Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/185
Comunicações Geológicas (2014) 101, Especial II, 1055-1058
IX CNG/2º CoGePLiP, Porto 2014
ISSN: 0873-948X; e-ISSN: 1647-581X
Occurrence and distribution of metals in urban roaddeposited sediments in a small urban area: preliminary
results of a study in Vila Real city, northern Portugal
Ocorrência e distribuição de metais em sedimentos urbanos de
uma pequena área urbana: resultados preliminares de um
estudo na cidade de Vila Real, NE de Portugal
A. R. Reis1,2*, A. I. Oliveira3, J. P. M. Pinto3, A. Parker4
Artigo Curto
Short Article
© 2014 LNEG – Laboratório Nacional de Geologia e Energia IP
Abstract: Nowadays, with a significant part of the world’s
population living in urban areas and with the increasing number of
industries in large cities, it has become necessary to find a balance
between the different processes that occur in urban soils. This study
presents the preliminary results on the contents of As, Cd, Co, Cr,
Cu, Fe, Mn, Ni, Pb, Zn and V in road-deposited sediments (RDS) of
Vila Real city (Northern Portugal), which integrates a study under
development with the aim of evaluate the contamination of roaddeposited sediments by metals in the mentioned urban area.
Keywords: Urban geochemistry, Metals, Sediments.
Resumo: Atualmente, com uma parte significativa da população
mundial a viver em áreas urbanas e com o número crescente de
indústrias em grandes cidades, tornou-se necessário encontrar um
equilíbrio entre os diferentes processos que ocorrem em solos
urbanos. Neste estudo são apresentados resultados preliminares sobre
a análise de As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn e V em amostras
de sedimentos depositados nas ruas da cidade de Vila Real (NE de
Portugal). O objetivo do estudo é avaliar a contaminação por metais
das poeiras depositadas nas ruas da área urbana de Vila Real.
Palavras-chave: Geoquímica urbana, Metais, Sedimentos.
1
Department of Geology, University of Trás-os-Montes e Alto Douro
(UTAD), Quinta de Prados, 5000-801 Vila Real, Portugal.
2
Center for Geophysics from the University of Coimbra, Coimbra, Portugal
3
Department of Biology and Environment, University of Trás-os-Montes e
Alto Douro (UTAD), Quinta de Prados, 5000-801 Vila Real, Portugal.
4
Soil Research Group, School of Human and Environmental Sciences,
University of Reading, Reading, UK.
*
Corresponding author / Autor correspondente: [email protected]
1. Introduction
Over the course of the 20th century, the world’s urban
population increased more than a tenfold, from 220 million
to 2.8 billion, and today more than half of the world’s
population lives in urban areas and anticipated to reach 6.3
billion by 2050.
Large towns and cities disturb the natural landscape on
which they develop, modifying watershed hydrologic
response, altering soil character and consequently affecting
the fate and transport of elements in urban areas (Berry
Lyons, 2012). According to Landsberg (1981) large cities
are also heat islands that, among other impacts, increase
energy demands, affect water quality, cause air pollution,
are prime generators of ozone, produce greenhouse gas
emissions and disturb adjacent atmospheric behaviour in a
way that alters downwind precipitation patterns. Large cities
have a high concentration of pollutants because of urban
activities such as burning of fossil fuels, industrial and
human activities, industrial and human waste disposal and
vehicle traffic. Therefore, urban pollutants may be
transported beyond the urban setting and can readily impact
geochemical cycles on a local, regional and even global
scale (Berry Lyons, 2012). For that reason it is extremely
important to understand how road-deposited sediments may
impact human health and the environment.
Road-deposited sediments (RDS), also commonly
termed “road-dust” or “street-dust”, is an accumulation of
particulates upon street surfaces and are commonly
contaminated and with great impacts in surface water
quality and on human health (Taylor & Robertson, 2009).
The presence of pollutants such as metals in RDS are also
important to determine urban stormwater quality, because
during rainfall, pollutants from both natural and
anthropogenic sources are transported into receiving waters,
were they affect markedly stormwater runoff quality (Lars
Herngren & Godwin, 2006). Road-deposited sediment has
become an increasingly important environmental sampling
medium for assessing anthropogenic metal levels. The
omnipresent nature, ease of sampling, strong association
with automobile emissions and relationship with nonpoint
source pollution make them a valuable archive of
environmental information (Sutherland, 2003). Road dust
has been documented to carry a loading of contaminant
species, including trace metals. These potentially harmful
elements (PHE) may cause deleterious health effects to
urban residents and commuters due to RDS high
susceptibility to remobilisation and transport – RDS is
spatially and temporally highly variable. Furthermore, urban
agglomerations tend to grow and so do the importance of
RDS characterization and monitoring: 50% of the world
population currently lives in urban centres, a figure which is
set to increase in the next decades.
