1. Pollution characteristics and health risk assessment of heavy metals
in street dusts from different functional areas in Beijing, China$
Xin Wei a,b
, Bo Gao a,n
, Peng Wang c
, Huaidong Zhou a
, Jin Lu a
a
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research,
Beijing 100038, China
b
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China
c
College of Environment Science and Engineering, Kunming University of Science and Technology, Kunming, 650500, China
a r t i c l e i n f o
Article history:
Received 15 May 2014
Received in revised form
30 October 2014
Accepted 7 November 2014
Keywords:
Street dusts
Heavy metals
Pollution assessment
Health risk assessment
Beijing
a b s t r a c t
Street dusts from Heavy Density Traffic Area, Residential Area, Educational Area and Tourism Area in
Beijing, China, were collected to study the distribution, accumulation and health risk assessment of heavy
metals. Cr, Cu, Zn, Cd and Pb concentrations were in higher concentrations in these four locations than in
the local soil background. In comparison with the concentrations of selected metals in other cities, the
concentrations of heavy metals in Beijing were generally at moderate or low levels. Ni, Cu, Zn and Pb
concentrations in the Tourism Area were the highest among four different areas in Beijing. A pollution
assessment by Geoaccumulation Index showed that the pollution level for the heavy metals is in the
following order: Cd4Pb4Zn4Cu4Cr4Ni. The Cd levels can be considered “heavily contaminated”
status. The health risk assessment model that was employed to calculate human exposure indicated that
both non-carcinogenic and carcinogenic risks of selected metals in street dusts were generally in the low
range, except for the carcinogenic risk from Cr for children.
& Elsevier Inc. All rights reserved.
1. Introduction
Street dusts receives various heavy metal inputs from a variety
of mobile or stationary sources, such as vehicular traffic, industrial
plants, power generation facilities, residential oil burning, waste
incineration, city construction and demolition activities and the
resuspension of surrounding contaminated soils (Bilos et al., 2001;
Manno et al., 2006), and these dust make a significant contribution
to metal pollution in the urban environment. The components and
quantity of street dust are also potential pollution indicators for
urban environment (Han et al., 2006). Because of a lack of bioa-
vailability, biodegradability and persistence, heavy metals could
accumulate and be enriched in urban environment. A previous
study found that the contamination contents (e.g., heavy metals
and other toxic trace elements) of road/street dusts are generally
higher than those in other media (e.g. soils) (Shi et al., 2008).
Moreover, heavy metals in street dusts could easily enter human
bodies through dust ingestion, inhalation and dermal contact
under dynamic conditions such as wind, traffic and other human
activities.
Elevated levels of heavy metals are ubiquitous in urban settings
as the result of a wide range of human activities, especially from
industrial sources (Duzgoren-Aydin et al., 2006). As a con-
sequence, adverse effects on human health may occur in urban
environments, particularly in metropolitan cities where urbani-
zation, industrialization and rapid population growth have been
taking place on an unprecedented scale. Although numerous stu-
dies on heavy metal contamination of street dusts have been
performed in developed countries (Chon et al., 1995; De Miguel
et al. 1997; Charlesworth et al., 2003), only limited information is
available for developing countries, especially for China. In addition,
most previous literatures on road/street dusts have primarily fo-
cused on the heavy metals concentration, distribution, source
identification and pollution assessments during the last decades
(Banerjee, 2003; Ferreira-Baptista and De Miguel 2005; Chen et al.,
2005; Ahmed and Ishiga, 2006; Tanner et al., 2008). In fact, the US
EPA’s health risk assessment method has been successfully em-
ployed to investigate heavy metal exposure from urban road dusts
for children and adults (US EPA, 1997; US EPA, 2001a; US EPA,
2002; Hu et al., 2011). In fact, the result of the health risk as-
sessment for heavy metals in street dusts is very useful for both
types of residents in terms of taking protective measures and for
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journal homepage: www.elsevier.com/locate/ecoenv
Ecotoxicology and Environmental Safety
http://dx.doi.org/10.1016/j.ecoenv.2014.11.005
0147-6513/& Elsevier Inc. All rights reserved.
