Acceptable Risk: The Discussion Continues

After the blog on “Acceptable Risk” I received an email and phone call from Harry Ettinger who, in addition to being a friend and colleague, is a Past President of the American Industrial Hygiene Association.  Harry has been around a long time and has a wealth of knowledge, wisdom and perspective.  Harry suggests that “Acceptable Risk” is an important subject that deserves additional attention.  He encouraged a panel discussion at a future AIHCE to air out the issues around this topic and the companion subjects:  “how safe is safe enough and how clean is clean enough”.    

If any readers of this blog are interested in participating on such a panel, please let me know (mjayjock@gmail.com) and I will put you on the list of potential participants.

Harry goes on to make the following points:

•        There is probably no definitive answer that will satisfy everyone (or perhaps anyone)
•         It depends on which side of the fence you are sitting on.
•         It needs

o    a balance so that the greatest good (whatever that means)       

o   to be is provided

§   to the greatest number of people who are most important (however that is measured)  

§  by ethical/unbiased/knowledgeable  decision makers (if these decision makers can be found or even exist)

§   in a long term time frame (rather than short term) 

Harry points out that, unfortunately, we typically define acceptable risk, to a large extent, on the basis of:

§  who has the most political clout

§  shouts the loudest

§  short term considerations

§  media influence

§  risk that has typically already been accepted

Harry advises that consideration should be added to any discussion of “acceptable risk” relative to the subjective perception and psychology regarding the source of the risk. 

He reminds us that we kill 38,000 people a year (approximately 100 deaths a day) in car incidents, and do not think very long about this death rate. We know that reducing the speed limit will reduce the death rate but when this restriction was introduced, many people objected.  Indeed,  New Mexico currently has a 75 mph speed limit on its Interstate.   If a rail car carrying chemicals such as Chlorine/Ammonia/shale oil/etc. derails, the subject is off the front page of the newspaper in 2-3 days (even if there are fatalities). If that same rail car was carrying protective clothing with minimal radioactive contamination (that is not readily released) the uproar would continue indefinitely.

Harry suggests that another topic to add to the discussion is that acceptable risk changes over time. What was unacceptable today was acceptable 10-20 years ago, and may or may not be acceptable in the future.  He believes that the definition of acceptable risk varies as a function of time and where it happens, and other relative risks extant at the time. This suggests that the 1/1000 definition in the benzene decision (which we still quote and use) probably needs to be updated.

I appreciate Harry providing his considerable insight on this subject and encourage you all to weigh in on this important topic.   As I get older I am beginning to appreciate more and more why some tribal folks highly value their elders. 

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: http://home.wxs.nl/~wtberge/qsarperm.html   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. 

What is ACCEPTABLE Risk?

In this week’s blog I go out on a limb, the topic is ACCEPTABLE RISK.

More than a few years ago, a then newly minted PhD, friend and colleague; Jack Hamilton asked my opinion about rules one might use to set a level of exposure and risk as ACCEPTABLE.   Being older and a lot grayer than Jack, I got to render my opinions.  I decided to share these opinions with you in this week’s blog to hopefully stimulate some discussion.  I do not pretend to have all, or maybe any, of the answers but I am willing shared my opinions to shine a light into this somewhat dark area in the hopes of bringing out additional discourse from you, my intelligent readers.

Finding and declaring ACCEPTABLE Risk Levels are almost never easy.   If it were easy we would have a life that was more dull and more people could do our jobs.  The question of risk acceptability is political and social.  Acceptable to who?  When?  The answer(s) always has (have) been a mix of politically recognized and derived subjective VALUES.

I have heard some folks on the extreme political left declare that Risk Assessment is a “Tool of the Capitalist Devil”.   I believe that to the extent that anyone independently determines what is "acceptable"for OTHER stakeholders this harshly worded judgment may have a ring of truth.  

Perhaps my most important mentor as I was learning and developing in this field was Dr. Irv Rosenthal.  Irv was a wonderfully intelligent and wise person and a gifted teacher.  Irv reminded me that we often ask permission to pass someone in a narrow hallway.  We say “excuse me” or “peg your pardon”.  Why then, Irv asked, would we not seek their permission to render them at risk (however small) from exposure to compounds we introduce into their environment?  Why can't they participate in drawing the line relative to their own exposures and the putative consequences?

