Science Matters

Plastic pollution: is this useful material hurting us?

Boyce Rensberger

(7/2023) They are everywhere.

They are in factories and office buildings. They have entered our schools. Many have made it into our homes. Some people even put them on their skin. And, most concerning of all, many people unwittingly eat and drink them.

I refer to plastic, all kinds of plastic. I am typing this on a keyboard made of plastic. The rugs in many homes are made of other kinds of plastic, such as nylon and polypropylene. Many items of clothing are made of yet another kind, polyester. Some women rubbed exfoliating lotions on their skin, lotions that, before they were banned, contained microbeads of, yes, plastic. And, deeply worrying, some municipal water systems deliver water inadvertently laced with microscopic particles of plastics of many kinds.

They may have been a novel idea in 1967 when the movie, "The Graduate," famously had an older man advising a young Dustin Hoffman that the future was in "Plastics." Indeed, it is hard to imagine our modern world without these highly useful and hugely different kinds of polymers, almost all of which are made from petroleum or other fossil fuels.

Plastic pollution includes not just the bits that we can’t see, but also the plastic bags that most of us use only once to carry something out of the store and then throw away. Or plastic foam packing materials that we throw away. Or the plastic toys, tools and gadgets that are thrown away. But where is "away"? Wherever it may be, a goodly portion of that plastic winds up in creeks, rivers, and oceans.

The best-known results of this are the Great Garbage Patches that accumulate in the centers of circular ocean currents. Some of it includes recognizable objects such as plastic bags and bottles, but more is made of smaller fragments. As the plastic is knocked around, it breaks into ever smaller bits.

A quick Web search will show you beaches littered with this stuff. The sun’s ultraviolet rays also turn plastic brittle, furthering its disintegration. Waves and tides put some on the shore but carry much more out to the open ocean.

Over time macroplastic (any big object) is broken into microplastic, defined as being smaller than five millimeters in size. (That’s about the width of the letter T at the beginning of this article.) Microplastic bits are eventually broken into ever smaller fragments, even to particles so small they are called nanoplastics, which are not yet officially defined, but that measure, at most, 1 micron. That’s about 1/25,000th of an inch. So just barely visible in a light microscope.

If you wonder how plastics get into the water supply, think of this: Every time you wash polyester clothing, tiny filaments break off and are flushed down the drain. That wastewater goes somewhere. If you are on a well-and-septic system, it goes into the groundwater. Otherwise it goes through a sewage treatment plant (even the most thorough water treatment has little effect on plastic) and then out to a river. There is no evidence that plastics are degraded by any biological process on a scale that can keep up with the constant hailstorms of microplastics people are releasing to the environment.

The Monterey Bay Aquarium Research Institute estimates that some 500 pounds of plastics of all sizes enter the world’s oceans every second. Already in the ocean is an estimated 14 billion tons of microplastics, mixing through the water column.

The physical bits of plastic are concern enough, but there is a deeper problem. Scientists have found that many microplastics can bind with other substances they meet along the way, including toxic metals, persistent pesticides and even various drugs that people take and, often enough, excrete.

Can this stuff get into our bodies? Absolutely. Recent studies in the U.K. and in the Netherlands have found nanoplastics in human lung tissue and even in blood. What remains unknown is whether this plastic or the attached molecules are doing us any harm. I have found no study with good evidence of harm but given that thousands of other substances can bind to microplastics, it seems likely that eventually something will be found. Moreover, the plastics themselves contain thousands of different kinds of additives—substances mixed in at the factory to give the plastic various desired properties. The additives, many of which are toxic, can leach out and drift on their own in the ocean.

How do nanoplastics get into our bodies? Consider this: The stuff has been found in bottled water. For example, a study published in Frontiers in Chemistry in 2018 analyzed hundreds of bottled water samples from eleven different brands and found nanoplastics in 93 percent. Also, numerous studies have found plastic particles in fish from many parts of the world, typically in the intestines. Plastic pollution in fish has been found to cause growth retardation and behavioral abnormalities. It’s not clear whether that is the result of the plastic itself or other molecules attached to the plastic.

So, what to do about this?

A current area of research is finding ways of breaking down microplastics all the way to nontoxic molecules such as water and carbon dioxide. Plastics are, after all, hydrocarbons. They are organic compounds made of long chains of carbon atoms with hydrogens attached at various points. The carbon chains (and rings) typically also have attached atoms of oxygen, sulfur, or nitrogen.

Some studies have found that certain microorganisms can make enzymes that break down plastics, but it’s not clear whether those processes can go all the way to nontoxic substances.

According to one study published this year: "Several types of microorganisms have the capacity for plastic biodegradation. These include bacteria, fungi, and algae. However, the breakdown depends on the physical and chemical characteristics of the plastics. If these microbes are harnessed, they have the potential to overcome this critical environmental issue."

The authors of that study are with the Biorefining Research Institute of Lakehead University in Ontario. It is funded by the provincial government to find environmentally acceptable ways of detoxifying waste materials using microorganisms. One approach is first to find microbes that already happen to have a gene for an enzyme that attacks plastic. Then genetically engineer the microbe to increase the number of those genes. It is well known that the more genes a cell has for any given product, the more it will make.

Once researchers learn what enzymes the microbes produce to break down plastic, the hope would be to synthesize lots of those enzymes and somehow use them in wastewater treatment. But that is clearly a long way off.

And we’re making more plastic than ever—more than 400 million tons in 2020, an amount expected to triple by 2050.

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