October 04, 2005

Mercury - Chemistry Explained

Mercury – What’s the real issue? – Dr. Lenny Howdt, PhD

Darn dam keeps tossing red herring at us, when people should focus on the primary issues at hand. The real deal of the Milltown Hill Dam is the cost/benefit analysis : where the money comes from and who makes howdt. The distraction is the Mercury in the water. Let’s talk Mercury.
The little silver balls that floated out of the thermometer that you broke when you were a kid were the metallic form of mercury. We pushed them around, watched them coalesce and ran them into one big ball that could be put in a jar and tickled for entertainment value. A little bit of sulfur quenches all toxicity of the metallic liquid element.
Mercury in the main ionic mercury form is a two plus cation Hg2+ found locally as cinnabar HgS and totally non-toxic. However, mercury bio-accumulates in fish, whatever that means, and hence is on EPA and DEQ’s *hitlist. Let’s look at some chemistry facts before we progress further.
Mercury (At #80) has 80 protons, 80 electrons and 120 +/-2 neutrons. It is a large molecule – atomic weight 200 compared to carbon at atomic weight 12. The chemistry of mercury is much like the chemistry of cadmium and zinc. These three elements are non transition metals. Mercury Hg2+ behaves like Barium Ba2+ - imagine giganto calcium. For those of you chemically literate folks, the outer configuration is 5d10 6s2.

For those of you who are lost and/or need a refresher– I can offer a $25 on-line chemistry for beginners in our on-line classroom YC.C with a critical mass of 20 people.
Mercury should always be kept in tightly closed containers and handled only in well ventilated areas. It may be generated in, and escape from, solutions of its salts due to adventitious reduction and/or disproportionation of Hg2 2+.
Mercury (I) Hg+1 does not exist – mercury I always occurs as a dual charged dimer – two atoms of mercury that share a pair of electrons and are two electrons deficient. There is a serious enthalpic (energy) advantage to sharing filled 6s orbital. But all counter-ions which promote precipitation in water solutions, cause disproportionation. The most toxic mercury compounds are organo-mercury(I) compounds.
Fish tend to be bio-accumulators, which means they collect mercury in their body tissue. This is actually part of the normal chemical transfer chain and when the fish spawn and die, the mercury gets distributed and scattered, to each react another way. There is speculation that fish can stabilize labile organo-mercury, but given the toxicity, I would speculate that the fish would die. Disproportionation renders the two mercury harmless after the separation event.
All the molecules of mercury that have ever been here, are still here, and will always be here. Mercury thiolates are known in nature and could potentially be transportation and/or storage receptacles for biological bodies to remove mercury from their system, via active transport in the bloodstream to the nearest hair follicle for expulsion.
For those of you who want to stop the dam – talk about water quantity and water quality and salmon spawning issues and other storage methods. A whole lot of small ponds connected with a satellite gating system, that have the depth to allow a helicopter bucket fill would give fire protection and resource water to the streams via late summer release programs. Keeping water in the streams year-round will help everybody, landowners, fish and wildlife, trees and forests. Let’s listen to the merits of all knowledge and make an informed decision at Milltown Hill.

[1] Cotton, et al. Advanced Inorganic Chemistry 6e (1999) John Wiley & Sons, Inc. p.600

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