Water Pollution: A Slow, Deadly Poison For Animals

Water pollution is a pressing issue that poses a grave threat to the lives of animals. Contaminants such as heavy metals, oil spills, pesticides, and plastic waste directly harm aquatic life, leading to deformities, reproductive issues, and even death. The ingestion of plastic, for instance, has disrupted the natural feeding patterns of wildlife, causing internal deterioration and poisoning. Additionally, certain pollutants reduce oxygen levels in the water, creating an uninhabitable environment for fish and other aquatic organisms. As pollution travels up the food chain, it reaches humans as well, with microplastics being found in our bloodstreams. This issue is not isolated to marine life, as terrestrial creatures are also affected by plastic consumption.

Plastic ingestion

Impact on Marine Life

Marine animals, including fish, seabirds, and mammals, are particularly vulnerable to plastic ingestion. Small plastic fragments, such as microplastics, can sit on the water's surface, resembling food to seabirds and other marine species. As a result, they ingest these plastics, leading to intestinal blockages, starvation, and suffocation. Over half of fish stocks have ingested plastic, and researchers have found traces of microplastics in hundreds of fish species, including commonly consumed fish like bass and sardines.

Marine mammals, such as whales, dolphins, and seals, are also at risk. They may mistake plastic bags for prey, such as squid, or consume plastic particles through the food chain. A juvenile sperm whale, for example, was found dead with nearly 30 kilograms of plastic in its digestive tract, causing fatal inflammation.

Impact on Terrestrial Animals

Long-Term Health Consequences

The presence of microplastics in the environment has long-term health consequences for various animal species. Microplastics can absorb toxins, which then transfer to the fatty tissues of organisms that ingest them. This leads to liver and cell damage and disrupts reproductive systems. For example, oysters may produce fewer eggs due to the presence of microplastics, threatening population growth.

Death and Ecosystem Disruption

Entanglement in discarded fishing gear

Marine debris, including discarded fishing gear, poses a significant threat to wildlife, leading to entanglement, injury, and death. Derelict fishing gear, or gear that has been abandoned or lost, can trap various marine animals, such as fish, crustaceans, birds, and even large marine mammals.

Discarded fishing gear, such as nets, lines, buoys, and traps, once out of the control of fishers, can continue to "ghost fish," entangling and capturing marine wildlife. This ghost gear can also entangle with other gear, creating larger masses that increase the risk of entanglement. The most common types of derelict fishing gear involved in ghost fishing are gillnets, pots or traps, longlines, and trawls.

Large marine species, such as whales, dolphins, seals, sea turtles, and sharks, are particularly vulnerable to entanglement in discarded fishing gear. Their long-distance seasonal migrations increase the likelihood of encountering debris in commercial fishing zones and shipping lanes. The impact of entanglement on these already threatened or endangered populations can be devastating, affecting their reproduction and long-term conservation.

Efforts to address this issue include the development of best practices and response training for entanglement incidents. The International Whaling Commission (IWC) launched the Global Whale Entanglement Response Network in 2011 to build safe and effective response capabilities worldwide. Additionally, organizations like the NOAA Marine Debris Program are partnering with fishers and other entities to remove and prevent the introduction of derelict fishing gear in the ocean.

Oxygen depletion

Water temperature also plays a crucial role in oxygen depletion. Warmer water holds less oxygen than colder water. During hot weather, the surface water warms up more rapidly than the deeper layers, creating a thermocline, which acts as a barrier between the warm surface water (epilimnion) and the cold bottom water (hypolimnion). This stratification prevents the mixing of the two layers, and since photosynthesis and oxygen production only occur near the surface, the deep layer becomes devoid of oxygen.

Additionally, certain human activities, such as industrial, agricultural, and residential practices, can introduce chemical contaminants, organic loading, and excess nutrients into water bodies. These substances can increase the biochemical oxygen demand as they are broken down by bacteria, leading to oxygen depletion. Weather conditions can also influence oxygen levels, with calm, sunny weather promoting algal growth and subsequent oxygen consumption during respiration at night or on cloudy days.

