## 4 Impact of Plastic Particles on Soil Properties  
Plastic particles, including microplastics and nanoplastics, have become pervasive in terrestrial environments, leading to significant concerns regarding their impact on soil properties. Recent reviews have highlighted the impact of microplastics (MPs) on soil properties, showing that plastic particles affect a wide range of soil physical, chemical, and microbiological properties, as well as microbial communities and ecological functions [25]. Therefore, our study will primarily focus on selected parameters such as soil aggregation, pH, and microbiology, which are crucial essential for substantiating the conclusions of this review. Soil aggregate formation, which is directly related to the rate of surface water infiltration and the availability of organic material in the soil, serves as a key indicator of soil quality and fertility [26]. Generally, the presence of MPs disrupts soil aggregates, potentially affecting the soil water regime and soil aeration [27; 28]. Additionally, the content of soil organic matter may be influenced, or disturbances may occur in the soil microbiome structure, subsequently impacting soil metabolism [29]. Consequently, these structural changes may lead to gradual erosion of the soil matrix and induce permanent shifts in soil microbiology [28; 29]. Currently, there is no consistent evaluation on whether and how MPs affect soil aggregate sizes and formation (see Figure 2). Numerous studies (as shown in Table S1, SI) indicate that the presence of MPs tends to increase formation of soil micro-aggregates(250-263 \(\upmu\)m) at the expense of macro-aggregates (>2000 \(\upmu\)m) [25; 29; 30; 31; 32]. This phenomenon could be due to MPs bound to micro-aggregates interfering with the formation of soil macro-aggregates, likely because of the MPs' hydrophobic nature and their interaction with soil organic matter via van der Waals forces [30]. Conversely, plastic microfibres have been reported to promote the formation of soil macro-aggregates by acting as mechanical crosslinkers, causing smaller aggregates to clump together [28; 33; 34; 35]. However, according to the literature (as shown in Table S1, SI), the effects of MPs on soil aggregate sizes and stability do not consistently correlate with changes in soil bulk density. In other words, this indicates that alterations in soil compaction or porosity may not always align with the impact of MPs on aggregate sizes [36], implicating MPs as potential carriers within the soil [37; 38; 39]. The influence of MPs extends beyond soil structure, affecting aspects such as pH, soil metabolism, nutrient cycling, and the distribution and bioavailability of chemical contaminants. Overall, the studies presented in Table S2 (SI) do not reveal a consistent trend regarding the impact of MPs on soil pH (see Figure 3), which varies depending on various factors. These include differences in the chemical composition of the MPs [40; 41], the concentration, shapes and sizes of the MP particles [42], their aging and weathering, and the functional groups on their surfaces [43], among other variable soil parameters [44; 45]. The majority of the studies in Table S2 (SI) reported a decrease in soil pH due to the presence of various MPs [29; 36; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53], while a few reported an increase [50; 54]. However, some studies showed biased results concerning MPs' effects on soil pH based on their chemical composition or concentrations [25; 40; 41; 45; 45; 55]. The scientific literature suggests that the decrease in soil pH due to the presence of MPs is associated with the release of acidic substances during the degradation process in the soil [51; 52], the increase in the soil aggregate size, soil porosity and aeration [42] and the increase in soil cation exchange [43].