Baseline toxicological assessment of biliary PAHs and heavy metals contamination in a commercially consumed native fish (Mugil cephalus) within Fiji coastal waters

Abstract The indirect exposure and effects of marine pollutants such as heavy metals and polycyclic aromatic hydrocarbons, present significant health concerns for human coastal communities that rely on fish consumption as a regular nutritional source. This study confirms a sentinel marine fish species, Mugil cephalus (“mullet”), for biomonitoring environmental health and conducting risk assessments using biomarkers in Fiji. Sampling was performed at two Fijian study areas, i.e., Laucala Bay and the Ba River Delta. Findings suggest that mullets from Laucala Bay exhibit biochemical responses that reflect a better habitat condition than those from the Ba River Delta. The lower K factor supports this conclusion, and HSI was observed in mullets from Laucala Bay. Analyses of polycyclic aromatic hydrocarbons revealed higher concentrations of four metabolites (naphthalene, phenanthrene, 1-hydroxypyrene, and benzo[a]pyrene) in samples from the Ba River Delta compared to Laucala Bay, with some metabolites showing statistically significant differences between the two sites. Four heavy metals (Cd, Cr, Pb, and Hg) were quantified in edible fish tissues of mullet from both study areas. The concentrations of Cr and Pb were higher in mullets from the Ba River Delta than in Laucala Bay, but below the safety limits set by the World Health Organization for human consumption. Cd and Hg concentrations were below the detection limits. Biotransformation processes (phase I and II) were assessed using ethoxyresorufin O-deethylase and glutathione S-transferase as biomarkers. The enzyme cascade of antioxidants, specifically glutathione peroxidase and glutathione reductase, demonstrated effectiveness and potential as biomarkers for future studies. Measuring lipid peroxidation and erythrocyte nuclei abnormalities provided evidence of higher levels of biological damage in mullet from the Ba River Delta compared to Laucala Bay. These findings 1) support the use of mullet as a suitable reference species for future ecotoxicology studies in Fiji, 2) are essential to take informed health and safety considerations regarding mullet consumption, 3) provide a baseline to compare future monitoring results and, 4) underscore the importance of incorporating biomonitoring practices in future environmental risk assessments. Doing so can establish a robust and comprehensive ecotoxicological framework to inform future environmental policies and legislation in Fiji.