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Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS FROM A BRICK MANUFACTURING
LOCATION IN CENTRAL MEXICO
Ana Lilia BARRÁN-BERDÓN
1
, Virgilio GARCÍA GONZÁLEZ
2
, Gustavo PEDRAZA ABOYTES
2
,
Ismael RODEA-PALOMARES
1
, Alejandro CARRILLO-CHÁVEZ
3
, Humberto GÓMEZ-RUIZ
4
and
Beatriz VERDUZCO CUÉLLAR
2*
1
Facultad de Ciencias, Departamento de Biología, Universidad Autónoma de Madrid
2
Facultad de Química, Universidad Autónoma de Querétaro
3
Centro de Geociencias, Universidad Nacional Autónoma de México
4
Departamento de Química Analítica, Facultad de Química, Universidad Nacional Autónoma de México
*Corresponding author; beatriz-verduzco@hotmail.com
(Recibido octubre 2011, aceptado junio 2012)
Key words: brick kilns, high pressure liquid chromatography, urban soil
ABSTRACT
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and may
have natural or anthropogenic origin. Most environmental PAHs are products of in-
complete combustion or pyrolysis of fossil fuels and can be introduced into the soil via
atmospheric deposition. PAHs are relevant for public health and the environment due
to their possible carcinogenic, mutagenic characteristics, and their harmful inFuence
on soil organisms and plants. In this study, the levels and composition of 13 PAHs in
46 soil samples from San Nicolás, a brick manufacturing community in central México
were analyzed. Total concentrations of PAHs ranged from 7 ng/g to 1384 ng/g with an
average value of 220 ng/g. The most abundant PAH was naphthalene (Nap) followed
by Fuorene (±l), crysene (Chr), benzo[a]anthracene (BaA) and dibenzo[a,h]anthracene
(DahA). When comparing PAHs levels in soil with Mexican and USA regulations, it
was found that around the 52 % and 76 % of soils of San Nicolás had PAHs levels
higher than those considered normal or not dangerous for residential use based on
either of the aforementioned regulations. Moreover, total benzo
[
a
]
pyrene equivalent
(BaPeq) concentrations in soils of San Nicolás were higher than the maximum accept-
able concentrations established by Canada in 40-60 % of soils. Of special concern was
the high amount of DahA and BaP, two PAHs with a high carcinogenic potential. All
these factors implied a potential cancer risk to exposed population in San Nicolás.
Palabras clave: ladrilleras, cromatografía líquida de alta presión, suelo urbano
RESUMEN
Los hidrocarburos aromáticos policíclicos (HAP) están ampliamente distribuidos en el
ambiente y su origen puede ser natural o antrópico. La mayoría de los HAP ambientales
son productos de la combustión incompleta o pirólisis de combustibles fósiles y pue-
den ser introducidos al suelo vía depositación atmosférica. Los HAP son importantes
para la salud pública y el ambiente debido a sus posibles efectos carcinogénicos y
Rev. Int. Contam. Ambie. 28 (4) 277-288, 2012
A.L. Barrán-Berdón
et al.
278
mutagénicos y a su infuencia dañina en los organismos del suelo y las plantas. En este
estudio se analizaron los niveles y composición de 13 HAP de 46 muestras de suelo
de San Nicolás, una comunidad manufacturera de ladrillos en el centro de México.
Las concentraciones totales de HAP estuvieron entre 7 y 1384 ng/g con un promedio
de 220 ng/g. El HAP más abundante Fue el naFtaleno (Nap), seguido por el fuoreno
(±l), el criseno (Chr), el benzo[a]antraceno (BaA) y el dibenzo[a,h]antraceno (DahA).
Al comparar los niveles de HAP en el suelo con las normas mexicanas y estadouni-
denses, se encontró que alrededor de 52 y 76 % de los suelos de San Nicolás tiene
niveles más altos que los considerados normales o no peligrosos para uso residencial
con base en cualquiera de las dos normas mencionadas. Más aún, las concentraciones
equivalentes de benzo[a]pireno (BaPeq) en los suelos de San Nicolás Fueron más altas
que las máximas aceptables establecidas por Canadá en 40 a 60 % de los suelos. De
especial preocupación son las concentraciones de DaH y BaP, dos HAP con un elevado
potencial carcinogénico. Todos estos factores implican un riesgo potencial de cáncer
para la población expuesta de San Nicolás.
INTRODUCTION
PAHs are organic chemicals consisting of two or
more fused-benzene rings (Barra
et al.
2006). They
are usually classi²ed based on the number oF struc
-
tural rings in Low Molecular Weight (LMW) and
High Molecular Weight (HMW) PAHs. LMW are
those PAHs with two or three structural rings (naph-
thalene, acenaphthene, acenaphthylene, fuorene,
phenanthrene, and anthracene) and HMW PAHs are
those with Four, ²ve and six structural rings, namely
fluoranthene, pyrene, benzo
[
a
]
anthracene, chry-
sene, benzo
[
b
]
fouranthene, benzo
[
k
]
fuoranthene,
benzo
[
a
]
pyrene and dibenzo
[
a,h
]
anthracene, (Za-
karia
et al.
2002, Vinas
et al.
2009). PAHs are relevant
for human health and the environment due to their
carcinogenic and mutagenic characteristics (IARC,
2010) as well as their possible harmFul infuence on
soil organisms and plants (Boumard
et al.
1998, Wang
et al.
2011). Sixteen PAHs are consider as environ-
mental priority pollutants by the US Environmental
Protection Agency (USEPA 2009). Benzo
[
a
]
pyrene
is included in the Group 1 of human carcinogens by
IARC (
-
tion/index.php), and seven of them are considered
possible human or animal carcinogens: naphthalene
benzo
[
a
]
anthracene, benzo
[
b
]
fuoranthene, benzo
[
k
]
fuoranthene, chrysene, dibenzo
[
a,h
]
anthracene and
indeno
[
l,2,3-cd
]
pyrene (InP) (IARC 2010).
