Abstract
The long-term discharge of poorly treated petroleum refinery effluent into the Ekerekana Creek, proximal to the Ogu Creek in Ogu, Rivers State, Nigeria, as well as contributions from artisanal refining have created worries about safety to health of consumers of the catfish delicacies, Clarias gariepinus and Heterobranchus longifilis from this coastal water. This research investigated the presence and levels of trace elements (Zn, Cr, Cd, Pb, Mg, Ca, K, Na, Fe and Mn) and hydrocarbons (Total Petroleum Hydrocarbon-TPHs, Benzene, Toluene, Ethylbenzene and Xylenes-BTEX, and Polycyclic Aromatic Hydrocarbons-PAHs) and Phenol in tissues of the fishes. In C. gariepinus , mean maximum accumulations in mg/kg were as follows: Mg 15.01±2.38 (muscle), Zn 10.25±2.62 (muscle), Fe 9.51±0.53 (gills), K 7.01±0.88 (muscle), Ca 0.42±0.05 (muscle), Pb 0.06±0.01 (muscle), Mn 1.58±0.45 (liver), TPH 6.65±0.42 (muscle), PAHs 0.24±0.05 (muscle), BTEX 0.07±0.01 (muscle) and Phenol 0.007±0.001 (muscle). In H. longifilis , accumulations in mg/kg were as follows: Mg 17.21±1.84 (muscle), Zn 11.27±2.49 (muscle), Fe 11.39±1.64 (gills), K 7.66±1.24 mg/g (muscle), Cd 0.47±0.043 mg/g (muscle), Pb 0.056±0.006 mg/g (muscle) and Mn 1.16±0.268 (liver), TPH 8.69±0.60 (muscle), PAHs 0.49±0.085 (muscle), BTEX 0.09±0.005 (muscle) and Phenol 0.0016±0.0003 (muscle). The accumulations of Cd, Pb, Mg, Ca, K, Na, Fe and Mn in C. gariepinus (Sig. values=0.001, 0.002, 0.011, 0.003, 0.004, 0.008, 0.000, 0.025 respectively) and those of Zn, Cd, Pb, Mg, Ca, K, Na, Fe and Mn (Sig. values=0.024, 0.000, 0.002, 0.002, 0.002, 0.008, 0.024, 0.005, 0.012 respectively) in H. longifilis differed significantly between tissues from impacted and reference locations at p<0.05. TQ/HQ values of, especially Cd and Zn were high (6.80-11.00 and 1.38-3.24 respectively) and exceeded regulatory limits in both fish species.  
Highlights
Beek (1999) and Neff (2002) explained that bioaccumulation is an increase in the concentration of a chemical in a biological organism over a period of time compared to the chemical's concentration in the environment
1.1 Bioaccumulation of trace elements At the impacted location and in C. gariepinus, Zn, Mg, and Fe concentrations ranged in the tissues from 6.88(liver)8.45(gills) (10.25±2.62), 10.42(gills)-18.45(muscle) (15.01±2.38) and 8.5(liver)-10.41(gills) (9.51±0.53) mg/kg, and in H. longifilis they ranged from 8.08(liver)-16.20(muscles) (11.28±2.49), 13.55(gills)-19.40(muscle) (17.22±1.84) and 9.14(liver)-14.60(gills) (11.39±1.64) mg/kg respectively
Ca, K and Na ranged in the tissues from 9.41(gills)-11.08(muscle) (10.21±0.48), 5.88(liver)8.75(muscle) (7.01±0.88) and 2.45(liver)-4.35(gills) (3.36±0.54) mg/kg in C. gariepinus and from 10.5(gills)12.50(muscle) (11.65±0.80), 5.50(liver)-9.80(muscle) (7.67±1.244) and 2.20(liver)-5.25(gills) (3.68±0.88) mg/kg in H. longifilis respectively
Summary
Beek (1999) and Neff (2002) explained that bioaccumulation is an increase in the concentration of a chemical in a biological organism over a period of time compared to the chemical's concentration in the environment. The longer the biological halflife of the toxic substance the greater the risk of chronic poisoning, even if the environmental levels of the toxin are not very high (Bryan et al, 1979). Some of these persistent pollutants such as trace elements and hydrocarbons are introduced contributed in the environment basically by various anthropogenic activities, including oil exploration, bunkering activities, mining activities in the deep sea (which processes involve the extraction of minerals and metal ores like zinc, cobalt, silver, aluminum and gold), as well as other industrial and domestic activities in catchment areas. Two factors contribute to the deleterious effects of most toxic substances that
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