please modify the answer in your own words...
Soil contamination or soil pollution 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 usage.
Causes :Accidental Spills, Acid rain, Intensive farming, Deforestation,genetically modified plants, Nuclear wastes,etc.
effects: decreases the soil fertility, land becomes waste, destroys the necessary microbes in the soil, etc....