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Comparative study of multimedia models applied to the risk assessment of soil and groundwater contam


Journal of Hazardous Materials 182 (2010) 778–786

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Journal of Hazardous Materials
journal homepage: www.elsevier.com/locate/jhazmat

Comparative study of multimedia models applied to the risk assessment of soil and groundwater contamination sites in Taiwan
Chihhao Fan a , Yen-chuan Chen b , Hwong-wen Ma c , Gen-shuh Wang d,?
a

Department of Safety, Health, and Environmental Engineering, Ming Chi University of Technology, 84 Gung-Juan Road, Taishan, Taipei County, Taiwan Energy and Environment Research Laboratories, Industrial Technology Research Institute, 195, Chun-Hsin Road, Chu-Dong, Hsinchu County, Taiwan Graduate Institute of Environmental Engineering, National Taiwan University, 71, Chou-Shan Road, Taipei, Taiwan d Institute of Environmental Health, National Taiwan University, 17, Xu-Zhou Road, Taipei 10055, Taiwan
b c

a r t i c l e

i n f o

a b s t r a c t
The purpose of this study was to explore the applicability of two popular multimedia risk assessment models to three different soil and groundwater contamination sites in Taiwan. The Multimedia Environmental Pollutant Assessment System (MEPAS) and the Multimedia Contaminant Fate, Transport, and Exposure Model (MMSOILS) were selected because of their wide application and use. Three soil and groundwater contamination sites in Taiwan were employed as illustrative examples in the comparison of these two risk assessment models. Three exposure pathways were investigated, categorized as oral ingestion, dermal absorption, and inhalation. The results show that MEPAS and MMSOILS calculated similar cancer risks and hazard quotients in general, but were different by two orders of magnitude in cancer risk estimates for sites contaminated by volatile organic compounds (VOC). Using MMSOILS may not be appropriate for risk assessment of such sites, as it does not account for indoor inhalation as a potential exposure pathway in its risk calculations. Water ingestion, dermal absorption when showering and indoor inhalation were the three most predominant contributing exposure pathways for risk development among sites contaminated by VOCs. On the other hand, crop and meat ingestion were more important exposure pathways in the context of sites with non-VOC pollutants, because these hydrophobic contaminants may be bio-accumulative in plants and animals, and consequently enter the human body via food chains. ? 2010 Elsevier B.V. All rights reserved.

Article history: Received 22 March 2010 Received in revised form 22 June 2010 Accepted 23 June 2010 Available online 30 June 2010 Keywords: Multimedia risk assessment models MEPAS MMSOILS Dioxin Volatile organic compounds Soil and groundwater contamination

1. Introduction Risk stands for the probability or chance of adverse health effects to human beings resulting from exposure to environmental pollutants. Risk assessment has been regarded as a useful method in evaluating the potential impact of various pollutants on the environment and public health since its ?rst application was established [1–3]. After adoption of suitable risk assessment tools, the corresponding health risk due to exposure to a speci?c pollutant can be calculated. For example, a 10?6 cancer risk is equivalent to an increased chance of one-in-a-million of developing cancer

Abbreviations: MEPAS, multimedia environmental pollutant assessment system; MMSOILS, multimedia contaminant fate, transport, and exposure model; PCE, perchloroethylene; TCE, trichloroethylene; 1,1-DCE, 1,1-dichloroethene; cis-DCE, cis-dichloroethene; VC, vinyl chloride; 1,2-DCEA, 1,2-dichloroethane; Hg, mercury; PCP, pentachlorophenol; DIOX, 2,3,7,8-tetrachloro-dibenzodioxin; MC, methyl chloride; BENZ, benzene. ? Corresponding author. Tel.: +886 2 33668098; fax: +886 2 23940612. E-mail address: gswang@ntu.edu.tw (G.-s. Wang). 0304-3894/$ – see front matter ? 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.06.102

due to lifetime exposure to a pollutant. For substances presenting risks other than cancer, the hazard quotient (HQ) is frequently used. HQ stands for the ratio of the estimated exposure to a pollutant to the tolerable daily intake (TDI) at which no adverse health effects are likely to occur. In most cases, the acceptable HQ is 1.0 for environmental contaminants. The intended use of the assessment model was for screening and comparison of different waste sites, remediation initiatives, and hazard evaluation. To calculate the associated risks, the parameters of potential risk sources, exposure pathways and receptors, as well as the physical and chemical characteristics of compounds of interest need to be considered. Previous studies in environmental practice have utilized either a simple single-medium model using deterministic calculation or a comprehensive stochastic multimedia model considering sitespeci?city [4,5]. The multimedia risk assessment model has become increasingly popular over the past few years due to its wide applicability and consideration of multiple contaminants and contact media [6–9]. However, the risks calculated from different multimedia risk assessment models may still vary due to the use of different conceptual algorithms. Therefore, the selection of an appropri-

Table 1 Concentrations and chemical characteristics of contaminants in Sites A, B and C. Parameter De?nition Considered in model development MEPAS Cwi Conc. in groundwater (mg l?1 ), * in surface soil (mg kg?1 ) ˇ MMSOILS ˇ Values for selected sites PCE TCE 1,1-DCE cis-DCE VC 1,2-DECA Hg 2.70E?02 PCP DIOX MC BENZ A: [15] Reference

7.80E?01 5.40E?01 1.71E?01 1.57E?01 6.59E?03

Kpi Kowi Kdi
gi

di

w

RfDigi RfDihi RfDdei CSFigi CSFihi CSFdei Bvi Bri Fmi Fdi

Skin permeability (cm hr?1 ) Octanol-water partition coef?cient (unitless) Soil-water distribution coef?cient (unitless) Decay coef?cient in aqueous phase (day?1 ) Decay coef?cient in surface soil (day?1 ) Decay coef?cient in plant surface (day?1 ) Reference dose of ingestion (mg kg?1 day?1 ) Reference dose of inhalation (mg kg?1 day?1 ) Reference dose of dermal contact (mg kg?1 day?1 ) Carcinogenic slope factor of ingestion (kg-day mg?1 ) Carcinogenic slope factor of inhalation (kg-day mg?1 ) Carcinogenic slope factor of dermal contact (kg-day mg?1 ) Bioaccumulation factor from soil to vegetables (kg kg?1 ) Bioaccumulation factor from soil to crops (kg kg?1 ) Bioaccumulation factor from soil to beef (day kg?1 ) Bioaccumulation factor from soil to milk (day l?1 )

ˇ ˇ

ˇ ˇ ˇ

3.00E?02 8.89E+01 1.86E?03* B: [16] 7.15E?02 7.92E?01 3.06E?01 1.88E+01 3.02E+00 3.81E+00 1.96E?01 C: [17] 4.88E?02 4.66E?02 1.27E?01 1.83E?02 7.3E?03** 2.08E?02 1.00E?03 9.50E?01 1.03E?02 6.11E?03 1.86E?01 [18], **[19] 3.80E+02 3.20E+02 1.35E+02 5.20E+01 1.52E+01 6.20E+01 0.00E+00 1.32E+05 4.62E+06 8.00E+00 5.20E+01 [18] 1.31E+00 4.50E?01 6.38E?02 3.88E?01 4.54E?01 1.36E?03 8.66E?04 1.49E?03 6.66E?03 5.13E?04 1.18E?03 7.45E?04 2.49E?03 4.44E?03 2.49E?03 5.00E?02 5.00E?02 5.00E?02 5.00E?02 5.00E?02 9.18E?01 4.08E+03 1.18E+00 8.37E+04 7.45E?03 0.00E+00 6.93E?01 1.62E?03 1.37E?02 0.00E+00 1.44E?02 3.20E?04 5.00E?02 0.00E+00 5.00E?02 5.00E?02 1.00E?01 3.00E?04 3.00E?02 1.00E?09 1.00E?01 8.57E?05 2.86E?02 1.14E?08 1.00E?01 3.00E?04 3.00E?02 1.00E?09 5.70E?03 0.00E+00 1.80E?02 1.50E+05 5.70E?03 0.00E+00 1.80E?02 1.50E+05 5.70E?03 0.00E+00 1.80E?02 1.50E+05 3.56E+00 1.90E?03 4.25E?02 5.44E?03 1.63E+00 2.40E?03 6.78E?02 3.01E?01 1.56E?06 1.60E?03 3.31E?03 2.40E?01 4.93E?07 4.70E?04 1.05E?03 4.54E?03 9.34E+02 8.57E?01 [10] 1.98E?02 2.85E?03 [18] 3.96E?02 3.64E?03 [18] 5.00E?02 5.00E?02 [20] 2.95E?02 1.71E?02 [18] 2.95E?02 1.71E?02 [18] 2.95E?02 1.71E?02 [18] 1.30E?02 1.00E?01 [18] 6.30E?03 1.00E?01 [18] 1.30E?02 1.00E?01 [18] 1.16E+01 2.13E+00 [10] 1.03E+01 2.52E+00 [10] 2.01E?07 3.79E?06 [10] 6.35E?08 1.20E?06 [10]

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786

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1.00E?02 7.00E?03 9.00E?03 1.00E?02 2.00E?05 1.00E?02 1.70E?01 9.00E?03 1.00E+10 1.43E?03 1.00E?02 7.00E?03 9.00E?03 1.00E?02 2.00E?05 5.20E?02 1.10E?02 6.00E?01 0.00E+00 2.70E?01 2.00E?03 6.00E?03 1.80E?01 0.00E+00 2.70E?01 5.20E?02 1.10E?02 6.00E?01 0.00E+00 2.70E?01 1.25E+00 1.38E+00 2.27E+00 3.95E+00 2.12E+00 2.71E+00 7.14E+00 3.22E+01 3.64E+00 4.78E+00 2.75E?05 2.50E?05 3.39E?06 1.31E?06 3.39E?06 3.12E?06 2.76E?06 1.07E?06 4.13E?07 1.07E?06

779

780

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786

Table 2 Parameters for site characterization, food chain and exposure pathways. Parameter De?nition Considered in model development MEPAS Site characteristic parameters IR Utilization frequency of irrigation water (L m?2 month?1 ) Density of surface soil layer (g cm?3 ) b tdd Depth of contaminated soil (m) P Areal density of agricultural soil (kg m?2 ) Food chain parameters TVlv Conductive factor of plant surface (unitless) rlv Sedimentation rate of plant surface (unitless) TClv Time for vegetable growth (day) Ylv Areal yield of vegetable (kg m?2 ) FIlv Ratio of irrigation to vegetable yield (unitless) Qft Animal forage intake (kg day?1 ) Qst Animal soil intake (kg day?1 ) Qwt Animal water intake (L day?1 ) Exposure Parameters EF Exposure frequency (unitless) ED Exposure duration (yrs lifetime?1 ) BW Body weight (kg) AT Contact time (yrs) Asd Human surface area (cm2 ) Add Human contact area of soil (cm2 ) AD Soil adsorptive factor (mg cm?2 ) Kc Indoor volatilization factor (L m?3 ) ETs Daily showering time (h day?1 ) Udw Daily water intake (L day?1 ) Usw Daily shower intake (L day?1 ) Ulv Daily vegetable intake (kg day?1 ) Ulr Daily crops intake (kg day?1 ) Umt Daily meat intake (kg day?1 ) Umk Daily milk intake (L day?1 ) Usi Daily inhalation during shower (m3 day?1 ) Uai Daily indoor inhalation (m3 day?1 ) Uds Daily soil intake (g day?1 ) ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ MMSOILS ˇ ˇ ˇ 0.841 1.5 0.1 240.0 0.9 0.25 60.0 200.0 0.68 55.0 0.5 50.0 0.959 (=350/365) 24.0 61.67 75.0(cancer)/24.0(non-cancer) 1.73E+04 4.98E+03 1.0 0.5 0.5 3.0 0.06 0.323 0.210 7.86E?03 5.59E?02 0.7 15.0 0.1 [21] [21] [21] [20] [20] [20] [20] [20] [20] [10] [10] [10] [14] [14] [14] [14] [14] [21] [20] [20] [14] [14] [20] [22] [22] [22] [22] [14] [20] [14] Value Reference

ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ ˇ

ˇ ˇ ˇ ˇ ˇ ˇ

ˇ

ate risk assessment model becomes critical in the risk evaluation process. This study investigated the applicability of two frequently used multimedia risk assessment models, the Multimedia Environmental Pollutant Assessment System (MEPAS) and the Multimedia Contaminant Fate, Transport, and Exposure Model (MMSOILS), in the evaluation of three soil and groundwater contamination sites. The MEPAS and MMSOILS were selected because of their wide applicability and use in the literature. As soil and groundwater contamination constitutes a serious environmental issue in Taiwan, three such sites were chosen in this study. The abundance of contaminants in these sites was con?rmed, and their presence has been shown to contribute to adversely affecting public health and severely deteriorating soil and groundwater quality. 2. Model description and background of case study sites 2.1. Model description and risk analysis MEPAS was developed by the Paci?c Northwest National Laboratory of the United States Department of Energy in 1995, and assesses chronic exposure and human health risks resulting from environmental emissions. The physics-based modules of contaminant processes in air, soil, groundwater, and surface water are integrated into MEPAS, which considers both chemical and radioactive potential impacts. It assesses the health risk resulting from environmental pathways and human exposure through higherorder mathematical calculations. Although MEPAS is commonly used for risk assessment of soil and groundwater contamination sites, it can also be used for risk assessment of contamination sources in surface water and the atmosphere.

