00.10.20.30.40.50.60.70.80.9

1

0.00E+00 5.00E-07 1.00E-06 1.50E-06 2.00E-06Lifetime Cancer Risk

Fra

ctio

n o

f P

op

ula

tio

n

mean=2.8E-795th=1.3E-699th=2.1E-6

Figure 1. Alternative Remediation: TCE with Fan.

00.10.20.30.40.50.60.70.80.9

1

0.00E+00 1.00E-06 2.00E-06Lifetime Cancer Risk

Fra

cti

on

of

Po

pu

lati

on

Figure 2. Baseline Case: TCE no Fan.

mean=3.4E-795th=1.6E-699th=2.6E-6

00.10.20.30.40.50.60.70.80.9

1

0.00E+00 1.00E-05 2.00E-05 3.00E-05Lifetime Cancer Risk

Fra

ctio

n o

f P

op

ula

tio

n

Figure 3. Baseline Case: Chloroform no Fan.

mean=3.5E-695th=1.7E-599th=2.8E-5

Summary:

Results Cumulative Risk from exposure to contaminants

Use of household appliances results in emissions of VOCs into indoor air from contaminated drinking water

Methods:

Remediation

Pollutant Emissions

Fate and Transport•Indoor air quality model

Ambient Concentrations

•Croom

ExposureCalculation

Exposure Factors•Breathing Rate

Human Health Effects

Human Activities•Water Uses

Location•Within the home•Away from home

(Note the difference in x-axis scaling between Figures 1,2, and 3)

Estimated Exposure and Risk to a Community Resulting from Use of A TCE Contaminated Water Supply

N J Giardino Brooks AFB, Texas, USA, and C R Wilkes Wilkes Technologies, Bethesda, Maryland, USA

A community's groundwater supply was contaminated with trichloroethylene (TCE) at a concentration of 25 ppb. This case study addresses the community's concerns about excess lifetime cancer risk due to exposure to TCE resulting from normal household water uses. Through modeling, the population based exposure and excess cancer risk is estimated for the inhalation, dermal, and ingestion exposure routes. The Total Exposure Model (TEM), used in this study, stochastically represents input parameters, such as activity patterns, building characteristics, and water-use behavior. TEM samples activity patterns from a representative database, and uses information from other sources to simulate water-use behavior within the sampled activity pattern. TEM then deterministically models the emission, fate, and transport of the contaminant, resulting in air and water concentrations. Combining these concentrations with occupant location results in an estimate of the resultant exposures. These exposures are subsequently provided as input for pharmacokinetic calculations, predicting the absorbed dose by each exposure route. Numerous simulations are executed to estimate the distribution of exposures, absorbed dose, and excess cancer risk for the studied population group.

This study examines the exposures and risks posed to the community by each of 3 scenarios: (1) using the contaminated water supply, (2) using a bathroom fan to reduce air concentrations, and (3) treating the water at a typical municipal treatment facility. The third option assumes the Maximum Contaminant Level (MCL) for trihalomethanes (MCL = 100 ppb) in the form of chloroform and bromoform at 50 ppb each.

Results:

1,100 Iterations

•••

Combined with activity/location patterns, uptake models, etc. to calculate exposure and dose

Ch

loro

form

Chloroform, all routes

0

100

200

300

400

500

600

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Absorbed Dose, mg

Fre

qu

en

cy

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 4 8 12 16 20 24

Time, hours

Co

ncen

trati

on

, m

g/m

³

Living Room

Bedroom

Hall/Entry

Kitchen

Bathroom

Shower

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 4 8 12 16 20 24

Time, hours

Co

ncen

trati

on

, m

g/m

³

Living Room

Bedroom

Hall/Entry

Kitchen

Bathroom

Shower

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 4 8 12 16 20 24

Time, hours

Co

nc

en

tra

tio

n, m

g/m

³

Living Room

Bedroom

Hall/Entry

Kitchen

Bathroom

Shower

Percentile of the Population

Municipal Water Supply, DBPs(50 µg/L Chloroform; 50 µg/L Bromoform)

Contaminated Groundwater SupplyTrichloroethylene (25 µg/L)

Without Fan during shower

With Fan during shower

Problem:

Individual Results Population Based Results

Uptake models used to calculate internal dose from exposure to contaminants

where Present Cost is the cost in 1999 dollars, Past Cost is the cost in 1985 dollars ($210,000,000), i is the inflation rate taken as 3% per year, and n is the number of years (in this case 14). Point-of-use remediation of the contaminated groundwater by use of a bathroom fan may be a feasible alternative to a large-scale remediation project or switching to a municipal water supply. This conclusion is based both on a comparative risk analysis, as well as a cost benefit tradeoff.

Finite difference modeling used to predict air and water concentrations as a result of water use

Exposure/Dose Results

We have demonstrated the comparatively higher risk due to the DBP chloroform as compared to the TCE contaminated drinking water, as well as the dramatic reduction in risk when a bathroom fan was run during the showering period. The cost to remove these chemicals from a contaminated groundwater supply, for this hypothetical population of 1,100 residences (2,200 individuals), is approximately $318,000,000 over a 20-year period (5). The cost for this 20-year project was adjusted to 1999 dollars assuming 3% inflation per year using Equation 1.  Present Cost = Past Cost(1 + i)n (1) 

Discussion:

Idealized Building

Other•Equilibrium Model (Dishwashers) VL CL

VG CG

Qg

Cg

QG

Co

LG HCCmEquilibriu :

H

CCAKS GinOL

QG Cin

QL Cin

QG CG

QL CL

VL CL

VG CG

z

L

OL

GinL

Q

AKZ

where

H

CCZQS

:

)exp(1

QL Cin

QG CGin

VG CG

QG CG

QL Cout

Approach Emission Models

Dermal

• Membrane Model (Bunge and McDougal, 1998) -- Combination steady-state and non-steady-state diffusion

Plug Flow Models• Showers, Faucets

CMFM (Completely Mixed Flow Models) (Bathtubs, Clothes Washers, Toilets)

sclagexpscscwsco

win ttfortPLR

CAM ,exp/

4.24

sclagexpscwsc

scowin ttfor

LRtPCAM ,

/exp 4.2)

3(

Inhalation

• Lung model assumes equilibrium between lung air and lung blood

Ingestion

• Assumes 100% uptake

Chloroform Bromoform

50th 95th 99th

0

0.1

0.2

0.3

0.4

0.5

0.6

50th 95th 99th

Inhalation

Dermal

Ingestion

0

0.1

0.2

0.3

0.4

0.5

0.6

50th 95th 99th

Inhalation

Dermal

Ingestion

Mean 95th 99th