## 3 Results and Discussion
### Plants Isotopic Values (C-N-S), Comparison Between Regions
#### 3.1.3 \(\delta^{34}\)S of Plants  
The sulfur isotope ratio (\(\delta^{34}\)S) of the studied plant products (fruits, nuts, cereals, herbal) ranged between \(-2.1\) and \(7.3\%\) (median \(\delta^{34}\)S = \(2.6\%\), sd = \(2.2\%\); see Table 1). As mentioned above, the primary factors affecting the sulfur isotopes of plants include the soil, the fertilizer, and the atmospheric pollution [8]. The studied plants show \(\delta^{34}\)S values lower than \(7.3\%\). However, the geology of Greece is characterized by a highly complex structural system, and it is important to consider that regional soil differences can influence sulfur isotopes. Nevertheless, it can be argued that a standard deviation of more than \(2\%\) indicates a relatively homogenous sulfur isotope dataset that cannot be attributed solely to soil sulfur. Considering that no significant isotopic fractionation occurs during plant uptake and metabolism [2], probably these plants take the sulfur mainly from the fertilizers [14] and less from the oxidation of mineral soils [2]. The \(\delta^{34}\)S value of the most common fertilizer is between \(-10\) and \(20\%\) [2; 14]. The lowest \(\delta^{34}\)S value measured for lentils and tomatoes is \(-2\%\). This value may be attributed to the elevated water uptake by these plants, as they grow in floodplains near river basins [64; 65], where \(\delta^{34}\)S values range from \(-5\%\) to \(+15\%\) [12; 13; 14; 15; 16; 17; 18; 19; 20]. This cultivating practice can have an important influence on sulfur isotopes due to the geochemical and biological processes occurring in the area's soil and water. So the lower \(\delta^{34}\)S value of \(-2\%\) in lentils and tomatoes could indicate that the sulfur available to these plants has a lighter isotopic signature, likely resulting from the elevated water uptake in these areas. The water in floodplains may be enriched with lighter sulfur isotopes, which can be taken up by plants, influencing their \(\delta^{34}\)S values. This could also reflect biological processes such as sulfate reduction or other microbial activity in the soil, which might preferentially utilize lighter isotopes of sulfur. In this way, the geochemical processes in floodplains, combined with the water uptake by plants, can lead to distinct sulfur isotope signatures in crops like lentils and tomatoes. The higher measured values of \(\delta^{34}\)S are \(>\)4%, corresponding to fruits (from Kiato and Sparta areas), nuts, and some cereals. It appears that the type of fertilizers, the aerosol  
Figure 6: Median of \(\delta^{34}\)S vs. \(\delta^{15}\)N isotopic data for plants from various localities of Greece. marine, and the soil claim an antagonistic role in the final sulfur value of the products. The potential influence of geological bedrock beneath the soil material in sulfur isotope is difficult to be assessed since the structural geology of Greece is too complex (Figure 7). The wild species from the Olympus Mt. area also present high values of sulfur isotope, depending on local soil sulfur sources and marine aerosol exposure. These terrestrial plants usually show \(\delta^{34}\)S values in the range from \(\sim\)\(\pm\)8 4.2%, corresponding to inland areas, to \(\sim\)\(\pm\)87.3%, in the case of coastal regions, due to marine sulfur deposition. The standard deviation of \(\delta\)1.5% is considered an adequately homogenous sulfur isotope dataset of the Olympus Mt. area soil sulfur. Figure 7: Geological map of Greece illustrating the sampling areas within particular masss, units, and belts, as described briefly below (names of sampling locations are captioned in Figure 1; modified after [PERSON] (2021) [66]). The geotectonic units and the tectonost stratigraphic terranes are shown in the corresponding legend at the rightmost part of the map.