☆
Capsule:The Tourism Area may be a reservoir of heavy metals among the dif-
ferent functional areas and the carcinogenic risk for Cr in children deserves con-
siderable attention in Beijing.
n
Corresponding author.
E-mail address: gaosky34@hotmail.com (B. Gao).
Ecotoxicology and Environmental Safety 112 (2015) 186–192

2. the government to alleviate heavy metals pollution of the street
environment.
Over the last three decades, urbanization and industrialization
have taken place at an unprecedented pace in China. Urban en-
vironmental pollution has become a very important issue for en-
vironmental researchers (Wei and Yang, 2010). Beijing, the capital
of China, is the political, economic and cultural central of the na-
tion. Beijing is also one of the oldest and most densely
populated cities in the world. In the past few decades, Beijing has
engaged in rapid development in terms urbanization and in-
dustrialization, which has exerted considerable of pressure on the
urban environment. Previous studies showed that heavy metals
pollution was found in the urban surface soils and street dusts of
Beijing over the past two decades (Chen et al., 2005; Tanner et al.,
2008; Chen et al., 2010a; Chen et al., 2010b; Xia et al., 2011).
However, the spatial distribution of heavy metals in street dusts
collected from different functional regions in the urban environ-
ment and the health risk assessment of heavy metals in street
dusts from Beijing is still unknown. The objectives of the present
study were as follows: (1) to determine the current status of heavy
metals concentrations and spatial patterns in urban street dusts
collected from different functional areas in Beijing; (2) to compare
heavy metal concentrations in the street dusts of Beijing with
those in other cities; (3) to evaluate and assess heavy meals pol-
lution in street dusts using the Geoaccumulation Index; and (4) to
assess the carcinogenic and non-carcinogenic health risks asso-
ciated with heavy metals by US EPA health assessment methods.
2. Materials and methods
2.1. Study area
Beijing, the capital of China, is situated at the northern tip of
the roughly triangular North China Plain, and its center is located
at 39.9 N and 116.4E. Beijing is one of the four municipalities in
China, and it consists of 18 administrative districts (counties),
among which eight districts constitute the urban area. The urban
area of Beijing is situated in the south-central part of the muni-
cipality and occupies an expanding part of the municipality’s area.
This region spreads out of the concentric ring roads, from which
the 6th Ring Road passes through several satellite towns. The city
has a typical monsoon-influenced climate, and it is characterized
by hot, humid summers from the East Asian monsoon and gen-
erally cold, windy, dry winters from the vast Siberian anticyclone.
The city’s annual temperature is approximately 11.5 °C and the
annual precipitation is approximately 600 mm. Over the past three
decades, Beijing has been undergoing some of the most rapid
economic development and urban construction in China, during
which the urban population has reached over 19 million.
2.2. Sample collection
One hundred fifty-four street dust samples were collected from
urban areas consisting of different land use areas in Beijing, in-
cluding four different functional sections as follows: (1) the Heavy
Density Traffic Area (HDTA), this section covers Chang’ an Avenue,
the 2nd ring and the 3rd ring road in the central area of Beijing,
and these sampling sites are the representative of the heaviest
traffic areas. In the (2) Educational Area (EA), thirteen universities
were selected including Beijing Normal University (BNU), China
University of Mining and Technology (CUMT), Tsinghua University
(THU), Beijing University of Posts and Telecommunications (BUPT),
Renmin University of China (RUC), Beijing Foreign Studies Uni-
versity (BFSU), the Graduate University of Chinese Academy of
Sciences(GUCA), Beijing Institute of Technology (BIT), Beijing Sport
University (BSU), China University of Agriculture (CUA), National
Defense University PLA China (NDU), North China Electric Power
University (NCEPU) and Beijing University of Agriculture (BUA).
For the (3) Tourism Area (TA), eight famous tourism sites were
selected from inside the TA area, including the Summer Place (SP),
Forbidden City (FC), Yuyuantan Park (YYP), Heaven Temple (HT),
Jingshan Park (JSP) and Shichahai Park(SCP). For the (4) Residential
Area (RA), Hui Longguan (HLG) was selected because it is one of
the biggest residential districts in the urban part of Beijing city. For
each sampling site, three$five subsamples (approximately 200 g
each) from one street were collected with a small brush and a
clean polymethyl methacrylate shovel from February to May 2010.
