How to measure dermal exposure? Experiences with the dermal assessment of VOCs

Jeroen Vanoirbeek

Centre for Environment and Health

Dermal exposure

• Prevention was/is mainly focused on airborne exposure

• Occupational disease did not decrease

• Inhalation: o traditionally perceived as the most

important exposure pathway

Considered during basic risk assessment

Occupational Exposure Limits (OELs) available

Sampling and validated analytical methods

developed

Respiratory protection: validated based on

statistical analysis of monitoring data

Control methods

• Dermal: o (often) perceived as a secondary

exposure pathway or even

completely ignored

Considered during basic risk assessment

OELs not available

No validated analytical methods

Controls = only reliance on PPE

No validation

Inhalation vs. dermal exposure

Bureau of Labor Statistics (BLS) Data, 2010

• 13 million workers in the US are

potentially exposed to chemicals that can

be absorbed through the skin

• Largest category of non-fatal

occupational illness;~16% of all non-fatal

occupational illness.

• Does not include estimates of systemic

diseases associated with skin disorders.

Skin exposure to chemicals in the workplace is a significant problem in the US. Both the number of cases

and the rate of skin disease in the US exceeds recordable respiratory illnesses. In 2010, 34,400 recordable

skin diseases were reported by the Bureau of Labor Statistics (BLS) at a rate of 3.4 injuries per 10,000

employees, compared to 19,300 respiratory illnesses with a rate of 1.9 illnesses per 10,000 employees.

Most chemicals are readily absorbed through the skin and can cause other health effects and/or contribute to

the dose absorbed by inhalation of the chemical from the air. Many studies indicate that absorption of

chemicals through the skin can occur without being noticed by the worker. In many cases, skin is a more

significant route of exposure than the lung. This is particularly true for non-volatile chemicals which are

relatively toxic and which remain on work surfaces for long periods of time. The number of occupational

illnesses caused by skin absorption of chemicals is not known. However, it is argued that an estimated

60,000 deaths and 860,000 occupational illnesses per year in the US attributed to occupational exposure, a

relatively small percentage caused by skin exposure would represent a significant health risk.

https://www.osha.gov/SLTC/dermalexposure/

Official awareness (OSHA)

Skin exposure to chemicals in the workplace is a significant problem in the US. Both the number of cases

and the rate of skin disease in the US exceeds recordable respiratory illnesses. In 2010, 34,400 recordable

skin diseases were reported by the Bureau of Labor Statistics (BLS) at a rate of 3.4 injuries per 10,000

employees, compared to 19,300 respiratory illnesses with a rate of 1.9 illnesses per 10,000 employees.

Most chemicals are readily absorbed through the skin and can cause other health effects and/or contribute to

the dose absorbed by inhalation of the chemical from the air. Many studies indicate that absorption of

chemicals through the skin can occur without being noticed by the worker. In many cases, skin is a more

significant route of exposure than the lung. This is particularly true for non-volatile chemicals which are

relatively toxic and which remain on work surfaces for long periods of time. The number of occupational

illnesses caused by skin absorption of chemicals is not known. However, it is argued that an estimated

60,000 deaths and 860,000 occupational illnesses per year in the US attributed to occupational exposure, a

relatively small percentage caused by skin exposure would represent a significant health risk.

https://www.osha.gov/SLTC/dermalexposure/

Official awareness (OSHA)

Official awareness (WHO)

WHO recommendations

WHO recommendations

Currently, study designs used to estimate dermal exposure

are mainly oriented to practical issues. There is no method

applicable for all circumstances, nor can a guide be

provided to aid in the selection of a proper method for

specific circumstances. To overcome the current gaps in

knowledge, comparative studies are needed. These should

help to compare the usefulness of the methods, to derive

harmonized protocols and, finally, to improve our

understanding of the underlying processes and

determinants of dermal exposure

WHO conclusion

Schneider et al. (1999)

established a multi-

compartment conceptual model

Modeling dermal exposure

Methods to assess dermal exposure

• Indirect methods

o Surface sampling methods (non-human)

o Biomonitoring

Surface sampling methods (non-human)

Indirect methods

Indirect methods Human Biomonitoring

Urine

Blood

“Classical” matrices

Hair

“Alternative” matrix

Methods to assess dermal exposure

• Indirect methods

o Surface sampling methods (non-human)

o Biomonitoring

• Direct methods - in situ techniques (e.g. video imaging)

o Removal techniques

o Interception techniques

In situ techniques

Video imaging

Rajan B. (2008) Controlling skin exposure to chemicals and wet-work. West Midlands, UK: RMS Publishing

The pixels intensity correlate with the

amount of mass deposited on the skin

Removal techniques

Wiping

Tape stripping Washing

Interception techniques

Patch method Glove method

Whole body method

Behroozy A, 2013, IJOEM

WHO, 2014

Studies with active charcoal patches

• Van Wendel de Joode B et al., 2005

o Measured parameters: benzene and toluene

• passive air monitoring (mg/m³) and dermal patches (wrist of hand; (µg/cm²x8h) and urinary

S-phenylmercapturic acid (SPMA)

o Cohort: petrochemical plant (n = 35)

o Results

• Both benzene and toluene could be measured in the air (far below MAK) and on patches

• Benzene : contribution of dermal exposure to internal dose were limited

• Substancial differences between jobs

• Some jobs more contribution of dermal exposure

o Conclusions

• More studies necessary, preferentially with higher exposure to solvents

• The design of the charcoal pads need to be improved to limit direct contact and splashes

