Plastics pollutions are traditionally considered as environmental issues[1]; they are more or less seen as pollution problems [2, 3]. More attention has been given to health issues recently in relation to pollution from microplastics[4, 5]. There have been a lot of news and reports about microplastics from various media and scientific journals recently in the world. The reports show that microplastics cause pollution in the soil [6], air [7], fresh water and sea [8]. For example, the tea made from the popular plastic tea bags in the market contains up to tens of billions of microplastic particles [9], and washing clothes can cause the release of microfibers to water[10], and more than 90% of the 39 different salt brands worldwide contain microplastics [11]. According to media reports, researchers have discovered "traces" of plastic particles in the Arctic and are shocked by the number. Although the Arctic is inaccessible, there are more than 10,000 plastic particles per liter of snow [12]. Recent researches have shown that various food products were contaminated with microplastic particles, indicating a widespread exposure [13–20]. Microplastics can be enriched in food chain and also introduced into foodstuffs through the air, indicating the ubiquitous presence of plastic particles [21, 22].
There is no uniform definition of microplastic size, but a well acceptable size range is between 100 nm and 5 mm. Plastic particles below 100 nm are commonly defined as nano-plastics [23, 24]. The particles below 150 µm in size are considered to be systemically bioavailable to humans, and particles below 4 µm can be taken up by intestinal cells [24, 25]. Hanvey et al [26] have tried initially to standardize analytical methods in order to better estimate human exposure. So far, how microplastics affect human health is still far from being fully understood. Plastic materials are usually considered as very unreactive chemically due to their large molecular sizes. A potential bioreactivity of microplastic particles is therefore more likely to be expected due to their increased surface-to-volume ratio with decreasing particle sizes due to their chemical properties. However, more recently, Stock et al [27, 28] systematically investigated the impact of the gastrointestinal passage on the physicochemical particle characteristics of the five most produced plastics (PE, PP, PVC, PS and PET). The results showed that all the plastic particles were highly resistant to the artificial digestive juices, and the main stages of the human gastrointestinal tract did not decompose the particles.
In this work, it is hypothesized that artificial digestion may affect only the surface of the microplastics or the whole particles. This work focuses on the surface microstructures and chemical properties of these microplastics, particularly the variations in their atom scale and chemicals. The impact of artificial digestion on the microplastics was studied by SEM, AFM, XPS and ATR-FTIR. This is essential for a reliable future risk assessment of microplastics.