All the samples were stored in sealed polyethylene bags, labeled
and then transported to the laboratory. The sampling locations in
Beijing are shown in Fig. 1.
2.3. Sample preparation and analysis.
The dust samples were dried at 100 °C for 5 h in an electric
oven and sieved through a 0.125 mm stainless steel sieve. The total
metal concentrations in the sediments were measured by an es-
tablished method (Liu et al., 1996). In Brief, a 40 mg mass of dry
sample was weighed and dissolved into 10 mL Teflon bombs.
Approximately 2 mL of HNO3 þ0.2 mL H2O2 was added to the
samples and they were left on a hot plate for one day. This step
was performed to remove organic materials from the dust sam-
ples. The samples were then taken evaporated to dryness at
120 °C. The residue was dissolved in 1 mL of HNO3 þ1 mL HF
sample. After 30 min of the ultrasonic procedure, the samples
were placed in sealed bombs that were then placed in an oven at
190 °C for 48 h. This procedure yielded clear solutions for the dust
samples. After evaporating at 120 °C, the samples were dissolved
in 1% HNO3. Inductively coupled plasma-mass spectrometry (ICP-
MS, Perkin Elmer Elan DRC-e) was used to determine the total
concentrations of Zn, Pb, Cr, Cd, Ni, and Cu. The quality controls for
the strong acid digestion method included reagent blanks, dupli-
cate samples, and standard reference materials. The QA/QC results
show no sign of contamination for all the analysis. The accuracy of
the analytical procedures that were employed to analysis the trace
elements in the dusts was checked by certified soil reference
material (ESS-1, GSBZ 50011-88), and the results were consistent
with the certified values (Supplementary informationTable S1).
3. Results and discussion
3.1. Heavy metal concentrations in the street dusts of Beijing
The heavy metal concentrations in the street dust samples are
summarized in Table 1, including the arithmetic means and the
standard deviation. The concentrations of Cr, Ni, Cu, Zn, Cd and Pb
varied between 32.0 and 227, 14.9 and 60.0, 5.46 and 623, 57.4 and
908, 0.130 and 5.01, and 16.7 and 2.45 Â 103
mg/kg, respectively.
The mean concentrations of Cr, Ni, Cu, Zn, Cd and Pb were 84.7,
25.2, 69.9, 222, 0.723 and 105 mg/kg, respectively. With the ex-
ception of Ni, the mean concentrations of Cr, Cu, Zn, Cd and Pb in
road dusts greatly exceeded the soil background values for Beijing
(CNEMC, 1990) and the values in urban soils from Beijing (Fer-
gusson, 1984). In fact, the Cu, Zn, Cd and Pb levels are even more
than 3 times higher than the soil background values for Beijing,
indicating that the pollution may come from anthropogenic
sources (vehicular traffic, industrial plants, city construction and
demolition activities).
Table 1 also shows the spatial variations for heavy metals
concentrations in street dusts from different areas in Beijing city.
In general, the Ni, Cu, Zn, and Pb concentrations in TA were the
X. Wei et al. / Ecotoxicology and Environmental Safety 112 (2015) 186–192 187

3. highest among the four different areas in Beijing city, especially for
Zn. In fact, the highest Cu concentration was 623 mg/kg, and there
were 908 mg/kg for Zn and 2.45 Â 103
mg/kg for Pb in several
parks. Similar results for Cu and Pb pollution were also found in
the park soil samples that were acquired during a previous study
in Beijing (Chen et al., 2005), suggesting that the TA areas may be a
reservoir of heavy metals in this urban environment. As we know,
there are many ancient buildings in the TA areas in Beijing. These
clearly high concentrations of heavy metals in the TA areas may
originate from a large mass of colored oil paints used to refurbish
the ancient structure because the oil pain in China always con-
tained a high concentration of heavy metals in ancient times.
