•Antibiotic residuals were widely detected in agricultural soils from the YRD region of China.•Higher concentrations of antibiotics were found in Jiangsu and Shanghai.•Manure application and wastewater irrigation were the main sources of antibiotic inputs.•The ARGs tetA, sulI, and qnrS were detected in the agricultural soils.This study focused on the occurrence and spatial distribution of 13 common antibiotics in the agricultural soils of the Yangtze River Delta (YRD), China. Antibiotics were detected in all the 241 soil samples (i.e., 100% detection rate) with the total concentrations ranging from 4.55 to 2,010 ng/g dry weight. The concentrations of three antibiotic classes decreased in the order: quinolones (mean 48.8 ng/g) > tetracyclines (mean 34.9 ng/g) > sulfonamides (mean 2.35 ng/g). Ciprofloxacin was the prevalent compound with a mean concentration of 27.7 ng/g, followed by oxytetracycline (mean of 18.9 ng/g). A distinct spatial distribution was observed, where high concentrations of antibiotics were detected in the sites adjacent to the livestock and poultry farms. The potential sources of antibiotics in the agricultural soils were the application of manure and wastewater irrigation in this region. Risk assessment for single antibiotic compound indicated that tetracyclines and quinolones could pose a potential risk, in which doxycycline and ciprofloxacin had the most severe ecological effect in the agricultural soils. Antibiotic resistance genes (ARGs), such as tetA, sulI, and qnrS, were detected in 15 analyzed soil samples, and sulI showed significant correlations with quinolones, tetracyclines, copper, and zinc. Further studies on the distribution of other ARGs in agricultural soil at a region-scale are needed for the risk management of extensively used antibiotics and major ARGs.Download high-res image (450KB)Download full-size image

Atrazine is one of the most widely applied and persistent herbicides in the world. In view of limited information on the regional contamination of atrazine in soils in China, this study investigated the spatial distribution and environmental impacts of atrazine in agricultural soils collected from the Yangtze River Delta (YRD) as an illustrative analysis of rapidly developing regions in the country. The results showed that the concentrations of atrazine in the YRD agricultural soils ranged from <1.0 to 113 ng/g dry weight, with a mean of 5.7 ng/g, and a detection rate of 57.7 % in soils. Pesticide factory might be a major source for the elevated levels of atrazine in Zhejiang Province. The contamination of atrazine was closely associated with land use types. The concentrations and detection rates of atrazine were higher in corn fields and mulberry fields than in rice paddy fields. There was no significant difference in compositions of soil microbial phospholipids fatty acids among the areas with different atrazine levels. Positive relationship (R = 0.417, p < 0.05, n = 30) was observed between atrazine and total microbial biomass. However, other factors, such as soil type and land management practice, might have stronger influences on soil microbial communities. Human health risks via exposure to atrazine in soils were estimated according to the methods recommended by the US EPA. Atrazine by itself in all the soil samples imposed very low carcinogenic risks (<10−6) and minimal non-cancer risks (hazard index <1) to adults and children.

•Soil N2O emission was affected by the ratio of biochar to N fertilizer.•When the ratio of biochar to N fertilizer was high, biochar suppressed N2O emission.•When the ratio of biochar to N fertilizer was low, biochar promoted N2O emission.•Biochar should be applied in proper ratio to N fertilizer to reduce N2O emission.Biochar amendment has been proposed as a potential solution for improving soil quality and suppressing greenhouse gas emission. Considering the serious nitrogen fertilizer overuse problem in China, it is important to investigate the effect of biochar on soil with excess nitrogen fertilizer. Therefore, two sets of soil column experiments were conducted to explore the effect of biochar on N2O emission from nitrogen fertilizer-overused soil. Three types of biochar (biochars pyrolzed at 300, 500 and 700 °C, respectively) and one type of nitrogen fertilizer (ammonium sulfate) were investigated at varying application rates. It was found that N2O emission was related to both biochar and N-fertilizer application rates, and increased N2O emission was negatively correlated with the TC/IN ratio (the ratio of total carbon to inorganic nitrogen) after biochar application. The soil TC/IN ratio determined the ammonium utilization pathway, affecting the intensity of nitrification and N2O emission. When the TC/IN ratio was relatively high (> 60), suppressed nitrification led to the suppression of N2O emission. Conversely, enhanced nitrification when the TC/IN ratio was relatively low (< 45) caused the promotion of N2O emission. In conclusion, biochar's suppression of soil N2O emission was conditional and biochar should be applied in a proper ratio to nitrogen fertilizer to avoid excessive N2O emission.Download high-res image (87KB)Download full-size image

