Content

Introduction

Introduction

Mercury (whose chemical symbol is Hg) is a natural component of the Earth's surface (earth's crust).

Despite being released into the environment by rocks, volcanoes and forest fires, its presence derives mainly from some activities carried out by man, including the use of coal to produce energy and for domestic use (heating and cooking), from certain industrial processes and mining activities for the extraction of mercury, gold and other metals.

Mercury exists in nature in different forms:

  • metallic mercury
  • inorganic mercury (or mercury salts such as mercuric sulfate known as the red-colored cinnabar mineral: widely used commercial paint dye)
  • organic mercury (including methylmercury and mercurials, once used as disinfectants)

Metallic mercury, at room temperature, is a shiny, silvery-white liquid, very mobile (commonly known in the past as'quicksilver') which, when exposed to air, joins in small drops and evaporates.

Thanks to its properties, in the past it has been used in instruments to measure atmospheric pressure (barometers), environmental or body pressure (thermometers) and that of fluids and gases (manometers).

Metallic mercury has also been used in batteries, in some types of light bulbs and in the material used by dentists (dental amalgam) for the fillings of teeth treated by caries.

Once released into the environment (eg water), metallic and inorganic mercury can be transformed by bacteria and other organisms into methylmercury which accumulates in fish, crustaceans and molluscs. In this way, the content of methylmercury in the body is higher than that present in water. The level of methylmercury increases in the food chain (biomagnification): in other words, predatory fish have higher levels of methylmercury contamination because they feed on many smaller fish which in turn have fed on small contaminated crustaceans (read the Buffalo ).

Fortunately, the majority of the uses of mercury described are currently very low or prohibited, and global emissions have also fallen significantly in recent years. However, there are still some countries (such as China) where the combustion of wood and coal is still very widespread today (about 2 thousand tons, equivalent to 30% of the total annual emissions of mercury in the air).

Sources of exposure

Sources of exposure

Mercury exposure can be both occupational (essentially inorganic and metallic mercury) and environmental.

For the general population, mercury exposure occurs through:

  • the diet, with the consumption of fish, crustaceans and molluscs (essentially in the form of methylmercury and, only in small part, of inorganic mercury). In January 2015, the European Food Safety Authority (EFSA) published a document describing the most effective way to obtain the health benefits associated with the consumption of fish and seafood, by reducing at the same time the risks deriving from excessive exposure to methylmercury. It is advisable to consume fish 2-3 times a week, varying the species and limiting the consumption of those that could have a higher content of methylmercury such as large predators (sharks, swordfish, pike, tuna and hake). Particular attention must be paid to the population groups most vulnerable to the effects of mercury such as children and pregnant women who could expose the fetus to the effects of methylmercury. However, this does not mean avoiding eating fish, which is an important food for both the growth and development of the baby during gestation and early childhood. actions were also shared by the two American Agencies dealing with food and environmental safety: the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA)
  • the environment, for the release into the air and water of mercury from production plants, incinerators, waste from dental clinics or the combustion of coal and wood used for the production of energy and heat
  • accidental breakage of glass or metal products which contain it (such as mercury lamps, thermometers or other measuring instruments). In this case, exposure to metallic mercury occurs by evaporation of the leaked mercury. There is no contact, and therefore there is no risk, until the container breaks
  • release of mercury from dental amalgam, resulting in exposure of both the person undergoing dental treatment and the staff of dental offices
  • use of disinfectants (e.g. mercurochrome) or medicines containing thimerosal (organic compound of mercury) as a preservative
Effects on health

Effects on health

The different forms of mercury have different health effects.

The factors that determine the type and severity of the consequences are: the form of mercury; the amount, duration and route of exposure (inhalation, ingestion, skin contact); the age of the exposed individual (the developmental stages of the fetus and child are, for example, the most critical).

Mercury is considered by the World Health Organization (WHO) to be one of the 10 chemical substances (or groups of substances) that cause greatest concern about the effects it can produce in the exposed population.

Metallic mercury is poorly absorbed in the intestine, but reaches the lung through breathing and, once absorbed, can pass the barrier that protects the brain (blood brain barrier) and the placenta.

The absorption of inorganic mercury through the digestive system and the skin depends on the solubility of the salts; methylmercury is readily absorbed after taking it by mouth (oral). Metallic mercury and methylmercury have likemain target the central and peripheral nervous system, while the inorganic salts of mercury are corrosive to eyes and skin and, if ingested, have effects on the gastrointestinal system and can cause kidney damage.

Sudden and rapid poisoning (acute form) associated with inhalation of high quantities of mercury vapors, manifests itself with disorders (symptoms) such as:

  • tracheitis 
  • bronchitis
  • cough and hyperthermia  
  • progressive nervous disorders (tremors and loss of sensation) which can lead to the death of the affected person

If, on the other hand, large quantities of mercury salts are ingested, the symptoms (symptoms) that appear are:

  • He retched
  • diarrhea
  • abdominal colic with bleeding
  • effects on the circulatory system (shock)
  • effects on the respiratory system (interstitial pneumonia)
  • effects on the kidneys

To prevent these effects, the EFSA (European Food Safety Authority) has established a tolerable weekly dose of inorganic mercury of 4 mg / kg body weight.

