Physiological ageing of microplastics in enzyme-containing gastric fluid alters kaolin-microplastic interaction and Pb adsorption behaviour

Li, Yuan, Gao, Zhenghui, Qian, Hang, Morgan, David ORCID: https://orcid.org/0000-0002-6571-5731, Sapsford, Devin and Harbottle, Michael 2026. Physiological ageing of microplastics in enzyme-containing gastric fluid alters kaolin-microplastic interaction and Pb adsorption behaviour. Biogeotechnics , 100260. 10.1016/j.bgtech.2026.100260

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Abstract

Microplastics (MPs) are synthetic polymer particles whose surface properties are susceptible to environmental and physiological ageing; however, how physiological ageing in enzyme-containing gastric fluid alters clayey soil-microplastic interactions and metal retention remains poorly understood. This study investigated how ageing of three representative MPs in simulated gastric fluid (SGF; containing pepsin as the enzymatic component) altered their interactions with kaolin (a simplified clay mineral model) and affected Pb adsorption behaviours. SGF exposure induced detectable modifications in MPs’ surface chemistry in part due to protein corona deposition, strong acid erosion, and oxidation of functional groups. These modifications influenced the MP vector effects for Pb (notably, the adsorption capacity of digested tyre-MPs decreased by ~35.6%), as well as kaolin-MP interactions and the Pb adsorption capacity of the mixtures. Aggregation between MPs and kaolin particles reduced Pb adsorption relative to the expected additive effect, likely due to the formation of heterogeneous aggregates through electrostatic interactions and physical entrapment that masked potential Pb-binding sites. Notably, zeta potential differences among kaolin-MP mixtures correlated strongly with their Langmuir adsorption capacities (correlation coefficient r = 0.933), highlighting the role of electric double layer in governing Pb adsorption. From a geo-environmental perspective, Pb adsorption in the clay-rich mixtures may be altered not simply by the addition of MPs as extra sites, but by the aggregation behaviour, interfacial charge, and mineral binding-site accessibility of the mixtures.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Chemistry Schools > Physical, Chemical & Environmental Sciences
Publisher:	Elsevier BV
ISSN:	2949-9291
Date of First Compliant Deposit:	3 August 2026
Date of Acceptance:	11 July 2026
Last Modified:	07 Aug 2026 23:45
URI:	https://orca.cardiff.ac.uk/id/eprint/188675

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