Pollution of the environment by mercury

In addition to lead, mercury has been studied most thoroughly in comparison with other trace elements.

Mercury is extremely poorly distributed in the earth’s crust (-0.1 x 10-4%), however it is convenient for extraction, since it is concentrated in sulphide residues, for example, in the form of cinnabar (HgS). In this form, mercury is relatively harmless, but atmospheric processes, volcanic and human activities have led to the accumulation of about 50 million tons of this metal in the world’s oceans. Natural removal of mercury into the ocean as a result of erosion of 5000 tons / year, another 5000 tons / year of mercury is carried out as a result of human activities.

Initially, mercury enters the ocean in the form of Hg2 +, then it interacts with organic substances and, with the help of anaerobic organisms, passes into toxic substances methylmercury (CH3Hg) + and dimethylmercury (CH3-Hg-CH3).

Mercury is present not only in the hydrosphere, but also in the atmosphere, since it has a relatively high vapor pressure. The natural content of mercury is ~ 0.003-0.009 μg / m3.

Mercury is characterized by a short residence time in water and quickly transforms into deposits in the form of compounds with organic substances located in them. Since mercury is adsorbed by sediments, it can slowly release and dissolve in water, which leads to the formation of a source of chronic pollution that lasts for a long time after the original source of pollution disappears.

World production of mercury is currently more than 10,000 tons per year, most of this amount is used in the production of chlorine. Mercury penetrates into the air as a result of burning fossil fuels. An analysis of the ice of the Greenland ice dome showed that, beginning in 800 AD, Until the 1950s, the mercury content remained constant, but already from the 50s. In this century, the amount of mercury has doubled.

Mercury and its compounds are life threatening. Methylmercury is especially dangerous for animals and humans, as it quickly passes from the blood into the brain tissue, destroying the cerebellum and the cortex of the brain. The clinical symptoms of such a lesion are numbness, loss of orientation in space, loss of vision. Symptoms of mercury poisoning are not immediately apparent. Another unpleasant consequence of poisoning with methylmercury is the penetration of mercury into the placenta and its accumulation in the fetus, and the mother does not experience any painful sensations. Methylmercury has a teratogenic effect on humans. Mercury belongs to the first class of danger.

Metal mercury is dangerous if it is swallowed and inhaled by its vapors. In this case, a person has a metallic taste in his mouth, nausea, vomiting, colic in the abdomen, his teeth turn black and begin to crumble. Spilled mercury disperses into droplets and, if this happens, mercury should be carefully collected.

Inorganic compounds of mercury are practically non-volatile, so the danger is the ingress of mercury into the body through the mouth and skin. Salts of mercury corrode the skin and mucous membranes of the body. The ingress of mercury salts into the body causes inflammation of the throat, difficulty swallowing, numbness, vomiting, and abdominal pain.

In an adult, when ingested about 350 mg of mercury, death may occur.

Mercury contamination can be reduced by banning the production and use of a number of products. There is no doubt that pollution with mercury will always be an acute problem. But with the introduction of strict controls on waste products containing mercury, and also for food products, the risk of mercury poisoning can be reduced.

Pollution of the environment by heavy metals

Metallurgical complex

The metallurgical complex includes ferrous and non-ferrous metallurgy, covering all stages of technological processes: from extraction and processing of raw materials to obtaining finished products in the form of ferrous and non-ferrous metals and their alloys. The metallurgical complex is an interdependent combination of the following technological processes:

– extraction and preparation of raw materials for processing (extraction, enrichment, obtaining of necessary concentrates, etc.);
– metallurgical redistribution – the main technological process with the production of pig iron, steel, rolled ferrous and non-ferrous metals, pipes, etc .;
– production of alloys;
– recycling of the main production waste and obtaining various types of products from them.

Depending on the combination of these technological processes, the following types of industries are distinguished in the metallurgical complex.

Production of the full cycle, which are represented, as a rule, by combines, in which all the named stages of the technological process operate simultaneously.

