Methyl mercury fungicides

An epidemic of intoxication from ingestion of fish contaminated with methyl mercury occurred in the Minamata district in Japan, and, as a result, methyl mercury intoxication is often referred to as Minamata disease." Infants born to mothers with exposure to large amounts of methyl mercury had microen-cephaly, mental retardation, and cerebral palsy with convulsions. In an incidence in Iraq, ingestion of wheat products contaminated with methyl mercury fungicide by pregnant women caused similar symptoms of neurological damage and mental retardation. The fetus is... 

Mercurial fungicides were abandoned in 1971 because of environmental pollution and hazard of conversion into poisonous methyl mercury. 

Mercury contaminated foodstuffs and water supplies are a concern because of the extreme toxicity of the element and its compounds. Elemental mercury is used in the production of chlorine gas, and organomercury compounds formerly found use as pesticides and fungicides. Alkyl mercury compounds are of greatest concern since they do not degrade readily, and methyl mercury compounds concentrate in fish lipid tissue [9]. Pregnant women are at greatest risk since methyl mercury readily crosses the placenta, affecting the fetus [6]. 

Various organomercury compounds (e.g. ethylmercuric chloride, methyl mercury, dimethyl mercury), found as environmental contaminants or used as fungicides, are irreversible neurotoxins. Damage cell bodies of neurones in the dorsal root ganglia and brain. See also mercury. 

Mercury used to get into the environment in large amounts from the production of chlorine, from slimicides and fungicides used in the paper industry, and from fumigants. Mercury is one of the electrodes for the electrolysis of salt water to produce chlorine and sodium hydroxide. The contaminated mercury used to be dumped into lakes and rivers (0.45 Ib/ton of CE produced) because it was believed to be so heavy that it would just settle to the bottom. However, it was found that certain microorganisms could convert the mercury to organic mercury compounds, almost exclusively methyl mercury, which can be quite toxic. 

Mercury has also been implicated in the etiology of acrodynia (pink disease) in children when mercury-containing teething powder was used. The methyl mercury contained in fungicides has been responsible for toxicity in children in Iraq. This toxicity is characterized by phalangeal erythema, muscular weakness, ataxia, hyperirritability, sensory impairment, visual disturbances, involuntary movement, and sometimes unconsciousness. 

Kimura and Miller [28] have also studied the decomposition of organic fungicides in soil to mercury vapour and to methyl- or ethylmercury compounds and devised methods for the determination of these compounds in the vapours liberated from the soil sample. The mixed vapours of mercury and organomercury compounds is passed successively through bubblers containing a carbonate-phosphate solution to absorb organic... 

Mercury dimethyl is a toxic environmental pollutant. It is found in polluted bottom sediments and in the bodies of fishes and birds. In the bodies of fishes and birds it occurs along with monomethyl mercury. The latter, as CH3Hg+ ion, is formed by microorganism-induced biological methylation of elemental mercury or agricultural fungicide mercury compounds that are discharged into the environment. 

Organic mercury compounds containing an alkyl group with a low carbon atom number are classed in this group. The fungicidal effect of the derivatives decreases with increasing carbon atom number (Gassner, 1951), so that, in practice, only methyl- and ethylmercury compounds are important. 

Finally, we note that mercury released to the environment, as metal, e.g., by losses from electrolytic cells used for NaOH and Cl2 production, or as compounds such as alkylmercury seed dressings or fungicides, constitutes a serious hazard.50 This is a result of biological methylation to give (CH3)2Hg or CH3Hg+. It is known that models for vitamin B12 such as methylcobaloximes or methylpentacyanocobaltate (Section 25-F) which have Co—CH3 bonds will transfer the CH3 to Hg2 +. There are a number of microorganisms that can perform the same function, possibly by similar routes. 

In addition, some occupational exposure to organic mercury compounds may occur in some countries, where alkyl- (mainly methyl-) and alkoxy- (mainly methoxyethyl-) mercury salts are used as seed dressings (Skerfving and Copplestone, 1976), and phenylmercury is sometimes used as a fungicide. 

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