Microplastic Safety Tests May Read Low Because Not All the Plastic Reaches the Cells

Researchers at the Netherlands Organization for Applied Scientific Research (TNO) report that a microplastic toxicity test understates the hazard by about a factor of two when it counts the dose added to the dish instead of the dose that reaches the cells.

The study was published Oct. 7, 2026, in Microplastics and Nanoplastics, and its authors aimed it at a fast-growing body of work that compares and ranks microplastic toxicity by polymer type, size and shape. They describe the question of how much of a dose actually reaches the cells as critical and often overlooked in that kind of screening.

The experiment used fluorescent polystyrene spheres 1 and 10 micrometers across and tracked their settling in a dish with no cells, then set the result against two models that predict how particles settle: RiskGONE and Stokes' Law. Neither size had fully settled within 24 hours. The smaller spheres behaved as RiskGONE predicted; the larger ones matched Stokes' Law.

The same particles were then put on THP-1 cells, a human immune cell line, in the same medium, plate setup and volume. The hazard calculated from the dose added came out lower than the hazard calculated from the dose that actually arrived.

M. Kloukinioti of TNO and Maastricht University Medical Center+ is the paper's first author, and L. A. Parker, also of TNO, is its corresponding author. The work belongs to MOMENTUM, a Dutch consortium on microplastics and health funded by the ZonMw Programme Microplastics and Health and by Health-Holland. It also drew funding from Plastics Europe, and the authors state that the funders had no influence on the manuscript. Microplastics and Nanoplastics published it open access as an accepted manuscript, ahead of a final edited version.