A. O. Ogunfowokan

Kinetic, equilibrium, and thermodynamic studies of the biosorption of cadmium (II) from solution by Stereophyllum radiculosum.

Biosorption of heavy metal ions can be an effective process for the removal of Cd(II) from wastewater. In this study, the batch removal of Cd(II) from dilute aqueous solution using Stereophyllum radiculosum as the biosorbent has been investigated. The Cd(II) uptake was dependent on the initial pH, contact time, initial metal ion concentration, and temperature. The residual Cd(II) in the solution was determined using Atomic Absorption Spectrophotometer. The optimum pH for the biosorption was pH 6. Maximum biosorption was obtained after 60 min of the process. Kinetic study showed that the pseudo-second-order rate equation best described the biosorption process. The adsorption isotherms obtained fitted well into the Freundlich and Langmuir isotherm. The Freundlich equation obtained was log Ⲅ = 2.6924 logC e + 0.1131, while the Langmuir equation obtained was 1/Ⲅ = 0.0008/C e + 17.41. The correlation factors obtained were 0.0995 and 0.9904, respectively. The free energy change obtained for the biosorption of Cd(II) at 300 K, initial Cd(II) concentration of 100 mg L-1 and pH 6 was -20.894 kJ mol-1. The thermodynamic study showed that the increase in temperature led to increase in the amount of the metal ion biosorbed. These results indicate that S. radiculosum has potential for the uptake of Cd(II) from industrial effluents.

Isolation and Determination of Polycyclic Aromatic Hydrocarbons in Surface Runoff and Sediments

The distribution of Polycyclic Aromatic Hydrocarbons (PAHs) was investigated in surface runoff and sediments of Lagos, Osogbo and Ile-Ife Western areas of Nigeria. Method for the analysis of PAHs was based on Liquid-Liquid extraction of the runoff and a soxhlet extraction of the sediments followed by a clean up adsorption procedure. The PAHs were separated and quantified by Gas Chromatography-Mass spectrometry (GC-MS) technique. A blank experiment was done using triply distilled water and following the same procedure for the samples to establish blank levels. In both street runoff and sediments 13 PAHs were identified and quantified. At Osogbo and Ile-Ife areas, the mean levels of PAHs in surface runoff ranged between 0.10–15.81 mg L-1 while in the Lagos area the levels were between 0.1–73.72 mg L-1. Generally, the PAH levels in surface runoff of Lagos constitute 53.03 mg L-1 average ∑ PAH detected in the study area compared to 31.96 mg L-1 average ∑ PAH contribution made by samples from Osogbo and Ile-Ife. The levels of PAHs in sediments are relatively higher compared to those of the street runoff in the study area. PAHs in sediment of Lagos contribute an average of 228.57 mg kg-1 ∑ PAH to the total sediment PAH burden compared to Osogbo and Ile-Ife areas that contribute only 91.13 mg kg-1 average ∑ PAH to the total PAH burden of the study area. The relatively higher average ∑ PAHs reported for Lagos area compared with those of Osogbo and Ile-Ife, is consistent with higher industrial activities and traffic density of the former (1000–10000 vehicles/hr) than the later (450–1500 vehicles/hr).

Speciation study of lead and manganese in roadside dusts from major roads in Ile-Ife, South Western Nigeria

A speciation study of Pb and Mn in roadside dust along major roads in Ile-Ife, South Western Nigeria, was investigated. Pb and Mn values obtained by total digestion ranged from 22.23 ± 3.52 to 43.48 ± 3.05 μg/g and 35.93±0.15 to 83.76 ± 0.06 μg/g, respectively. The results of speciation analysis of Pb and Mn in the samples showed that the mean levels of these metals in the various fractions followed the order: organic matter>residual>Fe-Mn>carbonate>exchangeable and organic matter-bound>exchangeable>carbonate-bound>residual>Fe-Mn oxide-bound respectively. The speciation study therefore revealed that most of the Pb and Mn were associated with the organic matter fraction and that they were least available in the exchangeable and Fe-Mn oxide fractions, respectively. The apparent mobility and potential bioavailability for these metals in the road dust was Mn>Pb. There is a significant difference between the means of Pb and Mn in the road dust of the study area at p≤0.05, which strongly suggests that they may not have come from the same source; different sources may be responsible, which may be anthropogenic, such as tyre wear, vehicular emission, brake linings and natural.