PAHs are ubiquitous in the environment and
may have natural or anthropogenic origins. Natural
sources oF PAHs include Forest ²res and volcanic
eruptions, but most environmental PAHs are products
of incomplete combustion or pyrolysis of fossil fuels
(Bostrom
et al.
2002). PAHs are introduced into the
soil from atmospheric deposits (Liu
et al.
2001) and
may remain in the soil for long periods of time due
to their non-polar characteristics, low solubility,
and high aF²nity to particulate material (Leonhardt
and Stahl 1998). Therefore, the soil is considered a
major reservoir of PAHs and is a good indicator of
environmental pollution and environmental risk for
human exposure to PAHs. In contrast to agricultural
and industrial soil, urban soil may also have a direct
effect on public health since pollutants in the soil
can be easily transferred to humans via ingestion,
inhalation or dermal contact (Mielke
et al.
1999,
Audebert
et al.
2012).
Methods for determining environmental de-
termination of PAHs include gas chromatography
with fame ionization detection (GC/±ID) and high-
performance liquid chromatography (HPLC) with
ultraviolet or fuorescence detector (HPLC-±LD)
(USEPA1986). While GC/FID is the most sensitive
technique, it is subject to background interferences
from other carbonaceous sources. HPLC provides
the necessary sensitivity in combination with higher
speci²city (Miege
et al.
2003).
PAH contamination in soils has been an issue
of increasing concern in recent years (Nadal
et al.
2007, Ray
et al.
2008, Agarwal
et al.
2009, de La
Torre-Roche
et al.
2009, Jiang
et al.
2009, Ma
et
al.
2009). Levels and pro²les oF PAHs have been
analyzed in soils from different land uses such as big
cities and industrial or agricultural soils around the
world revealing that, in general, the greatest amounts
of PAHs are found in big cities and heavy industrial
areas (Nadal
et al.
2007, Agarwal
et al.
2009, Jiang
et
al.
2009). In developing countries, there is a lack of
information about presence and distribution of PAHs
and other toxic substances in soils. Of special con-
cern is the presence of toxic substances linked with
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS
279
special activities developed in these countries, such
as indoor wood combustion, waste disposal, brick
manufacturing, and other home-made manufactur-
ing activities (Maríinez-Salinas
et al.
2009, Trejo-
Acevedo
et al.
2009). These low-scale industrial
activities are usually the principal economic activity
of these communities and are frequently carried out
within residential areas implying a possible increased
risk to exposed population.
San Nicolás, Querétaro (Mexico) is a com-
munity with a population of approximately 50 00
inhabitants whose principal economical activity is
fre-brick production in homemade kilns. This is a
typical way of life in many communities in Center
and Northern México. There are approximately 300
homemade kilns in San Nicolás. As combustion
agent, a variety of low quality fuels and residues
such as wood, garbage, tires, and fuel and waste
oils are used since they are less expensive than
readily combustible fuels. The combustion in the
kilns occurs at low temperatures (800 ºC) in which
incomplete combustions could lead to the forma-
tion of PAHs, especially those of higher molecular
weight and more carcinogenicity. Moreover the
kilns do not have any emission flters For PAHs
or other organic and inorganic pollutants such as
volatile organic compounds (VOCs), SO
2
, NO
x
, and
CO which are emitted directly into the atmosphere.
This emission of pollutants without safety condi-
tions could produce an increase of PAH levels in
soil especially in areas close to the kilns, leading
to high risk situations for the population and the
environment.
In this research project, the presence and dis-
tribution of PAHs in the soil of the community of
San Nicolás, a Mexican homemade brick producing
community were analyzed in order to obtain basic
information about PAHs contamination in soils. This
information may be relevant to future risk assessment
analyses associated with that economical activity
(Martinez-Salinas
et al.
2009). For this purpose RP-
HPLC-FLD analyses of 13 environmentally relevant
PAHs, including six carcinogenic PAHs, in 46 soil
samples from the aforementioned location were car-
ried out. The source of the PAHs was analyzed in
order to identify potential risk situations that would
affect the local population and/or the environment.
The levels of PAHs found in San Nicolás were com-
pared with the quality goals for PAHs in soils estab-
lished in three legal standards: The Norma Ofcial
Mexicana NOM-138-SEMARNAT/SS-20 (NOM,
2003), the Regional Screening Levels (RSL) for
Chemical Contaminants at Superfund Sites proposed
by USEPA (USEPA 2009) as well as the Canadian
Soil Quality Guidelines for Carcinogenic and other
Polycyclic Aromatic Hydrocarbons (CCME 2008)
which are all examples of more rigorous regulations.
MATERIALS AND METHODS
Sampling
San Nicolás is located in Central Mexico at lati-
tude 20º31´ N and longitude 99º54´ W at an altitude
of 1890 m above sea level. A total of 46 homoge-
neously distributed soil samples in San Nicolás and
surrogated areas were collected. Sampling sites are
depicted in
fgure 1a
. The samples were taken with
a stainless spoon from up to a depth of 2 cm from
the soil surface. These samples were transferred into
polyethylene bags and preserved at 4 ºC in the dark
for future analysis.
