Pollutants are substances released into ecosystems by human activities that decrease the quality of air, water, soil and food, and affect the health of human and non-human populations. Some pollutants are synthetic (produced by humans), including some chemical pesticides used to protect crops from insects and other organisms. Pollutants can also be substances that derived directly from the environment, such as heavy metals or fossil fuel that humans extract from the Earth. Human waste, including sewage and trash, often contain pollutants that can cause diseases in humans and other organisms.
Through various human activities, including the use of fossil fuels, farming, mining, urbanization, and industrial innovations, we have rapidly increased the volume and kinds of pollutants and waste that enter ecosystems across the globe.
The effects of pollutants and waste are having far-reaching impacts on the Earth system and the quality of human life. Some of these effects include:
- Decreasing air quality. The burning of fossil fuels releases an array of pollutants that reduce air quality and harm life, especially sulfur dioxide (SO2), nitrogen oxides (NOx), and airborne particles such as soot. Chemical reactions between air pollutants from the burning of fossil fuels and other industrial processes can also form surface-level ozone. Poor air quality can cause respiratory disease.
- Increasing the acidity of precipitation. Sulfur dioxide, nitrogen oxides, and carbon dioxide from the burning of fossil fuels react with water vapor, oxygen, and other chemicals to form acid rain. Acid rain can contaminate freshwater sources, resulting in harmful algal blooms that reduce water oxygen levels and harm fish populations and other wildlife. Additionally, acid rain increases chemical weathering of rocks, including manmade structures.
- Decreasing water quality. Pollutants such as oil, pesticides, fertilizers, heavy metals (e.g. mercury, arsenic, lead), and radioactive waste can contaminate rivers, lakes, ground water, and the ocean, harming the health of humans and other species. Polluted water can decrease species populations, disrupt species interactions, and decrease biodiversity. Additionally, power plants that burn fossil fuels cool their systems by removing freshwater from local rivers and lakes. The warm water returned to nearby ecosystems (also called thermal pollution) can cause stress for local species.
- Decreasing the availability and quality of food. Pollutants, such as heavy metals, pesticides, and industrial coolants can be absorbed by organisms, which can become concentrated in their tissues. These pollutants can be further concentrated in predators if they consume prey that have been exposed to pollutants, a process called biological magnification. High concentrations of pollutants in food can harm the health of humans and other species, and in polluted regions people may be advised to avoid consuming certain organisms because they contain concentrated contaminants.
- Increasing the amount of chemical nutrients in soil or water, especially nitrogen and phosphorous from the use of fertilizers for agricultural activities or from sewage waste. These nutrients increase plant and algae growth, which can lead to ecological degradation. For example, in aquatic environments bacterial decay of excess algal growth caused by nutrient-rich runoff can reduce oxygen levels in the water, killing fish and other species. This process is known as eutrophication.
- Destroying the ozone layer. Human-made chemicals developed in the 1960s called chlorofluorocarbons (CFCs) destroy ozone. CFCs are used for various products, including air conditioners, aerosol spray cans, and the manufacturing of Styrofoam. In 1986 over 70 counties signed the Montreal Protocol to reduce CFC production, and global cooperation and action have allowed the amount of stratospheric ozone to build back up again.
- Disrupting life cycles and altering traits of organisms, which can decrease species populations. For example, chemicals that make plastics flexible, called plasticizers, such as bisphenol-A (BPA) or phthalates, leach out of plastics over time. These chemicals, which mimic hormones, can interfere with the endocrine (hormonal) systems organisms use for reproduction and growth. These disruptions can change their development and mating behavior, as well as impact the health of the offspring in many animals, including fish, birds, reptiles, amphibians, and mammals.
Can you think of additional cause and effect relationships between pollutants and waste and other parts of the Earth system?
Visit the burning of fossil fuels, freshwater use, deforestation and reforestation, and habitat loss and restoration pages to learn more about how resource and land use affects global climate and ecosystems.
Learn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.
- Toxic river means rapid evolution for one fish species
- The mutations that make us human
- Ozone depletion: Uncovering the hidden hazard of hairspray