Concentration of Polycyclic AromaticHydrocarbons in Sewage

Sludge-Amended Soil

Patryk Oleszczuk and Stanisław Baran

Institute of Soil Science and Environmental Management,

Agriculture University, Lublin, Poland

Abstract: The objective of this research was to estimate the content of polycyclic

aromatic hydrocarbons (PAHs) in sandy soil fertilized with various doses of sewage

sludge. The experiment consisted of six plots to which the following doses of

sewage sludge were added: 30, 75, 150, 300, and 600 t/ha. Sixteen PAHs from the

United States Environmental Protection Agency list were determined by means of a

high-performance liquid chromatography (HPLC) with UV detection after preliminary

ultrasonic extraction. Content of PAHs in the control soil was 46 mg/kg. The appli-

cation of sewage sludge caused an increase in the PAH sum in relation to the dose

applied. In soil amended with 30, 75, 150, 300, and 600 t/ha of sewage sludge, the

increase of PAH content to 74, 177, 430, 883, and 1004 mg/kg, respectively, was

observed (in the 0- to 20-cm horizon). After 2 days from the introduction of the

sludge, an increase of the PAH content in the 20- to 40-cm horizon was also noted.

The composition of the PAH group also changed. A decrease in the share of 3-ring

PAHs at the expense of the 4- and 5-ring PAHs took place. The addition of sewage

sludge to sandy soil in an amount up to 300 t/ha did not cause an increase in the

PAH content in the soil to a level that could pose a danger of these compounds

migrating into the human food chain. However, an increase in PAH content in the

20- to 40-cm soil horizon shows the danger relating to PAH migration into the

deeper horizon with the possibility of contaminating groundwater.

Keywords: Persistent organic pollutants, soil fertilization, PAHs leaching, organic

contaminants

Received 12 September 2003, Accepted 2 September 2004

Address correspondence to Patryk Oleszczuk, Institute of Soil Science and Environ-

mental Management, Agriculture University, ul. Leszczynskiego 7, Lublin 20-069,

Poland. E-mail: patol@consus.ar.lublin.pl

Communications in Soil Science and Plant Analysis, 36: 1083–1097, 2005

Copyright # Taylor & Francis, Inc.

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1081/CSS-200056865

1083

INTRODUCTION

One of the methods of sewage sludge use is its application in agriculture. This

use is a preferred option in the countries of the European Union, the United

States, and Canada where more than one-third of sewage sludge is used in

that way (Wilson, Duarte-Davidson, and Jones 1996). Sewage sludge is a

cheap source of nitrogen and phosphorus; moreover, it influences improve-

ment of soil properties (Tester 1990). The agricultural use of sewage sludge

is a certain type of recycling as waste created by man is reused.

However, numerous research reports point to the danger of a permanent

introduction of organic pollutants into the soil with the biological use of

sewage sludge (Alcock et al. 1996; Litz and Muller-Wagener 1998; Madsen

et al. 1999; Litz 2000; Smith et al. 2001). Researchers have drawn attention

(Smith et al. 2001; Bodzek et al. 1997; Baran and Oleszczuk 2003; Stevens

et al. 2003) to the high content, relative to their origin, of polychlorinated

biphenyls (PCB), dioxins and furans (PCDD/F), pesticides, polycyclic

aromatic hydrocarbons (PAHs), and their derivatives.

PAHs are persistent organic pollutants often found in sewage sludge,

because of their low solubility in water and high hydrophobicity (log

Kow ¼ 3–8) that favor their sorption onto sludge particles during wastewater

treatment. PAHs entering the soil environment through sewage sludge appli-

cation are subjected to various processes, such as volatilization, abiotic and

biotic degradation, and plant root uptake (Smith et al. 2001). The latter is

very important because this might result in introduction of PAHs in the

human food chain and increase human exposure to these carcinogenic and/or mutagenic compounds (Wilson, Duarte-Davidson, and Jones 1996; Litz

2000; Smith et al. 2001).