MMSOIL, developed by the United States Environmental Protection Agency’s (EPA) National Exposure Research Laboratory, calculates the health risk associated with the release of contaminants from hazardous waste sites. This multimedia model analyzes the spread of chemical contaminants in groundwater, surface water, soil layers and the atmosphere, and their accumulation in the food chain. This model also estimates the exposure risks to humans through individual and combined exposure pathways. More details of MEPAS and MMSOILS and their application can be found elsewhere [7,9–13]. In the MEPAS evaluation for this study, the exposure pathways investigated were categorized into three groups: oral ingestion, dermal absorption, and inhalation. For pathways of inhalation, indoor breathing and breathing when showering were assumed to be the two major exposure pathways. For dermal absorption, showering and soil contact were assumed to be the two most important exposure pathways. Ingestion of drinking water, showering water, beef, vegetables, crops and soils were considered. For MMSOILS, the exposure pathways considered included ambient inhalation of volatiles and particulates, dermal contact, soil and water ingestion, and consumption of ?sh, plants and meat. Indoor inhalation pathways were not included in MMSOILS. To assess the risk contribution from food chain pathways, a scenario was assumed where contaminated groundwater was used for agricultural irrigation. Consequently, the soil was polluted during the ?ltration process, which resulted in the contamination of crops and vegetables through root absorption activity. Meat and milk products were then also contaminated because of vegetable and crop ingestion by domestic animals. Therefore, the food chain pathways included dermal contact with soil, and the ingestion of soil, meat, milk, vegetables and crops.

Table 3 MEPAS and MMSOILS calculated hazard quotients (and cancer risks) for Site A. Pathway (1) MEPAS Ingestion Water Shower Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Inhalation Indoor Showering Total risk (2) MMSOILS Ingestion Water Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Total risk PCE TCE 1,1-DCE cis-DCE VC 1,2-DCEA Total risk

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786

1.16E+00 (6.05E?04) 1.16E?02 (6.05E?06) 4.71E?06 (2.45E?09) 3.80E?06 (1.98E?09) 2.22E?02 (1.15E?05) 1.98E?02 (1.03E?05) 5.56E?06 (2.89E?09) 6.08E?01 (3.16E?04) 5.54E?05 (2.88E?08) 3.33E+00 (6.65E?05) 3.97E?01 (7.94E?06) 5.55E+00 (1.02E?03)

1.15E+00 (8.87E?05) 1.15E?02 (8.87E?07) 4.53E?06 (3.49E?10) 3.56E?06 (2.74E?10) 3.08E?02 (2.37E?06) 7.63E?02 (5.87E?06) 8.15E?06 (6.27E?10) 4.49E?01 (3.46E?05) 3.34E?06 (6.25E?09) 1.35E?01 (1.38E?04) 1.62E?02 (1.65E?05) 1.87E+00 (2.87E?04)

2.84E?01 (1.54E?03) 2.84E?03 (1.54E?05) 1.40E?07 (7.58E?10) 3.16E?07 (1.71E?09) 5.06E?03 (2.73E?05) 2.86E?02 (1.54E?04) 6.78E?07 (3.66E?09) 2.38E?01 (1.28E?03) 6.75E?06 (3.65E?08) 8.12E?01 (1.32E?03) 9.69E?02 (1.57E?04) 1.47E+00 (4.49E?03)

2.35E?02 2.35E?04 4.46E?09 1.00E?08 4.11E?04 1.53E?04 3.20E?08 2.83E?03 3.19E?19 6.70E?14 8.00E?15 2.71E?02

4.92E+00 (2.66E?05) 4.92E?02 (2.66E?07) 2.41E?06 (1.30E?11) 5.43E?06 (2.93E?11) 8.40E?02 (4.54E?07) 7.35E?02 (3.97E?07) 1.17E?05 (6.33E?11) 1.85E?E?01 (9.98E?07) 1.05E?06 (5.67E?12) 1.97E?01 (7.59E?05) 2.35E?02 (9.05E?06) 5.58E+00 (1.14E?04)

4.03E?04 (2.30E?07) 4.03E?06 (2.30E?09) 8.49E?11 (4.84E?14) 1.91E?10 (1.09E?13) 3.64E?06 (2.07E?09) 3.88E?07 (2.21E?10) 1.82E?10 (1.03E?13) 5.60E?05 (1.11E?04) 1.81E?09 (6.31E?10) 1.15E?03 (7.59E?05) 1.37E?04 (9.05E?06) 1.76E?03 (2.24E?04)

7.54E+00 (2.26E?03) 7.54E?02 (2.26E?05) 1.18E?05 (3.57E?09) 1.31E?05 (3.99E?09) 1.43E?01 (4.16E?05) 1.98E?01 (1.71E?04) 2.61E?05 (7.24E?09) 1.49E+00 (1.63E?03) 6.71E?05 (7.16E?08) 4.48E+00 (1.60E?03) 5.34E?01 (1.91E?04) 1.45E+01 (5.91E?03)

1.16E+00 (6.05E?04) 4.49E?06 (2.34E?09) 3.63E?06 (1.89E?09) 3.71E?03 (1.93E?06) 8.03E?03 (4.18E?06) 6.12E?09 (3.18E?12) 1.64E+00 (8.51E?04) 3.05E?04 (1.58E?07) 2.81E+00 (1.46E?03)

1.15E+00 (8.86E?05) 4.88E?06 (3.75E?10) 3.83E?06 (2.95E?10) 6.34E?03 (4.88E?07) 3.28E?02 (2.52E?06) 9.48E?09 (7.30E?13) 1.55E+00 (1.19E?04) 4.72E?04 (3.63E?08) 2.74E+00 (2.11E?04)

2.84E?01 (1.53E?03) 1.76E?07 (9.49E?10) 3.95E?07 (2.14E?09) 7.71E?04 (4.17E?06) 1.09E?02 (5.89E?05) 7.01E?10 (3.78E?12) 1.04E+00 (5.62E?03) 3.49E?05 (1.88E?07) 1.34E+00 (7.21E?03)

2.35E?02 4.11E?09— 9.25E?09 6.20E?05 5.71E?05 3.24E?11 1.24E?02 1.61E?06 3.59E?02

9.83E?03 (2.65E?05) 4.63E?09 (1.25E?11) 1.04E?08 (2.81E?11) 2.49E?05 (6.73E?08) 5.61E?05 (1.51E?07) 2.42E?11 (6.54E?14) 2.07E?03 (5.59E?06) 1.09E?08 (2.93E?11) 1.21E?02 (3.16E?05)

4.03E?03 (2.30E?07) 8.25E?10 (4.70E?14) 1.86E?09 (1.06E?13) 3.12E?06 (1.78E?10) 1.43E?06 (8.12E?11) 1.80E?12 (1.03E?16) 2.42E?03 (1.38E?07) 8.99E?08 (5.12E?12) 6.45E?03 (3.68E?07)

2.63E+00 (2.25E?03) 9.56E?06 (3.68E?09) 7.88E?06 (4.35E?09) 1.09E?02 (6.66E?06) 5.18E?02 (6.58E?05) 1.64E?08 (7.76E?12) 4.25E+00 (6.59E?03) 8.14E?04 (3.83E?07) 6.95E+00 (8.91E?03)