Chemicals
The 13 PAHs analyzed in this study were naph-
talene (Nap), acenaphthylene (Acl), ±uorene (²l),
anthracene (Ant), phenanthrene, (Phe), benzo
[
a
]
anthracene (BaA), chrysene (Chr), fluoranthene
(Flu), pyrene (Py), benzo
[
b
]
±uoranthene, (Bb²),
benzo
[
k
]
±uoranthene (Bk²), benzo
[
a
]
pyrene (BaP)
and dibenzo
[
a,h
]
anthracene (DahA). PAHs standards
were from Supelco (USA) with 99 % purity. All sol-
vents (n-hexane, acetone and acetonitrile) used were
of HPLC grade from Baker (USA). The water used
was HPLC grade.
Sample extraction
Sample extraction was performed essentially
as established in USEPA (SW846) Method 3540c
(Soxhlet extraction)(USEPA 1996): The samples
were oven-dried for 24 h at 110 ºC, smashed into
small pieces, homogenized with a mixer, and later
sieved through a 2 mm sieve. Subsamples of 15 g
were made and extracted in a Soxhlet apparatus for
8 h with 100 mL acetone-hexane 1:1. The extracts
were concentrated to 1 mL by using a rotary evapo-
rator, supplemented with 10 mL of acetonitrile and
concentrate, again to 1 mL, to exchange solvent for
acetonitrile.
Analysis
The concentration and composition of PAHs
were determined by means of high performance
liquid chromatography essentially as recommended
by USEPA (SW846) Method 8100 (Polynuclear
Aromatic Hydrocarbons)(USEPA 1986). HPLC was
A.L. Barrán-Berdón
et al.
280
equipped with a fuorescence detector (HPLC-FLD)
using a HP 1100 Series HPLC with HP-5972 FLD
with wavelength programming. A zorbax AAA col-
umn (150 mm × 4.6 mm and 4.1 μm particle size)
for reverse-phase HPLC was used. The PAHs were
eluted using a water/acetonitrile gradient, starting
with a 60 % acetonitrile, a linear gradient to 67 %
acetonitrile in 20 min, 67 % acetonitrile held for 26
min and linear gradient from 67 % to 100 % acetoni-
trile ±or 6 minutes. The column temperature was ²xed
at 25 ºC. The FLD was set to vary the excitation and
emission wavelengths throughout the period of the
analysis in order to ²x the conditions ±or each PAH.
Quantitative analysis of PAHs was made using the
external calibration method with calibration curves
with ²ve points ±or each individual component.
PAHs identi²cation was per±ormed by comparing
the retention time with those of the set of standards.
As example, a chromatogram of the PAH standard
used for calibration is shown in
fgure 2
.
Quality control
Procedural blanks, spiked blanks and duplicated
samples were routinely analyzed together with ²eld
samples. No interference was detected. Limit of
detection (LOD) was calculated as tree times the
noise of the chromatogram in a blank sample. Limit
o± quanti²cation (LOQ) was calculated as 10 times
the standard deviation of the blank. Both LOQ and
LOD are shown in
table I
.
The procedure was checked ±or recovery e±²
-
ciencies by analyzing uncontaminated soil spiked
with PAH standards essentially as recommended
by USEPA (SW846) Method 8100 (Polynuclear
Aromatic Hydrocarbons) (USEPA 1986), as fol-
lows: Uncontaminated soil samples were divided
in homogeneous subsamples of equal weight.
Subsamples were spiked with a PAH concentration
of 5 mg/L and were dried 110 ºC until a constant
weight was achieved. The percentages of recovery
were estimated comparing the difference of weight
between the spiked and un-spiked samples and the
inicial amount (5 mg) of PAH added. The average
recoveries (n=3) ranged from 87 to 90 %. The varia-
tion in duplicates was less than 10 %.
Total carcinogenic potency estimation
The total BaPeq concentration is an estimation of
the total carcinogenic potency of a mixture of PAHs
related to that of BaP. Total BaPeq concentrations
were calculated based on the toxic equivalency fac-
tors (TEFs) approach, also referred to as potency
equivalence factors (PEFs) approach (Nisbet
et al.
1
2
3
4
5
6
7
8
9
11
15
17
18
28
29
31
40
13
22
41
23
44
27
10
43
26
25
24
45
32
46
35
36
42
37
20
19
21
16
12
14
30
33
34
39
38
a
b
c
0 - 100 ng/g
101 - 300 ng/g
301 - 600 ng/g
> 601 ng/g
0 - 0.6 ng/g
0.61 - 5.3 ng/g
5.31 - 50 ng/g
> 50 ng/g
Fig. 1.
Sampling sites and brick kilns distribution (a), total PAH
concentrations (b) and total BaP
eq
concentrations (c), in
San Nicolás. Δ: Brick kiln
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS
281
1992, USEPA 1993, WHO/IPCS 1998, CCME 2008).
Based on this method, the BaPeq of each parental
PAH is calculated by multiplying its concentration by
its TEF. The TEF of a given compound is its toxicity
factor relative to the BaP carcinogenic potency. The
carcinogenic potency of a mixture could then be es-
timated from ΣBaPeq of each individual component.
Several TEFs (or PEFs) have been proposed for PAHs
(Nisbet
et al.
1992, USEPA 1993, Kalberlah
et al.
1997, CCME 2008) for a review see (Bostrom
et al.
2002). In the present research the TEFs suggested by
the Canadian Soil Quality Guidelines (CCME 2008)
were adopted. These Canadian TEFs are those of the
World Health Organization (WHO/IPCS 1998) with
minor changes based on the latest scientiFc informa
-
tion reported (CCME 2008).
RESULTS AND DISCUSSION
Total and individual PAHs concentrations in the
46 soil samples of San Nicolás are shown in
table
II
. Total PAHs concentrations ranged from 7 ng/g to
1384 ng/g with a mean concentration of 220 ng/g.
