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Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
Lourdes Monserrat MEZA TREJO
1
*, Margarito QUINTERO NUÑEZ
2
and Benjamín VALDEZ SALAS
2
1
Facultad de Ingenieria, Unidad Mexicali, Universidad Autónoma de Baja California, México
2
Instituto de Ingenieria, Universidad Autónoma de Baja California, México
*Corresponding author; montserrat.meza@uabc.edu.mx
(Recibido septiembre 2012, aceptado diciembre 2013)
Key words: heavy metals, sediments, urban roads and emission factors
ABSTRACT
A chemical sediment characterization of urban streets in the city of Mexicali at Baja
California, Mexico, was conducted to estimate the most important heavy metals along
with PM
10
and PM
2.5
emission factors (EF) to evaluate the amount of particulate matter.
Sampling was conducted from february to may 2008, following a random statistical
design, in 60 sampling sites on a georeferenced map at UTM 11 North. Samples were
identifed and treated in the laboratory, aFter undergoing cracking, drying, sieving,
and weighing to get less than 75 microns of sediment by using a dry method. Twelve
representative samples were selected for chemical characterization using energy dis-
persive X-rays (EDX) and inductively coupled plasma (ICP). The most signifcant
elements found were zinc (Zn) and lead (Pb) with concentrations ranging from 1 to 15
mg/kg and 11 to 25 mg/kg, respectively, corresponding to the third classifcation From
a reFerence set oF a study by US EPA in 1981-1997. The clay type known as illite was
identifed in Four specifc samples.
Palabras clave: metales pesados, sedimentos, calles urbanas y factores de emisión
RESUMEN
Se llevó a cabo la caracterización química de los sedimentos de las calles urbanas de
Mexicali, Baja California, México, para estimar los metales pesados más importantes.
Asimismo, se obtuvieron los factores de emisión (FE) de PM
10
y PM
2.5
que permitieron
cuantifcar la cantidad de material particulado en la ciudad. El muestreo se realizó de
febrero a mayo 2008, tomando como base un diseño estadístico al azar, en 60 sitios lo-
calizados en un mapa georeferenciado a UTM 11 Norte. Las muestras fueron evaluadas
en el laboratorio, atendiendo los procesos de pulverización, secado, tamizado y pesado
para de esa manera obtener sedimentos menores a 70 micrones al utilizar el método seco.
Fueron seleccionadas 12 muestras representativas para la caracterización química al usar
las técnicas de energía dispersiva de rayos X (EDRX) y plasma inductiva asociada (PIA),
mediante las cuales se identifcaron los elementos más signifcativos como el zinc (Zn)
y el plomo (Pb) con concentraciones que varían entre 1 y 15 mg/kg y 11 a 25 mg/kg,
respectivamente, que corresponden a la tercera clasifcación derivada de un estudio lle
-
vado a cabo por la agencia de protección ambiental de los EUA (USEPA) en 1981-1997,
asimismo se identifcó la arcilla tipo illita en cuatro muestras específcas.
Rev. Int. Contam. Ambie. 30 (1) 15-26, 2014
L.M. Meza Trejo
et al.
16
INTRODUCTION
Vehicular trafFc emissions have been a global
concern, since the number of vehicles is increas-
ing rapidly thus creating a threat to humans and the
environment. Most studies are based on the underly-
ing regulation for particle emission and gases from
exhaust pipes that can be of great concern as they are
emitted directly into the environment.
There are also emissions originating from tire
wear, lubricant leakage on urban roads, and particles
produced by the mechanical deterioration from ve-
hicle moving parts, which are considered the main
polluting sources for the environment. This together
with dust from roads caused by vehicular trafFc is
considered by some researchers (Abu-Allaban 2003,
Hassan
et al
. 2006, Ketzel
et al
. 2007, William
et al
.
2008, Goosens and Buck 2009, Malkoc
et al
. 2010,
Zafra
et al.
2011) as being a result of indirect emis-
sions from the road, tires and wake turbulence, as
shown in
fgure 1
.
According to research conducted in several coun-
tries like Venezuela (Machado 2008), Spain (Zafra
et
al
. 2007, 2011) Italy (Imperato
et al
. 2003), Jordan
(Hassan
et al
. 2006) and Turkey (Malkoc
et al.
