Adaptation of the DREAM tool


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

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Adaptation of the DREAM tool

  1. 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 Stewart51 Institute of Occupational Medicine2 Exposure Assessment Applications, LLC3 National Institute of Environmental Health Sciences4 Universidad Nacional de Costa Rica5 Stewart Exposure Assessments, LLC INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK
  2. 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. 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 3 Exposure Assessment (DREAM). Occup Environ Med (2005) vol. 62 (9) pp. 623-32
  4. 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 4
  5. 5. DREAMExposure Assessors estimate exposure from each ofthe 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. 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 6
  7. 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. 7 van Rooij et al (1993) Scand J Work Envir Hlth; 19:200-7
  8. 8. Major Updates - EvaporationOriginal DREAM Based onBoiling point <50ºC = 1 50 - 100ºC = 3 >150ºC = 10GuLF 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. 9. Major Updates - Evaporation Ratio Highest to Lowest Expected Evaporation RateExamined change in 600evaporation rate over 500 500expected range 400 300holding other 200parameters constant 100 0 1.67 11 1.1 Vapour Pressure Molecular Weight Wind Speed Temperature Developed DREAM multipliers within expected range 9
  10. 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 10
  11. 11. Comparison DREAM vs GuLF DREAMBoom Deployment,Near Shore DU: 0.15 GDU: 1.46Boom Retrieval,Near Shore DU 7.00 GDU: 20.26 11
  12. 12. Future Challenges • Matching DREAM categories to GuLF questionnaire categories • Addressing uncertainty (Monte Carlo approach?) • Model calibration • Exposure assessor training 12
  13. 13. AcknowledgementsWendy McDowell – McDowell Safety & Health ServicesHans Kromhout – IRAS, UtrechtAnne Sleeuwenhoek - IOM 13