Sorry to be late in responding to this message from June 1 (I just returned from travel), but I completely agree with Dr. Norwood.

Much of the recent agitation about risks associated with mercury exposures has arisen because of poor understanding of the molecular mechanism of mercury toxicity. Although it has been known since 1967 that mercury toxicity can be prevented by selenium, the reasons why this occurs have been generally overlooked or misunderstood for the ensuing four decades.  

Mercury binding to selenium is about a million times higher than it’s binding to sulfur, making it mercury’s highest affinity binding partner in the body. Unfortunately, in earlier years, many people were poorly informed about the physiological roles of selenium and  thought of it only as a toxicant (some seem to still have this impression). Therefore, they assumed that formation of HgSe complexes in the body was a novel, but unimportant aspect of the mercury issue. It is easy to understand why selenium’s protective effect initially caused little enthusiasm.

If I was telling you that we could prevent mercury poisoning by giving a carefully calibrated dose of arsenic to bind with the mercury, I wouldn’t be surprised to observe a general lack of excitement. But selenium’s role in the mercury issue is dramatically different from that of simply being a toxicant that can bind with mercury and mutually detoxify one another.

Although selenium’s role in the mercury issue did move forward from that primitive level of understanding, it was still commonly misunderstood. Those that were unaware of selenium physiology still thought that selenium in the body simply acted as a “tonic” that bound to mercury and prevented it from causing harm to biologically important molecules. However, over the past decade it became clear that selenium was the molecular “target” of mercury toxicity, and selenoenzymes are the biologically important molecules that mercury harms. A series of studies have recently confirmed this is the case. Methylmercury is a highly specific irreversible inhibitor of selenoenzymes.

Since these genetically unique and functionally elite enzymes are required to protect the brain and neuroendocrine tissues from oxidative damage as well as a multitude of other physiologically essential functions, life cannot continue if they are impaired. At present, over a dozen manuscripts by various authors that describe work confirming this is the case, many that are already out in publication, but a number more that are currently in press. There are also at least four book chapters describing confirmatory work on the “selenium sequestration” hypothesis of mercury toxicity that will be published in the coming year.

Elemental mercury exposures are particularly dangerous, and is quite likely to cause severe problems at high doses, especially if these doses are maintained for extended periods. However, the type of chronic exposure that would cause harm would need to involve more than a few hours in a room with a broken thermometer. However, long term exposures to mercury filled rooms (extended home or work situations) are an entirely different issue, and these are accompanied by risks that require improved understanding of the pathophysiology of the toxic etiology and awareness of proper therapeutic response.

Since mercury is an irreversible inhibitor of selenoenzymes, it clearly involves a bimolecular reaction. Unfortunately, because it was previously thought that mercury acted through pseudo-first order chemical reactions, everyone has largely been focused on measuring only mercury exposures. Not that we understand more about the molecular mechanism of toxicity, it is clear that we need to know the concentrations of both reactants. This has been amply demonstrated since the same amount of mercury exposure that causes lethal effects when mercury is in molar excess of selenium is completely without any observable effects when Hg:Se molar ratios are not as great. Therefore, exposure is not a good measure of risk. Evaluation of both absolute and relative (Hg:Se molar ratios) exposures provide risk assessments that are far more reliable and accurate than the current approach which is based on mercury exposures alone.   

The recommendation to develop a standardized response to mercury exposures is well warranted, and would help prevent such excessive over reactions in the future. Even more importantly, it would establish a safe and effective response that would actually accomplish the objective of protecting health. Continuing to work to eliminate mercury thermometers from school laboratories is an area I want to emphasize because exposures in any environment where people spend extended periods of time can result in chronic accumulation of substantial doses of mercury. Work is currently underway to assess dose and time dependencies of elemental mercury exposures that would be expected to endanger selenoenzyme activities of brain and neuroendocrine tissues.

Fortunately, in the United States the selenium status of most of the population tends to be remarkably good compared to the rest of the world. Therefore, our children will be better protected from damaging effects of mercury exposures than children in Northern Europe. This is the sort of information that should become part of the standardized mercury response information packet that could be made available on line in order to enable health and safety response professionals to deal with future mercury exposures.

We will be hearing a lot more about the tremendous progress that has been made on this issue.

Nick

us_md: Students, School Staff Isolated After Thermometers Break 

BALTIMORE -- A group of elementary schools playing with thermometers caused a hazmat situation Friday in Baltimore. 

Fire department spokesman Kevin Cartwright said more than a dozen people were isolated after broken thermometers prompted concerns about the mercury inside. 

The incident occurred at Rodman Elementary School on West Mulberry Street. 

The students and staffers affected were to be showered in a decontamination trailer. 

There were no injuries reported. 

Cartwright said the students were playing with thermometers that broke and released mercury.

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Y’all knew this was coming, right?

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Once again, the absence of someone (anyone) with a cool head and a mere modicum of common sense has caused a heinous over-reaction to a non-situation.

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Before several amongst you inundate me with claims of how this really is a serious event, let me pre-empt your knee-jerk reactions to my statement:

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1)  Unquestionably, mercury is hazardous, and represents a severe chronic threat, particularly when exposures occur over an extended period of time.

2)  Proper remediation of the spill must be performed any time mercury is spilled.

3)  As noted in the earlier discussion, EPA must be notified if more than 454g are released.

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But folks, seriously?  Decontamination of the staff and students?  This is patently and demonstrably asinine.  There is NO conceivable scenario, dealing with elemental mercury from a thermometer or two, in a room of moderate size and with normal ventilation, by which these folks were exposed to anything remotely warranting bringing in a “decontamination trailer”.  If there were an acute danger from playing with mercury from thermometers, I and most every science major in my generation would already be brain-damaged and/or dead.

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Again, my main focus here is the fact that we are reinforcing MINDLESS FEAR instead of understanding and respect for chemicals.  If we, the ‘experts’ in response, don’t exercise wisdom and judgment, if we make every call to us a local disaster response, eventually someone will not report something because they don’t want to cause a scene – and that’ll be the one we will have really wanted them to bring us in on.

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Okay, I’ll take your flames now.

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Brad

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Dr. Bradley K. Norwood

8302 Shady Ridge Lane

Mechanicsville, VA  23116

(804) 559-7212 (H)

(804) 271-5572 ext. 307 (O)

(804) 641-4641 (cell)

brad.norwood**At_Symbol_Here**aristalabs.com

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You cannot help the poor by destroying the rich.
You cannot strengthen the weak by weakening the strong.
You cannot bring about prosperity by discouraging thrift.
You cannot lift the wage earner up by pulling the wage payer down.
You cannot further the brotherhood of man by inciting class hatred.
You cannot build character and courage by taking away people's initiative and independence.
You cannot help people permanently by doing for them what they could and should do for themselves.

.....Abraham Lincoln

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