Hygienic significance of the mechanical structure, physical properties and chemical composition of soil for public health. Pollution, self-purification, and sanitary and hygienic protection of soils.
Soil is the Earth’s top layer, composed of minerals, organic matter, water, and air. It influences human health, agriculture, water quality, and disease control while providing a habitat for microorganisms, plants, and animals.
1. Mechanical Structure (Texture)
- It refers to the proportion of different particle sizes—sand, silt, and clay—in the soil. This composition determines the soil’s texture, porosity, drainage, and ability to retain nutrients and water.
- How do sand, silt, and clay proportions affect soil texture?
- Sandy soil: has large particles, which makes it drain water quickly, so it has low water retention, low nutrient availability, and low pathogen retention.
- Clay soil: has fine particles, which retain water and nutrients, and it can also hold pathogens for a long time.
- Loamy soil: is a balanced mixture of sand, silt, and clay. It has optimal water infiltration, good nutrient availability, and supports active microbial life.
Public Health Relevance: Soil texture affects water percolation, pathogen survival, and natural filtration, influencing the spread of soil-borne diseases such as tetanus and helminthiasis.
2. Physical Properties
- Porosity & permeability: Control water movement and gas exchange.
- Water-holding capacity, temperature, moisture: Affect microbial growth and pathogen survival.
- Porosity is the proportion of empty spaces (pores) in the soil that can hold air or water.
Hygienic Importance: Proper drainage prevents stagnant water, reducing breeding of vectors (mosquitoes, flies) and waterborne diseases.
3. Chemical Composition
- Organic matter: Provides energy for microbes, improves structure, retains nutrients and water, binds toxins.
- Minerals (N, P, K, Ca, Mg, Fe): Support plant growth and microbial activity.
- Contaminants (heavy metals, pesticides, nitrates): Can enter the food chain or groundwater → risk of poisoning and chronic diseases.
Public Health Relevance: Maintaining soil chemical quality ensures safe food and water and reduces exposure to toxic substances.
4. Soil Pollution
- Sources: Industrial waste, heavy metals, petroleum products, fertilizers, pesticides, sewage sludge.
- Health Impact: Contaminated crops and groundwater, accumulation of toxic metals, vector breeding.
5. Soil Self-Purification
Definition: Soil’s natural ability to reduce contamination and restore ecological balance.
Mechanisms with Examples:
- Physical Processes:
- Filtration: Soil traps suspended solids and microbes as water passes through.
- Adsorption: Pollutants like heavy metals stick to soil particles, reducing mobility.
- Chemical Processes:
- Oxidation: Organic pollutants are converted into less harmful compounds by chemical reactions with oxygen.
- Reduction: Anaerobic reactions convert nitrates or sulfates into harmless substances.
- Neutralization: Soil buffers acids and bases to maintain pH and reduce toxicity.
- Biological Processes: