Chen, Xiaoxin and Halsall, Crispin and Sweetman, Andrew (2024) Adsorption and release behavior of chemicals from microplastics during environmental aging. PhD thesis, Lancaster University.
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Abstract
Plastics are widely used in daily life due to their flexibility, durability and low cost. Due to their global usage, and poor handling at all stages of use from manufacture to disposal, an increasing quantity of microplastic debris has been detected in aquatic environments. As microplastics are composed of a wide range of chemical additives (e.g., plasticizers, flame retardants, fillers, etc.), with those chemicals are not tightly bound into the polymer, they can be released into the environment, and furthermore, due to the hydrophobicity of microplastics, contaminants present environment might be adsorbed by microplastics. Microplastics have been shown to undergo extensive aging after physical abrasion, UV irradiation, biodegradation, etc. The aging effect is an important process that determines the transport and transformation of microplastics in the environment, as well as their interactions with environmental contaminants. This study investigates the aging mechanism, factors affect the aging process, and evaluates how aging of microplastics (including UV irradiation, biofilms colonization, natural aging) affects their surface properties, adsorption/desorption performance, presence of additives, etc. Generally, the oxygen-containing groups on the surface of microplastics increase after aging, and sometimes the surface brightness and colour-difference are changed (e.g., yellowing). Together with the changes in surface roughness, all of them directly or indirectly affect the adsorption/desorption performance of bisphenols (typical endocrine-disrupting chemicals) on microplastics. The interaction mechanisms involved H-bonding, π-π interaction, hydrophobicity interaction, electrostatic interaction. In addition, suspect screening analysis suggested that additives (e.g., antioxidants, light stabilizers, plasticizers) might be vital in controlling the aging process, and the aging of microplastics affects the present of additives, leading to the changes of leaching behavior of additives from microplastics to the aquatic environment. This study combined both laboratory and field work, providing direct evidence of microplastic particles aging processes and their potential environmental risks due as a transport vector and exposure medium.