Differences in the sorption kinetics of various non-ionisable pesticides in a limited number of agricultural soils from the Mediterranean basin

Soil colloids can significantly enhance spreading of polybromodiphenyl ethers in groundwater by serving as an effective carrier

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites.

A comparative study of the adsorption and desorption process of selected natural Albanian clays toward methomyl and dimethoate pesticides

Natural soil components, such as clays, have recently piqued interest because of their potential as pesticide adsorbents. This research work sheds light on the possibility of the application of natural Albanian clays as adsorbents for methomyl and dimethoate pesticides from aqueous solutions. Natural Albanian clays from the regions of Brari, Currila, Dardha, and Prrenjasi were employed in the study and were characterized by granulometric analysis and powder X-ray diffraction. Each clay's adsorption capacity and desorption behavior were investigated toward the chosen pesticides. Within 48 h of contact time, methomyl and dimethoate solutions with different concentrations were evaluated at 25 °C to see how the insecticide concentration affected the adsorption & desorption processes for each natural clay type. The experimental data were fitted to Freundlich, Temkin and Dubinin-Radushkevich isotherm like functions and the results showed the best correlation on Freundlich like adsorption isotherm for almost all cases. Brari clay performed better adsorptive properties toward dimethoate, followed by Dardha, Currila and Prrenjasi clays. The dimethoate adsorbed quantities varied from 0.250 mg/g for C = 0.200 g/L to 0.822 mg/g for C = 0.500 g/L. In comparison to Dardha and Prrenjasi clays, Brari and Currila clays exhibit longer saturation times and improved methomyl retention. In the first 2 h of contact, 96.5% of methomyl and 81% of dimethoate were desorbed from Brari clay. The adsorption process was also investigated employing pseudo first-order and pseudo second-order kinetic models, with the results indicating that all clay-pesticide systems studied demonstrated second-order kinetic behavior. Based on the studied desorption process, it is possible to impregnate clays with various insecticides in agriculture and completely control the quantities of the insecticide released.

Sorption and desorption of naphthenic acids on reclamation materials: Mechanisms and selectivity of naphthenic acids from oil sands process water

This study investigated the application of materials peat-mineral mix (PT) and Pleistocene fluvial sands from different location (PF-1 and PF-2) obtained from surface mining of oil sands as sorbents of naphthenic acids (NAs) from oil sands process water (OSPW). To understand the sorption properties and mechanisms of NAs in the materials, sorption and desorption studies were performed using decanoic acid (DA) and 5-phenylvaleric acid (PVA). Additionally, the removal efficiency was evaluated using real OSPW to understand the effect of NA structure on sorption. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Langmuir isotherm best fitted the equilibrium data. Maximum sorption capacities for DA and PVA were, respectively, 16.8 × 10³ and 10⁴ mg/kg for PT, 142.9 and 81.3 mg/kg for PF-1, and 600 and 476.2 mg/kg for PF-2. Hydrophobic interactions, hydrogen bonding, and π-π interaction were the main sorption mechanisms. Desorption of model compounds from post-sorption materials was not observed for 14 days. The removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising sorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Sorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important sorption mechanism. The results suggest that some mobility of NAs is expected to take place if the reclamation materials come in contact with OSPW, which might occur in an oil sands reclamation landscape.

Those That Remain: Sorption/Desorption Behaviour and Kinetics of the Neonicotinoids Still in Use

In January 2023, the derogation loophole was closed on “emergency authorisations” for the use of three out of five neonicotinoids in all EU states. In this study, we analysed the sorption/desorption behaviour and kinetic parameters of acetamiprid and thiacloprid, the two neonicotinoids that are still approved for use, either regularly or under emergency authorisations in the EU, and widely used worldwide. Sorption and desorption curves in four soils with different organic matter content were analysed using four kinetic models, namely, Lagergren’s pseudo first-order model, two-site model (TSM), Weber–Morris intraparticle diffusion model and Elovich’s model. Kinetic parameters were correlated to soil physico-chemical characteristics. To determine the mutual influence of soil characteristics and sorption/desorption parameters in the analysed soils, a factor analysis based on principal component analysis (PCA) was performed. Even though the two insecticides are very similar in size and chemical structure, the results showed different sorption/desorption kinetics. The model that best fits the experimental data was TSM. Thiacloprid showed a more rapid sorption compared to acetamiprid, and, in all soils, a higher proportion sorbed at equilibrium. Intra-particle diffusion seemed to be a relevant process in acetamiprid sorption, but not for thiacloprid. Desorption results showed that acetamiprid is more easily and more thoroughly desorbed than thiacloprid, in all soils. The kinetic behaviour differences stem from variations in molecular structure, causing disparate water solubility, lipophilicity, and acid–base properties.

