Back in the 70’s, the Japanese determined that a set of symptoms found in the population around the city of Minimata were caused by pollution of their drinking water with methyl mercury, present in tiny amounts in the effluent of an industrial plant. This was an industrial plant where mercury was actually a raw material in the process, completely different from any plant in Canada.
It should be emphasized that methyl mercury is a compound, and bears no more relationship to mercury metal than common salt does to chlorine gas. Old-timers will recall mercury metal from high school lab days. It is liquid at room temperature, very heavy, with a high surface tension so it would form balls which could be rolled around on the science lab desks, split into smaller ones and reformed into bigger ones, smeared on a penny to make it look like a dime, until it wore off into tiny balls in your pocket, and so on. It was fun stuff. Its most common use was as the liquid in thermometers.
Minimata was worldwide news, and caused everybody to look at where there might be methyl mercury, or even other mercury compounds, including in Canada. We all remember ‘mercurochrome’, a mercury-based disinfectant slopped around with abandon in our hospitals, and there were a few other uses of mercury compounds, but these were all discontinued decades before. When no newsworthy mercury compounds were found, our scientifically illiterate press went looking for mercury metal. It was part of the amalgam used to fill teeth, but before the press could get their teeth into that one, they discovered chlor-alkali plants, much more fun to beat up on industry than people’s teeth.
Chlorine and sodium hydroxide are basic industrial chemicals, used as raw materials for many processes, and used as disinfectants in many ways. Our water is kept safe by injection of a tiny amount of chlorine gas; common bleach is made from chlorine, many soaps and cleaning chemicals are made from sodium hydroxide, they are present in some form in every house. They are produced in a chlor-alkali plant in a simple, elegant process which uses electricity to change common salt and water to chlorine gas and sodium hydroxide, plus a small amount of hydrogen gas, with no waste and no by-products. Mercury metal is used as a medium to carry the electricity and to transport the sodium away from the chlorine. It is very inert, in fact turning it into compounds like methyl mercury is quite a project, so it is not consumed or used up in the process, it is just part of the machinery.
Mercury is very expensive – the quantity purchased to start up a chloralkali plant represents millions of dollars. I recall when our plant in Dryden was being built, the mercury was being purchased in small quantities on the London metal exchange, and delivered in sealed flasks which were stored in a vault. A flask was heavy enough to require two hands to lift it, but would fit into a lunch kit and would be worth several thousand dollars. A tiny portion of the mercury used to carry the sodium, say one pound out of tons circulated, goes with the sodium and must be recovered, and a measure of a plant’s efficiency is how much mercury must be purchased to replace what is not recovered.
There was a brief flurry of sensationalist publicity around the chlor-alkali plants. There were 11 chloralkali plants in Canada at that time, including Dryden. Dryden was one of the most efficient, that is, lowest in mercury loss, and so did not get any more press or criticism than the others. After the brief flurry, the matter was almost forgotten by the press. Until?? Answer next week.