Ingestion of high quantities of methylmercury causes:

  • paralysis to the hands and feet
  • general muscle weakness  
  • damage to sight, hearing and difficulty in articulating words, with possible aggravations that can cause mental disorder, paralysis and coma, in the most serious cases

The most frequent effects are, however, associated with repeated exposures to generally low doses, which do not immediately cause the disorders (symptoms) described above.

In workers, exposure to mercury is a cause of occupational disease. The main target is the nervous system but effects on the kidneys, lungs, heart and immune system are also reported. Disorders (symptoms) such as memory loss, tremors, ache head, insomnia, cognitive dysfunction and movement dysfunction have been reported in workers exposed for several years to about 0.020 milligrams per cubic meter (mg / m3) of metallic mercury bearing in mind that, for mercury and its compounds, the maximum tolerable concentration in the air it is equal to 0.1 mg / m3.

Repeated exposure to methylmercury, mainly through diet, leads to neurological effects.

The European Food Safety Authority (EFSA) has established a tolerable weekly intake of methylmercury equal to 1.3 micrograms per kilo of body weight. Obviously those who, like fishermen and their families, consume usually fish and other fishery products, especially in some geographical areas (such as Brazil, Canada, China, and Greenland), have a high exposure and are, therefore, more subject to the effects of methylmercury.

Children are the most vulnerable because methylmercury alters the normal development of the brain causing learning and thinking processing difficulties (mental retardation), memory disorders, attention disorders, language disorders, and motor and visual dysfunctions.

A critical stage is that of pregnancy because the fetus can be exposed to mercury if the mother consumes contaminated fish.

The International Agency for Resercearch on Cancer (IARC) has classified methylmercury as a possible human carcinogen (category 2B).

How to determine mercury exposure

How to determine mercury exposure

In addition to a careful observation of the disturbances (symptoms) that may occur, the safest and most sensitive way to identify (diagnose) mercury poisoning is to measure its presence in the blood.

Due to the diffusion of this metal in the environment and the presence in some foods that are normally consumed, every person has measurable levels of mercury in the blood. This does not necessarily mean that there are diseases but only that there has been exposure to mercury The appearance of the effects in fact depends on the presence of more or less high levels of mercury in the organism; values ​​between 5 and 15 micrograms of mercury per liter of blood (in both children and adults) are warning signs that generally require further health studies.

Mercury exposure can also be identified through its determination in urine or hair.

Prevention and control

Prevention and control

Mercury poisoning can be prevented through careful control of exposure levels.

The importance of the effects of mercury on health has led to the adoption of a series of laws in various sectors to prohibit or limit the presence of this metal in the environment and, consequently, in the food chain.

In 2013 the governments of many countries agreed on the International Convention of Minamata, which takes its name from the Japanese city struck in the 1950s by a serious environmental and health disaster caused by heavy industrial pollution by mercury (released by a chemical industry from 1932 to 1968 in the waste water that ended up in the sea, in the bay of Minamata). The Convention, also signed by "Italy, provides for controls, reductions or prohibitions (from 2020) on the use of mercury in many products (for example in thermometers) and in industrial processes in which mercury is used, released or emitted.

In the meantime, small but important precautions can be used to safeguard human and environmental health, such as the correct disposal of waste containing mercury (such as thermometers and fluorescent lamps), move away and ventilate the premises in case of accidental breakage of products containing mercury. , observe the indications on the correct consumption of fish.

In the case of dental amalgam, according to the scientific committee of the European Commission SCENIHR, there are no indications that any mercury released causes health problems. Nor is it advisable, for the sole purpose of decreasing exposure, to remove the old dental fillings, unless an allergic reaction has occurred, or your doctor deems it necessary. Removal, in fact, would lead to a momentary increase in exposure, greater than keeping the filling intact.

The World Health Organization (WHO) in 2012 also established the safety of thimerosal (organic compound of mercury) contained in vaccines as a preservative.

The levels of mercury in food are established by the EC Regulation n.1881 / 2006 and strict controls are carried out at the border and during all the phases preceding the marketing.

Bibliography

Bibliography

Ministry of the Environment, Land and Sea Protection. Mercury pollution

Ministry of the Environment, Land and Sea Protection. Minamata Convention on mercury

Encyclopedia Treccani. Mercury

European Food Safety Authority (EFSA). Metals as contaminants in food

European Food Safety Authority (EFSA). EFSA provides risk assessment on mercury in fish: precautionary advice given to vulnerable groups (English)

World Health Organization (WHO). Mercury and health (English)

US Environmental Protection Agency (EPA). Basic information about mercury (English)

Agency for Toxic Substances & Disease Registry (ATSDR). Mercury ToxFAQs (English)

In-depth link

In-depth link

US Environmental Protection Agency (EPA). Mercury (English)

European Food Safety Authority (EFSA). Scientific opinion on the risk for public health related to the presence of mercury and methylmercury in food (English)

European Commission, Health and Food Safety. Final opinion on dental amalgam (English)

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