In the European Union, norms determining the amounts of some persi-

stent organic pollutants introduced to the soils with organic waste have already

been implemented (Oleszczuk and Baran 2003). In PAHs, the norms concern

the following compounds: fluoranthene (5 mg/kg of sewage sludge dry mass),

benzo[b]fluoranthene (2.5 mg/kg of sewage sludge dry mass), and benzo[a]

pyrene (2 mg/kg of sewage sludge dry mass) (Oleszczuk and Baran 2003).

The present studies consisted in determining the PAH content in peat soil

fertilized with various doses of sewage sludge. The experiments conducted are

part of a wider scope of study aimed at determining the durability of the

transfer of PAHs in soils fertilized with sewage sludge.

MATERIALS AND METHODS

Field Experiment

The study block consisted of six plots, 15 m2 each, founded on Halpic Podzols

soil (containing 86% sand, 7% silt, and 7% clay) originating from weak loamy

P. Oleszczuk and S. Baran1084

sand. The soils applied in the experiment were characterized by pH 6.0, poor

sorption properties (the cation exchange capacity, 3.4 mmol/kg; the total of

exchangeable bases, 59.9 mmol/kg; the degree of the base saturation, 22%),

and small content of organic carbon and total nitrogen, 10.7 and 1.4 g/kg,

respectively.

Plots were located according to increasing doses of sludge as follows: soil

without sewage sludge (0%); sewage sludge 30 t/ha (1% dry weight basis of

sewage sludge on 1 ha); 75 t/ha (2.5%); 150 t/ha (5%); 300 t/ha (10%);

600 t/ha (20%). Soil-like, fermented sewage sludge from a mechanical-

biological sewage treatment plant originating from communal (70%) and

industrial (30%) waste was used for the present experiment. The amount of

sludge applied was at fertilizing (30 t/ha), melioration (75–300 t/ha), and

extreme doses (600 t/ha). The choice of extreme doses was aimed at establish-

ing the degree at which soil becomes polluted with PAHs together with

durability of such compounds on this background.

Sludge doses were calculated by taking into consideration the dry mass

and the density of the solid soil phase. Sludge was mixed with a surface

soil layer up to a depth of 20 cm. The sewage sludge applied in the study

was characterized by pH 6.0, cation exchange capacity 500 mmol/kg,

total of exchangeable bases 548 mmol/kg, degree of the base saturation

99%, and a total content of organic carbon and total nitrogen 210.0 and

17.8 g/kg, respectively.

Chemicals

A total of 16 PAHs [naphthalene (Na), acenaphthylene (Ace), acenaphtene

(Ac), fluorene (Fl), phenanathrene (Phen), anthracene (Ant), fluoranthene

(Fln), pyrene (Pyr), benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF),

benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenz[a,h]anthracene

(DahA), benzo[ghi]perylene (BghiP), indenol[1,2,3-cd]pyrene (Ind) (each in

a concentration of 100 mg/mL)] (Promochem, Warszawa, Poland) were

used as standards. Dichloromethane was used for the extraction, and aceto-

nitrile, methanol, and 2-propanol (Merck KGaA, Germany, all HLPC grade)

were used for the purification according to a solid-phase extraction method

(Baran and Oleszczuk 2003; Oleszczuk and Baran 2003; Baran, Bielinska,

and Oleszczuk 2004).

Sample Collection and Preparation

Surface (0–20 cm) and subsurface (20–40 cm) soil and sewage sludge-

amended samples were collected (after a period of 2 days after sewage

sludge application) with a (5 cm id � 60 cm) stainless steel corer. Six

independent samples (replicates) were taken from each plot. The cores were

sliced into two parts (0–20 cm and 20–40 cm) and placed into zip-lock

Concentration of Polycyclic Aromatic Hydrocarbons 1085

plastic bags. Samples were transported to the laboratory, air-dried in air-

conditioned storage rooms (20–258C) for 2 days (in darkness), manually

crushed, and sieved (,2 mm) prior to chemical analyses.

