A potential
risk from human uptake of microplastics is the release
of plastics-associated xenobiotics, but the key physicochemical properties
of microplastics controlling this process are elusive. Here, we show
that the gastrointestinal bioaccessibility, assessed using an in vitro
digestive model, of two model xenobiotics (pyrene, at 391–624
mg/kg, and 4-nonylphenol, at 3054–8117 mg/kg) bound to 18 microplastics
(including pristine polystyrene, polyvinyl chloride, polyethylene
terephthalate, polypropylene, thermoplastic polyurethane, and polyethylene,
and two artificially aged samples of each polymer) covered wide ranges:
16.1–77.4% and 26.4–83.8%, respectively. Sorption/desorption
experiments conducted in simulated gastric fluid indicated that structural
rigidity of polymers was an important factor controlling bioaccessibility
of the nonpolar, nonionic pyrene, likely by inducing physical entrapment
of pyrene in porous domains, whereas polarity of microplastics controlled
bioaccessibility of 4-nonylphenol, by regulating polar interactions.
The changes of bioaccessibility induced by microplastics aging corroborated
the important roles of polymeric structures and surface polarity in
dictating sorption affinity and degree of desorption hysteresis, and
consequently, gastrointestinal bioaccessibility. Variance-based global
sensitivity analysis using a deep learning neural network approach
further revealed that micropore volume was the most important microplastics
property controlling bioaccessibility of pyrene, whereas the O/C ratio
played a key role in dictating the bioaccessibility of 4-nonylphenol
in the gastric tract.