For many centuries, humans have exploited the earth’s resources in favor of their own gratification. As time went one, humans have developed tools and techniques that have greatly improved their quality of life. However, little thought was given to how these tools would in turn affect the environment as well as the other organism’s humans share the earth with. Once such tool is plastic. In today’s day and age, the use of plastic has reached an all-time high. Plastic can be found almost anywhere from hospitals, to grocery stores, to electronic devices. Although plastic has been a great resource for humans, it has been very detrimental to many other species. Part of this stems from the fact that plastic is not disposed properly. In fact, about 80% of all plastic ends up the ocean (Not Whale Food). At first, this did not arise much concern because for many centuries, society has used the ocean as a convenient place to dump waste. However, as plastic has begun to accumulate in the ocean many marine organisms have suffered which began to elicit concern. Plastic as it turns out is very detrimental to marine organisms because it causes physical damage and serves as a chemical transporter for many toxin compounds.
Plastic is made up of small repeating units called monomers. These monomers –composed of hydrogen, carbon, sulfur, nitrogen, or chlorine –can link up to form long chains called polymers (How Plastics are Made). Polymers are synthesized from chemicals produced from oil, natural gas, and coal. Monomers are chemically boned to form polymers in a process called polymerization.
Plastics can be divided into two broad categories thermoplastics and thermosets. Thermoplastics are meltable plastics that occur when the monomers connect to form long chains. (How Plastics are Made). 92% of all plastics are thermoplastics. An interesting characteristic of thermoplastics is that it softens in the presence of heat, yet it returns to its original form when cooled down. Because of this, thermoplastics are widely used in the food packaging industry (How Plastics are Made). Some examples are polyethylene, polypropylene, and polyvinyl chloride (PVC). These plastics are commonly used in packaging film, water bottles and milk jugs, external prostheses, and electrical cable (How Plastics are Made).
Thermosets are another type of plastic. However, unlike thermoplastics, they are not meltable. This is because thermosets are formed when carbon forms two and three-dimensional networks, because of this they are very durable (How Plastics are Made). Since these plastics are not meltable, when they are heated they do not return to their original forms. Some examples of thermoset plastics are polyurethanes, unsaturated polyester, epoxies, and phenol formaldehyde. These plastics are commonly used in furniture, insulation, and boat hulls (How Plastics are Made).
Although plastic is useful in making products because it is lightweight and durable, it has a largely negative effect to the marine environment, especially one marine species. A large amount of the plastic produced ends up in waterways –or directly in the oceans –in the run-off after storms (Andres 10240). In a study by Lebreton et. al it was estimated that between 1.15 and 2.41 million tonnes of plastic currently enter the oceans every year thought the global river systems (Lebreton et. al. 1). The top 20 rivers contributing to this pollution are mostly located in Asia. Surprisingly, these rivers contribute 67% of the global total for plastic pollution (Lebreton et. al. 1). Furthermore, small pieces of plastic known as microbeads are commonly used in a variety of face washes, toothpastes, and shower gels. Since these pieces are so small, they are often not completely filtered out at waste plants (Tanaka and Takada 1).
Plastic is dangerous once it enters the ocean because it breaks down into smaller particles. When plastic particles are 0.33 mm and 5mm in size they are referred to as microplastics. Microplastics come from a variety of different sources including microbeads from facial products, pieces from larger products and fibers from synthetic clothing (Tanaka and Takada ?). Microplastics can be categorized into primary and secondary microplastics. Primary plastics were originally manufactured in small size whereas secondary microplastics have occurred as a result from the fragmentation and weathering of larger plastics as they lose their mechanical integrity (Watts el. al. 8823). The mechanical integrity of plastic decreases as a result of the solar UV radiation as it sits on the beach or floats on the water (GESAMP ?). After significant exposure to UV radiation surface cracks develops, which breaks down into smaller and smaller fragments over time.
Recently, the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) studied the impact of microplastics on marine life in their article, “Sources, Fate and Effects of Microplastics in the Marine Environment: A Global Assessment.” In this article, they claim that microplastics harm organisms in many different ways. One of the physical effects of microplastics is damage to the digestive tract. What’s the damage?
Furthermore, recent research conducted by Watts et. al. suggests that plastic can enter into the body of marine life through the gills. In a study performed on Carcinus Maenas, a shore crab, it was discovered that crabs exposed to water containing microplastics had a significant number of polyesterene microspheres (8-10 µm) in their gills (Watts et. al. 8827). Additionally, the posterior gills were found to contain a significantly greater number of microspheres than the anterior gills. It is believed that this is difference is due to the posterior gills having a larger surface area thereby increasing the possibility of them lodging microspheres in the lamellae (thin membranes that function in gas exchange) (Watts et. al. 8828). Furthermore, crabs that had microspheres in and on their gills, were still eliminating significant amounts of microspheres 21 days after the completion of the experiment which is quite interesting considering that crabs have mechanisms to remove dislodged particles from the gills (Watts et. al. 8828-8829).
