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July 10, 2007

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F. R.  Anscombe

It is unfair to attribute Minamata disease to microbes. At Minamata Japan during the 1950s, several manufacturing processes used mercury compounds to catalyze reactions with acetylene gas. The union of carbon and mercury likely yielded organic mercury wastes on an industrial scale, tons per year. These were washed away into an abundant fishery upon which people subsisted, resulting in a high-dose neurological tragedy.

Nature has microbic defenses that curb buildup of methylmercury, bacteria that demethylate. This natural defense against methylmercury buildup is given scant press by fear-mongers.
COMMENT ;
THANK YOU FOR THE MINAMATA CLARIFICATION.

HOWEVER, THE BIOMETHYLATION OF METALS IS ALSO UBIQUITOUS , WITNESS THE KILLING OF BALTIMORE HARBOR OYSTERS BY TIN TRIMETHYL PRODUCED BY MACROALAGAE AND THE BIOACCUMULATION OF UP TO 800 PPM OF METHYLCADMIUM IN COCKLES NEAR ZINC SMELTERS ON THE BRISTOL CHANNEL.

Fish have naturally contained very low levels of methylmercury since time immemorial. Since fish mercury burdens are a function of fish age and thus size, and since fishing pressures in modern times have reduced the sizes of fish caught in many locations, it is likely that human exposures to methylmercury via fish consumption are lower today than in pre-industrial times.

For risk-mongers, one of the wonderful blessings about mercury in fish is traces will always be present, allowing blame to be conveniently assigned to some human bugaboo.

F. R. Anscombe

Another element ubiquitous in fish at uber-trace levels is thallium, sitting betwixt lead and mercury on the periodic table and favored by Agatha Christie and Sadaam Hussein to dispatch opponents. I have read thallium, lead, mercury and beryllium are not known to have been gainfully incorporated into any living organism, a perhaps useful evolutionary perspective on their healthfulness.

Ubiquitous biomethylation of modern-day releases of metals seems a wise warning. It is fair also to be mindful of natural restraints on methylation, regardless of those who may cry treason.

B.  Heart

There may be perceptual or structural disincentives to fuller appreciation of risks posed by metals within the environment.

For example, some trendy "organic" growers are said to employ copper-based pesticides. Their skepticism of newer petroleum-derived pesticides must be greater than concerns about metals-based pesticides. Perhaps they think metals-based pesticides are reassuringly "traditional." The incongruous result: environmentally-conscious growers who choose metals-based pesticides.

There are many more organic chemists than inorganic. Also, there are many more organic materials of human synthesis than inorganic ones. These two structural factors may help focus more public attention on environmental risks posed by organic "pollutants," at a cost of less appreciation for risks posed by metals.

Adamant's mention of the ubiquitous biomethylation of metals is welcome.

COMMENT ;
ON THE OTHER HAND , ORGANOMETALLICS CAN BE FRAGILE RELATIVE TO HYDROLYSIS AND ENZYMATIC DEGRADATION, QV:
Jonathan G. Melnick and Gerard Parkin IN SCIENCE THIS WEEK, WHO NOTE

The extreme toxicity of organomercury compounds that are found in the environment has focused attention on the mechanisms of action of bacterial remediating enzymes. We describe facile room-temperature protolytic cleavage by a thiol of the Hg-C bond in mercury-alkyl compounds that emulate the lyase complexes . they propose facile access to a higher-coordinate species to account for the exceptional reactivity of [TmBut]HgR

IN ADDITION, COPPER METHYL IS RELATIVELY UNSTABLE, AND MANY ORGANOZINC COMPUNDS ARE JUST NOT VERY TOXIC TO BEGIN WITH--

Beau Heart

I agree that many organometallic compounds may be of low toxicity.

I am now gazing at a bottle of Mercurochrome, general antiseptic. It was said to "not irritate, burn, or injure tissue", though also says "for external use only." Used to be a staple of medicine cabinets. (I need to get a magnifying glass to read more of the label.)

Elemental mercury is not much absorbed by an intact human digestive system. For this reason, mercury used to be swallowed by patients suffering from painful afflictions like blockage of the intestines in hopes the heavy liquid mercury could dislodge the obstacle.

Caffeine is one of humanity's favorite chemicals. Yet it has been reported caffeine can be used to counter slugs (not just to combat our own sluggishness). If so, it could be claimed we humans love to drink an insecticide.

These anecdotal tales seem compatible with the general insight that the dose makes the poison and nothing is entirely non-toxic. This being so, human opinions about toxicity are very influential in shaping (and limiting) public consideration about what constitutes a pollutant. Adamant's appreciation of the dose-dependent potential toxicity of some metals within the environment renders public service.

Ron Schwarz

Oh c'mon, won't SOMEONE comment on the hypocrisy of Algore's sanctimony, while owning the country's ONLY cadmium source? (other than one recycling operation)

Beau Heart

Cadmium and zinc provide much value to society. Since I very much respect the mining of cadmium and zinc, it would seem hypocritical on my part to feign otherwise.

B.  Heart

Adamant's comment alluding to bioaccumulation of methyl-cadmium in cockles near zinc smelters on the Bristol Channel brings to mind an (imperfect) comparison.

It has been reported the compound thallium (III) is 43,000 times more toxic to plankton than cadmium. Like methyl-mercury, thallium(III) is formed by bacteria. Ref: Benjamin S. Twining, et. al. 2003. “Oxidation of Thallium by Freshwater Plankton Communities.” Environ. Sci. Technol., 37, 2720-2726

Thallium levels tend to be little analyzed in the environment, in marked contrast to its adjoining neighbor on the periodic table, mercury.

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