781

782

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786

2.2. Background of selected sites In this study, the three selected sites (Site A, Site B, and Site C) are characterized by the contamination of soil and groundwater as declared by the Taiwan Environmental Protection Administration [14]. These sites were contaminated due to the improper storage and disposal of raw materials and their degradation products, including various organic solvents. The risk assessment was performed to calculate the potential threats of using groundwater as the water supply in the neighboring areas of each investigated site. Site A was an abandoned factory for TV compartment production and assembly, where perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethene (1,1-DCE), cis-dichloroethene (cis-DCE), vinyl chloride (VC) and 1,2-dichloroethane (1,2-DCEA) were found to contaminate the groundwater. Site B was a petrochemical factory that was still in operation. At this site, considerable levels of mercury (Hg), pentachlorophenol (PCP), and 2,3,7,8-tetrachlorodibenzodioxin (DIOX) were measured in groundwater and surface soil layers. Site C was a vinyl chloride production factory. PCE, TCE, 1,1-DCE, VC, 1,2-DCEA, methyl chloride (MC), and benzene (BENZ) were found to be contaminating the groundwater. The concentrations and chemical characteristics of the contaminants in the groundwater of the three selected sites are listed in Table 1. All chemicals are either carcinogenic or harmful in other ways to humans. Table 2 summarizes the model parameters of site characterization, food chains and contaminant exposure in the risk calculation. 3. Results and discussion 3.1. Risk assessment for Site A For the risk assessment of Site A, the contaminants PCE (7.80 × 10?1 mg l?1 ), TCE (5.40 × 10?1 mg l?1 ), 1,1DCE (1.71 × 10?1 mg l?1 ), cis-DCE (1.57 × 10?1 mg l?1 ), VC (6.59 × 10?3 mg l?1 ) and 1,1-DCEA (2.70 × 10?2 mg l?1 ) were found hazardous to public health because their concentrations were above the regulated standards in many countries [9]. With the exception of cis-DCE, all other contaminants were shown to be carcinogenic, and therefore contributed to the subsequent cancer risk analysis. 3.1.1. MEPAS risk assessment Table 3 summarizes the cancer risks and hazard quotients of Site A through MEPAS calculation. The total cancer risk amounted to 5.91 × 10?3 . When comparing the cancer risk of individual contaminants, the contaminant 1,1-DCE was found to have the highest cancer risk at 4.49 × 10?3 . The cancer risks for PCE (1.02 × 10?3 ) and TCE (2.87 × 10?4 ) ranked second and third, respectively. Water ingestion (2.26 × 10?3 ), dermal absorption when showering (1.63 × 10?3 ) and indoor inhalation (1.60 × 10?3 ) were the three most important exposure pathways for these cancer risks. By ignoring the risk contribution of food chain exposure pathways, the total cancer risk was reduced to 5.71 × 10?3 . The contaminants 1,1-DCE, PCE and TCE were the major sources of cancer risk, with a risk of 4.31 × 10?3 , 1.00 × 10?3 and 2.79 × 10?4 , respectively. In comparison, the cancer risk associated with the food chain pathways was trivial (i.e., only 3.3% of the total risk). This was because the carcinogenic compounds in Site A were volatile and less bio-accumulative. The total hazard quotient for Site A was 14.50. For the investigated contaminants, VC, PCE and TCE were the three major contaminants, which resulted in hazard quotients of 5.58, 5.55 and 1.90, respectively. The three most important exposure pathways contributing to hazard quotients were water ingestion, indoor

inhalation, and dermal absorption when showering, with respective risks of 7.50, 4.50 and 1.49. Similar to the ?ndings from the cancer risk analysis, the total hazard quotient was slightly reduced to 14.10 when the risk contribution from food chain exposure was ignored. The calculated total cancer risk and hazard quotient were all above their respective general guidance values of 1.00 × 10?6 and 1.00, indicating that using groundwater at Site A as a daily water supply may cause severe health issues for the public. 3.1.2. MMSOILS risk assessment The calculated cancer risks and hazard quotients of MMSOILS are also presented in Table 3. The total cancer risk was 8.91 × 10?3 . The cancer risks resulting from exposure to 1,1-DCE, PCE and TCE were comparatively more signi?cant than those posed by other investigated contaminants, having cancer risks of 7.21 × 10?3 , 1.46 × 10?3 and 2.11 × 10?4 , respectively. The three main exposure pathways were found to be dermal absorption when showering, water ingestion and ingestion of crops, resulting in risks of 6.59 × 10?3 , 2.25 × 10?3 and 6.58 × 10?5 , respectively. Ignoring the food chain pathways reduced the total cancer risk to 8.84 × 10?3 . The chemicals 1,1-DCE, PCE and TCE were still the primary sources of cancer risk development, while water ingestion and dermal absorption when showering remained the two most important exposure pathways. The risk assessment results of both MEPAS and MMSOILS were in the same order of magnitude, even though exposure pathways of inhalation were not considered in the MMSOILS calculation. For Site A, the total hazard quotient was calculated to be 6.59. The contaminants PCE, TCE and 1,1-DCE, were the three main compounds contributing to the hazard quotient with calculated risks of 2.80, 2.70 and 1.30, respectively. Dermal absorption when showering, water ingestion and crops ingestion were the most important exposure pathways, resulting in risks of 4.25, 2.60 and 5.20 × 10?2 , respectively. When the risk contribution from food chain exposure pathways was disregarded, the total hazard quotient decreased slightly to 6.49. The contaminants PCE, TCE and 1,1-DCE remained the three most harmful contaminants. Dermal absorption when showering and water ingestion were the two most important exposure pathways when the food chain pathway was not considered in the risk calculation. Similar to MEPAS, MMSOILS calculated the total cancer risk and hazard quotient for Site A to be above general guidance values, demonstrating that the use of groundwater domestically can result in potential health threats to the public. 3.2. Risk assessment for Site B At Site B, Hg (3.00 × 10?2 mg l?1 as total mercury), PCP (8.89 × 101 mg l?1 ) and DIOX (1.86 × 10?3 mg kg?1 in soil) were detected, posing signi?cant threats to public health. Hg was the only contaminant that was not carcinogenic among the three contaminants at this site. Since the aqueous concentration of DIOX was below detection thresholds, risk assessment was conducted based on concentrations of Hg and PCP in the aqueous phase, and that of DIOX in the soil. 3.2.1. MEPAS risk assessment The cancer risks and hazard quotients calculated by MEPAS are presented in Table 4. The total cancer risk and hazard quotient were 7.55 × 10?2 and 3.85 × 102 , respectively. For Hg, the hazard quotient was calculated as 3.37 × 101 , the lowest among the three investigated contaminants. For PCP, the cancer risk and hazard quotient were 5.85 × 10?2 and 1.09 × 102 , respectively. DIOX concentrations in groundwater were minimal, implying that water ingestion, shower ingestion, dermal absorption when showering, indoor breathing and inhalation posed only negligible risks. The