Spatial distribution of total PAHs concentrations are
shown in
fgure 1b
. The highest total PAHs concentra-
tions were found in sampling sites 1, 2, 4, 5, 6, 7, 8,
15, 16, 17 and 43, located northwest of San Nicolás, an
area of great brick kiln density. The lowest total PAHs
concentrations corresponded to soil samples 25, 19, 33
and 36, located at the south of San Nicolás which is an
area with a minor prevalence of brick kilns. All 13 indi-
vidual PAHs were detected in soil samples at least one
time (
Table II
). The mean number of individual PAHs
detected by sample was four PAHs and the maximum
number was 10 PAHs. The concentration of individual
PAHs varied considerably in soil samples, from non-
detectable levels to maximum concentrations of 664
ng/g for Chr, 374 ng/g for Nap, 343 ng/g for Fl, 256
ng/g for BaA, 181 ng/g for Ph, 161 ng/g for Flu, 143
ng/g for Py, 139 ng/g for Ace and DahA, 59.4 ng/g for
TABLE I.
MAIN QUALITY CONTROL PARAMETERS
OF THE CALIBRATION CURVES GET FOR
THE STANDARD PAHs.
PAH
r
2
Concentration
range
(ng/g)
Retention
time
(min)
LOQ
(ng/g)
LOD
(ng/g)
Nap
0.98
2.40-12.0
6.99
0.19
0.32
Ace
0.98
2.20-11.0
11.15
0.19
0.31
Fl
0.99
1.85-9.25
11.38
0.10
0.17
Ph
0.99
0.90-4.50
12.65
0.05
0.09
Ant
0.97
0.42-2.10
13.86
0.15
0.25
Flu
0.98
1.38-6.90
16.78
0.35
0.58
Py
0.97
0.82-4.10
18.43
0.08
0.13
BaA
0.97
0.80-4.00
23.95
0.12
0.19
Chr
0.98
0.44-2.20
24.62
0.04
0.06
BbF
0.97
0.80-4.00
31.10
0.07
0.12
BkF
0.97
0.10-0.50
31.64
0.01
0.02
BaP
0.97
0.11-0.55
32.24
0.01
0.02
DahA
0.97
7.00-35.0
33.55
1.02
1.69
r
2
: Regression parameters, LOQ: Limit of quantiFcation,
LOD: Limit of detection.
Fig. 2.
Representative chromatogram of one of the concentrations of the standard solution of PAHs used for the
calibration
A.L. Barrán-Berdón
et al.
282
TABLE II.
CONCENTRATION (1 ng/g) OF TOTAL AND INDIVIDUAL PAHs AND COMPARISON WITH THE QUALITY
OBJECTIVES FOR PAHs IN SOILS ESTABLISHED IN TWO LEGAL STANDARDS: THE NORMA OFICIAL MEXI-
CANA NOM-138-SEMARNAT/SS-20 (SEMARNAT 2003) AND THE REGIONAL SCREENING LEVELS (RSL) FOR
CHEMICAL CONTAMINANTS AT SUPERFUND SITES (USEPA 2009)
Nap
2
Ace
Fl
Ph
Ant
Flu
Py
BaA
2
Chr
2
BbF
2
BkF
2
BaP
2
DahA
2
ƩHAPs
1
Nº. of
PAHs >
NOM
Nº. of
PAHs >
USEPA
NOM (ng/g)
2
2
8
2
2
USEPA
(ng/g)
140
3400
2300
17000
2300
1700
0.15
15
0.15
1.5
0.015
0.015
Sample
1
203.0*
63.7*
-
148.0
6.3
161.0
119.0
186**
200*
-
2*
1.3*
-
1090.3
1
5
2
168.4*
23.4*
30.8
181.0
-
84.6
143.0
256**
494*
-
1.6*
1.5*
-
1384.3
1
5
3
-
-
-
36.9
-
-
-
-
106*
7.8**
2.9*
1*
-
154.6
1
4
4
-
-
32.9
-
4.0
-
-
190**
151*
-
1.7*
1.1*
98.3**
479.0
2
5
5
-
-
89.5
10.5
4.4
-
-
222**
664*
-
0.6
1.2*
67.6**
1059.8
2
4
6
131.0
-
-
9.8
-
-
-
162**
81.8*
6.1**
0.5
1.3*
-
392.5
2
4
7
159.0*
-
343.0
-
-
21.1
-
-
-
-
-
-
-
523.1
0
1
8
113.9
34.3* 210.0
46.2
7.5
-
-
-
9.9
-
-
-
-
421.8
0
0
9
-
-
124.0
19.9
-
-
-
-
-
-
-
-
-
143.9
0
0
10
-
-
-
17.6
-
-
-
-
57.4*
-
-
-
-
75.0
0
1
11
-
-
-
-
4.3
73.1
-
-
-
7.9**
0.4
1*
46.4**
133.1
2
3
12
176.0*
-
-
-
-
-
-
-
-
-
-
-
-
176.0
0
1
13
-
-
-
8.5
-
-
5.8
-
-
-
-
-
78.8**
93.1
1
1
14
113.0
139.0*
-
-
-
-
-
-
-
-
-
-
-
252.0
0
0
15
192.0*
40.4*
-
-
-
-
-
39.8**
-
-
2.2*
0.9*
47.3**
322.6
2
5
16
219.0*
-
-
-
-
-
17.7
8.7**
11.7
-
-
-
62.7**
319.8
2
3
17
-
-
-
13.7
8.3
-
35.3
36.2** 194*
-
-
-
35.3**
322.8
2
3
18
-
-
-
-
-
-
-
6.63**
9.1
-
-
-
-
15.7
1
1
19
-
-
-
-
-
-
-
8**
-
-
-
-
-
8.0
1
1
20
-
-
-
-
-
-
-
15.6**
16.6*
-
0.7
2.02**
-
34.9
2
3
21
-
-
-
-
-
-
-
18.9**
23.1*
-
-
3.28**
-
45.2
2
3
22
-
-
-
15.2
-
-
-
49.6**
74.5*
8.3**
0.4
-
-
148.0
2
3
23
-
-
-
-
-
-
-
31.8**
-
17.8**
4.3*
1.9*
98.9**
154.7
