ARTICLE IN PRESS
Environmental Research 94 (2004) 57–66
Risk assessment of exposure to volatile organic compounds
in different indoor environments
H. Guo, S.C. Lee, L.Y. Chan, and W.M. Li
Department of Civil and Structural Engineering, Research Centre for Urban Environmental Technology and Management,
The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
Received 25 September 2002; received in revised form 21 January 2003; accepted 3 February 2003
Abstract
The lifetime cancer risks of exposure of cooks and food service workers, office workers, housewives, and schoolchildren in Hong
Kong to volatile organic compounds (VOCs) in their respective indoor premises during normal indoor activities were assessed. The
estimated cancer risk for housewives was the highest, and the second-highest lifetime cancer risk to VOC exposure was for the
groups of food service and office workers. Within a certain group of the population, the lifetime cancer risk of the home living room
was one to two orders of magnitude higher than that in other indoor environments. The estimated lifetime risks of food service
workers were about two times that of office workers. Furthermore, the cancer risks of working in kitchen environments were
approximately two times higher than the risks arising from studying in air-conditioned classrooms. The bus riders had higher
average lifetime cancer risks than those travelling by Mass Transit Railway. For all target groups of people, the findings of this study
show that the exposures to VOCs may lead to lifetime risks higher than 1 106. Seven indoor environments were selected for the
measurement of human exposure and the estimation of the corresponding lifetime cancer risks. The lifetime risks with 8-h average
daily exposures to individual VOCs in individual environments were compared. People in a smoking home had the highest cancer
risk, while students in an air-conditioned classroom had the lowest risk of cancer. Benzene accounted for about or more than 40% of
the lifetime cancer risks for each category of indoor environment. Nonsmoking and smoking residences in Hong Kong had cancer
risks associated with 8-h exposures of benzene above 1.8 105 and 8.0 105, respectively. The cancer risks associated with 1,1dichloroethene, chloroform, methylene chloride, trichloroethene, and tetrachloroethene became more significant at selected homes
and restaurants. Higher lifetime cancer risks due to exposure to styrene were only observed in the administrative and printing offices
and air-conditioned classrooms. Higher lifetime cancer risks related to chloroform exposures were observed at the restaurant and the
canteen.
r 2003 Elsevier Science (USA). All rights reserved.
Keywords: Risk assessment; Indoor environments; VOCs; Inhalation; Hong Kong
1. Introduction
Humans can be exposed to contaminants by inhalation, ingestion, and dermal contact. In the past,
scientists have paid much attention to the study of
exposure to air contaminants in outdoor air because
they have realized the seriousness of outdoor air
pollution problems. Currently, many studies are being
conducted on indoor air pollution because most people
spend a lot of their time indoors living, working, and
studying. Furthermore, in most cases, the concentrations of air pollutants are much higher indoors than
Corresponding author. Fax: +852-2334-6389.
E-mail address: [email protected] (H. Guo).
outdoors (Godish, 1989; Lee et al., 2001, 2002a, 2002b;
Li et al., 2001; Pellizzari et al., 1982; Spengler, 1995;
USEPA, 1991; Wallace, 1996). Therefore, indoor
exposures are found to be more important than outdoor
exposures. Inhalation exposure to air pollutants is the
most significant pathway compared to other exposure
pathways. Hence, the health risks due to inhalation
exposure gain the attention of indoor air quality
researchers.
A wide variety of health effects come from exposure
to indoor air pollutants. Volatile organic compounds
(VOCs), major air pollutants in the indoor environment,
are easily released into indoor air. In any indoor
environment, there is a potential variety of VOC
emission sources, including consumer and commercial
0013-9351/03/$ - see front matter r 2003 Elsevier Science (USA). All rights reserved.
doi:10.1016/S0013-9351(03)00035-5
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58
H. Guo et al. / Environmental Research 94 (2004) 57–66
products, paint and associated supplies, adhesives,
furnishing and clothing, building materials, combustion materials, and appliances (Guo et al., 2000;
Guo and Murray, 2000, 2001; Maroni et al., 1995).
