The world is littered with trillions of micro- and nanoscopic pieces of plastic. These can be smaller than a virus — just the right size to disrupt cells and even alter DNA. Researchers find them almost everywhere they've looked, from Antarctic snow to human blood.
In a new study , scientists have delineated the molecular process that causes these small pieces to break off in such large quantities. Since hitting the market 75 years ago, plastic has become ubiquitous — and so, presumably, have nanoplastics. As it turns out, the qualities that make plastic strong and flexible also make it prone to forming nanoplastics - this is true for 75-80% of all plastics used, which are termed as semicrystalline polymers in the community. Sanat Kumar , Michael Bykhovsky and Charo Gonzalez-Bykhovsky Professor of Chemical Engineering at Columbia Engineering, led the research effort.
If you look at a piece of plastic through a powerful microscope, you'll see alternating layers of hard material and soft material. In the hard layers, plastic molecules are rigidly organized in strong crystal structures. In the soft layers, the molecules lack structure and form a soft, amorphous mass. When thousands of these layers are stacked together, they create a material that's lightweight, durable, and extremely versatile. Importantly these materials derive their unique properties through the connectivity between the soft and hard phases.
In a paper published March 28 in Nature Communications, the researchers explain how nanoplastics form. They discovered that the process begins in the soft layers, which grow weaker over time due to environmental degradation and can break off even when the plastic is not under stress. By themselves, these soft pieces break down quickly in the environment. Problems arise when the failure of a soft layer allows hard layers to break off. These crystalline fragments are the nano- and microplastics that can persist in the environment for centuries and cause significant damage in living things, including humans.
We sat down with Kumar to learn more about this work.
How does this paper contribute to our understanding of nanoplastics?
There is a lot of anecdotal evidence of nanoplastics — people have found them all over the place and seen them form — but no one had determined the mechanisms behind how they form.
What did you discover?
75% of all plastic used has sort of a brick-and-mortar structure. It's made of really thin alternating layers: hard, soft, hard, soft, and so on. We've known since the 1950s that the soft stuff is holding the hard stuff together. What we show in the new study is how easily those soft connectors break even under quiescent conditions such as in a landfill. Once that layer fails, the hard segments have nowhere to go — they scatter into the environment.
Why is that a problem?
These pieces float around, and some end up in human bodies. The smallest pieces pass through cells and into the nucleus, where they can start messing with DNA. Nano- and microplastics, which seem to have similar sizes and shapes to asbestos, raise the potential that they could cause cancer, heart disease/stroke, and other diseases.
Is there an engineering solution to address this problem?
Our results suggest that engineering the architecture of the soft layers to be more resilient would decrease the amount of crystalline fragments that break off. Clearly, focus needs to be placed on this point to reduce the amount of micro and nano plastics created by normal polymer degradation.
How can better understanding nanoplastics improve human health?
Only 2% of plastics are recycled, mostly because it's too expensive. But if you just throw plastic into the environment, it creates micro- and nanoplastics that look like they are going to cause health problems. If you think about it that way, if you have to choose between the health problems that could be created by the nanoplastics vs. the cost of recycling, then maybe it's actually cheaper to recycle.