Production of the incomplete cycle is an enterprise in which not all the stages of the technological process are carried out, for example, in the iron and steel industry only steel and rolled products are produced, but there is no production of cast iron, or only rolling. The incomplete cycle also includes the electrothermy of ferroalloys, electrometallurgy, etc. The enterprises of the incomplete cycle, or “small metallurgy” are referred to as redundant ones, are presented in the form of separate units for the production of foundry iron, steel or rolled products as a part of large machine-building enterprises of the country.

The metallurgical complex is the basis of the industry. It is the foundation of mechanical engineering, which, together with the electric power industry and the chemical industry, ensures the development of scientific and technological progress in all parts of the country’s national economy. Metallurgy is one of the basic branches of the national economy and is distinguished by its high material intensity and capital intensity of production. The share of ferrous and non-ferrous metals accounts for more than 90% of the total volume of structural materials used in engineering in Russia. In total volume of transportations of the Russian Federation on metallurgical cargoes it is necessary over 35% of all cargo turnover. For the needs of metallurgy, 14% of fuel and 16% of electricity are consumed, i.e. 25% of these resources are spent in industry.

The state and development of the metallurgical industry ultimately determine the level of scientific and technological progress in all branches of the national economy.

Heavy metals (mercury, lead, cadmium, zinc, copper, arsenic) are among the most common and highly toxic pollutants. They are widely used in various industrial industries, therefore, despite the purification measures, the content of heavy metal compounds in industrial wastewater is quite high. Large masses of these compounds enter the ocean through the atmosphere. For marine biocenoses, the most dangerous are mercury, lead and cadmium. Mercury is transported to the ocean with continental runoff and through the atmosphere. As part of atmospheric dust contains about 12 thousand tons of mercury, a significant part – anthropogenic origin. About half of the annual industrial production of this metal (910 thousand tons / year) falls into the ocean in various ways. In areas contaminated by industrial waters, the concentration of mercury in solution and in suspensions greatly increases. At the same time, some bacteria transfer chlorides into highly toxic methylmercury. Infestation of seafood repeatedly led to the mercury poisoning of the coastal population. Lead is a typical dispersed element contained in all components of the environment: in rocks, in soils, in natural waters, in the atmosphere, in living organisms.

Pollution of the environment by lead and its compounds by the enterprises of the metallurgical industry is determined by the specificity of their production activity: direct production of lead and its compounds; Associated extraction of lead from other raw materials containing lead in the form of an impurity; Purification of the obtained products from impurities of lead, etc.

Analysis of sources of lead emission showed:

• 57% of lead is emitted into the atmosphere with large volumes of dusty reflective smelting copper (lead-containing) raw materials, which are sent to all chimneys using this technology in chimneys without dust cleaning;
• 37% of lead is emitted with the enveloped gases because of the lack or insufficiency of the degree of their purification from the rich in lead content of the distillation dust;
• An essential factor is the insufficient efficiency of dust collection facilities existing at non-ferrous metallurgy enterprises.

Contaminating soil, zinc and fluorine causes a decline in yield, not only due to direct toxic effects, but also by changing the nutrient balance in the soil. Soluble compounds move along the soil profile with a descending current of soil solutions and can enter groundwater. Soil pollution destroys the soil structure, reduces soil water permeability and depresses the growth of microorganisms, reduces the enzymatic activity of soils, reduces the yield of plants.

It should be noted the increased toxicity of heavy metals when combined with living organisms in the soil. The combined effects of zinc and cadmium have several times more potent inhibitory effect on microorganisms than at the same concentration of each element individually. Since heavy metals both in combustion products of fuel and in emissions from the metallurgical industry are usually found in various combinations, their effect on the nature surrounding sources of pollution is stronger than that assumed on the basis of the concentration of individual elements.

