After completing this chapter you should be able to...
- Distinguish between point source and nonpoint source water pollution.
- Name and describe common water pollutants, including chemical, biological, and physical pollutants.
- Explain the mechanism of eutrophication.
- Summarize the current state of wastewater treatment globally.
- Describe the process of wastewater treatment, including pretreatment, primary treatment, secondary treatment, tertiary treatment, and disinfection and discharge.
- Summarize strategies for reducing water pollution.
- Identify sources of air pollution.
- List common air pollutants.
- Explain how CFCs caused ozone depletion, and global efforts to address this issue.
- Describe the causes and consequences of acid deposition.
Water pollution may arise from a single origin (point source pollution), or it may arise from multiple dispersed sources throughout the watershed (nonpoint source pollution). Water pollutants may be chemical, biological, or physical. Oxygen-demanding waste increases biological oxygen demand and causes hypoxia, depriving aquatic organisms of oxygen. This results from eutrophication, in which excess nutrients cause algal blooms.
Pathogens are the most deadly form of water pollution. They cause waterborne diseases, killing 485,000 people every year. Resolution of the global water pollution crisis requires multiple approaches to improve the quality of fresh water. The best strategy for addressing this problem is proper wastewater treatment. Strategies to reduce water pollution in general include the Clean Water Act, remediation, and watershed management.
Air pollution can be thought of as gaseous and particulate contaminants that are present in the Earth’s atmosphere. Chemicals discharged into the air that have a direct impact on the environment are called primary pollutants. These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants. The commonly found air pollutants, known as criteria air pollutants, are particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm health and the environment and cause property damage.
The ozone depletion process begins when chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODS) are emitted into the atmosphere. Reductions in stratospheric ozone levels lead to higher levels of harmful ultraviolet radiation, particularly UVB, reaching the Earth’s surface. The sun’s output of UVB does not change; rather, less ozone means less protection, and hence more UVB reaches the Earth. The Montreal Protocol is an international effort to phase out CFCs, and has been successful in limiting ozone depletion.
Acid deposition occurs when certain air pollutants react with atmosphere to produce nitric and sulfuric acids. It can reach Earth as various forms of precipitation or as dry particles that later react to form acid. The precursors of acid deposition result from both natural sources, such as volcanoes and decaying vegetation, and anthropogenic (human) sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion. Acid deposition causes acidification of lakes and streams, contributes to the damage of trees and many sensitive forest soils. In addition, acid deposition accelerates the decay of building materials and paints, contributes to the corrosion of metals and damages human health. However, the severity of acid deposition has declined due ot regulations and technologies that limit air pollution.