Exposure to VOCs can lead to acute and chronic health
effects (Maroni et al., 1995; Otto et al., 1992). The
major potential health effects include acute and
chronic respiratory effects, neurological toxicity, lung
cancer, and eye and throat irritation (Burton, 1997;
Hodgson et al., 1991; Maroni et al., 1995; M^lhave,
1991; M^lhave et al., 1991, 1997; Ota and Mulberg,
1990). Fatigue, headaches, dizziness, nausea, lethargy,
and depression are classic neurological symptoms
associated with VOCs (California Department of Health
Services (DHS), 1989; Godish, 1981, 1990; USEPA,
1987, 1991). The United States Environmental Protection Agency (USEPA) sets a number of risk assessment
guidelines for carcinogenicity (USEPA, 1995). Otto and
Hudnell (1993) addressed the hazard identification of
potential neurotoxic indoor air pollutants. Sram and
Benes (1996) developed a neurobehavioral evaluation
system for the assessment of the impacts of air
pollutants on sensorimotor and cognitive functions in
children. Many indoor air pollutants, such as VOCs,
may cause lung cancer. Zhong et al. (1999) reported that
exposure to VOCs such as benzene in the form of the
toluene emitted from Chinese-style cooking is correlated
with the risk of lung cancer among Chinese women who
do not smoke. Wallace (1991) found that the upperbound lifetime cancer risk from VOCs is quite
comparable to the estimates of risk from radon and
environmental tobacco smoke among 800 Americans
investigated.
Awareness regarding human health and environmental risks has resulted in risk assessments being used in
regulatory decision-making processes (Gratt, 1996;
NRC, 1983; USEPA, 1985). Risk assessment has been
defined as ‘‘the characterization of the potential adverse
health effects of human exposures to environmental
hazards’’ (NRC, 1983). In a risk assessment, the extent
to which a group of people has been or may be exposed
to a certain chemical is determined, and the extent of
exposure is then considered in relation to the kind and
degree of hazard posed by the chemical, thereby
permitting an estimate to be made of the present or
potential health risk to the group of people involved
(USEPA, 1985). The approach for assessing the lifetime
cancer risks includes four stages, namely, hazard
identification, dose–response assessment, exposure assessment, and risk characterization (NRC, 1983). The
USEPA Carcinogenicity Assessment Section of the
Integrated Risk Information System (IRIS) chemical
files supply information on the hazard identification and
dose–response assessment steps (USEPA, 1992). To
complete the risk assessment, we need to develop
estimates of exposure and combine these estimates with
dose–response characteristics to develop estimates of
risks.
Some studies were conducted on the cancer risk
assessment of exposure to air toxics in different
environment. Morello-Frosch et al. (2000) and Woodruff et al. (1998, 2000) estimated a median excess
individual cancer risk of 1.8 104–2.7 104 for all
outdoor air toxics concentrations across the United
States. About 70–75% of the estimated cancer risk
was attributable to exposure to polycyclic organic
matter, 1,3-butadiene, formaldehyde, and benzene. A
scientist from Denmark compared different methods
for calculating maximal allowable concentrations of
potentially carcinogenic substances in indoor air
(Nexo, 1995). Concentrations of benzene, tetrachloroethylene, trichloroethylene, and vinyl chloride of the
order of 10, 20, 200, and 40 ppb, respectively, in
indoor air were found to correspond to a 104 lifetime
risk of cancer for all of the chemicals. In Sweden the
most likely lifetime risks of cancer death at the
average exposure levels were estimated for certain
pollution fractions or indicator compounds in urban
air (Tornqvist and Ehrenberg, 1994). The risk
amounted to approximately 50 deaths per 100,000 for
inhaled particulate organic material, and alkenes
and butadiene each caused 20 deaths per 100,000
individuals. Also, benzene and formaldehyde are expected to be associated with considerable risk increments. Tornqvist (1994) stated that exposure to 10 ppb
ethene—a level occurring in urban areas—is expected to
lead to a lifetime risk of cancer death amounting to
approximately 70 per 100,000. In a risk assessment of
personal exposure to nine particulate-phase atmospheric
polycyclic hydrocarbons (PAHs) in France, the total
PAH lung cancer lifelong risk was 7.8 105 and was
driven by exposure to benzo(a)pyrene (Zmirou et al.,
2000).
This study aimed to measure the exposure of target
groups among the population of Hong Kong to
airborne VOCs in their respective indoor premises
during normal indoor activities. The lifetime risks of
cancer associated with the VOC exposures for a
certain group of the population were then evaluated.
