A presentation given at X2012 as part of a session on the GuLF study.

1. WORKING FOR A HEALTHY FUTURE
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
Stewart5
1 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
INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org

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)
2

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
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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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5. DREAM
Exposure Assessors estimate exposure from each of
the three pathways of dermal exposure:
• Immersion
• Surface Contact
• Deposition
Number of Skin area Substance
exposure events exposed characteristics
Frequency x Intensity x Intrinsic Emission
DermalExposure =
ClothingProtectionFactor
5

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

8. Major Updates - Evaporation
Original DREAM Based on
Boiling point
<50ºC = 1
50 - 100ºC = 3
>150ºC = 10
GuLF DREAM uses equations used in IHSkinPerm and
NIOSH Skin Permeation Calculator (Kasting and Miller,
2006)
6320 ∗ V 0.78 ∗ VP ∗ MW
EvaporationRate =
0.76 ∗ R ∗ T ∗ 3 MW
Kasting and Miller (2006). Kinetics of finite dose absorption through skin 2: Volatile
Compounds. J Pharm Sci; 95(2):268-280. 8

9. Major Updates - Evaporation
Ratio Highest to Lowest Expected Evaporation Rate
Examined change in
600
evaporation rate over 500
500
expected range 400
300
holding other 200
parameters constant 100
0
1.67 11 1.1
Vapour Pressure Molecular Weight Wind Speed Temperature
Developed DREAM
multipliers within
expected range
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10. Major Updates – Exposure Pathway
Skin exposure less likely to be correlated with air
GM concentration when workers also exposed to
7821 contaminated surfaces (Burstyn et al, 2002;
µg/cm2 Pronk et al, 2006; Links et al, 2007)
GM
0.6 µg/
cm2
Also included different effect of
viscosity by exposure pathway:
GM
Exposure increases with
0.22 viscosity but effect is strongest
µg/cm2 for immersion
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11. 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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12. Future Challenges
• Matching DREAM categories to GuLF
questionnaire categories
• Addressing uncertainty (Monte Carlo
approach?)
• Model calibration
• Exposure assessor training
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13. Acknowledgements
Wendy McDowell – McDowell Safety & Health
Services
Hans Kromhout – IRAS, Utrecht
Anne Sleeuwenhoek - IOM
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