Notes

What Is Pollution?
Pollution is the presence of contamination or harmful substances in the environment—in the air, water, or land. For example, if you add a few drops of paint to clean water, the water becomes polluted and unsafe for drinking. Harmful substances polluting the environment are known as pollutants. Pollutants can be natural, such as volcanic ash, or artificial, such as garbage, exhaust from cars, and harmful chemicals from factories. Some of the major types of pollutants contaminating the environment are

fertilizers used for plants
organic waste, such as sewage or manure
pesticides and herbicides
pharmaceuticals, such as antibiotics and synthetic hormones in wastewater
endocrine disruptors in agricultural chemicals
organic contaminants, such as petroleum products (oil, gasoline), solvents (toluene, acetone), and refrigerants
heavy metals, such as lead and mercury
inorganic gases, such as carbon monoxide and sulfur dioxide
radioactive material, such as waste from nuclear power plants and production of nuclear weapons

Let’s examine the different types of pollution.

Air pollution: When you go for an early morning walk, you inhale fresh air. Fresh air suits our bodies and helps to regulate our health and life. In terms of chemical composition, almost 99 percent of the air we breathe consists of oxygen, nitrogen, water vapor, and other gases. Air pollution refers to the addition of substances other than natural components to the air. A common air pollutant is tiny particles from burning fuel, which appears like soot floating in air. For example, when you light a fire from wood, you will notice particles rising from the burning fire. Pollutants from burning wood sting your eyes and sometimes make it difficult to breathe.

Gases (such as nitrogen oxide, sulfur dioxide, and carbon monoxide emitted by vehicles) and chemical vapors produce smog and acid rain. Greenhouse gases, such as methane and sulfur dioxide, also pollute the environment when released in large amounts. Air pollution causes respiratory and cardiovascular diseases in humans and other species.



Land pollution: Land is mainly polluted by industrial wastes and household garbage. Hazardous wastes produced by industries include wastes from chemical production, mining, pesticide manufacturing, and petroleum refining. Common household garbage includes food scraps, newspapers, appliances, product packaging, furniture, clothing, bottles, paint, and batteries. According to the Natural Resources Defense Council, activities related to food production are the largest contributor to land pollution. It is estimated that in the United States, about 40 percent of food produced winds up in the trash every year.

Pesticides also pollute soil. They reduce the biodiversity and quality of soil, thereby affecting the growth of plants.

Water pollution: Water is polluted when harmful substances, such as fertilizers, pesticides, oil, metals, sewage, and chemicals, are added to it. These water pollutants come from different sources, such as water diversions, agricultural runoff, oil spillage, and channelization of streams. Polluted water is not only unsafe for drinking; the presence of excessive pollutants may make it unfit for fishing and swimming as well. Water pollution affects marine life severely. For example, sewage causes pathogens to grow, leading to diseases in living organisms. Sewage also causes low levels of dissolved oxygen in the water, thereby depriving living organisms of oxygen required for growth.



Nutrient pollution: This is a type of water pollution. Nutrients that are present in fertilizers are essential for plant growth. However, when nutrients like nitrogen mix with a water body, they lead to excessive growth of algae. Excessive algae block light from reaching beneath the water body. Eventually, the aquatic plants and organisms die due to lack of sunlight. Nutrient pollution is one of the biggest environmental problems in the United States.

Air, land, and water pollution are the major types of pollution we face. However, certain other types of pollution harm our environment as well.

Thermal pollution: This refers to the artificial warming of natural water by host water discharged from factories and power plants. Such water contains less oxygen, leading to death in aquatic species. Sudden changes in temperature can kill fish.

Noise pollution: We need sound to communicate. But when sound reaches harmful levels in the environment, it causes noise pollution. Noise pollution occurs from too much honking of car horns, sounds coming from planes and industries, and so on. Consequences can range from hearing loss and speech interference to stress-related illnesses and high blood pressure. Noise pollution from ships can also harm whales and other underwater species.

Light pollution: We need electricity to light our homes, offices, streets, and shops. However, overuse of electric lights causes sky glow or light pollution. Light pollution harms plants and animals, because they confuse artificial lights with sunlight. As a result, the flowering of plants alters and the migration schedule of animals can change.

Sources of Pollution
Contaminants polluting the environment can come from a single source or from multiple sources that pollute large areas. There are two types of pollution sources: point source pollution and non-point source pollution.

Point Source Pollution
In this type of pollution, pollutants come from a single, easily identifiable source. Let’s look at some examples of point source pollution of air, water, and land.

Air: A chemical factory can produce dangerous chemicals and toxic gases. If the factory releases untreated toxins and gases directly into the atmosphere, it becomes a point source of air pollution.

Water: Consider a factory that treats its products with a certain chemical. After treatment, the factory may directly release harmful chemicals into a stream. If the factory does not treat the chemicals prior to release, it pollutes the stream water.

Land: While repairing cars, a garage should accumulate waste oil and send it to a treatment company for recycling. Instead, if the garage simply releases the untreated waste oil into the ground, it contaminates the soil. In this example, the garage is a point source of land pollution. Another example of point source land pollution is when people directly dispose of garbage on open ground.

Non-Point Source Pollution
Here, pollutants reach the environment from multiple sources and spread across large areas, often mixed with runoff (such as rain or snow). It is difficult to identify these sources of pollution.