Organochlorine Pesticide Residues in Sediments and Waters from Cocoa Producing Areas of Ondo State, Southwestern Nigeria

This study investigated levels of organochlorine pesticide (OCP) residues in water and sediment samples from eleven rivers serving as drinking water sources and receiving runoff from nearby cocoa plantations in Ondo State, Nigeria. Twenty-two composite samples of surface water and sediments (0–3 cm) were collected randomly using grab technique and replicated thrice per season. The efficiency of the two techniques [supercritical fluid extraction (SFE) and liquid/liquid extraction (LLE)] was evaluated with percentage analyte recoveries to for SFE and to 1 for LLE. Determination of OCPs by gas chromatography with electron capture detection gave higher concentrations for sediments compared to the equivalent water samples. The commonly occurring pesticide residues in the sediments were (range, μg g−1) cis-chlordane 0.03–6.99; α-endosulfan 0.03–6.99; p,p′-DDE 0.08–19.04; and dieldrin 0.01–7.62; in the sediments and dieldrin (not detected-1.51 μg L−1) in water samples, during the dry season. OCP levels were significantly higher in dry season than wet season among the rivers. The study concluded that most of the rivers in cocoa growing areas were contaminated with OCPs associated with agricultural activities.

Electrochemical response of nitrite and nitric oxide on graphene oxide nanoparticles doped with Prussian blue (PB) and Fe2O3 nanoparticles

Electrocatalytic behaviour of graphene oxide (GO), iron(III) oxide (Fe2O3) and Prussian blue (PB) nanoparticles and their nanocomposite towards nitrite (NO2−) and nitric oxide (NO) oxidation in neutral and acidic media respectively was investigated on a platinum (Pt) modified electrode. Successful synthesis of these nano materials was confirmed using microscopic and spectroscopic techniques. Successful modification of the electrode was confirmed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the Pt–GO–Fe2O3 and Pt–GO–PB nanocomposite modified electrodes gave a faster electron transfer process in both a 5 mM Ferri/Ferro ([Fe(CN)6]3−/4−) redox probe and 0.1 M phosphate buffer solution (PBS). The Pt–GO–Fe2O3 and Pt–GO–PB electrodes also gave an enhanced NO2− and NO oxidation current compared with bare Pt and the other electrodes studied. Electrocatalytic oxidation of the analyte occurred through a simple diffusion process but were characterized with some level of adsorption. Tafel slopes b of 468.4, 305.2 mV dec−1 (NO2−, NO); and 311.5, 277.2 mV dec−1 (NO2−, NO) were obtained for the analyte at the Pt–GO–Fe2O3 and Pt–GO–PB electrode respectively. The Pt–GO–Fe2O3 limit of detection and sensitivity in NO2− and NO are 6.60 μM (0.0084 μA μM−1) and 13.04 μM (0.0160 μA μM−1) respectively, while those of the Pt–GO–PB electrode are 16.58 μM (0.0093 μA μM−1) and 16.50 μM (0.0091 μA μM−1). The LoD compared favourably with literature reported values. Pt–GO–Fe2O3 gave a better performance to NO2− and NO electrooxidation, good resistance to electrode fouling, a higher catalytic rate constant and lower limit of detection. The adsorption equilibrium constant β and the standard free energy change ΔG0 due to adsorption are 10.29 × 103 M−1 (−22.89 kJ mol−1) and 3.26 × 103 M−1 (−20.04 kJ mol−1) for nitrite and nitric oxide respectively at the Pt–GO–Fe2O3 electrode. An interference study has also been reported. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of nitrite and nitric oxide in food, water, biological and environmental samples.

Bromate and trace metal levels in bread loaves from outlets within Ile-Ife Metropolis, Southwestern Nigeria

Highlights • This study evaluates the levels of bromate and trace metals in the bread loaves sold within Ile-Ife, Nigeria.• Bromate was determine via spectrophotometric method while trace metals were profiled using Atomic Absorption Spectrophotometer.• Study revealed that many bread bakers had not fully complied with the bromate-free rule stipulated by government contrary to “bromate free” inscribed on the labels of the bread.• The bread samples contained both essential and toxic trace metals to levels that could threaten the health of consumers over prolonged regular consumption.

Determination of cadmium and lead in urine of some Nigerian subjects.

Forty-one urine samples of smokers and non-smokers from Ile-Ife, Nigeria were analyzed for normal cadmium and lead levels after acid digestion. Results of the preliminary study show that concentrations of cadmium obtained were generally low compared with lead. The mean urinary levels from non-smokers ranged from 0.05 - 0.02 to 0.16 - 0.01 w g ml -1 and from 0.02 - 0.03 to 0.88 - 0.04 w g ml -1 for cadmium and lead respectively, whilst, for smokers, urinary levels varied between 0.07 - 0.01 and 0.23 - 0.02 w g ml -1 and between 0.28 - 0.03 and 1.02 - 0.02 w g ml -1 were obtained for cadmium and lead, respectively. Cd levels in urine of smokers and non-smokers are higher than the recommended normal level of 0.0085 w g ml -1 , while levels of Pb are above the 0.08-0.15 w g ml -1 exposure range. Results of spiking experiments with urine gave high percentage recoveries for both elements (Cd, 87.9 - 0.40%) and (Pb, 90.40 - 0.12%). Blank determination was done for background correction.

