Health risk consequences of consumption of heavy metal-contaminated water, shrimp (Macrobrachium macrobrachion) and fish (Brycinus longipinnis) from Benin River in Nigeria were evaluated. Three stations around Koko Community (Abialegbe, Ebenco/Optima and Total Facility) with known anthropogenic activities (industrial and petrochemical installations and loading) were studied. Samples of surface water, shrimp and fish were collected and analyzed using Buck scientific atomic absorption spectrophotometer, model 210VGP. Health risk indices were reported as Estimated Daily Intake (EDI), Target Hazard Quotient (THQ) and Total Target Hazard Quotient (TTHQ). Eight heavy metals were analyzed in water, shrimp and fish. Nickel (Ni) was observed to be the most dominant heavy metal in water, while Iron (Fe) was the most dominant in shrimp and fish. Heavy metal levels in water were below recommended limits set by World Health Organization (WHO) and Standard Organization of Nigeria (SON) except for cadmium (Cd), nickel (Ni) and lead (Pb). Assessment of non-carcinogenic health risk by target hazard quotient (THQ) indicated that THQ estimated for heavy metals in water (dermal exposure) and shrimp were below the threshold value of 1. However, THQ for heavy metals in water (oral exposure) and consumption of fish were above threshold value of 1 indicating potential health risk. Total Target Hazard Quotient (TTHQ) estimated for heavy metals in water (oral exposure) and consumption of fish were above 1 indicating potential non-carcinogenic health risk to consumers. The continuous monitoring of heavy metals in Benin River is of necessity in order to ensure the safety of aquatic organisms and humans who rely heavily on aquatic resources.

The potential ecological and human health risk of heavy metal pollution in sediment and Benthic Fauna (Chrysichthys auratus and Tympanotonus fuscatus) of Benin River, Southern Nigeria, was evaluated. Three sampling sites associated with heavy anthropogenic activities along the course of the river were sampled. Heavy metals concentrations were determined in the samples using atomic absorption spectrophotometer (Model 210 VGP, Buck Scientific). In all sediment samples, only Pb exceeded the threshold/probable effect level (TEL). Very high contamination degrees (CD > 24) 181.74, 50.11, and 101.96) for stations 1, 2, and 3, respectively, were observed indicating serious anthropogenic pollution. Geoaccumulation index (i_geo) showed slight pollution with Pb and Cd and severely to extremely polluted with Fe across the stations. Cd exhibited moderate individual potential risk (\(E_{\text{r}}^{i}\)), and the other heavy metals showed low \(E_{\text{r}}^{i}\). Potential ecological risk index (RI) showed low risk of contamination for heavy metals in sediment. Human health risk assessment for Co, Cd, Cu, Zn, Mn, Fe, and Ni in C. auratus and Co, Zn, Mn, Fe, and Ni in T. fuscatus indicated no obvious health risk from these heavy metals over a lifetime of exposure. However, hazard quotient (HQ) values for Pb in C. auratus and Cd, Cu, and Pb in T. fuscatus indicated significant health risk. The hazard index (HI) values for both C. auratus and T. fuscatus were > 1 indicating significant adverse health risk of non-carcinogenic effect. Therefore, the consumption of these contaminated fish and shellfish by the people of Koko portends risks of the health of the public. The industries operating in this community should adopt more sustainable and eco-innovative management options in order to attenuate potential ecological and human health risk of metal pollution.

Engineered biological systems used for resource recovery often utilize anaerobic digestion to treat organic wastes by reclaiming the carbon as energy (methane gas) and a soil amendment (biosolids). This study explored the production of biogas from co-digestion of cow dung waste and water hyacinth (Eichhornia crassipes) using anaerobic biological conversion. Cow dung and water hyacinth biomass feedstock were collected from Abattoir and Ologbo River in Benin City, Nigeria. Samples were blended and substrate mixed in ratio 10:1 v/v due to balanced carbon/nitrogen (C: N) ratio of plant biomass and cattle rumen manure and charged into the fixed dome. Performance test was carried out after the biogas had been produced after twenty-one (21) days. The percentage composition of biogas produced shows that methane gas (CH4) has 56.4%, carbon-dioxide (CO2) is 35% and nitrogen (N2) is 6.9%. Optimal production was found to be a function of temperature, hydraulic retention time, pH, concentration of bacterial population and overall design consideration of the digester. Scrubbers were fitted to rid the gas of hydrogen sulphide (H2S), CO2, ammonia (NH3) and moisture. The gas was directed through a gas pipe to a burner for cooking in the staff canteen. This study is relevant for the implementation of Sustainable Development Goals (SDGs) and strengthening of the bio-based economy with respect to waste management. This can facilitate environmental and socio-economic sustainability leading to reduced carbon foot print and reduction in solid waste accumulation. Key words: Cow dung, water hyacinth, bio-digester, biogas.

Clarias gariepinusfingerlings exposed to lethal and sublethal concentrations of Gammalin 20 were investigated in a renewal static bioassay with particular reference to behaviour, survival, and histopathological changes. Early symptoms of gammalin 20 lethal poisoning were, respiratory distress, increased physical activity, convulsions, erratic swimming, loss of equilibrium, and increased breathing activity. Behavioural response was dose dependent and decreased with decreased concentration. The 96-hour lethal concentration (LC₅₀) value was 30 ppb. Histopathological changes of the gill, liver, and intestinal tissues of fish treated with sublethal concentration of gammalin 20 for twelve weeks showed gill distortion and fusion of adjacent secondary lamella as a result of hyperplasia and excessive mucus accumulation. The liver showed swelling of hepatocytes with mild necrosis, pyknosis, and vacuolation, while the intestine showed yellow bodies of the lamina propria at the tip of the mucosal fold.