Air: Air pollution from cars is caused by a variety of toxins, such as nitrogen oxide and hydrocarbons. Similar pollutants are generated by the burning of fuel and heating systems in homes and buildings. Buses and large trucks with diesel engines also produce hydrocarbons. Toxins in the air can cause widespread acid rain.

Water: Non-point source pollution is common in water. For example, acid rain enters waterways and water bodies. The life and growth of fish and other species in the polluted water are adversely affected. Other non-point sources that pollute water include farm pesticides, fertilizers, and animal feces.

Land: Non-point source pollutants (such as pesticides, chemicals, and sewage) can reach soil from the air or water. Plants absorb toxic pollutants from soil. These toxic plants enter the food chain when animals and humans consume them. Thus, the entire cycle is polluted, leading to diseases and deaths of plants, animals, and human populations.

Effects of Pollution
Let’s take a closer look at the effects of pollution on the environment and living organisms.

Air pollution: These are some of the effects of air pollution:

When an air pollutant like sulfuric acid mixes and reacts with clouds, it causes acid rain. Acid rain covers large areas and harms every form of life. It destroys plants, leaves, and trees. It also deteriorates the quality of soil and water in lakes and streams, thus harming aquatic life.
Air pollutants can make the air unsafe for breathing, leading to respiratory problems. Air pollutants can also combine to form smog, which makes breathing difficult.
Some air pollutants are greenhouse gases that contribute to global warming. Climate change results in the untimely arrival of seasons and affects plant, animal, and human lives.
Air pollutants can degrade the ozone layer in the atmosphere. This allows harmful ultraviolet (UV) rays to reach Earth.



Water pollution: Water pollution also causes multiple environmental problems:

Water pollution may be toxic to many species, such as fish, crab, and sea gulls, that depend on water bodies.
Eutrophication, a process in which a water body acquires high levels of nutrients, is a prominent source of water pollution in agricultural areas. When farmers supply fertilizers to plants for their growth, the nutrients often travel and mix with water bodies. Excessive nutrients lead to growth of a blanket of algae on lakes and rivers. The algae block sunlight from reaching below the water body, causing hypoxia. Hypoxia is the depletion of oxygen in water, and it kills aquatic life. Areas with hypoxia are known as dead zones.
Water pollutants enter the health systems of animals and plants that consume polluted water. Higher predators consume these animals and plants. In turn, the predators may be consumed by humans. Pollutants from water can cause diseases, such as cholera and hepatitis, and death in humans. Thus, water pollutants affect the entire food chain.
Pollutants degrade water quality. The polluted water tastes and smells bad, and it may also be unsafe for drinking.

Land pollution: The following are some effects of land pollution:

When contaminated water reaches the soil, it harms and pollutes the quality of the soil. Food (plants) grown on polluted soil may be unfit and unsafe for consumption.
Direct contact with polluted soil can cause skin problems, respiratory problems, and cancer in human beings.
Dumping of garbage creates a foul smell in the environment. In addition, rodents and insects breed in dumping sites. Infected rodents and insects can transmit diseases. Sometimes, pollutants from such landfills enter waterways and water bodies, causing water pollution. Some towns and cities get rid of garbage by burning it. Although burning of garbage prevents land pollution, burning of dangerous chemicals and metals can cause air pollution.
People often litter beaches with plastic bottles and cans. The trash not only pollutes the beach and seawater, it also discourages tourists from visiting the beaches.
Mining often contaminates the soil with harmful chemicals, such as strong acids and heavy metals. This affects terrestrial life adversely.

You can determine the severity of a pollutant based on three factors:

its toxicity to humans, animals, and plants
its concentration in a given volume of water, soil, or air
its persistence in the environment
Some pollutants are short-lived, while some stay in the environment for a long time. Short-lived climate pollutants (SLCPs) persist in the atmosphere for a few days to a few decades, and they can contribute to global warming. Let’s examine two examples of some short-lived climate pollutants.

Agricultural waste: The waste produced by livestock used in agricultural produces approximately 18 percent of anthropogenic greenhouse gases. On most farms, animals are kept in cramped conditions. Their manure and urine are thrown into huge waste lagoons. These cesspools often leak or overflow. This emits dangerous microbes and drug-resistant bacteria into water. Thus, it pollutes the water.

Pesticides: Pesticides and fertilizers are used extensively to prevent pests and invasive species from destroying the crops. These pesticides target pests that may have been in existence for many years. Thus, they contain chemical substances harmful to the soil. Some of them even mix with water and result in water pollution.

Other short-lived climate pollutants that are biodegradable include garbage, sewage, dead plants, and food waste.

Organic pollutants that persist in the environment for a long time are termed persistent organic pollutants (POPs). These are toxic chemicals that harm the environment and human health. They are commonly found in pesticides. Polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), and dioxins are examples of POPs.

POPs contain chemicals (like dioxins), which also result from burning of fuel. POPs also consist of chemicals that are useful in agriculture, disease control, manufacturing, and industrial processes. For example, PCBs are useful in paints and lubricants, electrical transformers, and large capacitors.

However, exposure to POPs can lead to diseases and abnormalities in wildlife. In humans, it can cause behavioral, neurological, endocrinal, developmental, and reproductive disorders. POPs can be transported to different places by wind and water. Therefore, they can affect the food chain and life in different countries in a similar manner.