6-ring PAHs increased

at the end of the experiment (Table 3), which was

particularly obvious in the diesel spiked soil.

Therefore, it is inferred that the primary process

limiting the removal of residual PAHs (especially high

molecular PAHs) at the end of incubation was more likely

degradation rather than desorption. The increase in PAH

concentration in green compost amended soils was also

observed by Antizar-Ladislao et al. . This observed

phenomenon can be explained by the fact that the strength

of the bonds between the PAHs initially adsorbed to the 20

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compost-soil mixture were weaken during organic matter

mineralisation (Oleszczuk, 2009), which led to an

increase in the bioavailability of the PAHs that were not

bioavailable earlier (Oleszczuk, 2007). This finding

emphasises that it is incorrect to automatically assume

that the residual PAHs after extensive bioremediation

treatment are recalcitrant and thereby may be left in

place without creating environmental risks. This is

consistent with Huesemann et al. .

Overall, influences of compost on desorption and

degradation varied with soil types. Degradation

predominated in the real soils throughout the incubation

process. In the diesel spiked soils, sorption was the

main process limiting PAH removal at the initial stage

but degradation contributed more than desorption to the

PAH loss at final stage. Increasing the compost ratio did

not necessarily increase PAH removal. However, the

initial PAH concentration levels seemed to strongly

influence removal rates, especially at the early stage of

the experiment. The initial ∑16PAHs in Soil A, B and C was

4.5, 150 and 211 mg kg-1, respectively. Lower removal 21

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after 3 months was observed in Soil A (3-29%), followed

by Soils B (21-29%) and C (45-76%). This agreed with

Sayara et al. , who demonstrated that at low

concentrations it was difficult to keep the required

activity of microorganisms in soils amended with

municipal composts.

3.5. Behaviour of individual compounds

Fig. 2 indicated that the bioavailable fraction of each

PAH is inversely correlated to the number of benzene

rings and the logKow. There was no obvious discrimination

between the 3-ring and 4-ring compounds as their

similarity was > 70%. The most significant differences

were between two PAHs (BNap and DbA) and the remaining

compounds (similarity < 40%). The formation of insoluble

aggregates of HPCD-BNap complexes at high HPCD

concentration (> 4 M), and the higher logKow of DbA (6.8)

compared to that of the other PAHs (3.3-6.7) might

contribute to the atypical behaviour of these compounds

in terms of solubility and bioavailability . Another

explanation was the extraction mechanism by HPCD, which 22

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is a cyclic oligosaccharide with a hydrophilic exterior

and a toroidal shaped hydrophobic interior where PAHs are

incorporated to form a water soluble inclusion complex .

We infer that both BNap and DbA could only achieve

partial inclusion with HPCD which made them ‘less

bioavailable’. For example, the molecular length of DbA

(1.32 nm) was much greater than the diameter of HPCD

cavity (0.78 nm) rendering it difficult to be wholly

encompassed in the HPCD interior . Although the BNap has

a smaller size (molecular length: 0.74 nm), the much

polar bromo- substitute would be exposed out of the HPCD

cavity into the water phase with the hydrophobic parts

inserted in the interior of HPCD . These findings implied

that HPCD extraction might not be a good choice for

predicting the bioavailability of PAHs with a high

molecular size or polar substituent which may potentially

form partial inclusion with HPCD.

4. Conclusions

This study showed that the slow biodegradation (< 40%) of

PAHs in unamended soils was potentially due to the lack 23

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of inorganic nutrients (N and P) rather than a limited

bioavailability. In the diesel spiked soil, compost

addition initially decreased PAH removal by up to 89%

because of the decreased bioavailability resulting from

strong sorption irrespective of compost type. But as time

increased, compost amendment enhanced PAH removal by more

than 2-fold compared with unamended control, to which 30%

was contributed by desorption and 70% by degradation. In

coal tar and coal ash contaminated soils, compost

addition was beneficial overall for enhancing PAH removal

up to 94% and 40% of the total loss was due to the

enhanced desorption. Cluster analysis demonstrated the

correlation between bioavailability and logKow and also

suggested the unsuitability of HPCD method for predicting

bioavailability of PAHs with large molecular size or

polar substituent. The overall results suggest compost

addition is an effective approach for enhancing PAHs

removal from soils, but increasing the ratio of compost

added does not necessarily help to increase removal.

Enhanced removal by compost addition seems more effective

for higher initial PAH concentrations. Further treatments24

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may be necessary for completely removing PAHs because

over 30% of the residual PAHs were still bioavailable.

Acknowledgement

This research was funded by the Program for Changjiang

Scholars and Innovative Research Team in University

(IRT0936).

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Reference

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ATSDR, 1995. Toxicological profile for polycyclic

aromatic hydrocarbons (PAHs). U.S. Department of

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Table 1 Physicochemical characteristics of the three

contaminated soils and two compost types (average values

standard error, n = 3. Values followed by the same

letter are not statistically different from each other.

