Soil Pollution: Causes, Consequences, and Approaches to Restoration

When Soil Is Considered Polluted

Soils naturally contain metals, salts, and organic compounds. Pollution is assessed not only by the presence of a substance but by levels above natural background, loss of soil functions, and risk to people or ecosystems. The same total concentration can have different mobility and toxicity depending on pH, organic matter, texture, and moisture. A laboratory result therefore requires context: sampling location, depth, historical land use, possible sources, and whether an exposure pathway exists.

Major Sources of Contamination

Industrial sites, mining, metal processing, fuel storage, transport, conflict damage, landfills, and illegal dumping can leave metals, petroleum products, solvents, acids, alkalis, and other chemicals. In agriculture, risks arise from excessive or incorrect pesticide and fertiliser use, contaminated sewage sludge, livestock waste, and irrigation with poor-quality water.

Heavy Metals and Metalloids

Lead, cadmium, mercury, arsenic, chromium, nickel, and other elements do not break down like organic compounds. They can change chemical form, bind to soil particles, or become more mobile when pH and redox conditions change. Risk depends not only on total concentration but on the fraction available to organisms. Some plants take up metals through their roots, allowing contaminants to enter food or feed. Inhalation of contaminated dust and accidental ingestion of soil are especially relevant for children.

Petroleum, Pesticides, and Persistent Organic Chemicals

Fuel and lubricants alter soil air and water conditions, can harm microorganisms, and may contain polycyclic aromatic hydrocarbons. Pesticides vary in persistence and mobility: some degrade quickly, while others remain for years or move into water. Persistent organic pollutants can accumulate in living organisms, meaning historical use may continue to create risk long after application has stopped.

Effects on Soil Functions

Toxic substances may reduce microbial diversity and disrupt organic matter decomposition, nutrient cycling, and soil structure. Plants may grow poorly even when contamination has no obvious visible sign. Loss of soil function increases erosion, reduces water retention, and weakens resilience to drought and intense rainfall — interacting with other forms of land degradation.

Transfer to Plants, Food, and Water

Mobile substances dissolve in soil water and can enter plant roots or leach toward aquifers. Erosion carries contaminated particles into rivers and ponds. During dry periods, wind spreads dust from exposed land. Risk varies with crop, soil type, rooting depth, end use, and food preparation — so a suspected site should not be assessed from only one sample.

How a Contaminated Site Is Investigated

Investigation starts with site history, maps, archives, and information about accidents, production, tanks, and waste. A conceptual model then identifies sources, contaminants, migration routes, and receptors. Samples must be representative and have a documented chain of custody. Results are mapped, compared with background and regulatory values, and evaluated for the intended land use — the aim is to understand the spatial pattern and actual exposure pathways.

Approaches to Remediation

Contaminated soil may be excavated and treated safely or isolated in place through engineered barriers, caps, and drainage. Soil washing separates contaminated fine material; thermal methods remove volatile organic chemicals; chemical stabilisation reduces metal mobility. Bioremediation uses microorganisms to break down organic contaminants; phytoremediation uses plants to extract or stabilise them. These biological methods can be less disruptive but require time and do not suit every substance or concentration. Long-term monitoring remains necessary after treatment.