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786 Table 4 MEPAS and MMSOILS calculated hazard quotients (and cancer risks) for Site B. Pathway (1) MEPAS Ingestion Water Shower Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Inhalation Indoor Showering Total risk (2) MMSOILS Ingestion Water Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Total risk Hg PCP DIOX Total risk

783

1.60E+00 8.01E?03 1.53E?02 2.46E?02 2.13E?01 2.45E?01 1.79E?04 1.11E?02 6.78E+00 2.10E+01 3.82E+00 3.37E+01

4.74E+00 (2.56E?03) 2.37E?02 (1.28E?05) 3.09E?03 (1.67E?06) 6.96E?03 (3.76E?06) 4.10E?02 (2.22E?05) 2.72E?04 (1.47E?07) 3.06E?06 (1.65E?09) 8.57E+01 (4.63E?02) 1.52E?04 (8.22E?08) 1.87E+01 (9.61E?03) 3.53E?05 (1.82E?08) 1.09E+02 (5.85E?02)

0.00E+00 (0.00E+00) 0.00E+00 (0.00E+00) 2.33E+01 (3.46E?03) 4.54E+00 (9.74E?04) 3.97E+00 (1.89E?04) 2.65E+02 (7.26E?03) 2.61E?02 (6.11E?07) 0.00E+00 (0.00E+00) 3.14E+01 (5.13E?03) 0.00E+00 (0.00E+00) 0.00E+00 (0.00E+00) 2.42E+02 (1.70E?02)

6.34E+00 (2.56E?03) 3.17E?02 (1.28E?05) 2.33E+01 (3.46E?03) 4.57E+00 (9.78E?04) 4.22E+00 (2.11E?04) 2.65E+02 (7.26E?03) 2.63E?02 (6.13E?07) 8.57E+01 (4.63E?02) 3.82E+01 (5.13E?03) 3.97E+01 (9.61E?03) 3.82E+00 (1.82E?08) 3.85E+02 (7.55E?02)

1.49E+00 1.29E?02 2.69E?02 1.77E?01 2.24E?01 1.92E?04 4.30E?02 9.58E+00 1.16E+01

1.33E+01 (2.39E?03) 5.75E?03 (1.04E?06) 1.30E?02 (2.34E?06) 1.16E?04 (2.09E?08) 1.85E?04 (3.33E?08) 5.64E?09 (1.01E?12) 3.82E+02 (6.88E?02) 2.81E?04 (5.05E?08) 3.96E+02 (7.12E?02)

0.00E+00 (0.00E+00) 5.20E+01 (7.80E?03) 7.00E+00 (1.05E?03) 2.44E+00 (3.65E?04) 1.35E+02 (2.02E?02) 9.24E?04 (1.39E?07) 0.00E+00 (0.00E+00) 4.60E+01 (6.90E?03) 2.42E+02 (3.63E?02)

1.48E+01 (2.39E?03) 5.20E+01 (7.80E?03) 7.04E+00 (1.05E?03) 2.62E+00 (3.65E?04) 1.35E+02 (2.02E?02) 1.12E?03 (1.39E?07) 3.82E+02 (6.88E?02) 5.56E+01 (6.90E?03) 6.50E+02 (1.08E?01)

cancer risk and hazard quotient for DIOX were 1.70 × 10?2 and 2.42 × 102 . Dermal absorption when showering (resulting in a cancer risk of 4.62 × 10?2 ) was the exposure pathway contributing most to cancer risk. Indoor inhalation and crop ingestion ranked second and third in terms of cancer risk, with risks of 9.61 × 10?3 and 7.26 × 10?3 , respectively. For hazard quotient, crops ingestion, dermal absorption when showering and indoor inhalation were the three most important pathways, which resulted in risks of 2.65 × 102 , 8.57 × 101 , and 3.97 × 101 , respectively. Indoor inhalation was not as signi?cant an exposure pathway as expected because of the presence of non-volatile pollutants at Site B. When the risk contribution from food chain pathways was ignored, the total cancer risk and hazard quotients were reduced to 6.36 × 10?2 and 1.74 × 102 , respectively. Under these circumstances, the hazard quotient for Hg was reduced to 3.32 × 101 . The exclusion of food chain pathways in risk assessment also reduced the cancer risks and hazard quotients to 5.85 × 10?2 and 1.09 × 102 for PCP, and 5.13 × 10?3 and 3.14 × 101 for DIOX, respectively. The obvious risk reduction for DIOX was due to its signi?cant bioaccumulation through oral ingestion, which implied that exposure through food chain cannot be ignored in risk calculations. When comparing the risks with and without food chain pathways, it was found that dermal absorption when showering, indoor breathing and dermal absorption through soil contact were the major pathways responsible for cancer risk and hazard quotient development. The calculated total cancer risk and hazard quotient for Site B were all above their general guidance values. This suggests that groundwater utilization at Site B may result in severe health effects. 3.2.2. MMSOILS risk assessment The cancer risks and hazard quotients for Site B as calculated by MMSOILS are also presented in Table 4. The total cancer risk and hazard quotient were 1.08 × 10?1 and 6.50 × 102 , respectively. The hazard quotients were 1.16 × 101 , 3.96 × 102 and 2.42 × 102 for Hg, PCP and DIOX, respectively, and the cancer risks were 7.12 × 10?2 and 3.63 × 10?2 for PCP and DIOX. Again, the pathways of water

ingestion and dermal absorption when showering were not considered in the DIOX cancer risk calculation because of non-detectable levels of DIOX concentration in the groundwater. Dermal absorption when showering, crop ingestion and meat ingestion were the three main exposure pathways contributing to cancer risk, for which the risks were calculated as 6.88 × 10?2 , 2.02 × 10?2 and 7.80 × 10?3 , respectively. For hazard quotients, dermal absorption when showering (3.82 × 102 ), crop ingestion (1.35 × 102 ) and dermal absorption through soil contact (5.56 × 101 ) were the three main risk-contributing pathways. Again, this calculated outcome may have resulted from the presence of non-volatile pollutants. It was found that the total cancer risk and hazard quotient were reduced to 7.81 × 10?2 and 4.52 × 102 when the food chain exposure pathways were not considered. Moreover, the hazard quotients of Hg, PCP and DIOX were reduced to 1.11 × 101 , 3.95 × 102 and 4.6 × 101 , respectively. When food chain pathways were ignored, the cancer risk for PCP and DIOX were 7.12 × 10?2 and 6.90 × 10?3 . As expected, the calculated cancer risks and hazard quotients were all above their general guidance values, implying that using groundwater as a water supply in this area would be harmful and inappropriate. 3.3. Risk assessment for Site C For Site C, PCE (7.15 × 10?2 mg l?1 ), TCE (7.92 × 10?1 mg l?1 ), 1,1-DCE (3.06 × 10?1 mg l?1 ), VC (1.88 × 10?1 mg l?1 ), 1,2-DECA (3.02 mg l?1 ), MC (3.81 mg l?1 ) and BENZ (1.96 × 10?1 mg l?1 ) were considered both for the cancer risk and hazard quotient assessment. Table 5 presents the calculated risks of each contaminant through various pathways using MEPAS and MMSOILS. 3.3.1. MEPAS risk assessment With MEPAS, the total cancer risk was calculated to be 5.80 × 10?2 for Site C. When comparing the cancer risks of all investigated contaminants, VC, 1,2-DCEA and 1,1-DCE were found to