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A. R. Reis et al. / Comunicações Geológicas (2014) 101, Especial II, 1055-1058
This study presents the preliminary results on the
contents of selected metals in road-deposited sediments
(RDS) of Vila Real city (Northern Portugal). It is integrated
in a study under development with the aim of evaluate the
contamination by metals of road-deposited sediments in
small urban areas.
2. Study area
Vila Real, locates in the northeast Portugal, in the Trás-osMontes region, in an upland surrounded by Marão (SW),
Alvão (W and NW) and Falperra (E-NE) Mountains. It is a
rural city, with 52781 inhabitants (INE, 2012), with few
pollutant industries. The major sources of pollution are
agriculture and urban activities.
Regarding the lithology outcropping in the area
surrounding Vila Real city, the bedrock is mainly granite
and schist. Palaeozoic metasediments outcrop in the
southern part, which are composed essentially of alternating
phyllites and greywackes, dating from the Cambrian (Sousa,
1982), and a conglomerate overlain by alternating quartzites
and phyllites, with iron-rich levels interlayered (Pereira,
1989), dating from the Ordovician. In the central and
northern part of the basin, granites intruded the older
metamorphic rocks. The oldest ones are two-mica, fine to
medium-grained (Pereira, 1989; Gomes, 1989; Matos, 1991;
Neiva & Gomes, 1991); the most recent are biotitic granites
(Pereira, 1989, Martins, 1998). The deposition of sediments
from the Cenozoic, over the crystalline rocks, in the Vila
Real basin (Baptista, 1998) was controlled mainly by the
major tectonic structure Penacova-Régua-Verin fault
(Gutiérrez Claverol et al., 1987).
The altitudes in the area are between 300-1400m. Vila
Real is located at an altitude of 450m, and the region is
characterized by a cold-wet period, running from October to
May, followed by a warm-dry period lasting from June to
August. The mean annual precipitation is 974 mm in Vila
Real, varying in the range 672-1900 mm.
In the urban area of Vila Real there are dispersed parks
with forest and gardens; locally and in the surroundings of
the city there are agricultural terrains. The industry is
concentrated, in general, in the industry park. Major
pollutant activities are agriculture (pollution by sediments,
metals and use of fertilizers) and urban activities such as
atmospheric deposition, vehicular traffic, residential
activities, soil erosion and industrial activities.
collected approximately 1 kg of road deposited sediments.
The sample preparation consisted, at first, in the
disaggregation of the sample, with an agate pestle and
mortar, the finer particulate material was separated with a
1mm sieve and kept in sealed plastic bags.
The samples were decomposed with aqua regia. The
concentrations of As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn
and V were obtained by ICP-AES. In each analytical
sequence, replicates were used to assess repeatability. To
ensure accuracy, an in-house reference material was also
used. The recovery rates ranged from 87% e 99%. The
precision of the measurements is about ±5%.
4. Results and discussion
Main descriptive statistics for As and metal contents in
road-deposited sediment samples are shown in table 1.
Cadmium and Co have not been included since most of the
observations were below the detection limit (1.5 µg g-1 and
3.2 µg g-1, respectively). The relative high values of
standard deviation suggest spatial variability in the sources
of the elements, in particular for As, Cr, Cu, Ni, Pb, and
Zn. In general, all the elements present a wide range of
variation, with V showing a more limited variation
amongst the sampling stations. Joshi et al. (2009) and
Ordónez et al. (2003) present values of concentrations of
metals within cities reported in the literature; in general,
the results of contents obtained in this study were within
the lower ranges of values reported (determinations for As,
Fe, Mn and V are not mentioned). Several factors
influence these results, in particular, the land use, intensity
of human activities, cleaning of the pavements. In
addition, differences in methodologies of sampling and
preparation of samples, as well as digestion methods for
the extraction of chemical elements, influence the results
which are obtained. Regarding the lowest levels found in
the set of collected samples, in the urban area of the city of
Vila Real, which correspond to sites localized distant from
the main streets and roads, all the elements present relative
enrichments, showing spatial variability.
Table 1. Descriptive statistics for As and metals (µg g-1) determined in
road-deposited sediments of Vila Real city.
Tabela 1. Parâmetros estatísticos relativos aos teores de As e metais (µg g-1)
determinados nos sedimentos de rua da cidade de Vila Real.
As
Cr
Cu
Ni
Pb
V
Zn
Fe
Mn
3. Methodology
Min
0
0
0
0
0
0
5493
93
A set of 22 road deposited sediment samples were
collected in the urban area of the city of Vila Real. The
sampling locations were defined according to the aim of
the study and in order to ensure a reasonable variety of
results, related with different urban activities. The samples
were collected in urban and periurban areas as well as in
public playgrounds and in the industrial area.
