Air Pollution's Watery Impact: A Complex Cascade

Air pollution is a pressing issue that has captured global attention due to its detrimental effects on human health, the environment, and various natural ecosystems. While the respiratory and cardiovascular dangers of inhaling polluted air are well-known, the impact of air pollution on water resources is equally concerning and often underestimated. The complex relationship between air and water pollution involves the deposition of toxic chemicals and compounds from the atmosphere into water bodies, leading to degradation and long-term harm. This process, known as atmospheric deposition, introduces harmful substances such as nitrogen, mercury, heavy metals, and pesticides into oceans, rivers, and lakes, endangering aquatic life and, ultimately, human health.

Atmospheric deposition

Nitrogen, mercury, combustion emissions, pesticides, and other heavy metals are among the air pollutants with the highest potential to harm water quality. These pollutants can settle in bodies of water, damaging the ecosystems within them and posing risks to public health. Mercury is considered the most hazardous air pollutant due to its environmental behaviour and toxicity to fish and other wildlife. High levels of mercury in fish from certain lakes have even triggered health warnings for anglers.

Pollutants such as sulfur can lead to excess acid levels in lakes and streams, damaging trees and forest soils. Atmospheric nitrogen can reduce plant biodiversity and harm aquatic life, and eutrophication, or the accumulation of nutrients in water, leading to algal blooms and the creation of "dead zones" where oxygen depletion causes the death of organisms that require oxygen to survive. Eutrophication can also occur in aquatic ecosystems deficient in nitrogen, such as coastal waterways and estuaries, due to acid precipitation from the release of nitrogen oxides.

Air pollution can also affect precipitation, which in turn impacts water bodies. Acid precipitation from rain and snow can alter soil chemistry, affecting plant growth and water quality. Soils with higher calcium carbonate content, such as limestone and dolomite, are more resistant to acid rain and can help neutralize acids. However, soils with lower calcium carbonate levels, such as those found on quartzite and granite, are more vulnerable to acidification.

Additionally, atmospheric deposition can result in the deposition of toxic organic compounds, such as polychlorinated biphenyl pesticides (PCBs) and nitrosamines, into water bodies. These compounds can bioaccumulate in aquatic organisms, including fish, posing hazards to human health. Climate change and melting conditions in the Arctic may also release previously settled pollutants from snow and ice back into the atmosphere, contributing to water pollution.

Acid rain

The impact of acid rain on water bodies depends on their buffering capacity, which is the ability of the water and surrounding soil to neutralize acidic compounds. In areas with low buffering capacity, acid rain can release toxic chemicals, such as aluminum, from soils into lakes and streams. This can be harmful or even lethal to many aquatic organisms, including fish. Acid rain can also cause slower growth or death of forests and other vegetation.

Some water bodies are particularly vulnerable to acid rain due to their geological characteristics. Soils with lower levels of calcium carbonate, such as those found on quartzite, gneiss, granite, and other metamorphic rock deposits, have a reduced ability to neutralize acids. Thin soils, such as those in high alpine areas, are also more susceptible to the effects of acid rain.

The effects of acid rain on water quality can be both short-term and long-term. Water bodies can experience a sudden and dramatic decrease in pH, known as "acid shock," which can be fatal to aquatic life. Alternatively, they can become more acidic over time due to ongoing exposure to acid precipitation. This gradual process can make it challenging for vegetation and aquatic wildlife to adapt, leading to reduced biodiversity and potential ecological disruptions.

Eutrophication

Cultural eutrophication occurs when sewage, industrial wastewater, fertilizer runoff, and other nutrient sources are released into the environment. Nutrient pollution, particularly from nitrogen and phosphorus, causes algal blooms and bacterial growth, resulting in the depletion of dissolved oxygen in the water. This leads to substantial environmental degradation and can create dead zones where organisms die from asphyxiation. Over 166 dead zones have been documented in the United States, including in the Chesapeake Bay and the Gulf of Mexico.

The growth of algae is favoured when soluble nitrogen becomes limiting and phosphorus inputs remain significant. Nutrient pollution, therefore, leads to an excess of nutrients in the water, causing algal blooms and the overcrowding of other aquatic plants, which compete for sunlight, space, and oxygen. When the prolific algal layer dies, it becomes oxygen-demanding waste, creating very low oxygen concentrations in the water (2 ppm O2). This can result in the death of aerobic organisms, such as fish and invertebrates, and affect terrestrial animals that rely on these water sources.

The impact of eutrophication on human health is primarily through excess nitrate in drinking water and exposure to toxic algae. High levels of nitrates in drinking water can cause blue baby syndrome in infants, and toxic algae can cause various health issues, including rashes, stomach or liver illness, and respiratory or neurological problems. Eutrophication also has economic impacts, with the tourism industry losing close to $1 billion annually due to losses in fishing and boating activities.

There have been various techniques proposed and implemented to prevent and mitigate eutrophication. These include the use of chemical coagulants, such as lime, magnesium sulphate, and ferric sulphate, which can effectively remove nitrate and phosphate from water. Biological techniques, such as wetland treatment, have also been successful in removing nutrients like nitrogen and phosphorus from wastewater. Additionally, the introduction of bacteria and algae-inhibiting organisms, such as shellfish and seaweed, can help reduce nitrogen pollution and control the growth of cyanobacteria.

Ozone layer depletion

The main culprits of ozone layer depletion are chlorofluorocarbons (CFCs), which are released by solvents, spray aerosols, refrigerators, air conditioners, and other cooling appliances. CFCs are broken down by ultraviolet radiation in the stratosphere, releasing chlorine atoms. These atoms react with and destroy ozone molecules. It is estimated that a single chlorine atom can destroy 100,000 ozone molecules. Other ozone-depleting substances (ODS) include hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, hydrofluorocarbons, and methyl chloroform. These substances are used in various applications, such as coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.

The depletion of the ozone layer has significant consequences for both human health and the environment. Ozone layer depletion increases the amount of harmful UVB radiation reaching the Earth's surface. UVB radiation has been linked to various adverse health effects, including non-melanoma skin cancer, malignant melanoma (the most lethal form of skin cancer), and the development of cataracts. It also weakens the immune system and contributes to premature ageing.

The increased UVB radiation also affects plants and aquatic ecosystems. It can alter plant growth, distribution of nutrients within plants, timing of developmental phases, and secondary metabolism. Phytoplankton, which form the foundation of aquatic food webs, are particularly vulnerable to UVB radiation, leading to reduced survival rates and disruptions in the aquatic food chain.

Heavy metals

Atmospheric deposition also plays a crucial role in heavy metal contamination of water. Air pollution containing heavy metals can be transported over long distances and deposited into water sources through rainfall or dust particles. Volcanic activity and the combustion of fossil fuels, such as coal and petroleum products, release heavy metals into the atmosphere, which can then be carried by wind and currents into water ecosystems.

The presence of heavy metals in water poses a significant threat to both human health and the environment. Heavy metals, such as arsenic, cadmium, chromium, lead, and mercury, are highly toxic and can cause multiple organ damage, even at low exposure levels. They are classified as human carcinogens and can accumulate in the food chain, affecting marine life, birds, mammals, and humans. The ingestion of contaminated water or the consumption of affected aquatic organisms can lead to severe health issues, including cancer, kidney damage, neurotoxicity, and liver and lung damage.

To address the issue of heavy metal contamination in water, several remediation strategies have been developed. These methods aim to reduce metal concentrations, prevent further pollution, and restore degraded ecosystems. Physical, biological, and chemical approaches are employed to manage heavy metal pollution and mitigate its adverse effects on the environment and human health.

Frequently asked questions