Systematic literature review of heavy metal contamination of the Nigerian environment from e-waste management: Associated health and carcinogenic risk assessment.

E-waste -the aftermath of large amount of electrical and electronic equipment ferried into Africa from which Nigeria receives a significant chunk, is composed of components known to be hazardous to health. Composition of series of heavy metals (HMs) in e-waste is traceable to many health conditions including cancer which is hitherto incompletely understood. This study harmonizes primary data on HMs from e-waste in different Nigerian environmental media including the air, soil, surface dust, water and plant. We estimated the possible health implications, single and aggregative soil and water pollution indices both in adult and children categories, carcinogenic and non-carcinogenic risks secondary to HM exposure and mapped out the possible mechanism of carcinogenesis. Analysis showed that soil, water, surface dust and plant matrices in Nigerian environment are variedly but considerably contaminated with combination of HMs. The significantly high values of the hazard quotient and hazard index of both water and surface dust matrices are indicative of adverse health effect of the non-carcinogenic risk. The highest HQ is generated by Pb and Cr through dermal exposure to soil and surface dust with mean values of 1718.48, 1146.14, 1362.10 and 1794.61 respectively among Nigerian children followed by the oral exposure. This pattern of observation is similar to that obtained for adult category. HI due to Pb and Cr in soil constitutes the highest HI (2.05E+03 and 1.18E+03 respectively) followed by surface dust. However, this study precipitates the observation that children are more at health risk than adults in contaminated environment. Carcinogenic risk also follows the same pattern of expression in the Nigerian environment. We conclude that exposure to e-waste poses significant carcinogenic and non-carcinogenic health risks and the induction of toxicity may be mediated via DNA damage, oxidative stress and inflammatory/immune cells dysfunction in Nigerian environment.

Micronucleus cytome assay in the differential assessment of cytotoxicity and genotoxicity of cadmium and lead in Amietophrynus regularis.

Amphibians are increasingly being used as bio-indicator of contamination in ecosystems due to their sensitivity to xenobiotics in the environment. Cadmium and lead compounds, ubiquitous mutagens and carcinogens, are capable of eliciting genome instability in adult toads which may enhance amphibian decline. Micronucleus cytome (MN-cyt) assay, a comprehensive cytogenetic test for the assessment of genome instability induced by xenobiotics in organisms, was utilized in the differential cytogenotoxic evaluation of Cd and Pb in adult Amietophrynus regularis. A. regularis was exposed to six concentrations (8 - 512 mg/L) of the metal solutions to determine 96 h acute toxicity. Four toads per group were exposed to five sub-lethal concentrations (5 - 75 %) of the 96 h LC50 of the metals for 14 days. At post exposure, bone marrow and peripheral erythrocytes were collected for MN-cyt analysis. The metals induced differential concentration and time-dependent increase in mortality with 96 h LC50 of 36.36 mg/L (Cd) and 112.06 mg/L (Pb). No observable effective concentrations (NOEC); Cd=8 and Pb=32 (mg/L) and Lowest observable effective concentrations (LOEC); Cd=16 and Pb=64 (mg/L) were recorded for the metals. Derived toxicity factor (TF) showed that Cd was 3.08 times more toxic to the toads than Pb. The metal solutions induced significant (p<0.05) increase in frequencies of MN, binucleated, nuclear bud, notch, lobe, vacuolated erythrocytes, apoptosis and necrosis compared to the negative control. Cd elicited 1.42 and 3.26 folds increase in MN and NAs respectively, than Pb. MN-cyt assay is a suitable cytogenetic tool for assessing genome instability in A. regularis. Increased genetic instability induced by Cd and Pb may be associated with genetic related syndromes; neoplasms, reproductive dysfunctions and mortality. This suggests threat to amphibian health and may enhance population decline.

Textile effluent induced genotoxic effects and oxidative stress in Clarias gariepinus.

Human and ecological disorder experienced in industrial settlements as a result of improper disposal of chemicals such as textile effluent calls for careful surveillance on the state of the environment. This study investigated the toxicity of textile effluent discharge using biochemical and cytogenetic responses to ascertain the acute and sub lethal effects on Clarias gariepinus. The 96 h LC50 of C. gariepinus exposed to the textile effluent was 8.203 ml L(-1). Fourteen day exposures to 1, 2, 4 and 6 ml L(-1) doses were conducted and several toxicological endpoints were evaluated. Sub lethal genotoxicity and biochemical study was also carried out for fourteen days. The genotoxicity studies utilized micronucleus test while the biochemical studies quantified serum anti-oxidant status Total Protein (TP), Catalase (CAT), Superoxide Dismutase (SOD) and Malondialdehyde (MDA) of the exposed fish. Toxicity factor indicates that the 96 h LC50 was significantly more toxic than the 24 h LC50 (p < 0.05). The textile effluent at the tested concentrations induced micronucleus and nuclear abnormalities in the peripheral blood of exposed fish. Micronucleus, notch and binucleated cell formation were significant (p < 0.05) compared to control while lobed and blebbed cells were insignificant (p < 0.05). SOD, TP and CAT significantly (p < 0.05) decreased compared to control group while MDA increased compared to control but was insignificant (p > 0.05). The results obtained from this study showed that textile effluent increase cytogenetic damage and altered anti-oxidant status in C. gariepinus. Chemicals in the effluent can be bioaccumulated and biomagnified in the aquatic organism hence affecting man.