Mercury bio-accumulates in human brain, the food chain and the environment and is highly toxic. Pregnant-to-be woman, the elderly and children, especially developing foetuses and infants, are particularly vulnerable to mercury. Here we demonstrate that mercury exposure occurs through multiple routes and that individuals can reduce significant exposure from sources like artisanal gold mining, fish consumption and mercury-based dental fillings.
Mercury related health effects, due to acute and low-level chronic exposure and demonstrated through evidence-based research, is interspersed throughout this report and indicated by the red/white cross.
Last updated: February 2020
Cover image Photo: Canthigaster valentini (fish species) by Jenny Huang
Introduction
SYNONYMS: Hg(2+) | Hg2+ | Mercuric ion | Mercury ion | Mercury(2+) | Mercury(2+) ion | Mercury(II) | Mercury(II) cation | Mercury(II) ion | Metallic mercury | Quicksilver
Hence the atomic symbol for Mercury is Hg, which comes from Greek name, Hydrargyrum, meaning “liquid silver”.
The most devastating tragedies related to Mercury (Hg) toxicity in recent history include Minamata Bay and Niagata, Japan in the 1950s, and Iraq in the 1970s.
Hair has been used in many studies as a bioindicator of mercury exposure for human populations. At the time of hair formation, mercury from the blood capillaries penetrates into the hair follicles. As hair grows approximately 1 cm each month, mercury exposure over time is recapitulated in hair strands. Mercury levels in hair closest to the scalp reflect the most recent exposure, while those farthest from the scalp are representative of previous blood concentrations.
Sequential analyses of hair mercury have been useful for identifying seasonal variations over time in hair mercury content, which may be the result of seasonal differences in bioavailability of fish and differential consumption of piscivorous and herbivorous fish species. Knowledge of the relation between fish-eating practices and hair mercury levels is particularly important for adequate mitigation strategies.
Mercury occurs in deposits throughout the earth, often as cinnabar (mercuric sulphide) which, when ground forms the red pigment, vermilion.
Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, mercury switches, mercury relays, though mercury in thermometers and sphygmomanometers is being phased out.
Used in fluorescent lighting because electricity passed through mercury vapor in a fluorescent lamp produces short-wave ultraviolet light, which then causes the phosphor in the tube to fluoresce, making visible light.
Mercury binds to both inorganic elements (chloride, selenium, oxygen and many others) and organic (containing carbon like Methyl compounds). Poisoning can result from exposure to water-soluble forms of mercury such as mercuric chloride or methylmercury, by inhalation of mercury vapor, or by ingesting any form of mercury.
Hg is a liquid at room temperature, known as metallic or elemental Mercury and is used in dental amalgams and various domestic and industrial applications.
Unfortunately, at room temperature, metallic or elemental Mercury gives off a gaseous form of Hg that is lipophilic (attracted to fatty tissue) and readily absorbed upon inhalation and then easily able to cross the placenta or the blood-brain barriers.
To make matters worse, once Mercury is in a human cell, it is rapidly oxidized by a catalase enzyme into inorganic Mercury (Hg2+), which in the neuron cells of the brain can be retained for years. Organic Mercury compounds like Methylmercury (MeHg) from fish or Ethyl mercury from the compound Thimerosal found in some vaccines (especially flu-vaccines) and Phenyl mercury can, however, penetrate into the blood brain barrier whereupon they are converted to inorganic Hg and then trapped in the brain or nervous tissue for years.
Adding fuel to this fire of body mercury bio-accumulation, is the realisation that individuals can be exposed to multiple sources of mercury at once. Fish consumption, dental amalgams and occasional vaccine shots combined with other exposures outlined below, make Mercury a toxic force to be acknowledged.
Ref: Toxno Mercury Profile
and Additional references used on Toxno
and Mercury exposure and health impacts in dental personnel
and Mercury (the element) on Wikipedia
Methylmercury in Fish and
baseline Mercury Hair-test values
Note that 1 μg = 1 microgram and 1 mg = 1 milligram. Additionally, 1 μg/g is 1 μg mercury per 1 gram of hair. Importantly, 1 μg/g is the same as 1 mg/kg which is the same as “ppm” (parts per million).
Additionally, Mercury is represented as the symbol Hg and MeHg is MethylMercury
The recommended limits for hair-mercury concentrations vary. Even the lowest official limit of 1.0 μg/g hair used by the US Environmental Protection Agency does not take into account the impact of exposure misclassification nor genetic predisposition to methylmercury toxicity. An updated calculation suggests a more protective exposure limit of about 0.58 μg/g hair.
