Histology-Based Sub-chronic Toxicity Assessment of Target Heavy Metals from a Crude Oil Spill Using Testicular Histo-morphometry in Wistar Rats

Toxicology studies the harmful effects of chemical, biological and physical agents in biological systems, which establishes the extent of damage in living organisms. Toxicity tests can measure lethal and/or sublethal effects. This study was aimed at evaluating, in histological terms, the sub-chronic toxicity of some target crude oil contaminants on the histo-morphometry of the testes of exposed Wistar rats. The following target chemicals (TCs; cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and nickel (Ni)) were selected based on findings from the literature review of chemical analysis done on the crude oil spill site. In estimation of the rat exposure dose (RED) for the study, OEDC (2001) reference oral LD50 dose for Wistar Rat (in mg/Kg of body weight) of the TCs – Cd (63mg/kg); Cr (46 mg/kg), Cu (481 mg/kg); Nickel (300 mg/kg) and Pb (600 mg/kg), was used as a guideline standard for the upper limits of dose administration. Thirty (30) inbred male Wistar rats of average weight 150-200g (5 for control and 25 for experimental – 5 for each of the five TC- treated groups) were obtained from the animal house of the Department of Anatomy, Faculty of Basic Medical Sciences, University of Benin for this study. Rats were later sacrificed, and the target organ (testis) excised and used for qualitative histological evaluation. Gross anatomical assessment showed that there was no significant difference (P> 0.05) when correlating weight gain between the treated and control groups. This implies that the RED does not have a significant effect on the weight of Wistar Rats, which is consistent with other studies in which Wistar Rats were exposed to heavy metals. Histological evaluation showed the following major lesions: glomerular congestion, degeneration and necrosis; tubular degeneration and necrosis; Interstitial inflammation, haemorrhage and necrosis. This study gives credence to the fact that histology-based evidence is a veritable tool for assessing sublethal levels of environmental stressors in the certification of toxicity.