Soil pollution as part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals, or improper disposal of waste .

The most common chemicals involved are petroleum
hydrocarbons , polynuclear aromatic hydrocarbons (such as naphthalene and benzo(a)pyrene ), solvents , pesticides, lead, and other heavy metals .

Contamination is correlated with the degree of industrialization and intensity of chemical substance. The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil, vapors from the contaminants, and from secondary contamination of water supplies within and underlying the soil.

Mapping of contaminated soil sites and the resulting cleanups are time consuming and expensive tasks, requiring extensive amounts of
geology, hydrology , chemistry,
computer modeling skills, and GIS in Environmental Contamination , as well as an appreciation of the history of industrial chemistry.

In North America and Western Europe the extent of contaminated land is best known, with many of countries in these areas having a legal framework to identify and deal with this environmental problem.

Developing countries tend to be less tightly regulated despite some of them having undergone significant
industrialization .

Causes

Soil pollution can be caused by the following (non-exhaustive list)
Oil spills
Mining and activities by other heavy industries
Accidental spills as may happen during activities, etc.

Corrosion of underground storage tanks (including piping used to transmit the contents) Acid rain Intensive farming Agrochemicals, such as pesticides , herbicides and fertilizers Industrial accidents Road debris Drainage of contaminated surface water into the soil Ammunitions , chemical agents , and other agents of war
Waste disposal Oil and fuel dumping Nuclear wastes Direct discharge of industrial wastes to the soil Discharge of sewage Landfill and illegal dumping Coal ash Electronic waste.

The most common chemicals involved are petroleum hydrocarbons , solvents, pesticides, lead, and other
heavy metals .

Source: Wikipedia