In each gill chamber, the crab has a gill raker that sweeps over the gills and pushes the particles into a water current that heads to the exhalent channel. Furthermore, crabs can reverse the flow of water of the gills momentarily to dislodge any particles captured in the gills (Watts et. al. 8829). However, considering that the crabs, in this study, were still expelling plastic particles after 21 days; it is clear that these mechanisms were not able to remove these particles efficiently. This could potentially be harmful to the crab because the gills have many physiological functions. The posterior gills specifically, function in respiration and ion exchange (Watts et. al. 8828). However, the effect of plastic on these processes still remains unclear. This study also studied the uptake of microplastics through feeding. Interestingly, no microspheres were found in the hemolymph of the crab. This result indicates that microspheres were not translocated from the gills to the digestive tract in this experiment (Watts et. al. 8828).
One of the microplastics especially harmful to marine life is nurdles. Nurdles are tiny plastic pellets used in manufacturing and packaging that are cylindrical and up to 5 mm in diameter (Ellison, 396). These particles routinely end up in our waterways because they are too small to be filtered out by most sewage systems. Because of their small size and round shape, nurdles mimic the appearance of fish eggs (Ellison, 396). Nurdles are very dangerous to marine life because they absorb and concentrate many toxic pollutants such as polychlorinated biphenyls (PCBs). Some of these particles, ingested by birds, were found to contain as much as one million times more toxic chemicals than their normal level in seawater (Ellison 396).
Plastic is especially detrimental to the sea bird population. In fact, sea birds ingest plastic particles and other forms of marine debris more than any other animal taxon (Ryan 623). According to National Geographic, plastic can be found in 90% of sea birds ( ). Sea birds living in southern Australia, South Africa, and South America have the highest concentration of plastic in their digestive tract (). These plastic pieces include bags, bottle caps, synthetic fibers from clothing, and microplastics. Of course, having any sort of foreign object, unless intentionally placed, is detrimental to the body. Sea birds, in particular, experience a slew of symptoms as a result of ingesting plastic. The negative effects of plastic on sea birds are commonly classified into three categories: physical blockage of the digestive tract, impairment of foraging efficiency, and the release of toxic chemical (Ryan ).
When sea birds ingest plastic, it is not broken down in the digestive tract (National Geographic). As a result, the ingested plastic may cause blockages at various points in the digestive system. Depending on the type of plastic, the risk of blockage may increase. Threads and fibers led in gastrointestinal blockages, more frequently than other types of plastic, because they form dense interwoven balls in the sea bird’s digestive tract. Furthermore, if these balls form in the bird’s gizzard, then it can block food from entering the intestine. This is very harmful, because food not processed in the gizzard is not properly digested and the birds eventually die of starvation.
In addition, sharp pieces of plastic can induce lacerations of internal organs. It is as if the bird ingested a razor blade. According to Peter G. Ryan, a professor at the University of Cape Town, cuts of the internal organs occurs more often than blockages (Ryan 625). Although these lacerations may not be lethal immediately, they could cause internal bleeding and infections, compromising the immune system and weakening the organism (Ryan 626).
Sea birds also ingest plastic through the fish they eat. If the fish is loaded with plastic, the bird will also indirectly consume the plastic when the fish is eaten (National Geographic). In addition to the GI blockade described above, plastic has other detrimental effects on a bird’s digestion. It tricks the body’s digestive signaling system to induce a false satiation sensation and reduce feeding and foraging behavior, eventually leading to weaker and disease ridden organisms (Ryan 626). As plastic is ingested, the bird’s stomach expands to accommodate new food. Since the plastic is not broken down in the digestive system, the stomach eventually fills with plastic leaving very little room for food. As a result, birds experience a false feeling of satiation while starving (National Geographic).
Lastly, ingested plastic is a source of toxic chemicals. Originally, the polymers forming plastic were thought to be chemically unreactive, but upon analysis – the ingredients of 50% of plastics are considered to be hazardous according the to the US Environmental Protection Agency or EPA (Rochman et al, 170). Some of these toxic chemicals include colorants, heat and UV stabilizers, and plasticizers (Ryan 629). Furthermore, it was discovered that pesticides and other chemicals can leech onto the plastic. This begins to pose a problem because the chemicals can accumulate in very high concentrations that could potentially be dangerous to health of humans and animals alike (Rochman et al, 170).
