pollution

• pollution 


  introduction of harmful materials into the environment. these harmful materials are called pollutants. Pollutants can be natural, such as volcanic ash. can also be created by human activity, such as trash or runoff produced by factories. damage the quality of air, water, and land.
• Many things that are useful to people produce pollution.

  Cars spew pollutants from their exhaust pipes.

  Burning coal to create electricity pollutes the air. industries and homes generate garbage and sewage that can pollute the land and water. 

  Pesticides—chemical poisons used to kill weeds and insects—seep into waterways and harm wildlife.
• air pollution 


  results when the by-product of an activity makes chemicals airborne. 
• Close to Earth’s surface, sulfur dioxide (SO2) interacts with the water cycle in the atmosphere to produce acid rain or other forms of acid deposition downwind. 
• Nitrogen oxides (NOx) in vehicle exhaust and sunlight combine to form photochemical smog.
• carbon dioxide and methane, which are largely by-products of burning wood, oil, natural gas, and other fossil fuels, help to enhance the atmosphere’s ability to retain heat emitted from Earth’s surface, which contributes to the phenomenon known as global warming.
• In the upper atmosphere, chlorofluorocarbons (that is, CFCs) and similar chemical compounds have contributed to the destruction of Earth’s ozone layer until relatively recently. 
• Land pollution often contributes to water pollution as nutrients and substances from polluted sites seep into groundwater or run off into lakes and rivers before reaching the oceans.
• Polluted air can be dangerous, even if the pollutants are invisible. It can make people’s eyes burn and make them have difficulty breathing. It can also increase the risk of lung cancer.
• Hydraulic fracturing, which is used to recover natural gas and oil from the ground, releases some of these hydrocarbons into the surrounding rock, which can then seep into the groundwater.
• Pesticides, along with nitrogen and phosphorus from agricultural fertilizers, run off of croplands and into waterways, where they affect the aquatic and marine food chains.
• Pesticides poison insects, fish, and the animals that eat them.
• Nitrogenous and phosphorus fertilizers “feed” algae and other aquatic plants, which cause larger-than-normal blooms.
• Toxic materials from petroleum spills and other chemical releases can damage the surrounding soil, seep into the groundwater, and run off into waterways.
• water pollution 


  occurs when harmful substances—often chemicals or microorganisms—contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading water quality and rendering it toxic to humans or the environment.
• This widespread problem of water pollution is jeopardizing our health. Unsafe water kills more people each year than war and all other forms of violence combined.
• Meanwhile, our drinkable water sources are finite: Less than 1 percent of the earth’s freshwater is actually accessible to us. Without action, the challenges will only increase by 2050, when global demand for freshwater is expected to be one-third greater than it is now.
• causes of water pollution

  1. Agricultural 2. Seawage and wastewater 3. oil pollution 4. radioactive substances
• Radioactive waste is any pollution that emits radiation beyond what is naturally released by the environment. It’s generated by uranium mining, nuclear power plants, and the production and testing of military weapons, as well as by universities and hospitals that use radioactive materials for research and medicine. Radioactive waste can persist in the environment for thousands of years, making disposal a major challenge
• Plastic pollution 


  is the addition of plastic waste to the landscape and waterways. It is caused by manufactured plastics that are not properly disposed of.
• It is a problem because plastic does not break down easily, the chemical additives in plastic may become endocrine disrupters, plastic waste flows downstream into rivers and oceans (sea life can ingest, choke on, or become trapped in plastic waste), and plastic is a source of polychlorinated biphenyls (PCBs), which are suspected carcinogens.
• noise pollution 


  unwanted or excessive sound that affects health and environmental quality. It is caused by machines and engines associated with industry, as well as airports and other transportation systems.
• Noise is problematic because it can cause physical damage to hearing organs in humans and other animals, it produces increased stress levels, and it disrupts ecosystems by driving certain species away and altering the habits of wildlife. Noise pollution occurs primarily on land located close to industry and transportation and at sea, where it emanates from ship engines and sonar.
• light pollution 


  is unwanted or excessive light caused by streetlights and illuminated buildings, towers, and other structures. Light pollution changes nighttime visibility of natural features, disorienting migratory animals and fostering bird collisions with lighted towers and buildings.
• thermal pollution 


  pollution is the addition of heat to a cool environment, and it is caused by water or air used as cooling fluids in power plants and manufacturing that becomes heated in the process.
• Heated cooling water from power plants may be 15 ˚C (27 ˚F) hotter than lake or stream water, which increases metabolic rates in fishes and reduces the amount of dissolved oxygen that the water may hold. In extreme cases, it can be hot enough to burn animal tissues.