784

Table 5 MEPAS and MMSOILS calculated hazard quotients (and cancer risks) for Site C. Pathway (1) MEPAS Ingestion Water Shower Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Inhalation Indoorv Showering Total risk (2) MMSOILS Ingestion Water Meat Milk Vegetables Crops Soil Dermal Showering Soil contact Total risk PCE TCE 1,1-DCE VC 1,2-DCEA MC BENZ Total risk

C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786

1.07E?01 (5.55E?05) 1.07E?03 (5.55E?07) 4.32E?07 (2.25E?10) 3.49E?07 (1.81E?10) 2.03E?03 (1.06E?06) 1.81E?03 (9.42E?07) 5.10E?07 (2.65E?10) 5.57E?02 (2.90E?05) 5.08E?06 (2.64E?09) 3.05E?01 (6.10E?06) 3.64E?02 (7.27E?07) 5.09E?01 (9.38E?05)

1.69E+00 (1.30E?04) 1.69E?02 (1.30E?06) 6.65E?06 (5.12E?10) 5.22E?06 (4.02E?10) 4.52E?02 (3.48E?06) 1.12E?01 (8.62E?06) 1.19E?05 (9.20E?10) 6.58E?01 (5.07E?05) 4.90E?06 (9.16E?09) 1.99E?01 (2.03E?04) 2.37E?02 (2.42E?05) 2.74E+00 (4.21E?04)

5.08E?01 (2.74E?03) 5.08E?03 (2.74E?05) 2.51E?07 (1.35E?09) 5.64E?07 (3.04E?09) 9.03E?03 (4.88E?05) 5.10E?02 (2.76E?04) 1.21E?06 (6.53E?09) 4.24E?01 (2.29E?03) 1.21E?05 (6.51E?08) 1.45E+00 (2.35E?03) 1.73E?01 (2.80E?04) 2.62E+00 (8.01E?03)

1.40E+03 (7.58E?03) 1.40E+01 (7.58E?05) 6.89E?04 (3.72E?09) 1.55E?03 (8.36E?09) 2.40E+01 (1.29E?04) 2.10E+01 (1.13E?04) 3.35E?03 (1.81E?08) 5.30E+01 (2.86E?04) 2.99E?04 (1.62E?09) 5.62E+01 (2.16E?02) 6.70E+00 (2.58E?03) 1.58E+03 (3.24E?02)

2.25E?01 (3.16E?03) 2.25E?03 (3.16E?05) 2.24E?08 (3.13E?10) 5.19E?08 (7.26E?10) 3.93E?03 (5.50E?05) 1.18E?03 (1.65E?05) 2.17E?07 (3.03E?09) 1.57E?02 (2.19E?04) 2.16E?06 (3.02E?08) 1.13E+00 (9.01E?03) 1.35E?01 (1.08E?03) 1.51E+00 (1.36E?02)

1.93E+00 (7.39E?04) 1.93E?02 (7.39E?06) 5.27E?08 (2.02E?11) 1.18E?07 (4.54E?11) 1.52E?02 (5.81E?06) 4.07E?03 (1.56E?06) 3.02E?07 (1.16E?10) 5.60E?02 (2.15E?05) 3.01E?06 (1.15E?09) 5.51E+00 (1.02E?03) 6.57E?01 (1.22E?04) 8.19E+00 (1.92E?03)

1.71E?01 (2.93E?04) 1.71E?03 (2.93E?06) 9.12E?08 (1.56E?10) 2.05E?07 (3.51E?10) 2.37E?03 (4.05E?06) 9.37E?04 (1.60E?06) 2.83E?07 (4.84E?10) 1.84E?01 (3.14E?04) 2.82E?06 (4.83E?09) 4.89E?01 (8.36E?04) 5.83E?02 (9.97E?05) 9.07E?01 (1.55E?03)

1.40E+03 (1.47E?02) 1.40E+01 (1.47E?04) 6.96E?04 (6.30E?09) 1.56E?03 (1.31E?08) 2.41E+01 (2.47E?04) 2.12E+01 (4.18E?04) 3.36E?03 (2.94E?08) 5.44E+01 (3.19E?03) 3.29E?04 (1.15E?07) 6.53E+01 (3.50E?02) 7.78E+00 (4.19E?03) 1.60E+03 (5.80E?02)

1.16E+00 (6.05E?04) 4.49E?06 (2.34E?09) 3.63E?06 (1.89E?09) 3.71E?03 (1.93E?06) 8.03E?03 (4.18E?06) 6.12E?09 (3.18E?12) 1.64E+00 (8.51E?04) 3.05E?04 (1.58E?07) 2.81E+00 (1.46E?03)

1.15E+00 (8.86E?05) 4.88E?06 (3.75E?10) 3.83E?06 (2.95E?10) 6.34E?03 (4.88E?07) 3.28E?02 (2.52E?06) 9.48E?09 (7.30E?13) 1.55E+00 (1.19E?04) 4.72E?04 (3.63E?08) 2.74E+00 (2.11E?04)

5.07E?01 (2.74E?03) 3.14E?07 (1.69E?09) 7.06E?07 (3.81E?09) 1.38E?03 (7.44E?06) 1.95E?02 (1.05E?04) 1.25E?09 (6.75E?12) 1.86E+00 (1.00E?02) 6.23E?05 (3.36E?07) 2.38E+00 (1.29E?02)

2.80E+01 (7.57E?03) 1.32E?05 (3.56E?09) 2.97E?05 (8.01E?09) 7.11E?02 (1.92E?05) 1.60E?01 (4.32E?05) 6.91E?08 (1.87E?11) 5.90E+00 (1.59E?03) 3.09E?05 (8.36E?09) 3.39E+01 (9.59E?03)

4.51E+00 (3.15E?03) 4.10E?07 (2.87E?10) 9.51E?07 (6.65E?10) 1.19E?02 (8.35E?06) 8.74E?03 (6.12E?06) 4.35E?09 (3.04E?12) 1.35E+00 (9.46E?04) 2.17E?04 (1.52E?07) 5.88E+00 (4.11E?03)