This plastic-driven bioaccumulation of toxins is exemplified in whales. In a recent TV documentary aired by BBC, Blue Planet II, a mother pilot whale and her dead newborn calf is shown. After birth, the newborn did not survive long, yet the mother refused to let the calf go for many days. Scientists believe plastic may have played a role in the death of this calf whale. In top predators like whales, chemicals can accumulate to lethal quantities because plastic combines with many pollutants that are consumed by many marine organisms. As a result, it likely the calf was poisoned by the mother’s contaminated milk.
Plastic is also dangerous because the chemicals that enter the organisms body may be transported to other tissues in the body (Rochman et. al. ?). In fact, in a species of bird known as Great Shearwaters, there appears to be a correlation in plastic ingestion and PCB concentration in eggs (Ryan 629).
Many chemicals found in plastic have been found to harm marine organisms. Phthalates and BPA’s, specifically, have been shown to affect reproduction and impairs development in crustaceans and amphibians (Thompson 2156). The biological effects of these compounds have been observed in concentrations as low as ng/L and µg/L in mollusks and amphibians. These compounds, known as plasticizers, are believed to interfere with normal hormonal functions which can occur through several pathways. Although, the relative effect depends on concentration. Furthermore, these compounds are especially dangerous because they can accumulate in organisms over time, thus increasing in concentration.
The plastic pollution “epidemic” is not limited to birds and fish alone. In fact, as of 2000, 267 species of marine life in total have been affected by ingesting marine debris, including at least 26 marine mammal species, 111 sea bird species, 33 marine fish species, 6 sea turtle species, and 1 invertebrate species (Stamper et. al. 197). The effects of plastic on sea turtles can be seen in a case study published by Stamper et al. This study was performed in 2016 on a juvenile sea turtle that was found off the coast of Florida. Upon discovery, the turtle showed signs of muscle wasting, lethargy, and anorexia. The turtle was taken to a rehabilitation center where it was nursed back to health. However, even with the care provided by the center, the turtle was not eating well. Interestingly, the turtle’s appetite increased 3-fold, 18 days after it was rescued, when it expelled a small amount of balloon-like material. Over the next month the turtle excreted over 74 foreign objects including balloons, string, plastic, nylon line, monofilament line, carpet material, and tar balls. As the debris evacuated the turtle’s gastrointestinal tract, its appetite began to restore. Within 46 days of treatment, the animal was deemed healthy and released back to the ocean. This case study, clearly shows how harmful plastic can be to marine animals. However, this study only shows the effects of larger plastic pieces on animals. As it turns out, even extremely small plastic particles, like nanoparticles, have a detrimental effect on animals.
Recent studies have discovered that plastic nanoparticles (nano-meter diameter) can cross the blood-brain barrier in fish and cause behavioral disorders (Mattson et. al. 1). Furthermore, these plastics can travel up the food chain, enter the brain of the top consumer, and affect its behavior which ultimately severely affects natural ecosystems (Mattson et. al. 1). In a recent study, Mattson et. al. tested the effects of plastic nanoparticles on Daphnia (a water flea). They discovered that 52 nm positively charged modified polyesterene nanoparticles are toxic to Daphnia. Additionally, fish that consumed these plastic nanoparticles exhibited visible changes in brain structure (Mattson et. al. 5). Interestingly, these fish also exhibit behavioral changes. Specifically, they had a longer feeding time, lower activity, and swam a longer distance to feed. These findings suggest a link between the presence of nanoparticles in the brain tissue and behavioral changes (Mattson et. al. 5). Although, further studies must be conducted to see if these particles can travel up the trophic levels indefinitely, this finding is still significant. Fish pay an important role in the marine ecosystem. Since all aspects of an ecosystem are intimately related, if the behavior of the fish changes, the whole ecosystem will be affected to some extent.
Although small pieces of plastic, like plastic nanoparticles and microplastics are detrimental to the environment and marine ecosystems, they are only part of the problem. In fact, large pieces of plastic, like casting nets, are also detrimental to marine animals. Up until the 1950’s, fishing nets were made with natural fibers, like cotton (Gregory 2015). These nets were then coated with tar to strengthen them. Because these nets were made with natural fibers, they decomposed rather quickly if they discarded in the ocean (Gregory 2015). However, plastic soon replaced other materials due to its light weight and extreme durability. Although, this allowed fishermen to use their nets longer without replacing them, it has caused a plethora problems for marine organisms and the environment. Many animals, including penguins, sea turtles, sea lion, sea birds, dolphins and whales, can become entangled in plastic nets discarded in the oceans (Gregory 2015). Once these animals are caught in the net, they can drown, die from starvation, or even die from injury. In addition, haphazardly discarded 6-pack plastic loops may also cause entanglement to smaller organisms (Gregory 2015). This is very dangerous, because as the animal grows, the plastic tightens around the animal, ultimately causing asphyxiation.