Four groups of the Hong Kong population were
selected for this study: cook and food service workers,
office workers, housewives and schoolchildren. In
addition, a total of seven indoor environments were
selected for a risk assessment of an 8-h average exposure
to individual VOCs. The purposes were to find out in
which indoor environment a person would have higher
potential lifetime risk and which VOC would contribute
more to lifetime cancer risks. The indoor environments
included two homes, an office, a printing office, a
Chinese restaurant, a canteen, and an air-conditioned
classroom. All the places were nonsmoking except one
home.
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H. Guo et al. / Environmental Research 94 (2004) 57–66
2. Methodology
2.1. Sampling and analysis
In this study, four groups of the population of Hong
Kong were selected for occupational exposure assessment during their daily activities. Their daily activities
(24 h) in different indoor environments were recorded.
In general, the 24 h included time in the workplace, at
home, time for travelling between workplace and home,
time for shopping, and time for dining at restaurant.
Since different groups of the population spend different
amounts of time in different indoor environments and
because the levels of VOCs are different in different
indoor environments, the lifetime cancer risks for
different groups of the population is different. At
homes, air samples were taken both in the living room
and in the kitchen.
In addition, two restaurants’ dining areas, one
administrative office, one printing office, two residential
households, and one air-conditioned classroom were
selected for risk assessment of 8-h average exposures to
seven different VOCs. In this case, air sampling at
homes was carried out in the living areas that were
always occupied. The major dining areas and kitchens of
the restaurant and the canteen were selected for air
monitoring. Air sampling was carried out at the
occupied offices and the classroom.
Indoor 8-h average VOC samples were collected at
each air sampling location. The Summa polished
canister sampling method was used to evaluate human
exposure to selected VOCs. A number of clean canisters
were placed in the indoor environments in which the
target groups of people were living, working, and
learning. Evacuated 6-L canisters assembled with mass
flow controllers (Model No. FC4104CV-G, Autoflow
Inc.) were used to obtain passive integrated VOC
samples within human breathing zones. Passive sampling is the appropriate method to determine average
VOC concentrations in indoor air (Crump and Madany,
1993); this sampling method is free of the complexity of
extensive laboratory testing and the problem of recovery
efficiency compared to a method using sorbent tubes.
Calculations of cancer risk related to VOCs require
the carcinogenic potencies of VOCs and the mean
exposures of the target groups of people. Risks were
calculated as a simple multiple of the exposures and the
potency factors. In order to measure individual VOC
exposures when commuting, two of the most popular
commuting modes in Hong Kong were selected for this
study. These included franchised public bus and the
Mass Transit Railway (MTR). According to the
monthly traffic and transport digest issued by the
Transport Department, on average there are about
90,000 and 60,000 fixed-route passenger journeys by bus
and MTR, respectively (Transport Bureau, 2000). Three
59
popular bus routes travelling through the Hong Kong
area, including urban-to-urban, urban–suburban and
urban-to-rural areas, were selected for air sampling. For
MTR air measurements, air samples were collected over
the three major routes, including the Tsuen Wan, Kwun
Tong, and Island lines. The concentrations of VOCs
measured for individual bus and MTR routes were
averaged to give average VOC exposures during
commuting.
A questionnaire was used to collect information about
indoor air quality and the potential sources of VOCs.
The questionnaire also provided information on the
location and type of the building, smoking by guests,
personal daily activities, and so on.
2.2. Risk calculation
Risk is simply expressed by the product of the chronic
daily intake (CDI) and a potency factor (PF) of a
specific cancer substance.
CDI in mg/kg/day can be computed according to the
following equation:
CDI ¼ ðCA IR ED EF LÞ=ðBW ATL NYÞ;
ð1Þ
where CA is the contaminant concentration (mg/m3); IR
the inhalation rate (m3/h); ED the exposure duration
(h/week); EF the exposure frequency (weeks/year); L the
length of exposure (years); BW the body weight (kg);
ATL the average time of lifetime (period over which
exposure is averaged, say, 70 years); and NY the number
of days per year (say, 365 days).
The USEPA developed IRIS to provide the values of
potency factors for selected VOCs for risk assessment.
The VOCs, including 1,1-dichloroethene, methylene
chloride, chloroform, benzene, trichloroethene, tetrachloroethene, and styrene were selected for risk calculation in this study due to the availability of potency
factors, high frequency of occurrence, and carcinogenicity. The cancer potency factors for inhalation of the
VOCs selected are shown in Table 1.
