# Stabilized Sewage Sludge as Fertilizer: Risks Related to the Presence of Microplastics
## 1 Introduction
Due to their physicochemical properties--such as hydrophobicity, structure, polarity, and interactions with the environment--microplastics can serve as carriers for chemical pollutants and pathogens, thereby increasing their potential risks to both health and ecosystems [10]. Therefore, it is essential to conduct detailed research on the presence of microplastics in the environment and take measures to reduce plastic usage. Special attention should be given to products that may contain microplastics, thus serving as a source of these pollutants in the environment. One such example is fertilizers produced from sewage sludge. Current analyses of these products primarily focus on detecting parasite eggs, bacteria, and heavy metals as well as assessing the levels of elements essential for agriculture, such as nitrogen, phosphorus, magnesium, and calcium [11]. However, they do not include research on other potentially harmful pollutants, including microplastics. Studies have shown that compost-based fertilizers contain microplastics, with concentrations ranging from 146 to 12 particles per kilogram of dry matter [12]. Additionally, significant amounts of microplastics were detected in recycled activated sludge, with a concentration of 113 \(\pm\) 57 microplastics per gram of dry sludge. This suggests that approximately 3.4 billion microplastic particles may accumulate in the 30 tons of sludge produced daily by wastewater treatment plants [13]. These results underscore the need for more detailed analyses of sewage sludge for detecting microplastics and implementing measures to mitigate their potential transfer to the environment through effective treatment and waste management practices. Further research is needed to assess the impact of microplastics on human health and ecosystems and develop effective strategies for their removal from the environmental cycle. Currently, there is increasing regulatory attention devoted to microplastics due to their environmental and health risks. The European Union, for example, has introduced regulations aimed at reducing microplastic pollution, including restrictions on the intentional addition of microplastics in products and guidelines for waste management. However, specific regulations addressing the presence of microplastics in fertilizers, especially those derived from sewage sludge, remain limited or underdeveloped at both the European Union (EU) and global levels. This regulatory gap underscores the importance of investigating microplastic contamination in sludge-derived fertilizers to inform future policy decisions. This study aimed to demonstrate the presence of significant amounts of microplastics in fertilizers derived from sewage sludge and to evaluate their potential for re-emission into the environment, which could lead to secondary pollution and further adverse ecological effects. The study hypothesizes that fertilizers contain a variety of microplastic types, primarily originating from synthetic textiles and other polymer sources. It also examines the potential ecological risks associated with these microplastics, including the contamination of soil and water systems. Furthermore, this research addresses a gap in current knowledge regarding the behavior and fate of microplastics in sludge-derived fertilizers, which has been insufficiently studied in previous works.