Tukey test, P < 0.05)

Property Soil A Soil B Soil C Compost A Compost B

pH7.9 ±

0.0a

8.2 ±

0.1a

8.2 ±

0.0a8.1 ± 0.0a 2.6 ± 0.6b

Moisture

(%)31 ± 1a 26 ± 4 32 ± 3 56 ± 5b 8 ± 0.1

LOI (%) 6 ± 1a 24 ± 2b 21 ± 3b 31±2c 54 ± 3d

TC (%) 3 ± 1a 17 ± 2b 17 ± 1b 20 ± 0.1b 32 ± 0.4c

% Org C 3 ± 0.6a 16±2b 16±1b 18±0.3b 31 ± 0.3c

AP (ppm)21 ±

0.4a37 ± 4b 30 ± 1b 150 ±14c 124 ± 25c

TP (ppm) 509 ± 4a 422 ± 6b 332 ± 8c 1806 ± 17d 2547 ± 13e

TN (%)0.2 ±

0.0a

0.5 ±

0.0b

0.5 ±

0.0b2.1 ± 0.1c 3.2 ± 0.0d

% Sand 72 ± 5a 74 ± 5a 56 ± 6b

% Silt 9 ± 4a 7 ± 5a 30 ± 6b

% Clay 19 ± 1a 19 ± 1a 14 ± 1b

35

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682

683

684

685

69

70

36

686

687

71

72

Table 2 Initial PAH distribution and bioavailability profiles in soils (average ± standarderror, n = 2)

Soil A Soil B Soil C Total

(mg kg-1)Bioavaila

ble(mg kg-1)

Bioavailable (%)

Total(mg kg-

1)

Bioavailable

(mg kg-1)

Bioavailable (%)

Total(mg kg-

1)

Bioavailable

(mg kg-1)

Bioavailable (%)

Nap 0.1 ±0.00 0.1± 0.00 76 1 ± 0 0 ± 0 60 3 ± 0 2 ± 0 88

Acy 0.1 ±0.00 0.1± 0.00 74 0 ± 0 0 ± 0 72 0 ± 0 0 ± 0 84

BNaP 0.6 ±0.00

0.3 ±0.00 59 0 ± 0 0 ± 0 60 0 ± 0 0 ± 0 53

Ace 0.2 ±0.02

0.2 ±0.01 78 1 ± 0 0 ± 0 56 3 ± 0 2 ± 0 77

Flu 0.4 ±0.01

0.3 ±0.01 86 1 ± 0 0 ± 0 70 2 ± 0 2 ± 0 76

Phe 0.3 ±0.00

0.3 ±0.01 83 17 ± 4 11 ± 2 64 16 ± 1 12 ± 0 76

Ant 0.4 ±0.02

0.2 ±0.01 51 18 ± 2 13 ± 1 68 23 ± 0 14 ± 1 62

FL 0.5 ±0.00

0.3 ±0.00 65 22 ± 3 15 ± 1 72 17 ± 5 11 ± 3 66

Pyr 0.4 ± 0.3 ± 71 17 ± 1 6 ± 0 37 25 ± 1 16 ± 2 64

37

688689

73

74

0.03 0.04Chr 0.2 ±

0.030.1 ±0.01 59 15 ± 4 11 ± 2 71 28 ± 2 17 ± 1 62

BaA 0.3 ±0.07

0.2 ±0.06 56 12 ± 0 8 ± 1 62 18 ± 1 10 ± 0 55

BbF 0.3 ±0.05

0.2 ±0.02 51 20 ± 4 10 ± 2 48 24 ± 2 14 ± 1 59

BaP 0.2 ±0.00

0.1 ±0.00 56 12 ± 0 4 ± 0 32 23 ± 2 10 ± 0 45

InP 0.1 ±0.00

0.0 ±0.00 35 8 ± 1 2 ± 0 25 15 ± 0 5 ± 0 35

DbA0.1± 0.01

0.0 ±0.00 40 1 ± 0 0 ± 0 40 1 ± 0 1 ± 0 48

BgP 0.2 ±0.01

0.1 ±0.00 51 6 ± 1 2 ± 0 38 11 ± 1 4 ± 0 38

∑ 2rings

0.6 ±0.00

0.4 ±0.00 62 1 ± 0 0 ± 0 60 3 ± 0 3 ± 0 83

3∑

rings 1.5 ± 0.2 1.1 ± 0.2 73 37 ± 3 24 ± 3 66 44 ± 1 30 ± 1 69 4∑

rings1.4 ±0.07

0.9 ±0.06 64 66 ± 9 40 ± 5 61 89 ± 6 55 ± 2 62

5∑

rings0.6 ±0.00

0.3 ±0.00 51 33 ± 4 14 ± 2 42 49± 0 26 ± 1 52

3875

76

6∑

rings0.3 ±0.00

0.2 ±0.00 45 13 ± 2 4 ± 0 31 26 ± 1 10 ± 0 36

∑16PAH4.5 ± 0.3 2.9 ± 0.2 64

150 ±12 82 ± 10 55

211 ±5 124 ± 1 59

Table 3 Percentage of the initial PAHs lost during incubation in relation to the number ofaromatic rings (negative values represent percentage increase in PAH concentrations).

