Air Pollution's Impact: Species Under Threat

Air pollution is not just harmful to humans, but also to animals, plants, and the environment. Ecosystems are communities of plants, animals, and other organisms, along with their environment, including the air, water, and soil. When one part of an ecosystem is affected by air pollution, it can have a detrimental impact on everything else. For instance, air pollution can affect the quality of the environment or habitat in which animals live, as well as the availability and quality of their food supply. Insects, worms, clams, fish, birds, and mammals are all vulnerable to air pollution, and their exposure and vulnerability can vary depending on their interaction with the environment.

Insects

Bees are a well-known example of insects affected by air pollution. Air pollutants break down plant-emitted scent molecules, which bees use to locate food. When these odors are modified by pollution, bees become confused and disoriented. This can lead to increased foraging time and decreased food supply for their colonies. The decline in pollination of wild plants may lead to increases in the population of plants that do not rely on pollinators, further impacting the ecosystem.

Air pollution can also affect the competition and predation between different insect species. For example, the loss of some fish species due to high levels of aluminum in the water can benefit insect populations that are food sources for certain types of ducks. However, the same loss of fish could be detrimental to other bird species, such as eagles and ospreys, that depend on fish as a primary food source.

The effects of air pollution on insects can have far-reaching consequences, impacting crop yields, ecosystems, and even economic productivity. With 70% of the world's crops depending on insect pollination, it is crucial to understand and address the factors affecting insect populations, including air pollution.

Fish

Additionally, air pollution contributes to the presence of toxic substances in the water, such as mercury, which is transported through the air and deposited into water bodies. The presence of mercury in the water not only harms fish but also poses risks to humans who consume them. These toxic substances can bioaccumulate in the tissues of fish and other organisms, leading to a concentration increase as they move up the food chain. This bioaccumulation can result in organ injury, increased stress and disease susceptibility, impaired reproductive success, and even death.

Furthermore, air pollution can indirectly affect fish populations by impacting their food sources. For example, nitrogen pollution can cause toxic algal blooms, reducing the oxygen available for fish and other aquatic life, and killing seagrasses that serve as nurseries for fish.

Research by Dr Holly Shiels, an animal physiologist specialising in marine life, has also revealed insights into the cardiovascular impacts of air pollution on fish. Her work has shown that exposure to polycyclic aromatic hydrocarbons (PAHs) from oil spills can cause arrhythmias and cardiotoxicity in fish. These findings have broader implications for understanding the cardiovascular effects of air pollution on humans as well, given the similarities in cardiac function at a molecular level.

Birds

Ground-level ozone (O3) and nitrogen oxides (NOx), two of the most common air pollutants, are powerful oxidants that can cause direct, irreversible damage to birds' lungs. Long-term exposure can lead to inflammation, ruptured blood vessels, and lung failure. Studies have shown that long-term exposure to polycyclic aromatic hydrocarbons (PAHs), toxic chemicals commonly emitted by traffic, may cause reduced egg production and hatching, increased abandonment of eggs or chicks, and reduced growth in birds. PAHs have also been found to cause DNA mutations in Double-crested Cormorants in Canada, which can then be passed on to their offspring. DNA mutations in birds, as in humans, may disrupt essential cell processes and cause cells to divide uncontrollably – a condition otherwise known as cancer.

Air pollution also affects bird habitats. Ground-level ozone damages the plant communities that birds rely on for food, nesting, and shelter. A study in Virginia found that increased ozone levels may reduce species diversity, alter water and nutrient cycles, and allow invasive plant species to thrive. Accumulation of nitrogen oxides and sulfur oxides causes soil and water to become more acidic. Soil and water acidification may reduce the abundance or the nutritional value of birds' food sources. In some areas, this means lower calcium availability in the environment. Since calcium is a necessary component of eggshells, less calcium means smaller clutch sizes, according to a study in the eastern United States.

Nitrogen oxides from air pollution are a significant cause of eutrophication – the excess of nutrients in a body of water. Eutrophication can reduce the populations of fish and invertebrates that birds depend on for food. Over time, nitrogen oxide accumulation may also allow invasive nitrogen-loving plants to thrive at the expense of native plants. Lichens, which some California birds use for forage and nesting material, are among the first flora to be affected by air pollution.

Mammals

Impact on Habitat

Acid rain, a product of air pollution, can alter the chemistry and quality of soils and water, making them uninhabitable for some mammals. For instance, acid rain can increase the release of heavy metals, such as aluminium, from soils into water habitats. This, in turn, can have devastating effects on aquatic mammals, such as seals, otters, and beavers. Additionally, air pollution can alter the migration patterns of some mammals, forcing them to leave their natural habitats.

Impact on Food Supply and Quality

Air pollution affects the food chain by allowing toxic substances to enter and damage the supply and quality of food. These toxic substances, such as heavy metals and persistent organic pollutants (POPs), collect within the tissues of mammals and increase in concentration as they are consumed by other mammals higher up in the food chain. This process, known as bioaccumulation, particularly affects top-level predators such as bears.

Furthermore, air pollution can directly poison mammals by disrupting their endocrine function, causing organ injury, increasing their vulnerability to stresses and diseases, impairing their reproductive success, and even leading to death.

Impact on Humans

It is important to note that air pollution does not only affect wild mammals but also humans and domesticated mammals. Mammals that live in cities, such as pets, are more exposed to pollutants than those in rural areas. Cattle, for example, often consume contaminated water and plants, and they also produce methane gas, which contributes to climate change.

Plants

Gaseous air pollutants enter plants through the leaves' stomata, while particulate pollutants are captured by the microstructure of leaf surfaces. The penetration of pollutants into plants is mainly through the leaves, with a slight penetration through the stems and trunk. Before reaching the leaf, the pollutant must pass through the "boundary layer", which is the layer of air in contact with the leaf that is not agitated. The thickness of this layer depends on the size and shape of the leaf, the presence of leaf hairs, and wind speed.

The phytotoxicity of air pollutants depends on their chemical nature. Some of the most phytotoxic pollutants include hydrofluoric acid, ozone, sulfur dioxide, and nitrogen dioxide. The pollutant will cause specific stress related to its own physicochemical characteristics. For example, pollution by hydrofluoric acid will disrupt the cellular metabolism of calcium, and sulfur oxides will disturb the functioning of the photosynthetic apparatus.

Air pollution can also cause indirect effects on plants through its impact on soil chemistry. Some air pollutants, like heavy metals from industrial activities, fall on the ground and change soil chemistry and pH, making it difficult for plants to obtain the nutrients they need to thrive.

The effects of air pollution on plants can be either direct or indirect. Direct effects occur when toxins harm plants by depositing on them directly from the air and affecting their leaf metabolism and carbon uptake. Indirect effects happen via soil and start at the roots.

Visible signs of damage to plants from air pollution include leaf damage (yellowing, falling leaves, or injuries), poor growth, root damage, and inability to photosynthesize properly, resulting in stunted growth and reduced productivity.

Frequently asked questions