2010),
heavy metals are found as a result of the mechanical
action of the vehicles on urban roads, either by the
interaction of tires with the road surface or the wear
of the brake and clutch.
This particulate matter (PM) is continuously
resuspended by the effect of vehicular trafFc due to
wake turbulence and wind speed, thus producing an
unequal distribution of the PM in the environment,
giving rise to an emission factor (EF). This EF is
expressed as the mass of particles in a unit area as
a result of vehicle kilometer traveling (VKT, g/km),
(Etyemezian
et al.
2003, USEPA 2006) and helps to
estimate the PM on the roadways.
Nowadays, there are European and American
models to estimate the independent parameters of the
EF where independent variables are the same, i.e.,
percentage of sediment load, speed, weight and type
of vehicle and weather conditions (wind speed and
direction and air temperature). The process in which
variables are measured is what makes them different
and characteristic of the site. Therefore, EF values are
not similar, because they sometimes do not exceed 1
kg/VKT, whereas in some desert regions the value is
above 10 kg /VKT (Meza
et al
. 2010).
The city of Mexicali, Baja California is located
in the Sonora desert, which is exposed to Santa Ana
winds and has a great deal of dust particles in the
air, derived from the soil which covers hundreds of
acres with a white blanket of dust from agricultural
activities and wind erosion; in addition to the emis-
sions caused by local activities. The PM deposited
on urban roads is pulverized by the mechanical ac-
tion of vehicles and then resuspended leaving wake
turbulence that is associated with the PM having an
aerodynamic diameter of 10 microns (PM
10
) and 2.5
microns (PM
2.5
).
Records show that since 1997, Mexicali has been
exceeding the maximum limit of PM
10
(120 μm/m
3
)
for 20 days according to NOM-025-SSA (2005), which
was the Frst year when formal measurement of air
quality monitoring stations in the city began. These vi-
olations increased by over 40 days from 2000 to 2006.
The information was obtained from the Air Quality
Fine fraction
(PM
2.5
and PM
10
)
Worn brake
and clutch
Identifie
s
Correlate
s
Identifies
Function
Pollutants from the
combustion of petrol
and diesel
PM
2.5
fraction
Vehicule maintenance
(not the weather and
road conditions).
PM
EMISSIONS
FROM
VEHICULAR TRAFFIC
External factor:
tire type,
turbulence induced
by vehicles
weather conditions
and road conditions.
Erosion of street, tire wear and
resuspension dust
Identifies
Fine fraction
(PM
2.5
and PM
10
)
Fig. 1
. Pollutants from gasoline and diesel combustion (Meza 2009)
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
17
System (AQS) data base of the USEPA and from Zuk
et al
. (2007), reporting 43 days of exceedences in 2005.
As a result, Mexicali occupies the Frst place amongst
the US-Mexico border cities in relation to reference
pollutants such as PM
10
. Based on the latter, we will
present a characterization study of sediments collected
at different sites of several urban streets in the city
of Mexicali, B.C., where estimated PM
10
and PM
2.5
emission factors showed that use of motor vehicles on
city roads are a major source of pollution.
MATERIALS AND METHOD
Study area
Mexicali is located in northwestern Mexico (32º
40’ N, 115º 27’ W), in the state of Baja California
(
Fig. 2
) bordering in the north with the state of
California. It presents important climatic contrasts
since the recorded summer temperatures reach 52 ºC;
whereas in the winter the minimum temperatures
range around 0 ºC. The average temperature during
the year is 25 ºC. It has an average annual rainfall of
75 mm. During the summer there is a predominance
of winds from the southeast and from the northwest
in winter (Quintero 2004, García
et al
. 2007,).
Design and feld work
Considering a population size (N) of 266 basic
geostatistical areas (BGA) of the city of Mexicali and
by applying an equation for sample size (n) (Carrillo
1999, de la Torre 2002) we found that n=30 BGA. By
following a randomized block design these 30 sites
were distributed on a georeferenced map to UTM 11
North to be sampled (Meza
et al
. 2010). Based on the
selection of four areas, northwest (NW), northeast
(NE), southwest (SW) and southeast (SE) and previ-
ous work (INE 1999, Mendoza 2007, Osornio 2011)
the points were identiFed as shown in
fgure 3
. We
followed the sampling technique known as Appen
-
dices C1, USEPA, AP-42, as criteria for where and
how samples should be collected (USEPA 1993a).
