Key Physicochemical Properties Dictating Gastrointestinal Bioaccessibility of Microplastics-Associated Organic Xenobiotics: Insights from a Deep Learning Approach

• Published in: Environmental science & technology 2020-10, Vol.54 (19), p.12051-12062
• Main Authors: Liu, Xinlei, Gharasoo, Mehdi, Shi, Yu, Sigmund, Gabriel, Hüffer, Thorsten, Duan, Lin, Wang, Yongfeng, Ji, Rong, Hofmann, Thilo, Chen, Wei
• Format: Article
• Language: English
• Subjects: Adsorption; Aging; Bioavailability; Contaminants in Aquatic and Terrestrial Environments; Deep Learning; Desorption; Entrapment; Humans; Microplastics; Neural networks; Nonylphenol; Physicochemical properties; Plastic pollution; Plastics; Polarity; Polyethylene; Polyethylene terephthalate; Polymers; Polypropylene; Polystyrene; Polystyrene resins; Polyurethane; Polyurethane resins; Polyvinyl chloride; Pyrene; Rigidity; Sensitivity analysis; Sorption; Urethane thermoplastic elastomers; Variance analysis; Water Pollutants, Chemical - analysis; Xenobiotics
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.0c02838

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.