Pollution is the introduction of contaminants into the natural environment that causes harm. It can take the form of chemical substances or energies like noise and heat. Pollutants can be foreign or naturally occurring, and become pollution when in high amounts. Common types of pollution include littering, noise, soil contamination from chemicals, radioactive contamination from nuclear activities, and thermal pollution from power plants. Pollution has widespread effects like increased diseases, reduced biodiversity, ocean acidification from CO2, and climate change from greenhouse gases. Controlling pollution through emissions standards and wastewater treatment helps protect the environment.