The content of lead in magmatic rocks makes it possible to classify it as a rare metal. It concentrates in sulphide rocks, which are found in many places in the world. Lead is easily isolated by smelting from ore. In the natural state, it is found mainly in the form of galena (PbS).
Lead, contained in the earth’s crust, can be washed out under the influence of atmospheric processes, moving gradually into the oceans. The Pb2 + ions are rather unstable, and the lead content in the ionic form is only 10 -8%. However, it accumulates in oceanic sediments in the form of sulfites or sulphates. In fresh water, the lead content is much higher and can reach 2 × 10 -6%, and in the soil it is about the same amount as in the earth’s crust (1.5 × 10 -3%) due to the instability of this element in the geochemical cycle.
Lead ores contain 2-20% lead. The concentrate obtained by the flotation method contains 60-80% Pb. It is heated to remove sulfur and lead is smelted. Such primary processes are large-scale. If waste is used to produce lead, the smelting processes are called secondary. The annual world consumption of lead is more than 3 million tons, of which 40% are used for the production of storage batteries, 20% for the production of alkyl lead, additives for gasoline, 12% are used in construction, and 28% for other purposes.
Annually in the world as a result of the influence of atmospheric processes about 180 thousand tons of lead migrate. During extraction and processing of lead ores, more than 20% of lead is lost. Even at these stages, the release of lead into the habitat is equal to its quantity, which enters the environment as a result of exposure to atmospheric processes on igneous rocks.
The most serious source of pollution of the living environment of lead organisms are the exhausts of automobile engines. The tetmethyl- or tetraethylsilane-antideadonator is added to the majority of gasoline, starting in 1923, in an amount of about 80 mg / l. When the car moves from 25 to 75% of this lead, depending on traffic conditions, is released into the atmosphere. The bulk of it is deposited on the ground, but a noticeable part remains in the air.
Lead dust not only covers roadside roads and soil in and around industrial cities, it was found in the ice of Northern Greenland, and in 1756 the lead content in the ice was 20 μg / t, in 1860 it was 50 μg / t, and In 1965 it was 210 μg / t.
Active sources of lead pollution are power stations and household furnaces operating on coal.
Sources of lead contamination in everyday life can be pottery covered with glaze; Lead, contained in the pigments.
Lead is not a vital element. It is toxic and belongs to the first class of danger. Its inorganic compounds disrupt the metabolism and are inhibitors of enzymes (like most heavy metals). One of the most insidious consequences of the action of inorganic lead compounds is its ability to replace calcium in bones and to be a constant source of poisoning for a long time. The biological half-life of lead in bones is about 10 years. The amount of lead accumulated in the bones increases with age, and at 30-40 years, in individuals who are not involved in lead contamination, 80-200 mg.
Organic lead compounds are considered even more toxic than inorganic compounds.
The main source from which lead enters the human body is food, along with these important roles are played by inhaled air, and in children – and swallowed lead-containing dust and paints. Inhalted dust is about 30-35% retained in the lungs, a significant proportion of it is absorbed by the flow of blood. Absorption in the gastrointestinal tract is 5-10% in general, in children 50%. Deficiency of calcium and vitamin D increases the absorption of lead.
Acute lead poisonings are rare. Their symptoms are salivation, vomiting, intestinal colic, acute form of kidney failure, brain damage. In severe cases – death in a few days.
The early symptoms of lead poisoning are manifested in the form of increased excitability, depression and irritability. When lead compounds are poisoned with organic compounds, its elevated content is detected in the blood.
Due to the global pollution of the environment with lead, it has become the ubiquitous component of any food and feed. Plant products generally contain more lead than animals.