Almost anyone or anything is a potential source of pollutants. So water quality experts group sources into two main categories of pollutants point sources and non-point sources.
Point and Non-point Sources
Point source discharges are discharges that come from a fixed pipe, like a wastewater treatment plant discharging wastewater into the stream. Point-source pollutants used to be the biggest water quality problem in the united states. The Clean Water act of 1972 addressed the problem, by laying out strict regulations controlling levels of discharge, effectively plugged the pipes.
Non-point source discharges no single particular pipe is able to be identified as the discharge, rather it is an over-land flow of the water that goes into creeks and drainage ways that ultimately end up in the river. That over-land flow picks up pollutants in its path, moving them into waterways. Regulations that worked so well on the point-source pollution problem are next to impossible to implement on a case-by-case basis, making the non-point source problem much tougher to solve.
Some water pollutants are easy to see like garbage. But the most serious pollution, like sediment, nutrients, chemicals, and pathogens, aren’t as obvious.
Sediment is simply soil and rock particles. At the root of the problem is erosion. Soil can erode off of farm fields or overgrazed pastures, construction sites, along river banks that lack vegetation; anywhere there is not proper sediment control structures in place. Sediment in the water can block sunlight, influencing what types of vegetation and species can thrive in that water. Sediment fills in waterways affecting transportation and recreation. And sediment can be a carrier for other pollutants, like toxic chemicals, which attach to the sediment.
Nutrients, which pose an entirely different problem. Nitrogen and phosphorous are natural components of manure, human sewage, and decaying organic matter, like leaves. They are also present in manufactured fertilizers, applied to farm fields backyard gardens, golf courses and lawns. They become a problem when precipitation washes these nutrients off the land and into waterways. Once they are in water, they do what they do on land - enhance plant growth. The water will turn green with “algae blooms.” When those algae blooms die and decompose, they take up all the oxygen in the water. This lack of oxygen is called “hypoxia,” and results in many problems for fish and plants.
One example of this is the “Dead Zone” At the end of the Mississippi river’s long journey lies the gulf of mexico & the dead zone. The dead zone is a seasonal phenomenon, a huge area where oxygen levels are too low to support aquatic life. Experts believe that excess nutrients, like nitrogen, washing down the river and into the gulf are responsible for the Dead Zone. Nutrients aren’t just damaging to watery ecosystems, they pose a real risk to humans. Nitrates, a byproduct of nitrogen, are especially dangerous. If nitrates make into the drinking water babies under 6 months of age can develop something called “blue baby syndrome” which prevents their blood from carrying enough oxygen.
Toxic chemicals are another class of pollutants. Some chemicals commonly used in manufacturing: mercury, PCBs, and lead are toxic to the environment and humans when they reach certain levels. Because of the health risks these chemicals pose, the EPA carefully regulates industrial waste. Special permits govern the disposal of toxic chemicals, but spills, accidents and improper disposal mean they still get into waterways. The problem isn’t just industrial. Agriculture also relies heavily on chemicals like herbicides and pesticides. Their application needs to be carefully controlled to prevent contamination of water. The list of chemicals we use everyday has grown faster than our knowledge of how they interact with the environment. Emerging contaminants, a buzzword in water circles, looks at chemicals not traditionally tracked like caffeine, over-the-counter drugs, antibiotics and disinfectants.
Pathogens are probably the most serious threat to our health. Pathogens are disease causing bacteria and viruses. They can come from human sewage or raw animal waste. If pathogens contaminate water and aren’t eliminated during treatment, the tiny organisms can can cause serious diseases like dysentery, hepatitis, food poisoning, parasitic infections or in some cases even death.
Assign directly to your students using the code or link above, without having them log in. Simply tell your students to go to
www.pbsstudents.org and enter the Assignment Code, or click on the Assignment URL to share the assignment as a link.