Sampling started in february 2008. It was car-
ried out twice a week and ended in May 2008. This
sampling was done using a geographic positioning
system (GPS) as a means to identify the site of sedi-
ment collection.
2.3 Laboratory work (dry and wet)
Two types of samples were processed following
the ±ow chart shown in
fgure 4
. The procedure
details are explained as follows:
The Frst sample was collected on site and identi
-
Fed as wet, to carry out the physical characterization,
i.e., the determination of soil texture, following the
Bouyoucos densimeter method (ASTM No. 152 and
NOM-021-RECNAT-2000).
For the second sample, the Appendix C.2.,
USEPA, AP-42 technique (USEPA 1993b) was used
to obtain the load and percentage of sediment less
than 75 microns in paved and unpaved roads. This
technique consists of a series of steps starting with
the quartering of the sample, followed by drying,
sifting and weighing. The objective was to obtain
sediment smaller than 75 microns, which was after-
wards identiFed as dry.
California, USA
32º
31º
30º
117º
29º
116º
115º
114º
113º
N
Mexicali
Tijuana
Ensenada
MEXICO
Baja
California
Fig. 2.
Geographic location of the City of Mexicali B. C., in northwestern Mexico
L.M. Meza Trejo
et al.
18
Twelve samples were selected and subsequently
treated (less than <75μm) from several sites which
were representative of the study area, based on the
working tool designed (GPS). The goal was the
chemical characterization of samples, using both the
dry and wet techniques.
The analytical dry method used was the dispersive
electron X-ray spectroscopy (EDX), which resulted in
an initial characterization of the general constituents
of the type of soil in the region, shown in
fgure 5
.
The second analysis known as wet method focused
on the characterization of heavy metals contained in
clay from the monitoring sites. Afterwards, there was
a digestion of the samples using the EPA technique
(USEPA 1996) and the method of inductive coupled
plasma (ICP), as shown in
fgure 6
.
The equipment for ICP analysis was a Thermo
Fisher ICAP6500, which is a coupled plasma emis-
sion spectrometer. Specimens were carefully pre-
treated in order to obtain a sample solution (particle
size less than 75 μm previously dried and sieved) in
aqua regia [diluted nitric acid (HNO
3
)] for the diges-
tion of heavy metals according to 3050 B (USEPA
1996) heated at 95 ºC and then Fltered, to obtain an
aqueous solutions to be analyzed by ICP.
RESULTS
The treatment of samples using the dry method
was core for the work carried out in the laboratory
and the chemical characterization utilizing the EDX
(a)
(b)
Fig. 3.
Location of monitored sites identiFed by the symbol “+”within their respective BGA (a) paved areas and (b) unpaved
areas
v
v
v
Sample
collected
in situ
Cracking, drying
and sieving
C.2 USE EPA, 1993
Texture (soil type)
Determination of pH
Determination of
conductivity
(NOM- 021-RECNAT-2000)
Sediment from
roads with a
size< 75μm
EDX
ICP
ACID
DIGESTION
Wet
method
analysis
Dry method
analysis
Results of soil
elements: C, O, Na,
Mg, Al, Si, S, Cl, K,
Ca, Ti y Fe.
Results for compounds,
in particular identifying
the type of clay.
Results for
significant metals
Cu, Pb and Zn
Fig. 4.
Methods of analysis for chemical and physical characterization in the laboratory
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
19
method, which helped to identify the elements from
the selected area (
Fig. 5
). The analysis resulted in
the semi-quantitative elemental composition of ele-
ments according to soil type in the study area; the
most important are Al, Fe, Si, Mg and K, reported as
percent by weight of elements in the sample (% Wt).
An analysis of
figure 5
shows derived salty
soils, with high levels of iron, with the possibility
of formation of crystals such as Fe
x
(SO
x
)
x
, NaCl,
as well as a high presence of aluminum and silica,
and the potential formation of magnesium (Mg) or
potassium (K) aluminate. The presence of inorganic
compounds is related to the characteristics of the
types of soils and clays. For unpaved roads a sandy
clay loam was found and for paved roads a sandy
loam, in accordance with the soil classifcation tri
-
angle by texture of the United States Department of
Agriculture (Schaetzl 2005).
