Mercury spill replay
A second story appeared in The Flint Journal concerning the recent mercury spill from a broken thermometer at As described in the post here, a student found a thermometer and while tapping it on his desk it broke and panic ensued as the entire school was locked down and evacuated. The newspaper says that he and the other students in the science classroom were isolated and subjected to tests and health exams....all because of a quarter of a teaspoon of mercury.
Of course, we all want to keep our children safe but as one resident worried, the degree of hysteria and the continued frightening commentary must make kids think they’re going to die because they were in the building or had it on their hands. The school superintendent admitted that the amount of mercury spilled was minuscule but told the press “when you’re talking about student safety, you don’t want to err on the side of underreacting.” And the hazardous materials team coordinator said, “we know a lot more about these chemicals than we ever did... it’s usually better to be safe.”
While high and prolonged exposures to asbestos dust clearly proved life-threatening for high-risk industrial workers during the 1930s to 1970s, the vast majority of the 600,000 people who’ve filed asbestos lawsuits have been found to never have, and probably never will develop, asbestos-related health problems. As the Pepperdine Law Review reported in an overview of the phenomenon and its causes, “80-90% of claimants have no illness recognized by medical science, let alone suffer any lung impairment. The epidemic of silicosis turned out to be a fear-drive scam.
A recent 20-month federal court investigation discovered “overwhelming evidence of fraud” and that the “phantom epidemic” of silicosis had been manufactured for profit. The plaintiffs in a Texas multidistrict litigation (6,000 of whom had made a habit of filing silicosis claims) had all been seen by 8,000 different doctors who never found silicosis and the “diagnoses” largely came from a handful of doctors employed by a few mobile-screening operations, which the judge called “assembly-line diagnosing.” Last month, the Wall Street Journal reported on the asbestos fraud, noting that the resultant bankruptcies alone are “one of the largest wealth transfers in history, shifting billions from companies and insurers to plaintiffs lawyers and their largely healthy customers.” Just over the next year, $30 billion (with a “b”) is involved.
But fear spreads when a fundamental principle of toxicology is neglected: the amount and type of exposure determines the risk. Exposure alone does not mean risk, even when something may be dangerous in high doses or with prolonged contact. Asbestos is naturally found in the soil and dust in areas of Southern California, for example, yet there’s not been a single report of asbestos-related illnesses, as Dr. John Ray, M.A., Ph.D. wrote about a few weeks ago.
The Michigan news story quotes the hazardous materials team coordinator as saying: “One (vaporized) droplet can travel 20 to 30 feet [and people] underestimate the toxicity of the product.” The reporter went on to write that the “U.S. Environmental Protection Agency lists numerous health dangers associated with breathing in mercury, including kidney and lung damage, tremors, muscular weakness, reduced mental functions, even death.”
Scary-sounding stuff, but nowhere did the news article, or the public health or school professionals quoted, give the full story about the dangers of mercury vapors. Nor did they mention that elemental mercury is no danger when handled. It is incredibly easy to drop a fear bomb and terrify people with “what-if” speculations of risks that are outside the realm of realistic concern based on credible science. But it takes a lot more effort to explain the evidence and what science knows — evidence that in the vast majority of instances can lessen fears. Falling back on the precautionary principle, “better safe than sorry,” only escalates needless fears over everything. So parents were left with no help as to what to tell their terrified children when they came home from school after the emergency evacuation.
Yes, the Centers for Disease Control and Prevention has documented a few cases of neurotoxicity in children — when exposed to high levels of mercury vapor in a confined place for a long time. In 1989, for instance, it reported on two Ohio children who had been living in an apartment for many months with mercury vapor concentrations of 50-400 mcg/m3, believed to have been due to a previous owner who’d spilled a large jar of elemental mercury and not cleaned it up. The children’s blood levels were more than 42 times above safe levels. No health problems were found among the families living in surrounding apartments with mercury vapor levels less than 10 mcg/m3. A similar incidence in North Carolina was reported by the CDC in 1988, where a 3-year old boy had been exposed for months to levels in his bedroom of 55 mcg/m3 and levels as high as 4400 parts per million in the home’s vacuum cleaner bag.
In contrast, mercury levels measured in school classrooms after a mercury spill is picked up have been reported at 1-2 mcg/m3. Not too many school science labs are carpeted and unventilated or let the children sleep in them for months at a time, either, as in those CDC cases. The dose makes the poison. Safe exposures for industrial workers, for example, have been set by NIOSH at 50mcg/m3 for workers in 10-hour shifts and WHO has limits at 25 mcg/m3 for shift workers.
By following proper clean-up procedures (i.e. don’t vacuum the stuff) — which should be well known among school and health officials and are clearly spelled in every publication on the matter, with cleanup kits available in most public buildings — children are not in immediate danger every time a bead of mercury is found.
To help put the risks into a reasoned, calm perspective, here’s a basic information guide for science teachers from the Association for Science Education. Hopefully, it will help worried parents, while also serving as an example of the type of evidence-based information missing in the public risk analysis in these situations:
The only problem with mercury is its toxicity, but even this is only a problem if somebody is exposed to the vapour over long periods of time. There is no immediate risk if a thermometer is broken in a lesson. The spilt mercury should be cleared up as quickly as possible, to prevent it becoming dispersed but, if this cannot be dome immediately, it is not a major problem. The only risk might be a teacher (or, more likely, to a technician) working day after day in a small, badly-ventilated room where mercury vapour levels might become unacceptably high, but even then there would need to be a succession of spills, never cleared up. Interestingly, a recent study in the USA showed that science teachers had no higher levels of mercury in their blood than teachers of other subjects.
The Occupational Exposure Standard for mercury is 25 mcg m3 [0.025 mg] averaged over an 8-hour day. A typical school thermometer contains 1g of mercury. In the very unlikely event that all this vaporised instantly, it would produce a concentration in a typical laboratory (volume about 240 m3) of 400 mcg m3 [4 mg]. Many laboratories will have 6 air changes per house, but even if there were as few as 2 air changes per hour then the mercury concentration would drop to acceptable levels in less then four hours.
In practice, however, mercury evaporates very slowly: experiments at CLEAPSS suggest that a drop of diameter 6mm loses only 0.01 g in seven months. Of course, if a thousand thermometers had been broken in the laboratory and no steps at all taken to clear them up or prevent evaporation, then there could be a problem. However if most of the mercury is cleared up mechanically and any remaining droplets dealt with chemically (with a calcium hydroxide/sulphur powder mixture), the vapour loss should remain insignificant. It might be different if a large quantity of mercury were split, which is why we suggest that barometric demonstrations should take place over a tray to contain any spills. Equally, in a prep room of small volume and poor ventilation, there could be more of a problem, which is why any spills should be carefully cleared up.
Lawyers at Overlawyered.com responded to these recent news stories with some fun observations. It turns out that ordinary table sugar dust is deemed dangerous when inhaled, too, but we don’t (well, sane people don’t) go around trying to scare people about the deadliness of sugar and evacuating schools when the baker spills sugar in the kitchen!
© 2007 Sandy Szwarc
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