Effects and Impacts of Different Oxidative Digestion Treatments on Virgin and Aged Microplastic Particles

Abstract

Although several sample preparation methods for analyzing microplastics (MPs) in environmental matrices have been implemented in recent years, important uncertainties and criticalities in the approaches adopted still persist. Preliminary purification of samples, based on oxidative digestion, is an important phase to isolate microplastics from the environmental matrix; it should guarantee both efficacy and minimal damage to the particles. In this context, our study aims to evaluate Fenton’s reaction digestion pre-treatment used to isolate and extract microplastics from environmental matrices. We evaluated the particle recovery efficiency and the impact of the oxidation method on the integrity of the MPs subjected to digestion considering different particles’ polymeric composition, size, and morphology. For this purpose, two laboratory experiments were set up: the first one to evaluate the efficacy of various digestion protocols in the MPs extraction from a complex matrix, and the second one to assess the possible harm of different treatments, differing in temperatures and volume reagents used, on virgin and aged MPs. Morphological, physicochemical, and dimensional changes were verified by Scanning Electron Microscope (SEM) and Fourier Transformed Infrared (FTIR) spectroscopy. The findings of the first experiment showed the greatest difference in recovery rates especially for polyvinyl chloride and polyethylene terephthalate particles, indicating the role of temperature and the kind of polymer as the major factors influencing MPs extraction. In the second experiment, the SEM analysis revealed morphological and particle size alterations of various entities, in particular for the particles treated at 75 °C and with major evident alterations of aged MPs to virgin ones. In conclusion, this study highlights how several factors, including temperature and polymer, influence the integrity of the particles altering the quality of the final data.

Fourier Transform Infrared Spectroscopy to Assess the Degree of Alteration of Artificially Aged and Environmentally Weathered Microplastics

“…This absorption band, highlighted at high signals in many spectra but more intense for the environmental samples, could be attributed to the hydrolysis reaction that occurred in the polymer chains with an increase in hydroxyl groups due to the effect of the permanence time in the environment [ 49 ]. Moreover, as suggested by [ 6 , 50 ], the consequent formation of surface cracks and fractures, increasing with the environmental exposition, could allow a more accessible and deeper infiltration of water and oxygen from the surrounding ambient, leading, in time, to an increased effect of ageing. The hydroxyl content of environmentally weathered PE particles showed a certain degree of variability among the particles of different colours and shapes.…”

“…Although plastic has a high resistance to degradation due to the presence of plasticizers, antioxidants, and stabilizers added during the production process, its ageing processes are induced by a combination of the interaction of biotic and abiotic factors. For example, biodegradation (by microorganisms), photodegradation, mechanical stress, and chemical and physical weathering (by air, wave action, wind, temperature, and sand-blasting) favour the creation of cracks, fractures, and alterations of the chemical structure of the plastic surface which produce, in time, a wide variety of particles, called microplastics, differing in shapes and sizes [ 4 , 5 , 6 ].…”

Assessing sources and fractions of metals associated with environmental plastics: a case study in Lake Como (Italy)

“…This approach does not allow comparison of the chemical species sorbed on MPs and the metals present in the bulk polymer, limiting the information for an effective bioavailability and exposure assessment. [39][40][41] Thereby, other methods have been applied to specically investigate loosely bonded or bioavailable fractions of metals, including single and sequential extractions. 29,[42][43][44][45][46] In our study, we tested a comprehensive analytical approach including total acid digestion, a single-step extraction and a sequential extraction protocol to assess the metal content and fractionation on MP samples.…”

“…This approach does not allow comparison of the chemical species sorbed on MPs and the metals present in the bulk polymer, limiting the information for an effective bioavailability and exposure assessment. 39–41 Thereby, other methods have been applied to specifically investigate loosely bonded or bioavailable fractions of metals, including single and sequential extractions. 29,42–46…”

Microfluidic Detection and Analysis of Microplastics Using Surface Nanodroplets

“…Filtration and centrifugation are typically done when collecting microplastics from water . If the sample contains biological material such as algae, it is digested using acids, oxidizing agents, or enzymes , prior to collection. Filtration relies on pores of defined size, so several filtrations with varying pore size filters are required considering the wide size distribution of microplastics.…”