Written by: David Han '24
Edited by: Angelina Cho ‘24
In the sediment at the bottom of the Mediterranean Sea, researchers from the University of Manchester made a shocking discovery: samples of the sea floor contained as many as 1.9 million pieces of plastic per square meter, a result hypothesized to be caused by water currents sweeping debris from above onto the sea bed . This study is just one of several confirming that plastics are quite literally everywhere. Alexandra ter Halle and her team of researchers discovered evidence of nanoplastics in samples of ocean water for the first time in 2017 . Studies have even found plastic in developing fetuses. The situation isn’t likely to improve in the near future, either. Production of plastic is estimated to double by 2050 from its current level of roughly 380 million tons per year, and around 8 million tons enter the ocean annually . The big problem is, as processes of degradation break down plastic in the ocean or landfills into microplastics, pieces smaller than 5mm, they become small enough for living organisms to unknowingly ingest. Even smaller than microplastics are nanoplastics, which are so tiny that they can easily pass through cell membranes and organ tissues. Despite how invasive these particles can be, scientists are still uncertain of their effects on human health.
Plastics are polymers, a class of molecules consisting of long chains of repeating organic compounds. Many plastics made today have been engineered to be extremely durable and cheap to produce. This manufacturing benefit is the cause of concern about microplastics, since they have the potential to stay in the environment for at least several decades. As a result, when an animal eats food contaminated with microplastics, the pieces could accumulate inside its body throughout its lifetime, a phenomenon called bioaccumulation. Predators that eat prey containing microplastics will then concentrate microplastics within their own body, and the process repeats up the food chain. What makes matters worse is that microplastics can also act as transporters for certain toxins that are attracted to their surface, like PCBs, which cause serious developmental problems in high concentrations .
For simple organisms, the effects of microplastics are relatively well known. When zooplankton were placed in an environment with high levels of microplastics, they showed a reduced ability to produce offspring and eat . Scientists suspect the same could be true of humans and larger animals as well; however, due to the relatively small amount of plastics in the body and wide variety of plastic types, we don’t have good controls to test for these effects. We do know that the presence of microplastics inside the body is associated with greater activation of the immune system, causing chronic inflammation and stress on immune cells. These effects are associated with greater risks of cancer . Significantly less research has been done on nanoplastics, since even identifying them is a difficult process .
One question that may spring to mind is, why isn’t plastic disposal and production being more tightly regulated to prevent microplastics from getting everywhere? The answer comes back to the research. Because no significantly alarming discoveries about the health effects of microplastics in humans have been made, policymakers shift their attention to more concrete problems. One exception was the 2015 Microbead-Free Waters Act, which banned the manufacturing and sale of cosmetics containing plastic beads smaller than 5mm in size. Rather than being for human protection, however, the FDA pushed for this law out of concern that wildlife was mistaking microbeads as food . They stated, “The new law does not address consumer safety, and we do not have evidence suggesting that plastic microbeads, as used in cosmetics, pose a human health concern.”
On the flip side, the scientific community has made impressive strides in learning what effects microplastics have on cells as well as developing ways to remove microplastics from water. For example, researchers in Germany studied the mechanical effects of microplastics on cell membranes, a previously unstudied interaction . The team found that microplastics displace sections of the lipid bilayer that they come in contact with. When large numbers of particles displace the membrane, the total membrane area is reduced and membrane tension increases . Larger particle size corresponded to greater membrane tension, which could impact membrane receptors, cell integrity, and protein function. In January 2021, a team from Hong Kong Polytechnic University created a biofilm from the bacteria Pseudomonas aeruginosa that can trap microplastics in water. The bacteria was used to create net-like structures that absorb the microplastics, then activation of a dispersion gene in the bacteria causes the plastic to be released . While only a proof of concept right now, this technique could be a powerful tool for removing microplastics in aquatic environments.
Is there currently reason to worry about microplastics poisoning you? Probably not. The long term health effects aren’t clear enough yet to warrant any concern, and other contributors to health likely have a much greater impact, such as lifestyle choices and genetics. That doesn’t mean plastic production and waste should be ignored either, however. Enough evidence exists to definitely say that plastic poses a serious threat to marine life, an essential part of the planet’s food chain. If plastic waste continues on its current course, those threats could soon come to humans and other animals that we consume.
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