Studies with active charcoal patches

• Vermeulen R et al., 2006

o Measured parameters: benzene and toluene

• passive air monitoring and dermal patches (palm of hand and abdomen; µg/cm²x1h) and

unmetabolized urinary benzene (Ubz) and toluene (Utol)

o Cohort: shoe factory (70 subjects, 113 observations on multiple days)

o Results

• Air concentrations very low (far below MAK)

• Concentrations on patches were barely measurable

• Only when performing gluing tasks

• Some abdominal exposure was found for toluene, but no correlation between hand and abdomen patch

o Conclusions

• Active charcoal patches are a useful technique to quantitatively assess dermal exposure

• Dermal exposure to benzene and toluene in shoe manufacturing factory is rare

Our experience

• Develop a suitable method for quantitative evaluation of

dermal exposure to different VOCs using dermal patches

• Apply quantitative dermal risk assessment in an industrial

setting, along with air sampling and biomonitoring

Selection of the monitoring tool

• Permea-Tec Patch (SKC inc)

• Can we use this qualitative indicative patch and perform quantitative

assessments of dermal exposure?

Active charcoal on patch Qualitative colorimetric evaluation

of solvents presence

Introduction

• Permea-TecTM patches (SKC Inc.)

• Desorption/recovery Efficiency

o “Phase Equilibrium method”

o 180 VOCs, divided over 10 standard solutions

DE (%) = peak area + patch

peak area - patch X 100

Hypothesis

• Method development based on existing VOC air method:

o Non-polar compounds (e.g. toluene, m-, p- and o-xylene) :

• DE nearly quantitative (approaches 100 %), conc. independent

o Polar compounds (e.g. acetone) :

• DE not quantitative, conc. dependent (Dubinin isotherm)

0,00

0,20

0,40

0,60

0,80

1,00

0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00

DE

Concentration

Study Design

0,001 %

0,005 %

0,01 %

Standard solution+patch

Standard solution

Compounds Conc. levels (% v/v) DE test

180 VOCs, divided over 10

standard solutions

0,001 %, 0,005 %, 0,01 % (per

standard solution)

+ patch (n=3)

- patch (n=1)

Study Design

Compound solution

Compound+patch

0,0005 % 1 %

Dubinin Desorption isotherm ?

Compounds Conc. levels (% v/v) DE test

Acetone, Acetonitrile

Acrylonitrile

14 concentrations

(0,0005 % => 1 %)

(per compound)

+ patch (n=3)

- patch (n=1)

Sample preparation

• Activated carbon is removed from patch and placed in vial

• 2 ml of standard solution is added (for evaluation)

• Automatic shaker for 30 minutes

• 1 ml transferred to autosampler-vial and analysed by GC-FID

GC-FID analysis

• Simultaneous injection on two columns with different stationary phase:

o Separation of 180 VOCs

o Identification of VOC based on set of two retention times (RT)

o Compounds with identical RT on a column can be separated on the other

column e.g. m-xylene and p-xylene

acetone

m+p-xylene

Column 1

acetone

p-xylene

m-xylene

Column 2

RT

GC-FID analysis

• Modifications for analysis of Permea-Tec patches :

o Longer temperature program (60 min) needed for baseline to stabilise

o Extra rinsing injections needed to avoid plugging of injection needle

DE-results for selected standard solution

0

10

20

30

40

50

60

70

80

90

100

110

120 0,001% v/v

0,005% v/v

0,01% v/v

DE-results from patches for 180 VOCs

• Lower conc. dependency, compared to activated carbon tubes

• Compounds can be classified into 3 different groups :

o (apolar) VOCs with constant DE near 100%

• toluene, m-xylene,…

o polar VOCs with constant DE (70-90%) (+/- 24)

• 2-butanol,...

o VOCs with concentration-dependent DE (+/- 10)

• 1-methoxy-2-propanol, 1-methyl-2-pyrrolidone,...

Conclusion

• Very promising results showing possibility for a method to evaluate dermal

exposure to 180 different VOCs • Accurate quantification on Permea-TecTM patches possible for VOCs with constant

desorption efficiency (DE)

• Additional tests needed (DE isotherms) for VOCs with conc.-dependent DE (e.g. 1-methoxy-

2-propanol, NMP,...)

• Further research: • Limit of detection (LOD), precision, storage stability,...

• Validation of utilization of patches as dermal monitors during field studies

Field study

• Solvent selection

o Frequently used for cleaning

o Dermal notation (DOEL, DNEL, …)

o Biological Exposure Index (BEI)

DE-results for selected VOCs

70

80

90

100

110

Chloroform THF Toluene m-Xylene p-Xylene o-Xylene Acetone Acetonitrile Acrylonitrile

0,001% v/v

0,005% v/v

0,01% v/v

non-polar VOCs with

constant DE near 100%

Central cleaning unit

• Disassembly Plate filters

Central cleaning unit

40

• Manual cleaning plate filters

Dermal monitors

Study design

Charcoal tube

for active air sampling

Urinary

biomonitoring

Charcoal patch

for dermal sampling

Overall results

• Inhalation: - high exposures, 1one monitoring result > OEL

- APF respiratory protection sufficient

• Biological monitoring urine - all results <10% of BEI

- but increase before & after shift = exposure

• PERMEA-TEC patches - no change in color on patches

- acetone detected on patches, below DNEL

- provided PPE sufficient, but actions identified based on observations.

Acknowledgment

• Dr. Katrien Poels

• Dr. Radu Duca

• Peter Collaerts

• Karin Vranckx

• Catherina Coun

• Prof. Lode Godderis

• And all collaborator for the field study