Analysis Soil, Sewage Sludge, and Sewage Sludge-Amended Soil

Sewage sludge (1 g), sewage sludge-amended soil (25 g), and soil (25 g)

samples were extracted in an ultrasonic bath (Sonic-3, Polsonic, Poland)

with two batches of dichloromethane (2 � 40 mL). Time of extraction was

45 min with the first batch of solvent and 30 min with the second batch. The

extracts were centrifuged, decanted, and evaporated to dryness. The residues

were then dissolved in 4 mL of acetonitrile:water mixture (1 : 1 v/v) and

purified by solid-phase extraction (SPE) using C18 octadecyl columns (JT

Baker-Mallinckrodt, Germany) with the method as described elsewhere

(Oleszczuk and Baran 2003; Baran, Bielinska, and Oleszczuk 2004). A quali-

tative and quantitative analysis of PAHs was conducted on the liquid chro-

matograph with UV detection (TermoSeparation Products) (Oleszczuk and

Baran 2003). The mobile phase was acetonitrile-water mixture (82 : 18,

v/v). A Spherisorb S5 PAH column (250 � 4.6 mm i.d., 5 mm) (Schambeck

SFD GmbH, Germany) was used for the separation of 16 PAHs (Baran and

Oleszczuk 2003; Oleszczuk and Baran 2003; Baran, Bielinska, and

Oleszczuk 2004). The column was installed in a thermostated oven at 318C(LCO 101; ECOM, Czech Republic). Detection was conducted at 254 nm.

Quantitative determination was performed by using the absolute cali-

bration curve method. The correlation coefficients of calibration functions in

the intervals of linearity were in the range 0.9982–0.9998 for individual

PAHs. A method blank did not show reagent or equipment contamination

with PAHs. Recoveries for the total procedures (sample preparation, extraction,

and SPE) ranged between 81 and 90% (in soil and sewage sludge-amended soil)

and 72 and 83% (in sewage sludge) for individual PAHs. Only in the case of

naphthalene recoveries were in the range 50–60% (in all samples). Precision

expressed as relative standard deviation (RSD) was below 21%. Therefore,

the concentrations reported here have not been corrected for losses.

All reported concentration values of PAHs are expressed on a dry weight

basis of soil (determined by drying the soils for 24 h at 1058C) and are the

average of triplicate extraction.

RESULTS AND DISCUSSION

Concentration of PAHs in Soil and Sewage Sludge

The concentrations of PAHs in soil and sewage sludge-amended soil are

presented in Tables 1 and 2 for the 0- to 20-cm and the 20- to 40-cm soil

horizons, respectively.

P. Oleszczuk and S. Baran1086

The surficial soil was characterized by very low PAH levels (46 mg/kg).

The contents of individual hydrocarbons ranged from 0.14 to 13 mg/kg

(Tables 1 and 2). The highest concentration was detected for the

3-ring compounds such as: acenaphthylene (13 mg/kg) and acenaphthene

(10 mg/kg). The sum of 5- and 6-ring PAHs did not exceed 12 mg/kg.

The PAH content determined is comparable with the PAH content in soils

originating from agricultural areas with limited man’s pressure on the environ-

ment (anthropopressure) in Poland (Maliszewska-Kordybach 1996) or in the

world (Menzie, Potocki, and Santodonato 1992). By considering information

from other authors, it can be said that such soils are nonpolluted and their PAH

content reflects a natural level of such compounds. According to classification

for soils polluted with PAHs that was proposed by the Polish Institute of Soil

Science and Plant Cultivation (IUNG in Puławy) (Maliszewska-Kordybach

Table 1. Concentrations of PAH (mg/kg dry wt) and total organic carbon (TOC)

(g/kg) and pH in sewage sludge-amended soil (0–20 cm)