In order to analyze the samples we used the EDX
method resulting in the presence of potassium associat-
ed with illite [(K, H
3
O) Al
2
Si
3
AlO
10
(OH)
2
], which was
confrmed in a second analysis oF Four samples tested.
This type of clay may not be considered a pollutant, but
the identifcation oF other elements that aFFect human
health and the environment, such as heavy metals, is
considered important as there are standards regulating
hazardous risks, which should be taken into account.
A method that helps to learn what kind oF con
-
taminants might be present on the roads is the ICP
method, and it was used For the identifcation oF heavy
metals that have some effects on health such as Pb,
Hg, Zn and Cd (Machado 2007).
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Wt
Analysis site
CO
Na
Mg
Al
SiSC
lK
Ca
Ti
Fe
27 unpav.
14 unpav.
9 unpav.
5 unpav.
22 unpav.
13 unpav.
19 unpav.
10 unpav.
22 pav.
6 pav.
3 pav.
26 pav.
Fig. 5.
Constituents of selected paved and unpaved sediment samples from urban roads
in the city of Mexicali obtained by using the EDX method
0
50
100
150
200
250
300
350
400
14
un
p
av.
27
un
p
av.
9 unpav.
5 unpav.
22 unpav.
13 unpav.
19 un
pav.
10 pav.
2
2
pav.
6
pav.
3
p
av.
2
6 pav.
14
p
av.
Metal concentration, mg/kg
Analysed
site
Ag, mg/kg
Bi, mg/Kg
Cd, mg/Kg
Cu, mg/Kg
Ni, mg/Kg
Pb, mg/Kg
Zn, mg/Kg
Fig. 6.
Metal concentrations in the analyzed sites obtained using the ECP method
L.M. Meza Trejo
et al.
20
Figure 6
shows the results from the sites of the
selected samples, under the following decreasing
order Al> Fe> Pb> Zn> Cu> Bi> Ni> Ag> Cd. The
presence of the Frst two elements is characteristic
of the type of soil, as discussed in the previous para-
graph and the other elements may be contributions
from anthropogenic sources.
Based on these results the elements selected for
analysis were in order of importance Pb> Zn> Cu
(
Fig. 7
). There is a particular interest on the effects
of these elements on health and its potential effect
in the community.
Malkoc
et al.
(2010) have conducted a number of
studies attempting to determine the sources of heavy
metals in roadside soils and they found that Pb, Zn, and
Cu largely come from trafFc pollution, whereas Ni is
correlated to naturally occurring sources, Cd originates
from industrial contaminants, and Cr found in roadside
soil is associated with atmospheric deposition.
Furthermore, some metals, such as Cd, Cu, Ni, Pb,
and Zn, were found to exacerbate various diseases
due to a rapid increase in their environmental con-
centrations attributable to urbanization and several
road sites with high concentration of Pb, Zn and Cu
are associated with trolley transportation (Imperato
et
al.
2003, Machado
et al.
2007, Zafra
et al.
2011 and
Xiao-san
et al.
2012) ) but in Mexicali it is related
to passenger trucks or trucks larger than three axles,
which are characteristic of the vehicular ±eet used
by the manufacturing and industrial sector.
DISCUSSION
Data from previous research (Meza
et al.
2010)
carried out in Mexicali produced the following emis-
sion factors: 0.923 kg/km PM
10
and 0.734 kg/km
PM
2.5
(VKT) on paved roads and 2.33 kg/km PM
2.5
(VKT) and 0.58 kg/km PM
10
(VKT) on unpaved
roads. The results were taken as mean products,
which gave opportunity to identify a normal distribu-
tion, and later a Spearman correlation analysis was
carried out that would provide a direct link between
signiFcant values as it is subsequently described.
Analysis by Spearman correlation
The EF associated to PM
10
and PM
2.5
were a di-
rect correlation of 0.89 for paved roads, which sets a
precedent to reconsider the following correlation of
inorganic elements found in the samples analyzed for
both values.
Table I
, shows an inverse correlation of
aluminum (Al) versus lead (Pb) and zinc (Zn) with
–0.7527 and –0.7308 values, respectively. It also
highlights the signiFcant value of the correlation of
Pb and Zn, equal to 0.7692.
