Methylmercury is a toxic organic form of mercury that easily accumulates in the food chain, especially in fish. It can cause irreversible neurological disorders, making it a concern for pregnant women and young children. Environmental agencies conduct tests to warn the public of dangerously high levels. Industrial processes and burning fossil fuels can produce elemental mercury, which can transform into methylmercury in specialized anaerobic environments.
Methylmercury is an organic form of mercury that can cause environmental problems because it is easily absorbed and difficult to get rid of. It can be produced directly through some industrial processes, and also by natural reactions in the environment. Concerns about methylmercury poisoning underlie recommendations to limit the consumption of certain fish to pregnant women. Environmental agencies in regions where this compound may be a problem conduct periodic tests for signs of dangerously high levels so they can warn the general population.
Chemically, this compound consists of a methyl group attached to a mercury atom, forming a positively charged ion. It easily attaches to proteins and does not release easily, making it a cause for concern in the wild. When an organism absorbs methylmercury, it cannot eliminate the cation. If that organism is in turn eaten by a larger organism, it receives a load of toxic mercury along with its meal. This creates a bioaccumulation effect, where concentrations of the compound can become high in animals further up the food chain, such as sharks.
Historically, some industrial processes produced methylmercury and companies released the compound directly into the environment, creating pollution. It was also used for tasks such as treating grain to prevent insect infestation, which occasionally led to accidents when animals ate the grain and were then eaten by humans. Environmental regulations have repressed this practice, reducing the quantity produced directly by man. However, elemental mercury continues to be produced, mostly through the burning of fossil fuels.
The entry of elemental mercury into the environment does not necessarily mean that methylmercury will be formed. It needs to fall into places with specialized anaerobic organisms that methylate it, adding the necessary methyl group. Also, the demethylation process in which the compound breaks down must be slow enough to allow it to accumulate. Lakes and streams are common sites for this transformation, which can affect animals that depend on them for water and food.
Humans can consume small amounts of methylmercury without significant problems, but if it starts to build up, they can develop neurological symptoms. It is especially harmful to developing fetuses and young children, who have rapidly growing nervous systems. Neurological disorders can develop due to exposure to methylmercury in the diet or via the placenta, in the case of a fetus. These are irreversible and can vary in severity depending on the timing and size of the dosage.
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