Isaac A. Ololade

Sorption of Glyphosate on Soil Components: The Roles of Metal Oxides and Organic Materials

Predicting the behavior, fate, and transport potential of a herbicide in any soil involves understanding the sorption characteristics. The sorption characteristics of glyphosate (GPS) on soil and their main components were investigated, indicating that the mineral phase is more important than the organic carbon in adsorption of GPS. Sorption isotherms were determined from each component using the batch equilibrium method at various concentrations (5, 10, 15, 20, 25, and 30 mg L−1) and sorption affinity of GPS was approximated by the Freundlich equation. The sorption strength K f [mg kg−1 (L mg−1)−n] across the various components ranged from 2.1–134.9 while the organic carbon-normalized Freundlich sorption capacity values, K foc, ranged from 1.28–3.53 mg kg−1-OC/(mg L−1)n. Infrared Fourier transform spectroscopy (FTIR) of the components showed significant structural differences. The results suggest that the presence of the oxides and hydroxides iron, in particular in soil solutions, enhanced GPS adsorption. They also suggest that reduction in OC% due to various treatments may enhance the remobilization of GPS into the aqueous phase (i.e., groundwater), though at different rates. Comparatively, contribution of surface area to the adsorption of GPS on the various components proved more significant than contents of organic carbon.

Equilibrium isotherm analysis of the sorption of congo red by palm kernel coat

The ability of Palm Kernel Coat (PKC), a waste agricultural product, in the abstraction of Congo Red (CR), an anionic dye, from aqueous solution was studied. The effects of sorbent dose and temperature were studied using batch sorption system. Isotherm experiments were conducted and the data obtained were fitted with different equilibrium isotherm equations namely, Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin, Harkins-Jura and Halsey isotherm equations. The Langmuir isotherm equation gave the best description of the sorption process and the maximum saturated monolayer sorption capacity of the PKC for CR was 79.37 mg g−1. Harkins-Jura isotherm equation gave the poorest description of the sorption process. The linear form of the Langmuir equation was used to analyze the data obtained when the sorbent dosage was optimized by method of continuous variation. The results obtained showed that the equilibrium monolayer sorption capacity, qm, of the PKC for CR decreased (79.37–17.07 mg g−1) with an increase in sorbent dosage. The relationship between the dimensionless parameter, KR, and initial concentration, Co, showed that the sorption of CR was favored at higher initial dye concentration and PKC dosages than the lower ones. The thermodynamic parameters, such as change in the free energy, the enthalpy and the entropy, were also evaluated. The thermodynamic analysis showed that the sorption is spontaneous and exothermic.

Surveillance and source diagnostic investigation of hydrocarbon residues in sediments

The nature and seasonal distribution of hydrocarbons were studied in Ondo coastal region in Western Nigeria. The petroleum hydrocarbons were screened by gas chromatography with flame ionization detector (GC/FID) and gas chromatography-mass spectrometry (GC-MS). Complex series of compounds were identified. The overall molecular compositions obtained were characteristic of petrogenic origin with very little biogenic input. The concentrations of two important polycyclic aromatic hydrocarbons (PAHs); phenanthrene and anthracene exceeded the threshold level where adverse effects on biota would occasionally occur; a conclusion suggested to be clarified by site-specific studies on resident organisms. The study is useful for ecological risk assessment in the context of contaminant input, nature, pattern and trend.

Influence of diffuse and chronic metal pollution in water and sediments on edible seafoods within Ondo oil-polluted coastal region, Nigeria.

