Figure 1: Probable biomarkers which can be used to determine oxidative,
inflammatory and genotoxic effects of fibers/particles, like asbestos, Adapted
from Bhattacharya et al., 2005 [18]
Journal
of Environmental Treatment Techniques, Volume 4, Issue 2, Pages 46-51,
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Comparative Health
Risk Assessment of Asbestos in Tehran, Iran
Hossein Tavakoli1; Aryandokht Azari2;
Maryam Pazoki2*
1-
Department of Civil and Environmental Engineering, Michigan Technological
University, Houghton, MI, USA,
2-
Graduate Faculty of Environment, University of Tehran, Tehran, Iran. P.O. Box:
14155-6135
Received:
01/05/2016 Accepted:
18/06/2016 Published:
30/09/2016
Abstract
Health risk assessment has been used to investigate the cancer and
non-cancer risk of Asbestos in the air of Tehran, Iran. This study focused on
the risk of lung cancer and mesothelioma on the residents of the region. It
presents an overview of Asbestos concentration in 31 samples with the average
concentration of 0.01f/ml in different districts in Tehran. Results provided by
EPA (IRIS) analysis showed the total lifetime cancer risk of 46.3 × 10−5. Based on the risk calculations presented in
EPA (1986a), the average cancer risk value of
lung cancer and mesothelioma was calculated as a discrete value for smokers and
nonsmokers. Assuming lifetime continuous exposure due to inhalation, the
expected incidence is 46 and 152 mesothelioma deaths, and 42 and 13 lung cancer
deaths per 100,000 persons for smokers and nonsmokers, respectively. In addition,
In accordance with the Air Quality Guidelines of the World Health Organization
database, the extra risk of lung cancer between 2.42×10-5 and
1.13×10-3, for smokers and 2.86×10-6 and 1.13×10-3
for nonsmokers was calculated.
Keywords: Health risk, Asbestos, EPA, Inhalation
Asbestos is a general term given to a group of six different fibrous
forms of highly durable silicate minerals, (amosite, chrysotile, crocidolite,
and the fibrous varieties of tremolite, actinolite, and anthophyllite) that
occur naturally in the environment. Chrysotile belongs to the serpentine family
of minerals, while all of the others belong to the amphibole family [1].
Because asbestos is composed of silicates that has particularly
interesting physicochemical properties such as flexibility and resistance to
traction, heat, and chemical reactions, it is used commercially into numerous
products of industrial activities such as cement, asphalt, and brake pads
[2-5].
The primary diseases associated with asbestos exposure are
asbestosis (caused by the inhalation and retention of asbestos fibers),
mesothelioma (an otherwise rare form of cancer associated with the lining
around the lungs), and lung cancer [6-10]. Inhaled asbestos, however, is
reported carcinogenic in populations non-occupationally exposed to asbestos,
giving rise to lung tumors and mesotheliomas [11-17]. Different factors are
involved in the impacts of Asbestos on human health such as concentration of
Asbestos, residence time, size, shape and chemical form of Asbestos fibers,
source of emissions, individual risk agents like smoking and suffering from lung
disease before affected by Asbestos.
Asbestos fibers have no detectable odor or taste. They do not
dissolve in water or evaporate and are resistant to heat, fire, chemical and
biological degradation [1]. Levels of asbestos (fibers.m3) can be
detected in almost any air sample (A cubic meter is the amount of air that we
breathe in 1 hour).
By asbestos fibers inhalation into lungs, some of the fibers will
be deposited in the air passages and on the cells that make up your lungs. Most
fibers are removed from your lungs by being carried away or coughed up in a
layer of mucus to the throat, where they are swallowed into the stomach.
Amphibole asbestos fibers are retained in the lung longer than Chrysotile
asbestos fibers [1]. One study found that nearly 70 percent of WTC rescue and
recovery workers suffered new or worsened respiratory symptoms while performing
work at the WTC site. The study describes the results of the WTC Worker and
Volunteer Medical Screening Program, which was established to identify and characterize
possible WTC-related health effects in responders. The study found that about
28 percent of those tested had abnormal lung function tests, and 61 percent of
those without previous health problems developed respiratory symptoms [19].
