Wild animals have provided complimentary protein for human populations across the world over the centuries. This study investigated on bioaccumulation of heavy metals in different organs of cane rat (Thryonomys swinderianus) and the health implications of its consumption. Four carcasses were collected from each of the four ecotomes (Mosinmi, Agbara, Omo forest reserve and Ibese) and concentrations of 7 heavy metals (Fe, Cu, Cd, Pb, Mn, Cr, Zn) were examined in four organs (skin, liver, lung and kidney) from each specimen used by Atomic Absorption Spectrophotometer. Analysis of variance revealed no significant difference (P>0.05) in the concentration of metals in the animal except Fe and Cu, while significant variation exists when specimens were compared across different ecotomes. Total mean concentrations were Fe (400.512±60.0107), Cu (8.569±1.0396), Cd (0.06±0.040), Pb (0.3156±0.1175), Mn (9.4200±1.0383), Cr (1.3013±0.2739) and Zn (72.771±10.5672). Average mean concentration for all the metals in the study area was found to be higher than the recommended level which suggests that consumption of animals from this ecotomes are hazardous to human health and no single organ is completely safe for human consumption.

Effects of petroleum refinery wastewater on Clarias gariepinus juvenile were investigated. Commercially obtained C. gariepinus fingerlings were acclimatized in a plastic tank (100 L capacity) of de-chlorinated tap water at 25±2°C for 14 days and fed with commercial feed pellet at 2% body weight of the fingerlings. Bioassay tests were carried out in four transparent plastics tank with nominal concentrations of 100 ml, 200 ml, 300 ml of the wastewater added to 40L of de-chlorinated tap water and only de-chlorinated tap water as control. Each tank contains twenty fish samples, while the assay was replicated three times concurrently. Following standard procedures, behavioural response, growth changes, haematological and histopathological tests were carried out on the samples. Significant reduction in the weight was observed in the fingerlings cultured with the wastewaters, while no significant difference occurred in the control fish. Highest values of Packed Cell Volume (PCV) (22), Haemoglobin (HB) (7.0), Red Blood Cell (RBC) (1.62) and endocochlear potential (EP) (5) were recorded for the control fish than exposed fish. On the other hand, Haptoglobin (HP), Mean Corpuscular Volume (MCV) and Mean Corpuscular Haemoglobin (MCH) were higher in the blood of exposed fish than in control. Histopathologically, exposed fishes showed no visible lesion in gills except from the thickening of the lamellae as the concentration of wastewater increases, indicating an increase in tissue disintegration. Similarly, gross tissue disintegration was observed in those fish exposed to 200ml wastewater as evidenced by the presence of large open spaces (hepatocytes) in the liver.

Comparison of heavy metal levels in Oreochromis niloticus and Chrysichthys nigrodigitatus caught inOgun River (Nigeria) was carried out to reveal the potential health risks associated with fish consumption from the river. Concentrations of copper, lead and cadmium were determined in the gills, eyes, bone, flesh, liver and stomach of the fish species. Ten fish of each species were obtained commercially and analyzed for the metals using Atomic Absorption Spectrophotometer. Data obtained were subjected to one-way analysis of variance (ANOVA) at 5% significant level. The highest concentrations of Cu were observed in the gills of O. niloticus and the eyes followed by liver of C. nigrodigitatus, while the lowest concentrations were detected in the eyes of O. niloticus and bone of C. nigrodigitatus. Lead concentrations were higher in the liver of O. niloticus and gills of C. nigrodigitatus, while the lowest concentrations were detected in stomach of O. niloticus and C. nigrodigitatus respectively. Also, in proximate analysis, composition of dry matter, crude protein, crude fat, ash and carbohydrate contents recorded high in C. nigrodigitatus and O. niloticus and significantly differs. All the metals studied exceeded standard permissible limit for human consumption. Therefore, monitoring of the river is highly recommended, while adequate information, education and training should be strengthened to control further pollution.

The research examined the accumulations of six heavy metals including chromium (Cr), lead (Pb), iron (Fe), zinc (Zn), cadmium (Cd), and copper (Cu) in water as well as in three male and female species of crab (Cardisoma armatum, Callinectes danae, Callinectes ornatus) sampled from Ojo River in Lagos State of Nigeria. Physico-chemical parameters of the water samples from the River and heavy metal concentrations in the crab species obtained also from the River were examined using standard methods. The results showed that total dissolved solute (TDS), electrical conductivity (EC), salinity, dissolved oxygen, biological oxygen demand and chemical oxygen demand varied significantly along the River course, with TDS and EC being relatively high. Heavy metals detected in the crabs were Fe, Cu and Zn, with Cu being the highest in the species examined. The species C. ornatus presented the highest content of Cu followed by C. armatum and C. danae. The content of heavy metals (mg kg–1) among the crab species showed that Cu (23.47±0.10) > Zn (19.06±0.01) > Fe (16.85±0.01) in all the species except in C. armatum where Fe (1.26±0.44) was > Zn (1.19±0.02). Furthermore, Pb, Cd and Cr were not found in the crabs and this could be associated with the fact that the area consists mainly of residential houses, farms and a few industries. Notably, the content of the heavy metals was larger in the female than the male crabs. This study reported different levels of heavy metal accumulation in male and female species of crabs. Also, the shell fishes from Ojo River might be considered safe for consumption, but the need for continuous monitoring to prevent bioaccumulation is recommended.