Toxin and Plastic Movement Through the Food Chain

By: Tess Briggs, Majd Hajja, Helen Serrano Hernandez

Introduction

Although plastic contamination is a major problem in the ocean, it still has an impact on all organisms because of its effect on the food chain. The transfer of plastic from organism to organism is an aspect of this danger which influences how effectively the food chain functions. The root of the problem is bioaccumulation, especially in species higher on the food chain. Plastic ingestion puts these organisms at higher risk of an unbalanced food web. Throughout the ocean, there is a worry of plastic and how it encompasses all aspects of the food chain.

Transfer Mechanisms of plastics from one organism to another

As a whole, plastics are subject to degradation over time and this alters the biological transfer of them from one organism to another. Researcher Fazel Abdolahpur Monikh explored and calculated the trophic transfer of sub-micron plastics within plants and the environment. Monikh also noted how plastics found within insects and plants affected fish, and other organisms, at a cellular level. As this experiment was conducted it was found that unlike chemicals, which are dissolved, the transfer of certain materials like SMPs can be influenced by the chemical properties of particles. These properties include size, shape, and chemical composition; which is important to note as transfer between SMPs varies depending on their material.

Further elaborating on the experiment, Monikh’s group isolated lettuce plants and treated them with SMPs, which were then fed to 6-day old black soldier fly larvae. Following this, fish were put in an environment to feed on lettuce-fed insects that contained the SMPs. After the fish had fed on the insects they were then transferred to a non-contaminated tank for 48 hours in which they were not fed any external food. The fish showed SMPs within various body parts such as their gills, liver and even some various tissues of the body including the intestines, however no SMP’s were present in their brain tissue. The liver showed to accumulate the greatest amount of SMPs, compared to the gills and the intestines.It was concluded that the liver was the primary target of SMPs within the organism; this being crucial considering that the liver is the main organ for detoxification, and is what plays a role in removing plastic from the bodies of the fish.

Taking this into account, Monikh also observed the percentage at which plastic was taken up from the soil, stating that out of the 1.31013 PS-SMPs and 1.21013 PVC-SMPs that were found first in 1 kg of soil, 5.5% of PS-SMPs and 7% of PVC-SMPs had actually been transferred within the food chain. This accounts for the transfer of the plastics as this uptake was measured in lettuce plants, then measured in insects and fish apart from the original experiment mentioned previously. The transfer indicated that plastic particles enter the biosphere from accumulation in different tissues and organisms. These particles keep their integrity from one organism to another, and, along with SMPs naturally in the biosphere, accumulate throughout organisms. Plastics are transferred from one organism to another through a process that begins with their absorption into the soil. From there, plants take up plastics, which are then consumed by herbivores or humans. These uptakes occur in most plant species. The effectiveness of this transfer, and the ability of SMPs to maintain their integrity from one organism to another, is due to the formation of a protein corona on the surface of the SMPs. This protein layer protects the SMPs as they move through the food chain.

In another experiment conducted by Monikh, daphnids, which are filter feeders, were measured to evaluate their effect on organisms at a higher trophic level from their transfers of nanoscale plastic debris (NPD). It was found that when the organisms were treated with plastic, the majority of it had been depurated from the organism, and therefore it was really only dependent on the size of the NPD with its effect on the daphnid. Monikh concluded that while the NPDs do have the potential to transfer to higher trophic levels, they will not accumulate within the individual organism unless the amount is large enough. Ultimately, the transfer of the plastics are dependent on their sizes as well as their behaviors within the environment. There is also a dependence on how much plastic the original organisms uptake, as the plastic will maintain its integrity throughout each environmental shift.

Bioaccumulation in Species Higher on the Food Chain

While looking at the transfer of plastic through the food chain, an important and specific aspect of the topic is bioaccumulation. Bioaccumulation refers to the build up of toxins in the body to a point where the concentration of said toxins are higher within the body than the surrounding environment (Extoxnet). This phenomenon occurs mainly in organisms higher on the food chain, like humans, and starts from the bottom of the food chain. As an example, a small fish can eat a piece of plastic, which is then transferred to a larger fish, which is then consumed by a human (“How do toxins”).

In discussions of bioaccumulation, the term biomagnification is often mentioned. It describes the process by which toxins move up the food chain, becoming increasingly concentrated in higher-level predators.

