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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An introduction to dermal exposure assessment
- 1. INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org Exposure Judgment: Improving Inhalation, Dermal & Noise Assessment Dermal exposure John Cherrie
- 2. Summary… • The skin and chemicals • Adverse effects • Routes of exposure and uptake • Solids, liquids and gases • A conceptual model of skin exposure • Measuring dermal exposure • Modeling exposure and uptake • Control and personal protection
- 3. The skin… • Two-way protective barrier • About 2m2 area for an adult • Hands comprise about 5% and arms 15% of area • Complex structure that is metabolically active
- 4. Structure of the skin…
- 5. Dermal permeation of chemicals… • Uptake by diffusion • Maximum flux at steady-state (Jmax,ss) Where, Sscis the saturated concentration of solute in the stratum corneum D is the diffusion coefficient hthe thickness of the stratum corneum
- 6. Flux and molecular weight… Magnusson, Anissimov, Cross, and Roberts. Molecular Size as the Main Determinant of Solute Maximum Flux Across the Skin. J Invest Dermatol 122:993 –999, 2004.
- 7. Solids, liquids and gases • Solids • Must dissolve in sweat before being taken up • Or, particles must be small and skin barrier disrupted • 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-propanol and 2-butoxyethanol Kielhorn J, Melching-Kollmub S, Mangelsdorf I (2006) Dermal absorption. EHC 235.
- 8. Key factors for uptake… • Mass on skin • Concentration of contaminant • Area exposed • Duration of exposure • Skin condition
- 9. Key factors for uptake… • Mass on skin • Concentration of contaminant • Area exposed • Duration of exposure • Skin condition
- 10. Key factors for uptake… • Concentration of contaminant • Mass on skin • Area exposed • Duration of exposure • Skin condition
- 11. Key factors for uptake… • Mass on skin • Concentration of contaminant • Area exposed • Duration of exposure • Skin condition Washed off
- 12. Key factors for uptake… • Mass on skin • Concentration of contaminant • Area exposed • Duration of exposure • Skin condition
- 14. Systemic effects… • Some chemicals can pass through the unbroken skin and contribute to total body burden • Solvents, metals, pesticides… • No dermal workplace exposure limits • Many chemicals show a theoretical potential for dermal absorption or toxicity, only but only a small fraction have a skin notation (Sk) • NIOSH has new publications on skin notation
- 15. Workplaces where dermal exposure is important • Painters • Petrochemicals • Dry cleaners • Farmers • Crop-harvesters • Shoe manufacturers • Engineers • Hairdressers, nurses and many, many more…
- 16. Routes of exposure… • Inhalation exposure (mg/m3) • Ingestion (mg/day) • Dermal exposure (mg or mg/cm2) Inhalation Ingestion Skin uptake • Ideally, we would have all measures on the same basis, i.e. uptake (mg) into the body
- 17. A conceptual model… Surface contamination layer Air compartment Clothing outer layer Skin contamination layer Source Clothing inner layer Schneider et al. Conceptual model for assessment of dermal exposure. Occup Environ Med (1999) vol. 56 (11) pp. 765-73
- 18. Rubber industry study… • Identified the exposure pathways in rubber manufacturing • They measured… • Air concentration – both near and far-field • Dermal loading • They showed that… • Hand (wrist) contamination was on average highest • Strong correlation between hand (wrist) and whole body contamination Vermeulen R, Heideman J, Bos RP, Kromhout H. (2000) Identification of dermal exposure pathways in the rubber manufacturing industry. Ann Occup Hyg.;44(7):533-541.