3-month 6-month 8-monthS A1 A2c B1d B2e S A1 A2 B1 B2 S A1 A2 B1 B2

SoilA

2-ring 32 44 26 47 78 52 87 88 81 83 46 93 91 95 903-ring 39 42 4 51 41 55 92 93 94 95 56 95 96 97 954-ring 26 33 48 23 -12 34 87 87 86 76 39 92 91 93 91 5-ring 19 4 -18 -30 -68 18 91 84 81 79 18 92 82 92 84 6-ring 11 -21 -61 -70 -115 14 94 90 91 92 14 95 92 94 94∑16PAH 29 29 13 22 3 40 90 89 88 85 38 91 89 94 90

SoilB

2-ring 16 13 21 -6 42 73 69 73 81 82 81 87 89 88 903-ring

12 37 30 27 32 28 79 90 86 89 32 95 95 96 98

39

690691692

77

78

4-ring 9 30 32 23 32 19 74 87 80 85 26 88 91 89 935-ring 10 27 0 18 25 16 74 85 78 85 22 87 92 89 936-ring 2 10 2 6 4 13 92 93 94 96 14 93 94 94 91 ∑16PAH 10 29 22 21 28 20 77 88 82 87 26 89 92 90 94

SoilC

2-ring 41 45 60 55 70 87 83 89 83 90 94 94 96 95 963-ring 14 35 62 52 70 25 89 95 86 97 32 96 98 96 984-ring 14 46 69 60 75 20 86 90 86 96 24 90 95 86 915-ring 4 56 68 63 82 12 87 92 85 96 15 92 96 89 956-ring 4 37 73 67 81 13 92 95 95 93 17 92 95 95 93 ∑16PAH 11 45 68 60 76 19 85 92 86 95 24 92 96 90 93

(S = unamended soils; A1 = Soils amended with Compost A at 250 t ha-1; A2 = Soils amendedwith compost A at 750 t ha-1; B1 = Soils amended with Compost B at 250 t ha-1; B2 = Soilsamended with Compost B at 750 t ha-1)

40

693694695696697

79

80

Table 4 Percentage of bioavailable fractions in total concentration of PAHs duringincubation process.

3-month 6-month 8-monthS A1 A2 B1 B2 S A1 A2 B1 B2 S A1 A2 B1 B2

SoilA

2-ring 43 35 45 43 44 35 34 22 32 31 33 34 15 31 353-ring 58 31 17 50 37 46 40 30 37 30 41 25 18 33 274-ring 41 41 32 36 37 33 26 16 31 24 29 19 12 24 225-ring 47 37 14 41 27 37 27 12 29 23 35 14 11 27 236-ring 47 23 16 29 21 32 19 11 21 19 27 8 6 21 17∑16PAH 48 34 23 39 32 37 31 19 31 25 34 16 12 26 24

SoilB

2-ring 49 42 19 31 59 54 43 59 47 50 40 43 52 40 303-ring 60 33 53 42 62 63 50 60 53 59 55 31 43 40 484-ring 56 39 53 41 62 57 43 59 54 57 53 33 39 26 295-ring 40 49 52 52 46 39 32 52 56 50 37 29 21 35 396-ring 30 44 40 46 42 30 22 30 29 38 26 28 20 37 42∑16PAH 51 41 51 44 56 51 41 56 53 55 47 31 32 31 35

Soil 2- 41 25 37 27 40 36 53 37 49 70 39 26 36 17 4141

698699

81

82

C ring3-ring 62 43 54 60 61 62 53 59 64 60 58 43 65 28 514-ring 58 48 59 50 55 57 46 67 48 52 55 50 53 44 555-ring 50 34 58 42 50 50 47 50 50 53 47 30 44 44 416-ring 34 36 43 29 42 33 12 34 12 26 30 29 34 31 20∑16PAH 54 42 55 48 54 53 47 60 51 54 50 42 49 41 47

(S = unamended soils; A1 = Soils amended with Compost A at 250 t ha-1; A2 = Soils amendedwith compost A at 750 t ha-1; B1 = Soils amended with Compost B at 250 t ha-1; B2 = Soilsamended with Compost B at 750 t ha-1)

42

701702703

83

84

Fig. 1 Contribution of desorption ( ) and degradation ( )

to the ∑16 PAH loss in soils amended with A1 (Compost A, 250 t

ha-1), A2 (Compost A, 750 t ha-1), B1 (Compost B, 250 t ha-1) and

43

704

705

706

707

85

86

B2 (Compost B, 750 t ha-1). The negative values indicate

sorption of PAHs to the compost amended soils.

44

708

709

87

88

45

b

a

89

90

Fig. 2 Comparison of the mass distribution profiles (bioavailable vs non-bioavailable) of

individual PAHs. (a) Dendogram from hierarchical cluster analysis; (b) Schematic of PAH

molecular structure. LogKow is presented in brackets.

46

711

712

713

91

92