When diving deeper into how the food chain causes bioaccumulation, it is helpful to look at where it all starts. When plastic enters the ocean, it is ingested by sea creatures. Many of the creatures ingesting the plastics, take it in as microplastics and not necessarily as big pieces of plastic. These smaller marine creatures are then prey to bigger, predator sea creatures. These fish start the build up process of small plastics through marine life which creates problems in marine ecosystems. The problem can also lie when people consume these fish like tuna and salmon. Although in some cases bioaccumulation can be normal and healthy for humans, like with vitamins, minerals, and fats, scientists say it can be concerning when the build up of a certain toxin reaches an unhealthy level (Extoxnet). Humans, though, are not the only species affected at the top of the food chain, and other organisms are impacted by bioaccumulation like humans. An example of a species higher on the food chain are sharks, the Expedition Leader at Ocean Tech, Choy Aming, says that when one organism eats another organism, they are also eating all the plastic and toxins that the prey ate. This cascade effect causes said pollutants to work up the food chain to organisms higher in the web (Sky News 0:37). Additionally, Dr. Robbie Smith explains that when plastics enter the food chain, the toxins only have one place to go, which is the top of the chain (Sky News 1:05). The plastics are consumed by smaller creatures, which are then eaten by predators. Due to this chain reaction, plastics are oftentimes found more abundant in the top of the food chain compared to the bottom.

In short, bioaccumulation is a major aspect of the movement of plastics through the food chain. Even though large predators, including humans and other top of the food chain organisms, do not directly eat plastics, they still end up consuming them because of how plastics move through the food chain. Bioaccumulation should not be taken lightly as it shows to be a serious problem throughout the food chain.

How plastic consumption affects the flow of the food chain

Although some might see microplastics as small harmless garbage, they actually cause a great impact on the marine food chain. As we know already, plastics have been entering our oceans on a larger scale throughout the years. The Water Research Journal researched deeply into microplastics and saw that they are now detected at every ocean around the world whether thats North America, Asia, or Europe (Eerkes, 2015). We may not see the effects of plastic pollution on a daily basis but it is certain that the effects are there. Many studies have proven that marine organisms are starting to die, have behavioral disorders, and overall poor health. The average person might not see how even the top animals in a food chain are being affected by something so small. It has been shown that microplastics transfer from organism to organism and end up building up inside these top predators. One research article shows how the build up of microplastics in a fish’s body became so much it started transferring to their brain and therefore caused the fish brain damage (Mattson, 2017). Microplastics might be one of the biggest threats in our oceans right now.

Plastic ingestion and transfer has been researched and written about on many accounts but something that is not commonly talked about is the true effects on the animals ingesting the plastics. As discussed in an article, top fish consumers who eat plastics tend to shift their behavior by making changes to the distance they decide to swim in order to find food as well as the amount of time spent looking for food.(Mattsson, 2017). That said, top consumers in the marine food chain may not always be able to effectively consume the animals they rely on, sometimes resulting in their death. There is definitely a huge effect on the health of these marine organisms but the overall productivity of the food web seems to still be in acceptable standing.

An experiment conducted to show consumption rate of predators concluded that, “both low and high levels of microplastics… do not suppress the feeding efficiency of shore crabs upon blue mussel prey” (Barcelo, 2021). This shows that predation is not significantly affected by the amounts of plastics consumed. It is mentioned that the animals may not have the greatest behavioral health but they were still able to continue their feeding habits. Because of experiments like this, it can be concluded that organisms have immense effects on their health and form of acting but the marine food web is not being significantly unbalanced.

A reason as to why the food chain is not being affected on a greater scale is because the bottom prey, such as plankton and small fish, are already known to have a shorter life span than these bigger predators at the top of the chain. That said, the death of bottom level organisms due to plastic consumption may not have a significant impact, as they are already prone to dying from their natural life spans or being consumed in their early stages. As plastic becomes of greater measure in the ocean, it disrupts the web because of the accumulation in organisms. If nothing is done to stop plastic pollution in the environment then there will be a drastic change in the food web. If plastic keeps accumulating and animals keep having health issues, there will be a decline in reproduction and therefore cause an unbalanced and ineffective food chain. As of right now, the ratio of prey to predators is not greatly indifferent and the food chain keeps its productivity. If we keep up with the increase of plastic production each day then we will lose a great population of organisms. But if we take the step to make a change in our environment and control plastic production while we still can, then our food web will remain in good standing.

Conclusion

We know of plastics entering the oceans but people should stop to think how it can lead back to them eating these plastics. With microplastics being transferred from organism to organism, the smaller prey cause the top predators to be left with high amounts of plastics in their bodies. Having this happen on a larger scale will completely shift the productivity of the food web, because animals will start having shorter life spans and more health issues, therefore affecting the amount of prey to predators.

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