Zahra Linsky
Flattening a flapping fish on the table, the scientist holds a hammer high. As the spray of the ocean mists their cheek, they sacrifice the fish with a blow to the head (McIlwraith et al.). They could expose it to clove oil, behead it, or freeze it, but this scientist’s organization believes crushing its brain is the most humane way to euthanize a fish. And for their research, they have a great many fish to euthanize, or “sacrifice,” as they will note in their papers.
These fish contain microplastics, also known as “MPs.” Killing the fish is merely the first step to understanding the effect MPs have on fish and, by proxy, us.
To exist is to use plastic. It takes significant effort and funds to avoid plastic consumption at this point in human history. Due to this conventional modern lifestyle, 8.3 billion tons of virgin plastic are expected to be manufactured by 2050 (Rhodes). When plastics break down, they form microplastics (MPs) (Boersma et al.). When MPs are released into the environment, MPs are taken up by animals and plants that ingest them and either expelled or built up in the organism.
In particular, fish across the world are being found containing alarming levels of MPs. The health effects in fish are being discovered in labs, while fish even in low MP-concentrations are found with MPs in their brains. The problem is becoming increasingly dire, and no one knows how it will affect those who consume fish. However, we can use the vast data on MPs in fish as a model to infer what may be happening to humans as we consume MPs. Humans aren’t easily dissected. Fish are.
Before the extent of the damage in fish can be found, fish are collected and prepared. Some studies raise fish from their larval stages to determine the health effects of specific kinds of MPs on fish (van Pomeren et al.). Many others are collected by electrofishing, netting, bottom trawling, spearfishing, and purchased from markets—the same methods non-scientists use to acquire fish for eating (Klangnurak and Chunniyom; Hurt et al.; Zhang et al.; McIlwraith et al.). Frozen, these fish are transported to laboratories and digested (Klangnurak and Chunniyom; Hurt et al.; Zhang et al.).
Digestion refers to dissolving every component of the fish to separate out certain inorganic components, like MPs (Li et al.; Zhang et al.; Covernton et al.). The Romans digested fish to make garum, their prized fermented fish sauce, by letting a jar of salted fish sit out in the sun for several months (Anatolius Vindanius or Vindonius et al.) Modern science doesn’t need several months to digest a fish; instead, it takes about a day using alkali metal digestion agents (Klangnurak and Chunniyom; Zhang et al.; Covernton et al.; Li et al.). The liquidated fish can then be filtered through a sieve to separate the fish from the MPs that were once within it (Klangnurak and Chunniyom; Zhang et al.). Viewed under a microscope, these filtered MPs can be counted and measured.
The accumulation of MPs in fish is important to identify due to the health effects on fish, which range from negligible to fatal. These effects can occur at any life stage—even before hatching. Zebrafish mothers can pass on MPs to their embryos while still contained in their ovaries (Pitt, Trevisan, et al.). If even the fish that can’t swim on their own can’t escape MPs, then no fish is safe.
Once laid, the larval fish can acquire MPs through the outermost layer of the egg and adsorb MPs in their eyes, gastrointestinal (GI) tracts, and skin (van Pomeren et al.). When MPs accumulate in larvae, they act as toxins—hindering development, reducing reproductive success, and causing damage to their offspring (Bhagat et al.). MPs can even cross the blood-brain barrier in fish and accumulate in their brains, increasing mortality rates across larvae (Sökmen et al.; Malafaia et al.). Even if these larvae survive with all the damage caused to their organs, they have difficulty swimming, making them easy targets for predators (Qiang and Cheng).
Larvae aren’t the only life stage at risk. Adult fish have difficulty detoxifying themselves and maintaining a healthy metabolism to the MPs changing even the function of their genes (Mak et al.; Limonta et al.; Zhao et al.). Even if they were healthy enough to reproduce, MPs reduce semen quality and the health of reproductive cells, alter the expression of hormones, and increase adverse birth outcomes (Plasticizer Exposure and Reproductive Health: Phthalates and Bisphenol A | SpringerLink).
Adult fish become prime prey as they lose their predator avoidance behavior and have worse swimming (Sarasamma et al.). Their circadian rhythms, which were in line with their food of choice, become altered, and they begin to starve (Sarasamma et al.). Despite this, these weak fish also become aggressive (Sarasamma et al.). Easy catches. And this only increases the accumulation of MPs up the food chain—including you.
You are not safe from MPs. You are likely eating a credit card’s worth of microplastics every week, as one review suggests (afkr221). This all comes down to what you consume.
At the grocery store, 56.5% to 100% of fish will contain MPs (Hurt et al.; Makhdoumi et al.). In one gram of muscle, fish worldwide contain 0.016 to 6.06 pieces of MP (Makhdoumi et al.). Keep in mind, that this is one gram, equivalent to 0.002 lb. In a 2 lb fillet, there will be at least 14.51 individual MPs, maybe even up to 5497.54. If one person eats 0.5 lb, they will consume up to 1374 MPs.
