Soil pollution occurs when toxic chemicals (pollutants or contaminants) are present in high enough concentrations in the soil to endanger human health and/or the ecosystem. All soils, whether polluted or not, contain a variety of naturally occurring compounds (contaminants). Metals, inorganic ions and salts, and many organic compounds are examples of contaminants. These compounds are primarily formed by soil microbial activity and organism decomposition. Various compounds also enter the soil from the atmosphere, such as precipitation water, as well as from surface water bodies and shallow groundwater flowing through the soil, as well as from wind activity or other types of soil disturbances. Pollution occurs when the amount of contaminants in the soil exceeds natural levels. Soil pollution is caused by two main factors: anthropogenic and natural factors.