Kinetic and thermodynamic studies on partitioning of polychlorinated biphenyls (PCBs) between aqueous solution and modeled individual soil particle grain sizes

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.

Adsorption and migration of sulfamethoxazole driven by suspended particulate matter in water body

The extensive use of antibiotics has led to significant antibiotic pollution in water bodies, and suspended particulate matter (SPM) is known to be a key carrier of antibiotics in rivers. In this work, the adsorption characteristics of sulfamethoxazole (SMX) on SPM was investigated through batch adsorption and annular flume experiments, and the MIKE 21 model was employed to simulate the migration of SMX and SPM. Results revealed that most SMX adsorption occurred rapidly within 20 min, and 80 % of the equilibrium adsorption capacity was reached. Multilayer adsorption was confirmed by Freundlich model, and adsorption process was found to be spontaneous, endothermic, disordered, and the equilibrium adsorption amounts of SMX on SPM increased with salinity and organic matter increase. SMX desorption from SPM occurred upon the sudden changes of hydrodynamic states, nearly reaching the one-fifth of the SMX equilibrium adsorption amounts within 30 min and the re-adsorption of SMX on SPM would occur with water remained stationary or the re-disturbance time prolonged. The dynamic adsorption process of SMX related with the physicochemical property changes of SPM, which was contributed to the hydrogen bonds, π-π interactions, surface complexation, significantly influenced by the pore filling at the macropore and mesopore scales. The MIKE 21 simulations confirmed hydrodynamic states as the primary factors affecting the migration of SMX and SPM. SMX concentrations in the water would decrease in the presence of SPM, leading to the slower downstream migration of SMX.

Preparation of Composites Derived from Modified Loess/Chitosan and Its Adsorption Performance for Methyl Orange

A modified loess/chitosan composite (ML@CS) was prepared via solution. The microstructure and physicochemical properties of ML@CS were characterised via scanning electron microscope (SEM), Zeta potential, X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), and thermogravimetric analysis (TGA). An aqueous solution of methyl orange (MO) was used as simulated wastewater from which the influence of the initial concentration and pH of MO, the dosage amount and regeneration performance of ML@CS, adsorption temperature, and time on the adsorption effect of MO were systematically investigated. The adsorption kinetics, isothermal adsorption, and adsorption mechanism were also analysed. The results indicate that ML@CS had a good adsorption effect on MO. When the initial concentration of MO was 200 mg/L, pH was 5.0, and ML@CS dosage was 1.0 g/L, the adsorption equilibrium could be reached within 180 min at room temperature, and the equilibrium adsorption capacity and removal rate reached 199.52 mg/g and 99.75%, respectively. After five adsorption-desorption cycles, the MO removal rate remained above 82%. The adsorption behaviour of ML@CS for MO conforms to the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model. The spontaneous exothermic process was mainly controlled by monolayer chemical adsorption and the physical adsorption only played an auxiliary role. ML@CS efficiently adsorbed MO in water and can be used as a high-efficiency, low-cost adsorbent for printing and dyeing wastewater treatment.

Contamination Status, Environmental Factor and Risk Assessment of Polychlorinated Biphenyls and Hexachlorobutadiene in Greenhouse and Open-Field Agricultural Soils across China

With the popularization and high-intensity utilization of greenhouse cultivation for crops growth, the pollution of greenhouse soils has been of concern. Therefore, a national-scale survey was conducted to investigate the contamination status, sources, influence factors and the risks of polychlorinated biphenyls (PCBs) and hexachlorobutadiene (HCBD) in greenhouse and nearby open-field soils. Contents of PCBs ranged from 10-6). This study provided a full insight on the contamination status and risks of PCBs and HCBD when guiding greenhouse agriculture activities.

