Lab study: microplastic surfaces generate reactive molecules in water and blood serum

Mixed · 2A new laboratory study led by Wei Min, a chemist at Columbia University, reports that microplastics generate highly reactive molecules when they contact water. 1 2 Mixed · 2The team tested particles of common plastics, including polystyrene, polyethylene and polypropylene; Scientific American also lists polyvinyl chloride and polyethylene terephthalate (PET). 2 1 Centre · 1Using techniques including fluorescence microscopy and electron spin resonance spectroscopy, they showed that hydroxyl radicals, a type of reactive oxygen species, form spontaneously at the plastic-water interface. Min links this to electric charges forming there, which may help strip electrons from OH- ions in water. 2

Left · 1Min explained that plastic surfaces repel water, so water molecules there cannot form the hydrogen bonds they keep in liquid form, which changes the local electrical environment and chemical reactivity. 1 Mixed · 2Surface area is central to the proposed effect: as plastics fragment, surface-to-volume ratio rises sharply. Min said a credit card broken into 10-micron particles gains more than 200 times its surface area, and Matthew Campen of the University of New Mexico said a half-centimetre plastic ball could degrade into a quadrillion 50-nanometre particles, raising surface area 100,000-fold. 1 2 Centre · 1In New Scientist's account, the charge attracted biological molecules such as DNA to the particle surface in water, and this appeared to damage proteins and red blood cells. When particles were suspended in blood serum, radical generation was weaker but "still detectable", Min said. 2

Centre · 1The most water-repelling plastics tested, such as polyethylene and polypropylene, showed stronger radical-generating activity than more hydrophilic ones such as PET. Adding a surfactant, a chemical that weakens the forces holding water molecules together, dampened radical generation. 2 Mixed · 2The work is framed as a possible mechanism for earlier findings that microplastics cause inflammation, oxidative stress and reduced mitochondrial activity, and for associations with conditions such as cardiovascular disease and dementia. 1 2 Mixed · 2Researchers stress the limits of the findings. Min said how this contributes to damage in human tissue is unclear, the potential size of the effect is unknown, other mechanisms could be involved, and "We have no idea right now" how much plastic is in a person. 1 2

Mixed · 2Independent researchers welcomed the work. Martin Wagner, a toxicologist at the Norwegian University of Science and Technology, said it implies microplastics are themselves a source of oxidative species. Hao Chen of the New Jersey Institute of Technology called the results "very important" but a "starting point", and Campen called them a "critical building block". 1 2 Centre · 1Campen urged calm, noting that in the body microplastics will usually be surrounded by lipids that act as surfactants. He said the main concern is whether exposure is worsening and that health effects need to be understood to avoid exposure. New Scientist also cautions that reports of microplastics in blood may reflect contamination and false positives. 2 Centre · 1Min suggested the findings could help design safer materials, though Campen noted the least active plastics are probably also those that break down more slowly in the environment, posing a trade-off. 2