Fungicide organomercury

Mercury is consumed in the manufacture of organomercurials, which are used in agriculture as fungicides, e.g., for seed dressing. 

Work has also been done on the absorption and inactivation of organomercurials by micro-organisms that tolerate and even thrive on mercurials [26, 27]. It has been postulated that inactivation occurred by the uptake of fungicide by micro-organisms, followed by metabolic breakdown and by possible utilization of portions of the byproducts. However, whether or not biological inactivation and mercury evolution occur together has not been determined. 

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... 

The use of sulfur and copper fungicides dominated the market until 1915 when organomercury seed treatments, derived from discoveries in the pharmaceutical and dyestuffs industries, were shown to be highly effective against cereal diseases. They remained popular until banned in the late 1970s on the grounds of adverse toxicology. 

In the 1930s, the use of organomercurial fungicides became popular primarily as seed treatments but it has since been banned because of its high toxicity and persistence in the environment. 

Figure 12.5 Two organomercury compounds that have been used for fungicidal purposes.

Outside of the antiknock field, the commercial applications of organolead compounds are relatively few and quite small. The largest of these applications is in the manufacture of organomercury fungicides by alkylation. This application is old and is relatively static. Other alkylations consume a little tetraalkyllead compound. A small amount of tetra-methyllead has long been used to fill Geiger counters. 

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]. 

Many human tragedies have been caused by organomercury compounds in food. In the twentieth century, mercury compounds, usually the most toxic types, were applied as fungicides to seeds. Large-scale poisoning occurred in Iraq in 1971-1972 as a result of an appalling error, when seeds contaminated with Hg compounds were sold for consumption. After that event, the application of Hg compounds in farming practice declined, but a fair amount of the element remains in the soil. 

Other sources of pollution include the use of organomercury-containing fungicides in wood pulp for paper-making. Effluent from such processing plants has contaminated rivers. Predatory fish (for the same reason as predatory birds) also tend to contain relatively higher levels of mercury than non-predatory fish, especially those from enclosed, relatively non-tidal areas like the Mediterranean Sea. 

In 1897 formaldehyde was introduced for the first time as a fumigant. In 1913 organomercurials were first used as fungicidal seed dressings against cereal smut and bunt diseases. 

Organomercury compounds, such as aryl and alkoxy-aryl, have been used in medicine, agriculture, and laboratory research. Their use in fungicides has been greatly reduced or eliminated. 

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. 

Organomercurials - particularly the alkyl- and arylmercury compounds - are more active as bactericides or fungicides than the inorganic salts. Phenylmercury acetate prevents the growth of a variety of fungi in vitro at concentrations of approximately 0.125 mg L whereas ethylmercury salts are active at 0.05 mg In contrast, mercuric acetate or chloride are active at 1.0 mg L . The difference may partly be attributed to lipid solubility, where penetra-... 

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