These factors in IRIS system (USEPA, 1998) are
adopted to calculate lifetime cancer risk. Inhalation
exposure is a simple multiple of the mean concentration
Table 1
Potency factors for selected VOCs according to the IRIS systema
Volatile organic compounds
Potency factor (mg/kg/day)1
1,1-Dichloroethene
Methylene chloride
Chloroform
Benzene
Trichloroethene
Tetrachloroethene
Styrene
1.16
0.014
0.081
0.029
0.013
0.0033
0.00057
a
USEPA (1998).
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H. Guo et al. / Environmental Research 94 (2004) 57–66
60
Table 2
Summary of general daily schedules and hours for males
Number of hours
Office workers
Home
Living room/bedroom
Kitchen
Office/school
Workplace/classroom
Transportation
MTR/bus
Shopping mall
Shopping area
Restaurant
Dining area
Cook and food service workers
Students
Nonholiday
Holiday
Nonholiday
Holiday
Nonholiday
Holiday
12.5
0.5
17.4
0.6
11.5
0.5
17.4
0.6
12.5
0.5
16
1
8
0
10
0
8
0
1
2
1
2
1
2
1
1.5
0
1.5
1
4
1
2.5
1
2.5
1
1
Table 3
Summary of general daily schedules and hours for females
Number of hours
Office workers
Home
Living room/bedroom
Kitchen
Office/school
Workplace/classroom
Transportation
MTR/bus
Shopping mall
shopping area
Restaurant
Dining area
Cook and food service
workers
Housewives
Students
Nonholiday
Holiday
Nonholiday
Holiday
Nonholiday
Holiday
Nonholiday
Holiday
11
2
14.4
3.6
11
1
14.4
3.6
15
4
15
4
12.5
0.5
16
1
8
0
10
0
0
0
8
0
1
2
1
2
1
1
1
2
1
2.5
0
1.5
2
2
1
4
1
1.5
1
2.5
2
2
1
1
of the VOC of interest and the corresponding exposure
duration. For risk assessment, certain assumptions are
made for average body weight and the amount of air
breathed. The USEPA suggests standard values, such as
average body weight and amount of air breathed per
day, for adults and children (Gratt, 1996; USEPA,
1994). For adults, the exposures were converted to a
daily dose by assuming 20 m3 inspired air per day and
average body weights of 70 kg for men and 60 kg for
women. The average body weight of a child was
assumed to be 10 kg and an average of 5 m3 of air per
day was used for the daily intake calculations for
children. An entire lifetime of 70 years was applied to all
groups of individuals. The absorption factor of the
VOCs for humans was assumed to be 90%.
Inhalation exposure is always related to exposure
frequency, duration, and activity pattern. The average
number of hours spent per day in various indoor
environments was used for the risk assessment. Tables 2
and 3 summarizes the daily schedules and times for each
group of people.
In order to ease the process of exposure and risk
assessment, several assumptions regarding individual
exposure, were made based on the best professional
judgment and questionnaire data. In Hong Kong, office
workers, spend, on average, 8 h in the office per day.
They work 5 days a week and normally have 118
holidays annually, including Saturday, Sunday, and
public holidays. There are 35 workweeks each year. The
work lifetime is assumed to be 40 years. In comparison,
cooks and food service workers have longer working
days, generally, they work for 10 h each day and spend 6
days each week in their workplaces. Normally, they can
enjoy 69 holidays each a year, which leads to 42
workweeks annually.