At Toxtest we use a level of 0.30 μg/g of hair as our sample population average level and indicate that 90% of our sample population have mercury hair levels ranging from 0 to 1.1 μg/g of hair.
Ref: Public health benefits of hair-mercury analysis and dietary advice in lowering methylmercury exposure in pregnant women and
Use of advanced cluster analysis to characterize fish consumption patterns and methylmercury dietary exposures from fish and other sea foods among pregnant women
In a recent statement, an international society of gynaecologists and obstetricians recommended that health professionals make environmental public health part of health care. Among the environmental chemicals that may adversely affect foetal development, methylmercury is of global public health concern. Methylmercury bioaccumulates in the muscle tissues of large, long-lived predatory fish such as swordfish, shark and tuna; seafood is therefore a significant source of exposure in humans. This is also a concern because on the other hand fish, molluscs and crustaceans provide considerable amounts of easily digestible protein of high biological value and, especially in the case of marine species, can constitute a good source of iodine, selenium and vitamins A and D and essential omega 3 fatty acids.
The ultimate goal of risk analysis in food science is to guide decision making to reduce the exposure to undesirable substances and optimize the coverage of nutrient intakes according to nutritional recommendations. Based on a sample of French pregnant women, a study shows that a global increase in fish consumption during pregnancy above the generally recommended amounts leads to Methylmercury exposure exceeding the toxicological limits, thereby questioning the overall (beneficial) effects that can be expected. Although total knowledge of consumer behavior is incomplete, the dietary advisories should take into account that different clusters exist, like conception age woman, infants, children and the elderly and that different strategies and messages may be needed. This underlines the complexity of communicated health benefits and also points to the difficulty that consumers face when a detailed risk/benefit information is provided.
Increased exposure to methylmercury can cause developmental neurotoxicity and associated losses of intelligence quotient (IQ) points. The societal costs in the EU from an annual loss of more than 600,000 IQ points have been calculated to be about €8–9 billion per year.
Hair heavy metal measurements of individual exposure levels is used to promote low-mercury seafood consumption among conception age women. Methylmercury is a predominant mercury compound in hair and Hair-mercury analysis is a non-invasive and inexpensive method making it also useful for infants and children. Hair-mercury concentrations correlates well with the frequency of seafood consumption.
Ref: Public health benefits of hair-mercury analysis and dietary advice in lowering methylmercury exposure in pregnant women and
Use of advanced cluster analysis to characterize fish consumption patterns and methylmercury dietary exposures from fish and other sea foods among pregnant women
Click on Images or Tables to make them larger
Table shows amounts of Methylmercury in different Fish species.
Analysis of mercury in hair specimens can supply useful information about exposure to organic mercury compounds such as methylmercury, particularly to help in reconstructing patterns of prior or seasonal exposure from fish consumption. However, it is important to consider all possible exposures to any forms of mercury when hair mercury levels are elevated. This report is an up-to-date collation of known mercury exposures at this point in time.
Full evaluation of mercury exposure in an individual patient ideally includes the presenting history, physical examination, consideration of the differential diagnosis, and when occupational exposures are suspected, mercury analysis of blood and urine specimens.
Hair from the initial 0.5 cm adjacent to the scalp represents on average 1-3 wk before collection. Longer hair length collected between 6-11cm has been shown to also detect inorganic mercury in addition to methylmercury. Literature reports describe hair mercury levels as high as 2400 μg/g. Hair mercury level is usually less than 1 μg/g in individuals who do not eat fish but may be greater than 30 μg/g in those who frequently consume fish with high mercury content. Hair mercury level is often not correlated with blood mercury concentration or symptoms of mercury toxicity, and hair can also be contaminated by mercury from outside sources.
REF: Interpreting Hair Mercury Levels in Individual Patients
Table demonstrates correlation between Hair-Mercury concentrations and individual diet/exposure/symptoms.
Dentistry and Mercury exposure
When people chew or grind their teeth while sleeping, dental amalgams emit Mercury vapour, which upon inhalation is absorbed and moved into the blood stream.
The World Health Organization (WHO) has recommended phasing out dental amalgams (the silvery filling) and change to alternative materials. Occupational dental personnel who work with amalgams are at risk of exposure to undesired metallic Mercury levels.
Mercury exposure for dentists has been associated with reproductive disturbances and allergies and with neurological and/or cognitive problems, fibromyalgia, and chronic fatigue syndrome. Mercury has a complicated metabolism with different organs showing accumulation and adverse effects to differing degrees.
Norway and Sweden have banned the use of amalgam. Japan and other EU countries are considering ban on amalgams. In France, Finland, Austria, Germany, and Canada, the use of dental amalgam have purposely been reduced for children, pregnant women, and subjects with kidney problems.