3
5
24
-
-
-
-
-
-
-
11.3**
-
-
1.4
1.1*
138.5**
152.3
2
3
25
-
-
-
-
-
-
6.4
-
-
-
0.5
-
-
6.9
0
0
26
-
-
-
-
-
-
10.1
28.7**
-
-
0.6
-
-
39.4
1
1
27
-
-
-
-
-
-
-
-
-
-
0.7
-
-
0.7
0
0
28
43.5
-
55.4
-
-
-
-
10.5**
-
-
0.9
-
-
110.3
1
1
29
37.9
-
-
-
-
-
-
-
-
-
-
-
-
37.9
0
0
30
10.6
-
-
-
-
-
-
11.5**
-
-
1
1.2*
123.6**
147.9
2
3
31
37.9
-
-
-
-
-
-
-
-
-
0.6
-
-
38.5
0
0
32
12.9
-
-
-
-
-
-
-
-
-
-
-
-
12.9
0
0
33
12.3
-
-
-
-
-
-
-
-
-
-
-
-
12.3
0
0
34
15.3
-
34.6
-
-
-
-
-
-
-
-
-
-
49.9
0
0
35
12.9
-
-
-
-
-
-
-
-
-
0.6
-
-
13.5
0
0
36
12.3
-
-
-
-
-
-
-
-
-
-
-
-
12.3
0
0
37
17.2
-
-
-
-
-
-
-
-
-
-
-
-
17.2
0
0
38
15.3
-
34.6
-
-
-
-
-
-
-
-
-
-
49.9
0
0
39
34.9
-
-
-
-
-
-
-
-
-
0.8
1.2*
-
36.9
0
1
40
93.3
-
-
8.4
9.4
-
-
19.1**
-
59.4**
7.4*
4.1**
98.6**
299.7
4
5
41
14.4
-
-
3.2
-
-
68.7
-
47.1*
-
0.3
0.9*
43.5**
178.1
1
3
42
53.4
-
-
7.9
7.3
-
-
-
-
-
-
-
-
68.6
0
0
43
125.0
-
-
-
-
-
18.8
97.2** 180*
19.8**
-
-
-
440.8
2
3
44
216*
-
-
-
-
-
22.5
-
-
-
-
-
-
238.5
0
1
45
45.6
-
-
-
3.9
2.7
-
-
-
-
-
-
-
52.2
0
0
46
374.0
-
-
-
-
-
-
-
-
-
-
-
-
374.0
0
1
1
ΣPAHs = Σconc. of (Nap, Ace, Fl, Ph, Ant, Flu, Py, BaA, Chr, BbF, BkF, BaP, DahA);
2
: PAH catalogued as possible human or animal carcinogen.
(Nisbet and Lagoy 1992, IARC 2010); NOM (ng/g): limit in ng/g for individual PAHs established by NOM-138-SEMARNAT/SS-20 (SEMARNAT
2003). USEPA (ng/g): limit in ng/g for individual PAHs established by the Regional Screening Levels (RSL) for Chemical Contaminants at Superfund
Sites (USEPA 2009); *Concentration of individual PAH higher than the established under USEPA criterion; ** Concentration of individual PAH higher
than the established under both USEPA and NOM criteria; - Below LOQ
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS
283
BbF and less than 10 ng/g for Ant, BkF and 10 BaP
(
Table II
). When comparing the PAHs levels detected
in San Nicolás with others previously reported, it was
found that PAHs concentrations were higher than those
reported in urban sites of the United States/ Mexico
border region, but were similar or higher than those
of these industrial sites (De La Torre-Roche
et al.
2009). On the other hand, levels of PAHs in San
Nicolás were lower than those reported from soils
in big cities around the world such as New Orleans
(Mielke
et al.
1999), Shanghai (Jiang
et al.
2009),
Beijing (Tang
et al.
2005), Harbin (Ma
et al.
2009)
or Delhi (Agarwal
et al.
2009).
Occurrence (%) and contribution (%) of indi-
vidual PAHs to the total sum of PAHs are shown
in
table III
. The parental PAH with the highest
abundance was Nap, present in 66 % of samples and
accounting for 26 % of the ΣPAHs followed by Fl,
Chr, BaA and DahA which accumulated 55 % of the
ΣPAHs and were present in 20 %, 35 %, 43 % and
26 % of samples, respectively. It is noteworthy the
low abundance of Ph, Flu, BbF and Py which have
been repeatedly reported as abundant PAHs in urban
contaminated sites. Also the high abundance and
distribution of Chr, BaA and DahA that are PAHs
usually reported in high quantities from industrial
areas (Nadal
et al.
2007, De La Torre-Roche
et al.
2009, Lu
et al.
2009, Ma
et al.
2009).
Low molecular weight (LMW) and high molecu-
lar weight (HMW) PAHs pro±les in soil samples of
San Nicolás are shown in
fgure 1
. LMW PAHs such
as Nap, Ace, Fl, Ph and Ant are considered general
markers of petrogenic origin of PAH contamination
in soils. HMW PAHs such as Flu, Pyr, BaA, Chr,
BbF, BkF, BaP and DahA are considered typical
markers of pyrogenic origin of PAH contamination
(Zakaria
et al.
2002, Vinas
et al.