A housewife is assumed to be a woman who has a
duty to look after her family and does not have full-time
paid work outside her home. According to this
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H. Guo et al. / Environmental Research 94 (2004) 57–66
61
Table 4
Eight-hour average of individual VOC concentrations in different indoor environmentsa
Concentration (mg/m3)
Home (n ¼ 6)
Living room
Kitchen
Office (n ¼ 6)
Administrative room
School (n ¼ 6)
Air-conditioned classroom
Restaurant (n ¼ 4)
Dining area
Shopping mall (n ¼ 6)
Shopping area
Transportation mode
Mass Transit Railway (MTR) (n ¼ 6)
Bus (n ¼ 6)
Methylene chloride
Chloroform
Benzene
Trichloroethene
Tetrachloroethene
Styrene
1.30
0.98
0.30
0.38
0.65
0.53
0.23
0.26
0.30
0.26
0.13
0.05
0.03
0.60
0.52
0.01
0.10
0.15
0.11
0.40
0.58
1.28
0.03
0.08
3.25
0.58
1.10
0.19
0.35
0.28
0.65
0.83
1.18
0.20
0.15
0.46
0.75
0.35
0.43
0.33
0.50
0.82
0.38
0.73
0.45
0.65
0.33
0.45
a
Sampling size, N. For offices, N ¼ 24; for shopping malls, N ¼ 36; for home in living rooms, N ¼ 12; for home kitchens, N ¼ 12; for schools,
N ¼ 36; for MTR, N ¼ 18; for buses, N ¼ 18; for restaurants, N ¼ 16:
assumption, a housewife spends the most time at home
compared to office workers and food service workers. It
was assumed that a housewife spends her lifetime on her
family (7 days per week; 52 weeks per year). On average,
many students in Hong Kong attend 5 school days in
each week. Students usually stay in schools for 8 h a day,
and have 153 school holidays; in other words, there are
30 weeks per year for lessons in school. Also, schoolchildren must attend school for 12 years from primary
school through secondary school. Housewives are
assumed to have more chances to cook in the kitchen
than their husbands. Hence, the average number of
hours spent in a kitchen is assumed to be greater for
women than for men. During nonholidays, all subgroups were assumed to have a 1-h commute to work or
school by bus or by MTR. Commuting times are longer
on holidays.
3. Results and discussion
3.1. Exposure assessment of various groups within the
population
The 8-h average VOC concentrations in various
indoor environments are presented in Table 4.
Benzene, styrene, methylene chloride, chloroform,
trichloroethene, and tetrachloroethene were the most
prevalent VOCs in selected indoor environments. Since
the concentrations of 1,1-dichloroethene were under the
detection limit in most cases, it was not included in the
estimation of lifetime cancer risks. Benzene is a proven
human carcinogen (USEPA, 1998). Methylene chloride
and chloroform are suspected carcinogens. The results
of total exposures to these six VOCs for the different
groups during their daily activities were used for
computing the associated cancer risks (Table 5). The
cancer risks associated with travelling by bus and related
to MTR travelling are also shown in Table 5.
The total estimated cancer risk for people staying at
home (housewives) was the highest (4.03 104), as they
spent most of their time at home. The second highest
total lifetime cancer risk from VOC exposure was for the
groups of female food service and office workers
(2.38 104 and 2.34 104, respectively). The pupils,
male office workers, and food service people had the
lowest lifetime risks of VOC exposure. Within a certain
group of the population, the lifetime cancer risk in the
living room was 1–2 orders of magnitude higher than
that in other indoor environments, since people spend
most of their time in the living room during their
lifetimes.
The bus riders had slightly higher average lifetime
cancer risks than those travelling by MTR. The
estimated lifetime risk of Hong Kong students travelling
by bus was about 1.24 105 (Table 5). This is
consistent with the findings of a previous study by
Chan et al. (1993). They reported that the lifetime risks
of students while commuting by bus in Taipei ranged
from 7.50 106 to 1.80 105.
The lifetime cancer risks of working in an office
environment were 3.25 105 for male workers and
3.80 105 for female workers, respectively. The female
office workers had a slightly higher cancer risk than
male office workers due to the fact that the females have
less mass. The estimated cancer risks of working in
canteen and restaurant kitchens were 5.84 105 for
male workers and 6.9 105 for female workers,
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H. Guo et al. / Environmental Research 94 (2004) 57–66
62
Table 5
Lifetime cancer risks of various groups in Hong Kong that commuted via different modes of transportation
Lifetime risk in various indoor environments due to exposure to VOCs
Home kitchen
Office worker
Male
Female
Cook and food service
worker
Male
Female
Housewife
Pupil
Home living
room
Workplace
Transportation mode
Bus
MTR
Shopping mall
Restaurant
4.03E-06
2.36E-05
1.13E-04
1.12E-04
3.25E-05a
3.80E-05a
1.13E-05
1.32E-05
1.12E-05
1.30E-05
1.61E-05
2.58E-05
2.49E-05
2.12E-05
4.07E-06
1.50E-05
4.84E-05
5.87E-06
1.05E-04
1.11E-04
2.27E-04
1.13E-04
5.84E-05b
6.90E-05b
0
2.04E-05c
1.02E-05
1.20E-05
1.54E-05
1.24E-05
1.01E-05
1.18E-05
1.51E-05
1.22E-05
5.27E-06
1.02E-05
5.19E-05
3.59E-05
2.14E-05
2.04E-05
6.07E-05
1.51E-05
a
Office.