The Impact of Solution Ionic Strength, Hardness, and pH on the Sorption Efficiency of Polychlorinated Biphenyls in Magnetic Nanocomposite Microparticle (MNM) Gels

Environmental conditions of groundwater and surface water greatly vary as a function of location. Factors such as ionic strength, water hardness, and solution pH can change the physical and chemical properties of the nanocomposites used in remediation and the pollutants of interest. In this work, magnetic nanocomposite microparticle (MNM) gels are used as sorbents for remediation of PCB 126 as model organic contaminant. Three MNM systems are used: curcumin multiacrylate MNMs (CMA MNMs), quercetin multiacrylate MNMs (QMA MNMs), and polyethylene glycol-400-dimethacrylate MNMs (PEG MNMs). The effect of ionic strength, water hardness, and pH were studied on the sorption efficiency of the MNMs for PCB 126 by performing equilibrium binding studies. It is seen that the ionic strength and water hardness have a minimal effect on the MNM gel system sorption of PCB 126. However, a decrease in binding was observed when the pH increased from 6.5 to 8.5, attributed to anion-π interactions between the buffer ions in solution and the PCB molecules as well as with the aromatic rings of the MNM gel systems. Overall, the results indicate that the developed MNM gels can be used as magnetic sorbents for polychlorinated biphenyls in groundwater and surface water remediation, provided that the solution pH is controlled.

Evaluating the fate and potential health risks of organochlorine pesticides and triclosan in soil, sediment, and water from Asa Dam River, Ilorin Kwara State, Nigeria

The quest for safe water due to exponential population growth and climate change has stressed the existing available water source. It is crucial to establish the present pollution level of the Asa River and the health risk it may pose to the people. Samples were collected along the Asa River, Ilorin, Kwara State, Nigeria, and treated using standard methods as stipulated by United States Environmental Protection Agency. The treated samples were analyzed and quantified for dieldrin, endrin, dichlorodiphenyltrichloroethane metabolites, mirex, hexachlorocyclohexane, hexachlorobenzene, and triclosan using the gas chromatography-mass spectrometry. The result showed that the levels of organochlorine pesticides (OCPs) ranged from 0.0045-0.947 μg/kg, 0.0036-0.093 μg/kg, and 0.001-0.007 μg/L in sediment, soil, and water samples, respectively. While the mean concentration of triclosan is 3.78 μg/kg, 2.995 μg/kg, and 0.064 μg/L in sediment, soil, and water samples, respectively. The levels of OCPs were lower than the limits in drinking water as set by World Health Organization and European Union. Health risk assessment for both children and adults was evaluated using non-carcinogenic and carcinogenic risk with the hazard quotient (HQ) and was found to be greater than unity (> 1) in children for the targeted OCPs. Associated cancer risk for OCPs ranged from low cancer risk to moderate risk for humans. The adverse ecological effects of OCPs showed to be very rare to occur and frequent effects may not likely occur except for HCH.

Assessment of an NDL-PCBs Sequestration Strategy in Soil Using Contrasted Carbonaceous Materials through In Vitro and Cucurbita pepo Assays

The present study aims to assess the respective efficiency of Biochars (BCs) and activated carbons (ACs) to limit PCB 101, 138, 153 and 180 transfer to plants. A set of 6 high carbon materials comprising 3 BCs and 3 ACs was tested and used to amend a soil at 2% rate. Then, the two most efficient carbonaceous materials were used as an amendment of an historically contaminated soil sampled in the St Cyprien vicinity (Loire, France). An environmental availability assessment was performed using the ISO/DIS 16751 Part A assay (n = 3). For the in vivo part, Cucurbita pepo were grown for 12 weeks. Significant decreases of transfer were found for both assays notably for powdered ACs (up to 98%). By contrast, significantly lower levels of transfer reduction were observed when BCs amendments were performed, ranging from 27 to 80% for environmental availability assessment and 0 to 36% for C. pepo. Reduction factors above 90% for the 2 selected materials were found from amended historically contaminated soils. Present results led to consider such a sequestering strategy as valuable to ensure plant production on non-dioxin-like polychlorobiphenyls (NDL-PCBs) contaminated soils.