Speciation study of the heavy metals in commercially available recharge cards coatings in Nigeria and the health implication

This work assessed levels of heavy metals exposure from silver coatings of mobile phones recharge cards of three major companies (designated as A, B and C) with price denominations 100, 200 and 400 from companies A, B and C respectively, which were carefully scratched using a plastic scraper into a glass tube. The coatings were acid digested for total metal concentration, while speciation experiment for Mn, Cu, Cd and Pb was carried out. Total metals and speciation analysis were done using AAS and XRF techniques. The total metal concentration from XRF analysis was in the range: Ca (70–2140 μg/g), K (20–4930 μg/g), Sc (80–270 μg/g), Ti (1530–12,580 μg/g), Fe (50–6660 μg/g), Ni (20–2040 μg/g), Cu (20–850 μg/g) and Zn (40–460 μg/g). Cr had the lowest concentration (10 μg/g) in A ( 400) while Ti had the highest concentration (12,580 μg/g) in C ( 500) for all the coatings analyzed. AAS and XRF results agreed closely except for Fe with higher concentration. A ( 100) contained high concentration of the metals compared with others. Speciation study identified Mn as the most mobile element when present in the environment.

Agama lizard: A potential biomarker of environmental heavy metal pollution assessment

In this study, the suitability of Agama lizard as a biomarker in assessing environmental pollution levels of arsenium (As), barium (Ba), cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) was investigated. Samples of top soil and agama lizards were taken from five sites within a university community in Nigeria for the study. Soil samples, livers and kidneys from the lizards were subjected to wet acid digestion and levels of heavy metals in the digested samples were determined using an atomic absorption spectrophotometer (AAS). Results of the study showed that the levels of the metals ranged from Cd, 20.4 ± 2.6 ig/g to Zn, 978.6 ± 2.2 ig/g in soil; Cd, not detected to Zn, 42.2 ± 0.3 ig/g in liver; As and Ba, not detected to 47.6 ± 1.0 ig/g Zn in kidney. The inter matrices correlation coefficient values obtained for the heavy metals showed that the kidney of lizards would be more relevant in assessing soil levels of such heavy metals as As, Ba, Cd, Mn and Pb among others. Key words : Agama lizard, environmental pollution, soil, heavy metals, liver, kidney.

Assessment of chemical quality of three streams under different agricultural land systems in Obafemi Awolowo University Ile-Ife, Nigeria

The chemical quality of streams under three agricultural land systems viz Agbogbo Amuta, and Abagbooro catchments was investigated with the aim of determining the physicochemical parameters of the streams and to understand nutrients loss and water pollution levels of the three different agricultural land systems. Mechanized farming is practiced in the Amuta catchment while peasant farming and tree cropping is practiced in Agbogbo and Abagbooro catchment areas, respectively. Stream water samples were collected and analyzed biweekly for a period of 12 months. Physicochemical parameters were determined using standard analytical techniques, while levels of trace metals – Zn, Cu, Co, Cd, Pb, Cr, and Ni were determined after nitric acid digestion using an Atomic Absorption Spectrophotometer (AAS). The pH of streams from the three catchment areas varied from slight acidity (6.10) to alkaline (8.60). The electrical conductivity (EC) ranged between 0.07 and 0.10 mS cm−1, 0.02 and 0.07 mS cm−1, and 0.03 and 0.06 mS cm−1 for Amuta, Agbogbo, and Abagbooro catchments, respectively. The nutrients; (1.76 ± 0.41 mg L−1), (0.19 ± 0.05 mg L−1), (1.98 ± 1.07 mg L−1), and (3.93 ± 1.30 mg L−1) were highest in the Amuta stream and lowest in the Abagboro stream: (0.77 ± 0.34 mg L−1), (0.14 ± 0.03 mg L−1) (1.83 ± 1.03 mg L−1), and (2.78 ± 1.23 mg L−1). The mean concentrations of some trace metals: Mn (2.56 ± 0.25 mg L−1), Fe (0.34 ± 0.10 mg L−1), Co (0.10 ± 0.02 mg L−1), and Cr (0.21 ± 0.18 mg L−1) were highest in the Amuta catchment area, while the levels of cadmium and lead were not significantly different at p ≤ 0.05 in the three sampling areas. The study showed that nutrients loss and water pollution were highest in the stream from the Amuta catchment area compared to the Agbogbo and Abagdooro catchment areas. Levels of physicochemical parameters and some trace metals investigated in this study therefore depended on the type of agricultural inputs and practices in the three catchment areas.