Work kitchen area.
c
Air-conditioned classroom.
b
Table 6
Eight-hour average individual VOC concentrations in selected indoor environments (sample size: n ¼ 4a)
Concentration
(mg/m3)
Office
Printing
room
Chinese
restaurant
Canteen
restaurant
Smoker’s
home
Nonsmoker’s
home
Air-conditioned
classroom
1,1-Dichloroethene
Methylene chloride
Chloroform
Benzene
Trichloroethene
Tetrachloroethene
Styrene
0.0019
5.90
0.091
11.92
2.00
1.44
642.5
ND
ND
0.08
7.46
0.99
3.90
579.4
ND
141.9
15.15
63.14
0.76
8.02
1.19
0.15
52.00
15.75
66.48
9.02
21.06
3.26
0.40
2.87
2.10
30.24
3.58
4.48
0.81
0.047
3.85
0.36
6.56
1.07
3.29
6.05
ND
0.20
0.032
3.26
ND
0.032
176.3
ND, not detectable.
a
For air-conditioned classroom, n ¼ 6:
respectively. Clearly, the estimated lifetime risks of food
service workers were about two times those of the office
workers. This is because the total VOC concentrations
in restaurants were higher (Table 4) and the working
hours for food service workers were longer (Tables 2
and 3). Furthermore, the cancer risks of working in
kitchen environments were approximately two times
higher than the risks arising from studying in airconditioned classrooms. This was probably due to the
absence of potential indoor sources of VOCs in the
classroom and a shorter stay in the classroom for
students than in the kitchen for food service workers
3.2. Exposure assessment in different indoor
environments
Seven indoor environments were selected for measuring human exposures and estimating the corresponding
lifetime cancer risks. Four of them were occupational
workplaces, including two restaurants’ dining areas, one
administrative office, and one printing office. Nonoccupational exposures were considered in two residential
households and one air-conditioned classroom. In each
indoor environment, four samples were taken for 8 h
(for the air-conditioned classroom the sample size was
6). Table 6 lists the 8-h average individual VOC
concentrations in the seven indoor environments. In
each indoor environment, the 8-h mean exposures
calculated for individual VOCs were obtained to provide
the proportion of individual lifetime risks from the
exposures to individual VOCs. Table 7 illustrates the
lifetime risks due to 8-h average exposures to individual
VOCs in each indoor environment.
The estimated total lifetime cancer risks due to 8-h
average exposures to individual VOCs in various indoor
environments ranged from 9.16 106 to 1.54 104.
People spending time in a smoking home had the highest
cancer risk, while students in an air-conditioned classroom had the lowest risk of cancer. Benzene accounted
for about or more than 40% of the lifetime cancer risk
for each category of indoor environment. The lifetime
risks for styrene accounted for a large proportion of the
total lifetime risks in the administrative office, the
printing room, and the air-conditioned classroom.