The situation with Human Health is such that we look for consensus among industrial colleagues, academics, regulators and judges as to what are historically "acceptable" levels of risk.  We get benchmarks like 1 in 1000 lifetime risk for carcinogens exposure to workers and 1 in 1,000,000 for non-workers.  This has been evolving somewhat in the courts (e.g., US Supreme Court Benzene decision) but I do not think it has ever been put directly to the ultimate stakeholders, those being exposed.  These folks personally deal with exposure and risk and my sense is that, properly educated and, much more important, properly empowered, I think they would come up with doable and workable limits.  

I mentioned this possibility at an American  Industrial Hygiene National Conference in a Forum on Risk Assessment in the 1990s and the reaction was somewhat predictable.  Very few expressed a willingness to open the process up to these type of potential complications and "problems."  I admit that it will not be easy - I just think it will be ultimately necessary to make the process more politically viable, legitimate and inherently ethical.

So to answer Jack’s question succinctly, I advised him to use his skill to determine the quantitative level of exposure and risk as best he could.  I suggest that, if pressed, he leave the issue of “acceptability” to the first viable choice from the following rough hierarchy.

    1. A "Gold Standard" or criteria you were given by the client or that the client agreed to.   Note:  This is also known as “Rendering unto Caesar those things belonging to Caesar”.

    2. A criteria that is acceptable to some standard-setting or regulatory authority AND seems to make sense to you.

    3. An unwritten but generally accepted "rule of thumb" or common practice that you can refer to and makes sense to you. 

    4. Your "gut feel" on what it should be. 

In every case above, it would be beneficial to identify which line of the above hierarchy was used and the reasoning for using it within the report.   Doing so is particularly important for #4.  Indeed, my advice to Jack was to avoid using #4 unless you are asked specifically to do so by the client OR you have an overwhelming personal need to make your opinion known.   We should always to keep in mind that the determination or declaration of ACCEPTABLE risk is a somewhat subjective risk management function and it is not strictly speaking risk assessment.

Finally, I believe that there should be a new line at the top of this hierarchy that does not exist yet:

Acceptable risk defined in quantitative terms by consensual agreement among all the principal stakeholders.   My sense is that this is a worthy goal.

Chemical exposure risk assessment – what might we be missing?

Over the last few weeks this blog has featured a discussion of dermal exposure and how we might accomplish it.  That series was enhanced and prolonged from an email I received last month from Chris Packham. Chris sent me a copy of a talk he was going to give at a Regional BOHS Meeting in the UK on November 18, 2014.

I thought there was a lot of good information and perspective in that piece and Chris granted permission to put it here after his talk.   We may not agree specifically on the approach but I think everyone will agree that dermal exposure is a very important route in many exposure scenarios and has been somewhat ignored.

Chemical exposure risk assessment – 

what might we be missing?

Chris Packham

It is well established that inhalation of toxic chemicals can result in systemic effects, i.e. damage to internal organs and systems. A great deal of research and development has been undertaken resulting in strategies and equipment to monitor inhalation exposure. As a result in many countries there are exposure limits for a wide range of chemicals. Far less attention has been paid to the potential for chemicals to penetrate the skin and either cause or contribute to systemic toxic effects. Yet there is considerable evidence showing the potential for skin exposure to do this, including with chemicals that are unlikely ever to be inhaled because of their physical properties.(1) There is also a view that inhalation exposure results in more serious damage to health than can occur from skin exposure, often regarded as “just a rash”. Yet the EU Classification, Labelling and Packaging Regulation (EU1272/2008) contains the Hazard Statement 'H310 – Fatal in contact with skin'. 

In this article the authors will review the evidence showing why, in considering risks of damage to health due to the use of chemicals, the potential for skin exposure to cause systemic damage must be an integral part of any chemical exposure risk assessment. Firstly we need to recognise that the skin is not an impermeable barrier. The outermost layer, the stratum corneum, which forms 90% of the barrier, is, over most of our body, only as thick as the cling film that we use to wrap sandwiches. The way in which our skin interacts with the (working) environment is extremely complex and by no means scientifically fully understood. It is certainly beyond the scope of this article to attempt an in-depth explanation. (emphasis added)

Indeed, the complexity is such that the European Agency for Safety and Health at Work has stated: “However, there is no scientific method of measuring the results of the body’s exposure to risk through dermal contact. Consequently no dermal exposure standards have been set.” - from “Occupational skin diseases and dermal exposure in the European Union (EU-25):policy and practice overview - European Agency for Safety and Health at Work 

So where does this leave the health and safety practitioner attempting to establish the risks to the health of the workforce due to the presence of chemicals in their workplace? In the U.K. those chemicals that have been assigned a limit for airborne presence (Workplace Exposure Limit or WEL) and that are known to be able to penetrate the skin will be listed in the official hazard classification documentation(2) with an sk notation. However, this is far from a comprehensive list. Not only are there many chemicals that do not appear in this list that are able to penetrate the skin on their own and could then cause systemic damage. There are others that have systemic toxic properties but due to their form are on their own unlikely to be able to penetrate the skin. However, should these be mixed with a skin penetrant the potential for them then to able to cause systemic damage can be considerable. So establishing and assessing the hazard of a chemical in the workplace may not be as simple as many might assume. 

