The Dark Side Of Chemicals: Ocean Pollution

Chemical pollution is the contamination of the marine environment with harmful, artificial, or anthropogenic pollutants. The most common of these can be grouped into pesticides and herbicides, detergents and other household products, and industrial chemicals. These pollutants introduce excessive nutrients, toxins, poisons, and metals into marine ecosystems, as well as instigating chemical bioaccumulation through the marine food web.

The most common process of ocean contamination by chemicals is through river and estuary systems. Rainwater, flooding, and stormwater transport any products on land into nearby streams, rivers, and estuaries. River systems then transfer these products into the ocean. Urban areas and agricultural activities are responsible for much of the industrial, commercial, and even recreational pollutants that end up in the ocean through sewage leaks and ineffective water treatment.

The transportation, distribution, and consequential impact of marine ecosystems are dependent upon the individual pollutant. This includes how persistent they are (how long they exist in the environment before degrading) and how water-soluble they are (more soluble pollutants dissolve more easily within the seawater and are therefore transported further offshore than those less soluble).

Chemical pollution has a wide range of effects on the marine environment. For example, fertilisers and sewage that contaminate ocean water provide excess nutrients such as nitrogen and phosphorus in a form that is highly beneficial to marine phytoplankton. This creates huge algal blooms that can be seen from space by satellite imaging. The growth and reproduction bloom of phytoplankton allows higher levels of the food web to benefit temporarily: zooplankton consume the abundant phytoplankton, and small fishes consume the zooplankton. More predatory fish or marine mammals then consume the small fish. This increase in populations results in an increase in animal waste and faeces; it also results in a natural increase in mortality. Another effect of the algal bloom on the sea surface is the reduction of sunlight reaching plants on the seafloor. This initiates mass mortality of seafloor plant species. The vast increase in waste and corpses end up on the seafloor, where aerobic bacteria known as decomposers break it down. This process requires oxygen, which is extracted from the water in great quantities. A reduction of oxygen levels in these areas causes more mobile animals to move away, and less mobile animals to die, providing yet more material for the decomposers. When oxygen levels become minimal, the environment is classed as anoxic, in these conditions, the only organisms that may survive are algal blooms and anaerobic bacteria, as they are able to decompose matter without the need for oxygen. At this point, the area is known as a dead zone: an area that can support no life but anaerobic bacteria.

There are currently 400 dead zones across the world’s oceans. One of the most significant is located by the mouth of the Mississippi river. The continuous outflow of fertiliser and sewage that is washed from the vast agricultural land of North America into the Mississippi river and transported into the Gulf of Mexico has established a dead zone of 6000 square miles.

Petroleum-based pollutants reduce photosynthesis in oxygen-generating marine microorganisms

Ocean pollution is a critical issue that poses severe threats to marine ecosystems and, consequently, human health and well-being. Among the myriad of pollutants, petroleum-based contaminants stand out as a significant concern due to their detrimental impact on oxygen-generating marine microorganisms. These microorganisms, including microalgae and certain bacteria, play a pivotal role in maintaining the delicate balance of aquatic ecosystems by producing oxygen through photosynthesis. However, when exposed to petroleum-based pollutants, their photosynthetic capabilities are severely hindered, leading to a cascade of negative consequences.

Petroleum-based pollutants, such as crude oil and its derivatives, find their way into the oceans through various human activities, including oil spills, runoff from land, and improper waste disposal. Once in the water, these pollutants form a thin layer on the surface, known as an oil slick, which prevents light penetration and disrupts the natural flow of gases and nutrients. This immediate impact on the physical properties of the water has far-reaching implications for the entire marine food web.

The oxygen-generating marine microorganisms, primarily comprising microalgae and some species of bacteria, are particularly vulnerable to petroleum-based pollutants. These organisms, which are crucial for maintaining the oxygen levels in aquatic environments, rely on photosynthesis to convert light energy into chemical energy, a process that is severely disrupted by the presence of oil. The oil slick formed by petroleum-based pollutants creates a barrier, blocking the necessary sunlight from reaching the microorganisms and inhibiting their photosynthetic process.

