Impacts of trace metals on African common toad, Amietophrynus regularis (Reuss, 1833) and depuration effects of the toad's enteric parasite, Amplicaecum africanum (Taylor, 1924) sampled within Lagos metropolis, Nigeria

Abstract

The study aimed at assessing the depuration potentials of endoparasite, Amplicaecum africanum on trace metals in its toad host, Amietophrynus regularis at sites of significant anthropogenic perturbations within the Lagos metropolis, in Nigeria. A total of 120 toads of both sexes, alongside 45 soil samples were collected from each of three (3) stations labeled Dumpsite, Lagoon front and Highrise, using hand nets and by hand-picking between February and October, 2018. The intestinal tissues sections of the toads were examined using a binocular dissecting microscope (American Optical Corporation, Model 570) and hematoxylin and eosin (H&E) stain. Oxidative stress in toad intestine was assessed by estimating the levels of glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (MDA). Trace metals in the water, soil, toad liver, intestine and parasite, Amplicaecum africanum were tested using Atomic Absorption Spectrophotometry (Philips model PU 9100). Lead (Pb), copper (Cu), nickel (Ni), cadmium (Cd), and chromium (Cr) were detected in the toads, with the infected toads having lower concentrations of most trace metals than the uninfected toads, irrespective of the locations and sex. Strong negative correlations between parasitological indices and concentrations of trace metals in the toads suggest that the parasites might have taken up significant amounts of trace metals from the host. The study demonstrated the potentials of parasite, A. africanum to depurate trace metal burden in Amietophrynus regularis. When the dominant factor impacting the toad is the parasitic infection, parasite intensity determines the trade-off between parasitological harm and depuration benefit to the host. Hence, under controlled conditions, parasites may serve as bioremediation agent in the event of pollution. Depuration potential of A. africanum in the study was supported by the mild tissue alterations observed in the intestine of infected toads, compared to the uninfected counterparts, which exhibited severe glandular hyperplasia, increased connective tissue, and severely stunted villi. Consistently lower activities of biochemical biomarkers which characterize the uninfected toads compared to the infected, irrespective of the sex and stations, further corroborate drawn inferences.

Keywords: Abundance; Allotment; Bioaccumulation; Correlation; Ecology; Environmental analysis; Environmental assessment; Environmental health; Environmental impact assessment; Environmental pollution; Environmental risk assessment; Environmental toxicology; Host; Intensity; Oxidative stress; Parasite; Toxicology; Zoology.

Figure 1

Map of Lagos metropolis, showing sampled stations.

Figure 2

Spatial variation of trace metals. Legends: A = Dumpsite, B= Lagoon front, C= Highrise. Bars of a metal with same alphabets are not significantly different (p > 0.05), while those with different alphabets are significantly different (p < 0.005).

Figure 3

Photomicrographs of intestinal tissues of A. regularis. A- Highrise: Normal epithelial mucosa, B- Lagoon front: severe glandular hyperplasia (black arrow) and infiltration of inflammatory cells (blue arrow), C- Dumpsite: focal areas of stunting of villi (blue arrow), glandular hyperplasia (dashed arrow), and infiltration of inflammatory cells (black arrow), mild congestion in submucosa (blue arrow). Scale bars = 25μm.