- 19. Different process – different pathways Curing Pre-treatment
- 20. Inhalation and dermal exposure… • Searching Scopus database for entries since 2000 • Search query: (inhalation) AND (dermal) AND (exposure) AND (occupational OR worker) • 361 papers • Screening on title gave about 60 possibly informative papers • Screening on abstract identified more than half of these as uninformative • Final assessment based on about 20 papers
- 21. Inhalation and dermal exposure Authors Substance Workplace Corr Comment Fent et al (2008) HDI Spray painters 0.79 Log transformed data Day et al (2007) Beryllium Cu-Be alloy plant 0.63 McClean et al (2004) PAH Asphalt workers 0.59 Based on pyrene analysis Hughson et al (2010) Nickel Various Ni production 0.48 Long-transformed hand data Sobus et al (2009) PAH Asphalt workers 0.32 Not statistically significant Cocker et al (2009) MbOCA Polyurethane elastomers None Aprea et al (2009) Imidacloprid Greenhouse None 21
- 22. Fent et al (2008) Fent K, Jayaraj K, Ball LM, Nylander-French L. (2008) Quantitative monitoring of dermal and inhalation exposure to 1,6-hexamethylene diisocyanate monomer and oligomers. J. Environ. Monit.;10(4):500-507.
- 23. Contribution to all exposure… Authors Substance Workplace % skin Comment Borak et al (2002) PAH Creosote impregnation >90 % Aprea et al (2009) Imidacloprid Greenhouse work >78 % Est. absorbed dose Sheenan et al (2008) Benzene Cleaning ≈50% Low levels Bader et al (2008) NMP Simulation 47% Vapour uptake at rest Chen 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 model Chao et al (2006) Jet fuel Fuel cell maintenance 3% Wang et al (2013) Flameretard ant Recycling 1% Most from diet Xing et al (2011) PCB Recycling 0% Most from diet
- 24. How do we measure? • Interception (e.g. patches) • The mass of chemical that lands on the skin over 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 surrogate compound retained on the skin
- 25. Interception sampling… • „Generic‟ protocols that prescribe sizes, numbers, location and method of attachment of patches are given by WHO, US- EPA, OECD • Possible to use whole suit, gloves, hood, socks… • “actual” and “potential” exposure
- 28. Tools for estimating exposure… • ConsExpo (by RIVM) • Estimates dermal exposure to consumer products • http://www.rivm.nl/en/healthanddisease/productsafety/Co nsExpo.jsp • ECETOC TRA (Targeted Risk Assessment for REACH), variant of EASE • http://www.ecetoc.org/tra • RISKOFDERM (TNO, task-based approach relying on similar dermal exposure operation units) • Incorporated in www.StoffenManager.nl • DREAM (DeRmal Exposure Assessment Method) • Derived from Schneider’s conceptual model • Generates a relative index of exposure
- 29. Tools for estimating uptake… • NIOSH Skin Permation Calculator • http://www.cdc.gov/niosh/topics/skin/skinPermCalc.html • IH SkinPerm • http://www.aiha.org/get- involved/VolunteerGroups/Pages/Exposure-Assessment- Strategies-Committee.aspx • These models are based on maximum flux from an area of skin exposed not mass loading
- 30. Preventing dermal exposure… • Elimination of the dermal hazard • Change the work method so exposure is no longer necessary • Substituting with lower hazard materials • Using a different form of the material to prevent exposure • Safe working distance • Total enclosure • Partial enclosure • Local exhaust ventilation • Process changes • Administrative changes • PPE
- 31. Safe Working Distance • Use a tool to prevent contact between hands and fluid • Scrubbing brush • Scoop • Long handles • Avoid immersion events • Use gloves if SWD not possible • Avoid repeated cycles of wet/dry • Can work be batched rather than continuous
- 32. Protective clothing… • Any protective clothing between the skin, or normal clothing, and the outside world • gloves • overalls • boots • hoods • chemical suits • Clothing is less effective in practice than might be expected from laboratory tests
- 33. Conclusions… • Dermal exposure may contribute importantly to total exposure • We understand the skin exposure at a conceptual level • Skin exposure may or may not be associated with inhalation exposure • Interpreting measurements is not straightforward • Control can be more than protective clothing
Editor's Notes
- 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