Although leaded gasoline has not been used in Beijing since 1997,
the soils and street dusts in TA could have acted as a reservoir for
Pb pollution over the years. These two reasons were explained in
relation to this interesting higher concentration in the TA. In ad-
dition, relatively high concentrations of Cr, Cu, and Zn were also
found in the HDTA area of Beijing city. The Chang’an Avenue 2nd
Ring Road and the 3rd Ring Road are principal roads with the
highest traffic volumes and traffic jams in Beijing. Therefore,
the vehicular-related deposition of particles was responsible for
the higher concentrations of Cr, Cu and Zn in road dusts from the
HDTA area. In fact, the vehicular-related deposition of particles
may primarily come from vehicle exhaust particles, lubricating oil
residues, tire wear particles, brake lining wear particles, particles
from atmospheric deposition, plant matter, and materials pro-
duced by the erosion of the adjacent soil (Li et al., 2001 and
Charlesworth et al.,2003). It is clear that Cd was present at its
highest concentration in the RA area relative to the other areas,
suggesting that this Cd pollution may come from different
anthropogenic sources.
3.2. A comparison of heavy metal concentrations in the street dusts
of Beijing with those of other cities from around the world
A comparison of heavy metal concentrations in the street dusts
of Beijing with those in other cities is summarized in Table 2. In
general, the heavy metal concentrations in the street dusts from
Fig. 1. Sampling site Locations in Beijing, China. (HDHA¼ Heavy Density Traffic Area, EA¼ Educational Area, TA¼ Tourism Area, RA¼ Residential Area).
Table 1
Heavy metal concentrations in road dusts from Beijing (mg/kg).
Sampling sites Cr Ni Cu Zn Cd Pb
HDTA(N¼56) 100 23.9 83.2 207 0.403 64.0
TA (N¼ 37) 70.4 26.6 86.0 272 0.848 235
EA (N¼50) 79.5 26.3 49.2 214 0.686 66.5
RA (N¼9) 76.9 20.3 37.1 167 2.41 41.0
Minimum value 32.0 14.9 5.46 57.4 0.130 16.7
Maximum value 227 60.0 623 908 5.01 2.45 Â 103
Mean7S.D. (N¼154) 84.7730.8 25.277.41 69.9768.3 2227120 0.72370.742 1057223
Background values for Beijing CNEMC (1990) 66.7 28.2 23.1 97.2 0.0534 24.7
Urban soils in Beijing Fergusson (1984) 35.6 27.8 23.7 65.6 0.15 28.6
X. Wei et al. / Ecotoxicology and Environmental Safety 112 (2015) 186–192188

4. Beijing were relatively lower than the concentrations reported for
cities in other countries. In Comparing of the metal concentrations
of street dusts among Chinese cities, the street dusts in from
Beijing also showed a relatively low level of heavy metals. In fact,
the heavy metal concentrations in street dusts from Beijing were
clearly lower than values from Shanghai. Finally, in comparing
with an earlier study in Beijing (Tanner et al., 2008), our results
showed that the Cu and Pb concentrations exhibited a consider-
able increasing tendency in recent years (Table 2).
3.3. Pollution assessment of heavy metals in street dusts
The contamination levels for heavy metals in street dusts have
been evaluated by using the Geoaccumulation Index (Igeo) in-
troduced by Müller (1979). The method has been widely employed
in European trace metal studies since the late 1960s. It is also
applied to pollution assessment of heavy metals from urban road
dusts (Lu et al., 2009, Wei and Yang, 2010). The Igeo is computed
by using the following equation (Müller, 1979):
⎛
⎝
⎜
⎞
⎠
⎟=I log
C
B1.5
geo
n
n
2
Where n is the measured concentration of the element in the en-
vironment and n is the geochemical background value. In this
study, heavy metal concentrations in the soil background in Beij-
ing are chosen as the background values for calculating the Igeo
values (CNEMC, 1990). The constant 1.5 allows us to analyze
natural fluctuations in the content of a given substance in the
environment and to find very small anthropogenic influences. The
Igeo for each metal is calculated and typically classified as follows:
uncontaminated (Igeor0); uncontaminated to moderately con-
taminated (0o Igeor 1); moderately contaminated (1o Igeor2);
moderately to heavily contaminated (2oIgeor3); heavily con-
taminated (3o Igeor4); heavily to extremely contaminated
(4o Igeor5); and extremely contaminated (IgeoZ5).