Uptake of PCBs into sediment dwellers and trophic transfer in relation to sediment conditions in the Salish Sea

We examined uptake of polychlorinated biphenyls (PCBs) into various marine sediment feeders relative to physical and geochemical factors and transfer to higher trophic levels. PCBs exceeding Canadian Council Ministers of the Environment Guidelines by 6–55× were found in industrialized harbours and some near-outfall sediments, indicating ongoing land input. Sediment PCBs were correlated with organic flux and content. Tissue PCBs were >10× sediment PCBs in all samples and highest in Victoria Harbour infauna, suggesting considerable uptake from these extremely contaminated, organically enriched, chronically disturbed sediments. Sediment PCBs were the primary predictor of tissue lipid PCBs followed by %fines. This results in generally higher tissue PCBs in more depositional regions. The lipid/sediment PCBs (uptake rate) declined with increasing sediment PCBs, acid volatile sulfides and benthos biomass turnover. PCB homologue composition did not change with uptake from sediments or at higher trophic levels, suggesting minimal metabolization in tissues. Trophic bio-magnification occurs since lipid PCBs were 2–100× higher in seal blubber than sediment feeders. PCBs were compared with polybrominated diphenyl ethers (PBDEs) for the same samples. PCBs were highest in industrialized harbours, whereas PBDEs were elevated in harbours but highest near wastewater discharges. This reflects differences in usage history, sediment dynamics, and affinities. PCBs appear to be more bio-accumulative and persistent at higher trophic levels than PBDEs.

Bioremediation strategies with biochar for polychlorinated biphenyls (PCBs)-contaminated soils: A review

Polychlorinated biphenyls (PCBs) are hazardous organic contaminants threatening human health and environmental safety due to their toxicity and carcinogenicity. Biochar (BC) is an eco-friendly carbonaceous material that can extensively be utilized for the remediation of PCBs-contaminated soils. In the last decade, many studies reported that BC is beneficial for soil quality enhancement and agricultural productivity based on its physicochemical characteristics. In this review, the potential of BC application in PCBs-contaminated soils is elaborated as biological strategies (e.g., bioremediation and phytoremediation) and specific mechanisms are also comprehensively demonstrated. Further, the synergy effects of BC application on PCBs-contaminated soils are discussed, in view of eco-friendly, beneficial, and productive aspects.

Evaluation of the effectiveness of VOC-contaminated soil preparation based on AHP-CRITIC-TOPSIS model

Currently, several methods have been adopted for the laboratory preparation of artificial volatile organic compound (VOC) contaminated soils (VCSs). However, it remains unclear whether the prepared contaminated soils are homogenous. In this study, two representative VOCs, toluene and perchloroethylene, were separately mixed with a kaolin-based soil using six preparation methods. Thereafter, the homogeneity and recovery of the contaminated kaolin prepared using these methods were determined and analyzed. The six procedures were quantitatively assessed according to the comprehensive evaluation mathematical model (AHP-CRITIC-TOPSIS), and the final score order of the different procedures was: A > C > E > B > F > D. Additionally, the qualitative evaluation of the procedures was performed based on the phase transformation and mass transfer during the mixing processes. Based on these discussions, method A, which was considered to be optimal, was then adopted for further investigations with various natural soils. The results showed that this optimal method could be applied to natural soils and revealed that the adsorption-related characteristics of natural soils, including total organic carbon, specific surface area, pore volume, pH, plastic limit, particle size, and mineral composition, influenced the homogeneity and recovery through mass transfer. In addition, it was also observed that the chemical properties of VOCs, including molecular structure, vapor pressure, and the octanol/water partition coefficient, could also affect the effectiveness of sample recovery. Through this study, researchers can prepare VCSs with excellent homogeneity and low loss rates to conduct standardized tests for technology development.

