## 4 Discussion  
Research shows that estrone mobility in soil experiences a linear decrease in the first 24 h [35; 36] followed by a nonlinear phase [37]. This behaviour is attributed mainly to sorption/desorption processes, considering the main mechanisms that affect estrone mobility in soil [29; 38]. The change between the phases is generally between 24 h and 3 days and was confirmed by [PERSON] et al. [38] among others, who discovered that an apparent sorption equilibrium is reached after 3 days. If estrone is not completely removed soon after that through further mechanisms, sorption becomes almost irreversible, and the contaminant accumulates in soil [39]. Though all three soils were different, looking at Figure 1 (Estrone) and Figure 2 (Enzymes) and at the values at each sampling time (Table 2), it is obvious that this transition pattern was present in each soil. It was the clearest in fluvisol, followed by chenozem, and lastly, although cambisol did not have a visible change in estrone values at 24 h, the enzymatic activity for this period suggested changes were happening here as well. No soil removed the estrone permanently by the end of the experiment; there were still traces of estrone in all the studied soils. Estrone behaviour in soil is influenced by many factors, with the most common being molecular structure [40; 41; 42], environmental parameters [36], soil properties [43], and soil hydrophobicity [27]. Texture [28; 36; 44] and hydrophobicity are considered to be the most relevant here, based on previous studies. They were taken together with the soils' characteristics measured and summarized in Table 1--soil properties used to analyze and compare estrone changes in the three soils. Its molecular structure indicates that estrone is a hydrophobic compound, and as soils tend to be generally more hydrophobic, estrone's sorption is high. This could explain why, at only 4 h into the experiment, already half of the initial concentration was gone (median 23.63 ug-kg\({}^{-1}\) was left from initial 50 ug\(\cdot\)kg\({}^{-1}\)). Soil hydrophobic character is directly influenced among others by the amount of carbon [29; 45; 46] and its type (aromatic C is more hydrophobic than aliphatic one) [27]. This property seems to be one of the most relevant soil properties in regard to the behaviour of pollutants in soils, and [PERSON] et al. [38] described the first 24 h of a compound transformation as the fast sorption phase, which occurs through the hydrophobic mechanism. This mechanism involves the attachment of the pollutant's molecules on the soil surface (generally hydrophobic), starting with the bigger pores until they fill up (normally in 24 h for estrone). This marks the point at which estrone transformation changes, from a fast to a slow sorption phase [47], when it is the turn of the micropores to fill up. These mechanisms show the importance of soil texture in addition to the amount of carbon. Soils properties from Table 1 show that fluvisol had the highest amount of carbon (C:N was 26) and a silty-clay texture. A first-order kinetics model calculated that estrone half-life was at 2.9 h from the start of the experiment, before the first sampling time (4 h). Silt has a higher soil surface area where estrone can bound strongly [48], but also smaller macropores than sand or loam. These factors could explain why fluvisol had the lowest measured estrone amount from the three soils at 4 h (it was sorbed the most), and why the changes in concentrations were less pronounced (smaller pores need more time to fill up). At the same time, the presence of estrone on the soil surface encouraged enzymatic activity, which was the highest between all the three soils in this fast phase (4 h-24 h) and increased even more during the transition phase (24 h-3 days), where it reached the highest average in the entire experiment (527 U).