2009). As shown
in
fgure 3
, both LMW and HMW were present in
the majority of samples of San Nicolás with highly
variable contents. LMW and HMW PAHs con-
tributed similarly to the total PAHs concentration,
47 % and 43 %, respectively, indicating a mixed
origin of PAHs (petrogenic and pyrogenic) in San
Nicolás. When some commonly used indexes, such
as: BaA/(BaA + Chr) or Ant/(Ant + Phe) (Yunker
et al.
2002, Agarwal
et al.
2009, Ma
et al.
2009)
based on individual PAH concentration ratios were
applied to identify possible sources of PAHs, values
of BaA/(BaA + Chr) = 0.38, and Ant/(Ant + Phe) =
0.1 indicating a mixed origin of PAHs were found.
[BaA/(BaA +Chr) ≤ 0.35 suggests petrogenic origin;
BaA/(BaA +Chr) > 0.4 suggest pyrogenic origin; and
values between these indicate a mixed origin. When
applying Ant/(Ant + Phe) index, Ant/(Ant + Phe) <
0.1 suggests petrogenic origin; Ant/(Ant + Phe) >
0.1 suggests pyrogenic origin, and Ant/(Ant + Phe)
= 0.1 indicates a mixed origin of PAHs. The mixed
origin of PAHs, both petrogenic and pyrogenic, in
the soils of San Nicolás may be related to the poor
operational conditions of the brick kilns and the
density of these kilns, approximately 300 kilns in the
area of the testing locations (
Figure 1a
). The fuels
TABLE III.
OCCURRENCE, CONTRIBUTION OF INDIVIDUAL PAHs TO THE
TOTAL SUM OF PAHS (%) AND SAMPLES (%) EXCEEDING NOM
AND USEPA CRITERIA
PAH
Occurrence
(%)
Contribution to
the total sum of
PAHs (%)
samples
exceeding NOM (%)
samples
exceeding USEPA (%)
Nap
60.87
26.23
-
17.39
(1.33)
1
Ace
10.87
2.97
-
0.00
Fl
19.57
9.42
-
0.00
Ph
30.43
5.19
-
0.00
Ant
19.57
0.55
-
0.00
Flu
10.87
3.38
-
0.00
Py
21.74
4.41
-
0.00
BaA
43.48
13.90
43.47
(35.23)
1
43.48
(469.84)
1
Chr
34.78
22.88
-
28.26
(11.74)
1
BbF
15.22
1.25
15.21
(9.07)
1
15.22
(121.05)
1
BkF
47.83
0.32
0.00
15.22
(1.91)
1
BaP
34.78
0.25
6.52
(1.41)
1
34.78
(104.17)
1
DahA
26.09
9.26
26.08
(39.14)
1
26.09
(5219.44)
1
1
: Fold that the mean concentration of a speci±c PAH is higher than that established
under the legal standard.
A.L. Barrán-Berdón
et al.
284
are hand supplied using tins to fll the Fuel reservoirs
of the kilns and also the direct disposal of fuels to the
soils frequently occurred as a result of this method
of refueling. Rain could spread the fuels in soils
generating a general petrogenic background PAH
contamination. In fact, Nap, the less non polar (semi-
polar) PAH, which may be easily spread by water,
appeared to be the most ubiquitous in San Nicolás.
On the other hand, the principal components of the
HMW fraction in San Nicolás had been previously
described as common markers of pyrolitic processes,
i.e, BaA and Chr have been described as markers of
both coal and diesel combustion (Simcik
et al.
1999,
Larsen
et al.
2003) and DahA is considered as an
ubiquitous product of incomplete combustion (Ray
et al.
2008). Even Nap in some cases could indicate
the presence oF signifcant combustion products From
low temperature pyrogenic processes (Jenkins
et al.
1996). In fact, De La Torre-Roche
et al.
(2009) found
an ubiquitous Nap contamination in soil of the United
States / Mexico border region, relating it to pyrolitic
activities occurring in
maquiladoras
and brick kilns
of Ciudad Juárez; this may suggest that part of the
high quantities of Nap found in San Nicolás could be
also related to brick kiln pyrolitic activity.
In order to evaluate whether the PAH concentra-
tions found in this study pose a potential risk for hu-
man health, the PAH levels found in San Nicolás were
compared with two environmental standards (criteria)
For PAHs in soil: the Mexican oFfcial standards For
PAHs in soils regulated by NOM-138-SEMARNAT/
SS-2003 (SEMARNAT 2003) and the Regional
Screening Levels (RSLs) for Chemical Contaminants
at Superfund Sites established by USEPA (USEPA
2009), as a more restrictive standard. Quality objec-
tives for PAHs in residential soils established by
NOM and USEPA criteria as well as soil samples
exceeding these criteria are shown in
Table II
.
México established environmental and safety qual-
ity objectives in residential soils for six HMW PAHs:
BaA, BbF, BkF, BaP, InP and DahA. Five of these PAHs
were analyzed and it was found that 24 soil samples
(52 %) had PAHs contents higher than those established
in these legal limits for at least one PAH. Some samples
accumulated legal exceedances for up to 3 or 4 different
PAHs (
Table II
). The accumulated legal exceedance
(%) for each individual PAHs is shown in
table III
.
The maximum number of accumulated exceedances
corresponded to B
[
a
]
A with 43 % of samples exceeding
NOM criteria, followed by DahA and BbF with a 26 %
and 15 % of samples exceeding these criteria. BaP was
found to exceed legal criteria in only 3 samples and no
exceedances were found for BkF. PAH concentrations
exceeding those of the legal limits, with means from
1.4-fold for BaP to 39 and 35-fold for DahA and BaA,
respectively, are shown in
table III
.
Fig. 3.
