From Ecological Threats to Monitoring Tools: Multi-Contaminant Profiles in Silurus glanis and Procambarus clarkii for Pollution Tracking and Preliminary Food/Feed Safety Assessment

Invasive alien species (IAS) such as Silurus glanis and Procambarus clarkii represent major ecological threats but may also serve as effective bioindicators of environmental contamination; therefore, this study aimed to evaluate their potential for multi-contaminant monitoring and assess their suitability as alternative feed and food resources within a circular economy framework. Multi-contaminant profiles were investigated in S. glanis and P. clarkii from Avigliana Lakes (NW Italy), analyzing trace elements, rare earth elements (REEs), and organic contaminants in fish muscle, and microplastics (MPs) in intestinal tracts. In S. glanis, total trace element concentrations and ΣREEs were markedly higher in Small Lake than in Great Lake, with ΣREEs reaching 0.445 and 0.056 mg/kg w.w., respectively. Mean concentrations of the regulated elements in Great Lake were 0.017 mg/kg w.w. (As), 0.003 mg/kg w.w. (Cd), and 0.16 mg/kg w.w. (Pb), increasing in Small Lake to 0.19, 0.03, and 1.86 mg/kg w.w., respectively. In P. clarkii, contamination levels were lower, with ΣREEs averaging 0.074 mg/kg w.w. and mean concentrations of As, Cd, and Pb of 0.25, 0.006, and 0.21 mg/kg w.w., respectively. Organic contaminants, including polycyclic aromatic hydrocarbons (PAHs), non-dioxin-like polychlorinated biphenyls (NDL-PCBs), and pesticides, were generally below limits of quantification. MPs were detected in 100% of specimens, with mean concentrations of 4.2 ± 2.15 and 4.4 ± 2.70 MPs per intestinal tract in S. glanis (Great and Small Lake, respectively) and 2.7 ± 2.39 MPs/intestinal tract in P. clarkii. Permutational multivariate analysis of variance (PERMANOVA) indicated significant site-related differences in S. glanis and species-related differences between S. glanis and P. clarkii within Great Lake. Most regulated contaminants were below applicable EU thresholds; however, Pb in S. glanis from Small Lake exceeded the maximum level established for fish muscle intended for human consumption.