Despite the term heavy metals enjoys great popularity and lacks a solid scientific basis. It is traditionally used to indicate a series of non-essential chemical elements for man which include both metals such as, for example, cadmium, lead, mercury and metalloids, such as arsenic, in the various forms in which they occur in nature. .
Heavy metals are components of the earth's crust and are naturally present in the soil, water and atmosphere in small quantities (at trace levels). From their storage sites they can be mobilized by man due to mining and industrial processes. They can contaminate the environment and food as a result of natural phenomena, such as volcanism, or human activities such as some industrial processes, "waste incineration, car traffic, some agricultural practices.
Human beings can be exposed to so-called heavy metals through the environment (eg by inhalation) or through ingestion of food (including water). The route of dietary exposure is by far the most significant for the general population.
Heavy metals lack physiological functions and are endowed with high long-term toxicity. Their accumulation in the human organism can cause, over time, important harmful effects as they interfere with normal cellular metabolism, hindering the proper performance of vital functions.
Heavy metals are the object of attention from international authorities such as the World Health Organization (WHO). The European Food Safety Authority (EFSA) assesses the risks to human health from their intake through diet and establishes appropriate Guiding Values for Health Protection (GVV) represented, as appropriate, by a tolerable daily dose, i.e. a dose that does not produce appreciable long-term effects, or a reference value based on a dose associated with a Minor health risk, such as a 1% increase in a certain effect (Benchmark Dose Lower Confidence Limit, BMDL).
The EC regulation 1881/2006 and its subsequent amendments and additions, which establish the maximum values of some contaminants in food products, provide legal limits for cadmium, lead, mercury, inorganic arsenic and inorganic tin in some types of food.
The most important heavy metals for food are cadmium, lead, mercury, arsenic and nickel. Total National Diet Study (TDS) conducted by the "Istituto Superiore di Sanità (ISS)" recently assessed dietary exposure for the Italian population and indicated the associated risk by comparing the estimated exposure with the Guide Values for Health Protection (VGPS) defined by the Authority European Union for Food Safety (EFSA).
Cadmium in food
The chemical properties of cadmium are similar to that of zinc. In nature it is mainly associated with zinc and to a lesser extent with lead and copper, especially in sulphides. In fact, cadmium is generally obtained as a by-product of the processing of these metals.It is used in many technological applications and released into the environment following the melting of other metals, the combustion of fossil fuels, the incineration of waste and the use in agriculture of phosphate fertilizers and sewage sludge. High concentrations of the metal in the "air, water and soil are often traceable to human activities."
In the body, cadmium mimics the action of other elements with essential functions such as zinc and calcium. It crosses the biological membranes with different mechanisms and once inside the cells it remains there for a long time because it is not easily eliminated. This explains the long residence time in storage tissues such as the intestine, liver and kidney. The cadmium absorbed by the body, in fact, is eliminated very slowly and it takes between 10 and 30 years to eliminate 50% of the quantity present. Its influence on the failure to maintain the necessary values of calcium, zinc and iron in the organism determines the toxicity to the cells.
The main adverse effects of cadmium are:
- kidney toxicity, linked to its accumulation within them
- bone demineralization, both through direct action on bone tissue and following renal damage, with effects on the metabolism of calcium and vitamin D
The availability in the body's tissues and the toxicity of cadmium are influenced by a variety of individual factors, including:
- state of nutrition
- quantity of iron reserves in the body
In 2009, the European Food Safety Authority (EFSA) identified a tolerable exposure level on a weekly basis of 2.5 micrograms per kilogram of body weight (reconfirmed in 2011) and reported the need to reduce exposure in the European population. .
For the general population, with the exception of smokers, the main source of cadmium exposure is diet.The National Total Diet Study (TDS) revealed, as already reported by the EFSA for the European population as a whole, that the Italian population's exposure to cadmium must continue to be monitored with particular attention to prevent negative health effects.
The main responsible foods are:
- cereals and derived products
- greens and vegetables
- crustaceans and molluscs
Lead in food
Lead is a contaminant present everywhere in the environment due to human activities: mining, metalworking, battery production. Important sources of contamination (for example lead paints, organic compounds used in petrol) have been eliminated or reduced since the 1970s following regulatory measures aimed at reducing human exposure to this toxic element. Others measures concerned the limitation of use in drinking water pipes and food cans containing lead. Taken together, these measures resulted in a documented reduction in exposure.