Prevalence of low molecular weight (LMW) PAHs and high molecular weight (HMW) PAHs in
soils from San Nicolás
Sample
12345678910
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
0
200
400
1000
1200
1400
LMW PAHs
HMW PAHs
Concentration (ng/g)
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS
285
When comparing the PAH levels found in the
soil samples from San Nicolás with the the Regional
Screening Levels (RSLs) for Chemical Contaminants
at Superfund Sites established by USEPA (2009) it
was found that 30 soil samples (63 %) had PAH con-
tents higher than those stipulated by these criteria
for residential use of soils for at least one PAH.
Some samples had PAH contents higher than those
established by these criteria for up to Fve different
PAHs (
Table II
). The accumulated legal exceed-
ance (%) for each individual PAH is shown in
table
III
. The maximum accumulated exceedeance cor-
responded to BaA with 43 % of samples above that
legal criteria, followed by BaP, Chr and DahA, with
a 34, 28 and 26 % of samples exceeding these crite-
ria, respectively. BkF, BbF and Nap also exceeded
their legal criteria in 15, 15 and 19 % of samples,
respectively. When analyzing the magnitude of the
mean exceedance of the legal limits of the PAH
concentrations in samples, (
Table III
), it was found
a very high exceedance for DahA, BaA, BbF and
BaP with mean concentrations exceeding 5219-fold,
469-fold, 121-fold and 104-folds those concentra-
tions established by USEPA criteria, respectively.
A high exceedance but not to the same extent was
also found for Chr with a mean concentration ex-
ceeding 10-fold its criteria (
Table III
). Finally it
was found a low exceedance for BkF and Nap with
mean concentrations exceeding the criteria 1.91-fold
and 1.33-fold, respectively. No exceedances were
found for Ace, Fl, Ant, Flu and Py.
Based on these regulations, it was found that 52 %
of soils in San Nicolás had PAH levels higher than those
considered as healthy or not dangerous for residential
use within NOM regulations and this percentage in-
creased up to 76 % of soils under USA regulations.
Moreover, some PAHs were found in concentrations
of up to 39 and 5219-fold higher than those estab-
lished in NOM and USA criteria, respectively. These
two factors could imply a generalized PAH contami-
nation in San Nicolás which may be considered as
very large in some areas (see
Fig. 1b
).
Total carcinogenic PAH (Nap, BaA, Chr, BbF,
BkF, BaP and DahA) concentrations in soil samples
of San Nicolás are shown in
table IV
. Total carci-
nogenic PAH concentrations ranged from 0 ng/g to
955 ng/g, with an average value of 105 ng/g with
a mean contribution to the ΣPAHs of 42 %. Total
benzo(a)pyrene equivalent (BaPeq) concentrations
are also shown in
table IV
. Total BaPeq concentra-
tions in soil samples of San Nicolás ranged from
0 ng/g to 140 ng/g, with a mean concentration of
24.89 ng/g. Spatial distribution of total BaPeq in
San Nicolás is shown in
Fig. 1c
. The distribution of
total BaPeq concentrations was more heterogeneous
than that of the total PAH concentration, see
Fig. 1b
,
Fnding the highest total BaPeq for sampling sites 4,
5, 16, 23, 24, 30 and 40 which are spread out all over
San Nicolás, but seems to be linked with the high
density of brick kilns of the northern area (samples
4, 5, 16 and 40, and) as well as with the major trafFc
point in San Nicolás (samples 23, 24, and 30). This
phenomena can be explained by the lower capacity
of the heavier PAHs to be spread far away from their
emission points accounting near of their source (De
La Torre-Roche
et al.
2009).
The Canadian Soil Quality Guidelines (CCME,
2008) established maximum acceptable concentrations
(MACs) for carcinogenic chemicals in soils based
on an incremental risk of cancer from soil exposure
(ILCR) of 10
–6
or 10
–5
, i.e., an incremental risk of 1 in
1 million or 1 in 100 000, respectively. This regulation
TABLE IV.
SUM OF TOTAL CARCINOGENIC PAH CON-
CENTRATIONS AND TOTAL TEFs AS
B[a]Peq
IN SOIL SAMPLES OF SAN NICOLÁS
Sample
Ʃ6HAPs
1
ƩTE±s
2
Sample
Ʃ6HAPs
1
ƩTE±s
2
(ng/g)
BaPeq
(ng/g)
(ng/g)
BaPeq
(ng/g)
1
389.3
22.2
24
152.3
140.9
2
753.1
32.2
25
0.5
0.1
3
117.7
3.1
26
29.3
2.9
4
442.1
120.1
27
0.7
0.1
5
955.4
97.7
28
11.4
1.1
6
251.7
18.9
29
0
0
7
0
0
30
137.3
126.1
8
9.9
0.2
31
0.6
0.1
9
0
0
32
0
0
10
57.4
0.6
33
0
0
11
55.7
48.3
34
0
0
12
0
0
35
0.6
0.1
13
78.8
78.8
36
0
0
14
0
0
37
0
0
15
90.2
52.4
38
0
0
16
83.1
63.7
39
2
1.3
17
265.5
40.9
40
188.6
111.4
18
15.73
0.7
41
91.8
44.9
19
8
0.8
42
0
0.1
20
34.9
3.8
43
297.3
13.5
21
45.2
5.4
44
0
0
22
132.8
6.6
45
0
0.1
23
154.7
106.2
46
0
0
1
: Σ6HAP = Σconc. of Nap, BaA, Chr, Bb±, Bk±, BaP and DahA;
2
: ΣTE±s = Σconc. X TE± of (Nap, BaA, Chr, Bb±, Bk±, BaP
and DahA). TEFs for individual PAHs were: BaA = 0.1, Chr =
0.01, BbF = 0.1, BkF = 0.1, BaP = 1, DahA = 1.
(CCME. 2008)
A.L. Barrán-Berdón
et al.