Near the enterprises, the plant’s natural phytocenoses become more diverse in species composition, since many species do not withstand the increase in the concentration of heavy metals in the soil. The number of species can be reduced to 2-3, and sometimes to the formation of monocenoses. In forest phytocenosis, lichens and mosses are the first to react to contamination. The most stable woody level. However, prolonged or high-intensity exposure causes dry-resistant phenomena in it.

The detection of soil contamination with heavy metals is carried out by direct methods of selection of soil samples in the studied areas and their chemical analysis for the content of heavy metals. It is also effective to use for this purpose a number of indirect methods: a visual assessment of the state of phytogenesis, an analysis of the distribution and behavior of species – indicators among plants, invertebrates and microorganisms.

To determine the spatial regularities of the manifestation of soil pollution, a comparative geographic method, methods of mapping the structural components of biogeocoenoses, including soils, are used. Such maps not only record the level of soil contamination with heavy metals and the corresponding changes in the ground cover, but allow predicting changes in the state of the natural environment.

Protection of soils from contamination with heavy metals is based on improving production. For example, for the production of 1 ton of chlorine with one technology, 45 kg of mercury are consumed, and for another, 14-18 kg of mercury. In the long term, it is considered possible to reduce this value to 0.1 kg. A new strategy for protecting soils from heavy metal contamination is also concluded in the creation of closed technological systems.

How do heavy metals pollute nature?

Recently, the issue of environmental problems has become the most acute, and one of them is heavy metals.
Heavy metals are elements of a periodic system with a relative molecular mass greater than 40. Not an exception, Group II of the periodic table, in particular mercury, zinc, cadmium.

Thus, more than 40 chemical elements with a relative density of more than 6 belong to heavy metals. The number of dangerous pollutants, if one considers the toxicity, persistence and ability to accumulate in the external environment, and also the scale of the distribution of these metals, is much less.
First of all, those metals that are most widely and in considerable quantities used in production activity are of primary interest and, as a result of accumulation in the external environment, represent a serious danger from the point of view of their biological activity and toxic properties. These include lead, mercury, cadmium, zinc, bismuth, cobalt, nickel, copper, tin, antimony, vanadium, manganese, chromium, molybdenum and arsenic.

Forms of being in the environment. In the air, heavy metals are present in the form of organic and inorganic compounds in the form of dust and aerosols, as well as in gaseous elemental form (mercury). In this case, the aerosols of lead, cadmium, copper and zinc consist mainly of their submicron particles with a diameter of 0.5-1 μm, and the aerosols of nickel and cobalt – from coarse particles (more than 1 μm), which are formed mainly by burning diesel fuel.
In aqueous media, metals are present in three forms: suspended particles, colloidal particles and dissolved compounds. The latter are represented by free ions and soluble complexes with organic (humic and fulvic acids) and inorganic (halides, sulfates, phosphates, carbonates) ligands. A great influence on the content of these elements in the water has hydrolysis, which largely determines the form of the element in aquatic environments. A significant part of heavy metals is transferred by surface waters in a suspended state.

Sorption of heavy metals by bottom sediments depends on the features of the composition of the latter and the content of organic substances. Ultimately, heavy metals in aquatic ecosystems are concentrated in bottom sediments and biota.

In soils, heavy metals are contained in water-soluble, ion-exchange and weakly adsorbed forms. Water-soluble forms, as a rule, are represented by chlorides, nitrates, sulfates and organic complex compounds. In addition, heavy metal ions can be bound to minerals as part of the crystal lattice.

Sources

Extraction and processing are not the most powerful source of environmental pollution by metals. Gross emissions from these enterprises are much less than emissions from thermal power plants. Not metallurgical production, namely coal combustion is the main source of many metals entering the biosphere. In coal and oil, all metals are present. Much more than in the soil, toxic chemical elements, including heavy metals, in the ashes of power plants, industrial and household furnaces. Emissions to the atmosphere during fuel combustion are of particular importance. For example, the amount of mercury, cadmium, cobalt, arsenic in them is 3-8 times higher than the amount of metals produced. It is known that only one boiler of a modern coal-fired power plant emits an average of 1-1.5 tons of mercury vapor per year. Heavy metals are contained in mineral fertilizers.