Sewage

sludge

dose

PAH concentration

0% 1% 2.5% 5% 10% 20%

PAH

Na 3.0 + 9 5.5 + 15 19 + 12 40 + 16 88 + 13 95 + 13

Ace 13 + 11 16 + 17 41 + 15 59 + 12 115 + 17 144 + 15

Ac 10 + 17 11 + 9 19 + 12 46 + 15 96 + 13 96 + 13

Fl 3.6 + 6 1.1 + 11 2.6 + 8 15 + 9 41 + 9 22 + 10

Phen 0.8 + 9 1.9 + 9 5.1 + 11 16 + 12 32 + 8 32 + 11

Ant 0.14 + 9 0.22 + 7 1.1 + 11 4.6 + 13 14 + 10 12 + 10

Fln 2.4 + 11 5.6 + 19 21 + 13 51 + 18 40 + 12 108 + 14

Pyr 1.8 + 8 3.3 + 16 2.5 + 12 41 + 9 110 + 8 111 + 7

BaA 1.4 + 4 5.0 + 6 6.7 + 9 20 + 10 66 + 7 62 + 8

Ch 1.2 + 14 1.1 + 9 10 + 10 14 + 13 35 + 15 47 + 11

BbF 3.6 + 21 4.4 + 15 10 + 17 58 + 17 62 + 15 70 + 19

BkF 1.2 + 18 2.8 + 12 5.2 + 14 7.9 + 15 24 + 17 30 + 16

BaP 1.7 + 15 4.8 + 16 11 + 15 18 + 17 54 + 13 46 + 15

DahA 2.2 + 6 3.9 + 9 6.3 + 8 14 + 6 44 + 9 64 + 8

BghiP 0.73 + 10 2.7 + 8 8.4 + 9 11 + 8 28 + 9 31 + 10

Ind 2.3 + 11 4.3 + 7 7.9 + 12 14 + 10 34 + 10 34 + 8

Soil properties

pHKCl 6.0 6.9 7.0 7.0 6.9 6.3

TOC 10.7 14.0 21.8 29.4 37.7 43.2

+ , relative standard deviation (RSD) (%); (n ¼ 3). Na, naphthalene; Ace, ace-

naphthylene; Ac, acenaphtene; Fl, fluorene; phen, phenanthrene; Ant, anthracene;

Fln, fluoranthene; Pyr, pyrene; BaA, benz[a]anthracene; Ch, chrysene; BbF, benzo[b]-

fluoranthene; BkF, benzo[k]fluoranthene; BaP, benzo[a]pyrene; DahA, dibenz[a,h]

anthracene; B(ghi)P, benzo[ghi]perylene; Ind, indeno[1,2,3-cd]pyrene.

Concentration of Polycyclic Aromatic Hydrocarbons 1087

1996) (Table 3), the soil studied in the present study as characterized as

non-polluted.

The PAH content in sewage sludge used for soil fertilization are given in

Figure 1. The total PAH content determined in sewage sludge (i.e.,

5712 + 197 mg/kg) is lower than the results obtained by other Polish

researchers (Bodzek et al. 1997; Baran and Oleszczuk 2003) or abroad

(Smith et al. 2001; Stevens et al. 2003; Manoli and Samara 1999).

However, as with similar works, in the sewage sludge analyzed by the

present author, 3- and 4-ring PAHs are predominant, constituting about

60% of the total amount of the 16 PAHs analyzed. The following PAHs had

the highest content observed: phenanthrene, benzo[a]pyrene, benzo[ghi]pery-

lene, indeno[1,2,3-cd]pyrene. The contribution of 5- and 6-ring PAHs, which

are considered the most mutagenic and carcinogenic, ranged from 1.7 to

Table 2. Concentrations of PAH (mg/kg dry wt) and total organic carbon (TOC)

(g/kg) and pH in sewage sludge-amended soil (20–40 cm)

Sewage

sludge

dose:

PAH concentration

0% 1% 2.5% 5% 10% 20%

PAH

Na 1.7 + 11 1.4 + 13 5.2 + 11 5.5 + 15 7.0 + 13 4.6 + 15

Ace 13 + 9 12 + 17 17 + 11 29 + 19 33 + 18 26 + 15

Ac 11 + 16 10 + 11 14 + 12 29 + 21 36 + 17 27 + 19

Fl 2.5 + 7 2.7 + 8 3.4 + 9 7.8 + 15 9.4 + 12 8.2 + 10

Fen 0.74 + 9 0.74 + 10 1.7 + 7 2.7 + 8 3.8 + 9 3.0 + 7

Ant 0.02 + 8 0.04 + 9 0.26 + 13 0.55 + 9 0.99 + 8 0.65 + 9

Fln 1.1 + 11 2.1 + 9 3.6 + 17 8.7 + 13 16 + 11 11.2 + 5

Pir 2.2 + 6 1.7 + 13 5.1 + 9 7.0 + 13 15 + 14 9.7 + 10

BaA 1.4 + 5 1.4 + 11 2.5 + 8 4.0 + 11 8.5 + 10 5.1 + 18

Ch 1.3 + 11 1.3 + 10 2.7 + 8 4.4 + 8 7.1 + 6 4.6 + 9

BbF 2.0 + 19 1.2 + 14 3.0 + 13 4.8 + 7 12 + 9 7.3 + 10

BkF 1.4 + 6 1.1 + 14 2.2 + 16 5.1 + 7 15 + 15 10 + 16

BaP 1.8 + 11 1.6 + 15 3.0 + 18 4.8 + 13 9.2 + 15 5.4 + 12

DahA 0.0 1.5 + 8 2.1 + 4 2.9 + 6 5.5 + 3 6.8 + 8

BghiP 0.44 + 9 0.74 + 9 1.2 + 10 2.7 + 9 4.6 + 8 3.9 + 8

Ind 2.4 + 7 2.2 + 8 3.1 + 11 5.5 + 10 7.4 + 6 6.2 + 7

Soil properties

pHKCl 5.5 6.1 6.2 6.5 6.0 6.0

TOC 10.7 12.4 14.2 15.9 14.2 13.7

+ , relative standard deviation (RSD) (%); (n ¼ 3). Na, naphthalene; Ace, ace-

naphthylene; Ac, acenaphtene; Fl, fluorene; Phen, phenanthrene; Ant, anthracene;

Fln, fluoranthene; Pyr, Pyrene; BaA, benz[a]anthracene; Ch, chrysene; BbF, benzo[b]-

fluoranthene; BkF, benzo[k]fluoranthene; BaP, benzo[a]pyrene; DahA, dibenz[a,h]an-

thracene; B(ghi)P, benzo[ghi]perylene; Ind, indeno[1,2,3-cd]pyrene.

P. Oleszczuk and S. Baran1088

11.1%. The contribution of benzo[a]pyrene, which is considered as represen-

tative of the whole group, was 10.4% and was considerably increased

compared with most of the other sewage sludge types (Stevens et al. 2003).

In Poland, standards for the PAHs content in sewage sludge used in agri-

culture have not yet been worked out. On the basis of the standards of the

European Union (Baran and Oleszczuk 2003) for the maximum content of

the three PAHs [i.e., fluoranthene (5 mg/kg), benzo[b]fluoranthene

(2.5 mg/kg), and benzo[a]pyrene (2 mg/kg)] in sewage sludge, no cases of

excess were found.

Concentration of Sum of PAHs in Sewage Sludge-Amended Soil

Figure 2 presents the content of the PAH sum determined in soils fertilized

with sewage sludge. A comparison of experimental data with the expected

PAH content (calculated from mixing proportion) would show good

Table 3. Proposed classes of soil contamination with PAH of

IUNG (13)

Class of soil contamination Sum of PAH (mg/kg)

Noncontaminated , 200

Weakly contaminated 200–600

Contaminated 600–1000

Heavily contaminated .1000

Figure 1. PAHs concentration (mg/kg) in sewage sludge used in plot experiment.

Error bars represent standard deviation (SD), n ¼ 3. Description of individual PAHs

in Tables 1 and 2.

