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© IWA Publishing 2012 Journal of Water Reuse and Desalination

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Carcinogenic health risk from trihalomethanes during reuse of reclaimed water in coastal cities of the Arabian Gulf

APPENDIX: RISK ASSESSMENT METHODOLOGY AND PARAMETERS The risk assessment approach is discussed in detail in the proceeding paragraphs. Exposure routes In this study, the potential exposure routes of receptors to trihalomethanes (THMs) in recycled water are dermal absorption and inhalation since recycled water in Abu Dhabi is predominantly used for irrigation and landscaping purposes. Receptors Cancer risk assessment from exposure to THMs in this study was conducted for the residential adult and child, and, site worker receptors. Also, default USEPA exposure factors

• •

Receptor height; Width of spray. The box length is defined by the product of the average

wind speed and the exposure time, the receptor height defines the depth of the box and the width of the spray defines the box width. The estimation of contaminant concentration in this model is based on the two-film, gas–liquid mass transfer theory. The overall mass transfer coefficient for each THM was calculated from the expression below (Gray et al. ). KL ¼ 1=kl þ RT =Hkg

1

(1)

where KL ¼ overall mass transfer coefficient for each THM

have been used for the risk calculation.

(m/hr); kl ¼ liquid phase mass transfer coefficient for each

Exposure model

each THM (m/hr); H ¼ Henry’s law constant for contami-

The outdoor box model which was used in this study is a

(293 K); R ¼ universal gas constant (8.2 × 105 atm.m3/

modification of the conventional shower model for environ-

mol.K).

mental risk assessment (Gray et al. ). In this model, the

THM (m/hr); kg ¼ gas phase mass transfer coefficient for nant (atm.m3/mol); T ¼ calibration water temperature

The gas and liquid phase mass transfer coefficients for

exposure space is represented with a hypothetical box. The

the THMs were estimated from standard values reported

model has the following assumptions:

for carbon dioxide (CO2) and water (H2O) using the

• • • •

The air in the box is fully mixed and ventilated;

expressions (Walden & Spence ):

There is a rate of mass volatilization of contaminant between the box and ambient air;

kg(VOC) ¼ kgðH2 OÞ

The contaminant concentration in the box is constant; The receptor(s) is/are inside the box. The dimensions of the box are defined by four par-

kl(VOC) ¼ klðCO2 Þ

ameters namely:

• •

18 MWTHM

44 MWTHM

0:5 (2)

0:5 (3)

Average wind speed;

where kg(H2O) ¼ gas phase mass transfer coefficient for

Receptor exposure time;

water at 20 C (m/hr); kl(CO2) ¼ liquid phase mass transfer W

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O. D. Aina & F. Ahmad

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Carcinogenic health risk evaluation in reclaimed water reuse in the Arabian Gulf

coefficient for carbon dioxide at 20 C (m/hr); 18 ¼ molecuW

individual THM (g/mol).

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2012

Spence ):

lar weight of water (g/mol); 44 ¼ molecular weight of carbon dioxide (g/mol); MWTHM ¼ molecular weight of

Journal of Water Reuse and Desalination

Fv ¼

K0 t 1e L 600 d

(9)

The gas phase mass transfer coefficient for water was assumed to be 3,000 cm/hr (30 m/hr) while the liquid

where Fv ¼ fraction of THM volatilized; KL ¼ adjusted over-

phase mass transfer coefficient of carbon dioxide was

all mass transfer coefficient (m/hr); d ¼ effluent droplet

assumed to be 20 cm/hr (0.2 m/hr) (Gray et al. ).

diameter (m); t ¼ effluent droplet drop time (seconds).

Since the effluent temperature differs from the calibration

The effluent droplet drop time is the length of time that a

water temperature, KL was adjusted to the effluent tempera-

particular droplet is available to contribute THM emissions

ture using the equation below (Gray et al. ):

to the outdoor box until it soaks into the soil, after which volatilization is assumed not to occur. The total amount of

