INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org

Interpretation of dermal exposure measurements

& model outputs

John Cherrie

Summary…

• Methodological and quality issues

• Contextual information

• Data analysis, what do the results mean?

What do we assess?

• Interception measurements assess cumulative amount of contaminant on skin

• In many cases they are unrealistic

• Removal samples recover what’s left

• They are more realistic but may underestimate because of losses

• Fluorescent monitoring is useful for assessing the area exposed

• May overestimate mass for reasons similar to interception sampling

• Biological monitoring integrates all routes

• It is difficult to interpret for this reason

Models…

• Dermal exposure models are generally poor at estimating exposure

• Generally overestimate exposure

• May be best for screening

• Multiple independent assessments reduces variability

• DREAM / Gulf DREAM are useful for assessing possible impacts of controls

• Conceptual model can help understanding

Measurements…

• No real standardisation of methods

• Quality assurance procedures are necessary, e.g. assessment of recovery efficiency

• Interception samplers will give results that may be an order of magnitude higher than recovery samples

• Preliminary data from Gorman-Ng et al

Ng, M. G., de Poot, S., Schmid, K., Cowie, H., Semple, S., & Van Tongeren, M. (2014). A preliminary

comparison of three dermal exposure sampling methods: rinses, wipes and cotton gloves. Environmental

Science: Processes & Impacts, 16(1), 141–147.

Wipe vs rinse for particles…

Calcium acetate = CA Epsom salts = ES Zinc oxide = ZO

Golve vs Wipe for liquids…

Contextual data…

• Contextual data are necessary to properly interpret measurements or modelled exposure

• The conceptual model from Schenider et al helps guide what data should be collected

• Use of the model to map out the exposure pathways can be helpful

• Linking to air concentrations and surface samples can further help quantify pathways

• Plan measurement survey using the conceptual model

Interpretation of risks…

• We do not generally have a dermal OEL

• Main exception are REACH dermal DNELs

• We can generate a pseudo OEL for skin exposure from the inhalation OEL, e.g. assuming a certain inhaled air volume for the working day

• If OEL is 10 mg/m3 and the worker inhales 10 m3 in the working day then then she will inhale 100 mg of the contaminant

An example…

• Heavy fuel oil (HFO): blended hydrocarbon residues from refinery distillation and cracking processes

• High MW compounds: aromatic, aliphatic and naphthenic hydrocarbons, along with asphaltenes and some heterocyclic compounds containing sulphur, nitrogen and oxygen

• UK crude is predominantly from the North Sea A barrel of North Sea crude oil will usually yield about 12% of HFO

What are the health concerns?

• Prolonged repeated contact with the skin may cause:

• oil acne

• oil folliculitis

• dermatitis.

• HFOs contains compounds that may cause skin cancer, including benzo(a)pyrene and other polycyclic aromatic hydrocarbons (PAHs)

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Composition…

Aims of our study…

• To develop a validated method for measuring dermal HFO exposure

• To collect exposure data using the validated method

• To collect contextual exposure information and use these data to apply the DREAM model

Methods…

• Removal method using clinical wipes saturated with 70% isopropyl alcohol –three sequential wipes

• 25 cm2 forearm and neck

• Palms of each hand

• Collected following the completion of task and before rest breaks

• Some pre-task samples also collected

• Filed blanks

• GG-MS analysis for marker PAHs

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Sites investigated…

• Production

• 2 oil refineries

• Distribution

• 2 fuel distribution terminals

• including 1 associated with distribution by shipping

• Use

• 2 Energy providers

• 1 Power plant engine building and repair

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Dermal exposure by activity…

Hands

Dermal exposure by activity…

Forearms

How do we interpret these data?

• Exposure levels much lower than predicted by ECETOC TRA

• Assuming the area of hands and arms is 3700 cm2

• Maximum mass of HFO on skin is then around 37 mg

• For comparison workers machining metal typically were exposed to 1400 –1600 mg MWF on hands

DNEL

• Target organ and developmental effects are associated with the types and levels of aromatic constituents

• 8hr dermal DNEL for HFO 0.065 mg/kg, which for a 70kg man would be 4.5 mg

• Maximum exposure 37 mg HFO

• Flux estimated for naphthalene as 0.45 x 10-3 mg/cm2/hr

• 1.6 mg naphthalene could be taken up in 1hr

Jakasa, I., Kezic, S., & Boogaard, P. J. (2015). Dermal uptake of petroleum substances.

Toxicology Letters, 1–17.

Summary…

• Interpretation of dermal exposure measurements is not straightforward

• There is no standardisation and generally no limit values to compare with

• You need to be a bit creative to come to some appropriate conclusions