## 4 Discussion  
Experimental studies showed that the accumulation of \({}^{57}\)Co, \({}^{54}\)Mn, \({}^{65}\)Zn, \({}^{60}\)Co, \({}^{137}\)Cs, and \({}^{241}\)Am by _C. uncialis_ proceeded immediately after deposition reaching equilibrium in the first days of the experiment as corroborated by our results (Figure 2). [PERSON] et al. 2006 reported that accumulation of metals by lichens occurs rapidly, in most cases within a few hours. In the case of Cu, maximum accumulation was observed after 3-6 h [23]. Short-term metal accumulation by lichens can be described as an \"ion exchange\" process involving carboxyl or hydrocarbonyl sites on outer cell walls or structural macromolecules [24]. Metals can be divided into two main categories: those essential for lichen metabolic processes and those that are trace elements with toxic properties. Essential elements for biological functions can easily cross the plasma membrane and are components of various enzymes, serving as enzyme activators [25; 26]. Moreover, a well-known detoxification mechanism includes the binding of metals to organic acids, oxalate crystals, lichen secondary metabolites, polysaccharides, and melanin pigments [27; 28]. Metals that are immobilised within cell wall components or situated extracellularly tend to be less detrimental to lichens. The absorption capacity of the elements increased in the order: \({}^{54}\)Mn \(<\)\({}^{57}\)Co \(<\)\({}^{60}\)Co \(\leq\)\({}^{65}\)Zn \(<\)\({}^{241}\)Am \(<\)\({}^{137}\)Cs (Table 4). Absorption rates were highest for \({}^{241}\)Am and \({}^{137}\)Cs, for which maximum values of Tag reached 0.64 m\({}^{2}\)/kg (Table 3). \({}^{137}\)Cs can be especially easily incorporated into the biological structure of plants due to its similarity to potassium ions [6]. \({}^{241}\)Am is an artificial element of recent origin, and thus does not have a biological role, however bioaccumulation by bacteria and fungi has been reported. The absorption of \({}^{241}\)Am by _R. arrhizus_ is related to contact time. The adsorption rate increased rapidly with time and rose up to 99% in 1 h. Later, the adsorption rate grew slowly and tended to the equilibrium [29]. While the computation of Tag values is relatively straightforward, their application necessitates a comprehensive understanding of the ecosystem. Elements like the time of year or the type of soil can introduce variability in the observed Tag values. The aggregated transfer coefficient for \({}^{137}\)Cs for lichen found in the literature calculated after the Chernobyl accident ranges from 0.8 m\({}^{2}\) kg\({}^{-1}\) to 2.3 m\({}^{2}\) kg\({}^{-1}\)[30]. These values were much higher than those calculated in this publication. The accumulation of metals and radioactive isotopes in plants are influenced by numerous factors, including element availability, species, age, as well as environmental conditions such as temperature, humidity, substrate characteristics, and pH [31; 32; 33]. Consequently, metal transfer from the soil to lichens can also occur in nature, potentially leading to variations in results. In the case of our experiment, the activity levels in the soil were low enough that accumulation from the substrate would not have significantly impacted the results in the lichens. However, since the Tag values varied by up to twofold during the experiment, a balance of the isotopes accumulated in the lichens relative to the introduced isotopes was conducted (Figure 4, Table 4). The accumulation coefficient for each aquarium was calculated using Formula (2). \[\text{Accumulation Coefficient}=\frac{\text{Activity of Lichen}\left[\frac{\text{ Bq}}{\text{B}}\right]\times\text{Total Mass of Culture}[\text{g}]}{\text{Isotope Contamination }[\text{Bq}]}[\text{unit}] \tag{2}\]  
For the four isotopes--\({}^{54}\)Mn, \({}^{57}\)Co, \({}^{60}\)Co and \({}^{65}\)Zn, the absorption efficiency at low concentrations (Aquarium A) was about 36-40% fallout. As the deposition increased (Aquarium B, C), the absorption efficiency decreased to 24-29% (Figure 5).