The Igeo values for the heavy metals in urban street dusts are
presented in Table 3. The average Igeo values for heavy metals were
À0.24 for Cr, À0.75 for Ni, 1.01 for Cu, 0.61 for Zn, 3.17 for Cd and
1.50 for Pb. On the whole, the street dusts in different areas have
different Igeo values among the urban areas of Beijing. The order
for the average Igeo values was follows: Cd4Pb4Cu4Zn4Cr4
Ni. The average Igeo values for Cd was 3.17, which was ranked as
“heavily contaminated”, indicating that the urban street dusts
were obviously polluted by Cd, especially in the RA area. The
average Igeo for Zn was 0rIgeor1, which was ranked as an
“uncontaminated to moderately contaminated” level. Cu and Pb
were ranked as “moderately contaminated” levels. In addition, the
Igeo for Ni and Cr were less than 0, indicating that the urban en-
vironment was scarcely contaminated by Ni and Cr. It is surprising
that the RA area was the most polluted in term of Cd level among
the four urban areas. The high Cd concentration in the RA region
with a higher population density was attributed to complicated
anthropogenic sources. In fact, more than one million people were
living and working in this relatively small region and their activ-
ities (coal combustion, traffic emissions, and industrial activities)
were the potential sources for this obvious Cd pollution.
3.4. Potential health risks assessment of heavy metals in street dusts
To quantify both carcinogenic and non-carcinogenic risks to
children and adults from absorbing street dusts, the health risk
assessment model that is employed to calculate human exposures
to heavy metals in street dusts is based on the method developed
by the Environmental Protection Agency of the United States
(US EPA, 1986). The following assumptions that form the basis for
the model were also applied in Beijing: (1) Human beings are
exposed to street dust through the following three primary
pathways: the ingestion of dust particles, inhalation of dust par-
ticles, and dermal contact with dust particles; (2) intake rates and
particle emission can be approximated by those developed for
dust; (3) some exposure parameters of people in the observed
areas are similar to those of reference populations; (4) the total
non-carcinogenic risk could be calculated for each metal (Cr, Ni,
Cu, Zn, Cd and Pb) by summing up the individual risks acquired
from three exposure pathways; and (5) the total carcinogenic risk
could be calculated for each metal (Cr, Ni and Cd) by summing up
Table 2
Heavy metal Concentrations in road/street dusts from different cities in China and other countries (mg kgÀ1
).
City Country Cr Ni Cu Zn Cd Pb Reference
New York USA – – 355 1.81 Â 103
8.00 2.58 Â 103
Fergusson (1984)
London England – – 108 539 2.70 2.10 Â 103
Rasmussen et al. (2001)
Coventry England – 130 226 386 0.90 47.1 Charlesworth et al. (2003)
Seoul Korea – – 101 296 3.00 245 Chon et al. (1995)
Ottawa Canada 41.7 14.8 38.1 101 0.33 33.5 Rasmussen et al. (2001)
Birmingham England – 41.1 467 534 1.62 48.0 Charlesworth et al. (2003)
Madrid Spain – 44.0 188 476 – 1.93 Â 103
De Miguel et al. (1997)
Oslo Norway – 41.0 123 412 1.40 180 De Miguel et al. (1997)
Xi’an China 167 – 95.0 421 – 230 Han et al. (2006)
Guangzhou China 78.8 23.0 176 586 2.41 240 Duzgoren-Aydin et al. (2006)
Shanghai China 159 84.0 197 734 1.23 295 Shi et al. (2008)
Baoji China – 48.8 1237 715 – 408 Lu et al. (2009)
Hong Kong China – – 173 1.45 Â 103
3.77 181 Li et al. (2001)
Nanjing China 126 55.9 123 394 1.10 103 Hu et al. (2011)
Urumqi China 54.3 43.3 94.5 294 1.17 53.5 Wei et al. (2009)
Beijing China 85.6 – 42.0 214 1.20 61.0 Tanner et al. (2008)
Beijing China 84.7 25.2 69.9 223 0.72 105 This study
Table 3
The Igeo of heavy metals in street dusts from Beijing, China.