More than 90% of the lead eventually entering the organism is generally contained in the skeleton, where it accumulates for a long time. During pregnancy and lactation, physiological phases of bone demineralization (ie loss of minerals, especially calcium), a part of the lead accumulated in the bone tissue is mobilized and transferred from mother to baby, first through the placenta and then with breastfeeding.
Lead exerts adverse effects on almost all systems of the body:
- blood (hematopoietic system)
In the blood (haematic) level, lead causes a reduction in the concentration of hemoglobin which can lead to anemia.However, lead's main biological target is the central nervous system, particularly in the critical phase of development. Even low levels of exposure during this phase can impair the development of the child's reasoning, memory and intellectual skills. The ingestion of dust in the house, or dirt, while playing outdoors, in contaminated areas, can represent an important source of exposure for children.
In 2010 the CONTAM Panel of the European Food Safety Authority (EFSA) identified the critical adverse effects on which to base the risk assessment:
- developmental neurotoxicity in young children, BMDL (minimum dose associated with a minor health risk, for example the "1% increase in a certain effect) equal to 0.50 micrograms per kilo of body weight per day
- nephrotoxicity in adults, BMDL equal to 0.63 micrograms per pound of body weight per day
- cardiovascular effects, BMDL equal to 1.50 micrograms per kilo of body weight per day
For the general population, the main source of exposure to lead is represented by the diet: as also indicated by the national Total Diet Study (TDS), the most important foods are beverages, such as tea and coffee, cereals and derivatives, vegetables and vegetables; among foods of animal origin, crustaceans and molluscs. However, the TDS revealed that the exposure to lead of the Italian population, even in the most vulnerable group (children up to 7 years of age), is limited.
Mercury in food
Mercury is released into the environment both from natural sources and as a result of human activities. The mercury present in the aquatic environment, both marine and freshwater, undergoes the chemical phenomenon called methylation. The methylmercury that is formed is subject to accumulate inside the organism.
In fish it binds strongly to the muscle and, therefore, its quantity increases both with the increase in muscle mass and with the lengthening of the exposure time. Predatory fish, especially those of large size and capable of living longer, are the organisms that reach concentrations of methylmercury higher in their muscle tissue (read the Hoax). Similarly, very high levels are found in large marine mammals.
The methylmercury ingested it is absorbed much more effectively than inorganic mercury and is able to enter the hair follicles, to cross the placental, blood-brain and blood-liquor barrier (barriers that protect the brain from the entry of toxic agents), with the result to accumulate in the hair, fetus and brain. The most important critical effect of the methylmercury is the toxicity to the nervous system, in particular the damage to the neurological development of the fetus.
The fetus is therefore the organism most sensitive to damage from methylmercury and exposure to the metal before birth through the mother's consumption of contaminated fish is particularly at risk.
Fish and other seafood are the only sources of exposure to methylmercury for the general population. To avoid hiring methylmercury in pregnancy (and not only) and being able to continue to eat fish, the European Food Safety Authority (EFSA) calls for reducing the consumption, especially in pregnancy and early childhood, of large predators such as swordfish, tuna, pike, sharaloids (such as dogfish) and to replace it with other fish, such as blue fish or sea bream, which contain much lower concentrations of methylmercury.
In 2010, EFSA's CONTAM Panel identified a tolerable weekly exposure level of 1.3 micrograms per kilogram of body weight (μg / kg bw). The national Total Diet Study (TDS) revealed that exposure to methylmercury of the Italian population must continue to be monitored, in particular to protect the health of children.
Arsenic in food
Arsenic is a nonmetal and its chemistry, in many respects, is similar to that of two essential elements, phosphorus and nitrogen. This aspect is considered important to explain its singular abundance in marine organisms. In fish, crustaceans and molluscs arsenic is present in the form of organic arsenic compounds which present a negligible health risk compared to the much more formidable inorganic arsenic.
