Health
risk assessment of heavy metals in roadside soil along the Hemmat Highway of
Tehran, Iran, in 2014
Abstract
Received: July
2016, Accepted: October 2016
Background:
The present study investigated the impact of land use on health risks (cancerous and non-cancerous) of heavy
metals in soil along the Hemmat Highway of Tehran, Iran. Materials and Methods: A
total of 28 soil samples were collected in August 2014 from the roadside soil
of the Hemmat Highway. The collected samples were air-dried and digested, and
then, analyzed for heavy metals using an atomic absorption spectrophotometer
(AAS). Non-carcinogenic
and carcinogenic health risks were calculated for different land uses (green
space, residential area, under construction, and natural) along the Hemmat
Highway. Results: The hazard index (HI) of Pb, Zn, Cd,
Cr, and Ni was, respectively, 0.28, 0.19 × 10-2, 0.032, 0.043,
0.006 for children, and was 0.037, 0.24 × 10-3, 0.014, 0.012, 0.76
× 10-3 for adults. Carcinogenic risk of metals was analyzed for Cd, Cr,
and Ni. The carcinogenic risk ýof Pb,
Ni, Zn, and Cd was 0.144
× 10-7, 0.427 × 10-6, and 9.41 × 10-2,
respectively. Conclusions: The carcinogenic risk levels of
the three studied metals were < 10-6 with higher values
attributed to Crý. HIs for all metals were
lower than their threshold values, indicating nil health hazards. The results
of risk assessment showed that the highest risk value was related to ingestion of Pb. |
Keywords: Health Risk, Land, soil, Heavy Metal
Introduction
Heavy metals have toxic, non-biodegradable, and accumulative properties,
due to which they could have potentially adverse health effects on inhabitants.
They may cause DNA damage, and may induce mutagenic, teratogenic, and
carcinogenic effects (1). For instance, the excessive intake of Pb can damage
the nervous, skeletal, circulatory, enzymatic, endocrine, and immune systems (2).
The chronic effects of Cr and Cd dust or aerosol articulate matter intake through
soil ingestion consist of lung cancer, pulmonary adenocarcinomas, prostatic
proliferative lesions, bone fractures, kidney dysfunction, and hypertension (2).
Cu and Zn can change the function of the human central nervous system and
respiratory system, and disrupt the endocrine system (3).
There is also evidence that chronic exposure to low doses of carcinogenic
heavy metals may cause many* types
of cancer (4). Thus, heavy metals are important issue in the environment. Both
natural (weathering, erosion of parent rocks, atmospheric deposition, volcanic
activities, and etc.) and anthropogenic (sewage irrigation, the addition of
manures, fertilizers and pesticides, domestic waste, industries and
transportation, etc.) activities cause soil contamination by heavy metals (5-7).
The most common heavy metals released by vehicles on roads are cadmium (Cd),
chromium (Cr), lead (Pb), nickel (Ni), and zinc (Zn) (8); thus, we studied
these metals.
Pollutants enter the human body through respiration, inhalation, and
direct skin contact causing negative health effects (2,9-10),
especially in children, due to their underdeveloped immune systems and inadvertent
ingestion of much dust through the hand-to-mouth pathway (3,11). It is
estimated that 50-200 mg/day soil could be ingested by children (1).
Young children are particularly sensitive to heavy metal poisoning,
because childhood is the period of maximal brain and body growth (8). Therefore, it is important
to assess the health risk of toxic metals in the environment. Metal levels of roadside
dust are usually higher than other media (e.g., soils), and roadside dust can be
re-suspended frequently; thus, individuals bicycling or walking on the roadside
could easily be exposed to the toxicants in the dust (1). Therefore, dust
samples were studied in the present study.
Roadside dust particles in urban regions have a high surface area and
are easily transported and deposited, and carry a potentially toxic element
load (8).
Tehran (the capital of Iran) is rated as one of the world’s most
polluted cities wherein, with rapid urbanization, industrialization, and
population growth during the last two decades, the heavy metal pollution in
urban soil and roadside dust has turned into a serious issue (12).
While numerous studies of heavy metal contamination via roadside soil
have been carried out in developed countries (13), only limited information is
available in this regard in developing countries. For example, Junhua et al. found
that the hazard index (HI) for all metals were lower than their threshold
values, indicating the lack of health hazards in Maha Sarakham, Thailand (3).
Olawoyin et al. showed that mean concentrations (0–15 cm) of Zn (58.3 ±
37.0), Cd (1.3 ± 1.0), Cr(VI) (13.2 ± 5.5), Pb (895.1 ±
423.9), and Ni (42.7 ± 20.3) were higher than some guidelines and standard
values. The risk assessment with the use of United States Environmental
Protection Agency (EPA) models showed that metals with the highest cancer risk
values (Pb = 2.62E-02 and Cr(VI) = 1.52E-02) have the potential of affecting
the health status, especially of children in the Niger USA (14).
Wu et al. measured the concentrations of As, Cd, Co, Cr, Cu, Hg, Mn,
Ni, Pb, V, and Zn in the soil in Dongguan, China (9). The mean concentrations were
lower than both the soil environmental quality standards of China and the
Canadian soil quality guidelines. Risk assessment was performed using the Department
of Energy (DoE) model. They reported that the element of As
may pose both carcinogenic and non-carcinogenic risks to human health. They also
showed that the main exposure pathways of As to the
human body are ingestion and inhalation of soil particles (9).
