Soil - surface layer of the earth's crust, which is a complex of mineral and organic particles with a huge number of microbes. The type of soil, the chemical composition depends vegetation areas, the chemical composition of food products of plant and animal origin. From physico-chemical properties of the soil and bedrock depend on the depth of the location and composition of the underground water. The type of the soil affects the climate, the relief of the soil taken into account in the planning of settlements, the ability P.-purification is used for disposal of liquid and solid waste.
Soil differ in physical properties (size, porosity, moisture, air permeability), chemical composition (mineral compounds and organic matter) and microflora. Depending on the size and composition of particles there are clay, loam, sabulous and sandy soil.
A variety of soil microflora: bacteria, fungi, spirochaetes, filterable viruses, the simplest. Most soil microbes - saprophytes (see). The number of microorganisms and their species composition are determined by physical and chemical properties of soil, humidity and air permeability. So, in the upper soil layers are created favorable conditions for the development of aerobic microbes (see Aerobes), and in the deeper layers, where the oxygen content is less dominated by anaerobic microorganisms (see Anaerobes). Pathogenic microbes get in Petrograd from the faeces of humans and animals, sputum, saliva and other secretions, with the corpses of men and of animals that died from infectious diseases. Most of the pathogen survives in soil from a few hours to several months (bacterial dysentery the Flexner survive in different soils from 25 to 100 days or more, bacteria titportfoli groups up to 400 days. Long remain viable spore-forming bacteria, pathogens tetanus, botulism, gas gangrene. With the excreta into the soil fall helminth eggs, some of them remain viable in the soil for several years.
Human infection can occur by direct contact with the soil, through grown on the soil and not washed before eating vegetables, through products, contaminated by flies (see). Serious danger is represented by the penetration of pathogenic bacteria and viruses from the soil to the water supply sources - rivers, reservoirs, groundwater and artesian water. Pollution of water supply sources is possible with groaning in a reservoir of rain and melt water, when percolation through the soil pollution from absorbing wells, septic tanks, pomolic not equipped waterproof receivers for solid and liquid waste.
Physico-chemical properties and P. flora are essential to its self-purification, i.e. processing of organic substances into the soil as a result of vital activity of living organisms, and are made from industrial and domestic waste and garbage. The process of transformation of organic matter in the soil runs continuously and is in decay into simpler substances and education of mineral salts, and then in the subsequent synthesis of complex chemical compounds of humus substances (humus), play a major role in soil fertility. While in soil decreases the amount of microbes, die helminth eggs and dissolved toxic compounds. The soil's ability to cleanse itself is not unlimited, and in case of excessive contamination of the soil does not recycling and disposal made to her waste and waste. Adverse impact on the purification of soil contaminated with toxic substances that may be released into the soil with industrial waste and the application of pesticides (see agricultural Pesticides).
Sanitary protection of soil from pollution by solid and liquid waste occupies an important place in the system of prevention of infectious diseases and the spread of worms.
Of particular importance sanitary protection of soil has in rural areas, where relatively little developed various cleaning systems. Among priority measures for sanitary protection of soil in these conditions shall be: the regular removal of liquid and solid waste and proper disposal of them is solid waste disposed of by composting (see), liquid - in the fields of access to sanitation and zapugivaniya (see sewage disposal); the device waterproof vygreba in bathrooms residential and public buildings and pomolic; the device of local sanitation for public building, children's and medical institutions; collection and composting of manure; fighting flies. Sanitary supervision over a condition of the soil by using helminthological, bacteriological and chemical methods of research.

Soil is the top layer of the earth's crust (lithosphere), exposed to climate, vegetation, activity of living beings (germs, worms, insects and other).
A great role in the formation of soils, and the changing of its composition belongs to a man. Much is made in paragraph different chemicals: fertilizers, pesticides, industrial waste and construction of human activity.
In the soil of settlements also be changes, particularly in the older and larger cities where natural P., typical of the surrounding area is completely replaced by artificial: the bulk soil, moved on, In the change of properties and composition P. settlements, declining groundwater level varies biocenosis P. accumulate inorganic, and often toxic substances in the soil are pathogenic bacteria, viruses, helminthes. As a result, in P. slow down and even completely stopped the biological processes; such modified P. cannot grow green areas.
From the purity of Petrograd and its composition depends on the quality of groundwater and surface sources. In P. stored for a long time pathogenic bacteria, viruses, Mature eggs of soil-transmitted helminths. The soil may contain toxic substances are expelled with waste and industrial pollution, pesticides used in agriculture. Radioactive waste coming in Petrograd, determine the improvement of the level of natural radioactive background.
Large positive value of the property of auto purification of P.: decomposition and synthesis of organic substances, including waste, as a result of life ammonifiers, nitrifying, mumifizierung bacteria, fungi, actinomycetes. As a result of circulation of substances in Petrograd, the accumulation of harmless to humans and are very useful for plants of organic matter (humus) and mineral salts.
Sanitary protection of soil is an important part of activity of bodies of sanitary control. Hygienic criteria of sanitary state of Peterhof is the detection of substances and organisms which may cause harm to the health, well-being or impair the living conditions (food, water, air, construction materials). Sanitary supervision P. performed using helminthological, bacteriological, chemical and radiological methods. Results of research can be recommended the following indicators (see table).

The characteristic of soil The number of larvae and pupae of the fly by 0.25 m2 soil The number of helminth eggs, causing worms person, per 1 kg of soil Colitits Title anaerobov
Very dirty
Very very dirty
Not more than 10
More than 100
1.0 and above
0.001 and below
1.0 and above
0,0001 and below