An introduction to dermal exposure assessment


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Slides presented as part of a workshop at the 2013 American Industrial Hygiene Conference (AIHce) in Montreal, Canada.

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  • Dermatitis can be very uncomfortable and have a big social impactThese are extreme examples
  • Page 28 of Bob’s book
  • Where to look…What’s your experience?Show tables (P26) in book
  • The methods that we have available have been around for a long time and they are all very practical pragmatic techniques. We can either reply on interception, removal or in-situ assessments (Questionnaires, which one might reasonably include here are going to be dealt with by Dr Bello in the next talk).Not all techniques are applicable in all situations. Clearly relying on washing or wiping for materials that are either rapidly transferred into the body or are lost to the environment would not be sensible. A lot of work has been done on sampling recovery, the distribution of exposure across the body, the appropriateness of sampling only part of the skin. For wiping and washing there are also issues about the number and timing of samples collected.
  • Discuss psychological aspects – gloves make people think they are “protected”What will happen when things go wrong – they put their hand in?Hazard perception
  • An introduction to dermal exposure assessment

    1. 1. INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.orgExposure Judgment: ImprovingInhalation, Dermal & Noise AssessmentDermal exposureJohn Cherrie
    2. 2. Summary…• The skin and chemicals• Adverse effects• Routes of exposure and uptake• Solids, liquids and gases• A conceptual model of skinexposure• Measuring dermal exposure• Modeling exposure and uptake• Control and personal protection
    3. 3. The skin…• Two-way protectivebarrier• About 2m2 area for anadult• Hands comprise about5% and arms 15% ofarea• Complex structure thatis metabolically active
    4. 4. Structure of the skin…
    5. 5. Dermal permeation ofchemicals…• Uptake by diffusion• Maximum flux at steady-state (Jmax,ss)Where, Sscis the saturated concentration ofsolute in the stratum corneumD is the diffusion coefficienththe thickness of the stratum corneum
    6. 6. Flux and molecularweight…Magnusson, Anissimov,Cross, and Roberts.Molecular Size as theMain Determinant ofSolute Maximum FluxAcross the Skin. J InvestDermatol 122:993 –999,2004.
    7. 7. Solids, liquids and gases• Solids• Must dissolve in sweat before being taken up• Or, particles must be small and skin barrierdisrupted• Liquids• Must be less than about 500 Dalton• Volatile liquids may evaporate quickly• Gases and vapors• Almost always have very low dermal uptake• Some exceptions: e.g. 1-methoxy-2-propanoland 2-butoxyethanolKielhorn J, Melching-Kollmub S, Mangelsdorf I (2006) Dermal absorption. EHC 235.
    8. 8. Key factors for uptake…• Mass on skin• Concentration of contaminant• Area exposed• Duration of exposure• Skin condition
    9. 9. Key factors for uptake…• Mass on skin• Concentration of contaminant• Area exposed• Duration of exposure• Skin condition
    10. 10. Key factors for uptake…• Concentration of contaminant• Mass on skin• Area exposed• Duration of exposure• Skin condition
    11. 11. Key factors for uptake…• Mass on skin• Concentration of contaminant• Area exposed• Duration of exposure• Skin conditionWashed off
    12. 12. Key factors for uptake…• Mass on skin• Concentration of contaminant• Area exposed• Duration of exposure• Skin condition
    13. 13. Contact dermatitis…
    14. 14. Systemic effects…• Some chemicals can pass through theunbroken skin and contribute to totalbody burden• Solvents, metals, pesticides…• No dermal workplace exposure limits• Many chemicals show a theoreticalpotential for dermal absorption ortoxicity, only but only a small fractionhave a skin notation (Sk)• NIOSH has new publications on skinnotation
    15. 15. Workplaces where dermalexposure is important• Painters• Petrochemicals• Dry cleaners• Farmers• Crop-harvesters• Shoe manufacturers• Engineers• Hairdressers, nurses andmany, many more…
    16. 16. Routes of exposure…• Inhalation exposure(mg/m3)• Ingestion (mg/day)• Dermal exposure (mgor mg/cm2)InhalationIngestionSkinuptake• Ideally, we wouldhave all measures onthe same basis, i.e.uptake (mg) into thebody
    17. 17. A conceptual model…Surface contaminationlayer Air compartmentClothing outer layerSkin contamination layerSourceClothing inner layerSchneider et al. Conceptual model for assessment of dermal exposure. Occup EnvironMed (1999) vol. 56 (11) pp. 765-73
