Baseline study of biomarkers of exposure to metal and polycyclic aromatic hydrocarbon in wild Mugil cephalus from the coastal waters of Fiji

Abstract

The indirect exposure and effects of marine pollutants such as 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 verified Mugil cephalus (“mullet”) as an adequate sentinel species for biomonitoring environmental health and conducting risk assessments using biomarkers in Fiji. A non-parametric Kruskall Wallis Test was employed at a 5 % significant difference level to test sample group differences. Sampling was performed over five months in two Fijian study areas, i.e., Laucala Bay and the Ba River Delta by local fishers based on Fiji’s wet season (Nov-Mar). The K factor and hepatosomatic index (HSI) were relatively lower in mullet from Laucala Bay compared to the Ba River Delta, with HSI having a significant difference (χ2= 3.64, d.f. = 1, p-value = 0.057). No significant differences were observed for metals (Pb and Cr) at an instrumental limit of detection of 0.05 mg kg−1, but an important finding was that the levels of Cr in edible tissues of mullet from both study sites exceeded the permissible limits for human consumption set by the World Health Organisation (0.05–0.15 mg kg−1) by approximately 2-fold in Laucala Bay and 3-fold in Ba River Delta. The levels of Hg and Cd in the two sample groups were determined to be below the instrumental limit of detection of 0.1 mg kg−1. Total biliary polycyclic aromatic hydrocarbons (PAHs) were significantly higher in mullet from the Ba River Delta (χ2 = 21.14, d.f. = 1, p-value < 0.001), particularly for phenanthrene (χ2 = 24.678, d.f. = 1, p-value < 0.001). No statistical variations were observed in phase I biotransformation (ethoxyresorufin O-deethylase); however, phase II biotransformation activity (glutathione S-transferase) was found to be significantly higher in mullet from the Ba River Delta compared to Laucala Ba (χ2 = 35.85, d.f. = 1, p-value < 0.001). Similarly, no remarkable variations were observed in glutathione peroxidase activity, but glutathione reductase activity was significantly higher in mullet (χ2 = 5.05, d.f. = 1, p-value = 0.025) from Laucala Bay compared to Ba River Delta. Considering biological damages from oxidative stress, levels of lipid peroxidation were significantly higher (χ2= 4.10, d.f. = 1, p-value = 0.043) in mullet from Ba River Delta, including higher occurrences of micronuclei (χ2= 12.66, d.f. = 1, p-value = <0.001) and other abnormal erythrocyte nuclei (χ2= 26.67, d.f. = 2, p-value < 0.001), suggesting genotoxic damage. 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.