Kinetic and isotherm studies on the adsorption–desorption of technical-grade endosulfan in loamy soils under Theobroma cacao L cultivation, Southwestern Nigeria

The fate of pesticides in soils is dependent on the adsorption–desorption kinetics, isotherms and soil types. Interactions of technical-grade endosulfan with top soils (top 0–15 cm) from CRIN, Igba and Sore Bale Theobroma cacao L farms in Southwestern Nigeria were studied using the OECD batch isotherm method. The soils were predominately basic (pH 7.1–8.33), while the orders of the total organic carbon (1.32–2.03%) and clay content (10.92–19.11%) were CRIN > Igba > Sore Bale and Igba > CRIN > Sore Bale, respectively. The adsorption of endosulfan was bi-continuous: initially rapid, followed by a slow process, with pseudo-equilibria and plateaus formed between 120 and 240 min. Endosulfan adsorption by soils was due to their greater affinity for organic matter than clay. The adsorption rates fitted better into a pseudo-second-order model (PSOM) than a pseudo-first-order model (PFOM), with the adsorption (kads) and desorption (kdes) rate constants for both isomers ranging from 7.60 × 10−3 to 11.52 × 10−3 min−1 and 1.39 × 10−3 to 3.42 × 10−3 min−1, respectively (i.e. kads > kdes), while kdes (β-isomer) > kdes (α-isomer) for PFOM, but k2_ads < k2_des for the two isomers in PSOM. Additionally, α-endosulfan was adsorptive, with the β-isomer more prone to leaching; both isomers were moderately leachable according to their FAO mobility rankings. The adsorption model did not fit well into a Langmuir isotherm (R2 ≤ 0.948); however, the desorption model did (R2 ≥ 0.991). Freundlich isotherm plots fitted better (R2 ≥ 0.992) and exhibited non-linear curves of types L and S for the adsorption and desorption processes, respectively. The adsorption/desorption coefficients (Kfads and Kfdes) and strengths of adsorption/desorption (1/nads and 1/ndes) for both isomers were from 1.33 ± 0.10 to 4.81 ± 0.18 μg1−1/n (mL)1/n g−1 and 0.503 to 1.402, respectively, in all soils, with Kfads < Kfdes and 1/nads < 1/ndes. Positive hysteresis was observed. CRIN exhibited the highest hysteresis index. The Kfom values were ≤127.14 ± 6.23 mL g−1, while the values of the standard free energy were ΔG0 = −5.11 to −14.05 kJ mol−1 K−1, depicting a spontaneous physisorption process, driven by van der Waals forces, among others. Endosulfan could easily be leached and contaminate the surface and groundwater owing to its faster PSOM desorption rate constant, but TOM and clay could be used as mitigants to reduce its mobility in soils as they have significant affinity for the pesticide

Disinfection of water with new chitosan-modified hybrid clay composite adsorbent

Hybrid clay composites were prepared from Kaolinite clay and Carica papaya seeds via modification with chitosan, Alum, NaOH, and ZnCl2 in different ratios, using solvothermal and surface modification techniques. Several composite adsorbents were prepared, and the most efficient of them for the removal of gram negative enteric bacteria was the hybrid clay composite that was surface-modified with chitosan, Ch-nHYCA1:5 (Chitosan: nHYCA = 1:5). This composite adsorbent had a maximum adsorption removal value of 4.07 × 106 cfu/mL for V. cholerae after 120 min, 1.95 × 106 cfu/mL for E. coli after ∼180 min and 3.25 × 106 cfu/mL for S. typhi after 270 min. The Brouers-Sotolongo model was found to better predict the maximum adsorption capacity (qmax) of Ch-nHYCA1:5 composite adsorbent for the removal of E. coli with a qmax of 103.07 mg/g (7.93 × 107 cfu/mL) and V. cholerae with a qmax of 154.18 mg/g (1.19 × 108 cfu/mL) while the Sips model best described S. typhi adsorption by Ch-nHYCA1:5 composite with an estimated qmax of 83.65 mg/g (6.43 × 107 cfu/mL). These efficiencies do far exceed the alert/action levels of ca. 500 cfu/mL in drinking water for these bacteria. The simplicity of the composite preparation process and the availability of raw materials used for its preparation underscore the potential of this low-cost chitosan-modified composite adsorbent (Ch-nHYCA1:5) for water treatment

Metal speciation in sediments from crude oil prospecting in the coastal area of Ondo State, Nigeria

Information obtainable from metal speciation is far more valuable with respect to bioavailability, toxicity and fate of metals than information from total metal data. Therefore, metal speciation on sediment to assess the bioavailability, fate and mobility of As, Cd, Cr, Fe, Mn, Ni, Pb, and V in the crude oil prospecting area of Ondo state Nigeria was carried out in this study.  Five operationally defined metals species: exchangeable specie, carbonate bound specie, iron/manganese bound specie, organic bound specie and the residual specie were obtained using sequential extraction method.  The concentrations, spreads and relative abundances of the species were used to assess their fate, mobility and toxicity potential.  The crude oil exploration site and the mouth of the estuary had the highest concentrations of these metals compared to other sites.  The high risk species, exchangeable and the organic bound, were the most predominant in the crude oil exploration sites but their concentrations reduced away from these sites downstream.  The residual fraction which was least in the crude oil prospecting site was the most predominant in the farthest distant sites downstream.  There are indications of self-management of the metals in the costal system through favourable biogeochemical reactions that is partitioning the metals from the high risk species to the low risk ones and the non-toxic residual fraction.  It could however be concluded that the sediments from the crude oil prospecting area may serve as non-point sources of metal contaminant to the coastal system, they have higher metal bioavailability and higher toxicity risk potential than the other sites which should be curtained

Unlocking sustainable agricultural development in Africa via bio-nanofertilizer application - challenges, opportunities and prospects

A combination of rapid population growth, climate change, and environmental degradation have placed immense pressure on global food sources and increased food security concerns especially in developing economies like those of African countries. Notably, efforts to produce food for the rising human population have continued to burden arable lands across the globe, necessitating heavy use of chemical fertilizers to increase crop yield. While the widespread use of conventional fertilizers has indeed enhanced crop productivity, its sustainability is threatened by rapid soil degradation and rising environmental concerns resulting from chemical compound accumulation across several ecosystems. The invention of nanotechnology, which is the synthesis and manipulation of materials at the nanometer (1 to 100 nm) range, promises potential solutions to these agricultural sustainability challenges. Specifically, theoretical, and experimental research on nanofertilizers have highlighted significant potential for their employment in sustainable farming practices. The current review examines the benefits conferred by the delivery of nutrients to plants at the nanoscale, outlining the progress, challenges, and opportunities for adopting this emerging technology by African countries, and highlighting future perspectives and areas of possible collaborations globally