Yesterday I ran across an interesting scientific paper comparing short-term exposure to smelly (around 5 PPM) levels of H2S in combat veterans with and without PTSD (Vermetten et al, 2007, pdf attached). Tables 2 and 4 in their paper show a large (seemingly clinically significant) negative influence of H2S on symptoms in PSTD veterans. In addition, the same paper shows this adverse influence of H2S can also be seen with brain imaging (PET) procedures. In my mind, these results broadly suggest acute exposure to smelly levels of H2S may exacerbate at least some forms of anxiety-related disorders. I think this study may be used as solid evidence for potential clinically meaningful adverse effects of short-term H2S exposure in the smelly range of concentration, i.e. the smelly gas emanating from our geothermal plant is not a trivial matter as recently suggested by our State DOH Director. Yesterday, I shot an initial draft of this idea off to Dr. Adler in the context of a comment on the recent draft Report from his Study Group: Why a Stinky Geothermal Gas is an Emotional Issue It is currently within the DOH Director’s discretion to impose more appropriate permit conditions to further limit air pollutants and operations affecting air quality standards on a case-by-case basis. In this regard, over two decades have elapsed since DOH responded to the Hawaii Supreme Court order for the Hawaii DOH to promulgate standards on geothermal hydrogen sulfide (H2S) emissions and regulate these gas levels through the permit process. In addition, the science of H2S physiology and toxicology has advanced considerably over the last two decades, but no further changes in two decades have made by DOH concerning standards and regulations on H2S emissions. This improved scientific knowledge makes it easy to assert that the current 25-PPB average/hour standard is grossly insufficient for adequately protecting the public health during planned and accidental H2S releases by the PGV plant. As such, the DOH Director should be requested to immediately convene a panel of experts to review the available scientific evidence with intent to revise those standards. In particular, the DOH needs a new standard that is a far shorter interval than a one-hour average. To this end, an adequate system of down-wind monitoring is needed for reliably detecting peak levels of H2S in the lower end of the toxic range. The American Conference of Governmental Industrial Hygienists (ACGIH), a broadly recognized authority on the health effects of toxic gases, has recently changed its recommended threshold limit values (TLVs) for airborne hydrogen sulfide (H2S) exposure. One ACGIH recommendation for limits on airborne H2S exposure is a STEL of 5 ppm (15-minute short-term exposure limit). ohsonline/articles/2011/09/01/monitoring-h2s-to-meet-new-exposure-standards.aspx. This revised standard by ACGIH for a STEL of 5 ppm is at the bottom end of the very steep toxicology curve for humans, at a point where H2S definitely has an unpleasant odor (Guidotti, 2010; ijt.sagepub/content/29/6/569.short). The nasty smell of H2S gas is probably more than just a nuisance at this lower concentration. H2S exposure at this level may have, within minutes, some properties that influence human emotions in other, more maladaptive ways. It is at the above pivotal point in concentration that human toxicology experiments can be done with short-term exposures to H2S within controlled laboratory settings. For example, a study by Fiedler et al. (2008; ncbi.nlm.nih.gov/pmc/articles/PMC2199294) showed that anxiety symptoms in healthy, highly educated, humans were significantly (P < .0001) greater within 10-min after exposure to 5.0 ppm compared to 0.05 ppm of H2S. This result is consistent with an earlier experimental finding showing that an unpleasant H2S odor significantly enhances the emotional startle-reflex amplitude in humans (Miltner et al., 2007; onlinelibrary.wiley/doi/10.1111/j.1469-8986.1994.tb01030.x/abstract). In combat veterans with PTSD, exposure to lower (smelly) levels of H2S for 60 seconds enhanced PTSD symptoms (plus emotional and distress measures) relative to a neutral odor and also when compared to non-PTSD combat veterans (Vermetten et al, 2007, Table 2; online at ncbi.nlm.nih.gov/pmc/articles/PMC3236699/pdf/nihms340157.pdf). In summary, H2S at the concentrations where it is smelly, enhances anxiety and even more dramatically so in those who have one form of anxiety-related disorder. In the human brain, H2S at concentrations that smell noxious, directly activates the most central anatomical structure for human fear, what is called the amygdala. And like the behavioral data, the amygdala activation by “smelly” levels of H2S is greater for combat PTSD veteran than non-PTSD veterans (see above, Vermetten et al, 2007, Table 4). These results are consistent with other finding on H2S and the amygdala (Zald and Prado, 1997, ncbi.nlm.nih.gov/pmc/articles/PMC20578/pdf/pq004119.pdf); Walla and Deecke, 2010, mdpi/1424-8220/10/9/8185). At the neurochemical level, H2S-induced anxiety is in part mediated via enhancement of N-methyl-D-aspartate receptor (NMDAR) activity because the effect of H2S can be abolished by a NMDAR antagonist (Barcus et al., 2010, ncbi.nlm.nih.gov/pubmed/19836379). In addition, H2S at physiological levels, enhances corticotropin releasing factor, another powerful modulator of anxiety (Kimura, 2002, ncbi.nlm.nih.gov/pubmed/12392053). Hence, the above behavioral effects of H2S on fear are not just subjective or soft but are also seen in neurobiological measures of anxiety. At the level of health epidemiology, it thus is perhaps not surprising that the draft (V-3, 7-27-2013) version of the Geothermal Public Health Study recommends that in a more comprehensive health study “a priority should be placed on… monitoring for anxiety disorder[s]” (broadly conceived) in individuals exposed to geothermal gases (accord3/pg68.cfm). Aloha, Michael Kelley
Posted on: Fri, 23 Aug 2013 05:50:58 +0000