Physical properties and soil evaluation
In hygienic practice, terrain is empirically divided into "healthy" (dry, elevated, and sunny areas) and "unhealthy" (damp, low-lying, with frequent fogs). The main evaluation criterion is physical characteristics determining the capacity for self-purification:
- Porosity and air permeability. Free spaces between solid particles filled with air are essential for aeration. Oxygen accelerates the oxidation of organic matter.
- Moisture capacity and capillarity. High values retain water, making the soil damp and cold. Excessive capillarity leads to dampness in basements and ground floors.
- Temperature regime. Soil accumulates solar heat, influencing the surface atmospheric layer. Dark and dry areas, as well as southern slopes, heat up faster. The vital activity of microorganisms directly depends on temperature. Daily fluctuations in air temperature penetrate no deeper than 1 meter.
- Freezing. Depending on the climate, soil freezes to a depth of 1–2 meters (permafrost forms in northern regions), which must be accounted for when laying sewer pipes and foundations.
Biogeochemical provinces and endemics
Chemical elements from the soil migrate through food chains and enter the human body via water and food. Academician A.P. Vinogradov developed the doctrine of natural biogeochemical provinces—territories with an abnormal excess or deficiency of trace elements. Living in such zones causes geochemical endemics:
- Iodine deficiency leads to endemic goiter.
- Fluorine excess causes fluorosis, while deficiency causes dental caries.
- Molybdenum excess provokes endemic gout.
- Strontium excess leads to chondrodystrophy and osteodystrophy.
- Boron excess is the cause of boron enteritis.
There are also artificial provinces. They form as a result of economic activity (around metallurgy and chemical industry centers). In such territories, maximum allowable concentrations of lead, manganese, pesticides, and radionuclides can be exceeded by 10 times or more.
Epidemiological and sanitary role
The sanitary function of soil lies in the fact that in a clean environment, pathogenic microorganisms die quickly. However, with severe organic contamination (e.g., sewage), the survival rate of bacteria increases sharply. Dysentery pathogens live up to 2 months, cholera up to 4, and tuberculosis up to 7. Specific soil inhabitants, such as anthrax spores and anaerobic infection agents, can persist for decades.
Soil is of particular importance for the spread of helminthiases.
- Geohelminths (ascarids, whipworms, hookworms) develop directly in the soil without an intermediate host. For example, ascarid eggs lie in the ground for up to a year until the larva becomes infective.
- Biohelminths (beef tapeworm, echinococcus) end up in the soil, but for further development, they necessarily require an intermediate animal host.
Biological factor and self-purification
Chemical processes of organic destruction and synthesis occur continuously in the soil. Soil organisms play a crucial role in the nutrient cycle. Flora (viruses, bacteria, fungi) and fauna (protozoa, worms) promote self-purification and fertility enhancement.
However, soil fauna also has a negative epidemiological significance. Rodents (rats, mice) can infect the soil with leptospires, and ticks are vectors of severe vector-borne infections, particularly encephalitis.
Briefly: answers to topical questions
What stages does the process of biochemical self-purification of soil from organic matter include?
Biochemical self-purification of soil from organic matter includes the main transformation processes: mineralization, nitrification, and humification.
- Mineralization—breakdown and oxidation of organic substances; carbohydrates and hydrocarbons are oxidized to carbon dioxide and water, fats to the same products.
- Ammonification—destruction of proteins with the formation of amino acids, ammonium salts, and ammonia.
- Nitrification—subsequent oxidation of ammonia to nitrites and then to nitrates.
- Humification—one of the main processes of organic matter transformation during soil self-purification.
Which pathogenic microorganisms belong to specific (permanent) inhabitants of the soil?
Specific (long-term) soil inhabitants include spore-forming microorganisms capable of maintaining viability in this environment for decades.
- Anthrax pathogen (Bacillus anthracis)—has a centrally located spore within the cell.
- Tetanus pathogen (Clostridium tetani)—has a terminal spore location.
- Botulism pathogens—have a subterminal spore location.
- Gas gangrene pathogens—are also characterized by a subterminal spore location.
By what sanitary-microbiological indicators is the epidemiological safety of soil assessed?
The epidemiological safety of soil is assessed by the number of sanitary-indicator microorganisms (SIM), which serve as indirect indicators of potential pathogen contamination. The following indicators are used for assessment:
- SIM titer—the smallest volume (in ml) or weight (in g) of the test material in which at least one SIM individual is present.
- SIM index—the number of SIM cells detected in a specific volume or weight of material.
- Total microbial count (TMC)—the count of all microorganism colonies grown on a nutrient medium when inoculating 1 g or 1 ml of material.
Helminth rule: Geohelminths only need earth (ascarids develop directly in the soil), Biohelminths need another's life (tapeworms require an intermediate host).
Class and exam questions
Why is soil with high water-holding capacity considered unfavorable?
It retains a large amount of water, which makes it damp and cold. This reduces air permeability, impairs aeration, and slows down the self-purification processes from organic matter.
What are artificial biogeochemical provinces?
These are territories around large cities and industrial enterprises where the soil is heavily contaminated with heavy metals and xenobiotics, and maximum allowable concentrations of harmful substances are exceeded dozens of times.
How long does anthrax persist in the soil?
Anthrax spores, like the agents of anaerobic infections, can survive in the soil for decades.
What else to study on this topic
- Morphological composition of soil: parent material, humus, microorganisms
- Global environmental issues: arable land degradation and erosion
- Classification of soil particles by diameter (stones, sand, dust)
- Problems of risky agriculture and permafrost in Russia
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