Eagle Decline: Air Pollutants And Their Impact

Air pollution is a pressing issue that poses significant risks to both human health and the planet. It is the world’s fourth-largest risk factor for early death, causing approximately 4.5 million deaths from outdoor air pollution and 2.2 million deaths from indoor air pollution in 2019 alone. Wildlife is also vulnerable to the harmful effects of air pollution, with pollutants such as heavy metals, toxic chemicals, and persistent organic compounds (POPs) entering the food chain and causing damage to the supply and quality of food. Top predators, including eagles, are particularly susceptible to the bioaccumulation of these pollutants, which can lead to health issues, reproductive problems, and even death. While eagles play an essential role in the aquatic food web, they are also indicators of environmental contamination. This is evident in the case of bald eagle deaths in the southeastern United States, where EPA researchers discovered that the eagles contracted a neurological disease from ingesting a toxin produced by cyanobacteria. As we continue to face the challenges posed by air pollution, it is crucial to address its impact on both human populations and vulnerable wildlife, such as eagles, to ensure the well-being of our planet and its inhabitants.

Bromine-produced cyanobacteria

Bald eagles are at the top of the aquatic food web, making them good indicators of environmental contamination. Nestling eagles are particularly useful because their food comes from a definable local area. In 2001, bald eagles began dying in Georgia, South Carolina, and North Carolina, and the cause was a mystery for over a decade.

An invasive water plant, Hydrilla verticillata, was found to be a breeding ground for a lethal cyanobacteria. Cyanobacteria are a group of autotrophic gram-negative bacteria of the phylum Cyanobacteriota that can obtain biological energy via oxygenic photosynthesis. They are probably the most numerous taxon to have ever existed on Earth, and the first organisms known to have produced oxygen. They are usually found in marine environments and play important roles as primary producers. They produce a range of toxins known as cyanotoxins that can cause harmful health effects in humans and animals.

The cyanobacteria grow on the leaves of the invasive water plant under specific conditions: in man-made lakes when bromide is present. Bromine is a chemical element that can be an indicator of pollution when found in the environment. While it can occur naturally, it is scarcely found in freshwater and is usually introduced into nature through anthropogenic, or human-caused products, such as pesticides, dyes, gasoline, and plastic casings for electronics.

Scientists believe that the presence of bromide triggers the toxic production of the cyanobacteria. They studied the tissues of diseased American coots, a type of waterfowl that eagles prey on, and found that the toxin is absorbed through the gut and accumulates in the body. This toxin affects not only birds but also fish, frogs, insects, and worms. It accumulates in the tissues of animals that ingest hydrilla coated with the bromine-produced cyanobacteria, and the toxin moves up through the food chain as animals consume diseased prey.

DDT and DDE

DDT, a popular and widely used pesticide after World War II, was banned from use in the United States in 1972. However, it continued to be produced and shipped to other countries until 1985. DDT can take over 30 years to degrade in cold, clay soils and can be transported long distances through the atmosphere, infusing soil and water with its toxic chemicals. DDE is one of the most common breakdown products of DDT.

Bald eagles are at the top of the aquatic food web, making them good indicators of environmental contamination. Nestling eagles are particularly useful because their food comes from a definable local area. Their feathers, which are molted and grown anew each year, harbor long-term contamination that builds up (bioaccumulates) and can cause health and reproductive problems.

Eaglets raised in the Apostle Islands had higher concentrations of DDE than eaglets from other areas. This is likely due to the slow breakdown of contaminants in the deep, cold waters of Lake Superior. From 2006 to 2015, DDE concentrations decreased at a rate of 5.8% per year across the region. This rate of decline is consistent with the 5.5% per year decline seen over 26 years among eaglets from the two Lake Superior study areas.

Top-level predators such as eagles are particularly susceptible to the bioaccumulation of air pollutants. These pollutants can collect and increase in concentration as they move up the food chain, causing health issues and even death.

PCBs

While there are no explicit mentions of PCBs being the air pollutant that caused eagle deaths, PCBs are considered a persistent organic pollutant (POP) that affects wildlife. As top-level predators, eagles are particularly susceptible to the bioaccumulation of POPs.

Despite these restrictions, PCBs persist in the environment due to their resistance to degradation. They can be released into the air, water, or soil, and they bioaccumulate in the tissues of living organisms. This means that they are stored in the body and can increase in concentration as they move up the food chain, posing a significant threat to top-level predators like eagles.

Monitoring of bald eagle nestlings in the Great Lakes region and the Mississippi River has detected the presence of PCBs. While the levels of PCBs have generally remained below the estimated threshold for adverse reproductive effects, certain areas have shown higher concentrations. For example, nestlings from Pools 3 and 4 of the Mississippi River exhibited the highest levels of total PCBs.

The impact of PCBs on eagle populations is a cause for concern. Even though acute reproductive effects have not been observed at current levels, PCBs can still have detrimental effects on eagle health and reproduction. PCBs can interfere with endocrine function, cause organ injury, increase vulnerability to stresses and diseases, and lead to lower reproductive success. Therefore, continued monitoring and efforts to reduce PCB levels in the environment are crucial for protecting eagle populations and ensuring their long-term survival.

Climate change

One of the key impacts of climate change on eagles is the alteration of their food sources and availability. For example, bald eagles in Upstate New York, a region exposed to various climate change hazards, are facing challenges due to the sensitivity of freshwater fish populations to thermal changes. Rising temperatures can lead to changes in the distribution and abundance of these fish, making it difficult for bald eagles to find enough food. Furthermore, extreme weather events can impact wind patterns, facilitating the spread of airborne pollutants like mercury, which accumulates in fish and poses risks to bald eagles that feed on them.

In the Puget Sound region, climate change can affect air temperatures, wind velocity, cloud cover, and precipitation, all of which have implications for bald eagle energy demands and food availability. Changes in river temperatures and flows may also reduce the availability of salmon carcasses, a crucial food source for overwintering eagles.

The effects of climate change on eagle populations have significant ecological implications. Bald eagles play a vital role in the ecosystem, and their decline could disrupt the entire food chain. Addressing air pollution and mitigating climate change are crucial for protecting eagle populations and preserving the health of the planet and its inhabitants.

Acid rain

Air pollution is a significant issue that detrimentally impacts human health and the planet. It is the fourth-largest risk factor for premature death globally, causing approximately 4.5 million deaths from outdoor air pollution and 2.2 million deaths from indoor air pollution in 2019 alone.

One of the many pollutants that harm wildlife is acid rain. It occurs when emissions from burning fossil fuels react with sunlight, forming smog. This smog contains harmful substances that can be carried by wind and deposited onto soil and water bodies through precipitation. Acid rain alters the chemistry and quality of these environmental elements, making the water potentially too acidic for some animals to survive or maintain normal physiological functions.

Top predators such as eagles are particularly susceptible to the bioaccumulation of pollutants. Bioaccumulation occurs when pollutants are ingested and stored within an animal's tissues, increasing in concentration as they move up the food chain. For example, eagles that prey on waterfowl or fish affected by acid rain can accumulate toxins in their bodies, leading to health issues and even death.

In addition to acid rain, eagles are vulnerable to other air pollutants such as heavy metals, toxic chemicals, and persistent organic pollutants (POPs). These contaminants can enter the food chain, damaging the supply and quality of food available to eagles and other wildlife. Human activities, including the use of pesticides like DDT, have also been linked to eagle deaths. While DDT was banned in the United States in 1972, its persistence in the environment and long-range transport continue to pose risks to eagle populations.

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