Exposure to Mercury

Exposure to Mercury

 

■ Characteristics of Mercury

 

Mercury (Hg) is the only metal that is liquid at room temperature. It evaporates easily because it has low vapor pressure, which means it can be inhaled through the respiratory system. Most occupational exposure to mercury has occurred through inhaling mercury vapor. Historically, many cases of mercury poisoning were reported among hat makers in 19th century Europe.

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■   Minamata Disease - The First Pollution-Related Illness

Minamata disease, also known as the first pollution-related illness, emerged as a result of mercury poisoning.

Around 1906, a carbide factory was established near Minamata City in Kumamoto Prefecture, located at the southern tip of Kyushu, Japan, and it began operations in 1908. From around 1953, a mysterious disease began to appear in the coastal villages around Minamata Bay near the factory. Initially, dead fish were found floating in the sea, and seagulls were seen losing their balance. On land, cats began to suffer from convulsions, fell into comas, and started dying. Fishermen suddenly developed abnormal gaits, their limbs became numb, and they became unable to speak. These symptoms primarily appeared among the poor fishermen.

This incident became known on April 1, 1957, when according to an article by the Asahi Newspaper, the mysterious disease caused high fever, paralysis of the limbs, and central nervous system damage, leading to disabilities in speech, hearing, and motor functions, with a mortality rate of 30%. The Japanese government set up a "Strange Disease Countermeasures Committee" to conduct an epidemiological investigation, and the results revealed that the disease was caused by poisoning from methylmercury, a mercury compound. A research team from Kumamoto University traced the source of the methylmercury and, three years after the outbreak began in 1956, identified the culprit as the Shin Nihon Chisso Fertilizer Company located in Minamata. The mercury contained in the wastewater from this factory had flowed into the sea, contaminating fish and shellfish, which, when consumed by the local residents, led to mercury poisoning (1).

 

■   Occupational exposure

Mercury has been used in thermometers, barometers, manometers, and valves due to its consistent volume expansion with temperature changes, as well as in various industrial applications. In the medical field, mercury is used in dental amalgam for fillings. During the preparation of these materials, dentists and dental hygienists can be exposed to mercury. This occupational exposure can pose health risks, necessitating proper safety protocols and equipment to minimize mercury vapor inhalation and skin contact.

 

■   Environmental exposure

Mercury in the environment can accumulate from past and present human activities, or from natural sources such as geological phenomena, volcanic eruptions, and evaporation from oceans and soils. The U.S. Environmental Protection Agency (EPA) estimates that 40-75% of mercury in the American atmosphere results from human activities, with emissions from coal-fired power plants being a significant contributor. Mercury is stable in the environment and can persist for over a year, allowing local pollution to circulate globally. This circulated mercury is methylated by microorganisms in the sediments of fresh and saltwater bodies. Methylmercury then accumulates through the food chain in aquatic organisms such as plankton, herbivorous fish, carnivorous fish (e.g., tuna and sharks), and marine mammals (e.g., whales). The concentration of mercury in the tissues of top predators can be 1,800 to 80,000 times higher than in the surrounding water. Therefore, consuming large fish like tuna is considered one of the primary environmental exposure pathways to mercury.

 

■   References

The content is primarily based on Casarett and Doull’s Toxicology 9th edition and Mercury Substance report.

(https://www.hbm4eu.eu/wp-content/uploads/2022/07/Mercury_Substance-report.pdf ).

(1)   Minamata disease: https://en.wikipedia.org/wiki/Minamata_disease. Access date: 2024-03-01