This study was conducted to evaluate the levels and seasonal variations of some organochlorine pesticides (OCPs) in the cultivated land of Oke-Osun farm settlement, Osogbo, Nigeria. A field sampling programme was conducted in the rainy and dry seasons for 4 months each resulting in the analysis of a total of 40 samples. Soil samples collected at 20-m intervals were air-dried to a constant weight, sieved through a mesh of 2.0-mm pore size and selected by coning and quartering method. Solid-liquid extraction was used to extract OCPs from the soil. Qualitative identifications and quantitative evaluation of the OCPs were carried out with the aid of a Perkin Elmer gas chromatograph coupled with electron capture detector. Seasonal mean ranges of OCPs in soil (μg/kg) were 13.09 ± 21.66 β-BHC-42.01 ± 17.50 p, p(')-DDT in rainy season and 30.74 ± 17.38 α-BHC-82.88 ± 32.24 p, p(')-DDT in the dry season. The results obtained from this study revealed that agricultural soil samples of Oke-Osun farm settlement were contaminated with persistent organochlorine pesticides mainly as a result of their applications by farmers. Higher levels of OCPs were obtained for dry season than the rainy season. There were indications from this study that pesticides that have deleterious health effects on humans previously placed under legal restrictions by regulatory agencies were still being used by the farmers of Oke-Osun farm settlement and this gives cause for environmental concern.

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Organochlorine pesticides (OCPs) are persistent pesticides whose usage have been banned or restricted worldwide and the presence of its residues in vegetables could affect its nutritional quality as well cause adverse health effects. This study quantified the OCP residue levels in commonly grown and consumed vegetables and assessed the carcinogenic and non-carcinogenic health risks from the consumption of the contaminated vegetables. The OCP residues levels in the extract from the vegetables were determined using a Gas Chromatograph coupled with Electron Capture Detector (GC-ECD). Health risk estimates were analysed using Estimated Average Daily Intake (EADI), Hazard Index (HI), and Hazard Ratio (HR) for children (16.7 kg) and adults (60 kg) weight categories. The residue analysis indicated that amaranths had the highest mean concentration of endrin aldehyde (2.987 AE 0.391 mg kg-1) and endosulfan sulfate (0.661 AE 0.280 mg kg-1), while in fluted pumpkin, the highest mean concentrations were endrin aldehyde (3.491 AE 0.376 mg kg-1) and endosulfan sulfate (2.775 AE 0.644 mg kg-1). The percentage of the detected OCP residues above Maximum Residue Limits (MRLs) ranged from 25% to 100% for both vegetables. Non-carcinogenic health risk estimates for the children weight category showed that aldrin, dieldrin, endrin, endrin aldehyde, and heptachlor detected in both vegetables had HI > 1. While for adults, only aldrin, dieldrin, endrin, and endrin aldehyde revealed non-carcinogenic effect in both vegetables. Human risk estimations for the carcinogenic health effect for the two vegetables showed that aldrin and dieldrin could pose carcinogenic health risks to adult, while aldrin, dieldrin, heptachlor and heptachlor epoxide could pose carcinogenic health risks to children. The results revealed both non-carcinogenic and carcinogenic health risks for the consumers of the contaminated vegetables from the selected locations in Southwestern Nigeria.

Electrocatalytic behaviour of graphene oxide (GO), iron(iii) oxide (Fe2O3) and Prussian blue (PB) nanoparticles towards nitrite (NO2−) and nitric oxide (NO) oxidation was investigated on a platinum modified electrode.