Concentration of Polycyclic Aromatic Hydrocarbons 1089

agreement for all sludge doses except for the 10% (300 t/ha). Within an

increase in the sludge dose, there was an almost twofold increase of the

PAH content with each increment up to a dose of 10% (300 t/ha). The differ-

ence between the PAH content in soil with a 10% (300 t/ha) addition of sludge

and soil with a 20% (600 t/ha) addition was not statistically significant.

An explanation of this phenomenon can be found in the sorption proper-

ties of the soils studied in relation to polycyclic aromatic hydrocarbons. Soil

with a sewage sludge content at a dose of 20% (and, hence, with a higher

value of organic matter content) can show higher sorption abilities in

relation to PAH than soil with a 10% sludge addition. Hence, it can be

gathered that sorption processes at an increased amount of organic matter

[soil with sewage sludge in dose 600 t/ha (20%)] are more intense and

clearer than in soil fertilized by sewage sludge in dose 300 t/ha (10%).

Moreover, with an increase in sewage sludge mass added, there is an

increase in the amount of organic matter of anthropogenic origin (dust, ash,

and soot) (Kogel-Knabner and Totsche 1998), which exerts a stronger

influence on the PAH than the influence exerted by natural matter. This

effect is due to the “highly” aromatic character of this type of matter and its

considerable specific surface area compared with natural organic matter

(Kogel-Knabner and Totsche 1998).

One of the important issues relating to the fate of organic contaminants,

including PAH, in soils fertilized with sewage sludge is the danger of their

leaching into the deeper layers of the soil profile, posing the danger of ground-

water contamination by these compounds. It has been determined (Jones et al.

1989; Tebaay, Welp, and Bremmer 1993; Cousins, Gevao, and Jones 1999)

that PAHs are accumulated mainly in the 0- to 10-cm soil horizon.

However, studies showed that PAH transportation into the depths of the soil

Figure 2. The concentration of S16 PAH in sewage sludge-amended soil.

P. Oleszczuk and S. Baran1090

profile is possible (Jones et al. 1989; Tebaay, Welp, and Bremmer 1993;

Cousins, Gevao, and Jones 1999; Baran, Oleszczuk, and Baranowska 2003).

Surfactants (Loser et al. 2000), dissolved organic carbon (Raber and

Kogel-Knabner 1997; Marschner 1998), soil colloids (McCarthy and

Zachara 1989), and some microorganisms and invertebrates (Jenkins

and Lion 1993; Belfroid, Sijm, and van Gestel 1996) can exert influence on

solubility and desorption of PAHs.

As can be seen in the data presented (Figure 2), after 3 days from the

introduction of sludge, only at the lowest dose (1%) was no increase in the

PAH sum in the 20- to 40-cm soil horizon noted. In the remaining doses, a

systematic increase of the PAH sum content up to a dose of 10% was

observed (Figure 2). A PAH sum content more than 26% higher was

observed in soil with a 10% sludge addition than in soil with the 20%

sludge dose added. At a depth of 0–20 cm, the differences in the PAH

content between sewage sludge doses of 20% and 10% were very small. As

has been already mentioned, the introduction of sewage sludge increases the

amount of organic matter in the soil (mainly in the 0- to 20-cm horizon)

(Table 1), which in organic pollutants such as PAHs plays the role of a

strong sorbent (Pignatello and Xing 1996) and significantly regulates the

fate of these compounds in the soil profile.

After 2 days from the application of sewage sludge, an increase of the

PAH sum content in the deeper horizon of the soil profile (20–40 cm) was

noted. The factors mentioned above, such as surfactants, DOC, and microor-

ganisms, can be responsible for this situation. An evaluation of the surfactants

on the migration abilities of atrazine and PAHs in sewage sludge-amended soil

was conducted by Litz and Muller-Wegener (Litz and Muller-Wagener 1998).

These authors found a clear influence of surfactants on the behavior of PAHs.

