Spectroscopic analyses for possible transport of polyaromatic hydrocarbons onto fish in Mediterranean Sea

Metal pollution in the Mediterranean coast is a growing environmental concern. The effect of trace metals and polycyclic aromatic hydrocarbons (PAHs) on fish was subjected to DFT:B3LYP/6-31G(d,p) computational study. Both alanine (Ala) and phenylalanine (PAla) were used as model molecules for protein of fish. The interaction of Ala and PAla with metals resulted in significant decrease of the HOMO-LUMO bandgap energy of Ala and PAla from 2.6647 and 1.5772 eV, down to 1.2871 and 1.2675 eV, respectively, reflecting increased reactivity for further interaction with the surrounding environment. Results also indicated that interaction of both metals and PAHs with protein resulted in changing the structure of the amide groups with significant shift in their band positions. Changes in the geometrical parameters of protein were detected which, in turn, changed the amount of energy required to vibrate its funcitonal groups, thus leading to a change in the vibrational features of COOH and NH₂. FTIR spectra of fish gills, liver, and muscle tissues collected from four sites in Alexandria (El-Shatby, Qaitbay, Al Asafra, and El-Max) confirmed the computational findings, revealing alterations in protein secondary structures. Experimental studies further assessed the effects of pollutants on fish health. Bacterial analysis showed the highest levels of Staphylococcus aureus (1.5 × 10⁴ CFU/ml) and Escherichia coli (5.0 × 10³ CFU/g) in El-Max, while the lowest bacterial counts were recorded in El-Shatby. Micronucleus analysis indicated significant genotoxic effects, with higher micronuclei frequencies in fish from El-Max than in El-Shatby. Gene expression analysis revealed that fish from El-Max exhibited upregulated levels of Cytochrome c, P53, and TNF genes, suggesting oxidative stress and apoptosis as potential responses to environmental pollution. One-way ANOVA confirmed significant differences between control and polluted groups (p < 0.05), with the highest expression levels observed in Tilapia liver samples. These findings highlight the detrimental impact of PAHs and heavy metals on aquatic organisms, emphasizing the need for continuous environmental monitoring and pollution control measures in the Mediterranean coastal waters.