Every day the byproducts of our daily lives—sewage, exhaust, trash, agricultural and lawn chemicals, industrial and powerplant emissions and more—make their way via the air and water into the natural environment and become pollutants. As big as our planet is, it is not big enough to dilute or absorb all the waste, chemicals and nutrients that billions of people are continuously producing.
Since the 1960s, the United States has made great progress in reducing air and water pollution. We have succeeded at controlling many point source pollutants —pollutants that can be traced back to a specific source such as a sewage treatment or industrial plant.
However, there are many nonpoint source pollutants—pollutants that come from many diffuse sources—that are still regularly released into the environment. These chemicals and nutrients continue to wreak havoc on wildlife and ecosystems.
Phosphorus and nitrogen are limiting factors for plants. Water and soils with little nitrogen and phosphorus have very little plant growth. For this reason, these two nutrients are the key elements of fertilizers.
After fertilizers are used on farms, many of the excess nutrients not absorbed by plants runoff into nearby streams, lakes and rivers. The chemicals in fertilizers also combine with excess nutrient runoff from lawns, septic systems and livestock farms. All those nutrients can wreak havoc in our waterways.
Normally, algae do not have enough nitrogen and phosphorus to grow in excess. With the overflow of nutrient runoff, there is nothing to keep algae growth in check. Algae can grow into giant blooms that block sunlight underwater plants need to survive. Algae blooms can create underwater “dead zones”, because they take oxygen from the water that fish and invertebrates need to survive. Every summer, a big dead zone caused by algal blooms forms in the Gulf of Mexico near where the Mississippi River enters the Gulf.
Global Warming Pollution
Science shows a direct relationship between the amount of global warming pollution being released into the atmosphere and the increase in surface temperatures around the globe. Carbon dioxide, one of the biggest global warming pollutants, is the product of human activities such as burning fossil fuels (primarily oil, natural gas and coal) for our vehicles, heat and power generation. Even if we stopped burning all fossil fuels right now, the carbon dioxide that is already in the atmosphere will continue to contribute to global warming for hundreds of years into the future.
Persistent Organic Pollutants
Persistent organic pollutants are synthetic toxic chemicals—such as PCBs, DDT and dioxins—that are easily carried by wind or water and can persist in the environment for a long time. They can accumulate in the tissues of plants, animals and people, and pass from one species to another through the food chain. As the chemical move up the food chain, they become more concentrated (a process known as "biomagnification"). Populations of raptors, such as the bald eagle, declined dramatically in the 50's and 60's because of DDT, which thinned the shells of their eggs so they were not able to produce young. DDT is now banned in the U.S.
These are only some of the many pollutants that threaten wildlife. The Environmental Protection Agency and the USGS have additional information on threats to wildlife and people from pollutants.
National Wildlife Magazine Articles:
Persistent Organic Pollutants: A Global Issue, A Global Response (EPA)
Sustaining Life: How Human Health Depends on Biodiversity. Chivian, Eric and Aaron Bernstein, Eds. Oxford University Press, New York: 2008.
Precious Heritage: The Status of Biodiversity in the United States. Stein, Bruce A., Lynn S. Kutner and Jonathan S. Adams. Oxford University Press, New York: 2000.
Smaller Than Expected, but Severe, Dead Zone in the Gulf of Mexico (NOAA)