# Land Suitability Mapping Using Geochemical and Spatial Analysis Methods
## 4 Results and Discussion
### Element Content in the Soil of Study Area and Source Apportionment
#### 4.2.2 Cobalt  
The majority of soil sampling sites (95.5%) in the Ioannina plain contained Cd concentration higher than the median value of European soil [58]. The geochemical spatial  
Figure 5: Graduated symbol plots of Cd content in soil of Ioannina plain concerning land uses (**A**) and geology (**B**).  
distribution map of Co incorporated in the Geochemical Atlas of Europe [58] illustrated Co content in the soil of the Ioannina basin varying between 16 and 25 mg kg\({}^{-1}\), while this study revealed Co concentration in soil ranging from 4.0 to 90.0 mg kg\({}^{-1}\) (Table 1). Cobalt content in the soil of the area studied shows similar spatial distribution to Cd, suggesting a common origin or similar dispersion mechanism (Figure 6A,B). [PERSON] [55] reported that Fe-Mn oxides within Quaternary deposits could be considered as a geological source of Co in the soil of the study area. However, Co concentration in soil has no spatial association with a lithological formation in the study area (Figure 6B). Many studies [31; 67] recorded an increase in Co content in roadside soil of other cities attributed to the traffic inputs, especially the aircraft engine wear. [PERSON] et al. [68] reported that Co is detected in the debris derived from high-pressure turbines due to aircraft engine wear, the so-called honeycomb structures built into the compressor region of the engine downstream the combustor. The soil at sampling sites located at the Ioannina plain's eastern edge had significantly higher Co (ranging from 41 to 90 mg kg\({}^{-1}\)) than the central part of the area studied. The Co emission for aircraft engines is up to 8.78 \(\times\) 10\({}^{-3}\) mg per kg of combusted fuel [65]. The mean of Co concentration in PM\({}_{10}\) samples at Barcelona airport is 0.4 ng m\({}^{-3}\)[69], suggesting that airport operations are an emitter of Co.  
The primary anthropogenic sources of Co in the Ioannina plain can be attributed to road traffic emissions and aircraft operations (Figure 6A,B). The spatial distribution of Co in the soil in the area revealed element build up mainly at the eastern edge of the study area and the Ioannina Airport's proximity (Figure 6A,B). According to [PERSON] et al. [68], Co, among other elements, is a significant occurring metal in emissions from different jet engines at various combustion conditions. Furthermore, [PERSON] et al. [70] concluded that airport traffic had been proved to be an important emitter of Co (mean 4.0 mg kg\({}^{-1}\)) in the soil of Santorini island (Greece). Another possible anthropogenic source of Cd in the topsoil of Ioannina plain is the vehicle recycling industry and discarded vehicles' scrapyard. High levels of Co (41-90 mg kg\({}^{-1}\)) in the eastern part of the study area could be attributed to stores of scrap and related activities. According to [PERSON] et al. [71], Co mean content in topsoil (mg kg\({}^{-1}\)) in the vicinity of vehicle scrapyard in Ribeira Pires (Brazil) and Madrid (Spain) are 6.9 and 120, respectively, revealed a link between vehicle recycling activities and Co, supporting the findings of this study.