Methyl mercury

Description

Much of the notoriety of methylmercury has been generated from three separate mass poisoning events, two in Japan and one in Iraq. These events, at Minamata Bay in Niigata prefecture, and in Basra, demonstrated the potential lethality of methylmercury after it was a known toxic substance, and, though mercury is still an important risk factor for developmental toxicity, since the 1970s there have not been any large-scale poisonings of this type. Methylmercury is formed naturally in aquatic environments through the action of anaerobic bacteria on inorganic mercury.

Chemical properties

Water soluble, lipid soluble, high vaporpressure.

The Uses of Methyl mercury

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

Definition

Either of two com-pounds that contain the methyl group and commonsalts of monomethylmercury.

Hazard

Mutagen; possible carcinogen; teratogen;central nervous system poisons that easily passthrough the blood–brain barrier.

Safety Profile

A poison. An experimental teratogen. Experimental reproductive effects. Mutation data reported. Used as a fungicide. When heated to decomposition it emits toxic fumes of Hg.

Potential Exposure

Methyl mercury has been used as seed disinfectants and for fungicides. It has also been used in organic synthesis.

Environmental Fate

Inorganicmercury introduced as a pollutant into natural waters is scavenged by particulate matter and deposited into bottom sediments. Free Hg2+ is gradually released from this pool of slightly soluble inorganic mercury and is then transformed by microbial activity into methylmercury. Methylmercury diffuses into thewater column and is takenupbyfishand other organisms (either directly through water or through the food chain), and accumulated in their tissue. The degree to which mercury is transformed into methylmercury and transferred up the food chain through bioaccumulation depends on a variety of factors, including water chemistry and the complexity of the food web.

Shipping

UN2025 Mercury compounds, solid, n.o.s., Hazard Class: 6.1; Labels: 6.2-Poisonous materials, Technical Name Required.

Toxicity evaluation

All mercury compounds exhibit high affinity for sulfhydryl groups in proteins. As a result, a variety of enzymes and structural proteins containing free sulfhydryl groups can be modified and their functions affected. Inhibition of protein synthesis is an early biochemical event following exposure. The integrity of the blood–brain barrier can be disrupted by methylmercury, which results in the alteration of amino acid uptake and subsequent brain metabolism. Methylmercury can alter cell division during critical stages of central nervous system (CNS) development, at least in part through inhibition of microtubule function. However, there is uncertainty whether methylmercury or the mercuric ion following cleavage from methylmercury is the ultimate toxicant.

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. May be sensitive to light.