KL0 ¼ KL

T μe Te μl

0:5

each THM that volatilized was calculated from the (4)

where KL0 ¼ adjusted overall mass transfer coefficient (m/ hr); KL ¼ overall mass transfer coefficient for each THM (m/hr); T ¼ calibration water temperature (293K); Te ¼ effluent temperature (K); μe ¼ effluent viscosity at Te (kg/m-s); μl ¼ water viscosity at Tl (kg/m-s). The viscosity was calculated from the relationship below depending on the value of the mean effluent temperature (Walden & Spence ). Note that the unit of temperature

expression below (Walden & Spence ): Me ¼ Fv Q te Cw

(10)

where Me ¼ mass of each THM volatilized from effluent (mg); Fv ¼ fraction of each THM volatilized (mg/mg); Q ¼ effluent supply flowrate (m3/min); te ¼ duration for which the sprinkler was flowing (min); Cw ¼ measured THM concentration in effluent (mg/m3). With the total mass of each THM volatilized known, the THM concentration in the air within the hypothetical box,

W

in these expressions is C.

or the point-of-exposure concentration for receptor was calIf Te < 20 C: W

μ ¼ 100:10y

(5)

where,

Y¼

culated from the expression below (Gray et al. ): CairðTHMÞ ¼

1301

(11)

where Cair(THM) ¼ concentration of each THM in the sur-

998:33 þ 8:1855ðTe 20Þ þ 0:00585ðTe 20Þ2 3:30233

Me Vair

(6)

rounding air in the box (mg/m3); Me ¼ mass of each THM volatilized from effluent (mg); Vair ¼ volume of air within the hypothetical box (m3).

If Te < 20 C: W

μ ¼ 1:002:10

y

(7)

The volume of air in the box is calculated from the dimensions of the box as shown in the expression below

where,

y¼

(Gray et al. ):

1:3272ðTe 20Þ 0:001053ðTe 20Þ2 Te þ 105

(8)

Vair ¼ mean wind speed exp osure time receptorheight sprinkler width

From the adjusted KL value, the fraction of each THM that volatilized into the surrounding air in the box was calculated

using

the

expression

below

(Walden

&

From the values of the THM concentration in the surrounding air, the lifetime average daily dose (LADD) for

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the inhalation exposure was calculated from the expression

where LADDderm ¼ lifetime average daily dose (mg/kg-day);

below (Gray et al. ).

Cw ¼ concentration of individual THM in effluent (mg/m3); SA ¼ total skin surface area (m2); FS ¼ fraction of skin in

LADDinhal ¼

Cair InhR AAFinhal LRF ET EF ED 365 BW LT

contact with water; PC ¼ chemical-specific skin per-

(12)

meability coefficient (m/hr); ET¼ exposure time (hr/day); EF ¼ exposure frequency for playing/gardening (days/

where LADDinhal ¼ lifetime average daily dose from inhala-

year);

tion (mg/kg-day); Cair ¼ concentration of individual THM in surrounding air (mg/m3); InhR ¼ vapor inhalation rate (m3/

LT ¼ lifetime

lated from the expressions below:

(unitless); ET ¼ exposure time (hr/day); EF ¼ exposure frequency for playing/gardening (days/year); ED ¼ exposure duration (years); LT ¼ lifetime (years); BW ¼ body weight (kg); 365 ¼ total days in a year. Also, the intake rate through dermal absorption was calculated from the equation (Wang et al. ):

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(years);

based on the exposure pathway for each THM was calcu-

factor for inh. route (mg/mg); LRF ¼ lung retention factor

Table A1

duration

The individual excess lifetime cancer risk (IELCR)

hr); AAFinhal ¼ chemical-specific absorption adjustment

LADDderm ¼

ED ¼ exposure

(years); BW ¼ body weight (kg); 365 ¼ total days in a year.

IELCRinhal ¼ LADDinhal CSFinhal

(14)

IELCRderm ¼ LADDderm CSFderm

(15)

where, IELCRinhal ¼ cancer risk though inhalation of vapor (dimensionless).

Cw SA FS PC ET EF ED 365 BW LT

(13)

LADDinhal ¼ lifetime average daily dose through vapor inhalation (mg/kg-day).