Table I
also presents other signiFcant correlations
(values listed in bold) as is the case of silver (Ag)
with bismuth (Bi) and zinc (Zn), along with cadmium
(Cd) and nickel (Ni). Nevertheless our attention
focused on Pb and Zn for their effects on health in
certain countries that count with urban soil content
standards in this subject (Machado
et al
. 2007, 2010,
Zafra
et al.
2007).
Figure 8 (a)
and
(b)
show the tendencies for Al vs.
Pb and Zn. In order to correlate Al with heavy metals
(Pb and Zn), the analysis was based on the fact that
the sampling site was identiFed as being sandy clay
loam or clay type. In previous research (El-Hasan
et al
. 2006), Al was classiFed as an immovable ele
-
ment. Hence, it indicates that the greater amount of
aluminum, the lower content of Pb and Zn.
Also, the Zn/Pb correlation is signiFcant because
the characteristics in some images that were obtained
from the semi-quantitative analysis by EDX, as
0
50
100
150
200
250
300
350
400
27 un
pa
v.
14 un
pa
v.
9
u
np
av
.
5 un
p
av
.
2
2 un
pa
v
.
13
unpa
v.
19 un
pa
v
.
10
p
av
.
22 pav
.
6 pa
v.
3
p
av
.
26 pa
v
.
14 pa
v.
Metal concentration, mg/kg
Analysed
site
Cu, mg/Kg
Pb, mg/Kg
Zn, mg/Kg
Fig. 7.
Heavy metals: lead (Pb), zinc, (Zn) and copper (Cu)
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
21
TABLE I.
SPEARMAN CORRELATIONS OF METALS AND HEAVY METALS IN DIFFERENT URBAN ROADS
Variable
Al
mg/kg
Ag
mg/kg
Bi
mg/kg
Cd
mg/kg
Fe
mg/kg
Ni
mg/kg
Pb
mg/kg
Zn
mg/kg
Cu
mg/kg
Al mg/kg
1.0000
0.4869
0.4903
–0.2479
0.3681
–0.0604
–0.7527
–0.7308
–0.4505
Ag mg/kg
0.4869
1.0000
0.6137
0.1760
–0.1073
0.0963
–0.5034
–0.6630
0.0825
Bi mg/kg
0.4903
0.6137
1.0000
0.3277
0.2061
0.4067
–0.2507
–0.3371
0.0780
Cd mg/kg
–0.2479
0.1760
0.3277
1.0000
–0.2981
0.7186
0.4393
0.3452
0.4707
Fe mg/kg
0.3681
–0.1073
0.2061
–0.2981
1.0000
0.1484
–0.0220
–0.0495
–0.0604
Ni mg/kg
–0.0604
0.0963
0.4067
0.7186
0.1484
1.0000
0.4066
0.2582
0.1923
Pb mg/kg
–0.7527
–0.5034
–0.2507
0.4393
–0.0220
0.4066
1.0000
0.7692
0.4780
Zn mg/kg
–0.7308
–0.6630
–0.3371
0.3452
–0.0495
0.2582
0.7692
1.0000
0.4835
Cu mg/kg
–0.4505
0.0825
0.0780
0.4707
–0.0604
0.1923
0.4780
0.4835
1.0000
Pb, mg/kg(L)
Zn, mg/kg(R)
600
0
4
6
8
10
12
14
16
18
20
22
24
26
28
20
40
60
80
100
120
Pb mg/kg
Zn mg/kg
140
160
180
200
220
240
800
1000
1200
1400
1600
1800
2000
Al, mg/kg
0
20
40
60
80
100
120
140
160
180
200
220
240
(a)
(b)
Pb, mg/kg
4
6
8
10
12
14
16
18
20
22
24
26
28
Zn, mg/Kg
Al, mg/kg:Pb, mg/kg:
r = -0.6192, p = 0.0240
Al, mg/kg:Zn, mg/kg:
r = -0.7023, p = 0.0074
Pb:Zn r=0.76, p=0.0028
Fig. 8.
Pb vs. Zn correlation in paved and unpaved roads
L.M. Meza Trejo
et al.
22
shown in
fgure 9
, may be due to the presence of Zn
(silver color) and Pb (gray color) for Site 19 (
Fig 11
)
which was not paved.
Figure 10
shows signifcant heavy metals such as
zinc (a), and lead (b), which become relevant based on
their concentrations and observing the standards. The
graph of lead is always above the standard (
Fig. 10a
)
and zinc just in the last two urban roads (
Fig. 10b
).
