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's 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've succeeded at controlling many point source pollutants—the pollutants that can be traced back to a specific source, such as a sewage treatment or industrial plant. However there are many non-point source pollutants—coming from many diffuse sources—that are still regularly released into the environment. These chemicals and nutrients continue to wreak havoc on wildlife and ecosystems.

Excess Nutrients: 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 run off 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 cause serious problems for our waterways.

Normally algae don't have enough nitrogen and phosphorus to grow in excess. With the overflow of nutrient runoff, there's nothing to keep algae growth in check. Algae can grow into giant blooms that block the sunlight underwater plants need to survive. Algae blooms can create underwater “dead zones” when 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.

Climate Change Pollution: Science shows a direct relationship between the amount of climate change 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 already in the atmosphere will continue to contribute to climate change 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 chemicals 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 1950s and 60s because of DDT, which thinned the shells of their eggs so they were not able to produce young. DDT is now banned in the United States.

Harmful Algae Blooms

Harmful algal blooms (HABs) are becoming an increasingly common occurrence across the United States and around the world. Blooms (large numbers or colonies) of the algae or related organisms produce one or more toxins that can be dangerous to fish, wildlife, pets, and livestock. People can also be exposed to toxins through outdoor recreation activities and consuming contaminated drinking water. HABs can occur in both freshwater and coastal marine waters.

Algae include phytoplankton (or microscopic, free-floating plants) and are an essential part of any aquatic ecosystem, with green algae serving as the food base for microscopic animals (zooplankton) and some fish. Harmful algae types, including cyanobacteria or "blue-green algae," are a less desired food item for zooplankton and fish, and in addition, can produce toxic chemicals threatening other organisms in the water.

Conditions that contribute to HABs are nutrients, particularly phosphorus and nitrogen; warm temperatures, adequate sunlight; and calmer waters. All types of algae need nutrients to survive and grow, and excessive nutrient levels can lead to blooms. Key sources of nutrient pollution in our waters are agricultural sources, like inorganic fertilizers and manure runoff, and point sources, particularly wastewater treatment plants. Studies have shown reducing nutrient inputs to waters is important to reducing HAB occurrences.

According to Dr. Jay Martin of The Ohio State University, "With climate change and warmer climates we see longer growing seasons. This is going to increase the opportunity that these organisms can grow. We also expect to see wetter and stormy winters and springs in the future, especially in the Midwest, which impacts the Great Lakes and Lake Erie. So because of this we expect to see an increase in nutrients coming into the lakes, which will increase the photosynthetic rate. Lastly, with higher carbon dioxide emissions and higher carbon dioxide concentrations in the atmosphere, this will increase the dissolved organic carbon or DOC, and this will also increase the photosynthetic rate." To get more information from Dr. Jay Martin, listen to his webinar: "Climate Change & Harmful Algal Blooms."

In fish, toxins (such as microcystins) are taken up by the live, and at sufficient exposures, can affect the liver function and cause liver damage. In some cases, fish kills have been associated with HABs. Wildlife can also be at risk from the toxins, both through direct ingestion or through consuming food containing the toxins. Though there have been few lab studies on impacts to birds, field studies have attributed deaths in songbirds, ducks, gulls, pheasants, and hawks to HAB exposures. Research in the Chesapeake region associated great blue heron deaths with toxic algae. Pets and livestock are also at risk from exposure to HABs, with deaths documented at a number of locations around the country.

There are ongoing federal programs that protect water quality and limit the sources of nutrient runoff that contribute to HABs. Programs include the Waters of the U.S. Rule, which will ensure adequate protection of additional wetlands to help reduce nutrient runoff into our rivers and lakes; the U.S. Farm Bill, including conservation programs targeted at priority watersheds to reduce nutrient runoff from fields and increased efforts to improve nutrient management at confined animal feeding operations; and the Great Lakes Restoration Initiative, including ongoing support of projects to reduce nonpoint source pollution in targeted watersheds in the Great Lakes.

Mercury Pollution

Mercury is one of the most harmful pollutants faced by fish and wildlife. Mercury is a naturally occurring, toxic heavy metal. However, human activity has significantly increased mercury levels in the environment over the past several centuries. Coal-fired power plants burn coal and release mercury into the atmosphere as a byproduct. Coal-fired power plants are the single largest source of mercury contamination in the United States, responsible for approximately 50 percent of human-caused mercury emissions. Other sources include waste incinerators that burn mercury-containing products and chlorine manufacturers. However, unlike these sources, power plants haven't had to limit their mercury pollution.

Once emitted to the air, mercury falls to the Earth and builds up in our waters and soils, where it is transformed into methylmercury—a highly toxic form that accumulates in the tissues of wildlife and people. It's a potent neurotoxin that impacts the function and development of the central nervous system in both people and wildlife. Exposure to mercury is particularly dangerous for pregnant and breastfeeding women, as well as children, since mercury is most harmful in the early stages of development. Scientists have found alarming levels of mercury accumulation in a wide range of wildlife species, causing dangerous reproductive and neurological problems. Fish have difficulty schooling and decreased spawning success. Birds lay fewer eggs and have trouble caring for their chicks. Mammals have impaired motor skills that affect their ability to hunt and find food. In addition, some evidence indicates elevated mercury levels can adversely affect species' immune systems. All these effects combine to create a severe threat to wildlife survival.

Mercury increases in concentration with each step up the food chain. As a result, large predator fish such as walleye and trout can have mercury levels over a million times that of the surrounding water. In turn, people and wildlife who consume fish or other species with high mercury levels are at risk of serious health problems.

In 2011 the Environmental Protection Agency finalized air pollution standards that put national limits on the amount of mercury spewing from the nation’s coal-fired power plants. The pollution limits on power plants were estimated to cut mercury emissions by 91 percent, while also cutting acid gas, arsenic, lead and nickel emissions. The National Wildlife Federation had campaigned for these standards since 1999, organizing hundreds of thousands of our members and supporters to attend public hearings, sign postcards, make phone calls, and urge decision makers to put stricter limits on mercury emissions.


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)

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