Table 7
Average chronic dose intakes and estimated lifetime cancer risks due to 8-h average exposures to individual VOCs in various indoor environments
Office
Printing Room
Chinese Restaurant
Lifetime
risk
Chronic dose intake
(mg/kg/day)
Lifetime
risk
Chronic dose intake
(mg/kg/day)
Lifetime
risk
1,1-Dichloroethene
Methylene Chloride
Chloroform
Benzene
Trichloroethene
Tetrachloroethene
Styrene
Total lifetime risk
5.08E-08
1.59E-04
2.46E-06
3.21E-04
5.38E-05
3.89E-05
1.73E-02
5.90E-08
2.23E-06
1.99E-07
9.32E-06
6.99E-07
1.28E-07
9.88E-06
2.25E-05
0.00E+00
0.00E+00
2.17E-06
2.01E-04
2.67E-05
1.05E-04
1.56E-02
0.00E+00
0.00E+00
1.76E-07
5.83E-06
3.48E-07
3.45E-07
8.90E-06
1.56E-05
0.00E+00
3.82E-03
4.08E-04
1.70E-03
2.04E-05
2.16E-04
3.21E-05
0.00E+00
5.35E-05
3.31E-05
4.93E-05
2.65E-07
7.13E-07
1.83E-08
1.37E-04
Canteen restaurant
Smoker’s home
Nonsmoker’s home
Air-conditioned classroom
VOC
Chronic dose intake
(mg/kg/day)
Lifetime
risk
Chronic dose intake
(mg/kg/day)
Lifetime
risk
Chronic dose intake
(mg/kg/day)
Lifetime
risk
Chronic dose intake
(mg/kg/day)
Lifetime
risk
1,1-Dichloroethene
Methylene Chloride
Chloroform
Benzene
Trichloroethene
Tetrachloroethene
Styrene
Total lifetime risk
4.00E-06
1.40E-03
4.24E-04
1.79E-03
2.43E-04
5.67E-04
8.79E-05
4.64E-06
1.97E-05
3.44E-05
5.20E-05
3.16E-06
1.87E-06
5.01E-08
1.16E-04
3.83E-05
2.73E-04
2.00E-04
2.88E-03
3.41E-04
4.27E-04
7.73E-05
4.44E-05
3.82E-06
1.62E-05
8.35E-05
4.44E-06
1.41E-06
4.41E-08
1.54E-04
4.45E-06
3.67E-04
3.48E-05
6.25E-04
1.02E-04
3.13E-04
5.76E-04
5.16E-06
5.14E-06
2.82E-06
1.81E-05
1.32E-06
1.03E-06
3.28E-07
3.39E-05
5.98E-10
8.95E-06
1.48E-06
1.49E-04
0.00E+00
1.46E-06
8.05E-03
6.94E-10
1.25E-07
1.20E-07
4.32E-06
0.00E+00
4.81E-09
4.59E-06
9.16E-06
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chronic dose
intake (mg/kg/day)
H. Guo et al. / Environmental Research 94 (2004) 57–66
VOC
63
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64
H. Guo et al. / Environmental Research 94 (2004) 57–66
Compared to the nonsmoker’s home, the smoker’s home
had a greater lifetime risk related to the exposure to
benzene. The results indicate that active smoking was a
major source of exposure to benzene. In the United
States, a comprehensive study was conducted to
investigate the risks from outdoor and indoor exposure
to VOCs at residential indoor environments (Wallace,
1991). The researcher found that the lifetime cancer
risks associated with 24-h exposure to benzene in
smoking homes and nonsmoking homes are 12 105
and 72 105, respectively. Nonsmoking and smoking
residences in Hong Kong had cancer risk associated
with 8-h exposures to benzene above 1.8 105 and
8.0 105, respectively. The large difference may be due
to different exposure duration, daily life, weather, and
ventilation mode. Also, Wallace (1991) showed that
cancer risks arising from exposures to styrene and
benzene were more significant in smoking homes than
those estimated in nonsmoking homes. The findings of
this study are consistent with what Wallace found in his
research.
Lifetime risks caused by trichloroethene and 1,1dichloroethene in the smoker’s home were the highest,
while the highest, lifetime risks by chloroform and
tetrachloroethene were in the canteen restaurant. The
highest 8-h average cancer risk due to styrene occurred
in the administrative office and for methylene chloride in
the Chinese restaurant. Since 1,1-dichloroethene, methylene chloride, chloroform, trichloroethene, and tetrachloroethene are primarily used as solvents, detergents,
and insecticides, the cancer risks associated with these
VOCs became more significant at the selected restaurants and homes. Higher lifetime cancer risks associated
with airborne exposures to styrene were only observed
in the administrative and printing offices and airconditioned classrooms. Airborne styrene mainly
originated from vehicle emissions. As these indoor
environments were located near highly trafficked roads,
the indoor levels of styrene recorded at these sampling
sites were probably elevated due to the infiltration of
outdoor air contaminated with automobile exhaust. The
restaurant, the canteen, and two homes were susceptible
to the influence of airborne chloroform. Higher lifetime
cancer risks related to the chloroform exposures were
observed at the restaurant and canteen.
3.3. Uncertainty analysis
Uncertainties exist in the risk assessment of exposure.