When large pieces of plastic enter the ocean, they are carried by wind-driven circular current systems to a spot in the ocean with a calm center, known as gyres. Over time, the plastic begins to accumulate. Eventually this heap of plastic forms a garbage patch. The North Pacific Subtropical gyre contains the Great Pacific Garbage Patch which is the largest garbage patch on Earth. This garbage patch contains an assortment of marine debris that extends from North America to Japan. Because of the circular motion of the gyre, marine debris gets trapped inside the gyre.
Interestingly, this garbage patch is not an “island of trash” suspended on the ocean; rather it a combination of large pieces or plastics and their corresponding fragments, microplastics. These microplastic fragments cause the water to become like a cloudy soup. Oceanographers and ecologists revealed that ~70% of the debris actually sinks to the ocean floor. As the plastic stays in the ocean gyre, it is broken down into tiny pieces by the UV radiation from the sun in a process known as photo degradation. As a result, the number of plastic pieces in the Garbage Patch continues to increase. According to National Geographic, scientists have found up to 1.9 million pieces of microplactics per square mile of the Great Pacific Garbage Patch. However, as the years go by, these pieces will be broken down and this number will continue to increase. Scientists claim that most of the plastic, found in the gyre, originates from plastic bags, plastic water bottles, and Styrofoam cups.
This debris can be very detrimental to the marine food web in the gyre. As microplastics accumulate on the surface of the ocean, they prevent the sunlight from reaching the algae and plankton near the surface of the water. These organisms are autotrophs, in other words, they synthesize their nutrients from carbon, oxygen, and sunlight. As plastic particles block sunlight form reaching the plankton, the plankton cannot synthesize the nutrients it needs and as a result, it cannot survive (National Geographic). If these organisms die, the population of fish and sea turtles that feed on them will have a decreased food supply and many of them will eventually die. However, the effect does not stop there. The population of larger predators, that feed on fish and turtles, such as sharks, tuna, and whales will also be disturbed. If this cycle continues, the seafood industry will be affected, which can greatly impact the economy of third world countries that heavily rely upon the fishing industry as a source of revenue.
Another organism negatively affected by microplastics is coral polyps. Since micro plastics are so small, they often affect a wide variety of marine invertebrates near the bottom of the food chain, like corals. Coral polyps in particular, feed on organisms within the size range of micro-plastics. In a recent study by researchers at Duke University, it was discovered that corals ingest plastic because they confuse them with prey (Allen et. al. 200). Corals use chemoreceptors to detect prey. Interestingly, it seems that microplastics contain chemicals that act as phagostimulants. As a result, the corals confuse them with prey and ingest them. In this study by Allen. et al. it was discovered that a portion of the ingested plastic were retained by corals for at least 24 hours. This result is surprising considering corals digest food rapidly (Allen et. al 203). Furthermore, Hall et. al. discovered that the plastic particles can get wrapped up in the mesentery tissue which is the main tissue used in digestion (Hall et. al. 728). Because the mesenterial tissue is located deep within the polyp, removing the plastic particles from the tissue is quite challenging. Furthermore, if the particles are not removed, they may affect digestion (Hall et. al. 728). This can be very dangerous because plastics do not break down in the digestive tract which can lead to blockage, false satiation, and eventually starvation (Allen et. al. 198).
Coral reefs are very important. They house hundreds of thousands of species of marine animals. Furthermore, they have a huge economic value. They protect the coastline and provide an avenue for tourism, fishing, and discovery of new drugs. It is estimated that about 15% of the world’s populating live within 100 km of a coral reef. Coral reefs help protect the coastlines from storm damage, erosion, and flooding by hampering the strength of the waves close to the coast (Hoegh-Guldberg 839). In addition, corals are vital to the reef ecosystems. They are home to 25% of all marine fish species. In fact, corals are considered a priority species by the WWF (World Wildlife Fund). Priority species are defined as “one of the most ecologically, economically, and/or culturally important species on our planet” (WWF, 2017). Therefore, protecting them is of the utmost importance.
