Microplastics serve as a potential vector for the transfer of naphthalene from freshwater to the human gastrointestinal system

Ubiquitous microplastics (MPs) may act as potential carriers of pollutants by transferring them from aquatic environments to humans, thus posing risks to human health. However, little is known about the vector effects of MPs, which refers to their ability to sorb contaminants from the environment and to release them in the body of a sensitive receptor, (e.g., humans or other biota), after intake (e.g. by ingestion or inhalation). Therefore, this transfer of contaminants can constitute a risk to humans and the environments and must be quantified.Vector effects were investigated for three types of MPs, i.e., medium-density polyethylene (MDPE), polypropylene (PP), and polystyrene (PS) to transfer naphthalene (model contaminant) in freshwater. Firstly, kinetic and isotherm studies characterized the sorption behaviour of naphthalene into MPs. Then, a physiologically based extraction test (PBET) was conducted on naphthalene-loaded MPs to determine gastric and intestinal bioaccessibility (i.e., an estimate of solubility for an ingested dose of a contaminant). Results suggest that sorption kinetics follow a pseudo-second order model for all tested MPs. External mass transport is the rate-controlling step for naphthalene sorption on MPs. Furthermore, isotherm results indicate that Langmuir and linear models provide the best fit for this sorption, which is characterized by a hydrophobic interaction mechanism. The sorption capacities of naphthalene on MPs followed the decreasing order of MDPE > PP > PS. The bioaccessibility of naphthalene was higher in the intestinal phase (28–60 %) than in the gastric phase (24–40 %). These findings demonstrate that MPs can serve as vectors for naphthalene transport from freshwater systems to the human gastrointestinal tract (GIT). This vector effect should be investigated further and taken into consideration to estimate associated risks to human health.