1.93E+00 (7.39E?04) 5.48E?08 (2.10E?11) 1.23E?07 (4.72E?11) 1.69E?02 (6.46E?06) 1.49E?02 (5.70E?06) 2.99E?09 (1.15E?12) 3.40E?01 (1.30E?04) 1.49E?04 (5.70E?08) 2.30E+00 (8.81E?04)

1.71E?01 (2.92E?04) 8.68E?08 (1.48E?10) 1.95E?07 (3.34E?10) 2.98E?04 (5.09E?07) 3.52E?04 (6.03E?07) 2.88E?10 (4.93E?13) 9.17E?01 (1.57E?03) 1.44E?05 (2.46E?08) 1.09E+00 (1.86E?03)

3.74E+01 (1.52E?02) 2.34E?05 (8.42E?09) 3.91E?05 (1.51E?08) 1.12E?01 (4.44E?05) 2.44E?01 (1.67E?04) 9.36E?08 (3.40E?11) 1.39E+01 (1.56E?02) 1.25E?03 (7.68E?07) 5.09E+01 (3.06E?02)

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be the three main compounds contributing to cancer risk, with respective risk values of 3.24 × 10?2 , 1.36 × 10?2 and 8.01 × 10?3 . Indoor breathing was the most signi?cant exposure pathway, which resulted in a cancer risk of 3.50 × 10?2 . This was followed by pathways of water ingestion (1.47 × 10?2 ) and inhalation when showering (4.19 × 10?3 ). When food chain pathways were disregarded, the total cancer risk was reduced to 5.72 × 10?2 . The three main contaminants contributing to cancer risk were still VC (3.21 × 10?2 ), 1,2-DCEA (1.35 × 10?2 ) and 1,1-DCE (7.69 × 10?3 ). Similarly, the three most important exposure pathways remained the same. The cancer risks from food chain exposure pathways were relatively minimal (0.9% of total risk). This was due to the fact that the contaminants found at Site C were volatile organic compounds which were less bioaccumulative in the food chain. Table 5 also shows the hazard quotient assessment for Site C using MEPAS. The total hazard quotient was 1.60 × 103 . Among the contaminants analyzed, VC, MC, and TCE, causing the respective hazard quotients of 1.58 × 103 , 8.19 and 2.74, were the three main risk-contributing contaminants. For the exposure pathways, water ingestion (1.40 × 103 ), indoor breathing (6.53 × 101 ) and dermal absorption when showering (5.44 × 101 ) ranked as the top three exposure pathways for hazard quotient development. When food chain exposure pathways were disregarded, the total hazard quotient was reduced to 1.54 × 103 . The contaminants of VC, MC and TCE remained the predominant contaminants for hazard quotient development, resulting in risks of 1.53 × 103 , 8.17 and 2.56, respectively. Water ingestion, indoor breathing, and dermal absorption when showering remained the most common exposure pathways. At Site C, VC was the most dominant contaminant both for cancer risk and hazard quotient development, followed by the contaminants 1,2-DCEA and 1,1-DCE, which ranked second and third for cancer risk development. For the hazard quotient, MC and TCE ranked second and third. 3.3.2. MMSOILS risk assessment The calculated cancer risks by MMSOILS for Site C are shown in Table 5. The total cancer risk was 3.06 × 10?2 . The contaminants 1,1-DCE, VC and 1,2-DCEA were the three most risk-contributing chemicals, resulting in cancer risks of 1.29 × 10?2 , 9.59 × 10?3 and 4.11 × 10?3 , respectively. The pathways of dermal absorption when showering, water ingestion, and crops ingestion were the three main exposure pathways, resulting in cancer risks of 1.56 × 10?2 , 1.52 × 10?2 and 1.67 × 10?4 , respectively. By ignoring the contribution of food chain pathways, the total cancer risk did not change signi?cantly, and remained at 3.06 × 10?2 . The most dominant contaminants were 1,1-DCE, VC and 1,2-DCEA with cancer risks of 1.27 × 10?2 , 9.59 × 10?3 and 4.10 × 10?3 , respectively. Dermal absorption when showering and water ingestion remained the primary exposure pathways. The risk resulting from food chain pathways was minimal because the investigated contaminants were volatile and exhibited less bioaccumulation. The total hazard quotient was calculated as 5.09 × 101 . The contaminants of VC, 1,2-DCEA and PCE resulted in hazard quotients of 3.39 × 101 , 5.88 and 2.81, respectively. The analysis of exposure pathways revealed that water ingestion (3.74 × 101 ), dermal absorption when showering (1.39 × 101 ) and crop ingestion (2.44 × 10?1 ) were the most important exposure pathways for hazard quotient development. Ignoring the contribution of food chain pathways produced a negligible decrease in total hazard quotient. The contaminants VC, 1,2-DCEA and PCE remained the most dominant sources for the hazard quotient. Water ingestion also remained the main exposure pathway. For Site C, the cancer risks

calculated from MEPAS and MMSOILS were in the same order of magnitude (10?2 ). 3.4. Comparison between MEPAS and MMSOILS assessments By comparing the assessment results for all the sites investigated, it was found that the calculated results using MEPAS and MMSOILS were broadly similar. However, using MMSOILS to assess the risk of volatile organic compounds may lead to an underestimation of the potential threats to public health since MMSOILS does not take into account indoor inhalation as an exposure pathway. A closer inspection of the assessment results reveals that calculated cancer risks through ingestion pathways in both model calculations were comparable, while cancer risks from dermal absorption pathways using MEPAS were lower than for MMSOILS, in which exposure pathways of inhalation were not considered. The cancer risks from inhalation pathways using MEPAS compensated for the relative risk overestimation from dermal absorption using MMSOILS, resulting in comparable total cancer risk evaluations for both models. For Site A, MEPAS calculated the total hazard quotient one order higher than MMSOILS while comparable cancer risks were obtained from both models. Similar results were also observed for Site C. One thing that should be noted is that both Sites A and C were contaminated by volatile organic compounds. The VOC contaminants at Site A were more diverse while VC was the major contaminant at Site C. For these two sites, water ingestion and dermal absorption when showering were important both for cancer risk and hazard quotient development. Using MEPAS, indoor inhalation also exhibited the potential to cause adverse health effects on the public. For Site B, organic contaminants (PCP and DIOX) posed more of a threat to the public compared to Hg for hazard quotient development. However, the risk assessment results from both MEPAS and MMSOILS were comparable. This may be due to the fact that toxicological characteristics of DIOX and Hg were different to those of VOC, and similar algorithms were employed to estimate the possible risks in both models. For Site C, the measured concentration of VC was higher than that of other contaminants, resulting in the highest risk estimate for VC. MEPAS results suggested that inhalation and water ingestion were important exposure pathways for cancer risk while MMSOILS showed that dermal absorption when showering was the most important exposure pathway. Water ingestion and dermal absorption when showering were the two most signi?cant pathways for hazard quotient development. As Site B was contaminated by nonVOC pollutants, it was found that indoor inhalation pathways were less signi?cant in risk development than at sites contaminated by VOCs. The cancer risks and hazard quotients developed through crop ingestion became important because these non-VOC pollutants are hydrophobic and bio-accumulative in plant and animal tissue. Although both Site A and C were contaminated by ?ve chlorinated VOCs (PCE, TCE, 1,1-DCE, VC, 1,2-DCEA), MEPAS calculated a lower total cancer risk for Site A (5.91 × 10?3 ) than MMSOILS did (8.91 × 10?3 ) while the MEPAS result (5.80 × 10?2 ) was higher than that of MMSOILS (3.06 × 10?2 ) for Site C. Such differences may be due to the variation in physical and chemical characteristics between contaminants, as well as the primary pathways by which exposure may occur. In the MEPAS cancer risk assessment for Site A, the main contaminant was 1,1-DCE (4.49 × 10?3 , 76% of total cancer risk). Water ingestion, indoor inhalation, and dermal absorption when showering were the three most important pathways for 1,1DCE, which accounted for 34.3%, 29.4% and 28.5% of the 1,1-DCE cancer risk, respectively. For the MEPAS evaluation of Site C, most of the total cancer risk resulted from VC (3.24 × 10?2 , 55.9% of total cancer risk). The exposure pathways of indoor inhalation, water

