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

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

SAPK: A Novel Composite Resin for Water Treatment with Very High Zn²⁺, Cd²⁺, and Pb²⁺ Adsorption Capacity

A new sulfonated aniline-modified poly­(vinyl alcohol)/K-feldspar (SAPK) composite was prepared. The cation-exchange capacity of the composite was found to be 5 times that of neat feldspar. The specific surface area and point of zero charge also changed significantly upon modification, from 15.6 ± 0.1 m²/g and 2.20 (K-feldspar) to 73.6 ± 0.3 m²/g and 1.91 (SAPK). Zn²⁺, Cd²⁺, and Pb²⁺ adsorption was found to be largely independent of pH, and the metal adsorption rate on SAPK was higher than that on neat feldspar. This particularly applies to the initial adsorption rates. The adsorption process involves both film and pore diffusion; film diffusion initially controls the adsorption. The Freundlich and Langmuir models were found to fit metal-ion adsorption on SAPK most accurately. Adsorption on neat feldspar was best fitted with a Langmuir model, indicating the formation of adsorbate monolayers. Both pure feldspar and SAPK showed better selectivity for Pb²⁺ than for Cd²⁺ or Zn²⁺

Microscale scavenging of pentachlorophenol in water using amine and tripolyphosphate-grafted SBA-15 silica: Batch and modeling studies

Mesoporous silica SBA-15 meets most criteria for selection of water treatment adsorbents such as high specific surface area, large pore-size, chemical inertness, repertory of surface functional groups, good thermal stability, selectivity, regenerability, and low cost of manufacture. However, its use for water treatment is still largely unexplored. SBA-15 and its functionalized derivatives of aminopropyltriethoxysilane (SA) and tripolyphosphate (ST) were synthesized, characterized, and used to investigate pentachlorophenol (PCP) removal from aqueous solutions. Functionalization improved SBA-15 capacity for PCP removal from solution in accordance with the trend SBA-15 < ST < SA. Sorption rate experiments data fit the Lagergren pseudo-second order kinetics model. Intra-particle diffusion indicated that the sorption is controlled by two mechanisms: intra-particle and equilibrium diffusion. Adsorptive pore-filling and electrostatic interactions were implicated in the removal of PCP from solution. Electrostatic interaction led to ≥75% increase in sorption upon functionalization. The equilibrium sorption data of the PCP on these mesoporous materials fits the Freundlich isotherm. Desorption hysteresis was low for the pristine SBA-15, but the functionalized SBA-15 materials showed higher hysteresis. The results imply that functionalized SBA-15 sorbents are promising materials for microscale scavenging of PCP in solution