Sapienza University (Rome, Italy) researchers studied how cortisone sorption is affected by different microplastics. Their findings were published in the Journal of Chromatography A (1).
Environmentalists filter the microplastic waste contaminated with the seaside sand. | Image Credit: © wonderisland - stock.adobe.com
Plastics are used across various daily activities due to their strength, durability, and flexibility, among other qualities. As such, global plastics production has grown exponentially; in 2022, 400 million tons of plastics were made across the globe (2). While these materials can be useful, their excessive production--in addition to poor management—has led to plastics being uncontrollably released into the environment, making plastics some among the most hazardous types of waste in the world.
When these plastics degrade, either through mechanical, chemical, or biological factors, they form microplastics (MPs), which can range from 5 mm to 1 µm in size. MPs can easily enter the environment through various routes, with the most found MPs in aquatic environments being polyethylene (PE), polystyrene (PS), and polypropylene (PP). As such, MPs sorption studies are crucial for understanding how these substances retain contaminants.
According to the researchers, there are limited amounts of studies that evaluate sorption kinetics and isotherms, with none investigating the sorption behavior of cortisone, a natural glucocorticoid used for years to treat various diseases due to its anti-inflammatory effects, on MPs. With this study, cortisone’s sorption behavior was evaluated on three types of PP, PS, and high-density (HD) PE MPs in Milli-Q (ultrapure) water and artificial seawater.
To determine analytes, high-performance liquid chromatography (HPLC) was used alongside an ultraviolet (UV) detector. Kinetic and isotherm studies were conducted using batch sorption experiments under controlled conditions: 1 g of MP pellets, each 3–5 mm in diameter; magnetic agitation at 1000 rpm; and 20 ± 2 °C. Depending on the aqueous matrix, notable differences in the sorption kinetics of cortisone were observed–
namely, the pseudo-second order model provided the best fil for all MPs in the Milli-Q water. In artificial seawater, the pseudo-first order model better described the PP and PS MPs. However, the behavior of HDPE MPs was not affected by environmental changes, leading to the pseudo-second order model being most suitable. The overall sorption capacity followed the order, regardless of the type of water used: PS > PP > HDPE. Up to 0.6 µg of cortisone was retained per gram of plastic under equilibrium conditions.
With the isotherm studies, the experimental data for PP and PS MPs in Milli-Q water were best described using the Langmuir model (an adsorption equilibrium model that is applicable for high and low pressures), suggesting a homogenous sorption process with a monolayer of adsorbed cortisone. A separate model, the Freundlich model (an empirical adsorption model used to describe equilibrium data) provided a better fit for the results obtained with HDPE MPs, thus indicating a multilayer sorption mechanism (4). In artificial seawater, the Freundlich model provided the best fit for the selected MPs, suggesting that under saline conditions, heterogeneous multilayers of cortisone form on the MP surface.
With this study, a specific knowledge gap on steroid hormones’ behavior in the presence of MPs was addressed, providing critical data for understanding environmental risks. Further, the aqueous matrix’s role in modulating sorption efficiency was underscored, something that has not been deeply explored in prior studies. Future studies, according to the researchers, should focus on including artificially or naturally weathered MPs. Nonetheless, these findings could greatly help in advancing scientists’ knowledge of contaminant dynamics in aquatic environments.
(1) De Santo, R.; Antonelli, L.; Gentili, A.; González-Sálamo, J. Sorption of Cortisone on Polypropylene, Polystyrene, and Polyethylene Microplastics. J. Chromatogr. A 2025, 1756, 466082. DOI: 10.1016/j.chroma.2025.466082
(2) Plastics – The Fast Facts 2023. Plastics Europe 2023. https://plasticseurope.org/knowledge-hub/plastics-the-fast-facts-2023/ (accessed 2025-06-03)
(3) Langmuir Isotherm. ScienceDirect 2021. https://www.sciencedirect.com/topics/engineering/langmuir-isotherm (accessed 2025-06-03)
(4) Freundlich Equation. ScienceDirect 2021. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/freundlich-equation (accessed 2025-06-03)