Along with burning of mineral fuel, the most important way of technogenous dispersion of metals is their release into the atmosphere during high-temperature technological processes (metallurgy, burning of cement raw materials, etc.), as well as transportation, dressing and grading of ore.
The technogenic supply of heavy metals to the environment occurs in the form of gases and aerosols (sublimation of metals and dust particles) and in the composition of sewage.
Metals are relatively quickly accumulated in the soil and are very slowly evolved from it: the period of zinc removal is up to 500 years, cadmium – up to 1100 years, copper – up to 1500 years, lead – up to several thousand years.

A significant source of soil contamination with metals is the use of fertilizers from slurries derived from industrial and sewage treatment plants.
In emissions of metallurgical industries, heavy metals are mainly in an insoluble form. As the distance from the source of pollution, the largest particles settle, the proportion of soluble metal compounds increases, and the relationships between soluble and insoluble forms are established. Aerosol contaminants entering the atmosphere are removed from it through natural self-cleaning processes. An important role is played by atmospheric precipitation. As a result, industrial emissions into the atmosphere, wastewater discharges create the prerequisites for heavy metals to enter the soil, groundwater and open water, plants, sediments and animals.

The range of distribution and levels of air pollution depend on the source capacity, emission conditions and meteorological conditions. However, in conditions of industrial-urban agglomerations and urban development, the parameters of the distribution of metals in the air are still poorly predicted. With the removal of pollution sources, the decrease in the concentration of metal aerosols in atmospheric air often occurs exponentially, so that the zone of their intensive exposure, in which there is an excess of MPC, is relatively small.

In urbanized areas, the total effect of the detected air pollution is the resultant addition of many scattered fields and is due to the removal from the emission sources, the urban planning structure and the presence of the necessary sanitary protection zones around the enterprises. The natural (background) content of heavy metals in an uncontaminated atmosphere is a thousandth and ten thousandths of a microgram per cubic meter and lower. Such levels in modern conditions on any inhabited territories are practically not observed. The background content of lead is assumed to be 0.006 μg / m3, mercury – 0.001-0.8 μg / m3 (in cities – several orders of magnitude higher). The main industries with which environmental pollution is associated with mercury include mining, metallurgical, chemical, instrument-making, electrovacuum and pharmaceutical. The most intensive sources of cadmium environmental pollution are metallurgy and electroplating, as well as the burning of solid and liquid fuels. In the uncontaminated air above the ocean, the average concentration of cadmium is 0.005 μg / m3, in rural areas – up to 0.05 μg / m3, and in the areas where the enterprises that contain it are emitted (non-ferrous metallurgy, thermal power plants operating on coal and oil, Plastics, etc.), and industrial cities – up to 0,3-0,6 mkg / m3.
The atmospheric path of the entry of chemical elements into the environment of cities is the leading one. However, even at a small distance, particularly in suburban agricultural areas, the relative role of sources of environmental pollution with heavy metals can change and the greatest danger will be represented by sewage and waste accumulated in landfills and used as fertilizers.

The maximum ability to concentrate heavy metals is suspended matter and bottom sediments, then plankton, benthos and fish.
Precipitation. The zone of maximum concentrations of metals in the air extends up to 2 km from the source. In it, the content of metals in the surface layer of the atmosphere is 100-1000 times higher than the local geochemical background, and in snow – by 500-1000 times. At a distance of 2-4 km is the second zone, where the metal content in the air is approximately 10 times lower than in the first. A third zone with a length of 4-10 km is planned, where only individual samples show an increased content of metals. As far as the distance from the source, the ratios of the different forms of the scattered metals change. In the first zone, water-soluble compounds make up only 5-10%, and the main mass of deposition is formed by small dust-like particles of sulfides and oxides. The relative content of water-soluble compounds increases with distance.