In Iran, Saeedi et al. reported that traffic and related activities, and
petrogenic and pyrogenic sources could be the main anthropogenic sources of
heavy metals and polycyclic aromatic hydrocarbons (PAHs) in street dust in Tehran
(15). Keshavarzi et al. performed human health risk assessment, and studied
chemical speciation and pollution level of selected heavy metals in urban
street dust in Shiraz (Iran) (12). They showed that carcinogenic risk and non-carcinogenic
risk due to urban street dust exposure is acceptable in Shiraz. Gholampour et
al. investigated the exposure and health impacts of outdoor particulate matter (PM)
in both urban and industrialized areas of Tabriz (16). According to the
cardiovascular and respiratory mortalities associated with Total Suspended
Particles TSP and PM10.
Numerous researches have been carried out on heavy metals
contamination; distribution and source identification of street dust have been
carried out in innumerable cities. However, there is no information available
on potentially toxic metals in surface dust of Tehran city.
Hemmat is one of the relatively new and heavily traveled highways of
Tehran and few environmental studies have been conducted on it. For this
reason, the Hemmat highway was selected as the study area in this study.
The main aim of this study was to evaluate the
concentration and health risk of Cd, Cr, Ni, Pb, and Zn in roadside soil from
Hemmat Highway of Tehran according to distance from edge of the road and land
use in the study area.
Table 1:
Exact location of sampling stations
Sample |
N |
E |
Distance from edge of the road (m) |
Land use in the study area |
1 |
35˚ 45.655
́ |
051˚ 14.858
́ |
0-10 |
Green space |
2 |
35˚ 45.650
́ |
051˚ 14.858
́ |
10-20 |
Green space |
3 |
35˚ 45.468
́ |
051˚ 13.830
́ |
0-10 |
Residential |
4 |
35˚ 45.487
́ |
051˚ 13.816
́ |
10-20 |
Residential |
5 |
35˚ 45.421
́ |
051˚ 13.248
́ |
0-10 |
Under construction |
6 |
35˚ 45.415
́ |
051˚ 13.251
́ |
10-20 |
Under construction |
7 |
35˚ 45.507
́ |
051˚ 12.346
́ |
0-10 |
Green space |
8 |
35˚ 45.510
́ |
051˚ 12.360
́ |
10-20 |
Green space |
9 |
35˚ 45.472
́ |
051˚ 11.826
́ |
0-10 |
Under construction |
10 |
35˚ 45.479
́ |
051˚ 11.826
́ |
10-20 |
Under construction |
11 |
35˚ 45.361
́ |
051˚ 11.313
́ |
0-10 |
Natural |
12 |
35˚ 45.369
́ |
051˚ 11.316
́ |
10-20 |
Natural |
13 |
35˚ 45.702
́ |
051˚ 10.041
́ |
0-10 |
Natural |
14 |
35˚ 45.479
́ |
051˚ 11.826
́ |
10-20 |
Natural |
15 |
35˚ 45.531
́ |
051˚ 10.408
́ |
0-10 |
Natural |
16 |
35˚ 45.541 ́ |
051˚ 10.406
́ |
10-20 |
Natural |
17 |
35˚ 45.361
́ |
051˚ 11.313
́ |
0-10 |
Under construction |
18 |
35˚ 45.369
́ |
051˚ 11.316
́ |
10-20 |
Under construction |
19 |
35˚ 45.472
́ |
051˚ 11.826
́ |
0-10 |
Residential |
20 |
35˚ 45.479
́ |
051˚ 11.826
́ |
10-20 |
Residential |
21 |
35˚ 45.507
́ |
051˚ 12.346
́ |
0-10 |
Green space |
22 |
35˚ 45.510
́ |
051˚ 12.360
́ |
10-20 |
Green space |
23 |
35˚ 45.421
́ |
051˚ 13.248
́ |
0-10 |
Under construction |
24 |
35˚ 45.415
́ |
051˚ 13.251
́ |
10-20 |
Under construction |
25 |
35˚ 45.468
́ |
051˚ 13.830
́ |
0-10 |
Green space |
26 |
35˚ 45.487
́ |
051˚ 13.816
́ |
10-20 |
Green space |
27 |
35˚ 45.655
́ |
051˚ 14.858
́ |
0-10 |
Residential |
28 |
35˚ 45.650
́ |
051˚ 14.858
́ |
10-20 |
Residential |
Material and Methods
Sampling was conducted from the East to West and West to East of Hemmat
Highway (round trip) from the intersection of Azadegan Boulevard and Hemmat
Highway by Pazhohesh Boulevard.
The samples were collected at the distance length of 14 km from the
highway. The distance between sampling stations was 1 km. At each station, samples were collected at two
distances of 0-10 and 10-20 m from the edge of the highway. Efforts were made
to collect samples from surface soil (0–10 cm) and avoid other sources of
contamination at each site. The area surrounding the highway has different land
uses, including green space, construction, residential, and natural land uses
(Figure 1). In case of heavy rainfall, strong storm, and waste discharge in the
sample stations, they were excluded from the study.
A total of 28 soil samples were collected in August 2014 from roadside
soil of Hemmat Highway. Details of the exact locations of sampling stations are
presented in table 1.
