1. Summary

Such a large-scale production and use of plastics endangers the environment. Plastics that end up in the environment age and undergo chemical and physical changes. They are oxidized under aerobic conditions, fragment due to mechanical stresses and over time, the macroscopic pieces disintegrate into smaller and more mobile micro- and nanoparticles. The smaller/larger particles are dispersed in the environment. They can be also found in the atmosphere, hydrosphere and pedosphere. Ecosystems on Earth cannot deal with these synthetic materials. As their quantity increases, their impact on the Earth’s climate must be taken seriously [6]. Greenhouse gases are emitted at each stage of a plastic’s lifecycle: during mining and transport of raw materials used to produce plastics, manufacturing, waste treatment and release into the environment. Energy recovery of plastic waste and plastic packaging waste incineration are less energetically favorable, no to mention that greenhouse gasses, air pollutants and other hazardous waste is also produced during burning. Micro/nanoplastic particles enter the biosphere – the smaller they are, the easier access they have – and may even end up in the human body through the food chain. Their real health risks are yet unknown. Scientists are researching and trying to estimate with great effort the effects of micro/nanoparticles that are inhaled, ingested or carried on our skin, including the various other micropollutants attached to them. Due to their extremely high surface area to volume ratio and hydrophobic properties, they can bind and concentrate many substances on their surface, including polycyclic aromatic hydrocarbons, heavy metals, drug molecules and pesticides. The smaller the plastic particles are, the more likely is this to happen [7].

What exactly do we mean by microplastics, what kind of substances are they? Although there is no conventional definition regarding size limits, the term ‘microplastics’ generally refers to pieces of plastic which are smaller than 5 mm in diameter, and ‘nanoplastics’ are plastic particles with a diameter of less than 100 nm [8]. Based on their source, they can be primary or secondary microplastics. Primary microplastics are plastics produced directly in this form, e.g. microparticles, granules used for medicines, cosmetic and industrial products, which then end up in wastewater. Secondary microplastics are particles produced by the physical, chemical, and biological degradation of larger pieces of plastic [9]. Microplastics occur in a large variety of chemical composition, shape, size, density and color. Depending on their chemical composition, PE, PP, PET, PS, PVC, PC, PA, PUR, etc. microparticles are distinguished [10]. The most common microplastic particles found in water are PP, PE and PS. In terms of form, microplastic pellets, spheres, fibers, films and fragments with irregular shape can be also detected. The most commonly observed forms are fragment and fiber. Based on their size, plastic debris can be categorized into macroplastics (> 25 mm), mesoplastics (5–25 mm), microplastics (< 5mm) and nanoplastics (< 100 nm) [11].

The small-sized, low-density microplastic particles float on the surface of water or remain close to the surface even far from their place of origin. Particles with a higher density or those that form heteroaggregates with other organic matter (biofouling) tend to accumulate in the sediment near the riverbed or the sea floor. Plastics are very resistant to environmental influences; normally their decomposition is extremely slow, it might last for decades. Fragmentation of microplastic particles is mainly produced by photo-oxidation, thermal, mechanical or biodegradation [12]. Due to their hydrophobic properties and high surface area to volume ratio, micro/nanoplastic particles can easily adsorb other, mainly hydrophobic organic pollutants or heavy metals [13], [14], [15], and their surface may also be suitable for the formation of biofilms of some microorganisms [16].