Human waste can be household garbage or biological waste (feces, urine). Emissions from our daily activities, such as carbon by-products from burning fossil fuels through gasoline in our cars or coal in a household furnace (activities that are said to create a “carbon footprint”), can also affect the environment.   

Industrial by-products, such as mercury dumped into rivers from chemical plants or emitted into the air from coal fired power plants, are pollutants that can cause immediate harm to the environment and linger in the land and water for centuries. They can cause damage long after the original pollution occurred.

Living organisms produce all kinds of toxins that can have harmful effects on other organisms or the environment. Human activities can influence the production of toxins. For example, sewage overflows can trigger harmful algal blooms, and large amounts of carbon dioxide in the air can increase the acidification of oceans as the water absorbs the CO2.