# Stabilized Sewage Sludge as Fertilizer: Risks Related to the Presence of Microplastics
## 4 Conclusions  
The analysis indicates that organic fertilizers derived from sewage sludge contain significant amounts of microplastics, both in terms of mass and particle count. The observed average--exceeding 2 g of microplastics per square meter of agricultural land--suggests a tangible risk of accumulation in soil and, in the long term, in crops and the food chain. The morphological (e.g., fragments, fibers) and dimensional diversity of the particles implies complex sources of origin, as well as varied mechanisms of transport and retention in the organic matrix. The higher microplastic content observed in the June samples compared to those from July (approximately 17%) may indicate seasonal variations in fertilizer composition or differences in processing methods. The detection of larger particles (>4000 \(\upmu\)m) in both sample sets raises concerns about the limitations of current filtration and purification methods used in fertilizer production. Polyethylene, identified as the most widely used plastic type, likely originates from commonly used packaging materials and agricultural films. This finding aligns with trends reported in other studies of agricultural microplastic pollution. The obtained results are particularly significant for the management of sewage sludge intended for use as a fertilizer. The analysis confirmed a considerable presence of microplastics in fertilizer derived from stabilized sewage sludge, highlighting a serious environmental concern due to the persistence and potential effects of microplastics. Notably, current legislation--such as Regulation (EU) 2019/1009 on the marketing of EU fertilizing products--does not regulate or limit the microplastic content in such materials [30]. Our findings suggest a pressing need to revise existing regulations to include criteria related to microplastic contamination. This is especially important given the long environmental persistence of microplastic particles, their potential for bioaccumulation, and their ability to adsorb other pollutants. In light of the widespread microplastic contamination and the continued use of sewage sludge as an organic fertilizer, it is crucial to develop effective purification methods. It is imperative to design technologies that allow for the selective removal of microplastics while preserving the fertilizing properties of the sludge. Such processes must not only be technically effective but also economically viable to ensure practical implementation on an industrial scale in wastewater treatment plants. Advancing such solutions could significantly reduce the introduction of microplastics into terrestrial ecosystems, thereby contributing to improved soil quality, the protection of water resources, and enhanced food safety. The accumulation of polyethylene (PE), the dominant polymer identified in this study, can have adverse effects on soil health by altering soil structure and porosity, which may impact water retention and aeration. Moreover, PE particles may interfere with soil microbial communities, which play a crucial role in nutrient cycling and the decomposition of organic matter. Such disruptions could have downstream effects on soil fertility and the functioning of ecosystems. The presence of microplastics in sewage sludge raises critical questions regarding its suitability for use in fertilizer production, particularly in the context of sustainable recycling of nutrients and organic matter into agricultural ecosystems. The implementation of circular economy (CE) strategies requires that secondary products be free from secondary contaminants that pose a threat to ecosystems and human health. The results of this study provide a basis for developing guidelines on environmental risk assessment and for adapting technological processes to reduce microplastic emissions. Conceptualization, J.W. and K.S. ; methodology, J.W., J.C. and K.S. ; formal analysis, J.W. and K.K. ; investigation, J.W. and K.K. ; writing--original draft preparation, J.W. ; visualization, J.W. and K.K. ; writing--review and editing J.W., K.S.