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C. Fan et al. / Journal of Hazardous Materials 182 (2010) 778–786 of good modelling practice for physiologically based pharmacokinetic models for use in risk assessment: The ?rst steps, Regul. Toxicol. Pharm. 50 (2008) 400–411. A.B.A. Boxall, D. Oakes, P. Ripley, C.D. Watts, The application of predictive models in the environmental risk assessment of ECONOR, Chemosphere 40 (2000) 775–781. Y.C. Chen, H.W. Ma, Model comparison for risk assessment: a case study of contaminated groundwater, Chemosphere 63 (2006) 751–761. Z. Liu, Y. Zhang, G. Li, X. Zhang, Sensitivity of key factors and uncertainties in health risk assessment of benzene pollutant, J. Environ. Sci. 19 (2007) 1272–1280. C.H. Fan, G.S. Wang, Y.C. Chen, C.H. Ko, Risk assessment of exposure to volatile organic compounds in groundwater in Taiwan, Sci. Total Environ. 407 (2009) 2165–2174. United States Environmental Protection Agency (USEPA), MMSOILS Model: Multimedia Contaminated Fate, Transport, and Exposure Model: Documentation and User’s Manual 4.0. Of?ce of Research and Development, Washington, DC, 1996. G.F. Laniak, J.G. Droppo, E.R. Faillace, E.K. Gnanapragasam, W.B. Mills, D.L. Strenge, G. Whelan, C. Yu, An overview of a multimedia benchmarking analysis for three risk assessment models: RESRAD, MMSOILS, and MEPAS, Risk Anal. 17 (1997) 203–214. W.B. Mills, J.J. Cheng, J.G. Droppo, E.R. Faillace, E.K. Gnanapragasam, R.A. Johns, G.F. Laniak, C.S. Lew, D.L. Strenge, J.F. Sutherland, G. Whelan, C. Yu, Multimedia benchmarking analysis for three risk assessment models: RESRAD, MMSOILS, and MEPAS, Risk Anal. 17 (1997) 187–201. United States Department of Energy (USDOE), Multimedia Environmental Pollutant Assessment System (MEPAS): Exposure Pathway Module Description, Richland, WA, 2006. Taiwan Environmental Protection Administration (TEPA), Guideline for Parameter Selection, Principles of Soil and Groundwater Contamination Site Risk Assessment, Taiwan Environmental Protection Administration, Taipei, Taiwan, 2005 (In Chinese). L.J.H. Lee, C.C. Chan, C.W. Chung, Y.C. Ma, G.S. Wang, J.D. Wang, Health risk assessment on residents exposed to chorinated hydrocarbons contaminated in groundwater of a hazard waste site, J. Toxicol. Environ. Heal. A 65 (2002) 219–235. Taiwan Environmental Protection Administration (TEPA), Investigation of soil and groundwater pollution in China Petrochemical Development Corporation Anshun Plant contamination site, Taiwan Environmental Protection Administration, Taipei, Taiwan, 2005 (In Chinese). Miao-Li County Environmental Protection Bureau (MLEPB), Investigation and veri?cation of groundwater pollution in Taiwan VCM Corporation Toufen Plant contamination site, Miao-Li County Environmental Protection Bureau, Miao-Li, Taiwan, 2005 (In Chinese). California Environmental Protection Agency (Cal/EPA), CalTOX: A Multimedia Total-Exposure Model for Hazardous Waste Sites. Sacramento, CA, 1993. United States Environmental Protection Agency (USEPA), Dermal exposure assessment: principles and applications. Of?ce of Health and Environmental Assessment. Washington DC, 1992. J.A. Droppo, G. Whelan, J.W. Buck, D.L. Strenge, 1989 Supplemental Mathematical Formulations: The Multimedia Environmental Pollutant Assessment System (MEPAS). Paci?c Northwest Laboratory, Richland, Washington, USA. C.D. Tang, Exposure and Health Risk Assessment of Groundwater Contamination – A Case Study of Contamination Site of Tao-Yuan RCA. Master Thesis, National Taiwan University, 1999 (In Chinese). Taiwan Department of Health (TDOH), Nutrition and Health Survey in Taiwan, 1993?1996, Taiwan Department of Health, Taipei, Taiwan, 2000 (In Chinese).

ingestion, and inhalation when showering accounted for 66.7%, 23.4% and 8.0% of the VC cancer risk, respectively. More speci?cally, the risk contributions of 1,1-DCE for Site A and VC for Site C via indoor inhalation varied signi?cantly (29.4% vs. 66.7%). In the MMSOILS evaluation, indoor inhalation was not considered, and its exclusion resulted in a higher total cancer risk for Site A and a lower total cancer risk for Site C. This ?nding suggests that utilization of various models which incorporate different exposure pathways for given contaminants leads to different assessment ?ndings. Special attention should be paid to these variations during model selection. 4. Conclusions In this study, risk assessments were carried out for three different soil and groundwater contamination sites. The models MEPAS and MMSOILS were applied to assess the cancer risks and hazard quotients from various exposure pathways. Each model calculated the risks using different mathematic algorithms by considering various exposure pathways. The results of this study revealed that MEPAS and MMSOILS calculated comparable cancer risks and hazard quotients in general, but were different by 1 to 2 orders of magnitude for cancer risk at sites contaminated by volatile organic compounds. For the risk assessment of volatile organic compounds, MMSOILS may not be an appropriate tool because it does not account for indoor inhalation exposure pathways in its risk calculation. For sites contaminated by non-VOC pollutants, food chain pathways may become important as these pollutants are bioaccumulative. Based on the results obtained in this study, water ingestion, dermal absorption when showering, and indoor inhalation were the three most important pathways for risk development. References
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