Default exposure factors used in risk calculation

Residential Exposure parameters

Unit

Adult

Child

Construction site worker

Reference

Body weight (BW)

kg

70

15

70

USEPA () USEPA () USEPA ()

Exposure duration (ED)

years

24

6

Site specific

USEPA (1994)

Exposure frequency (EF)

days/years

350

350

Site Specific

USEPA () USEPA ()

Exposure time (ET)

hr/day

4

1

8

USEPA () USEPA () Gray et al. ()

Lifetime

years

70

70

70

USEPA ()

Inhalation rate (InhR)

m3/day

20

10

20

USEPA () USEPA () USEPA ()

Skin surface area (SA)

m2

1.8

0.66

1.8

USEPA ()

Fraction of skin exposed (FS)

unitless

1.10E-01

1.10E-01

1.10E-01

Gray et al. ()

Dermal permeability coefficient (PC)

m/hr

Chemical Specific

Chemical Specific

Chemical Specific

Walden & Spence () Q2

Adjustment factor for inhalation (AAFinh)

unitless

1

1

1

USEPA ()

Lung retention factor (LRF)

unitless

1

1

1

Walden & Spence ()

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Table A2

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Constants used in individual excess lifetime cancer risk calculation

Constants

Value

Unit

Reference

T

293

K

Walden & Spence () Walden & Spence ()

30

kg(H2O)

m/hr


kl(CO2)

0.2

m/hr


D

0.002

m


T

10

sec


te

4

hr


0.1

Q

3

m /min

Table A4

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Cancer slope factors for trihalomethanes for risk calculation (Wang et al. 2007) Slope factors [(mg/kg-day)1]

Compounds

Oral

Dermal 3

Inhalation 2

3.05 × 10

8.05 × 102

CHCl3

6.10 × 10

CHCl2Br

6.20 × 102

6.33 × 102

6.20 × 102

CHClBr2

8.40 × 10

2

1

1.40 × 10

8.40 × 102

CHBr3

7.90 × 102

1.32 × 102

3.05 × 103


REFERENCES CSFinhal ¼ chemical-specific cancer slope factor through inhalation (mg/kg-day)1. IELCRderm ¼ cancer risk though dermal absorption (dimensionless). LADDderm ¼ lifetime average daily dose through dermal absorption (mg/kg-day). CSFderm ¼ chemical-specific cancer slope factor through dermal absorption (mg/kg-day)1. Default exposure factors used for the cancer risk calculation and other constant parameters are shown in Tables A1 and A2 respectively.

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Table A3

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Physicochemical properties of trihalomethanes (Howard 1991)

Molecular Compounds

weight (g/mol)

Henry’s law coefficient Solubility (mg/L)

(Pa m3/mol)

W

440

W

160

W

86

W

54

CHCl3

119.4

7,500 (at 25 C)

CHCl2Br

163.8

3,320 (at 30 C)

CHClBr2

208.3

1,050 (at 30 C)

CHBr3

252.7

3,190 (at 30 C)

Gray, D., Pollard, S. J. T., Spence, L., Smith, R. & Gronow, J. R.  Spray irrigation of landfill leachate: estimating potential exposures to workers and bystanders using a modified air box model and generalised source term. Environ. Pollut. 133 (3), 587–599. Howard, P. H.  Handbook of Environmental Fate and Exposure Data for Organic Chemicals: Pesticides. CRC, Lewis Publishers, Chelsea, MI, USA. USEPA  Risk Assessment Guidance for Superfund (RAGS). USEPA, Washington, DC. USEPA  RAGS Volume I: Human Health Evaluation Manual Supplemental Guidance ‘Standard Default Exposure Factors’. OSWER No. 9285.6-03Cal-EPA DTSC 1994 (Second Printing 1999), Preliminary Endangerment Assessment (PEA) Guidance Manual. USEPA  Supplemental guidance for developing soil screening levels for superfund sites. OSWER 9355, 4–24. USEPA  Guidelines for Water Reuse. USEPA, Washington, DC. Walden, T. & Spence, L.  Risk-based BTEX screening criteria for a groundwater irrigation scenario. Human Ecol. Risk Assess. 3 (4), 699–722. Wang, G. S., Deng, Y. C. & Lin, T. F.  Cancer risk assessment from trihalomethanes in drinking water. Sci. Total Environ. 387 (1–3), 86–95

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Author Queries Journal: Journal of Water Reuse and Desalination Manuscript: JWRD-D-12-00062APPENDIX Q1

Please indicate where in the main text Table A3 & A4 should be mentioned.

Q2

Please confirm the change of citation from Walden et al. (1997) to Walden & Spence (1997) as per the reference list.

Q3

USEPA (1994) not listed in reference list. Please check.