Crayfish as Bioindicators of Heavy Metal Pollution in Egyptian Waters: A Study on Bioaccumulation, Metallothionein Induction, and Human Health Risk Assessment

This research explored the heavy metal distribution patterns that were found in environmental matrices of Egyptian aquatic ecosystems. The study addressed sediment, water, and crayfish tissues from three geographically diverse locations: Kafr El-Sheikh, El-Sharqia, and Mostorod. Seven heavy metals: copper, zinc, cadmium, lead, manganese, iron, and nickel were analyzed to reveal bioaccumulation patterns, matrix-specific distribution, and ecological risk assessment. The result of the principal component analysis showed that the characteristics of the environmental matrix were markedly the major factors that influenced heavy metal distribution, while the first two components accounted for 95.8% of the total variance. In all cases, sediments exhibited the highest concentrations of metals, especially copper (0.500- 0.813mg/ kg) and zinc (0.800- 1.200mg/ kg). Consequently, the role of these sediments as the main sinks in aquatic geochemical cycles was validated. The sediment-to-water partitioning coefficients were larger than 10:1 for most metals, with copper reaching 30:1-45:1, thus the affinity for the solid phases was quite strong. Crayfish (Procambarus clarkii) showed remarkable bioaccumulation properties, as cadmium concentrations in their tissues were 13-205 times higher than those in water, hence, they are a species that can particularly accumulate metals in their cells. Concentrations in the water column were low at all sites and manganese (0.011-0.038 mg/kg) and zinc (0.030-0.072 mg/kg) were the most dissolved elements. Bioaccumulation factors differed substantially between locations, and Kafr El-Sheikh showed high values of Cd, Cu, and Mn accumulation. In the same trend, when using metallothionein (MT) analysis, the highest concentrations of MT were recorded in the Kafr El-Sheikh area, which supports the effectiveness of using this technique in detecting pollutants. Health risk assessment showed that the metal consumption amounts are within safe limits for human consumption. The results of the present study offer significant clues about environmental monitoring strategies and pollution control measures in Egyptian freshwater ecosystems.