## 3 Results and Discussion
### Heavy Metals Concentrations  
The results of the current study confirmed the presence of all of the heavy metals being investigated in the trout from the two rivers. The descriptive statistics (range, mean, and standard deviation) of the nine metals measured in the trout during the sampling period and from the two rivers are shown in Table 4. During the study period, the mean concentrations of each of the heavy metals did not show any significant variation between the two rivers (\(p>0.05\)). Heavy metal concentrations in the trout, independent of the sample's origin, followed the order Zn > Al > As > Ni > Co > Hg > Cr > Cd > Pb. Considering that the maximum levels established by the European Commission (EC) for Cd, Pb, and Hg in fish for human consumption are 0.05, 0.3, and 0.5 mg/kg of wet weight, respectively, the results for all of samples were lower than the legislated limits [30]. Among the investigated heavy metals, Zn and Al had the highest concentrations in the trout samples, whereas the Cd and Pb concentrations were much lower. Zn is an essential metal for animals and humans because of its important role in biological systems, as it is necessary for the function of many metalloenzymes [31]. The average Zn levels reported in the trout muscle in the present study are higher than those found in farmed rainbow trout from several countries [31; 32; 33]. Atmospheric fallout is considered to be the main source of Zn pollution in the environment. However, upstream industrial and municipal wastewater discharges and the use of galvanized metals and metal surfaces also contribute to this pollution. Amongst the non-essential metals, Al was the most abundant metal in the analyzed samples. The presence of Zn and Al could have several origins, namely: the industrial plants present along both rivers that produce aluminum frames, the runoff water coming from the roofing drainage systems that are often made of metallic materials, or guardrails and construction materials such as plumbing and stormwater drainpipes. Furthermore, it should be considered that galvanized metals have a variety of applications in the modern community, but they have also a large potential for contributing heavy metals to runoff during their life cycle. To facilitate stormwater drainage, metal culverts were previously installed along the Mavone and Ruzzo rivers, and, although it is known that corrosion affects the internal surface of these metal culverts, it is difficult to determine whether this corrosion caused the significant elevation in Zn/Al concentrations reported in this study. Al is considered, along with Cd, to be one of the most potent metalloestrogens. It interferes with most physical and cellular processes. It can interfere with cell growth regulatory processes through many pathways, including altering gene expression [34]. Fish exposure to Al causes a pathological alteration in cardiovascular, respiratory ion-regulatory, changes in hemoglobin concentration, and reduction in fish growth besides endocrine disruption [35; 36; 37]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Rivers** & **Al** & **Cr** & **As** & **Cd** & **Pb** & **Hg** & **Co** & **Ni** & **Zn** \\ \hline
**Mavone** & 0.39 \(\pm\) 0.32 & 0.03 \(\pm\) 0.02 & 0.09 \(\pm\) 0.02 & 0.01 \(\pm\) 0 & 0.01 \(\pm\) 0 & 0.03 \(\pm\) 0.04 & 0.04 \(\pm\) 0.03 & 0.04 \(\pm\) 0.02 & 16.26 \(\pm\) 5.67 \\ \hline
**Ruzzo** & 1.72 \(\pm\) 3.4 & 0.02 \(\pm\) 0.01 & 0.11 \(\pm\) 0.04 & 0.01 \(\pm\) 0 & 0.01 \(\pm\) 0 & 0.05 \(\pm\) 0.02 & 0.03 \(\pm\) 0.02 & 0.04 \(\pm\) 0.02 & 12.40 \(\pm\) 7.61 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mean values and standard deviation (SD) of heavy metal concentrations in trout from the Mavone and Ruzzo rivers. All of the concentrations are expressed as mg/kg wet weight. As was the second non-essential metal broadly present in the fish, but at lower levels compared with those reported in other studies [31; 32; 33].