Adsorption of toluene on various natural soils: Influences of soil properties, mechanisms, and model

This study investigated toluene adsorption on natural soils. The linear partition model was found to represent the adsorption isotherm well (R² = 0.958-0.994), compared with the Freundlich model (R² = 0.901-0.991). Therefore, the coefficient, K_d, of the linear model indicated the adsorption capacity of soils A to F. Traditionally, K_d and the total organic carbon (TOC) content have a good linear relationship. However, this relationship was weak (correlation coefficient (r) = 0.689) when TOC values (8.43-12.9 mg/g) were low and close. To correct this deviation, this study investigated the influences of physicochemical properties, such as special surface area, mineral composition, functional groups, pH, and potentials. As soils B and C consisted of a large amount of active clayey minerals (69.4% kaolinite and 79.3% nacrite, respectively) and rich functional groups, they demonstrated the strongest adsorption capacity. Additionally, the r for pH-K_d, zeta potential-K_d, and redox potential-K_d were high, at 0.806, 0.914, and 0.932, respectively. To explore adsorption mechanisms, the adsorption thermodynamic parameter (enthalpy) was used initially to determine the forces. Combined with the analysis of soil properties, the mechanisms identified were hydrophobic interaction and hydrogen-pi bonding, involving co-adsorption with water molecules. Based on all studies, the properties were quantified and simplified by the plastic limit (PL), and TOC was simplified by soil organic matter (SOM). Then, PL and SOM were weighted by the entropy-weight method to obtain the determination factor, DF, a logarithmic parameter to replace TOC. Finally, a new model describing toluene adsorption on natural soils was established and expressed as K_d = 4.80 + 3.53DF. This new model had significantly improved the correlation between K_d and TOC (r = 0.933) and expanded the engineering adaptability.

Mechanochemical treatment with CaO-activated PDS of HCB contaminated soils

Mechanochemical methods with co-milling reagents have been widely used to degrade organic pollutants. In this study, calcium oxide and persulfate were employed as co-milling reagents in a mechanochemical process that showed highly effective degradation of hexachlorobenzene in contaminated soil. The influences of soil particle size and organic matter content were also investigated. The interaction between different factors was analyzed by response surface methodology, and a multi-variate regression equation was obtained relating the soil-to-oxidant mass ratio, rotation speed and organic matter content. The existence of SO₄^- and OH during the mechanochemical reaction was proved by the indirect detection of benzoquinone and p-hydroxybenzoic acid for the first time, providing a new method for testing free radicals in solid-phase reactions. Finally, a possible activation mechanism and hexachlorobenzene degradation pathway were proposed. This study successfully presents a mild degradation method in the field of hexachlorobenzene contaminated site remediation.

Bioaccessibility of polycyclic aromatic compounds (PAHs, PCBs) and trace elements: Influencing factors and determination in a river sediment core

Organic matter (OM), clays, sand or time are factors possibly influencing the bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls (PCBs) from sediments. An experimental design was performed to monitor and quantify this process. The bioaccessible fraction, linked to the rapidly-desorbing fraction (F_rap) of contaminants, was assessed through a non-exhaustive extraction using a carboxymethyl-β-cyclodextrin polymer. OM content was the most influential factor as regards F_rap. Clay percentage was a slightly influential factor for PAHs while the interaction sand × OM was a slightly influential factor for PCBs. F_rap was also determined in a sediment core collected from Martot's Pond (France). The higher the PAH/PCB concentration in this sediment, the higher the bioaccessible fraction. The relationship between a lower bioaccessibility and a higher number of PAHs cycles or PCB chlorines was linear. OM content impacted on F_rap only for PAHs. Sequential extractions of some trace elements were also performed to evaluate their mobility. Cu, Cr, Pb, Ni were the less bioaccessible. A great part of As, Cd and Zn was found in the most bioaccessible sediment fractions. The 40-65 cm section might be considered as the most negatively impacting on the aquatic fauna, due to Cd and Zn high bioaccessible concentrations.