The skin we live in
Many years ago, in a laboratory far, far away, I used to work as a research scientist. One of the chemicals used in the laboratory was Dimethyl Sulfoxide (DMSO). You could do a neat trick with DMSO, as I discovered.
At the suggestion of one of the post-docs in the lab (yes, that’s you Paddy!) I put a small drop of liquid on my fingertip and then watched it intently. The drop of liquid disappeared, as if by magic.
A few seconds later, a rather bitter, almost acrid, taste appeared on the back of my tongue. I have heard people describe it as a strong garlic taste, but I remember it as the kind of bitter taste that you associate with really strong 85% cocoa chocolate. The DMSO hadn’t evaporated away. Instead, the liquid had passed through the skin on my fingertip, diffusing into the tissue and blood stream beneath. Once in the blood stream it had passed everywhere, including to my taste buds, where it produced this characteristic taste.
I wasn’t supposed to have done this. . .
Students of NEBOSH Certificate and Diploma courses will recognise the route of entry here – absorption through the skin. This is a significant route of entry for hazardous substances that have the ability to diffuse across the skin, which, in other circumstances, presents an impermeable barrier to the outside world. Water does not pass the skin barrier significantly. If it did we would all dehydrate in a matter of hours. And having a shower would be a rather more weighty experience than it currently is. The skin has a complex structure; in particular, the top layer of the epidermis, made up of layer upon layer of dead cells coated with sebum (an oily liquid secreted by the sebaceous glands), makes the skin waterproof. This topmost layer is called the stratum corneum, or ‘horny layer’, which I think is just joyful.
Certain substances can soak though the skin barrier as if it were tissue paper. Examples include benzene, carbon tetrachloride and hydrogen cyanide. One way of checking to see if a substance will do this is to look at its safety data sheet (SDS). Another way, as all of you Diploma Unit B students out there will be screaming at me now, is to look in Table 1 of EH40 – the table that contains the list of chemicals that have been assigned a Workplace Exposure Limit (WEL). In the ‘comments’ column of that table you will find a Sk notation, which indicates that the substance can be absorbed through the skin.
When this route of entry is available to a hazardous substance and the potential for significant workplace exposure exists, then it is important to factor the route of entry into the exposure assessment (COSHH assessment). Otherwise, the amount of substance getting into the body may reach harmful levels, even though the other routes of entry (such as inhalation and ingestion) may be well controlled.
This is because even though the concentration of an airborne substance may be very well controlled and, consequently, the amount of the substance inhaled by the worker may be well below the Workplace Exposure Limit (WEL), the worker may receive a significant dose of the substance by the skin-absorption route. WELs only address the inhalation route of entry; they do not tackle or address other routes of entry.
The limit that does address skin absorption as a route of entry (along with all other routes) is the Biological Monitoring Guidance Value (BMGV). The BMGV is a concentration of a substance (or its metabolic breakdown product) in blood, urine or breath that gives an indication that a worker’s exposure to the substance may be at an unacceptably high level. BMGVs are listed in Table 2 of EH40. The principal limitation with BMGVs is that there aren’t many of them – Table 2 of EH40 contains just 16 entries.
Anyway, I am getting distracted.
The Dead Kennedys have a song about DMSO. Rather originally, it’s called “DMSO”. Check it out on YouTube (other video-sharing website are available).
The reason why I mention the DKs here (apart from a childish devotion) is that they have another song, called ‘Kepone Factory’, which is about occupational exposure to hazardous chemicals. I know! What are the chances that a bang-on, West-Coast, angry-liberal protest punk-rock band would sing a song about occupational health and safety? But there you go – they did. (And before you write in, that’s West Coast USA; not UK. And yes, when I say ‘bang-on’ I mean bang-on in the context of early 1980′s and, yes, I am aware that I am showing my age yet again in a blog by revealing my poor musical tastes).
The song concerns an insecticide, kepone – a relative of DDT, which was produced at Hopewell, Virginia, USA. Environmental contamination and worker-health issues led to a ban on the production of kepone in 1975. The song lyrics are pretty accurate on the chronic health effects of kepone exposure. If you want to read more about this incident you might want to take a look at this retrospective published by the local newspaper:
Incidentally, the mention in the Dead Kennedys’ lyrics of ‘Minamata’ are a cross-reference to the poisoning that took place between 1951 and 1968 in Minamata, Japan, where the Chisso Corporation allowed methylmercury to escape into Minamata Bay in wastewater. This organic form of mercury is highly toxic and accumulates in the food chain. Locals in the bay area ate contaminated seafood and ingested the poison. Well over 2,000 officially recognised victims exist and the real (though not officially recognised) number may be more than 10,000. This industrial pollution event lead to the Minamata Convention of 2013 (yes, it really took that long), which aims to restrict the mining, use and release of mercury.
These historical incidents make for salutary reading, and they should be a constant reminder to us that industrial poisonings can and do still happen, and that there is a reason why the NEBOSH Diploma Unit B focuses heavily on substances hazardous to health.
I think I have had enough now. I am off for a healthy walk in the fresh air to try to shake off the depression I have just managed to plunge myself into as a result of writing this blog.
If I can galvanize myself then I will continue this blog in ‘The skin we live in’ Part II…
Jim Phelpstead BSc, PhD, CMIOSH
Working in health and safety for 18 years Jim is a long-standing RRC Associate Tutor, who loves the great outdoors.