Rice Straw as Green Waste in a HTiO2@AC/SiO2 Nanocomposite Synthesized as an Adsorbent and Photocatalytic Material for Chlorpyrifos Removal from Aqueous Solution

A nano-HTiO2@activated carbon-amorphous silica nanocomposite catalyst (HTiO2@AC/SiO2) is utilized to photo breakdown catalytically and adsorb chlorpyrifos insecticide. SEM, TEM, and X-ray diffraction were used to examine HTiO2@AC/SiO2, synthesized through sol–gel synthesis. With an average size of 7–9 nm, the crystallized form of HTiO2 is the most common form found. At varied pH, catalyst doses, agitation speed, initial pesticide concentrations, contact periods, and temperatures, HTiO2@AC/SiO2 was examined for efficiency under visible light and in darkness. Because of the pseudo-second-order kinetics observed for chlorpyrifos, chemisorption is believed to dominate the adsorption process, as indicated by an estimated activation energy of 182.769 kJ/mol, which indicates that chemisorption dominates the adsorption process in this study. The maximal adsorption capacity of chlorpyrifos is 462.6 mg g−1, according to the Langmuir isotherms, which infer this value. When exposed to visible light, the adsorption capacity of HTiO2@AC/SiO2 increased somewhat as the temperature rose (283 k 323 k 373 k), indicating an exothermic change in Gibbs free energy during the process (−1.8 kJ/mol), enthalpy change (−6.02 kJ/mol), and entropy change (0.014 J/mol K), respectively, at 298.15 K. Negative (ΔS) describes a process with decreased unpredictability and suggests spontaneous adsorption. HTiO2@AC/SiO2 may be a promising material.

Ageing of copper, zinc and synthetic pesticides in particle-size and chemical fractions of agricultural soils

The transformation and mobility of heavy metals and synthetic pesticides in soil depend on ageing, involving their chemical and physical distributions among soil fractions over time. Heavy metals and synthetic pesticides often co-occur in soil, although their ageing is usually evaluated separately and in bulk soil. Here, contrasting vineyard and crop soils were spiked with copper (Cu; 700 mg kg^-1) and zinc (Zn; 200 mg kg^-1) a and/or synthetic pesticides (5 mg kg^-1), i.e., the fungicide metalaxyl (MTY) and herbicide S-metolachlor (SMET), to evaluate within 200 days their distribution among soil physical and chemical fractions. More than 90% of MTY and SMET in soil was released into the water phase, even 200 days after spiking. This emphasizes the potential mobilization of MTY and SMET from the soil following field application. MTY, SMET, Cu and Zn were associated mainly with the silt fraction and to a lesser extent (<30%) with the sand and clay fractions. Overall, the ageing of MTY, SMET, Cu and Zn in agricultural soil was affected mainly by the soil type and sterilization and only to a minor extent by their co-occurrence. Sorption controlled the dissipation of MTY and SMET in soil, while biodegradation contributed to less than 10%. A large fraction (37 ± 2%) of Cu was associated with Fe oxides after 200 days of ageing, while Zn was found (33 ± 2%) in the residual soil fraction. The silt fraction of the nonsterile vineyard soil became enriched in ⁶⁵Cu over time (Δδ⁶⁵Cu = 0.25 ± 0.07‰), whereas the clay fraction was depleted in ⁶⁵Cu (Δδ⁶⁵Cu = -0.20 ± 0.07‰). Cu isotope fractionation mirrored the Cu distribution in soil chemical fractions, suggesting that Cu stable isotopes may help to follow-up Cu ageing. In contrast, no significant Zn isotope fractionation was observed among soil experiments or over time. Overall, our study emphasizes the variability in ageing of synthetic pesticides and heavy metals co-occurring in agricultural soils and their interplay in physical and chemical fractions of the soil.