•Biochar-microbial interactions and mechanisms in soil were reviewed.•Effect mechanisms of biochar on microbial activities were highlighted.•Biochar altered soil carbon sequestration related microbial functions.•Biochar as electron shuttle can enhance contaminant mitigation and remediation.•Potential biochar-microbial interactions on soil improvement were prospected.Biochars have attracted tremendous attention due to their effects on soil improvement; they enhance carbon storage, soil fertility and quality, and contaminant (organic and heavy metal) immobilization and transformation. These effects could be achieved by modifying soil microbial habitats and (or) directly influencing microbial metabolisms, which together induce changes in microbial activity and microbial community structures. This review links microbial responses, including microbial activity, community structures and soil enzyme activities, with changes in soil properties caused by biochars. In particular, we summarized possible mechanisms that are involved in the effects that biochar-microbe interactions have on soil carbon sequestration and pollution remediation. Special attention has been paid to biochar effects on the formation and protection of soil aggregates, biochar adsorption of contaminants, biochar-mediated transformation of soil contaminants by microorganisms, and biochar-facilitated electron transfer between microbial cells and contaminants and soil organic matter. Certain reactive organic compounds and heavy metals in biochar may induce toxicity to soil microorganisms. Adsorption and hydrolysis of signaling molecules by biochar interrupts microbial interspecific communications, potentially altering soil microbial community structures. Further research is urged to verify the proposed mechanisms involved in biochar-microbiota interactions for soil remediation and improvement.Download high-res image (319KB)Download full-size image

•TiO2 nanoparticles disturb metabolic flux in rice.•Tricarboxylic acid cycle and the pentose phosphate pathway are elevated significantly.•Starch and sucrose metabolism, and glyoxylate and dicarboxylate metabolism are inhibited significantly.•The non-enzymatic antioxidant is significantly elevated.The wide occurrence and high environmental concentration of titanium dioxide nanoparticles (nano-TiO2) have raised concerns about their potential toxic effects on crops. In this study, we employed a GC-MS-based metabolomic approach to investigate the potential toxicity of nano-TiO2 on hydroponically-cultured rice (Oryza sativa L.) after exposed to 0, 100, 250 or 500 mg/L of nano-TiO2 for fourteen days. Results showed that the biomass of rice was significantly decreased and the antioxidant defense system was significantly disturbed after exposure to nano-TiO2. One hundred and five identified metabolites showed significant difference compared to the control, among which the concentrations of glucose-6-phosphate, glucose-1-phosphate, succinic and isocitric acid were increased most, while the concentrations of sucrose, isomaltulose, and glyoxylic acid were decreased most. Basic energy-generating ways including tricarboxylic acid cycle and the pentose phosphate pathway, were elevated significantly while the carbohydrate synthesis metabolism including starch and sucrose metabolism, and glyoxylate and dicarboxylate metabolism were inhibited. However, the biosynthetic formation of most of the identified fatty acids, amino acids and secondary metabolites which correlated to crop quality, were increased. The results suggest that the metabolism of rice plants is distinctly disturbed after exposure to nano-TiO2, and nano-TiO2 would have a mixed effect on the yield and quality of rice.Download high-res image (285KB)Download full-size image

A georeferenced multimedia model was developed for evaluating the emissions and environmental fate of di-2-ethylhexyl phthalate (DEHP) in the Yangtze River Delta (YRD), China. Due to the lack of emission inventories, the emission rates were estimated using the observed concentrations in soil as inputs for the multimedia model solved analytically in an inverse manner. The estimated emission rates were then used to evaluate the environmental fate of DEHP with the regular multimedia modeling approach. The predicted concentrations in air, surface water, and sediment were all consistent with the ranges and spatial variations of observed data. The total emission rate of DEHP in YRD was 13.9 thousand t/year (95% confidence interval: 9.4–23.6), of which urban and rural sources accounted for 47% and 53%, respectively. Soil in rural areas and sediment stored 79% and 13% of the total mass, respectively. The air received 61% of the total emissions of DEHP but was only associated with 0.2% of the total mass due to fast degradation and intensive deposition. We suggest the use of an inverse modeling approach under a tiered risk assessment framework to assist future development and refinement of DEHP emission inventories.

