A pollutant is a substance or contaminant that has an adverse effect on the environment, including water, air and land. Pollution occurs when pollutants are introduced into the natural environment, causing harm to ecosystems, human health, and quality of life. Examples of pollutants include chemicals, heavy metals, radiation, noise, and waste materials such as plastic or garbage. The presence of these substances in excessive amounts can lead to environmental degradation, climate change, and other negative impacts on the planet.