Sampling sites Igeo
Cr Ni Cu Zn Cd Pb
HDTA(N¼56) 0.00 À0.82 1.26 0.50 2.33 0.79
TA (N¼37) À0.51 À0.67 1.31 0.90 3.40 2.66
EA (N¼50) À0.33 À0.68 0.51 0.55 3.10 0.84
RA (N¼9) À0.38 À1.06 0.10 0.20 4.91 0.15
Minimum value À1.64 À1.51 À2.67 À1.35 0.32 À1.15
Maximum value 1.19 0.50 4.17 2.64 5.97 6.05
Mean (N¼154) À0.24 À0.75 1.01 0.61 3.17 1.50
X. Wei et al. / Ecotoxicology and Environmental Safety 112 (2015) 186–192 189

5. the individual risks calculated for three exposure pathways (US
EPA, 1986; Shi et al., 2011).
According to the Exposure Factors Handbook (US EPA, 1997),
the formulas for calculating the average daily dose (ADD)
(mg kgÀ1
dayÀ1
) of potentially toxic metals via soil ingestion, in-
halation and dermal contact as exposure pathways are listed as
follows (US EPA 1989, US EPA, 1996):
=
× × × ×
×
=
× × ×
× ×
=
× × × × × ×
×
=
× × ×
× ×
ADD
C IngR CF EF ED
BW AT
ADD
C InhR EF ED
PEF BW AT
ADD
C SA CF AF ABF EF ED
BW AT
LADD
C CR EF ED
PEF BW AT
dermal
ing inh
Where ADDing is the daily amount of exposure to metals through
ingestion (mg kgÀ1
dayÀ1
); ADDinh is the daily amount of ex-
posure to metals through inhalation (mg kgÀ1
dayÀ1
); ADDdermal is
the daily amount of exposure to metals through dermal contact
(mg kgÀ1
dayÀ1
); LADD is the lifetime average daily dose
(mg kgÀ1
dayÀ1
); and CR is the contact frequency, whereas
CR¼IngR in this study (US EPA, 1996, US EPA, 2001a, 2001b). The
exposure factors that were applied to the above models in this
study are shown in Table 4. The values of these factors are selected
by using reference standards from the US EPA and real data for
Chinese locations (Environmental site assessment guideline 2009).
After the average daily dose (ADDs) for the three exposure
pathways (ADDing, ADDinh and ADDdermal) were calculated, Hazard
Quotient (HQ), Hazard Index (HI) methods and carcinogenic risk
methods (RI) were applied to evaluate the human health risk of
heavy metal exposure from street dusts in Beijing. HI refers to the
“sum of more than one Hazard Quotient for multiple substances
and/or multiple exposure pathways” (US EPA, 1989). Hence, a
combination of non-cancer risk for humans from different ex-
posure pathways can be estimated by adding the HI of each ex-
posure pathway (ingestion, dermal contact and inhalation)
together (US EPA, 1989). The estimated value for the Carcinogenic
Risk is the probability that an individual will develop any type of
cancer from lifetime exposure to carcinogenic hazards. The po-
tential non-carcinogenic and carcinogenic risks for individual
metals were calculated by using the following equations (US EPA,
1989):
∑= = = ×HQ
ADD
R D
HI HQ RI LADD SF
f
i
The reference dose (RfD) (mg kgÀ1
dayÀ1
) is an estimation of
maximum permissible risks to human population through daily
exposure by considering sensitive group (children) during a
lifetime. The threshold RfD value can be used to assess whether
there is an adverse health effect during a life time. If an average
daily dose (ADD) value is lower than the reference dose, there is
unlikely to be any adverse health effect; otherwise, if the ADD
value is higher than the RfD, it is likely that the exposure pathway
will cause adverse human health effects (US EPA, 1993). The ratio
of the average daily dose to the reference dose can be used to
estimate the non-cancer risk to humans: when HQr1, there are
no adverse health effects and HQ 4 1 indicates that there are
likely adverse health effects (US EPA, 1986). The HI is the sum of
the HQ and indicates the total risk of non-carcinogenic for a single
element. If the value of HIr1, no significant risk of non-carcino-
genic effects is believed to occur. If HI 41, then there is occur a
possibility of non-carcinogenic effects, and the probability in-
creases with the increasing HI value (US EPA, 2001a, 2001b). The
estimated value for the Carcinogenic Risk (RI) is the probability
that an individual will develop any type of cancer from lifetime
exposure to carcinogenic hazards. In general, the US EPA re-
commends that and RI lower than 1 Â 10À6
can be regarded as
negligible and an RI above 1 Â 10À4
is likely to be harmful to hu-
man beings. An RI within a range from 1 Â 10À6
$1 to 10À4
in-
dicates an acceptable or tolerable risk for regulatory purposes and
desirable remediation. The acceptable or tolerable risk for reg-
ulatory purposes is in a range of 1 Â 10À6
$1 Â 10À4
. The SF (mg
kgÀ1
dayÀ1
)À1
is the slope factor for carcinogenic exposure (US
EPA, 2001a, 2001b). The values for SF, RfD and other calculated
parameters are listed in Table 5.
