Methyl Mercury

Mercury exists in various forms in the environment, either naturally-occurring or deposited as an industrial pollutant. There are three forms of mercury that can cause severe health problems in humans: elemental (or liquid) mercury, inorganic mercury salts, and organic mercury. The organic mercury compounds, dimethylmercury and methyl mercury, are the most toxic forms of mercury, and consumption of contaminated fish and wildlife comprise the most significant source of human exposure to methyl mercury [1].

Methyl mercury (CH3Hg+) is a known neurotoxin that has a dose-dependent effect on the human central nervous system (CNS). Exposure to large amounts of methyl mercury can cause serious neurological damage in adults and especially in developing embryos [2]. Neurological symptoms resulting from large amounts of methyl mercury include “numbness or pain in certain parts of your skin, uncontrollable shake or tremor, inability to walk well, blindness and double vision, and/or memory problems [3].” More commonly, people are exposed to only low levels of methyl mercury. However, even exposure to small amounts of methyl mercury can have serious, albeit delayed, effects such as immune system repression, neurodevelopmental delays in children, and compromised cardiovascular health in adults [4].

The formation of methyl mercury takes place in aquatic environments when inorganic mercury undergoes a process called methylation. Mercury is deposited in surface waters from both industrial and naturally-occurring atmospheric sources where it can attach to particles suspended in the water. These particles eventually settle into the sediment where the mercury can be “methylated” during a complex chemical process facilitated by anaerobic organisms, thus forming methyl mercury. Many factors dictate the occurrence rate of the methylation process. For example, studies have shown that water with a lower pH and higher dissolved organic carbon (DOC) content generally results in higher levels of methylation [1].

Methyl mercury is easily absorbed into the tissue of animals, but is not easily eliminated. Therefore, methyl mercury bioaccumulates in organisms higher in the aquatic food chain, with predators containing the largest concentrations of methyl mercury. Methyl mercury accumulates in muscle tissue more than in skin and fat, indicating that it cannot be filleted or cooked out like PCBs, dioxins, and other organic contaminants [1]. The number of state advisories against fish consumption is steadily increasing, with advisories for methyl mercury now accounting for more than three-quarters of all fish consumption advisories in the United States [1]. Even though the government has started putting regulations on the amount of industrial mercury pollution, historical deposits of mercury still exist and, therefore, methyl mercury poisoning remains an issue.

The Chicagoland Division of Microbac Laboratories, Inc. is currently providing analytical testing services for methyl mercury (EPA method 1630) in fish tissue, soil, and aqueous matrices.  In addition to methyl mercury, Microbac Laboratories can also provide analysis for total and low level mercury (EPA method 1631). Microbac can also provide the field services necessary for sample collection. For more information regarding testing services for methyl mercury, please contact



USGS. “Mercury in the Environment.” U.S. Geological Survey. 2009. 27 July 2010.

Davidson PW, Myers GJ, Weiss B. Mercury Exposure and Child Development Outcomes. Pediatrics. 2004;113(suppl 4):1023-9

Heller JL. "Mercury." Medline Plus. 2009. 27 July 2010.

Mergler D, Anderson HA, Chan LHM, Mahaffey KR, Murray M, Sakamoto M, et al. Methylmercury exposure and health effects in humans: a worldwide concern. Ambio. 2007;36:3-11.


Authored by Calli Merkel, PhD, Microbac Laboratories, Inc.