Size-dependent heavy metal and parasite bioaccumulation in Mugil cephalus from lake manzala: human health risks and fish histopathological lesions.

Pollutants, such as heavy metals (HM) and parasites, pose significant threats to aquatic environments. These contaminants can gather in fish, adversely affecting their health and potentially posing health risks to human consumers. Understanding the dynamics of these pollutants and their accumulative impact on fish of different sizes and the associated human health is crucial for the sustainability of aquatic ecosystems and food security. This study investigated the bioaccumulation of HM in the muscles of three different sizes of Mugil M. cephalus from the northeastern part of Lake Manzala, revealing significant size-related variations. Small-sized fish showed the highest levels of iron (Fe) and zinc (Zn), followed by medium-sized fish, while large-sized fish exhibited the lowest Fe and Zn concentrations. Conversely, larger fish accumulated higher levels of copper (Cu) and cadmium (Cd) compared to medium- and small-sized fish. Across all size groups of M. cephalus, the levels of both Fe and Cu exceeded the guidelines established by the Egyptian Organization for Standardization (EOS, 2005). The Metal Pollution Index (MPI) indicated that small-sized fish accumulate more HM, with medium- and large-sized fish showing lower MPI values compared to small-sized fish. In small- and medium-sized fish, Fe recorded the highest EDI values, followed by Zn > Cu > Pb > and Cd. In contrast, large-sized fish exhibited an EDI pattern of Fe > Cu > Zn > Pb > Cd for both normal and habitual consumers. Pearson correlation coefficients indicated strong negative correlations for Fe and Zn with fish size and strong positive correlations for Cd and Cu, while Pb showed a weak positive correlation. Principal Component Analysis (PCA) identified Cd, Cu, and Zn as primary contributors, with Fe and Zn showing negative loadings associated with smaller fish, and Pb had a significant positive loading in larger fish. The Target Hazard Quotient (THQ) and Hazard Index (HI) values revealed a size-related variation in health risks. Small-sized fish posed the highest non-carcinogenic risk for normal consumers; habitual consumers revealed significant health hazards (HI > 1) across all fish sizes, but it is particularly pronounced in consumers of small-sized fish. Although normal consumers recorded negligible carcinogenic risk, habitual consumers recorded low risk. The histological investigation showed significant alterations in the gills, liver, and kidneys of M. Cephalus is related to Myxobolus infection and HM accumulation, particularly Cd and Cu. Medium- and large-sized fish displayed more severe tissue alterations associated with higher HM load and increased prevalence of Myxobolus parasites. The findings emphasize that fish size is a critical factor affecting the synergistic interactions among heavy metal load and associated human health risks, parasitic infection, and histopathological lesions in fish. Underscoring the importance of continuous monitoring and risk assessment of HM and parasitic infections in aquatic ecosystems.