Additionally, the complex mixture of chemicals and toxic compounds in petroleum-based pollutants directly harm the microorganisms. Some of the toxic compounds found in crude oil, such as polycyclic aromatic hydrocarbons (PAHs), are highly toxic to these organisms, damaging their cells and impeding their metabolic processes. This disruption to their cellular functions further reduces their ability to carry out photosynthesis efficiently, compounding the negative impact on oxygen production.

The consequences of this disruption are far-reaching. Firstly, the reduction in oxygen production contributes to the creation of hypoxic or anoxic zones in the ocean, commonly known as "dead zones," where marine life struggles to survive due to the lack of oxygen. Moreover, the impaired photosynthetic activity of these microorganisms can lead to a decrease in their population, further reducing the oxygen supply in aquatic ecosystems. This depletion of oxygen-generating microorganisms can have cascading effects on other marine organisms that rely on them for food or that are sensitive to changes in oxygen levels.

In conclusion, petroleum-based pollutants in the oceans have a detrimental impact on oxygen-generating marine microorganisms by reducing their photosynthetic capabilities. This, in turn, affects the delicate balance of aquatic ecosystems and poses a threat to marine life and, ultimately, human health. Addressing this issue requires a concerted effort to reduce the input of petroleum-based pollutants into marine environments and to develop effective remediation strategies, such as utilizing the synergistic relationship between certain bacteria and microalgae to break down these complex pollutants.

Ocean acidification destroys coral reefs and impairs shellfish development

Ocean acidification and its effects on coral reefs and shellfish development

Ocean acidification is a process by which the ocean absorbs carbon dioxide (CO2), causing it to become more acidic. This occurs when excess CO2 in the atmosphere mixes with seawater, leading to a decrease in the ocean's pH level. The increasing acidity of the ocean water has detrimental effects on coral reefs and shellfish development.

Coral reefs

Coral reefs are essential for marine life, as they provide habitats and food sources for many species. Ocean acidification poses a significant threat to coral reefs by making it more difficult for corals to build their skeletons. Corals grow their skeletons upward toward sunlight, thickening and reinforcing them. However, ocean acidification impedes this thickening process, resulting in skeletons that are less dense and more vulnerable to breakage.

The rising acidity of the ocean water also affects the chemical composition of the water, making it harder for corals to extract the necessary minerals, such as calcium carbonate, from the seawater to build their skeletons. This leads to thinner and weaker coral structures.

Shellfish development

Shellfish, such as oysters, scallops, and clams, are also negatively impacted by ocean acidification. As the ocean becomes more acidic, the availability of carbonate ions decreases, making it challenging for shellfish to build and maintain their shells. This process is known as shell-building or calcification.

Additionally, ocean acidification can affect the metabolism of shellfish, including their feeding and respiration rates. It can also impact the early developmental stages of shellfish, leading to slower growth and higher mortality rates.

The effects of ocean acidification on coral reefs and shellfish development have far-reaching consequences for marine ecosystems and the species that depend on them. It disrupts the food chain and can lead to a decline in biodiversity. Additionally, shellfish are an important source of food for many communities, and the impairment of their development can have economic and social implications.

Plastic pollution threatens marine life and accumulates in mid-ocean gyres

Plastic pollution is a significant threat to marine life, with harmful impacts on marine populations, species, and ecosystems. Large plastic debris can cause entanglement and ingestion in hundreds of species of wildlife, leading to tissue laceration, mortality, and population decline. For example, a recent study found a correlation between plastic debris and disease in coral reefs. The impact of plastic pollution is not limited to larger organisms, as microplastics, small plastic particles found in ocean sediments and surface waters, can be ingested by marine and coastal organisms, leading to bioaccumulation and harmful effects on their health. These microplastics can then concentrate in humans and other organisms through food chains, potentially impacting human health.

