WORKING FOR A HEALTHY FUTURE

INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org

Development of the DREAM model for dermal exposure assessment of oil clean-up workers in the GuLF STUDY

Melanie Gorman Ng1, John W Cherrie1, Mark Stenzel2,

Richard Kwok3, Berna van Wendel de Joode4, Patricia

Stewart51 Institute of Occupational Medicine

2 Exposure Assessment Applications, LLC

3 National Institute of Environmental Health Sciences

4 Universidad Nacional de Costa Rica

5 Stewart Exposure Assessments, LLC

2

GuLF STUDY – Dermal Exposure

• Over 150,000 air measurements

• No dermal or surface contamination measurements

• Need to assess dermal exposure to:

Oil Residues, (e.g.. VOCs, PAHs, BTEX)Dispersants (e.g. 2-butosyethanol, propylene glycol)

3

DREAM

• Develop estimates from task descriptive information

• Estimates are reproducible between assessors

• Estimates exposure in “Dream Units” - DU

• Validation study showed reasonable correlation with measurement data

van Wendel de Joode et al. Accuracy of a semiquantitative method for Dermal Exposure Assessment (DREAM). Occup Environ Med (2005) vol. 62 (9) pp. 623-32

4

Challenges for GuLF STUDY

• Poor precision when range of exposure levels is small (less than half an order of magnitude)

• Does not take into account many factors that may be important (e.g. heat, use of sun screen, insect repellents, etc)

• Model is ten years old and based on limited data

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DREAM

Exposure Assessors estimate exposure from each of the three pathways of dermal exposure:

• Immersion• Surface Contact• Deposition

ctorotectionFaClothingPr

Emission IntrinsicIntensityFrequencysureDermalExpo

xx

Substance characteristics

Skin area exposed

Number of exposure events

6

Updating DREAM

• Update/review literature on model parameters relevant to GuLF STUDY:• viscosity and stickiness• evaporation • gloves and protective clothing• seawater and sweat• sun screens & insect repellents

• Amend other variables as necessary based on recent literature

7

Major updates -PPE

• Available biomonitoring studies suggest gloves are less effective than DREAM had previously assumed

• E.g. Pesticide applicators: 90% vs. 40% (Brouwer and van Hemmen, 1997)

• E.g. Creosote workers: 60% vs. 50% reduction in 1-hydroxy-pyrene (vam Rooij et al, 1993)

Brouwer and van Hemmen (1997). Brighton Crop Protection Conference: 1059-65.

van Rooij et al (1993) Scand J Work Envir Hlth; 19:200-7

8

Major Updates - Evaporation

Original DREAM Based on Boiling point

<50ºC = 150 - 100ºC = 3>150ºC = 10

GuLF DREAM uses equations used in IHSkinPerm and NIOSH Skin Permeation Calculator (Kasting and Miller, 2006)

Kasting and Miller (2006). Kinetics of finite dose absorption through skin 2: Volatile Compounds. J Pharm Sci; 95(2):268-280.

3

78.0

76.0

6320

MWTR

MWVPVnRateEvaporatio

9

Major Updates - Evaporation

Ratio Highest to Lowest Expected Evaporation Rate

500

1.67 11 1.10

100

200

300

400

500

600

Vapour Pressure Molecular Weight Wind Speed Temperature

Examined change in evaporation rate over expected range holding other parameters constant

Developed DREAM multipliers within expected range

10

Major Updates – Exposure Pathway

Skin exposure less likely to be correlated with air concentration when workers also exposed to contaminated surfaces (Burstyn et al, 2002; Pronk et al, 2006; Links et al, 2007)

Also included different effect of viscosity by exposure pathway:

Exposure increases with viscosity but effect is strongest for immersion

GM 7821 µg/cm2

GM 0.6 µg/cm2

GM 0.22 µg/cm2

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Comparison DREAM vs GuLF DREAM

Boom Deployment,

Near Shore

DU: 0.15

GDU: 1.46

Boom Retrieval,

Near Shore

DU 7.00

GDU: 20.26

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Future Challenges

• Matching DREAM categories to GuLF questionnaire categories

• Addressing uncertainty (Monte Carlo approach?)

• Model calibration

• Exposure assessor training

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Acknowledgements

Wendy McDowell – McDowell Safety & Health Services

Hans Kromhout – IRAS, Utrecht

Anne Sleeuwenhoek - IOM