Risk of lung cancer is expected to be up to ten times higher in
smokers than in non-smokers exposed to the same inhaled asbestos concentrations
[15, 6]. Therefore, in order to quantitate degree of Asbestos risk, it is
essential to assess health risk associated with Asbestos.
The case study’s location is Tehran which is the most populated
city in Iran with a population of approximately 8,245,000 people. Asbestos is
vastly used in Tehran in a wide range of car brake caliper, manufactured
products, mostly in building materials, friction products, and heat-resistant
fabrics. In 1390, Tehran with land measurement of 730 square kilometers
encompassed about 8 million and 245 thousand people [20]. At the end of autumn
2013, the number of cars with license plate of Tehran exceeded 2 million and
422 thousand people. Tehran’s air pollution is critical for 318 days in 2010.
Smokers in the population of Tehran, who are more inclined to the lung cancer
risk, included 25.4 percent of the whole population [21]. Carcinogenic nature
of asbestos (classified as Group I human carcinogens based on the International
Agency for Research on Cancer), inferior building stuff, climate, geographic
pattern and traffic promote this study to evaluate the recent asbestos exposure
status in Tehran’s air.
Figure 1: Probable biomarkers which can be used to determine oxidative,
inflammatory and genotoxic effects of fibers/particles, like asbestos, Adapted
from Bhattacharya et al., 2005 [18]
Determination of the dose-response is the first step to start this
study. For monitoring asbestos in air, a known volume of air is drawn through a
25-mm diameter cassette containing a mixed-cellulose ester filter (OSHA method
ID-160). The cassette must be equipped with an electrically conductive 50-mm
extension cowl. The sampling time and rate are chosen to give a fiber density
of between 100 to 1,300 fibers.mm-2 on the filter. A portion of the
sample filter is cleared and prepared for asbestos fiber counting by Phase
Contrast Microscopy (PCM) at 400X [22]. Sampling rate was 1.5 L.min-1,
air volume was 2000 Liter, the instruments were calibrated, and the detection
limit is 0.001 fibers.cc-1. There are thirteen monitoring stations
located in the city. The monitoring data for asbestos is consisting of values
of concentrations observed at each station in different dates from months of
2010. The monitoring station data were obtained from the Air quality control
company, City of Tehran. Exposure assessments on Tehran’s population were
conducted based on the route of inhalation. The input parameters for evaluating
the exposure assessment and risk calculations are summarized in Table 1.
The equations used to calculate the chronic daily intakes are shown
below:
Where, CDI is chronic daily intake (f.ml-1), Cair
is mean concentration of asbestos in Tehran’s air (f.ml-1), EF is
number of days exposed to Asbestos in a year with assumption of 350
days.year-1, ED is average age equal to 70 years, ET is number of hours exposed
to Asbestos during a day with assumption of 5 hours.day-1 inhalation in the
open air, and AT is possible time for Tehran residents being threatened by
cancer which is equal to life-time. In order to assess total cancer risk caused
by inhalation of Asbestos equations used is shown below:
where, UR summarizes the cancer unit risk for inhalation of
asbestos (f.ml-1). These values were taken from California EPA or
IRIS (1986). The lifetime cancer risk for inhabitants of Tehran was calculated
using the asbestos concentrations and the input parameters above mentioned.
In addition, this study provides the calculation of life time
cancer risk due to exposure assessment of asbestos based on other scientific
researches. A linear dose-response relationship was assumed for lung cancer and
mesothelioma respectively, and the corresponding slopes were defined as potency
factors: KL for lung cancer and KM for mesothelioma [2]. Most
studies specially evaluated the risk of asbestos-related lung cancer in
occupationally exposed workers indicate that the dose-response relationship is
best described by a relative risk model, given by the equation [1]:
Using this equation, EPA (1986a) calculated the value of KL (the
fractional increase in relative risk of lung cancer per f-year.mL-1)
for 14 sets of lung cancer mortality data from the past studies. The resulting
geometric mean value was 0.010 (f-yr/mL-1) [1]. Based on national
average lung cancer risk data for male and female and smokers and nonsmokers,
EPA (1986a) calculated that lifetime exposure to 0.0001 f.mL-1
corresponded to the excess lung cancer risks [1]. For the purposes of
calculating risk levels of lung cancer, the results were presented for both men
and women, and smokers and nonsmokers. Also, based on several studies on
Mesothelioma, EPA (1986a) fit exposure-incidence data from four studies to the
following equation [23-26]:
In which KM equals an empirical constant, f is intensity of
exposure (f.mL-1), T is latency (years since first exposure) and d
is the duration of exposure (years). Based on an analysis of the relative
cancer risk of mesothelioma, a value of 1×10-8 was identified as the
most reasonable estimate for KM (method EPA 1986a) [1]. Finally, there is
another practical assumption for a quantitative risk assessment of lung cancer
due to inhalation of asbestos presented in the paper (method WHO 1987).