The abundance of MPs can depend on where the fish are feeding and what kind of feeder they are. Demersal fish that live near the bottom of the Gulf of Thailand and the Andaman Sea ingest marginally fewer MPs than pelagic fish, which live in the water column (Klangnurak and Chunniyom). Demersal fish from the Yangtze River estuary contain significantly higher levels of MPs than other animals (Li et al.). Carnivorous fish, which consume lower trophic level fish, contain more MPs than omnivorous fish, signaling an increased impact of MPs on higher trophic level organisms (Huang et al.). Keep in mind, if you are eating fish, then you are one of those carnivorous organisms. You contain more MPs than those who do not eat fish.
The Nandu River in the Hainan Province of China has a comparably low microplastic pollution level compared to other Chinese rivers, due to the total ban on non-biodegradable plastics issued in 2019 (Chen et al.). Despite this ban, 90.5% of the fish examined were found to contain MPs three years later, suggesting that MPs will take years to clear out of ecosystems after contaminating them (Chen et al.).
One study provides a light at the end of the tunnel for those hoping for decreased MP abundance in fish. All species studied by Pitt et al. did not actively capture microfibers (a shape of MP) (Pitt, Kozal, et al.). Before this study, it was commonly assumed that the fish actively chose to eat MPs instead of food, due to their similar appearance. When MPs appear in the gastrointestinal (GI) tract, it suggests that the fish are eating MPs instead of food (Yin et al.; Li et al.). Fish that do not use vision to search for food have an even decreased concentration of MPs (Roch et al.).
Studies have found that the majority of MPs are expelled from fish, even when facing the risk of long-term accumulation. After 24 hours of exposure to common MPs, 5.3% of fish livers had at least one MP particle, while after 30 days 1% contained MPs (Jovanović et al.). After being exposed to MPs for four weeks, fish exposed to a theoretical 10404 MP particles only contained 5 MP particles by the end (Bour et al.). Goldfish who were exposed to 50 MP particles across successive meals evacuated 50% of MPs after 10 hours and 90% of MPs after 33.4 hours (Grigorakis et al.).
Some fish have difficulty expelling MPs due to intestinal blockages. Benthic fish, who rest on the sea floor, have a digestive system so slow it has been referred to as ‘inactive.’ Due to this, their digestive systems are more vulnerable to damage and blockages (Li et al.). Other fish have difficulty discerning between MPs and food, especially cultured (or domesticated) fish that humans often eat (Roch et al.).
Additionally, the mass of the fish is a factor in determining the risk of MPs in fish. The concentration of MPs accumulated in the organisms decreases as mass increases since larger organisms ingest larger MPs and have more space in the digestive tract, which leads to fewer total MPs that can be accommodated (Li et al.). In other studies, the MP concentration in fish decreased logarithmically with an increase in body weight (Chen et al.).
Despite this, there is still hope to decrease the MP concentration in fish as a whole. The gut bacteria isolated from Indian mackerel, Pseudomonas sp., has been shown to effectively degrade plastics in a mineral salt medium, so the isolated gut bacteria may be degrading the MPs accumulated in the fish gut over time (Rajendran et al.).
MPs are accumulating in fish from around the world. Strategies must be put in place so that fewer fish ingest MPs and, in turn, fewer humans suffer the effects of MPs. The effects of MPs on humans is not known (Blackburn and Green). What has affected fish and other organisms can be extrapolated to human health. It is believed MPs can disrupt the gut microbiome in humans and cause increased inflammatory responses (Smith et al.). These put more stress on the body, increasing the risk of unrelated diseases. Additionally, MPs cross the blood-brain barrier and enter the placenta—penetrating vulnerable and important structures for the development of healthy humans (Seltenrich). This is especially dangerous when MPs can carry dangerous bacteria and viruses from host to host (Bhuyan). Humans certainly eat MPs, but no one knows how MPs interact with human biological tissue, especially due to the difficulty in conducting studies on humans (Smith et al.). The world may someday become a clinical study on MPs as humans continue to ingest high levels of MPs. By then, we can hope that the health effects of MPs can be countered.
However, the effects of MPs on the ecosystems fish inhabit currently is known, and it is dire. When fish all over the world are consuming MPs, and when plastic has even been found in the deepest waters of the world, the global health of the seas is at risk (Plastic Pollution In The Mariana Trench | Ocean Blue Project). The health effects on individual fish lead to impacts on the food web in which these fish live. You may be an upper-level consumer enjoying the bounty of the sea—perhaps at increased risk for disease in a few decades—but there are entire ecosystems at stake right now. From the Adriatic Sea to the Gulf of Mexico, MPs will only cause greater harm.
Be afraid. Be aware. When a scientist bludgeons a fish or digests its innards, it is not only for your sake.
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Zahra Linsky ‘25 (she/they) studies chemistry at Cedar Crest College. She has been recognized for her writing by YoungArts and Scholastic Art & Writing, and now she pursues writing further as an editor of Pitch: A Journal of Arts and Literature.