L"inorganic arsenic (arsenite or trivalent arsenic and arsenate or pentavalent arsenic) is the chemical species of arsenic on which the human health risk assessment is based. It is a human carcinogen, that is, it can increase the risk of appearance of tumors if it is introduced orally for a long time and has high short and long-term toxicity (acute and chronic), with effects on numerous organs and systems:
- respiratory system
- cardiovascular system
- immune system
- genitourinary system
- reproductive system
- gastrointestinal system
- nervous system
Fish is not an important source of inorganic arsenic, shellfish and crustaceans contain a little more. On the other hand, inorganic arsenic is the prevalent and sometimes exclusive form in various foods of plant origin; apart from "niche" products (for example, some edible algae), other foods attract more attention, also by virtue of high consumption, in particular:
- rice and products derived from it, due to the strong ability to accumulate arsenic linked to the particular environment in which the plant is grown
- cereals, especially wheat
Rice is, however, the food with the highest content.
In some aquifers the inorganic arsenic reaches levels higher than those normally found: these contaminations of natural origin can cause a significant increase in human exposure and drinking water for food use (cooking) can, in these cases, become the main source of exposure to inorganic arsenic. The World Health Organization (WHO) has established a maximum tolerable dose for arsenic contained in drinking water which coincides with the legal limit in force in Europe equal to 10 micrograms / liter (read the Bufala).
In 2009 the CONTAM Panel of the European Food Safety Authority (EFSA) identified BMDL (minimum dose associated with a minor health risk) for the effects that, based on solid scientific evidence, are believed to be associated to chronic oral exposure to inorganic arsenic, ie tumors of the bladder, lungs, skin and skin lesions. Considering the uncertainties in the available data, the BMDLs are in the range of 0.3-8 micrograms per kilogram of body weight per day (μg / kg bw / day).
The National Total Diet Study (TDS) revealed that the main sources of exposure in Italy are:
- cereals and derived products
- alcohol-free drinks
- greens and vegetables
According to the results of the TDS, the exposure to inorganic arsenic of the Italian population is limited. However, it should be remembered that exposure can double in areas with certain geological characteristics (eg volcanic soils), if the presence of arsenic in drinking water is not controlled with adequate purification plants.
Nickel in food
Nickel is a transition metal present in the environment in inorganic form and widely used for the manufacture of various types of steels and other alloys.
It is, therefore, contained in a variety of commonly used objects:
- articles of costume jewelery
- jewelry store
- metal accessories for clothing
- metal tools
Nickel, like the other elements considered, is not essential for humans. In 2015 the CONTAM Panel of the European Food Safety Authority (EFSA) indicated, on the basis of studies on rodents, the toxic effects on reproduction and pregnancy as critical effects of chronic nickel exposure and identified a tolerable daily dose of 2.8 micrograms per kilo of body weight per day (μg / kg bw / day).
However, nickel, if taken orally, also has the ability to cause allergic reactions through the skin in people already sensitized; this effect can also occur for an acute (short-term) intake.
Nickel allergy is the most common type of metal allergy found in the general population, with a frequency of around 15%. It is allergic contact dermatitis (ACD); however, some people who suffer from it can develop a systemic nickel allergy syndrome (SNAS), ie an "allergy that is not limited to the point of contact with nickel but extends to other sites and organs in the body. The disorders are mainly gastrointestinal in nature. The risk of allergies is always difficult to manage. quantify; however, according to EFSA's assessment this risk is considered low if the acute intake of nickel does not exceed 11 micrograms per kilo of body weight per day (μg / kg bw / day).
Sufferers must limit the consumption of plant-based foods rich in nickel such as:
- dried fruit
- crustaceans and molluscs
Another important preventive measure is to avoid drinking tap water that has had a long stay in the pipes because, in some circumstances, it can reach particularly high concentrations of nickel.
The use of crockery containing nickel, especially when cooking foods with higher acidity, can make a contribution to the intake of nickel, even if it is difficult to quantify.
The National Total Diet Study (TDS) indicated that nickel contamination of food supply chains must be kept under control to prevent possible chronic health effects, especially in children.
The main contributions to the exhibition come from:
- cereals and derived products
- greens and vegetables
- water and soft drinks
It should be remembered that meals including foods particularly rich in nickel can cause sudden and intense reactions in people with specific hypersensitivity.
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