The Effects of Environmental Pollutants

Pollution is the release of substances that cause deleterious effects to human health or the health of the environment. Pollution can be point-source, in which case it's released from a single location (a factory pipe, for example), or it can be non-point source, in which case it emanates from a larger area like a district or municipality. Depending on where it's released and what the pollutant is, pollution can cause a wide range of serious problems.

Toxic Contaminants

• Toxic chemicals can poison plants and animals. Some toxic chemicals can act as mutagens, agents that cause mutations in DNA and thereby increase the risk of birth defects or cancer in animals. Others are endocrine disruptors that interfere with the activity of hormones in animals. Chemicals and substances with any of these properties can kill organisms and thereby upset the balance of an ecosystem or even render it temporarily uninhabitable if they are present in sufficient concentrations. Toxic chemicals can also accumulate up the food chain, since a predator that consumes multiple prey organisms--each of which has a low concentration of the toxin in its tissues--will end up with a higher concentration.

Acid Rain

• Sulfur dioxide and nitrogen oxides produced by combustion may be released into the atmosphere, where they can react with water and oxygen to form sulfuric acid and nitric acid. These strong acids greatly decrease the pH of the water in which they are dissolved, even when they are present in low concentrations, leading to acid precipitation--better known as acid rain. Acid rain can damage plants or vegetation that have a low tolerance for acidic environments, thereby damaging and altering ecosystems.

Nutrient Pollution

• Release of excess nutrients--especially nitrogen and phosphorus--into waterways and natural bodies of water can boost algae growth, causing an algae bloom. The rapid increase in the algae population supports a rapid increase in the population of decomposers, who consume the oxygen in the water and drive the oxygen levels down so the water can no longer sustain fish and other organisms that need water. This phenomenon is called eutrophication.

Climate Change

• When solar radiation strikes Earth, some of it is absorbed and warms the surface of the Earth and its atmosphere. Earth's surface re-radiates some of this warmth in the form of infrared radiation, some of which is absorbed and re-radiated by greenhouse gases in the atmosphere. Greenhouse gases effectively act a little like a blanket that helps to trap some of the warmth, so a large increase in the amount of greenhouse gas will tend to increase mean surface temperature. Many scientists and environmentalists are concerned that human activities are leading to increased concentrations of greenhouse gases, especially carbon dioxide and methane, and that temperature rises caused by greenhouse gas accumulation could result in long-term changes in climate patterns--with far-reaching and dramatic consequences.

Ozone Depletion

• Ozone is a relatively unstable molecule composed of three oxygen atoms. Ultraviolet light striking oxygen molecules in Earth's upper atmosphere leads to the formation of ozone; this ozone can in turn absorb UV rays, breaking up in the process. Certain chemicals, most notably chlorofluorocarbons (CFCs) and some bromine compounds, break down in the upper atmosphere to release atoms of chlorine and bromine, which in turn catalyze the breakdown of ozone. Consequently, release of CFCs can contribute to depletion of Earth's ozone layer. Since the ozone layer helps reduce the amount of UV radiation that reaches Earth's surface--and since UV radiation can cause mutations in DNA, thereby harming humans and other organisms--many scientists and environmentalists believe CFCs and similar chemicals have the potential to cause environmental problems.