Soil pollution occurs when soil becomes contaminated with harmful substances. These substances, called pollutants, can become concentrated in plants that grow in the soil. The concentrated pollutants might then poison animals—including people— that eat the plants. Pollutants can also leach (leak) from the soil into nearby waterways. The pollutants may even reach water beneath the surface, contaminating supplies of drinking water.
Soil pollution can also harm the soil itself by damaging the bacteria, fungi, and other organisms that live in it. Such organisms decompose (break down) dead plants and animals. This process restores to the soil nutrients (nourishing substances), which living plants require for growth. Soil pollution can thus disrupt both decomposition and plant growth. Because much food comes from plants that grow in soil—or from animals that eat those plants—soil pollution can threaten the food supply.
Manufacturing, mining, and other activities produce a variety of industrial wastes that can pollute the soil. These wastes include heavy metals, such as arsenic, lead, and mercury. They also include organic (carbon-based) compounds used to make many products. Industrial wastes can enter the soil from leaks in underground pipes and storage tanks. They may also leach into soil from landfills or contaminated bodies of water.
Other soil pollution comes from agricultural wastes, including the pesticides and fertilizers used on farms. Pesticides are chemical poisons that can directly harm the beneficial organisms living in the soil and also accumulate in plants. Fertilizers can disrupt normal cycles of decomposition and alter the soil’s acidity. They can also run off, contaminating nearby waterways.
Burning fossil fuels, such as coal, oil, and natural gas releases gases into the air. These gases cause acid rain, which makes soils more acidic and harms plants and soil organisms (see Acid rain ). In addition, burning fossil fuels release nitrogen compounds into the air, which can fall on soil in a process, called nitrogen deposition. These compounds cause problems similar to those caused by excessive fertilizers.