In the case of copper it was not possible to com-
pare it with a standard on urban soils as there is no
one reported in the literature. In addition to this, the
correlation was not signifcant For Cu in
table I
.
However, Machado (2007) considered that copper is
important because it is attributed mainly to vehicular
traFfc on the city roads, thereFore more research
should be done in this subjet.
Osornio
et al
. (2011) identifed elements such as
Cu and Zn in PM
10
and PM
2.5
using a high volume
sampler and soil samples in the periphery of the
samplers in the city and rural areas of Mexicali that
were classifed as being oF anthropogenic origen, but
Pb was not detected.
Heavy metals at a spatial level
Another way of observing the behavior of concen-
tration values oF heavy metals identifed was by means
oF a spatial analysis based on the work tool selected,
where the sampling sites were taken using the UTM
coordinates (x, y). The coordinate (z) represents the
concentration oF metals identifed on a single base,
which were analyzed using the wet ICP method.
Afterwards, the information was organized in
an Excel 2007 table with three columns, supported
by the SurFer tool. The kriging interpolation option
was utilized, which is based on the result of the
chemical analysis of the compound samples of the
analyzed sites. Two graphs were obtained (
Figs. 12
and
13
) and were superposed on a map of the city
of Mexicali.
Figures 11
and
12
show the values of metal
concentrations (Zn and Cu), spatially distributed.
When wind direction is taken into consideration, it
is possible to identify areas with high concentrations
of these heavy metals; where the highest values are
associated to the south-east part of the city, disregard-
ing the central area, close to an air quality monitoring
station.
Regarding copper (
Fig. 12
) there was also a high
concentration peak Found in the heavy traFfc area,
in addition to the drag of dust deposited by the wind
direction predominantly from the north. This is due
to the fact that the sampling moment corresponds to
the months of April and May.
The latter relates to a study by Osornio
et al
.
(2011) where soil samples were taken on the roads
near the north-east and the south-east sites for inocu-
lation of live cells in the laboratory to see the effect
of composition on the potential generation of cancer,
that may be caused by particulate matter taken From
soil samples . The presence of copper and zinc in the
Osornio’s soil samples can be compared with those
of points 14 and 22 located in paved roads tested.
1.2
0.9
0.7
0.5
0.2
0.0
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
Fe
Ti
Ca
K
Cl
S
Si
Al
O
KCnt
C
Fe
Na
9.00
Mg
Fig. 9.
EDX analysis of site 19, which was unpaved, North-East zone (NE)
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
23
0
50
100
150
200
250
(a)
(b)
27 unpav.
1
4 unpav.
9 unpav.
5
u
npav.
22 unpav.
13
unpav.
19 unpa
v
.
10 pav.
22 pav.
6 pav.
3 pav.
26 pa
v
.
14 pav.
Concentration, mg/kg
Analysed
site
Pb, mg/Kg
Standard Pb,
1-10 mg/kg
0
5
10
15
20
25
30
2
7 un
pav.
14
u
npav.
9 unpav.
5 unpav.
22 unpav.
13 unpa
v.
19 unp
a
v.
10
p
av.
22 pav.
6 pav.
3
pav.
26 pav.
14 pav.
Concentration, mg/kg
Analysed
site
Zn, mg/Kg
Stantard
Zn,
11-25 mg/kg
Fig. 10.
Heavy metal behavior in paved and unpaved roads a) lead and b) zinc
ESTADOS UNIDOS DE AMERICA
ESTADOS UNIDOS MEXICANOS
3614000
3612000
3610000
3608000
3606000
3604000
638000
640000
642000
644000
East (m)
North (m)
646000
648000
650000
652000
Fig. 11.
Isolines of zinc values in paved and unpaved roads for particulate matter less than 75
μ
m (Meza
2009)
L.M. Meza Trejo
et al.
24
With regards to zinc (
Fig. 11
), points 27 (unpaved)
and 26 (paved) can be taken as an example of a high
value, since they are above existing standard, 11.25
mg/kg (Machado
et al
. 2007)
Figure 13
highlights the presence of lead, where
some studies have linked it to tire wear, brake and
clutch. The highest concentrations are in the center
of the city of Mexicali which represents sampling
point 14, with associated concentrations of 180 mg / kg
of lead in soil. This is in a way explainable as in the
south-east and north-east parts of the city there are
more vehicles per day. In samples collected from
the outskirts of the city, lower concentrations of Pb
were found.