They also suggested that surfactants exert a greater influence on PAH deso-

rption (from soil matrix) than dissolved organic carbon. Pestke et al. (1997)

observed also that surfactants are more effective in solubilizing PAHs than

DOC. In our opinion, in the experiment described, all the above factors

play a role in PAH transfer, and to state which one of them is the most

important factor, further and more detailed studies are required. However,

the correlation coefficient calculated between the 16 PAHs content and the

total organic carbon content in the 20- to 40-cm soil horizon is not statistically

significant (0.624), suggesting only a slight contribution of DOC in PAH

migration in this experiment. It should be noted, however, that the assump-

tions presented can only be indicative, and additional studies are required to

confirm the role of DOC in PAH migration.

The difference in the PAH content in the individual soil horizons

increased with increased sludge doses (Figure 2). At a sludge dose of 1%,

the PAH content in the soil horizon at a depth of 0–20 cm was 1.76 times

that in the 20- to 40-cm soil horizon; and at doses of 10% and 20%, respect-

ively, the above values were 4.5- and 7.2-fold. Differentiation of the PAH

content at the depths analyzed was also strongly related to the PAH type.

Concentration of Polycyclic Aromatic Hydrocarbons 1091

In the cases of a 1% and 2.5% addition of sewage sludge, the PAH content

in the soils increased but did not exceed the level of the natural content

(,200 mg/kg dry wt) according to the proposal of IUNG (Maliszewska-

Kordybach 1996). In addition to the above classification, the dose of

sewage sludge at 5% qualified the soils for the weakly contaminated group

(Table 3). On the other hand, a sewage sludge addition of 10% and 20% classi-

fied the soils studied as polluted.

PAH Profiles in Sewage Sludge-Amended Soil

Of the 16 PAHs analyzed, 3-ring PAHs were the most abundant in soils with

from 1 to 10% sewage sludge supplement (0- to 20-cm soil horizon) and in all

experimental variants in the 20- to 40-cm soil horizon. The levels of ace-

naphthylene and acenaphthene were the highest (in both horizon) ranging

from 13 to 30% of the total PAHs and from 10 to 26%, respectively. By

increasing the sludge dose, their contribution decreased. The third most

abundant PAH was naphthalene, with an abundance ranging from 7 to 11%

(in 0- to 20-cm horizon).

The share of the remaining PAHs as a rule did not exceed 5% (horizon

0–20 cm). Certain variations were observed only in the cases of fluoranthene

and pyrene. In soil with a sludge addition of 20%, 5%, and 2.5%, fluoranthene

constituted about 10% of total PAHs, whereas in the remaining soils it was

below 7%. A similar situation was observed in pyrene; the only difference

was that the 10% share was observed in soils with the highest level of

sludge addition (20%, 10%, and 5%) (horizon 0–20 cm).

Variations similar to those observed at the 0- to 20-cm horizon were

observed also for fluoranthene and pyrene. The shares of benzo[b]fluoranthene

and benzo[k]fluoranthene were also higher, because their proportion in the

soils with 20% and 10% sludge addition was close to 10% of the total PAH

content.

When evaluating the potential migration abilities of individual PAHs into

the depths of the soil profile, it was found that acenaphthylene, acenaphtene,

and fluorene migrated relatively quickly. This determination was especially

evident in the case of the lowest doses (1–5% of sewage sludge). With

increased sludge content, the differences between the horizons in acenaphthy-

lene, acenaphtene, and fluorene and the remaining PAHs were more and more

evident.

On the basis of correlation coefficients calculated between the content of

individual PAHs in the soil horizon of 20–40 cm and the content of organic

matter (20–40 cm), positive and statistically significant values (p � 0.05)

were found only in naphthalene (0.806), with a less significant correlation

(p � 0.10) with acenaphthylene (0.737), acenaphtene (0.692), fluorene

(0.677), and phenanthrene (0.688). These correlations indicate the main role

P. Oleszczuk and S. Baran1092

of DOC in the migration of these four PAHs, whereas in the remaining PAHs

(more hydrophobic), surfactants can play a more significant role.