The samples were collected with a shovel and a broom;
kept by number in individual sealed plastic bags and
between each sampling, the sampling material was cleaned
to avoid contamination. In each sampling site it was
Max
42
66
93
53
177
15
2331 40151
412
Mean
11
11
36
6
31
2
327 13242
174
Med
SD
46
6
2
18
0
9
0
122
9917
133
13
18
36
14
44
4
551
8051
80
The spatial distributions of the studied metals show
clear differences. Figure 1 shows the variability of
contents of As, Cr, Cu, Ni, Pb, V and Zn within samples.
Zinc, Cu, Pb and Ni are the metals exhibiting higher
contents within samples. The samples 1, 9, 10, 13, 14, 15,
Chemical quality of urban road-deposited sediments
1057
parks, suggesting the influence of the use of fertilizers
(Alloway & Ayres, 1997). The observation of some of the
mentioned correlations in samples taken in the periphery
of the urban area, but showing relative lower contents,
suggest an influence of geogenic source.
22, and to a less extent samples 4, 5 and 21, are the ones
exhibiting higher contents and/or anomalous values of the
studied elements. These higher contents are related with
sampling sites located in the streets with higher vehicular
traffic levels and in the industrial area, in particular
sampling site 22 locates near a metal finishing and
processing plant. Sample collected in site 5 locates in a
residential area, but very windy, and site 10 in the main
path of the Corgo Park, but also exposed, which may
suggest influence from atmospheric deposition.
Table 2. Correlation coefficients between As and metals in the urban
street sediments of Vila Real city (n=22, p=0.05%).
Tabela 2. Coeficientes de correlação entre As e metais em sedimentos de
rua da cidade de Vila Real (n=22, p=0.05%).
As
As
1500
1250
Zn
1000
Cr
Cu
Ni
Pb
V
Zn
Fe
Mn
1,00
Cr
0,08
1,00
Cu
0,25
0,26
1,00
Ni
-0,07
0,48
0,26
1,00
Pb
0,11
0,46
0,57
0,19
1,00
V
0,12
0,65
-0,05
0,45
-0,18
1,00
Zn
0,12
0,28
0,38
0,17
0,30
-0,10
1,00
Fe
0,23
0,48
0,39
0,29
0,14
0,45
0,75
1,00
Mn
0,22
0,70
0,23
0,58
0,02
0,82
0,27
0,72
V
Pb
Ni
750
Cu
Cr
As
500
250
1,00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
5. Conclusions
-1
Fig. 1. Arsenic and metal distribution (µg g ) among samples and
sampling sites, in road-deposited sediments of Vila Real city.
Fig. 1. Distribuição de As e metais (µg g-1) em sedimentos de rua da
cidade de Vila Real.
Table 2 shows the correlation coefficients between
each of the studied elements. A few significant
correlations are observed amongst the elements, which
may suggest an association to common sources (Cu-Pb;
Cr-V; Fe-Zn; Cr-Mn; V-Mn; Ni-Mn; Mn-Fe). Correlation
factors with minor significance are observed amongst NiFe; Cr-Pb; V-Ni; Cr-Fe; V-Fe. Zinc does not show
significant correlations with other elements; this is
probably owing to the significant anomalous high values
associated to a few samples.
Studying in detail the suggested correlations, it is
verified that there is no statistical linear correlations. The
scatter of projected points forms subsets of samples, which
suggest association of samples by location in the sampling
area, in the same subset, depending on a predominant
urban activity. The association of Cu, Pb and Zn, the urban
elements (De Miguel et al., 1999), is observed in samples
collected in the streets with high traffic density and
industrial activity (e.g. town centre, near the hospital,
industrial park). These metals have been associated to,
amongst other sources, corrosion of building materials,
mechanical abrasion of vehicles, tyre wear, oil spills on
road surfaces (e.g. Taylor & Robertson, 2009;
Charlesworth et al., 2003; Ordónez et al., 2003; Robertson
et al., 2003). In general, higher relative contents of Fe and
Mn are found in these samples, as well as As, although in a
less extent. Associations between V, Cr, Ni, Fe and Mn are
found in samples collected near garden areas and in green
The studied total concentrations of As, Cr, Cu, Fe, Mn, Ni,
Pb, Zn and V, in road-deposited sediments from the urban
area of Vila Real, indicate relative enrichments in samples
collected in the main streets and roads, showing spatial
variability. The association of Cu, Pb and Zn is observed
in samples collected in the streets with high traffic density
and industrial activity; in general, higher relative contents
of Fe and Mn are also found in these samples.
Associations between V, Cr, Ni, Fe and Mn are found in
samples collected near garden areas and in green parks.
Further work is presently been carried out to evaluate
the exact contribution of each source to the observed
element contents and associations. This comprises
information on geochemical and mineralogical properties
of road-deposited sediments of Vila Real. Information on
soils will be also included. Moreover, information on risk
assessment to population can be provided by the study of
the potential availability of metals by sequential extraction
analysis.
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