Fig. 13.
Isolines of lead values in paved and unpaved roads in particulate matter less than
75
μ
m (Meza
et al.
2009)
3614000
3612000
3610000
3608000
3606000
3604000
638000
640000
642000
644000
East (m)
North (m)
646000
648000
650000
652000
Fig.12.
Isolines of copper values in paved and unpaved roads collected from particulate matter
less than 75
μ
m (Meza 2009)
14pav
22pav
13Unpaved
3pav
6pav
26pav
10pav
159
14Unpaved
115.3
140.1
105.7
9Unpaved
85
63.2
118.8
219.6
19Unpaved
45.5
162.8
22Unpaved
193.6
96.4
378.3
27Unpaved
5Unpaved
638000
640000 642000 644000
East (m)
North (m)
646000 648000 650000 652000
3604000
3606000
3608000
3610000
3612000
3614000
HEAVY METALS IN URBAN ROAD SEDIMENTS OF THE CITY OF MEXICALI, MEXICO
25
The above charts show a future line of research on
the importance of mechanical maintenance of vehicles,
which indicates that not only particulate matter emis-
sions from tailpipes, but also indirect emissions that
have been studied (tire wear, brake wear, etc.) in some
regions of North America, Europe and recently in
Mexico, are important to consider (Meza
et al.
2009).
CONCLUSIONS
1. On paved roads EF values for PM
10
kept a close
relationship to the EF for PM
2.5
with a Spearman cor-
relation of 0.9235. Periodic maintenance and cleaning
on main roads in the city, counteract the accumulation
of Fne particulate matter.
2. In four samples selected in the area under
research, illite type clay was identiFed, which was
analyzed by the EDX method. This compound is
considered hazardous to health, as it has a very
large surface area as a substrate and works as a
carrier of heavy metals and inorganic elements. The
most signiFcant Fndings in relation to heavy metals
were the relationship amongst Al, Pb and Zn, and
for other metals there was a signiFcant afFnity of
Ag with Bi and Zn along with Cd with Pb and Ni.
This supports the argument of heavy metals found
as a result of the mechanical action of the vehicles
on urban roads.
3. After the digestion of sediments process in the
four areas selected in the study zone, all of them were
analyzed by using the ICP, resulting in a comparative
concentration values which were above the limits of
international standards established by EPA.
4. Vehicles may contribute to air pollution, apart
from fuel combustion or from the traveling along the
streets of the city, derived from the wear of the compo-
nents such as the breaking system (Zn, Cu, Cr, Ni and
Mn), tires (Pb) and clutch (Cu, Zn, Cd, Sb, Ba, and Pb),
which are very important for their effects on health.
REFERENCES
Abu-Allaban M., Gilles J.A., Gertler A.W., Clayton R. and
ProfFt D. (2003). Tailpipe, resuspended road dust, and
brake-wear Emission ±actors from on road vehicles.
Atmos. Environ. 37, 5283-5293.
De la Torre C. (2002). Metodología de la Investigación.
Mc. Graw Hill, México, D.F., pp. 141-160.
El-Hasan T., Batarseh M., Al-Omari H., Anf Ziadat, El-
Alali A., Al-Naser F., Berdanier B.W. and Jiries A.
(2006). The distribution of heavy metal in urban street
dust of Karak City Jordan. Soil & Sediment Contam.
15, 357-365.
García C.O.R., Jauregui O.E., Toudert Z.V. and Tejeda
M.A. (2007). Detection of the urban heat island in
Mexicali B.C., Mexicali B. C., Mexico and its relation-
ship with land use. Atmósfera 2, 111-131.
Goossens D. y B. Buck. (2009). Dust emission by off road
driving: Experiments on 17 arid soil types, Nevada,
USA, Geomorphology, 107, 118-138.
Imperato M
.
, Adamo P., Naimo D., Arienzo M., Stanzione D.
and Violante P. (2003). Spatial distribution of heavy
metals in urban soils of Naples city (Italy), Environ.
Pollut. 124, 247-256.