Plastic pollution also accumulates in large mid-ocean gyres, such as the "Great Pacific Garbage Patch" discovered by Captain Charles Moore in 1996. These gyres are found in the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Oceans. The presence of plastic debris in these gyres contributes to the widespread contamination of plastic pollution across all ocean basins, ecosystems, habitats, and food webs.

The sources, transformations, and effects of plastic pollution are complex and far-reaching. Plastic debris interacts with planetary cycles and affects physical and biological processes. For example, plastic pollution can impede the production of oxygen by marine microorganisms and contribute to ocean acidification, which has detrimental effects on coral reefs and calcium-containing organisms at the base of the marine food web.

The understanding of plastic pollution in the oceans has evolved, and it is now recognized as a global issue that requires attention from multiple levels of government. Efforts to address plastic pollution involve understanding its sources, fates, and impacts, as well as developing policies and actions to mitigate its harmful effects on marine life and ecosystems.

Consumption of contaminated seafood exposes humans to chemical pollutants

Seafood is a primary source of exposure to chemical pollutants for humans. Over 80% of ocean pollution comes from land-based sources, and these chemical and plastic pollutants contaminate seas and marine life from the Arctic to the deepest depths of the ocean. Marine organisms, including those consumed by humans, contain these pollutants. Plastic waste, toxic metals, pharmaceuticals, pesticides, and sewage are all part of the complex mixture of ocean pollutants.

The consumption of contaminated seafood exposes humans to chemical pollutants like mercury, PCBs, and other persistent organic pollutants. These accumulate in high concentrations in fish and marine mammals, and when consumed by pregnant women, can damage the developing foetus's brain, lower IQ, and increase the risk of autism, ADHD, and learning disorders in children. The EPA has estimated a lifetime cancer risk of approximately 1 in 100,000 from eating fish contaminated with TCDD.

In addition, certain drugs used to control disease in cultured food-producing aquatic animals may pose a risk to human health. While the magnitude of human exposure to these drugs is uncertain, there is concern about the consumption of large amounts of imported cultured seafood treated with drugs by the American public. Cultured seafood imported into the United States, for example, is not inspected for drug residues.

Furthermore, global warming and rising sea temperatures are exacerbating the problem by liberating legacy pollutants from ice and permafrost and increasing the abundance and geographic range of marine pathogens, such as Vibrio cholerae, the agent that causes cholera. Ocean acidification, caused by increasing carbon dioxide absorption, also increases the toxicity of certain heavy metals and organic pollutants, further endangering human health.

Industrialized agriculture increases harmful algal blooms (HABs)

Industrialized agriculture is a major source of nutrient pollution, specifically nitrogen and phosphorus pollution. The use of fertilizers on crops and animal manure from concentrated animal feeding operations (CAFOs) are the main contributors to nutrient pollution.

Nitrogen pollution from crop farming fertilizers exceeds that of animal manure and human waste, while phosphorus pollution from manure and fertilizer use are comparable. The increase in the proportion of nitrogen to phosphorus pollution through farming practices can lead to larger, more toxic HABs.

The number of CAFOs, the main source of meat production in the United States, has increased by almost 10% in the last decade, leading to a sharp increase in nutrient pollution in the surrounding areas. In 2019, the U.S. produced almost 8.7 billion animals from CAFOs, creating localized sources of pollution that threaten the health and safety of nearby communities.

HABs occur when there is an excess of nutrients like nitrogen and phosphorus, which feed algae, causing them to bloom. When the blooms die, the decomposition process uses up the available oxygen in the water, creating a dead zone where no aquatic life can survive.

HABs have severe negative impacts on water quality, aquatic ecosystems, and animal and human health. They can cause skin irritation, throat irritation, and gastroenteritis in more severe cases. HABs can also lead to economic losses, affecting industries such as fishing and tourism.

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