Abstract
The presence of trace metals in the sediment, water, and biota of the Epe lagoon has been recently linked to oil exploration and municipal perturbations around the lagoon. The study was aimed at assessing the concentrations and associated health risks of Fe, Zn, Cu, Ni, Pb, Cd, Cr, Mn, Co and V in the water, sediment, and Gymnarchus niloticus of Epe lagoon and to evaluate the role of the enteric parasite Nilonema gymnarchi in bioaccumulation of the metals in the fish. The temperature, pH, redox potential, conductivity, turbidity, dissolved oxygen (DO), total dissolved solids (TDS), and salinity were determined in-situ using a handheld multi-parameter probe (Horiba Water Checker Model U-10). The concentrations of Fe, Zn, Cu, Ni, Pb, Cd, Cr, Mn, Co, and V were determined in the surface water, bottom sediment, Gymnarchus niloticus, and its enteric parasites, Nilonema gymnarchi in Epe lagoon using the Flame Atomic Absorption Spectrometer (Philips model PU 9100). The bioaccumulation factors and target hazard quotients of the trace metals in the infected and uninfected fish were estimated and compared. The intestinal tissue sections of the infected and uninfected fish were examined using a binocular dissecting microscope (American Optical Corporation, Model 570) using hematoxylin and eosin (H&E) stain. Biochemical markers such as reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (MDA) were determined in the liver of the infected and uninfected fish. The SOD level was higher in the uninfected fish than the infected ones supports the indications deduced from the bioaccumulation analysis. Strong positive correlations between SOD and most of the metals- Fe (0.916), Zn (0.919), Cu (0.896), and Ni (0.917) suggests that the metals may have inflicted more toxicity in the uninfected. The histopathological comparisons made between the uninfected and infected fish showed consistency with the outcomes of other comparisons made in this study. These evidence were marked by tissue alterations in the infected fish ranging from no observed changes to mild alterations, while the uninfected exhibited more severe tissue injuries such as hemorrhagic lesions, severe vascular congestion, edema, the increased connective tissue of the submucosa, and vascular congestion. The condition factors of the infected (0.252) and uninfected (0.268) fish indicated slenderness and unfitness possibly due to environmental stressors such as trace metals. The parasitized fish showing better-coping potentials than the uninfected, coupled with the significant bioaccumulation interferences exhibited by the parasite Nilonema gymnarchi is an indication that the parasites may be a good metal sequestration agent for the fish and can be used to forestall the significant health hazard quotient posed by the current level of iron and the synergy of all metals analyzed in the lagoon.
Highlights
Predominant oil exploration activities around Epe lagoon are primarily responsible for the attendant oil spill incidences at the lagoon
The pH of the surface water samples from Epe lagoon was lower than the established range by FEPA suggesting the water was acidic (Table 1)
The physicochemical parameters of the lagoon appeared to be in fair conditions, the G. niloticus in the lagoon exhibited notable sub-lethal toxicity effects
Summary
Predominant oil exploration activities around Epe lagoon are primarily responsible for the attendant oil spill incidences at the lagoon. Previous reports have linked the use of petroleum products, combustion of fossil fuels, and tons of municipal wastes to pollution of the lagoon (Doherty and Otitoloju, 2016; Akinsanya et al, 2019; Isibor et al, 2020). This pollution has been characterized by poor water quality and its impact on the sentinel species in the aquatic ecosystem (Akinsanya et al, 2019). Their result showed that metal accumulation varied depending on species-specificity, feeding behavior, fish size, and age
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