Anthropogenic Sources of Mercury in the Environment

Meanwhile, similar diseases had been discovered at a number of locations around the world. A friend of this author visited a number of these places and found that they were indeed Minamata disease. In most of those places, the sources of mercury appeared to be chentical plants, particularly associated with paper/pulp mills. The chemical plant in Minamata was not involved in the paper/pulp production instead they were producing acetaldehyde. 

acetaldehyde (CH3CHO) is produced from ethylene (C H ), a petroleum product. In earlier days, though, it was produced by adding water to acetylene (C H ) (the reaction is -1- H O CH3CHO). This reaction requires a catalyst, mercury sulfate (HgSO ). The waste liquid containing mercury compounds was released into the Minamata bay. 

Paper/pulp mills often produce sodium hydroxide they need in small factories attached. A simplest way to produce sodium hydroxide (NaOH) of high quality is to electrolyze a brine solution (NaCl). That is, 2NaCl -electrolysis- 2Na(metal)+Cl. When steam (H O) is added to the sodium metal, sodium hydroxide is obtained 2Na+2H20 2NaOH + H2. Because electric current is used to accomplish this reaction, electrodes are required. The electrodes used are carbon rod (for anode) and mercury (liquid) metal for the cathode, because mercury binds many metallic elements including sodium. Lax procedures at small factories often allow some of the mercury to escape into the environment. This is the major source of mercury in the environments. 

By the way, note that chlorine (Cl ) is a by-product of this process. Chlorine-containing compounds have caused a number of environmental problems as talked about in Chap. 16, and the chlorine source for these compounds was essentially this process, i.e., electrolysis of the brine to produce sodium hydroxide. Because of the environmental concerns, this process called chloroalkali process is now often 

Another anthropogenic source is power-generating plants, where coal is used. Coal often contains a little of mercury, and as coal is burned mercuric substances tnm to metallic mercury, which is volatile. Hence, mercury will be spewed out along with the smoke. 

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