Richard Denison, Ph.D., is a Senior Scientist.
A hearing held yesterday by the West Virginia Legislature’s Joint Legislative Oversight Commission on State Water Resources created quite a stir, when a witness – West Virginia Environmental Quality Board vice-chairman Scott Simonton – said that the human carcinogen formaldehyde had been detected in several water samples drawn from a Charleston, WV, restaurant, and that people in the area affected by the January 9 spill could be expected to have inhaled the chemical, which he identified as a likely breakdown product of the spilled material, crude MCHM. See stories in the Charleston Gazette and USA Today.
State officials and the West Virginia American Water company were quick to call Simonton’s claims “unfounded” and “misleading and irresponsible,” respectively. The controversy led even the American Chemistry Council – which has laid low ever since the spill – to quickly issue its first statement related to the spill through its Formaldehyde Panel.
While experts are noting that data are insufficient to identify the spill as the source of any formaldehyde detected in the water samples, this new kerfuffle does point to yet another major data gap on crude MCHM.
The one part-per-million (1 ppm) “safe” level state and federal officials set was based on limited data from studies in which rats were exposed to crude or pure MCHM through oral ingestion. Absolutely no data are available on the chemical with respect to exposure through inhalation. Yet officials did not hesitate to tell residents the 1 ppm level would be safe not only for drinking the water, but also for bathing and showering.
(It’s curious that the Eastman Chemical Company apparently performed no inhalation studies on crude or pure MCHM, given that Eastman said its motivation for the studies it did perform was to understand risks to workers in industrial settings, and its safety data sheet for crude MCHM prominently notes the potential for health concerns for workers from inhalation.)
[UPDATE 1/31/14: This morning, Eastman posted an updated version of its Q&A document on its website (linked to in the above paragraph), and took down the earlier version. Here is the original version, the updated version dated 1/31/14, and a redline comparison of the two versions.]
Clearly the material that spilled is volatile – that’s why people can smell it. Taking a hot shower in such water means that people would clearly be exposed via inhalation of the vapor; how much exposure would occur has not been ascertained. But in the absence of any data as to toxicity of the chemical via inhalation, there is simply no scientific basis on which to say or imply that showering in water contaminated at 1 ppm level was OK.
Chemicals can be more or less toxic by inhalation than by ingestion, with one study finding inhalation to be the more toxic route for half of the chemicals examined and oral ingestion to be the more toxic route for the other half. Benzene, for example, is estimated to be several hundred times more toxic by inhalation than by ingestion, while inhalation of chloroform is estimated to be about 25-fold lower in toxicity than it is by ingestion.
What such comparisons indicate is that extrapolating from data on oral toxicity to predict inhalation toxicity – which is effectively what government officials did in this case – is about as accurate as flipping a coin.
3 Comments
It’s not “volatile”. Volatility is the property of having a high vapor pressure, of evaporating easily. MCHM is not at all volatile. It has a boiling point of around 200 C. Its vapor pressure is 0.133 mmHg at 25 C. By Raoult’s law, a 1 ppm by weight solution of MCHM, which is far higher than is present now, has a vapor pressure of approximately 2E-7 mmHg. As I’m sure you must have learned in whatever classes you have to take as an environmental scientist, atmospheric pressure is around 760 mmHg, so you have approximately 0.3 ppb molar of MCHM vapor or about 2 ppb by weight over a 1 ppm solution of MCHM in water. If you compare this to exposure limits of similar substances, like 2-ethylhexanol, http://environment.gov.ab.ca/info/library/6675.pdf , maybe you’ll stop needlessly scaring people who are already scared enough. It’s highly doubtful that the vapor should be detectable by smell at all at the present levels under 0.1 ppm. The fact that the chemical is very similar to ubiquitous natural and artificial flavoring and scent agents routinely present in much higher concentrations suggests that many anecdotal reports of the smell are not due to MCHM.
Ben,
Your comparison with 2-ethylhexanol is interesting but there may be an even closer comparison, The CRC Handbook of Chemistry and Physics, 48th Ed., includes chemical data for 2-cyclohexyl-ethanol, which has exactly the same molecular weight and is chemically almost identical to MCHM. The chemical number shown in my old copy of the CRC Manual is “e354.” Perry’s 4th Edition includes vapor pressure data for cyclohexyl-ethanol on Page 3-50. The boiling points are similar, so I assumed the vapor pressure of cyclohexyl-ethanol (1 mm Hg at 50.4 C) and Raoult’s Law in an almost identical analysis. With 1 ppmw MCHM in water and 50 C, I calculated a molar concentration of 0.14 ppmm in water, a partial pressure of 0.14 x 10 (exp. -6) mm Hg, and 1.8 x 10 (exp -10) molar concentration in air. This equates to about 9.2 x 10 (exp. -7) mg/liter of air. Breathing 10 liters/min. of this air during a 15 minute shower calculates to a maximum exposure by inhalation of 0.000137 mg MCHM. Exposure from a 24 hr. exposure equals 0.0133 mg MCHM, still essentially negligible.
My analysis was done several days ago for exactly the same reason, to produce data to disprove public statements that needlessly scare people who are already scared enough. My conclusion was different, however – that the MCHM is chemically stable under mild, dilute conditions and the exposure to these levels is real. I concluded that the extreme low partial pressure is an indication of just how stinky this stuff really is. My results were published in an op-ed article in last Tuesday’s (Feb. 4) Charleston Daily Mail. Much of the reported sickness and nausea in the news from breathing the vapors, I think, is psychological, much as smelling rotten eggs can induce nausea.
Privately, I have some question about how closely Raoult’s Law applies in this case. There is likely some non-ideality, so I applied an arbitrary factor of 100 in calculating the likely exposure level, also essentially negligible. However, MCHM is almost immiscible in water, with a solubility of only 0.23%, meaning that different relationships (think steam stripping, where partial pressures the two pure components are additive) may be required to calculate partial pressures in air. I haven’t explored this point further, and my poor (retired) memory of those calculations is rather rusty without checking some old references.
Best wishes.
B. J. Garner, P.E. (Inactive)
BSChE, MSChE, MS (Industrial Hygiene)
Retired (39 years professional experience)
Charleston, WV
I’m sure it doesn’t obey Raoult’s law exactly, but we’re not trying to come up with exact figures, given the lack of exact figures for the water concentration. I would agree that it’s probably fairly stable in air, at least until it gets into sunlight, but the point is that if you compare established exposure limits for similar alcohols to the levels you would expect from the water cocentrations that were present, there’s clearly no reasonable expectation of a health hazard, especially for the sorts of brief exposures we’re talking about here. Dimethyl CHM and especially methylethyl CHM (p-menthan-7-ol) are both widely used in perfumes, as well, which are obviously going to have concentrations vastly higher than this and obviously have been quite thoroughly tested both in labs and by many decades of real world experience. I just grabbed data on ethylhexanol because the inhalation studies were easily available. I think any branched 8ish carbon aliphatic alcohols should be pretty similar.