So what is the evidence that this is something that needs to be considered as significant when chemicals are being used in a workplace? The following statements and case studies should serve to illustrate why. 

1. Systemic uptake of 5-Hydroxy-N-methylpyrolidone

In this study(3) a comparison was made between the concentration of this chemical in urine arising from inhalation at 10mg/m3 over an 8 hour period with just 15 minutes exposure of one hand to a 15% solution in water. Despite the fact that skin exposure stopped after just 15 minutes, the concentration in urine continued to increase for several hours and matched that of the full 8 hour
respiratory exposure. The implications of this when conducting risk assessment are important as the assumption that the skin exposure is only for a very short period and therefore not of significance may not be correct. 

2. Systemic uptake of methylene diamine 

In a factory using this chemical in the manufacture of helicopter rotor blades this study (4) identified 14.7 μg/l of this chemical in urine under the actual working conditions initially observed. These did not include any effective control measures. By eliminating respiratory exposure the concentration was reduced to 12.1 μg/l. By allowing respiratory exposure but eliminating skin exposure the concentration was reduced to 2.6 μg/l. The conclusion that has to be drawn is that the major route of uptake was via the skin. 

3. Systemic effects in the rubber industry 

In his doctoral thesis (5) on genotoxic effects of dermal exposure in the rubber industry, Vermeulen comments: “Little attention has been paid to dermal exposure in this particular industry. Falck et al and Kilpikari already suggested in the early eighties that dermal absorption of chemical compounds could play an important part in the rubber industry. Direct evidence for this hypothesis was found in a study by Bros et al in an aircraft tire retreading company where a direct relation was found between dermal exposure to cyclohexane soluble matter and urinary mutagenicity while no relation was found between urinary mutagenicity and rubber particulates and fumes in air.” 

What should be clear from the above is that if we do not include the potential for skin uptake and the consequences we may well be missing a significant risk of serious damage to health. We need also to include the potential for ingestion as a route of uptake. 

The fact is that for systemic damage what is important is the total dose reaching the target organ, irrespective of the route of uptake. So what we need to identify is the combined uptake of all three routes: inhalation, dermal and ingestion. One of the immediate consequences of this is that with many chemicals the concept that ensuring airborne exposure is below the prescribed regulatory level represents adequate control may not be valid in terms of the true risk of damage to health. It may be necessary for regulatory compliance, but should the combination of the uptake of the three routes be sufficient to cause systemic damage, worker health can be severely, possibly permanently and potentially fatally, compromised. A consequence of this is that considering each of the three routes in isolation is no longer an acceptable approach. 

The problem now arises as to how we can develop a comprehensive risk assessment approach, combining the data on all three routes. Unfortunately very little seems to exist in terms of scientific studies or guidance on this. At the present time our only reliable technique appears to be that of biological monitoring of workers to establish their level of exposure, such as was carried out in the case study of exposure to methylene diamine described earlier in this article. Obviously it would be impracticable to do this for every chemical exposure risk assessment, but perhaps where there is evidence that the chemical which forms the subject of the risk assessment has properties that can cause systemic damage and that, under the particular circumstances prevailing in the work environment, there is potential for more than one form of exposure, biological monitoring should at least be considered. 

Ideally a database of results would be set up by a suitable organisation to build an evidence based overview of the true significance of this issue so that effective guidelines can be produced and perhaps new techniques developed. Until then the risk remains that we will continue to expose workers to situations that are putting their health in jeopardy.

References
(1) OSHA Technical Manual, Section II, Chapter 2 
(2) EH40/2005 Workplace exposure limits 
(3) Akrill et al (2002). Toxicol. Lett. 265 – 269 
(4) Weiss T, Schuster H, et al.; Dermal uptake and excretion of 4,4’-Methylenedianiline during rotor blade production in helicopter industry – an intervention study; Ann.Occup.Hyg, 2011, 55, 8, 886-892 
(5) Vermeulen R, genotoxic exposure and biological effects in the rubber manufacturing industry – relevance of the dermal route – doctoral thesis (2001)