Assessment of the Presence of Microplastics in Stabilized Sewage Sludge: Analysis Methods and Environmental Impact  
[PERSON]  
1 AGH University of Krakow, Faculty of Energy and Fuels, 30-059 Krakow, Poland; [EMAIL_ADDRESS]  
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2 AGH University of Krakow, Faculty of Physics and Applied Computer Science, 30-059 Krakow, Poland; [EMAIL_ADDRESS] (K.K.); [EMAIL_ADDRESS] (J.C.)  
[PERSON]  
2 AGH University of Krakow, Faculty of Physics and Applied Computer Science, 30-059 Krakow, Poland; [EMAIL_ADDRESS] (K.K.); [EMAIL_ADDRESS] (J.C.)  
[PERSON]  
3 AGH University of Krakow, Academic Centre for Materials and Nanotechnology, 30-059 Krakow, Poland; [EMAIL_ADDRESS]  
[PERSON]  
4 Department of Chemistry, University of Tras-os-Montes e Alto Duovo, 5000-801 Vila Real, Portugal; [EMAIL_ADDRESS]  
[PERSON]  
1 AGH University of Krakow, Faculty of Energy and Fuels, 30-059 Krakow, Poland; [EMAIL_ADDRESS] (J.C.)  
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various chemical additives. There are two sources of MPs (see Figure 1). Primary MPs are produced in the form of tiny particles designed for commercial use, while secondary MPs come from larger fragments that have been partially degraded in the environment [7].  
MPs are a serious problem for wastewater treatment plants. The removal of its fractions via wastewater treatment processes is complex. Moreover, the methods applied for oxidation, especially those for organic pollutants, may affect the comminution of MPs. The treated wastewater in the environment contains not only micropollutants [8; 9] but can also contain a significant number of MPs that will accumulate in lakes, rivers, seas, and oceans [10; 11; 12; 13].  
Sewage sludge is another source of secondary re-emission of MPs into the environment. It is also used to make fertilizers [14]. Microplastic fractions accumulate in sewage sludge in large numbers [15; 16]. The processes to which sludge is subjected during fertilizer production do not eliminate MPs from it [17; 18]. There are also no legal standards regulating the content of MPs in such products.  
Water is considered the largest carrier of microplastics [19]. There are few studies on the content of microplastics in sewage sludge samples, which is where they are retained due to their hydrophobic nature. Scientists warn that 90% of microplastics are retained in sewage sludge [20]. Studies also show that sewage sludge is the largest source of the emission of microplastics from fertilization, and it is more significant than the release of microplastics from other sources into the oceans or other water bodies [21; 22; 23; 24]. In the case of Europe and North America, approximately 50% of the sludge is used to produce fertilizer [23]. Similarly, scientists determined levels from 87.6 to 545.9 MPs/kg of soil after annual fertilization with sludge-based products [20].  
The purpose of this study was to analyze the forms and sizes of MPs included in stabilized sewage sludge collected in one of the wastewater treatment plants that uses it to produce organic-mineral fertilizers [9]. It should be noted that stabilized sewage sludge may also contain pharmaceuticals such as ibuprofen or diclofenac, as well as heavy metals. There is a risk of co-emission of pollutants because MPs can absorb the mentioned micropollutants [14; 25].