Approximately 600 g per sample of roadside soil was collected with
stainless steel scoops from 0-5 cm of ground surface, and then, placed into
polyethylene bags for transportation to the laboratory. According to the EPA,
stainless steel scoops are suitable because they do not contaminate soil
samples with the metals used in the construction of the samples (17).
The collected samples were air-dried at room temperature, ground, and
sieved through a 230 mesh nylon sieve. For the total heavy metal content
analysis, 600 mg of each dried sample was digested by HClO4, HCl,
HNO3, and HF (Merck & Co., USA) (18). The solutions of digested
samples were analyzed for Cd, Ni, Pb, Cu, Zn, and Cr using an atomic absorption
spectrophotometer (AA-700 series, Shimadzu
Corp., Japan) flame mode. The detection limits of the spectrometer were 0.0150 mg/ml for Cd,
0.1250 mg/ml for Pb, 0.0075 mg/ml for Zn, and 0.0500 mg/ml for Ni.
Different models are available for human health risk assessment of
heavy metals in soil which are presented below.
1) World Health Organization Model
The approach proposed by the World Health Organization (WHO) was
applied using the AirQ software (version 2.2.3, WHO European Centre for
Environment and Health, Bilthoven Division, Netherlands) (12).
2) Department of Energy Model (19)
In this model, three ways of human body exposure to heavy metals were
considered; (a) direct oral ingestion of soil particles (CDIing), (b) dermal
absorption of elements (CDIdermal), and (c) inhalation of re-suspended soil
particulates through the nose or mouth (CDIinh).
3) ýUnited States Environmental
Protection
Agency Model
This Model is similar to the DoE Model (20). In the EPA model, the
exposure dose was calculated for children and adults.
The model used in this study to calculate the human exposure to roadside
dust metals is based on that developed by the EPA.
Health risk assessment model: The EPA model
is based on five assumptions (21). The first assumption is that human beings
are exposed to roadside dust through the three main pathways of ingestion of
dust particles, inhalation of dust particles, and dermal contact with dust
particles. The second was that intake rates and particle emission can be
approximated by those developed for soil. The third was that some exposure parameters
of residents of the observed areas are similar to those of reference
populations. The fourth was that total non-carcinogenic risk could be
calculated for each metal (Pb, Cr, Zn, Cd, and Ni) by summing the individual
risks of the three exposure ways. The fifth assumption was that total
carcinogenic risk could be computed for each metal (As, Cd, and Cr) by summing
the individual risks calculated for the three exposure ways.
The equations provide by the EPA for calculating exposure amounts of
potentially toxic metals through the three routes are listed below (20).The
dose received via each of the three paths was calculated using the following Equations
(20):
×10-6
, ×10-6
Where Ding is the daily dose of hand-to-mouth ingestion of
substrate particles, Dinh is the daily dose of inhalation of
re-suspended particles through the mouth and nose, Ddermal is the
daily dose of dermal absorption of trace elements in particles adhered to
exposed skin, LADD is the lifetime average daily dose for carcinogenic elements
through inhalation. The meaning and corresponding unit values of other
parameters are provided in table 2.
Table 2: Meaning and corresponding unit values of parameters
Values |
Meaning (unit values) |
Parameter |
|
Adult |
Child |
||
- |
- |
Exposure-point
concentration (mg/kg) |
C |
100 |
200 |
Ingestion rate (mg/day) |
IngR |
20 |
7.6 |
Inhalation rate (m3/day) |
InhR |
1.36 × 109 |
1.36 × 109 |
Particle emission factor (m3/kg) |
PEF |
5700 |
2800 |
Exposed skin area (cm2) |
SA |
0.7 |
0.2 |
Skin adherence factor [mg/(cm2hour)] |
SL |
0.001 |
0.001 |
Dermal absorpton factor (unitless) |
ABS |
24 |
6 |
Exposure duration (year) |
ED |
180 |
180 |
Exposure frequency (day/year) |
EF |
70 |
15 |
Average body weight (kg) |
BW |
ED × 365(for
non-carcinogens) 70 × 365(for carcinogens) |
Average time (day) |
AT |
The non-carcinogenic risks
for individual metals were calculated using the following equation:
where HI is the
hazard index, HQ is the hazard quotient, D is average daily dose calculated for
each element and exposure pathway, and Rfd is specific reference dose given for
each pollutant parameter. The particular reference dose (Rfd)
(mg/kg.day) was an estimate of maximum permissible risk of a human population
through daily exposure during a lifetime. If HQ or HI exceeds 1, there is a
chance of occurrence of non-carcinogenic effects, with a probability which
tends to increase as the value of HQ or HI increases (20).
The potential was
calculated using the following equation:
CR = D × SF
where SF
is the corresponding slope factor.
According to the EPA, if the value of CR is above 10-4-10-6,
the exposed population is at risk.
Results
Concentrations of heavy metals in roadside soil
The concentrations of heavy
metals in roadside soil are shown in table 3.
The mean Pb, Cr, Ni, Zn, and
Cd concentrations were 144 ± 89.90, 17.20 ± 9.02, 18.91 ± 6.62, 86.84 ± 46.72, and
3.86 ± 2.02 mg/kg, respectively.
Table 3: Concentrations of heavy metals
(mg/kg) in roadside soil
Mean |
Maximum |
Minimum |
Heavy metals |
144 |
370.38 |
53.58 |
Pb |
17.20 |
45.90 |
10.39 |
Cr |
18.91 |
28.13 |
10.50 |
Ni |
86.84 |
173.74 |
12.99 |
Zn |
3.86 |
7.94 |
0.44 |
Cd |
Health risk assessment of heavy metals
The results of health risk assessment are shown in table 4. As is depicted, non-carcinogenic
health risks for children were higher than adults.
