## 5 Discussion
### Geochemical Source Apportionment of Potentially Toxic Elements  
The combination of contamination indices, correlation analyses, and geological context enables a more straightforward interpretation of the origins of potentially toxic elements (PTEs) in the study area. Metals such as Cr, Cu, and Zn show the highest contamination levels, with very high contamination factors (CF > 6) and enrichment factors (EF > 10) in specific samples (e.g., Cu and Zn in K4, Cr in K8). These patterns, together with strong positive correlations (Cu-Zn: r = 0.97; Ni-Cu: r = 0.77), suggest anthropogenic inputs, potentially originating from industrial waste, mining residues, or urban runoff.  
In contrast, elements such as V, Co, Ni, Th, and U display relatively low enrichment (EF < 2) and low to moderate CF values, indicating a dominantly geogenic origin. This interpretation is further supported by the spatial alignment of elevated V and Co concentrations with regions underlain by ophiolitic rocks (e.g., peridotites and gabbros) and Eocene-aged plutonic rocks prevalent in the Elazig geological setting. These lithologies, which include the Elazig Migmatic Complex, Maden Complex, and ophiolitic nappes, are known to host naturally elevated levels of trace metals such as Co, Ni, and V due to their mafic-ultramafic mineral composition.  
Moreover, the strong correlations observed among Th-U (r = 0.95) and their association with granodioritic intrusions suggest that these elements are likely derived from radioactive mineral-bearing lithologies, such as plutonic units rich in zircon and monazite. The low variability and consistent distribution of these elements across samples further support a lithogenic source rather than anthropogenic contamination.  
Several inverse correlations (e.g., Co-Th, V-U) may indicate differing redox behaviours or environmental partitioning. For example, U and Th tend to be more mobile under oxidising conditions, whereas V and Co are often stable in reducing environments, contributing to their spatial and statistical separation.  
The study area is situated within the upper part of the Elazig Basin and encompasses a stream catchment that ultimately drains into the Keban Dam Lake. The stream flows through both rural and urban environments, including the central part of Elazig city, which has a population of around 400,000. Urban land use dominates the middle and lower reaches of the catchment, with residential zones, road networks, and small-scale industrial facilities present along the stream. There are also municipal wastewater outlets discharging directly into the stream, which may contribute to elevated levels of certain metals such as Cu and Zn. In addition, informal car repair shops, construction activities, and urban surface runoff likely exacerbate localised contamination, especially downstream (K4-K10). Although there are no active large-scale mining operations within the immediate catchment, historical small-scale mining and quarrying activities have been reported in nearby regions, particularly related to chromite and copper deposits. Residual waste and altered landforms from these activities may still influence the sediment geochemistry through erosion and leaching, especially during periods of high precipitation. Anthropogenic pollution is evident for Cu, Zn, and Cr, particularly in localised zones such as K4-K10. Geogenic signatures dominate for V, Co, Ni, Th, and U, consistent with the regional mafic, ultramafic, and plutonic geological formations.