Sunday, December 21, 2014

Dermal Exposure from the Air

We can get a significant dermal exposure to a toxicant from having exposed skin in contact with that toxicant in ambient air.   I am not talking about splashing or the settling of mist onto the skin, the mode of exposure discussed in this blog is pure vapor in air-to-skin-to-systemic absorption.  This manner of exposure can become very important when the respiratory route is reasonably well guarded via the use of a respirator.

The classic example of this type of exposure is phenol which has a relatively low exposure limit indicating that it is quite toxic via inhalation.   It is also quite irritating to the respiratory tract and thus may provide some good warning indications of exposure via that route.  Thus, folks who have to work in environments at greater than the OEL (ACGIH TLV and OSHA PEL = 5 ppm as an 8 hour time weighted average) would almost certainly be using respirators.

Phenol also readily penetrates the skin and, again, I believe dermal exposure to liquid phenol placed or splashed onto the skin surface would be very irritating or even corrosive. 

A more subtitle route of exposure is as vapor molecules going from the air above the skin, into the skin and then through the stratum corneum and dermis to be systemically absorbed.  This presents a real problem to the Industrial Hygienist trying to evaluate or estimate this exposure potential.  

One method would be to put absorbent patches on the skin to be subsequently desorbed and analyzed.   These could provide a measure of the weight per square centimeter to which the skin was exposed.   Multiply this weight by the total amount of exposed skin for at least some measure of what the exposure might be.

Other than involving a lot of logistics and laboratory development, the above method has the problem of being done AFTER the fact of exposure.   What we need is a method that is prospective; this is, before and predictive of the exposure.   

I have discussed Dr. Wil ten Berge’s work before here.  He developed SKINPERM which has been around for a long time and, working with Daniel Drolet, Rosalie Tibaldi  and Tom Armstrong, has produced the more recent, more user-friendly IHSkinperm model.  The basic modeling engine that Wil developed is the only one I know of that will take the airborne concentration of a chemical (along with other physical-chemical properties) and estimate the dermal exposure potential of that chemical to exposed skin.   

You can find SKINPERM on Wil’s website:   In addition to the model, Wil has a wealth of educational material on dermal exposure on this web site that has been around serving the risk assessment community for some time.   Put “IHSkinperm” into Google and the first two hits are the manual and the spreadsheet.

Unless someone is wearing well-fitted vapor barrier clothing, you might want to give some consideration to the possibility that even skin ostensibly covered with cloth clothing is at least somewhat “exposed” to vapors.   Considering the person naked (about 2 m2 of skin) would represent a worst case or bounding condition for these estimates.

It is the Holiday Season and I would like to take this opportunity to wish everyone reading this, along with their loved-ones, according to their preference, a Merry Christmas, Happy Hanukah, or whatever holiday you observe including the Return of the Sun during this special time of year. 

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