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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
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.
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
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