For non-carcinogenic effects, the HQ values for the different
exposure pathways of heavy metals that were studied in children
decreased in the following order: ingestion4dermal con-
tact4inhalation (Table 5). The contributions of the HQing to the HI
(the total risk of non-carcinogenic exposure) were the highest
(95.7% for children and 54.7% for adults), indicating that ingestion
was the primary pathway for heavy metals in city dusts that were
harmful to human health. This result is also consistent with other
earlier investigations (Ferreira-Baptista and De Miguel 2005).
Among the six studied non-carcinogenic elements, The HI for both
adults and children decreased in the order Pb4Cr4Cu
4Ni4Cd4Zn (Table 5). In fact, the non-carcinogenic health risk
for adults was lower than the values for children in terms of heavy
metals exposure to street dusts. However, the HI values for the
studied elements were all lower than the safe level (HIr1), in-
dicating that there were no non-carcinogenic risks from these
elements for children and adults. In terms of the two population
groups, the non-carcinogenic risks for children were nearly one
order of magnitude higher than the risks for adult, indicating that
children faced more potential harmful health risks from the heavy
metals in street dusts from Beijing city.
Table 4
Exposure factors for metal doses.
Factor Definition Unit Value References
Children Adult
C Heavy metals concentrations in dusts mg/kg This study
Ring ingestion rate of soil mg/day 200 100 US EPA (2001a, 2001b)
EF exposure frequency days/year 350 350 Environmental site assessment guideline (2009)
ED exposure duration years 6 24 US EPA (2001a, 2001b)
BW average body weight kg 15 55.9 Environmental site assessment guideline (2009)
AT average time days 365 Â ED 365 Â ED US EPA (1989)
CF conversion factor kg/mg 1 Â 10À6
1 Â 10À6
Li et al. (2011)
Rinh inhalation rate m3
/day 7.63 12.8 Li et al. (2011)
PEF particle emission factor m3
/kg 1.36 Â 109
1.36 Â 109
US EPA (2001a, 2001b)
SA surface area of the skin that contacts the dust cm2
1600 4350 Environmental site assessment guideline (2009)
AF skin adherence factor mg/cm2
0.2 0.7 US EPA (2011)
ABF dermal absorption factor – 0.001 0.001 US Department of Energy (2000)
X. Wei et al. / Ecotoxicology and Environmental Safety 112 (2015) 186–192190

6. For the carcinogenic risk (RI), Cr, Ni and Cd were assessed
through the ingestion exposure modes for street dusts. Table 5
shows that the RI values were 1.28E-08 (Cr), 7.58E-10 (Ni) and
1.63E-11 (Cd) for children and 5.74E-07 (Cr), 3.41E-10 (Ni) and
7.32E-11 (Cd) for adults. As shown here, among the three ele-
ments, Cr contributed more than 99.3% to the overall RI for chil-
dren and adults, followed by Ni, and Cd. In fact, the RI values of Cr,
Ni and Cd for adults and children as obtained in this study were all
lower than 1 Â 10À6
, suggesting that the carcinogenic risk ex-
posure from Cr, Ni and Cd in street dusts could be negligible in
Beijing. However, the carcinogenic risk level of Cr (1.28E-06) for
children is slightly higher than 1 Â 10À6
, showing that the carci-
nogenic risk of Cr is in need of attention for pollution control by
the government.