However, the lung cancer incidence can still be expressed as a linear function
as [27]:
where 
the underlying lung-cancer is risk with no asbestos exposure, and
is a constant representing
the increase in relative risk due to exposure to asbestos.
Table 1: Input parameters for exposure assessment
|
Input
parameter |
Unit |
Value |
Reference |
|
Unit Risk |
f.ml-1 |
0.23 |
IRIS |
|
Concentration of asbestos |
f.ml-1 |
0.010068977 |
Air quality control co. (2011) |
|
Exposure frequency (EF) |
Days per year |
350 |
Lee et al. (2004) |
|
Exposure duration (ED) |
years |
70 |
Lee et al. (2004) |
|
Exposure time (ET) |
Hours per day |
5 |
|
|
Average lifetime (AT) |
days |
70*365 |
Lee et al. (2004) |
The US Environmental Protection Agency (1985) and World Health
Organization (1987) found values for ranging from 0.0004 to 0.016
(expressed per fiber-year per ml air = f-y.ml-1) [28, 29]. Smoking
has no bearing upon the risk of mesothelioma, but increases the risk of lung
cancer from asbestos exposure approximately tenfold. The World Health
Organization (1987) used a range of to calculate a range for the
lifetime lung-cancer risk due to asbestos exposure, assuming that the risk of
lung cancer in the absence of asbestos
exposure (I°L) is roughly 10% for smokers and ten times lower for
non-smokers [27]. So, the risk evaluation includes all the above-mentioned
calculations are presented in results.
The spatial distribution map of asbestos air contamination (Figure
2) showed the maximum concentrations in east districts with 0.024f.ml-1
while the lowest concentrations in north districts were 0.006f.ml-1 and the
mean concentration were seen 0.01f.ml-1. In addition, the lowest
contaminant levels for asbestos are predominantly along with a north-south
axis.
Figure 2: Spatial distribution of asbestos in Tehran’s air
This study shows that the maximum and minimum concentrations of
asbestos were seen in point 12 and 2 with 0.027 and 0.004 f.ml-1
respectively, while the mean concentrations were 0.010 f.ml-1.
Although the variance in sample point 2 is high, the median asbestos
concentrations for most points are near the mean values (Table 2). The
occupational exposure level of 0.1 f.ml-1 is equivalent to the PEL proposed
by OSHA.
3.2 Lifetime cancer risk of asbestos
Using the average concentration of each THM
species, the lifetime cancer risks through inhalation, was calculated based on
the assumptions on Table 1, Equation 1 and Equation 2. Table 3 presented the result
for CDI and total cancer risk due to asbestos exposure (inhalation). As it is
shown, the expected incidence is 47 deaths per 100,000 persons.
Table 3: Chronic daily index and lifetime cancer risk via inhalation of
asbestos in Tehran
|
CDI (f/ml) |
0.002011497 |
|
Cancer Risk |
4.63E-04 |
Using the Equation 3 (EPA 1986a), the absolute risk of lung cancer
due to asbestos exposure is determined. Risks for males and females, both for
smokers and nonsmokers, corresponding to a lifetime lung cancer and
mesothelioma risk were calculated and shown in Figure 3 and Figure 4,
respectively.
