Pollution is the introduction of contaminants into the natural environment that causes adverse change. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants. Pollution is often classed as point source or nonpoint source pollution.

 Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological materials that cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment.

The atmosphere is a complex dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems.Indoor air pollution and urban air quality are listed as two of the World’s Worst Toxic pollution problems.

Dirty water is the world's biggest health risk, and continues to threaten both quality of life and public health in the United States. When water from rain and melting snow runs off roofs and roads into our rivers, it picks up toxic chemicals, dirt, trash and disease-carrying organisms along the way. Many of our water resources also lack basic protections, making them vulnerable to pollution from factory farms, industrial plants, and activities like fracking. This can lead to drinking water contamination, habitat degradation and beach closures.

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infrastructure.

Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Governments have made efforts since the 1970s to reduce the release of sulfur dioxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. The chemicals in acid rain can cause paint to peel, corrosion of steel structures such as bridges, and erosion of stone statues.

Soil pollution can arise from a number of sources, including when farmers use an excessive amount of fertilizer and other chemicals on their land. Often soil pollution arises from the spilling or leaking of waste into the ground, such as an oil spill, or seepage from a landfill or even radioactive contamination. Damage to an underground tank that is storing toxic chemicals can also be the source of the problem. Polluted soil can be a serious threat to humans who come in contact with the soil or eat food grown in it.

Sometimes soil pollution can contribute to the pollution of water. This occurs through surface runoff, often when it rains and polluted soil is carried to nearby bodies of water. This is a common problem near farmlands, where fertilizers and manures are used to help crops grow. Soil pollution can also infect water when the polluted soil leaches into groundwater, such as into wells and other drinking water sources.