It is notable that the risk values of both non-carcinogenic and
carcinogenic materials obtained in this study were generally
within the acceptable range, although some assumptions that
were applied in the models seemed to be idealized. Our results
reflected the fact that toxic metals exposure from street dusts
would not cause serious health impacts in Beijing on their own,
with the exception of Cr. However, the calculated risk of both non-
carcinogenic and carcinogenic materials for metal exposures from
street dusts was affected by a high degree of uncertainty (Shi et al.,
2011). Until the present, there have been no integrated methods
and fitting parameters for a health risk assessment of the practical
situation in China. On the one hand, there was a lack of exposure
estimation parameters in addition to metal toxicity data beyond
the six metals selected in this study. The human health risk as-
sessment has been showed to be a powerful tool for distinguishing
the toxic heavy metals and exposure routes of most concerns in
urban environments. In fact, other metals (i.e., As, Sn, Hg, Mn, and
others) that enter human bodies through the ingestion pathway
should be assessed in future research.
4. Conclusion
The concentrations, distribution, accumulation and health risk
assessment of the heavy metals (Zn, Pb, Cr, Cd, Ni, and Cu) in street
dusts from four different functional regions in Beijing were in-
vestigated and assessed in depth in the present study. The Cr, Cu, Zn,
Cd and Pb concentrations in street dusts were higher than the local
soil background and street soil values, indicating that this pollution
may result from anthropogenic inputs. Among the four studied areas,
the Ni, Cu, Zn and Pb concentrations in the TA area were the highest
among the four different areas. In comparison with the concentra-
tions of selected metals in other cities, the heavy metals concentra-
tions in Beijing were generally at medium or low levels. The as-
sessment performed by Geoaccumulation Index indicates that Cr and
Ni are present at unpolluted level, and Cu and Pb are at “un-
contaminated to moderately contaminated” levels, and Cd were
ranked as “heavily contaminated”. The pollution levels of the heavy
metals are as follows: Cd4Pb4Zn4Cu4Cr4Ni, and Cd is the
predominant element among them. The health risk assessment
model was employed to calculate human exposure to heavy metals
from street dusts. For non-carcinogenic effects, the HQ values for the
exposure pathway of the studied heavy metals decreased in children
in the following order: ingestion4dermal contact4inhalation. The
HI values for the studied elements in street dusts were lower than
the safe level. The carcinogenic risk probabilities for Ni and Cd in
children and for Cr, Ni and Cd in adults were under the threshold
value (1 Â 10À6
). However, the carcinogenic risk level of Cr (1.28E-
06) for children is slightly higher than 1 Â 10À6
. This research will be
quite useful both for residents to take protective measures and for
the government to alleviate the heavy metals pollution of the urban
street environment.
Table5
HealthriskfromheavymetalsinstreetdustsofBeijing.
MetalsC(mgkgÀ1
)RfDing(mg/kgday)RfDinh(mg/kgday)RfDderm(mg/kgday)SFinh(mg/kgday)À1
HQingHQinhHQdermChildrenAdults
ChildrenAdultsChildrenAdultsChildrenAdultsHIRiskHIRisk
Cr84.723.00E-032.86E-056.00E-054.20Eþ013.61E-014.84E-021.06E-034.78E-042.89E-027.38E-023.91E-011.28E-061.23E-015.74E-07
Ni25.152.00E-022.06E-025.40E-038.40E-011.61E-022.16E-034.38E-071.97E-079.53E-052.43E-041.62E-027.58E-092.40E-033.41E-09
Cu69.944.00E-024.02E-021.20E-022.24E-023.00E-036.24E-072.81E-071.19E-043.04E-042.25E-023.30E-03
Zn222.653.00E-013.00E-016.00E-029.49E-031.27E-032.66E-071.20E-077.59E-051.94E-049.57E-031.47E-03
Cd0.721.00E-031.00E-031.00E-056.30Eþ009.21E-031.24E-032.58E-071.16E-071.47E-033.76E-031.07E-021.63E-095.00E-037.32E-10
Pb105.063.50E-033.52E-035.25E-043.84E-015.15E-021.07E-054.82E-064.09E-031.05E-023.88E-016.19E-02
X. Wei et al. / Ecotoxicology and Environmental Safety 112 (2015) 186–192 191

7. Acknowledgments
This research is financially supported by the China National
Instrumentation Program (Grant no. 2011YQ14015009).
Appendix A. Supplementary material
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.ecoenv.2014.11.
005.
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