Mercury -- Cleopatra’s rouge is said to have been made from it; so, what’s the problem with it now?
A few days ago, the fifth and final round of the UN-led negotiations for a new international convention on mercury, commonly known as Minamata Convention, concluded in Geneva. What’s the outcome and scope?
Mercury Minerals
Mercury and some of its compounds have been used by mankind for well over two millennia. Cleopatra’s rouge is said to have been cinnabar, the red mercury (sulfide) mineral. The "solubility product" (a chemical term) of cinnabar is so low that you could never get any poisoning from consuming it. In other words, it is safe to eat – if you so desired. The few other known mercury containing minerals are essentially curiosities without any commercial importance.
Liquid Mercury
Elemental mercury has some unique properties. First, it is the only metal known to be a liquid at room temperature. That property has been made use of for centuries in such things as mercury thermometers used to check if it was cold enough outside to go skating or if your offspring had a fever.
Elemental mercury is also quite dense with nearly twice the weight of iron for a given volume. That density property of elemental mercury has also found many important applications. For example, the rotating frames holding the Fresnel lenses in most light houses were floating on a pool of liquid mercury. The reason for that was to keep the system perfectly level. Some of those light houses are still in operation today.
Like all metals, elemental mercury is also a good conductor of electricity. That property has been used widely in mercury-activated switches. For example, my old Chevy had such a switch under the hood, turning on a light when the hood was raised.
Mercury Vapor
Mercury vapor emanates from liquid elemental mercury in open air. Prolonged exposure to it can result in neurological damage and disease. That’s why many of the fluorescent type light bulbs (which are now mandated in numerous jurisdictions for energy conservation reasons) are considered hazardous waste and must not be disposed of with common household garbage.
Amalgams
Amalgams are combinations of elemental mercury with other metals. The most important one is silver amalgam (SA). SA has been around for a hundred years-plus and continues to be the dental cavity-filler material of choice. Its thermal expansion modulus is close to that of the apatite mineral in our teeth, it is easy to apply, sets fast and has the right hardness and resistance to chemical attack by saliva. Although some carbon-based polymers are quite good for some applications, the old SA continues to be used widely all around the globe for that purpose.
In simple terms, amalgams are practically like novel metals which bind the mercury together with another metal in an insoluble new material. The widespread fears of SA leading to a form of mercury poisoning are entirely unsubstantiated.
The mercury in SA is bound so strongly that saliva and our body’s enzymes cannot liberate it. No one has ever developed symptoms of "mercury poisoning" from the SA-cavity-fillings in his or her teeth.
Environment
Mercury is common in the environment, despite its low concentration in most rocks. Analysis of fish samples from freshwater lakes and rivers as well as the oceans all show low levels of mercury in various chemical entities.
For example, the Province of Ontario has been publishing detailed fish consumption guidelines for about three decades which include (natural) mercury as a contaminant of concern in approximately 10% of the tested samples. The mercury content of concern in those fish, however, is not elemental mercury but a mercury derivative, namely so-called methyl-mercury (MM). MM is the product of bacterial activity on mercury compounds in sediments of low oxygen content. Of course that also applies to the naturally occurring mercury compounds accumulating there from the slow dissolution of many types of rocks. MM accumulates through the food web. That’s why older fish (of any given species) have generally higher levels of MM than the younger cohorts. Natural background levels of MM in fish are in the order of 1 ppm (part per million).
In contrast to cinnabar, MM indeed has some toxicological significance. For several years it was unrecognized as the cause of MM resulting from large-scale discharges of mercury sulfate salt to the ocean in the area of Minamata Bay in Japan, back in the 1950’s. That discharge led to the formation of high levels of MM in the local water column which was then accumulated through the entire food web. In the end, it caused severe disease and even many deaths in people who were frequent consumers of fish from the area which contained several hundred ppm of MM. The disease became known as Minamata-Disease.
That’s’ a brief background to the Minamata Convention meeting which just concluded; now to the proposed regulations.
The Minamata Convention
The conclusions and draft regulations of the latest UN meeting on the Minamata Convention (MC) provide for a substantial restrictions of the use of mercury and its derivatives throughout the world. If and when ratified by at least fifty countries, the draft regulates inter alia the "supply of and trade in mercury" in all forms. The official MC statement includes the Swiss delegation’s position that "it shall support, in particular, a ban on the opening of new mines and the closure of existing ones." In short, if that convention becomes adopted, mercury will eventually become unavailable in any form or for any purpose whatsoever.
Obviously, that proposal is going overboard on a grand scale. You might call it crazy. The idea that the world could or should do entirely without an important natural element is preposterous by itself. Apart from mercury’s many uses in drugs, pesticides, dental amalgam and other applications, it simply could not be banned from existence on Earth. But that’s exactly what the convention appears to be aiming at.
Cleopatra would not be impressed!