Health risk assessment of heavy metals in
different land uses
The non-carcinogenic risk was also calculated for
different land uses and both adults and children, and the corresponding results
are presented in tables 5-8.
Green space
As denoted in table 5, the non-carcinogenic health
risk for children was higher than adults.
Table 4: Exposure dose, hazard quotient, and
risk for each element and exposure pathway (mg/kg.day)
|
Pb |
Zn |
Cd |
Cr |
Ni |
RfDing |
3.50 × 10-03 |
0.30 |
0.001 |
0.003 |
0.02 |
RfDinh |
3.50 × 10-02 |
0.30 |
0.001 |
0.286 × 10-4 |
0.02 |
RfDd×10rmal |
5.25 × 10-04 |
0.06 |
0.1 × 10-4 |
0.06-3 |
0.54 × 10 |
Sfinh |
|
|
6.30 |
42 |
0.84 |
Child |
|
|
|
|
|
Ding |
0.95 × 10-3 |
0.57 × 10-3 |
2.54 × 10-5 |
0.11 × 10-3 |
0.12 × 10-3 |
Dinh |
2.65 × 10-8 |
0.16 × 10-9 |
7.09 × 10-10 |
3.16 × 10-9 |
3.47 × 10-9 |
Ddermal |
2.65 × 10-6 |
0.16 × 10-7 |
7.11 × 10-8 |
3.17 × 10-7 |
3.48 × 10-7 |
LADD |
|
|
2.29 × 10-9 |
10.17 × 10-9 |
11.2 × 10-9 |
HQing |
0.27 |
0.04 |
0.006 |
0.002 |
0.025 |
HQinh |
7.59 × 10-7 |
5.32 × 10-8 |
7.09 × 10-7 |
0.11 × 10-3 |
1.74 × 10-7 |
HQdermal |
0.005 |
2.67 × 10-5 |
0.007 |
0.005 |
6.45 × 10-5 |
HI = ΣHQi |
0.28 |
0.19 × 10-2 |
0.032 |
0.043 |
0.006 |
Cancer risk |
|
|
0.144 × 10-7 |
0.427 × 10-6 |
9.41 × 10-9 |
Adult |
|
|
|
|
|
Ding |
0.0001 |
6.12×10-5 |
2.72 × 10-6 |
1.21 × 10-5 |
1.33 × 10-5 |
Dinh |
1.49 × 10-8 |
0.9 × 10-10 |
4.00 × 10-10 |
1.78 × 10-9 |
1.96 × 10-9 |
Ddermal |
4.05 × 10-6 |
2.44 × 10-6 |
1.09 × 10-7 |
4.84 × 10-7 |
5.32 × 10-7 |
LADD |
|
|
2.29 × 10-9 |
10.17 × 10-9 |
11.2 |
HQing |
0.029 |
0.2 × 10-3 |
0.0027 |
0.004 |
0.0007 |
HQinh |
4.26 × 10-7 |
3 × 10-8 |
0.40 × 10-8 |
6.23 × 10-5 |
9.8 × 10-8 |
HQdermal |
0.03 |
0.20 × 10-3 |
0.27 × 10-2 |
4.04 × 10-2 |
0.67 × 10-3 |
HI = ΣHQi |
0.037 |
0.24 × 10-3 |
0.014 |
0.012 |
0.76 × 10-3 |
Cancer risk |
|
|
0.144 × 10-7 |
0.427 × 10-6 |
9.41 × 10-9 |
Rfd: Specific reference dose; ýSF: Slope factor; D: Average daily
dose; LADD: Lifetime average daily dose; ýýHQ: Hazard quotient; HI: Hazard
index
Table 5: Exposure dose, hazard quotient, and
risk for each element and exposure pathway (mg/kg.day) in the green space
|
Pb |
Zn |
Cd |
Cr |
Ni |
RfDing |
3.50 × 10-3 |
0.30 |
0.001 |
0.003 |
0.02 |
RfDinh |
3.50 × 10-2 |
0.30 |
0.001 |
0.286 × 10-4 |
0.02 |
RfDdermal |
5.25 × 10-4 |
0.06 |
0.1 × 10-4 |
0.06 × 10-3 |
0.54 × 10-2 |
Sfinh |
|
|
6.30 |
42 |
0.84 |
Child |
|
|
|
|
|
Ding |
0.797 × 10-3 |
0.748 × 10-3 |
3.06 × 10-5 |
0.104 × 10-3 |
0.1 × 10-3 |
Dinh |
2.23 × 10-8 |
2.09 × 10-8 |
8.56 × 10-10 |
2.91 × 10-9 |
2.79 × 10-9 |
Ddermal |
2.23 × 10-6 |
2.09 × 10-6 |
8.58 × 10-8 |
2.91 × 10-7 |
2.8 × 10-7 |
LADD |
|
|
2.76 × 10-9 |
9.37 × 10-9 |
0.9 × 10-8 |
HQing |
0.228 |
0.002 |
0.03 |
0.035 |
0.005 |
HQinh |
6.36 × 10-7 |
6.97 × 10-8 |
8.56 × 10-7 |
0.0001 |
1.397 × 10-7 |
HQdermal |
0.004 |
3.492 × 10-5 |
0.0086 |
0.0049 |
