Kinetic field dissipation and fate of endosulfan after application on theobroma cacao farm in tropical Southwestern Nigeria

Endosulfan, 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano,2,4,3-benzodioxathiepin-3-oxide, is still a pesticide of choice for most cocoa farmers in Southwestern Nigeria, in spite of its persistence, bioaccumulative, toxicological properties, and restriction. A single treatment of 1.4 kg ai/ha (0.5% ai) of technical grade endosulfan (Thiodan, 35EC) was applied to 0.0227 ha of cultivated Theobroma cacao L. (Cocoa) farm at the Cocoa Research Institute of Nigeria (CRIN). Levels of parent endosulfan (α-, β-endosulfan) and major metabolite (endosulfan sulfate) were determined in vegetation and surrounding matrices at days 0, 7, 14, 21, 28, 42, and 60 using GC-MS. Their kinetic variables were determined. Order of ∑endosulfan distribution at day 0 was dry foliage > fresh foliage > bark > pods > soil (0–15 cm). No residual endosulfan was found in cocoa seeds and subsurface soil (15–30 cm). Low residual levels in pods on day 0 may be due to endogenous enzymatic breakdown, with α-isomer more susceptible and α/β-endosulfan ratio being 0.90. Fell dry foliage as mulch was predominantly the receiving matrix for non-target endosulfan sprayed. Volatilization was key in endosulfan dissipation between days 0 and 7 from foliage surfaces (> 60% loss), while dissipation trend was bi-phasic and tri-phasic for vegetation and soil, respectively. ∑endosulfan loss at terminal day ranged between 40.60% (topsoil) and 99.47% (fresh foliage). Iteratively computed half-lives (DT′ 50 ) ranged from 6.48 to 30.13 days for ∑endosulfan in vegetation. Endosulfan was moderately persistent in pods—a potential source for cross contamination of seeds during harvest. Iteratively determined DT′ 50 and initial-final day DT 50 are highly correlated (R = 0.9525; n = 28) and no significant difference (P = 0.05) for both methods

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

Evaluation of pyrene sorption–desorption on tropical soils

Sorption–desorption processes control soil-pollutant interactions. These processes determine the extent of pyrene transport in soils. Understanding sorption characteristics of pyrene is necessary in ascertaining its fate in soil. Laboratory batch experiments were conducted to study the sorptions–desorption of pyrene on eight soils from varying tropical agro-ecological zones (AEZs). The results showed that pyrene sorptions equilibria were attained within 720 min. Solution pH had a reciprocal effect on pyrene sorptions. Sorption was exothermic and increased with pyrene concentration in solution. The quantities of pyrene sorbed by each soil as well as the hysteresis were proportional to the percentage organic matter, and to some degree, the clay mineralogy. Sorption isotherms showed distributed reactivity involving several linear and non-linear isotherms. The present investigation showed that pyrene is likely to be more available to biota and reach the aquifer faster in low organic matter soils than those with relatively higher organic matter and more so in warmer climes

Equilibrium and Kinetics Studies of the Adsorption of Basic Dyes onto PVOH Facilely Intercalated Kaolinite - A Comparative Study of Adsorption Efficiency

Communication in Physical Sciences, 2021, 7(4): 331-347 Authors: Chigbundu C. Emmanuel* and Adebowale O. Kayode Received:29 September 2021/Accepted 23 November 2021 Most basic dyes are known for their toxic impact on the environment, especially in the aquatic ecosystem. . Unfortunately, consistent discharge of dye containing wastes into most water bodies has generated serious challenges, which can only be solved through consistent research approaches. his study is designed to compare the adsorption capacities of purified (PRK) and polyvinyl alcohol (PVOH) intercalated raw kaolinite (PIK) for the adsorption of some basic dyes from an aqueous solution. Scanning electron microscope (SEM) with energy dispersive X-ray (EDX), Fourier-transform infrared (FTIR) Spectroscopy and X-ray diffractometer (XRD) were used to verify changes in morphology, surface functional groups and crystal lattice sequence adjustment in PIK adsorbent. Cation Exchange Capacity (CEC) and Point of Zero Charge (PZC) of both adsorbents were determined by methylene blue adsorption and salt addition technique, respectively. The adsorption characteristics of both adsorbents were investigated under various conditions such as varying adsorbent dosages, period of contact, temperature and pH. Thermodynamic parameters were used to evaluate the effect of temperature on the adsorption process, while non-linear regressions were used to fit the experimental data to various adsorption and kinetic models. UV-visible spectrometer was used to determine the absorbance of dyes left in the solution un-adsorbed throughout the experimental study.&nbsp; The morphology of PIK revealed a compacted structure with pores, while the crystal lattice adjustment of PIK showed basal plane contraction to 4.06Å when compared with PRK respectively. Surface functionality study revealed several peaks such as CH3 and CH2 assigned to 2893 and 2990 cm-1 respectively on PIK but absent on the FTIR graph of PRK.&nbsp; The adsorption isotherm model showed that PIK was twice efficient for the uptake of BR2 and BG5 compared to PRK. The Elovich model equation suitably described the adsorption kinetics while the thermodynamic parameters revealed that the adsorption was spontaneous and endothermic. In comparison to other desorption agents, acetic acid was found to be a good desorption agent

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

Mechanism on the sorption of heavy metals from binary-solution by a low cost montmorillonite and its desorption potential

The potential of a low-cost Nigerian montmorillonite for the adsorption of Ni(II) and Mn(II) ions from aqueous solution was investigated by batch mode. XRD, SEM and BET analysis were used to characterize the adsorbent. The experiments were performed as a function of pH, particle size, adsorbent dose, initial metal ion concentration, contact time, ligands and temperature. The process was found to be dependent on all the parameters investigated, with a pH of 6.0 obtained for optimum removal of both metal ions. The Langmuir monolayer adsorption capacity of 166.67 and 142.86 mg/g was obtained for Ni(II) and Mn(II) ions respectively. The Freundlich isotherm gave the best fit to the experimental data than the Langmuir, Temkin and Dubinin–Radushkevich isotherms. The scatchard plot analysis indicated the existence of more than one type of active site on the montmorillonite which corroborates the good fit of the Freundlich model. The pseudo-first order, pseudo-second order and intraparticle diffusion models were applied to the kinetic data. The best fit was achieved with the pseudo-first order model and the existence of intraparticle diffusion mechanism was indicated. Thermodynamic studies showed an endothermic, dissociative, spontaneous and a physical adsorption process between the metal ions and the montmorillonite. Desorption studies revealed over 90% desorption of both metal ions from the metal loaded adsorbent

Triacylglycerols in some underutilised tropical seed oils I. Systematic studies of ten oils

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 , Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal