Nanoplastics, pieces of plastic measuring between 1 and 1,000 nm, have found their way into waterways, food systems, and human tissues. Now, using real-world waste samples, scientists have shown that nanoplastics readily and rapidly adsorb heavy metals such as lead and cadmium (ACS ES&T Water 2025, DOI: 10.1021/acsestwater.4c01191).

Extracting nano-sized plastic particles from real-world waste has proven to be a challenge in the past, so scientists have largely studied laboratory-made nanoplastics. But Somenath Mitra and his colleagues at the New Jersey Institute of Technology used a technique that they previously developed to mill nanoplastics from real-world waste and then exposed those nanoplastics to heavy metals.

In total, the researchers exposed three types of nanoplastics—made from polyethylene, polystyrene, and polypropylene—to cadmium, cobalt, lead, manganese, and zinc. To carry out the exposure, the researchers mixed nanoplastics and metal ion solutions in conical flasks. In addition to using real-world nanoplastics, Mitra chose the concentrations of heavy metals to mimic real-world conditions. The levels were close to concentrations found in waterways, he says.

Polypropylene had the highest adsorption capacity of the nanoplastics, but all three showed a strong capacity to grab on to the metals. Lead was adsorbed the fastest, with 99% of it being adsorbed within 5 min by all three types of nanoplastics.

Real-world nanoplastics vary in shape and size and have rough edges, whereas those manufactured in the lab are consistently spherical. That means the nanoplastics that Mitra extracted for his latest study had a higher surface area than their lab-made counterparts. “Adsorption is a surface phenomenon. If you have a very high surface area, it stands to reason that your adsorption would be higher,” says Mitra.

Other nanoparticles commonly found in water, such as clay and humic material, show even greater capacity to adsorb heavy metals than nanoplastics do, says Mitra. “But they are easily removed from water when we settle sediments and sludge, but microplastics and nanoplastics are difficult to remove.”

A 2019 study carried out by researchers at the University of Victoria estimated that Americans are ingesting as many as 52,000 nanoplastic particles per year (Environ. Sci. Technol., DOI: 10.1021/acs.est.9b01517). That number rises to 121,000 when inhalation is considered.

“We're finding them, not only in the gastrointestinal tract, but also in the liver, kidney, brain, and other regions,” says Jonathan H. Shannahan, a toxicologist at Purdue University who was not involved in the study.

Mitra's findings that these plastics can also carry heavy metals with them are potentially worrisome for human health because heavy metal exposure can lead to an increased risk of cancer, neurological problems, and developmental delays in children. “But it’s the dose that makes poison,” says Shannahan. “That’s important to understand, and we don’t yet know what the exposure dose is that people are facing. That’s hard to figure out and will take time. Essentially, it’s TBD [to be determined] whether heavy metal exposure from nanoplastic pollution is a health concern.”

The study’s focus on real-world conditions makes Mitra’s findings especially impactful, says Shannahan. “It’s getting us closer to the point where we can answer some of the questions about human health concerns of nanoplastic pollution.”