    18. 18. Rubber industry study…• Identified the exposure pathways inrubber manufacturing• They measured…• Air concentration – both near and far-field• Dermal loading• They showed that…• Hand (wrist) contamination was on averagehighest• Strong correlation between hand (wrist) andwhole body contaminationVermeulen R, Heideman J, Bos RP, Kromhout H. (2000) Identification of dermal exposure pathways inthe rubber manufacturing industry. Ann Occup Hyg.;44(7):533-541.
    19. 19. Different process –different pathwaysCuring Pre-treatment
    20. 20. Inhalation and dermalexposure…• Searching Scopus database for entriessince 2000• Search query: (inhalation) AND (dermal)AND (exposure) AND (occupational ORworker)• 361 papers• Screening on title gave about 60 possiblyinformative papers• Screening on abstract identified more thanhalf of these as uninformative• Final assessment based on about 20papers
    21. 21. Inhalation and dermalexposureAuthors Substance Workplace Corr CommentFent et al (2008) HDI Spraypainters0.79 Log transformed dataDay et al (2007) Beryllium Cu-Be alloyplant0.63McClean et al (2004) PAH Asphaltworkers0.59 Based on pyreneanalysisHughson et al (2010) Nickel Various Niproduction0.48 Long-transformedhand dataSobus et al (2009) PAH Asphaltworkers0.32 Not statisticallysignificantCocker et al (2009) MbOCA PolyurethaneelastomersNoneAprea et al (2009) Imidacloprid Greenhouse None21
    22. 22. Fent et al (2008)Fent K, Jayaraj K, Ball LM, Nylander-French L. (2008) Quantitative monitoring of dermal and inhalationexposure to 1,6-hexamethylene diisocyanate monomer and oligomers. J. Environ. Monit.;10(4):500-507.
    23. 23. Contribution to all exposure…Authors Substance Workplace %skinCommentBorak et al (2002) PAH Creosote impregnation >90%Aprea et al (2009) Imidacloprid Greenhouse work >78%Est. absorbeddoseSheenan et al (2008) Benzene Cleaning ≈50% Low levelsBader et al (2008) NMP Simulation 47% Vapour uptakeat restChen et al (2008) PAH Metal machining 37%Lindsay et al (2006) Toluene Coating work <9%Kim et al (2007) Jet fuel Fuel cell maintenance 4% PBTK modelChao et al (2006) Jet fuel Fuel cell maintenance 3%Wang et al (2013) FlameretardantRecycling 1% Most from dietXing et al (2011) PCB Recycling 0% Most from diet
    24. 24. How do we measure?• Interception (e.g. patches)• The mass of chemical that lands on the skinover the sampling time (integrated flux)• Removal (e.g. wipe/wash)• The mass of contaminant left on the skin• In-situ (e.g. fluorescence)• The mass of a surrogatecompound retained onthe skin
    25. 25. Interception sampling…• „Generic‟ protocols thatprescribe sizes, numbers,location and method ofattachment of patchesare given by WHO, US-EPA, OECD• Possible to use wholesuit, gloves, hood,socks…• “actual” and “potential”exposure
    26. 26. Removal sampling…26
    27. 27. Fluorescence tracers…
    28. 28. Tools for estimatingexposure…• ConsExpo (by RIVM)• Estimates dermal exposure to consumer products•• ECETOC TRA (Targeted Risk Assessment forREACH), variant of EASE•• RISKOFDERM (TNO, task-based approach relyingon similar dermal exposure operation units)• Incorporated in• DREAM (DeRmal Exposure Assessment Method)• Derived from Schneider’s conceptual model• Generates a relative index of exposure
    29. 29. Tools for estimatinguptake…• NIOSH Skin Permation Calculator•• IH SkinPerm•• These models arebased on maximumflux from an areaof skin exposed notmass loading
    30. 30. Preventing dermal exposure…• Elimination of the dermal hazard• Change the work method so exposureis no longer necessary• Substituting with lower hazardmaterials• Using a different form of the materialto prevent exposure• Safe working distance• Total enclosure• Partial enclosure• Local exhaust ventilation• Process changes• Administrative changes• PPE
    31. 31. Safe Working Distance• Use a tool to preventcontact between handsand fluid• Scrubbing brush• Scoop• Long handles• Avoid immersion events• Use gloves if SWD notpossible• Avoid repeated cyclesof wet/dry• Can work be batchedrather than continuous
    32. 32. Protective clothing…• Any protective clothing between the skin,or normal clothing, and the outside world• gloves• overalls• boots• hoods• chemical suits• Clothing is lesseffective in practicethan might be expected fromlaboratory tests
    33. 33. Conclusions…• Dermal exposure may contributeimportantly to total exposure• We understand the skin exposure at aconceptual level• Skin exposure may or may not beassociated with inhalation exposure• Interpreting measurements is notstraightforward• Control can be more than protectiveclothing
    34. 34. Questions?