## 3 Results and Discussion
### Levels of Heavy Metals in Flamingo Tissues  
In flamingo samples, mean measured values are shown in Table 2, with full data provided in the Supplementary Information (Table S3). Data on heavy metals in flamingos are limited, frequently involving non-destructive biomonitoring tools (e.g., feathers) [10]. Although the measured concentrations were not alarming, our results showed that the liver was the primary organ for heavy metal accumulation. In contrast to our soil/sediment results, Pb was the element that accumulated the least in flamingo tissues. As discussed below, major differences were generally observed between the liver and muscle or fat. Our results suggest that the low availability of heavy metals in the study area translates into low bioaccumulation in flamingo tissues. Nonetheless, the risk of accumulation of such  
Figure 3: Depth profiles of Pb (circles) and Zn (squares). Mean values (\(\pm\)SD) in sediments from Petrola Lake (\(n=90\)). pollutants for the flamingos inhabiting the lake cannot be ruled out, given the constant input of pollutants into the Petrola lake-aquifer system [71,72]. The highest Cd values were measured in liver (mean = 0.304 mg/kg dw) and were within the range of previous studies on liver tissues of flamingos from the Ebro Delta (0.55 mg/kg dw) [95], but significantly lower than those reported by [96] in the protected area of Migliarino San Rosmore Massaciuccoli (MSRM) Park (1.30 mg/kg dw). The Cd values in muscle (mean = 0.040 mg/kg dw) were higher than those measured in fat (mean = 0.007 mg/kg dw) and were well comparable to those in flamingos from the Canargue region (0.040 mg/kg dw) [97]. Highest Hg values were recorded in liver samples (mean = 0.534 mg/kg dw) as opposed to muscle and fat tissue, as has been described for birds before [8]. Although these levels appear quite high, they are lower than those reported in liver tissues of flamingos from MSRM Park (3.83 mg/kg dw) [96]. The bird muscle tissues from Petrola Lake were also significantly lower (0.088 mg/kg dw) than those in MSRM Park (0.59 mg/kg dw) [96] or Carmargue (2 mg/kg dw) [97]. The comparably low Hg concentrations in flamingos reflect the low levels detected in sediments and point to a very low mercury burden in the system. The concentrations of Cu were similar in both liver (mean = 34.6 mg/kg dw) and muscle (mean = 24.0 mg/kg dw) tissues (Table 2). This is surprising and stands in contrast to many other publications on copper in anatid birds [8,99], where copper usually occurs in significantly higher concentrations in liver versus muscle tissue. Cu in muscle samples was well comparable with values obtained by [99] (14.3 mg/kg dw), whereas those authors reported mean levels of 79.9 \(\pm\) 13.3 mg/kg in liver. The uptake and excretion of copper, as an essential trace element, is usually highly regulated metabolically [101], and the low liver values here correlate well with the low concentrations in sediments. This points to a copper depletion in the system rather than a contamination with this element. We also recorded the highest Pb concentrations in flamingo tissues in liver (mean = 0.160 mg/kg dw), similar to the values reported by [100] in birds from the Ebro Delta (0.138 mg/kg dw). In contrast, muscle and fat samples showed much lower mean Pb values (0.025 and 0.075 mg/kg dw, respectively), also well comparable to the values found by [99] in Dofana National Park (0.05 mg/kg dw). Lead in birds has been frequently investigated because gunshot pellets made from Pb continue to be distributed widely everywhere, and hunters still use them on waterfowl [102,103]. This can lead to lead poisoning through ingestion [8], potentially explaining the higher values in liver tissues compared to muscle and fat. The highest Pb concentrations in sediments were recorded at 10-15 cm depth. This may also reflect the accumulation of gunshot pellets from hunting. Such activity was prohibited by law in Petrola Lake in 1993. It is, however, still ongoing in