Jane HoulihanSean Gray

Richard Wiles

Children’s exposure to arsenic-treated wood

A preliminary Monte Carlo risk assessment

Presentation to EPA’s Science Advisory PanelOctober 23, 2001

Monte Carlo method of risk analysis

Varies by child

Body weight and surface area

Range of arsenic concentrations in contaminated soil

Range of dislodgeable arsenic that adheres to hand

Contaminated soil ingested daily

Fixed (2 scenarios considered)

Dislodgeable arsenic - hand loads per day ingested

Bioavailability of ingested dislodgeable arsenic

Fraction of dislodgeable arsenic absorbed through skin

Bioavailability of arsenic from ingested soil

Soil adherence to skin

Fraction of soil arsenic absorbed through skin

Exposure frequency and duration

Monte Carlo simulation

One million children

Age 6 months through age 5

Subset of population playing on play structure three days a week

0.1

1

10

100

1000

0 0.5 1 1.5 2 2.5 3 3.5

Dislodgeable arsenic on hands

(ug/100 cm2)

CADHS(1987)

MaineDOHS(1998)

Woodindustry(SCS 1998)

Arsenic that rubs off onto hands from contact with arsenic-treated wood

0.1

1

10

100

1000

10000

Dislodgeable arsenic (ug/100 cm2)

CPSC (1990)

Stilwell coupons (1998)

EWG/HBN new wood

Stilwell playset 1 (1998)

Stilwell playset 2 (1998)

Stilwell playset 3 (1998)

Wood industry study (SCS1998)Riedel playset A (1991)

Riedel playset B (1991)

Riedel playset C (1991)

Riedel playset D (1991)

Riedel playset E (1991)

Riedel playset F (1991)

Riedel playset G (1991)

Riedel playset H (1991)

Riedel playset I (1991)

Riedel playset J (1991)

Dislodgeable arsenic on the surface of arsenic-treated wood

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16

Age of deck, years

Soil arsenic, mg/kg

Stilwell and Gorny 1997, 7 Connecticut decks, sandy loamTownsend and Solo-Gabriele 2001, 9 Florida structures, sandOsmose,Florida research plot data

Wood industry (SCS 1998) 10 prefabricated Virginia decks

Arsenic levels in soil beneath arsenic-treated wood

0.1

1

10

100

1000

10000

Soil ingestion (mg/day)

Binder et al (1986)Clausing et al (1987)Calabrese et al (1989)Davis et al (1990)Van Wijnen et al (1990)

Soil ingestion

05

1015202530354045

12 24 36 48 60 72 84Age (Months)

Weight (kg)

NHANESWeight Data

99th PercentileModel Child

95th

90th

85th

75th

50th

25th

15th

10th

5th

1st Percentile

Body Weight: 1st to 99th percentiles

Trend Analysis for 0-2 Year OldsSA/BW = -0.0148Ln(BW) + 0.0821

(R2 = 0.9152)

Trend Analysis for 2-18 Year OldsSA/BW = -0.0116Ln(BW) + 0.0753

(R2 = 0.9862)

0.02

0.03

0.04

0.05

0.06

0.07

5 10 15 20 25 30 35Weight (kg)

SA/BW (m2/kg)

Gehan and George (1970):

SA = 0.02350 HT0.42246 BW0.51456

Source: Environmental Working Group analysis of NHANES III height-weight data using Gehan and George (1970).

Surface area calculated from body weight

3

8

13

18

23

28

33

0 1 2 3 4 5 6Age (Years)

Percentage of Total Body Surface Area

Legs

Arms

Hands

Linear(Arms)Linear(Hands)Linear(Legs)

Source: Environmental Working Group analysis of U.S. Environmental Protection Agency Data (1985).

Legend

Dermal absorption: Regression analysis of body part area percentages

Exposures assessment parameter Gradient (2001) EPA (2001)

Dislodgeable arsenic - hand loads per day ingested

0.25

0.8 (avg) and up to 4.95 (3 fingers, 50% removal efficiency, 9.5 (avg) up to 20 times per hour, 1-3 hour(s) per day)

Bioavailability of ingested dislodgeable arsenic

47% 100%?

Fraction of dislodgeable arsenic absorbed through skin

0% (considered negligible) 6.4%

Contaminated soil ingested daily25 mg/day (half of assumed

daily ingestion of 50 mg/day)100 mg/day and 400 mg/day

Bioavailability of arsenic from ingested soil

16.3% 25%

Soil adherence to skin 0.2 mg/cm2 1.45 mg/cm2

Fraction of soil arsenic absorbed through skin

3% 6.4%

Differences in exposure parameters

Excess lifetime cancer riskto children exposed to arsenic-treated wood

1.E-06

1.E-05

1.E-04

1.E-03

0 2000000 4000000 6000000 8000000 10000000

Number of Children

Excess Lifetime Cancer Risk

Play Structure(Ingestion Only)

+ Dermal Absorption

+ Soil Exposure

+ Home DeckExposures

Comparison between EPA and wood industry exposure assumptions

1.E-06

1.E-05

1.E-04

1.E-03

0 2000000 4000000 6000000 8000000 10000000

Number of Children

Excess Lifetime Cancer Risk

EPA Scenario

Wood IndustryScenario

Model sensitivity to assumed dislodgable arsenic transfer rates

1.E-05

1.E-04

1.E-03

1.E-02

0 2000000 4000000 6000000 8000000 10000000

Number of Children

Excess Lifetime Cancer Risk

Assuming a 4.6:1Transfer Rate

Assuming a 1:1Transfer Rate

Excess lifetime cancer riskto children exposed to arsenic-treated wood

1.E-04

1.E-03

1.E-02

1.E-01

0 2000000 4000000 6000000 8000000 10000000

Number of Children

Excess Lifetime Cancer Risk

Bladder Cancer --ED01 (1.5)

Bladder Cancer --LED01 (2.8)

Lung Cancer --LED01 (12)

Bladder Cancer +Lung Cancer