Figure 3: Lifetime risk of Lung cancer according to method EPA 1986a
Figure 4: Lifetime risk of Mesothelioma according to method EPA 1986a
The results of these calculations from lung cancer indicate that
the concentration of 0.01007 f.mL-1 corresponds to a lifetime excess
risk level of 25×10-5 and 2×10-5 for men, smoker and
nonsmoker, and 15×10-5 and 2×10-5 for women, smoker and
nonsmoker, respectively (Figure 3). The data show that asbestos exposure and
cigarette smoking do not interact with mesothelioma. The research estimates
lifetime cancer risks from mesothelioma based on levels of asbestos detected
18×10-5 and 23×10-5 for men, smoker and nonsmoker, and
26×10-5 and 28×10-5 for women, smoker and nonsmoker, respectively
(Figure 4).
Assuming the population of 6,150,000 nonsmokers in Tehran, the
expected incidence is 13 lung cancer deaths and 152 mesothelioma deaths per
100,000 persons. The results estimated that continuous lifetime exposure to air
containing 0.01007 f.mL-1 of asbestos for a population of 2,100,000
smokers in Tehran would result in about 42 cases of lung cancer and 46 cases of
mesothelioma per 100,000 persons.
Table 2: Statistical information for all water districts
|
Points |
Minimum
asbestos (f.ml-1) |
Maximum
asbestos (f.ml-1) |
Mean
asbestos (f.ml-1) |
Median
asbestos (f.ml-1) |
|
No. 1 |
0.0032 |
0.0098 |
0.007075 |
0.00765 |
|
No. 2 |
8.3E-06 |
0.009 |
0.004504 |
0.004504 |
|
No. 3 |
0.008 |
0.008 |
0.008 |
0.008 |
|
No. 4 |
0.0071 |
0.0071 |
0.0071 |
0.0071 |
|
No. 5 |
0.005 |
0.005 |
0.005 |
0.005 |
|
No. 6 |
0.008 |
0.008 |
0.008 |
0.008 |
|
No. 7 |
0.007 |
0.017 |
0.012 |
0.012 |
|
No. 8 |
0.0041 |
0.0041 |
0.0041 |
0.0041 |
|
No. 9 |
0.005 |
0.012 |
0.008333 |
0.008 |
|
No. 10 |
0.001 |
0.0058 |
0.00376 |
0.0048 |
|
No. 11 |
0.001 |
0.021 |
0.008825 |
0.00665 |
|
No. 12 |
0.00053 |
0.097 |
0.026808 |
0.00485 |
|
No. 13 |
0.018 |
0.018 |
0.018 |
0.018 |
|
Tot. |
0.0000083 |
0.097 |
0.010069 |
0.007 |
As it has mentioned, the World Health Organization (1987) used
another equation to calculate a range for the lifetime lung-cancer risk due to
asbestos exposure. With the lowest and highest values of KL (0.0004
and 0.016 f-yr.ml-1, respectively) calculated by Liddell from cohort
studies, a lifetime lung-cancer risk after exposure to 0.01007 f.mL-1
of asbestos can be estimated. The extra risk of lung cancer is between 2.42×10-5
and 1.13×10-3, for smokers and 2.86×10-6 and 1.13×10-3
for nonsmokers (Figure 5). So, the average extra risk of lung cancer for a
population with 25.4% smokers would be 1.9×10-4. The approximate
content of the risk of lung cancer due to asbestos exposure estimated in this
way is 19 lung cancer deaths per 100,000 persons.
Figure 5: Lifetime lung cancer risk according to method WHO 1987
This study provided a lifetime general population risk assessment
of asbestos inhalation in which the estimated value of the risk was assessed
seriously high. The southeast and western part of Tehran inhaled mostly
polluted air which leads to higher cancer cases caused by asbestos fibers. The
determination of cancers for 8,245,000 total inhabitants is close to 50 per
100,000. Also, the expected incidence is estimated 13 lung cancer deaths and
152 mesothelioma deaths per 100,000 persons among nonsmokers and 42 cases of
lung cancer and 46 cases of mesothelioma per 100,000 persons among smokers
(method EPA 1986a). According to WHO 1987 guidelines the extra risk of lung
cancer accounts for a range between 2.42×10-5 and 1.13×10-3,
for smokers and 2.86×10-6 and 1.13×10-3 for nonsmokers
which will probably be acceptable in comparison with other methods. However; it
is important to keep in mind that the validity of the given risk calculations
is difficult to judge but it surely helps risk management considerations to
make a good choice for the general population of Tehran.
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