Our planet is facing a silent but pervasive environmental threat: microplastics. These tiny fragments (less than five millimeters in size), derived from larger plastics breaking down, are now ubiquitous. They have infiltrated the most remote corners of the Earth, from the icy realms of the poles to the soil beneath our feet. They can also be found in our drinking water and food, which explains why microplastics are easily found in human poop and even in our blood.

Yet, while microplastics often make headlines, a new study is putting the spotlight on their often-ignored smaller cousins: nanoplastics. These are even smaller derivatives of microplastics — smaller than one millimeter — which are barely visible and potentially more harmful.

The new study reports a startling fact: the average liter of bottled water holds approximately 240,000 detectable plastic fragments — a figure vastly exceeding previous estimates.

The minuscule size of nanoplastics allows them to bypass bodily barriers, entering the bloodstream directly from the intestines or lungs. From there, they can travel to crucial organs such as the heart and even the brain. They also possess the alarming ability to invade individual cells and cross the placenta, potentially affecting unborn babies.

The pervasiveness of plastic pollution: from the very large to the very small

The scale of plastic production and pollution is staggering. Annually, nearly 400 million metric tons of plastic are produced globally. Of this, over 30 million tons are discarded, contaminating oceans, rivers, and landscapes. Unlike natural materials, plastics do not degrade into benign substances; they merely break up into ever-smaller particles, with no limit to how small they can become.

The issue of plastics in bottled water first gained significant attention in 2018, with studies revealing an average of 325 particles per liter. However, these studies were limited to particles larger than 1 micrometer. If people were concerned by these earlier findings, wait until they learn about how many plastic fragments there actually are once you zoom in even closer.

“Previously this was just a dark area, uncharted. Toxicity studies were just guessing what’s in there,” said study coauthor Beizhan Yan, an environmental chemist at Columbia Climate School’s Lamont-Doherty Earth Observatory. “This opens a window where we can look into a world that was not exposed to us before.”

The new study employs a technique called stimulated Raman scattering microscopy, pushing the boundaries of detection to particles as small as 100 nanometers — about 1,000 times smaller than the width of a human hair. This method not only detects size but also identifies the types of plastics present.

Developed by Columbia biophysicist Wei Min, this method utilizes dual lasers to make specific molecules in a sample resonate. By focusing on seven types of common plastics, the researchers crafted a sophisticated algorithm to accurately interpret the data. “It is one thing to detect, but another to know what you are detecting,” Min said.

The study examined three widely consumed bottled water brands in the United States, analyzing plastic particles as small as 100 nanometers. Remarkably, each liter of water contained 110,000 to 370,000 plastic fragments, with a staggering 90% identified as nanoplastics and the remaining 10% as microplastics.

Ubiquitous plastic and uncertain consequences

One frequently detected type of plastic was polyethylene terephthalate (PET), commonly used in manufacturing water bottles, as well as other beverage containers and various food products. PET particles likely seep into the water due to bottle manipulation or exposure to heat. Another study suggests that repeated opening and closing of the bottle cap could also release plastic particles into the water.

Surprisingly, PET was outnumbered by polyamide, a type of nylon. The researchers suspect this comes from the plastic filters used in water purification processes before bottling. Other plastics identified include polystyrene, polyvinyl chloride, and polymethyl methacrylate, all widely used in various industrial applications.

An unsettling revelation from the study is that the seven types of plastics that they identified constitute only about 10% of all nanoparticles discovered in the samples. The authors currently don’t know anything about the nature of the remaining 90% of the fragments. They could be other forms of nanoplastics or different substances entirely.

Researchers are now expanding their focus to tap water, which also contains microplastics, though in lower quantities. Other projects are underway to study the impact of microplastics and nanoplastics from sources like laundry wastewater and even snow from Antarctica. However, the ultimate goal is to assess the presence of nanoplastics in human tissues and their effects on our development and health. At the moment, it is not clear at all what impact plastic fragments have on human health and how concerned we all should be. Hopefully, we will have our answer soon.

The findings appeared in the Proceedings of the National Academy of Sciences.