5.186 × 10-5 |
HI = ΣHQi |
0.232 |
0.0025 |
0.039 |
0.039 |
0.005 |
Cancer risk |
|
|
1.74 × 10-8 |
3.94 × 10-7 |
7.56 × 10-9 |
Adult |
|
|
|
|
|
Ding |
8.54 × 10-5 |
8.02 × 10-5 |
3.28 × 10-6 |
1.12 × 10-5 |
1.07 × 10-5 |
Dinh |
1.26 × 10-8 |
1.18 × 10-8 |
4.83 × 10-10 |
1.64 × 10-9 |
1.58 × 10-9 |
Ddermal |
3.41 × 10-6 |
3.2 × 10-6 |
1.31 × 10-7 |
4.45 × 10-7 |
4.28 × 10-7 |
LADD |
|
|
2.76 × 10-9 |
9.37 × 10-9 |
0.9 × 10-8 |
HQing |
0.024 |
0.00027 |
0.0033 |
0.0037 |
0.00054 |
HQinh |
3.586 × 10-7 |
3.93 × 10-8 |
4.828 × 10-7 |
5.734 × 10-5 |
7. 879 × 10-8 |
HQdermal |
0.0065 |
5.331 × 10-5 |
0.0131 |
0.0074 |
7.918 × 10-5 |
HI = ΣHQi |
0.031 |
0.00032 |
0.016 |
0.011 |
0.0006 |
Cancer risk |
|
|
1.74 × 10-8 |
3.94 × 10-7 |
7.56 × 10-9 |
Rfd: Specific reference dose; ýSF: Slope factor; D: Average daily
dose; LADD: Lifetime average daily dose; ýýHQ: Hazard quotient; HI: Hazard
index
Table 6: Exposure dose, hazard quotient, and
risk for each element and exposure pathway (mg/kg.day) for the residential area
|
Pb |
Zn |
Cd |
Cr |
Ni |
RfDing |
3.50 × 10-03 |
0.30 |
0.001 |
0.003 |
0.02 |
RfDinh |
3.50 × 10-02 |
0.30 |
0.001 |
0.286 × 10-4 |
0.02 |
RfDdermal |
5.25 × 10-04 |
0.06 |
0.1 × 10-4 |
0.06-3 |
0.54 × 10-2 |
Sfinh |
|
|
6.30 |
42 |
0.84 |
Child |
|
|
|
|
|
Ding |
0.11 × 10-2 |
0.82 × 10-3 |
3.43 × 10-5 |
0.11 × 10-3 |
0.17 × 10-3 |
Dinh |
3.01 × 10-8 |
2.29 × 10-8 |
9.59 × 10-10 |
3.01 × 10-9 |
4.84 × 10-9 |
Ddermal |
3.02 × 10-6 |
2.29 × 10-6 |
9.61 × 10-8 |
3.02 × 10-7 |
4.85 × 10-7 |
LADD |
|
|
3.09 × 10-9 |
9.71 × 10-9 |
1.56 × 10-8 |
HQing |
0.308 |
0.0027 |
0.034 |
0.036 |
0.0087 |
HQinh |
8.601 × 10-7 |
7.634 × 10-8 |
9.590 × 10-7 |
0.105 × 10-3 |
2. 419 × 10-7 |
HQdermal |
0.0057 |
3.825 × 10-5 |
0.0096 |
0.005 |
8.977 × 10-5 |
HI = ΣHQi |
0.031 |
0.003 |
0.044 |
0.041 |
0.009 |
Cancer risk |
|
|
1.94 × 10-8 |
4.08 × 10-7 |
1.31 × 10-8 |
Adult |
|
|
|
|
|
Ding |
0.12 × 10-3 |
0.82 × 10-3 |
3.43 × 10-5 |
0.11 × 10-3 |
0.17 × 10-3 |
Dinh |
1.7 × 10-8 |
1.29 × 10-8 |
5.41 × 10-10 |
1.7 × 10-9 |
2.73 × 10-9 |
Ddermal |
4.61 × 10-6 |
3.5 × 10-6 |
1.47 × 10-7 |
4.61 × 10-7 |
7.4 × 10-7 |
LADD |
|
|
3.09 × 10-9 |
9.71 × 10-9 |
1.56 × 10-8 |
HQing |
0.033 |
0.293 × 10-3 |
0.368 × 10-2 |
0.39 × 10-2 |
0.927 × 10-3 |
HQinh |
4.85 × 10-7 |
4.305 × 10-8 |
5.408 × 10-7 |
5.941 × 10-5 |
1. 364 × 10-7 |
HQdermal |
0.877 × 10-2 |
0.84 × 10-6 |
0.0147 |
0.77 × 10-2 |
0137 × 10-3 |
HI = ΣHQi |
0.042 |
0.004 |
0.018 |
0.012 |
0.001 |
Cancer risk |
|
|
1.94 × 10-8 |
4.08 × 10-7 |
1.31 × 10-8 |
Rfd: Specific reference dose; ýSF: Slope factor; D: Average daily
dose; LADD: Lifetime average daily dose; ýýHQ: Hazard quotient; HI: Hazard
index
Residential
The risk assessment results
indicated that in residential use, the highest risk value was related to ingestion of Pb in
children, whereas the highest risk value was related to ingestion of Cd in
adults (Table 6).
