Risk assessment of exposure to volatile organic compounds in ...

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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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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.

ARTICLE IN PRESS 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

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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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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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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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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


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


Lifetime risk


Lifetime risk


Lifetime risk


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)


VOC

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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


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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