Exploring the release of microplastics' additives in the human digestive environment by an in vitro dialysis approach using simulated fluids

Ingestion of microplastics represents a significant exposure pathway to harmful additives to humans. In the last years, many studies have been focused on assessing the additives' fraction that could be released in gastrointestinal simulated fluids to estimate their potential health risk. In the present study, oral bioaccessibility (i.e., fraction dissolved in gastrointestinal fluids) and bioavailability (i.e., fractions absorbed in simulated blood) of plastic additives were simultaneously assessed by an in vitro method including a dialysis membrane filled with simulated human plasma. To this end, a method consisting of a vortex-assisted liquid-liquid extraction (VALLME) prior to gas chromatography-tandem mass spectrometry (GC-MS/MS) determination was successfully validated for the analysis of 38 multi-class additives in simulated fluids. This methodology was novelty applied to 3 conventional petroleum-based polymers (high-density polyethylene (r-HDPE), polypropylene (r-PP) and polyethylene terephthalate (PET)) and biopolymer (polylactic acid (PLA), polyhydroxy butyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBv)) microplastics, as well as after additional mechanical recycling and marine-ageing processes to explore changes in additives' release. Biopolymers were observed to release 4-fold more additives in bioaccessible fractions than conventional polymers, being tri-n-butyl phosphate (TnBP) the most profuse (101 ng g^-1, by average); whereas diethyl phthalate (DEP) was only quantitated in bioavailable fractions (mean of 8.6 ng g^-1), with a ratio of 14.1 %. Moreover, different additives were released after marine ageing and additional recycling, observing an increase in bioaccessible additives concentrations for PLA, PET, and r-HDPE, and reduced for PHB and r-PP; while a decrease in bioavailable additives was observed for PLA and r-HDPE.