286
was established for all land use with the following
values: a MAC of 0.6 ng/g of BaPeq for an ILCR of
10
–6
and a MAC of 5.3 ng/g of BaPeq for an ILCR of
10
–5
. When comparing total BaPeq in soil samples of
San Nicolás with these MACs, it was found that 41
% and 60 % of soil samples of San Nicolás had total
BaPeq levels higher than those established as MACs
for ILCRs of 10-5 and 10
–6
, respectively. The mag-
nitude of the mean exceedace of these MACs was of
41-fold and 4-fold the MACs for both 10
–6
and 10
–5
ILCRs, respectively. Moreover, some samples (4, 5,
13, 16, 23, 24, 30 and 40), had BaPeq concentrations
higher than 100-fold of those established as MAC for
an ILCR of 10
–5
. These high levels of total BaPeq
concentrations implied a generalized carcinogenic
risk for the exposed population in San Nicolás, which
may be considered very high in some areas. When
discussing carcinogenic PAHs, of special concern
is the high presence of BaP (detected in 34 % of
samples) which has been classifed as carcinogen
for humans (Group 1 of IARC) (2010). The case
of DahA was also remarcable: it was detected in 26
% of samples with a mean contribution to the total
BaPeq concentrations of 90 % in those samples with
the higher total BaPeq: samples 4, 5, 11, 13, 15, 16,
17, 23, 24, 30, 40 and 41 (
Table IV
and
Figure 1a-
c
). DahA have been classifed as probable human
carcinogen, and included in the group 2A of IARC
(IARC 2010). The high abundance of, chrysene and
benzoFuoranthenes was also remarkable: despite the
low TEFs values generally assigned to them based
on laboratory rodent data, recent studies using other
biomarkers of carcinogenic potency such as bacterial
mutagenicity tests or enzymatic activity tests suggest
that chrysene and benzoFuoranthenes can be more
carcinogenic than BaP (Bosveld
et al.
2002). In the
same line, Nap can be also a source of carcinogenic
risk since it has been recently included in the group 2
of the IARC list of possible carcinogenic substances
for humans (IARC 2010). Taking in to account the
high abundance and distribution of this PAH, the
carcinogenic risk for population can be even higher.
The nature of the homemade brick-kiln activity in
San Nicolás implies that all members of the family
contribute to that economical activity. In fact, the
majority of the kilns are located in the back yards
of the houses. Children play near the kilns. Children
have been recognized as being the most sensitive to
environmental contaminants having specifc path
-
ways of exposure to contaminants, such as: inges-
tion through hand to mouth activities (Calabrese
et
al.
1997, Lu
et al.
2009) or ingestion through breast
milk (Hooper 1999, Rodas-Ortiz
et al.
2008). They
may be exposed at certain stages of development
that may lead to health issues that will appear later
in life (IPCS 2006). Martinez-Salinas
et al.
(2009)
when analyzing urinary 1-hydroxypyrene (1-OHP)
in children of different communities in Mexico as
biomarker of exposure to PAH contamination, found
that children living in communities with brick kiln
industry were at risk of PAH genotoxic exposure
levels. Trejo-Acevedo
et al.
(2009), when analyzing
blood and urine of the children of San Nicolás found
levels of HBCs (metabolites of PCBs) and lead at
concentrations higher than those reported to cause
neurotoxic damage as well as high levels of lindane,
arsenic and DDE (main metabolite of DDT). They
concluded that San Nicolás is a hot spot of special
concern in Mexico due to the high health risk for
population caused by the exposure to persistent
organic pollutants (POP’s) and other contaminants
(Trejo-Acevedo
et al.
2009). We suggest the need of
cancer risk assessment analyses and ongoing moni-
toring in San Nicolás and other brick manufacturing
communities in Mexico in order to determine the
extent of the risk to human health, especially for
children related to this economic activity. In this
way, corrective and preventive strategies to reduce
the exposed population and hopefully reduce the risk
of this exposure could be estabilished.
CONCLUSIONS
Results of this study showed that residential soils in
San Nicolás are polluted by PAHs. Nap, Fl, Chr, BaA
and DahA are the most abundant PAHs. By applying
several approximations to assess the origin of PAHs, a
mixed origin of PAHs both petrogenic and pyrogenic
could be derived. When comparing PAHs levels in
soil with Mexican and USA regulations, it was found
that approximately 52 % and 76 % of soils of San
Nicolás had PAHs levels higher than those considered
as healthy or not dangerous for residential use under
those two aforementioned regulations. Moreover, total
BaPeq concentrations in the soils of San Nicolás were
higher than the maximum acceptable concentrations
established by Canada for an ILCR of 10
–6
in 60 %
of soils and for an ILCR of 10
–5
in 40 % of soils.
Of special concern was the high presence of BaP, a
known human carcinogen, as well as DahA, a PAH
with a high carcinogenic potential. All these factors
could imply a generalized carcinogenic risk for the
exposed population. We suggest the need for cancer
risk assessment analyses and ongoing monitoring in
San Nicolás and other brick-manufacturing communi-
POLYCYCLIC AROMATIC HYDROCARBONS IN SOILS
287
ties in México in order to determine the extent of the
risk for human health. This is especially important for
the children linked to this economic activity. We also
propose the perform of civil engineering studies in
order to establish the possibility of ongoing strategies
to reduce the emission of PAHs, as well as decontami-
nation strategies to reduce the continued exposure for
the population and the health risks thereof.
ACKNOWLEDGEMENTS
This study was supported by grant QRO-
2004-C01-26 Fondo Mixto CONACyT, Querétaro
State Government (Mexico). The authors would like
to thank Dr. Francisca Fernandez Piñas for her sug
-
gestions and acknowledge Silvia C. Stroet for editing
the English content of this document.
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