Ketzel M., Omstedt G., Johansson C., During I., Pojola
Mia, Oettl D., Gidhagen L., Wahlin P., Lohmeyer A.,
Haakana M. and Berkowicz R. (2007). Estimation and
validation of PM
2.5
/PM
10
exhaust and non-exhaust
emission factors for practical street pollution model-
ling, Atmos. Environ. 41, 9370-9385.
Machado A., Garcia N., Garcia C., Acosta L., Cordoba
A., Linares M., Giraldoth D. and Vazquez H. (2007).
Metal pollution (Pb, Zn, Ni and Cr) in air, road and
soil sediment in a high trafFc area, Int. J. Environ.
Pollut. 24, 171-182.
Semra M., Yazici B. and Koparalt S. (2010). Assessment
the levels of heavy metal pollution in roadside soil
of Eskisehir, Turkey. Environ. Toxicol. Chem. 29,
2720-2725.
Meza T.L. and Quintero N.M. (2007). “Methodology for
the calculation and emissions of particulate matter
PM
10
and PM
2.5
: Case Study “paved and unpaved path
-
ways of the City of Mexicali, “ El Segundo Coloquio
de Graduados, editor Ojeda, B. S. UABC Mexicali,
BC, 330-339.
Meza T.L, Quintero N.M, García C.R. and Ramírez J.
(2009). Estimated emission factors for PM
10
and PM
2.5
in urban roads in Mexicali, Baja California, Mexico.
CIT, 21, 45-56.
Quintero M. and Sweedler A. (2004). Air quality evalu-
ation in the Mexicali and Imperial Valleys as an ele-
ment for an outreach program. In: Imperial–Mexicali
Valleys: Development and Environment of the U.S.-
Mexican Border Region (K. Collins, P. Ganster, C.
Mason, E. Sánchez López and L.M. Quintero-Núñez,
Eds.), San Diego State University Press, pp. 263-279.
Osornio-Vargas A.R., Serrano J., Rojas-Bracho L., Miran-
da J., García-Cuellar C., Reyna C.M.A., ±lores G., Zuk
M., Quintero-Núñez M. Vázquez I., Sánchez-Pérez Y.,
López T. and Rosas I. (2011). In vitro biological effects
of airborne PM2.5 and PM10 from a semi-desert city
on the Mexico-US border. Chemosphere 83, 618-626.
Schaetzl R. and Sharon A. (2005). Soils genesis and geo-
morphology. Cambridge, 827 pp.
L.M. Meza Trejo
et al.
26
USEPA (1993a). AP42. Volume I, chapter 13, appendix
C1, Procedures for sampling surface/ bulk dust load
-
ing samples. United States Environmental Protection
Agency. 5th ed. On line: http://www.epa.gov/ttn/chief/
ap42/appendix/app-c1.pdf. Accessed 09/02/2013.
USEPA (1993b). AP42. Volume I, chapter 13, appendix
C2, Procedures for sampling surface/ bulk dust load
-
ing samples. United States Environmental Protection
Agency. 5th ed. On line: http://www.epa.gov/ttn/chief/
ap42/appendix/app-c2.pdf. Accessed 09/02/2013.
USEPA (1996). Method 3050B, Acid digestion of sedi-
ments, sludge and soil. United States Environmental
Protection Agency. On line: http://www.epa.gov/osw/
hazard/testmethods/sw846/pdfs/3050b.pdf. Accessed
12/06/2013.
USEPA (2006). AP-42. Miscellaneous sources. Volume I,
chapter 13. United States Environmental Protection
Agency. 5th ed. On line: http://www.epa.gov/ttn/chief/
ap42/ch13/index.html. Accessed 08/31/2009.
William D.S., Shukla M. K. and Ross J. (2008). Particulate
matter emission by a vehicle running on unpaved road.
Atmos. Environ. 42, 3899-3905.
Xiao-san L., Shen Y., Yong-guan Z. and Xiang-dong L.
(2012). Trace metal contamination in urban soils of
China. Sci. Total Environ. 421-422.
Zafra M.C.A., González J.T. and Tejero M.J.I. (2007).
Contaminación por escorrentía superFcial urbana:
metales pesados acumulados sobre la superFcie de una
vía. Rev. Ing. e Invest. 27, 4-10.
Zafra C.A., Temprano J. and Tejero M
.
J.M
.
(2011). Dis-
tribution of the concentration of heavy metals associ-
ated with the sediment particles accumulated on road
surfaces. Environ. Technol. 32, 997-1008.
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