These include uncertainties in measurement (Fritz and
Schenk, 1987), uncertainties in values assigned to
population exposure variables (Wallace, 1991), and the
uncertainties introduced in risk characterization due to
day-to-day, place-to-place variations in concentrations
(Kim et al., 2002). Uncertainty in risk analysis has
suffered from the lack of consistent terminology and of
an understanding of the mathematical foundations of
the estimation process. The risk analysis process usually
involves the estimation of the components of the risk. In
many cases, assumptions must be made to quantify a
risk estimate (Gratt, 1996).
Measurement uncertainty is defined as ‘‘a parameter
associated with the result of a measurement that
characterizes the dispersion of values that could reasonably be attributed to the measurement’’. Any analytical
measurement, no matter how carefully made, is subject
to some uncertainty. No correction can be made for any
component part of uncertainty. In chemical analysis,
uncertainty may arise from a number of possible sources
not necessarily independent of one another. These
include poor sampling, incomplete extraction of the
analyte, and variability in weighing or in the measurement of volume or temperature.
The uncertainties in values assigned to population
exposure variables also affect the risk assessment, such
as uncertainties in potency calculations. The pharmacokinetics of testing animal species with high doses may
not be exactly the same as low doses in humans. At
present, the true cancer risk from exposure to individual
VOCs cannot be ascertained, even though dose–
response data are often used in quantitative cancer risk
analysis, because of uncertainties in the low-dose
exposure scenarios and the lack of a clear understanding
of the mode of action (USEPA, 1998). A range of
estimates of risk is recommended, each having equal
scientific plausibility. The range estimates are maximum
likelihood values and were derived from observable dose
responses using a linear extrapolation model to estimate
low environmental exposure risks. The use of a linear
model is a default public health protective approach and
an argument both for and against recognizing supra and
sub linear relationships at low doses and nonthreshold
or threshold modes of action on exposure to individual
VOCs (USEPA, 1998). Therefore, the true risk could be
either higher or lower.
In this study, the exposure levels of selected VOCs
were based on short-term monitoring in indoor environments. This ignores potential daily variations that
could exert a marked influence on exposures over
prolonged periods (Kim et al., 2002). Also, the VOC
levels were measured in several indoor environments for
several groups of the general population in Hong Kong.
This does not accurately represent the actual exposure
to VOC levels for the entire population. The degree of
the representative accuracy of the obtained VOC levels
increases with larger sampling size.
4. Conclusions
The estimated cancer risk for people staying at home
(housewives) was the highest, and the second highest
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H. Guo et al. / Environmental Research 94 (2004) 57–66
lifetime cancer risk due to VOC exposure was for the
groups of food service and office workers. Within a
certain group of the population, the lifetime cancer risk
in the living room was 1–2 orders of magnitude higher
than that in other indoor environments. The estimated
lifetime cancer risks of working in office environments
were 50% lower than those in kitchen environments.
The health risks of working in the canteen kitchen were
30% higher than the risks arising from studying in the
air-conditioned classroom. The bus riders had estimated
cancer risks higher than those of the MTR riders.
The average lifetime risks due to 8-h average
exposures to individual VOCs in administrative and
printing offices, Chinese restaurants, the canteen, the
smoker and nonsmoker homes, and air-conditioned
classrooms were compared. It was found that benzene
accounted for about or more than 40% of the total
lifetime cancer risks for each category of indoor
environment. Nonsmoking and smoking residences in
Hong Kong had cancer risks associated with 8-h
exposures of benzene above 1.8 105 and 8.0 105,
respectively. The cancer risks associated with 1,1dichloroethene, methylene chloride, chloroform, trichloroethene, and tetrachloroethene became more significant at the selected homes and restaurants. Higher
lifetime risks related to inhalation exposure to styrene
were observed in the offices and air-conditioned classroom. On the other hand, higher lifetime cancer risks
associated with chloroform exposures were observed at
the restaurant and canteen. For all target groups of
people, the findings of this study show that the
exposures to VOCs may lead to lifetime risks greater
than 1 106. Some precautions should be taken to
reduce the risks, such as the development of low-VOCemission materials and products indoors, an increase of
ventilation for the dilution of VOC concentrations, and
the usage of air cleaners in indoor environments.
Acknowledgments
The study is supported by a Research Grant (V749)
from the Hong Kong Polytechnic University and the
Research Grant Council of Hong Kong Government
(BQ500). The authors thank Mr. W. F. Tam for his
technical assistance.
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