Attention should be drawn to the fact that the difference between the

naphthalene content in the 0- to 20-cm and 20- to 40-soil horizon was very

clear in all experimental variants (as with the 5- and 6-ring PAHs). In

addition, a high, positive correlation between total organic carbon (TOC)

and naphthalene occurred. On the basis of the above information, it can be

expected that naphthalene transfer in soil fertilized with sewage sludge is

related mainly to volatilization, whereas leaching is only slightly related to

transfer (and directly related to DOC as a carrier of this compound).

Figures 3 and 4 present the contribution individual PAHs according to

the number of rings in the horizon 0–20 and 20–40 cm, respectively. The

contribution of 2-ring naphthalene to the total PAHs remained at a stable

level for sludge doses of 20–2.5% at a horizon of 0–20 cm, whereas at a

dose of 1%, a considerable decrease was measured. The contribution of

naphthalene to total PAHs in soil without sludge was the lowest (Figure 3)

(horizon 0–20 cm). The share of naphthalene in the 20- to 40-cm soil

horizon remained at a constant level (about 4%) except for the experiment

with the sludge dose of 2.5% (75 t/ha).

In 3- to 5-ring PAHs, a clear differentiation of their share related to

the sludge dose was observed. With a decreased amount of additional

sewage sludge, an increase in the share of 3-ring PAHs was observed, and

the share of 4-and 5-ring PAHs was clearly decreased. This tendency can be

observed in both soil horizons; however, it is especially clear in the 0- to

20-cm horizon (Figure 3). There is no doubt that the phenomenon observed

was related to the composition of the sewage sludge. As can be seen in

Figure 1, 2- and 3-ring PAHs have a low share in the sewage sludge used

Figure 3. Contribution of PAHs according to the number of rings (horizon 0–20 cm).

Concentration of Polycyclic Aromatic Hydrocarbons 1093

for the present experiment. Four-ring PAHs and 5-ring benzo[a]pyrene were

predominant. Hence, an increase in the sludge dose was directly related to

the increase of these PAH groups.

The correlation coefficients calculated for changes in the contribution of

3-ring PAHs in relation to 4-ring PAHs (Figure 5) in the 0- to 20-cm soil

horizon showed a significant (p � 0.01) negative correlation r ¼ 20.935;

also in the 5-ring PAHs, there was a negative correlation, but it is not as

clear as in the 4-ring PAHs (r ¼ 20.792).

CONCLUSIONS

From the present results, the following conclusions can be drawn:

1. The addition of sewage sludge to sandy soil in an amount up to 300 t/ha

did not cause an increase in the PAH content in the soil to a level that

could pose a danger of these compound migrating into the human food

chain. Additional sewage of above 10% (dry weight basis of sewage

sludge on 1 ha) qualified the soils for the III8 pollution group (Table 3),

thus creating a danger for plants grown in these soils to become

polluted by PAHs.

2. Adding sewage sludge significantly influences the group content of PAH.

It decreases the contribution of mobile 3-ring hydrocarbons at the expense

of 4-ring hydrocarbons or especially mutagenic and carcinogenic 5-ring

PAHs.

Figure 4. The contribution of PAHs according to the number of rings (horizon

20–40 cm).

P. Oleszczuk and S. Baran1094

3. Introducing sewage sludge to soils is well justified from economical and

ecological points of view; however, usage requires, as has been shown by

the data presented in this work that the amount of dangerous compounds

in them be determined. This determination is especially important when

ecological agriculture is developed.

4. At 2 days after the introduction of sewage sludge at the lowest dose, an

increase in PAH content in the 20- to 40-cm soil horizon was noted. It

clearly shows the danger relating to PAH migration into the deeper

layers of the soil profile with the possibility of contaminating

groundwater.

ACKNOWLEDGMENTS

Financial support from the State Committee for Scientific Research (MNiI,

Warsaw), project no. 3P06S 042 25 is gratefully acknowledged.

P. Oleszczuk received a granted by the Foundation for Polish Science.

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