Ocean Food Chain: Pollution's Impact And Reach

The ocean is a vast body of water that covers about 70% of the Earth's surface and is home to a diverse array of plant and animal life. Unfortunately, human activities have led to the introduction of various pollutants into the ocean, which can have far-reaching consequences for the delicate balance of marine ecosystems. One of the most significant ways pollution affects the ocean food chain is through the process of bioaccumulation, where toxins accumulate in the tissues of organisms over time. This can lead to a concentration of toxins in top predators, which can have detrimental effects on their health and behaviour.

Bioaccumulation of toxins

Bioaccumulation is the gradual accumulation of chemicals in the living tissue of an animal. This occurs when an animal consumes something that is polluted or absorbs a chemical through its skin. Instead of expelling the chemical through waste, the animal stores the contaminant in its fatty tissues. If a toxin does not kill an animal immediately, the concentration of the substance tends to increase with the age of the affected species.

Substances that bioaccumulate include organic pollutants like hexachlorobenzene and the natural toxins released by dinoflagellate algae blooms. Heavy metals such as mercury, lead, and silver can also bioaccumulate in animals. These heavy metals are primary toxicants in our water, and they are not the only ones. Arsenic and cadmium are also present in our water systems and are dangerous to human health.

When a predator consumes an animal affected by bioaccumulation, the toxin in question biomagnifies. For example, a bird that eats multiple insects that have ingested a pollution-related chemical will consume large amounts of the toxin. When biomagnification affects a food web, the animals on the upper trophic level tend to eat and store more pollutants.

Compounds that biomagnify tend to be lipophilic, meaning they dissolve in fat rather than water, such as organonochlorines, or have a high affinity for proteins, like methylmercury. Pollutants that are mostly water-associated, like heavy metals, do not tend to biomagnify. However, they can bioaccumulate to very high concentrations in some organisms.

The effects of bioaccumulation multiply as they move up the food chain. This is a concern for humans, as we are at the top of the food chain.

Eutrophication

The excess nutrients lead to algal blooms, which block sunlight and cause the death of other plants. When the algae eventually die, they are decomposed by bacteria, which consumes the remaining oxygen in the water, creating "dead zones" that lack sufficient oxygen to support most organisms. This has severe implications for the food chain, as it can kill fish and other wildlife.

The economic impacts of eutrophication can be significant, with shellfish industries losing millions of dollars annually. Additionally, eutrophication can affect potable drinking water sources, leading to tainted water supplies and potential health risks for humans.

There have been efforts to combat eutrophication, such as the use of chemical coagulants and biological techniques like wetland treatment, which have shown some success in removing excess nutrients from wastewater. However, the success of these treatments can be limited by factors such as hydraulic loading rates. Overall, eutrophication is a complex ecological challenge that requires collective efforts to reduce nutrient inputs and develop effective long-term management strategies.

Trophic transfer of nanoplastics

Nanoplastics are plastic particles with a diameter of less than 100 nm. They are easily transferred through the food chain, as demonstrated by a study that exposed algae to nanoplastics, which were then consumed by water fleas, followed by secondary-consumer fish, and finally end-consumer fish. The nanoplastics were found in the digestive organs of the higher trophic level species, indicating trophic transfer.

The study also revealed that nanoplastics can negatively impact fish activity and induce histopathological changes in their livers. Additionally, they can penetrate embryo walls and accumulate in the yolk sac of hatched juveniles, potentially causing health risks.

Another study examined the trophic transfer of polystyrene nanoplastics and di(2-ethylhexyl) phthalate (DEHP) in a freshwater food chain consisting of algae, water fleas, and fish. The results showed that both nanoplastics and DEHP accumulated in the lower trophic level organisms and were transferred to the higher trophic level fish. However, only the nanoplastics were trophically amplified through the food chain, indicating that more nanoplastics may be accumulated by higher-level consumers in longer food chains.

The trophic transfer of nanoplastics and DEHP caused oxidative stress, histopathological damage, and disturbances in lipid metabolism in the fish. These findings highlight the potential negative impacts of nanoplastics on aquatic organisms and the importance of further research to understand their effects on the environment and human health.

Biomagnification of pollutants

The ocean food chain is susceptible to the harmful effects of pollution, with toxins accumulating in marine organisms and biomagnifying as they move up the food chain. This process, known as biomagnification, occurs when predators consume prey that have accumulated pollutants, resulting in higher concentrations of toxins in the predators' bodies. This is particularly detrimental in the ocean ecosystem, where pollutants are introduced from both atmospheric and riverine sources, impacting coastal environments and vulnerable species.

One of the primary concerns with biomagnification is the transfer of toxic chemicals, such as POPs, which tend to adhere to the fat cells of organisms. These chemicals, including pesticides, industrial chemicals, and unintentional pollutants like DDT, PCBs, and hexachlorobenzene, are highly toxic to both humans and wildlife. They have been linked to various health issues, including allergies, reproductive and hormone problems, immune system disorders, and cancer.

The biomagnification of pollutants also extends to microplastics, which are now recognized as a significant threat to marine life. Microplastics act as vectors, absorbing and transporting toxic chemicals throughout the food chain. As smaller organisms ingest microplastics, larger predators then consume these contaminated organisms, leading to a buildup of plastic and associated toxins in their systems. This transfer of nanoplastics, known as trophic transfer, has been observed in various marine species, including fish, birds, and seals.

The impact of biomagnification is not limited to individual species but also has broader ecological consequences. For example, the death of even small organisms, such as natural forest decomposers, due to pollution, can disrupt the entire ecosystem. This, in turn, affects the availability of food sources for other species, leading to scarcity and potential competition or migration. Thus, the biomagnification of pollutants in the ocean food chain has far-reaching effects, highlighting the urgent need for research and mitigation strategies to address this pressing environmental challenge.

Impact of microplastics

Microplastics are pieces of plastic debris under five millimetres in length. They enter the ocean food chain in several ways.

Firstly, they can pass through water filtration systems and are then ingested by marine life, from fish to shellfish. They can also be transported in the atmosphere, spreading to even the most remote corners of the Earth.

Microplastics are also making their way onto farmland through sewage sludge being used as fertiliser. Much of this will then end up in waterways as a result of runoff from the top layer of soil.

Microplastics in the ocean can be divided into two categories: primary and secondary. Primary microplastics are those that were originally manufactured to be small, such as microbeads in cosmetics and plastic pellets (nurdles) used in industrial manufacturing. Secondary microplastics are degradation products of plastic materials from larger items.

Microplastics can act as carriers of toxic chemicals and pollutants, which are absorbed by marine creatures when they ingest the plastic. These chemicals include pesticides, industrial chemicals, and unintentional pollutants such as DDT, PCBs, and hexachlorobenzene. These pollutants are considered highly toxic to humans and wildlife and can cause health problems such as allergies, reproductive and hormone issues, immune system disorders, and cancer.

The impact of microplastics on human health is still relatively unknown. However, a recent study has shown a link between microplastics and an increased likelihood of heart attack, stroke, or death. Another study links microplastics with inflammation and noncommunicable diseases.

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