Several studies have shown that dental personnel have higher Hg concentrations in urine than the average population and that dental nurses had higher Hg values than dentists. After occupational exposure to Hg vapour even at low doses, inorganic Mercury is found in the brain of dental personnel with autopsys’ undertaken later revealing significant inorganic Mercury deposits remaining in the brain.
REF: Mercury exposure and health impacts in dental personnel
Mercury, Food and Gut Microbes
So far we have seeen that Mercury can exist in various forms (Elemental/Metallic, Inorganic and Organic) and that human cellular enzymes can facilitate the inter-changing between these forms. All forms are neuro-toxic with Methylmercury (MeHg) able to cross the blood-brain-barrier. The general public may be exposed to MeHg through seafood, freshwater food and/or rice consumption.
In addition, MeHg can be formed when exposed to inorganic Hg by the gut microbiota (bacteria living in the gut) in aquatic organisms, terrestrial invertebrates, and mammals. Equally these intestinal microbes were capable of the demethylation of MeHg. Sulfate reducing bacteria and methanogen gut bacteria can both methylate inorganic Hg and demethylate MeHg. Iron reducing bacteria and fermentative Firmicutes gut microbes can also form MeHg.
However non-bacterial photo-chemical processes are mostly responsible for the formation of MeHg in water and air and other niches in the environment with methyl group providers like methyl iodide, methylbenzene, and dimethyl sulphide reacting with Mercury.
“Fish, both marine and freshwater fish, has been found to be the major source of MeHg for the general public. The chemical form of Hg in edible muscle of both marine and freshwater fish is nearly all MeHg although the greater part of Hg in water is in the inorganic form. It was generally believed that the MeHg in fish were from their diet (through trophic transfer) and water while MeHg was formed in the sediments and water columns. However, it has been found that microbes that are known to be able to form MeHg also existed in intestine of investigated fish like grass carp, gold fish, and rainbow trout.” This process has also been seen in rats. This is important when considering the risk assessment for inorganic Hg intake.
A recent genetic discovery found that gut bacteria with a two-gene cluster, hgcA and hgcB, could convert Hg to MeHg while those bacteria without these genes could not.
The intestinal methylation of inorganic mercury to MeHg should always be kept in mind for risk assessment in people exposed to inorganic Hg contaminated foodstuffs, especially for those people living near areas with inorganic Hg contamination. Besides, the further methylation of MeHg to dimethylmercury (Me2Hg) is also possible with Me2Hg even more dangerous than MeHg.
Additional Mercury Compounds on Toxno with synonym details (in grey) and links to exposure and health information
Some substances are medications. Clicking on link takes you to side effects information
Toxno, Toxtest and Environmental Analysis Laboratory (EAL) at Southern Cross University in Lismore, NSW, Australia, collaborate to provide innovation and an Australian first in hair, water, soil/compost or dust testing of 32 heavy metals and minerals. Our Hair analysis (also called Hair Tissue Mineral Analysis (HMA or HTMA)) is AU$98. Order forms can be downloaded below.
All results are published (de-identified) online and updated regularly as new health or exposure route information becomes available for each metal/mineral. All results are dynamic, contain instructions, have full support and contain clickable links to current health and exposure information for each metal/mineral.
Hair results are live and use innovative moving graphical visualisations, while our water and soil analyses concurrently visualise your results based on human, animal and agricultural guidelines - a true Australian innovation.
Toxno, Toxtest and Environmental Analysis Laboratory (EAL) at Southern Cross University in Lismore, NSW, Australia, collaborate to provide innovation and an Australian first in hair, water, soil/compost or dust testing of 32 heavy metals and minerals. Our Hair or Water analysis is AU$98. Order forms can be downloaded below.
All results are published (de-identified) online and updated regularly as new health or exposure route information becomes available for each metal/mineral. All results are dynamic, contain instructions, have full support and contain clickable links to current health and exposure information for each metal/mineral.
Hair results are live and use innovative moving graphical visualisations, while our water and soil analyses concurrently visualise your results based on human, animal and agricultural guidelines - a true Australian innovation. See a large list of example Hair, Water, Soil and Dust results.
For the first time in Australia, human and animal hair testing is available to the public using the absolute latest Perkin Elmer Inductively Coupled Plasma–Mass Spectrometer at Environmental Analysis Laboratories in Lismore, Australia. Instrument detection limits are at or below the single part per trillion (ppt) level for many of substances tested. Because this test and the expertise is now available in Australia, we can keep the cost under $100. Doctors, veterinarians, health practitioners and trainers can utilise these tests for their clients.