Removing the Oxamyl from Aqueous Solution by a Green Synthesized HTiO2@AC/SiO2 Nanocomposite: Combined Effects of Adsorption and Photocatalysis

The photocatalytic degradation and adsorption of the oxamyl pesticide utilizing a nano-HTiO2@activated carbon-amorphous silica nanocomposite catalyst (HTiO2@AC/SiO2). Sol-gel Synthesis was used to produce HTiO2@AC/SiO2, which was examined using Scanning Electron Microscopy, Transmission Electron Microscopy, and an X-ray diffractometer. The analyses confirmed that HTiO2 is mainly present in its crystalline form at a size of 7–9 nm. The efficiency of HTiO2@AC/SiO2 was assessed at various pHs, catalyst doses, agitating intensities, initial pesticide concentrations, contact times, and temperatures under visible light and in darkness. Oxamyl adsorption kinetics followed a pseudo-second-order kinetic model, suggesting that the adsorption process is dominated by chemisorption, as supported by a calculated activation energy of −182.769 kJ/mol. The oxamyl adsorption is compatible with Langmuir and Freundlich isotherms, suggesting a maximum adsorption capacity of 312.76 mg g−1. The adsorption capacity increased slightly with increasing temperature (283 K < 323 K < 373 K), suggesting an exothermic process with the Gibbs free energy change ΔG, enthalpy change ΔH, and entropy change ΔS°, being –3.17 kJ/mol, −8.85 kJ/mol, and −0.019 J/mol K, respectively, at 310 K for HTiO2@AC/SiO2 under visible light. This indicates spontaneous adsorption, and negative (ΔS) explain a decreased randomness process. HTiO2@AC/SiO2 would be a promising material.

Adsorption behaviours and transfer simulation of levofloxacin in silty clay

Fluoroquinolone antibiotics in soil can cause serious antibiotic pollution. Adsorption is the main factor that influences their destination and transport of antibiotics. Therefore, research on the behaviour of antibiotics once they reach the soil environment is meaningful to design appropriate measures to reduce their potential risks. This research took levofloxacin (LVFX) as the research object and used a static adsorption experiment to study the adsorption behaviour of the vadose zone of silty clay on the North China Plain. The results showed that LVFX had high retention in silty clay, with an average adsorption ratio of more than 90%. Adsorption of LVFX on silty clay reached equilibrium in 24 h with an adsorption amount of 93.5 mg/kg at an initial LVFX concentration of 10 mg/L. Acidity, cations and soil organic matter could affect the adsorption of LVFX, with adsorption variation ratio of 3.3%, 3.4% and 0.6%, respectively. In addition, numerical simulation with Hydrus-1D was utilized, and the results show that LVFX may infiltrate into underground water through silty clay after 28 days and completely penetrate in 100 days.

Mechanisms by which different polar fractions of dissolved organic matter affect sorption of the herbicide MCPA in ferralsol

Exogenous dissolved organic matter (DOM) modifies the sorption of 4-chloro-2-methylphenoxyacetic acid (MCPA, a polar herbicide) in soil. However, how the chemodiversity and diverse fractions of DOM affect MCPA sorption is still unknown. Here, DOM was extracted from compost and rice straw; the structure-activity correlations between DOM chemodiversity and their effects on MCPA sorption were investigated by redundancy analysis. Moreover, the mechanism involved was explored by spectroscopic techniques, microbeam and modeling. DOM mainly affected MCPA sorption by altering soil surface properties and MCPA complexed form. Hydrophobic neutral (HON) and acid insoluble matter (AIM) were the fractions of DOM that most inhibited MCPA sorption through soil pore blockage, and were related to the humic-like substances with high aromaticity and large molecular weight. The hydrophobic acid fraction (HOA) only showed an intermediate inhibition on the sorption, although the largest competitive sorption occurred. This was because HOA contained abundant aromatic acid and polar groups with moderate polarity. Thus, the reduced effect caused by competitive sorption was partly compensated by the greatest co-sorption by HOA. The hydrophilic matter (HIM) had the weakest inhibition on MCPA sorption, because this fraction was rich in simple sugars, poly- and oligosaccharides, but lacked aryl groups. The results will aid in the risk assessments and prevention of MCPA in DOM-introduced soil.