Nanoplastics are not always what they seem

Prof Bernd Nowack's team has investigated the release of nanoparticles during the clothes washing. Image: Empa.

It is well known that textiles release microfibres and nanoplastics during washing, but researchers have now shown that nanoplastics are not necessarily plastic particles, but could be water-insoluble oligomers.

Plastic household items and clothing made of synthetic fibres release microplastics - particles less than 5mm in size - that can enter the environment unnoticed, often carried in wastewater leaving homes. It is estimated that synthetic clothing contributes to about 35% of the release of primary microplastics into the world oceans.

Textiles made of synthetic fibres release micro- and nanoplastics during washing, and some of these particles are so small that they are measured in nanometers. Such nanoplastics are the subject of intensive research, as nanoplastic particles can be absorbed into the human body due to their small size, but as of today, little is known about their potential toxicity and risk to humans.

Scientists at the Empa materials research laboratory in Switzerland have now shown that some of the supposed nanoplastics do not actually comprise plastic particles at all, but are water-insoluble oligomers, and the effects they have on humans and the environment are not yet well-understood.

"Not everything that looks like nanoplastics at first glance is in fact nanoplastics."

Professor Bernd Nowack, Empa

Empa researchers led by Professor Bernd Nowack have now joined forces with colleagues from China to take a closer look at nanoparticles released from textiles, and a detailed examination has now shown that not everything that appears to be nanoplastic at first glance actually is nanoplastic. The released particles were in fact clumps of oligomers - small-to-medium-sized molecules that represent an intermediate stage between the long-chained polymers and their individual building blocks - monomers.

These molecules are even smaller than nanoplastic particles, and hardly anything is known about their toxicity either.

For the study, the researchers examined twelve different polyester fabrics, including microfibre, satin and jersey. The fabric samples were washed up to four times, and the nanoparticles released in the process were analysed and characterised.

This was not an easy task according to Nowack, "Plastic, especially nanoplastics, is everywhere, including on our devices and utensils. When measuring nanoplastics, we have to take this 'background noise' into account."

The researchers used an ethanol bath to distinguish nanoplastics from clumps of oligomers. Plastic pieces, no matter how small, do not dissolve in ethanol, but aggregations of oligomers do.

It was found that around one-third to almost 90% of nanoparticles released during washing could be dissolved in ethanol.

"This allowed us to show that not everything that looks like nanoplastics at first glance is in fact nanoplastics," says Nowack.

It is not yet clear whether the release of so-called nano-particulate oligomers during the washing of textiles has negative effects on humans and the environment.

"With other plastics, studies have already shown that nanoparticulate oligomers are more toxic than nanoplastics," says Nowack. "This is an indication that this should be investigated more closely."

The researchers were able to establish that the nature of the textile and the cutting method – scissors or laser – has no significant influence on the quantity of particles released, but the mechanism of release has not yet been clarified for either nanoplastics or oligomer particles.

The good news is that the amount of particles released decreases significantly with repeated washes. It is conceivable that the oligomer particles are created during the manufacturing of the textile or split off from the fibres through chemical processes during storage.

Further studies are required in many areas, and Prof Nowack and his team are focusing on larger particles for the time being. In their next project, they want to investigate which fibres are released during washing of textiles made from renewable raw materials, and whether these could be harmful to the environment and health.

"Semi-synthetic textiles such as viscose or lyocell are being touted as a replacement for polyester," says Nowack, "but we don't yet know whether they are really better when it comes to releasing fibres."

The researchers published their findings in the journal Nature Water.