The bioconcentration levels of 3 non-essential elements (Pb, Cd and Ni) have been investigated in three different seafoods; Fish (Tilapia zilli), Crab (Callinectes sapidus) and periwinkle (Littorina littorea), to investigate the ecosystem health status in Ondo oil-polluted coastal region, Nigeria. The seafood samples were chosen based on their popularity as a food source and the potential of the species to contain high levels of metals based on past research results. Metal concentrations in the biota showed marked interspecific differences with C. sapidus recording the highest concentrations of all the metals. The bioconcentration factor (BCF) showed that C. sapidus and T. zilli have the greatest potential to concentrate Cd (BCF = 3–10) and Pb (BCF = 11–84) respectively. Lead uptake from both water and sediment (BCF ≈ BSAF: 0.003–0.018) were abysmally low in L. littorea as compared with other organisms. The high concentrations of Pb in fish species, effective bioaccumulation of Cd in species of crab and periwinkles, as well as very high BSAF of Ni found in species of crab indicated a strong influence from anthropogenic pollutant source on the biotic community. Oil pollution appears to be a major source of bioavailable metal contaminants for the selected biota. The study shows that C. sapidus and L. littorea can effectively compartmentalize potentially toxic metals such as Cd, Pb and Ni within their tissues. In terms of toxicity, C. sapidus had Cd concentrations greater than the 3,000 ng/g limit set by the Commission of the European Communities while Pb concentration exceeded their limits in both C. sapidus and T. zilli. All levels of Ni were below the U.S. Food and Drug Administration action levels for these metals in fish, crustaceans and shellfish. The study revealed anthropogenic enrichment of the metals studied which can possibly pose potential threats to the ecology of the area.

Influence of organic carbon and metal oxide phases on sorption of 2,4,6-trichlorobenzoic acid under oxic and anoxic conditions

Chlorobenzoic acids represent crucial recalcitrant metabolites in the environment; thus, the influence of soil components on the sorption of 2,4,6-trichlorobenzoic acid (TCB) under oxic and anoxic conditions was studied. The surficial physiognomies of untreated and isolated soil samples were studied using FTIR, XRD, specific surface area, and PZC determination. The roles of redox potential, dissolved organic carbon (DOC), and pH, particularly under anoxic condition, were appraised. Batch equilibrium adsorption studies on soils of variable Fe/Mn oxides and organic carbon showed that adsorption was low across all components (log Koc = 0.82–3.10 Lg−1). The sorption of 2,4,6-TCB was well described by the pseudo second-order kinetic model. The fluctuation of both redox potential and pH during anoxic experiment had a negative impact on the sorption, partitioning, and the oxidation of organic matter. Linear relationships were observed for Kd with both soil total organic carbon (TOC) and surface area (SA). The results showed the existence of DOC-mediated sorption of 2,4,6-TCB which seems to be enhanced at lower pH. The reductive dissolution, particularly of iron compounds, possibly impeded sorption of 2,4,6-TCB under anoxic condition. It could be inferred that habitats dominated by fluctuating oxygen concentrations are best suited for the development of environmental conditions capable of mineralizing 2,4,6-TCB and similar xenobiotics.

Influence of Soil Components on Sorption of Atrazine under Aerobic and Anoxic Conditions

The adsorption of atrazine onto untreated and soils when oxides and hydroxides of Fe, Mn, and organic matter have been reduced was studied under aerobic and anoxic conditions. The Freundlich model appeared to fit the isotherm data better than the Langmuir model, while second-order reaction rates were best fit for atrazine in the aqueous phase. Simple regression analysis indicated that the Fe content of the geosorbents is the most important primary factor controlling the sorption processes of atrazine (r2 = 0.947). Similar sorption capacity of atrazine by geosorbents but different isotherm nonlinearity indicated different sorption domains due to structural modifications and hydrophobicity. The sample treated to significantly remove organic carbon exhibited the greatest organic carbon–normalized sorption capacity. There existed apparent sorption–desorption hysteresis for each sorbent–sorbate system with desorption being more significant under anoxic conditions. The study suggests that, in remediation exercise, in situ redox barriers such as Fe2+-enriched zones can be created by stimulation of Fe3+ through chemical reduction. This study observed that soil predominated by Fe and with low OC content is probably a more effective sorbent for atrazine, implying that atrazine applied to such soils is less likely to leach into groundwater.