Table 7: Exposure dose, hazard quotient, and risk
for each element and exposure pathway (mg/kg.day) in the under construction
area
|
Pb |
Zn |
Cd |
Cr |
Ni |
RfDing |
3.50 × 10-03 |
0.30 |
0.001 |
0.003 |
0.02 |
RfDinh |
3.50 × 10-02 |
0.30 |
0.001 |
0.286 × 10-4 |
0.02 |
RfDdermal |
5.25 × 10-04 |
0.06 |
0.1 × 10-4 |
0.06-3 |
0.54 × 10-2 |
Sfinh |
|
|
6.30 |
42 |
0.84 |
Child |
|
|
|
|
|
Ding |
0.11 × 10-2 |
0.556 × 10-3 |
2.93 × 10-5 |
0.104 × 10-3 |
0.148 × 10-3 |
Dinh |
3.01 × 10-8 |
1.55 × 10-8 |
8.19 × 10-10 |
2.92 × 10-9 |
4.13 × 10-9 |
Ddermal |
3.01 × 10-6 |
1.56 × 10-6 |
8.21 × 10-8 |
2.93 × 10-7 |
4.14 × 10-7 |
LADD |
|
|
2.64 × 10-9 |
9.41 × 10-9 |
1.33 × 10-8 |
HQing |
0.307 |
0.185 × 10-2 |
0.029 |
0.0348 |
0.0074 |
HQinh |
8.588 × 10-7 |
5.183 × 10-8 |
8.1948 × 10-7 |
0.102 × 10-3 |
2. 063 × 10-7 |
HQdermal |
0.574 × 10-2 |
2.597 × 10-5 |
0.821 × 10-2 |
0.488 × 10-2 |
7.658 × 10-5 |
HI = ΣHQi |
0.313 |
0.00188 |
0.0375 |
0.0399 |
0.00746 |
Cancer risk |
|
|
1.64 × 10-8 |
3.95 × 10-7 |
1.11 × 10-8 |
Adult |
|
|
|
|
|
Ding |
0.12 × 10-3 |
0.596 × 10-6 |
0.314 × 10-6 |
0.112 × 10-6 |
0.158 × 10-6 |
Dinh |
1.7 × 10-8 |
8.77 × 10-9 |
4.62 × 10-10 |
1.65 × 10-9 |
2.33 × 10-9 |
Ddermal |
4.60 × 10-6 |
2.38 × 10-6 |
1.25 × 10-7 |
4.47 × 10-7 |
6.31 × 10-7 |
LADD |
|
|
2.64 × 10-9 |
9.41 × 10-9 |
1.33 × 10-8 |
HQing |
0.033 |
0.199 × 10-3 |
0.314 × 10-2 |
0.37 × 10-2 |
0.791 × 10-3 |
HQinh |
4.84 × 10-7 |
2.923 × 10-8 |
4.621 × 10-7 |
5.756 × 10-5 |
1. 163 × 10-7 |
HQdermal |
0.876 × 10-2 |
3.965 × 10-5 |
0.0125 |
0.744 × 10-2 |
0.117 × 10-3 |
HI=ΣHQi |
0.0417 |
0.238 × 10-3 |
0.0157 |
0.0112 |
0.908 × 10-3 |
Cancer risk |
|
|
1.64 × 10-8 |
3.95 × 10-7 |
1.11 × 10-8 |
Rfd: Specific reference dose; ýSF: Slope factor; D: Average daily
dose; LADD: Lifetime average daily dose; ýýHQ: Hazard quotient; HI: Hazard
index
Under construction
The results of risk assessment in under construction areas are
presented in table 7, wherein the highest risk value is related to ingestion of Pb.
Natural use
As demonstrated in table 8 and by the results of the used
models, the non-carcinogenic health risks of children were higher than adults
in natural areas.
Table 8: Exposure dose, hazard quotient, and
risk for each element and exposure pathway (mg/kg.day) in natural areas
|
Pb |
Zn |
Cd |
Cr |
Ni |
RfDing |
3.50 × 10-3 |
0.30 |
0.001 |
0.003 |
0.02 |
RfDinh |
3.50 × 10-02 |
0.30 |
0.001 |
0.286 × 10-4 |
0.02 |
RfDdermal |
5.25 × 10-04 |
0.06 |
0.1 × 10-4 |
0.06 × 10-3 |
0.54 × 10-2 |
Sfinh |
|
|
6.30 |
42 |
0.84 |
Child |
|
|
|
|
|
Ding |
0.845 × 10-3 |
0.105 × 10-3 |
4.27 × 10-6 |
0.142 × 10-6 |
7.69 × 10-5 |
Dinh |
2.36 × 10-8 |
2.95 × 10-9 |
1.19 × 10-10 |
3.97 × 10-9 |
2.15 × 10-9 |
Ddermal |
2.37 × 10-6 |
2.95 × 10-7 |
1.20 × 10-8 |
3.98 × 10-7 |
2.15 × 10-7 |
LADD |
|
|
3.85 × 10-10 |
1.28 × 10-8 |
6.93 × 10-9 |
HQing |
0.241 |
0.352 × 10-3 |
0.427 × 10-2 |
0.0474 |
0.385 × 10-2 |
HQinh |
6.74 × 10-7 |
9.823 × 10-9 |
1.194 × 10-7 |
0.139 × 10-3 |
1.075 × 10-7 |
HQdermal |
0.45 × 10-2 |
4.921 × 10-6 |
0.0012 |
0.663 × 10-2 |
3.99 × 10-5 |
HI = ΣHQi |
0.246 |
0.356 × 10-3 |
0.0055 |
0.054 |
0.0039 |
Cancer risk |
|
|
5.82 × 10-9 |
5.37 × 10-7 |
2.42 × 10-9 |
Adult |
|
|
|
|
|
Ding |
9.05 × 10-5 |
1.13 × 10-5 |
4.58 × 10-7 |
1.52 × 10-5 |
8.24 × 10-6 |
Dinh |
1.33 × 10-8 |
1.66 × 10-9 |
6.73 × 10-11 |
2.24 × 10-9 |
1.21 × 10-9 |
Ddermal |
3.61 × 10-6 |
4.51 × 10-7 |
1.83 × 10-8 |
6.07 × 10-7 |
3.29 × 10-7 |
LADD |
|
|
3.85 × 10-10 |
1.28 × 10-8 |
6.93 × 10-9 |
HQing |
0.0259 |
3.767 × 10-5 |
0.46 × 10-3 |
0.0051 |
0.41 × 10-3 |
HQinh |
3.802 × 10-7 |
5.539 × 10-9 |
6.734 × 10-8 |
7.828 × 10-5 |
6.061 × 10-8 |
HQdermal |
0.0069 |
0.751 × 10-5 |
0.0018 |
0.0101 |
0.609 × 10-4 |
HI = ΣHQi |
0.0327 |
0.452 × 10-4 |
0.0023 |
0.0153 |
0.47 × 10-3 |
Cancer risk |
|
|
5.82 × 10-9 |
5.37 × 10-7 |
2.42 × 10-9 |
Rfd:
Specific reference dose; ýSF: Slope
factor; D: Average daily dose; LADD: Lifetime average daily dose; ýýHQ: Hazard quotient; HI: Hazard index
Discussion
The mean concentrations of Pb (144 ± 89.90 mg/kg) and
Cd (3.86 ± 2.02 mg/kg) were considerably higher than the background level (100
mg/kg for Pb) (0.8 mg/kg for Cd) (22). The mean concentrations of these heavy
metals obtained by other researchers in Tehran were also higher than background
level. Saeedi et al. reported the mean concentrations of Pb, Zn, Ni, and Cd in
roadside soil of Tehran–Karaj Highway, Iran as 669.30 mg/kg, 614.312 mg/kg, 90.32
mg/kg, and 3.90 mg/kg, respectively (15). The HQs of children through
ingestion were averaged 7.5 times higher in comparison to adults. Outputs of the
model indicated that the order of the major exposure routes to street dust for
both adults and children were ingestion > dermal contact > inhalation. Ingestion is the
major route of exposure to street dust for both adults and children. The
potential health risk through inhalation is almost negligible as compared to
other exposure routes. Similar results were obtained by Wu et al., who
performed health risk assessment of heavy metals in Dongguan, China (9). Moreover,
Zheng et al. (23) studied exposure to heavy metals in street dust in a zinc
smelting district and Fang et al. (24) investigated exposure to heavy metals in
surface dust of the Wuhu urban area, China. The order of non-cancerous HIs
of metals were Pb > Cr > Cd > Zn for children and Pb > Cr > Cd
> Ni > Zn for adults, indicating similar highest and lowest HIs of metals.
Pb depicted the
highest risk value (0.28), whereas Zn indicated the lowest risk value (0.0019). Similarly, Olawoyin et al. reported
the maximum total risk for Pb as 2.6E-02. Furthermore, Keshavarzi et al. showed
HI level in the order of Pb > Hg > Cu > Zn > Ni> Mn > Sb >
Cr > Fe, wherein Pb had the highest risk value (0.223), and Fe exhibited the
lowest value (0.00012). The HQs for children averaged 2.5-7.5 times higher than
adults, especially for Zn, Pb, and Ni. The HQs and HIs for all heavy
metals were lower than 1, indicating that the adverse health impact on children
and adults exposed to heavy metals in road dust was relatively low in Tehran
city (12).
Some heavy metals (for example Pb) have a cumulative
effect (25). It has been reported that elements such as Zn, Pb, and Ni in the
environment have a major influence on children's health. Considering the higher
ingestion rate for children, the exposure of children to soil may exhibit
higher potential health risks. Among the carcinogenic metals, Cd, Cr, and Ni
were analyzed. The carcinogenic risk levels of these metals were < 10-6
with higher values attributed to Cr (0.427 × 10-6), followed by Cd (0.144 × 10-7) and Ni (9.41 × 10-9). Thus, the carcinogenic risks of
these three studied metals were lower than the threshold values range (10-6-10-4), above which environmental
and regulatory agencies consider the risk unacceptable; therefore, it can be
safely suggested that there was no cancer risk in Tehran city (9, 3, 12, 14).
The non-carcinogenic health risk for children was
higher than that for adults. The risk assessment results showed that the highest risk value pertained
to ingestion of Pb. In the green space, HI values decreased in the order of Pb
> Cr > Cd > Ni > Zn for both children and adults; Pb exhibited the
highest risk value, whereas Zn indicated the lowest risk value. The HQs for
children averaged 2.3-8.2 times higher than adults. The HQs
and HIs for all heavy metals were lower than 1, which indicated that the
adverse health impact on children and adults exposed to heavy metals in road
dust was relatively low in Tehran city. Among the carcinogenic metals, Cd, Cr, and Ni were analyzed
for the said land use (green space). The carcinogenic risks for the studied
metals were lower than the threshold values range (10-6-10-4).
