Of all 104 chemical elements known to mankind today, 82 are metals. They occupy a prominent place in the lives of people in the industrial, biological and environmental fields. Modern science divides metals into heavy, light and noble. In this article we will consider a list of heavy metals and their features.
Definition of heavy metals
Initially, it was customary to call heavy metals those representatives who have an atomic mass above 50. However, the use of the term today is more often not from a chemical point of view, but depending on their impact on environmental pollution. Thus, the list of heavy metals includes those metals and metalloids (semimetals) that pollute the elements of the human biosphere (soil, water). Let's look at them.
How many items does the heavy metals list include?
To date, there is no consensus on the number of elements in the above list, since there are no general criteria regarding metals to be heavy. Nevertheless, a list of heavy metals can be formed depending on the various properties of metals and their characteristics. These include:
- Atomic weight. Based on this criterion, more than 40 elements with an atomic mass exceeding 50 amu (g / mol) belong to the named ones.
- Density. Based on this criterion, those metals in which the density is equal to or greater than the density of iron are considered heavy.
- Biological toxicity combines heavy metals that negatively affect the life of a person and living organisms. There are about 20 items in their list.
Effects on the human body
Most of these substances have a negative effect on all living organisms. Due to the significant atomic mass, they are poorly transported and accumulate in human tissues, causing various diseases. So, for the human body, cadmium, mercury and lead are recognized as the most dangerous and heaviest metals.
The list of toxic elements is grouped by hazard according to the so-called Mertz rules, according to which the most toxic metals have the smallest exposure range:
- Cadmium, mercury, thallium, lead, arsenic (the group of the most dangerous metal poisons, exceeding the permissible norms of which can lead to serious psycho-physiological disorders and even death).
- Cobalt, chromium, molybdenum, nickel, antimony, scandium, zinc.
- Barium, Manganese, Strontium, Vanadium, Tungsten
However, this does not mean that none of the elements grouped above, according to the rules of Mertz, should not be present in the human body. On the contrary, the list of heavy metals contains in it these and more than 20 elements, a small concentration of which is not only not dangerous for human life, but also necessary in metabolic processes, especially iron, copper, cobalt, molybdenum and even zinc.
Heavy metal pollution
Soil and water are elements of the biosphere contaminated by heavy metals. Most often, the culprits of this are metallurgical enterprises that process light and heavy non-ferrous metals. The list of pollutants is also replenished by waste incineration plants, car exhausts, boiler houses, chemical production, printing companies and even power plants.
Most often, toxins are: lead (automobile manufacturing), mercury (distribution example: broken thermometers and fluorescent lighting devices), cadmium (formed as a result of burning garbage). In addition, most factories in production use one or another element that can be described as heavy. The metal of the group, the list of which was given above, in the form of waste most often enters the reservoirs and further along the trophic chain reaches the person.
In addition to the technogenic factors of nature’s pollution with heavy metals, there are also natural ones — these are volcanic eruptions, in the lava of which an increased cadmium content was found.
Features of the distribution in nature of the most toxic metals
Mercury in nature is most localized in water and air. In the waters of the oceans, mercury comes from industrial discharges; mercury vapors are also formed due to the combustion of coal. Toxic compounds accumulate in living organisms, especially in seafood.
Lead has a wide distribution area. It accumulates in the mountains, and in soil, and in water, and in living organisms, and even in the air, in the form of exhaust gases from automobiles. Of course, lead also enters the environment as a result of anthropological action in the form of waste from the industrial sector and unused waste (batteries and batteries).
And the source of environmental pollution with cadmium is the wastewater of industrial enterprises, as well as natural factors: weathering of copper ores, leaching of soils, as well as the results of volcanic activity.
Scope of heavy metals
Despite the toxicity, modern industry creates a huge variety of useful products by processing heavy non-ferrous metals, the list of which includes alloys of copper, zinc, lead, tin, nickel, titanium, zirconium, molybdenum, etc.
Copper is a highly plastic material from which a variety of wires, pipes, kitchen utensils, jewelry, roofing and much more are obtained. In addition, it is widely used in engineering and shipbuilding.
Zinc has high anticorrosive properties, so the use of zinc alloys for coating metal products (the so-called galvanization) is common. Fields of application of zinc products: construction, mechanical engineering, printing (manufacturing of printing plates), rocket science, chemical industry (production of varnishes and paints) and even medicine (antiseptic agents, etc.).
Lead is easy to melt, therefore it is used as a raw material in many industries: paint and varnish, chemical, automotive (included in batteries), electronic, medical (the manufacture of protective aprons for patients during x-ray studies).