Every day, microplastics are quietly infiltrating every facet of human life, including our own bodies.
It's a vicious cycle that can begin and end at home. First household products and litter are thrown away, and eventually they break down into teeny tiny bits of plastic, and those teeny bits make end up in the ocean, and then in the bodies of the sea creatures that eventually wind up back at home on our dinner table.
New research published Wednesday in the journal Environmental Health Perspectives provides the first wide-scale review of the scientific literature on this subject, revealing high levels of microplastics in our seafood — especially mollusks.
What they found — Researchers from the University of Hull conducted a sweeping review of 50 different studies published between 2014-2020.
These studies examined microplastics in four types of marine animals: mollusks, crustaceans, fish, and echinodermata (sea urchins, sea cucumbers, etc.). The overwhelming majority of the studies found microplastics in these sea creatures' bodies.
Microplastics can wind up in plenty of these animals' body parts, including the liver and intestines. Humans eat some creatures whole — like oysters — but consume certain body parts of other sea creatures, like fish.
By reviewing the numerous studies, researchers could better understand the infiltration of microplastics in the organisms and body parts that we're most likely to consume.
Evangelos Danopoulos, a lead author on the study and a postgraduate student at Hull York Medical School, said in a press release accompanying the research: "Seafood species like oysters, mussels and scallops are consumed whole whereas in larger fish and mammals only parts are consumed."
"Understanding the microplastic contamination of specific body parts, and their consumption by humans, is key."
The researchers found considerable levels of microplastics (MPs) in each of the four subgroups, but mollusks had the highest amounts per each gram of seafood:
- Fish: 0–2.9 MPs/gram
- Crustaceans: 0.1–8.6 MPs/gram
- Mollusks: 0–10.5 MPs/gram
Based on additional data from the Food and Agriculture Organization of the United Nations, researchers were also able to estimate how much humans consume through their seafood.
Globally, scientists estimate that humans consume a maximum of 53,864 MPs per capita each year, which they broke down by subgroup.
Although mollusks contain more microplastics per gram, it turns out that fish and crustaceans also pack a heaping punch of microplastics when you look at the big picture:
- Fish: 31–8,323 MPs
- Crustaceans: 206–17,716 MPs
- Mollusks: 0–27,825 MPs
Of course, not all nations consume seafood in equal measure, so the level of microplastics you consume depends on the food habits of the region where you live.
The study notes high levels of microplastic consumption via mollusks in Australia, Japan, China, the U.S. and Canada. Latin America and Africa, on the other hand, had much lower rates.
The study also suggests that there may be a difference in microplastic levels between farmed and wild seafood, though the data is inconsistent.
It's possible that a wild mollusk, plucked straight from the sea, may have more microplastics than the mollusk that you find in the market, which may have undergone treatment that ends up removing microplastics. The study's findings corroborate this hypothesis.
Why it matters — The study describes microplastics as "extremely persistent particles" that have "contaminated all compartments of marine ecosystems."
And that problem is only going to get worse with time.
As the world population grows, so does the consumption of plastic. The research states that plastic waste is expected to triple by 2060, reaching an astonishing 155–265 million metric tons per year.
Much of that waste, will, inevitably end up in oceans, leading to ever-increasing amounts of microplastic in the bodes of sea creatures — and our own.
By charting the presence of microplastics in these marine animals and in our own human consumption, the researchers have taken the first step toward understanding the harms of microplastic in our seafood.
"A critical step in understanding the full impact on human consumption is in first fully establishing what levels of microplastics humans are ingesting. We can start to do this by looking at how much seafood and fish is eaten and measuring the amount of MPs in these creatures," Danopoulos said.
What's next — By conducting such a broad overview, researchers found that there were serious shortcomings in the methodology of existing microplastics studies.
Issues ranged from a lack of standardization of practices like appropriate sample size. Any researcher conducting a scientific study needs a large enough sample size to draw accurate conclusions and test their hypothesis.
But according to this new research, many of the studies did not meet the criteria laid out by the European Commission's Institute for Environment and Sustainability, which requires a minimum of 50 sampled specimens per species and age group.
There wasn't even necessarily a scientific consensus on what, exactly, constitutes a microplastic. The study recommends, "In particular, a consensus is needed in the definition of MPs because some studies include nonsynthetic and/or nonsynthetic polymers in their results."
Going forward, the researchers urge the development of standardized models across the microplastic literature, so that future scientists can draw more accurate and confident conclusions about potential harms to humans.
The study concludes: "A key finding of this work is the need for harmonization and standardization of methods and procedures throughout the research process, starting from sampling design on through to reporting."
Ultimately, further research is still required to calculate the impacts of these alarming levels of microplastics on our frail human bodies. In any case, you might want to reconsider your next clam bake.
"No-one yet fully understands the full impact of microplastics on the human body, but early evidence from other studies suggests they do cause harm," Danopoulos said.
Abstract: BACKGROUND: Microplastics (MPs) have contaminated all compartments of the marine environment including biota such as seafood; ingestion from such sources is one of the two major uptake routes identified for human exposure. OBJECTIVES: The objectives were to conduct a systematic review and meta-analysis of the levels of MP contamination in seafood and to subsequently estimate the annual human uptake. METHODS: MEDLINE, EMBASE, and Web of Science were searched from launch (1947, 1974, and 1900, respectively) up to October 2020 for all studies reporting MP content in seafood species. Mean, standard deviations, and ranges of MPs found were collated. Studies were appraised systematically using a bespoke risk of bias (RoB) assessment tool. RESULTS: Fifty studies were included in the systematic review and 19 in the meta-analysis. Evidence was available on four phyla: mollusks, crustaceans, fish, and echinodermata. The majority of studies identified MP contamination in seafood and reported MP content <1MP=g, with 26% of studies rated as having a high RoB, mainly due to analysis or reporting weaknesses. Mollusks collected off the coasts of Asia were the most heavily contaminated, coinciding with reported trends of MP contamination in the sea. According to the statistical summary, MP content was 0–10:5 MPs=g in mollusks, 0:1–8:6 MPs=g in crustaceans, 0–2:9 MPs=g in fish, and 1MP=g in echinodermata. Maximum annual human MP uptake was estimated to be close to 55,000 MP particles. Statistical, sample, and methodological heterogeneity was high. DISCUSSION: This is the first systematic review, to our knowledge, to assess and quantify MP contamination of seafood and human uptake from its consumption, suggesting that action must be considered in order to reduce human exposure via such consumption. Further high-quality research using standardized methods is needed to cement the scientific evidence on MP contamination and human exposures. https://doi.org/10.1289/EHP7171