In residential use, HI values decreased in the order of Cd > Cr > Pb >
Ni > Zn for children, and in the order of Pb > Cd > Cr > Zn > Ni
for adults; Pb
demonstrated the highest risk value for adults whereas for children Cd presented
the highest risk value. Nevertheless, in children, HQs averaged 2.3-8.2 times
higher than adults. The HQs and HIs for all heavy metals were lower than 1
in residential use. The
carcinogenic risks for metals viz. Cd (1.94 × 10-8), Cr (4.08 × 10-7), and Ni (1.31 × 10-8) were lower than the threshold
values range (10-6-10-4). Likewise, Olawoyin et al. reported that soil
contamination in the industrial and residential regions are similarly significant (14). However,
the risk assessment proved that, based on the concentration of pollutants in
the soil, metals with the highest cancer risk values (Pb = 2.62 × 10-2
and Cr(VI) = 1.52 × 10-2) have the potential to affect the
health status of residents, especially children. The chronic daily intake of
metals is of major concern as their cumulative effect could result to numerous
health complications in children and adults in the region.
The results of risk assessment in under construction areas are shown in
table 7, wherein the
highest risk value pertained to Pb ingestion. In under construction use, HI values decreased in the order
of Pb> Cr > Cd > Ni > Zn for children, and in the order of Pb > Cd >
Cr > Ni > Zn for adults. Pb demonstrated the highest risk value, whereas Zn
indicated the lowest value in both age groups. The HQs for children averaged
2.3-8.2 times higher than adults. The HQs and HIs for all heavy
metals were lower than 1, which indicated that the adverse health impact on
children and adults exposed to heavy metals in road dust was relatively low in
under construction areas. Moreover, the carcinogenic risks for Cd (1.64 × 10-8), Cr (3.95 × 10-7), and Ni (1.11 × 10-8) were lower than the threshold
values range (10-6-10-4).
As indicated in table 9, for natural use, the
non-carcinogenic health risk for children was higher than adults. The
results of risk assessment exhibited that the highest risk value was related to ingestion of Pb. The
order of non-cancerous HIs of metals in natural use was Pb > Cr > Cd > Ni
> Zn in both children and adults. Pb (0.313) exhibited the highest risk value, whereas Zn
(0.002) showed the lowest risk value. The HQs for children averaged 2.3-8.2
times higher than adults. The HQs and HIs for all heavy metals were lower than 1.
The carcinogenic risk
levels of these metals were < 10-6, with higher values attributed
to Cr (5.37 × 10-7), followed by Cd (5.82 × 10-9), and Ni (2.42 × 10-9). Thus, the carcinogenic risks
for these three metals were lower than the threshold values range (10-6-10-4), above which environmental
and regulatory agencies consider the risk unacceptable, this signifies no
cancer risk for natural
use in Tehran city. Junhua et al. collected surface dust samples from 14
different sites in 5 different function areas in Maha Sarakham and Thailand
municipality (7). Function areas were classified as commercial, parking lot,
residential, park, and traffic. The order of non-cancerous HIs of metals was Cd > Pb
> Cu > Zn for children and Pb > Cd > Cu > Zn for adults. The HQs
and HIs for all heavy metals were lower than 1, which indicated adverse health
effects on children and adults exposed to heavy metals. However, surface dust was
relatively light in Maha Sarakham city, and in terms of Cd, there was no cancer
risk in Maha Sarakham city.
Conclusion
The non-cancerous risk was calculated for different
land uses, and both adults and children. The results of risk assessment showed
that the highest risk
value was related to ingestion of Pb. In all the selected land uses (green
space, residential area, under construction, and natural), the non-carcinogenic
health risk for children was higher than adults. However, the exception was in
the case of residential area, wherein non-carcinogenic health risks of Zn in
adults were higher than children. For children and adults, HI values decreased
in the order of Pb > Cr > Cd > Ni > Zn in green space and natural
use areas. In the residential area, HI values decreased in the order of Pb >
Cd > Cr > Ni > Zn for both children and adults. As indicated,
non-carcinogenic risks of Cd were higher than Cr and health risk of Cd increased
in the residential area.
A noteworthy observation in this study was that the
risk of non-carcinogenic metals was slightly different in the two groups, and
HI values decreased in the order of Pb > Cr > Cd > Ni > Zn for
children, and Pb
> Cd > Cr > Ni > Zn for adults. Thus, it can be safely concluded
that Pb had the highest non-carcinogenic risk value and Zn had the lowest
non-carcinogenic risk value. Regarding land use, only the non-carcinogenic
risks of Cd and Cr changed. Among the carcinogenic metals, Cd, Cr, and Ni were
analyzed for the land uses of green space, residential area, under
construction, and natural. The carcinogenic risks of the studied metals were
lower than the threshold values range (10-6-10-4), which signifies nil cancer
risk in Tehran city.
Acknowledgments
The authors are grateful to the authorities of the Islamic
Azad University, Science and Research Branch, for their assistance in and funds
for this research. The authors also appreciate their useful feedback.
Conflict of Interest: None declared
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