The effects of oxygen depletion on aquatic life are severe. Fish and other aquatic organisms require adequate levels of dissolved oxygen to survive. When oxygen levels drop, fish exhibit distress behaviours, such as gathering at the surface to gulp air. If the oxygen depletion continues, it can lead to fish kills, where large numbers of fish die due to suffocation. Oxygen depletion can also cause physiological stress and decreased growth in fish populations.

Toxic algae consumption

Toxic algae, also known as Harmful Algal Blooms (HABs), are a type of bacteria called cyanobacteria. They produce toxins that can injure animals' livers, kidneys, or brains. These toxins can cause mild to life-threatening symptoms in animals, and even lead to death. Animals can be exposed to these toxins through drinking contaminated water, licking their fur after swimming in contaminated water, or eating other animals that have already ingested the toxins. Birds, for example, have died from eating dead fish contaminated with toxic algae, which then poisons them.

HABs occur when certain environmental conditions favour the growth of cyanobacteria, such as warm weather, stagnant water, and fertilizer runoff. They can grow in any water source, be it fresh or salt water, and have been observed in lakes, oceans, and other bodies of water worldwide. The impact of HABs extends beyond the immediate area of the bloom, as toxins can be transported in the air and affect animals even if they do not enter the water. For instance, toxins from a Karenia brevis red tide (a type of HAB) in Florida were found to be carried in the air up to 4 miles inland.

Animals that ingest water contaminated with HABs may experience stomach pain or vomiting, and in some cases, these toxins can cause neurotoxicity, leading to mass mortalities in fish, seabirds, sea turtles, and marine mammals. The toxins can also cause mechanical damage to organisms, such as disrupting the epithelial gill tissues in fish, resulting in asphyxiation. Additionally, HABs deplete the dissolved oxygen needed by aquatic animals, which can further contribute to fish die-offs and the creation of "dead zones" in affected areas.

The frequency and severity of HABs have been increasing due to global warming and pollution, with blooms forming in previously unheard-of locations, such as under ice sheets and in mountainous regions. This trend is concerning, as HABs have been linked to human and animal illnesses and deaths in 50 countries and 27 US states in a single year. The problem is not limited to wild animals, as domesticated dogs have also died from swimming in algal blooms, and tap water supplies can be affected when HABs grow in reservoirs.

Heavy metal poisoning

Aquatic animals, such as fish, are particularly vulnerable to heavy metal poisoning. They absorb these metals through their gills, body surface, and digestive tract. High levels of heavy metals in the water can lead to the accumulation of metals in the fish's body, causing toxicity. This toxicity can result in weight loss, reduced size, and decreased competitiveness for food and habitat among fish. Additionally, heavy metals can cause alterations in the structure and function of vital organs, including the lungs, heart, kidneys, liver, and neurological system. For example, zinc accumulation in fish gills can lead to tissue respiration issues and hypoxia, resulting in mortality.

Mercury poisoning is another significant concern. It can cause brain damage, skin damage, and an increased risk of cancer development. Animals affected by mercury poisoning cannot produce meat, liver, or kidneys fit for human consumption. Mercury can also lead to abortions, congenital deformities, and developmental differences in young animals.

Heavy metal pollution in the aquatic environment poses a threat to both freshwater and marine habitats. It can directly harm marine organisms such as mollusks, marine birds, and other sea-dwelling creatures. Additionally, it can indirectly affect humans by entering the food chain through contaminated fish and shellfish consumption. For example, in the Jinzu river basin of Japan, the local population suffered from an endemic illness called "itai–itai" due to consuming rice contaminated with high levels of cadmium from upstream mining activities.

The presence of heavy metals in the environment is a growing concern due to industrialization, climate change, and urbanization. These metals are non-biodegradable and tend to accumulate in living organisms, negatively impacting their health. Therefore, it is crucial to prioritize the removal of heavy metals from water sources and implement effective wastewater treatment methods to mitigate their detrimental effects on both the environment and human health.

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