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IntroductionThe Nubui River is a primary source of water for drinking purposes and other domestic activities in the rural communities dotted along its riparian zone, with agriculture being the major activity occurring in this important ecotone. The river has become a potential sink for agrochemical residue, including heavy metals, and has apparent aesthetic water quality issues, with associated health consequences. This study, therefore, assessed the health risks of heavy metals within the rural populations in the catchment areas, who have limited sources of improved water supply.MethodsThe concentration of iron (Fe), lead (Pb), cadmium (Cd), mercury (Hg), and zinc (Zn) was assessed on cumulatively 275 water samples, using a Perkin Elmer PINAAcle 900 T atomic absorption spectrophotometer for 11 months. A cross-sectional survey was conducted amongst 338 community members, following field observations on utilisation types, aesthetic appeal, and perceived quality of water from the Nubui River. To determine the potential human and ecological risks of heavy metals, the hazard quotient, chronic daily intake, contamination factor, and health pollution indices of heavy metals were computed. STATA version 16 was used to analyse the survey results.ResultsDescriptive statistics of average concentrations of heavy metals in surface water at all sampling stations showed the pattern Hg < Pb < Cd < Zn < Fe, with relatively low concentrations, between 0.001 and 0.004 mg/L for Hg, 0.0011 and 0.0019 mg/L for Pb, 0.0461 and 0.0739 mg/L for Zn, and 0.2409 and 0.377 mg/L for Fe. The findings, however, showed relatively high cadmium levels between 0.0215 mg/L and 0.0383 mg/L in two of five sampling stations in comparison with the World Health Organisation (WHO) drinking water guideline values in some months. Hazard quotient values indicate that the population is safe from the non-carcinogenic health risks of exposure to heavy metals through oral routes. The contamination factor and heavy metal pollution indices for cadmium exceed recommended guideline values of 1 and 100, respectively. Meanwhile, 73.1% of community members evidently preferred the Nubui River for various domestic activities with 86.1% of them utilising it for drinking purposes. This occurrence results in exposure to associated health risks.

The pollution resulting from the generation of waste tires is currently causing adverse environmental problems worldwide. Heavy metals present in water is also a significant cause of health and environmental problems in developing countries. This study focuses on the development of activated carbon using waste tire pyrolytic char as a precursor and using the resulting activated carbon to treat water containing Pb2+. The results obtained from the study showed that waste tire activated carbon could effectively remove Pb2+ from aqueous solution far better than waste tire pyrolytic char. The effects of process variables: Temperature (ºC), Contact time (min), and Initial metal concentration (mg/l) were studied and the optimum operating conditions were obtained as 25°C, 120 min, and 400mg/l for the temperature, contact time, and initial metal concentration, respectively. Adsorption kinetics revealed that the experimental data gave the best fit for the pseudo-second-order kinetic model. Adsorption thermodynamics illustrated that the adsorption process was exothermic and spontaneous in nature by calculating adsorption parameters ?H, ?G and ?S as -85.57 kJ/mol.K, 4.211 kJ/mol.K, and -0.279 kJ/mol.K respectively at 298.15K.

The environmental impacts caused by the disposal of waste tires on land and impacts of metals in water is of great concern. In this study activated carbon was prepared from waste tire pyrolysis char using a chemical activation process where KOH was used as an activating agent at 600 °C in a tube furnace. The characterization techniques namely proximate analysis and X-ray fluorescence (XRF) were used. The adsorption results revealed that waste tire activated carbon (WTAC) was more effective than waste tire pyrolysis char (WTPC) on the removal of lead ions from aqueous solution. The effect of adsorption process parameters such as: adsorbent dosage and pH on adsorption of lead ions onto WTPC and WTAC were determined and optimized. A high lead ions removal efficiency was obtained at following process conditions namely: pH of 7 and adsorbent dosage of 0.25g/100ml. Adsorption isotherms studies revealed that the experimental data was best fitted with Freundlich isotherm model. The proximate analysis and XRF analysis confirmed that chemical activation of waste tire pyrolysis char took place. Keywords: Waste tire activated carbon, Adsorption, Adsorption isot