Plastic is also very detrimental to small organisms found on the shore. Plastic is commonly deposited on the shore through rivers or washed on the shore from the ocean. Since, the sight of plastic and other marine debris is not aesthetically pleasing, individuals often demand that it is removed. However, this may result in the destruction of some very important ecological habitats. The shore line is a home to many diverse organisms including marine birds, crustaceans, invertebrate biota and occasional vertebrate visitors. Shorelines are often cleaned by a large tractor-pulled sieving device (Gheskiere et. al. 246). This machine removes the litter by collecting the upper sediment layer with a fast-turning brush and replacing the sand after sifting it. Once the sand is replaced, it is pressed down by a dragged weight. This process of cleaning the beach is of growing concern because it removes every macroscopic item regardless of whether or not it needs to be removed. This has a harmful effect on nematodes which dominate the meiofauna (small invertebrate organisms) that live in the sediment layer (Gheskiere et. al. 260). Nematodes are extremely important to the shoreline ecosystem because they break down organic debris (Gheskiere et. al. 246). However, when the beach is clean, the nematodes habitat is disrupted resulting in decreased nematode density and decreased species-specific densities.
Plastic can also affect the ecological structure of an ecosystem by introducing exotic species. Plastic is often colonized by sessile, hard-shelled organisms like barnacles, tube worms, algae and bivalve mollusks (Gregory 2018). In New Zealand, over 150 marine species have been stranded on shore from plastic shores (Gregory 2019). In fact, a bryozoan that thrives on plastic around northern New Zealand is a recent arrival. This bryozoan is believed to have originated in Australia. Furthermore, a common tropical oyster has been found attached to synthetic rope of on the beaches of New Zealand (Gregory 2020). From this data, it is clear that plastic can transport organisms across the ocean. The ecological impacts of this could be astronomical. When species are taken from their native environment and transported into a new area, they sometimes outcompete the native species in the new area. This occurs because the new species that is introduced usually lacks its natural predators in the new environment so the size of the population is not regulated.
Plastic has also affected the community structure of the ocean floor. Plastic is buoyant and typically floats on the surface of the ocean. However, as sediments settle on plastic, the plastic begins to sink. Eventually, the plastic will end up on the ocean floor. The once pristine environment at the bottom of the ocean is now littered with plastic debris including plastic bags freely drifting at depths of 2000 meters. Scientist, Murray Gregory elaborates on the gravity of this situation when he states, “Once [plastics] reach the sea floor, particularly in deeper and still waters, they are doomed to a slow yet permanent entombment” (Gregory 2017). Several studies conducted in shallow waters have confirmed that gradual changes are occurring in the community structure of the sea floor. In the short term, the deposition of plastic may enrich biodiversity. However, as time goes on the plastic will become buried in sediment, and thus remain trapped in the ocean for a very long time.
It is obvious that plastic is extremely detrimental to the marine environment, but the effect does not stop there. Everything on Earth is held in a delicate balance. Effects on the ocean will soon have detrimental effects on terrestrial environments. Even if one species, like coral, goes extinct the negative effects could be extraordinary. Additionally, it is wrong to assume that plastic ingested by marine animals will not make its way up the trophic levels to humans. If a fish ingests plastic and a human eats that fish, the plastic and the toxins that may be present on the plastic can be transferred to the individual. Recently it has been discovered that phthalates, BPA and a slew of other additives in plastic as well as their metabolites are present in the human population (Thompson et. al. 2157). It is believed humans are exposed to these compounds through inhalation, ingestion, and even dermal contact. Just like in animals, there are many health risks associated with consumption of plastics for humans. Interestingly, there is a substantial relationship between BPA urine levels, and cardiovascular disease, type 2 diabetes, and abnormalities in liver enzymes (Thompson et. al. 2157).
All these findings ultimately show that plastic is extremely harmful. Plastic, which was created to benefit people, is harming thousands of organisms each and every day, ultimately leading to their death. Therefore, this plastic pollution must end. Precautions must be to be taken to reduce the use of plastic. Furthermore, policies need to be established to ensure that plastic is disposed safely, in a way that it will not end up in the ocean, because if the amount of plastic entering the ocean is not reduced, it will not be long before the effects will be irreversible. Lastly, everything on Earth is intimately connected. If any organism goes extinct as a result of plastic consumption it will not be long before the entire ecosystem collapses. As a result, economies may be wrecked, the cost of fish could increase, etc. It is impossible to predict the exact effect the loss of species will have in the long run. One thing is crystal clear, the negative impact will ultimately be experienced by humans. However, if we wait too long to intervene, to save the environment, it may be too late to do reverse the plastic pollution. There might not be anything left to save, and that’s a scary scenario.