To date, there is limited knowledge on the methoxylation of polychlorinated biphenyls (PCBs) and the relationship between hydroxylated polychlorinated biphenyls (OH-PCBs) and methoxylated polychlorinated biphenyls (MeO-PCBs) in organisms. In this study, rice (Oryza sativa L.) was chosen as the model organism to determine the metabolism of PCBs in plants. Limited para-substituted 4′-OH-CB-61 (major metabolite) and 4′-MeO-CB-61 (minor metabolite) were found after a 5-day exposure to CB-61, while ortho- and meta-substituted products were not detected. Interconversion between OH-PCBs and MeO-PCBs in organisms was observed for the first time. The demethylation ratio of 4′-MeO-CB-61 was 18 times higher than the methylation ratio of 4′-OH-CB-61, indicating that formation of OH-PCBs was easier than formation of MeO-PCBs. The transformation products were generated in the roots after 24 h of exposure. The results of in vivo and in vitro exposure studies show that the rice itself played a key role in the whole transformation processes, while endophytes were jointly responsible for hydroxylation of PCBs and demethylation of MeO-PCBs. Metabolic pathways of PCBs, OH-PCBs, and MeO-PCBs in intact rice plants are proposed. The findings are important in understanding the fate of PCBs and the source of OH-PCBs in the environment.

Adsorption is the most widely used technology for the removal of indoor volatile organic compounds (VOCs). However, existing adsorbent-based technologies are inadequate to meet the regulatory requirement, due to their limited adsorption capacity and efficiency, especially under high relative humidity (RH) conditions. In this study, a series of new porous clay heterostructure (PCH) adsorbents with various ratios of micropores to mesopores were synthesized, characterized and tested for the adsorption of acetaldehyde and toluene. Two of them, PCH25 and PCH50, exhibited markedly improved adsorption capability, especially for hydrophilic acetaldehyde. The improved adsorption was attributed to their large micropore areas and high micropore-to-mesopore volume ratios. The amount of acetaldehyde adsorbed onto PCH25 at equilibrium reached 62.7 mg·g−1, eight times as much as the amount adsorbed onto conventional activated carbon (AC). Even at a high RH of 80%, PCH25 removed seven and four times more of the acetaldehyde than AC and the unmodified raw PCHs did, respectively. This new PCH optimized for their high adsorption and resistance to humidity has promising applications as a cost-effective adsorbent for indoor air purification.

Combined pollution by polycyclic aromatic hydrocarbons (PAHs) and heavy metals are commonly found in industrial soils. This study aims to investigate the effect of the coexistence of heavy metals on the sorption of PAHs to soils. We focused specifically on the relationship of the sorption capacity with the estimation of the binding energy between PAHs and heavy metals.The sorption of typical PAHs (naphthalene, phenanthrene, and pyrene) to soils coexisting with heavy metals (Cu(II), Pb(II), and Cr(III)) was characterized in batch sorption experiments. The binding energy between PAHs and heavy metals in aqueous solution was estimated by quantum mechanical (QM) method using density functional theory (DFT) at the M06-2x/def2svp level of theory.Sorption capacity and nonlinearity of the PAHs to the soils were enhanced by the coexisting heavy metals. The extent of increment was positively associated with the hydrophobicity of the PAHs and the electronegativity and radius of the metal cations: Cr(III) > Pb(II) > Cu(II). The cation-π interaction was revealed as an important noncovalent binding force. There was a high correlation between the binding energies of the PAHs and Kf′ (Kf adjusted after normalizing the equilibrium concentration (Ce) by the aqueous solubility (Cs)) (R2 > 0.906), indicating the significant role of the cation-π interactions to the improved PAH sorption to soils.In the presence of heavy metals, the sorption capacities of naphthalene, phenanthrene, and pyrene to soils were enhanced by 21.1–107 %. The improved sorption capacity was largely contributed from the potent interactions between PAHs and heavy metals.

Surfactants can affect the biodegradation process and the fate of hydrophobic organic compounds (HOCs) in the environment. Previous studies have shown that surfactants can enhance the biodegradation of HOCs by increasing cell surface hydrophobicity (CSH) and membrane fluidity. In this study, we took this work one step further by investigating the expression levels of three genes of Arthrobacter sp. SA02 in the biodegradation of phenanthrene as a typical HOC at different concentrations of sodium dodecyl benzenesulfonate (SDBS), which is a widely used surfactant. The Δ9 fatty acid desaturase gene codes for Δ9 fatty acid desaturase, which can convert saturated fatty acid to its unsaturated form. The ring-hydroxylating dioxygenase (RHDase) and the 1-hydroxyl-2-naphthoate dioxygenase (1H2Nase) genes code for the RHDase and 1H2Nase enzymes, respectively, which play a key role in decomposing doubly hydroxylated aromatic compounds. The results show that these three genes were upregulated in the presence of SDBS. On the basis of the genetic and physiological changes, we proposed a pathway that links the gene expression with the physiological phenomena, including CSH, membrane fluidity, and intracellular degradation. This study advances our understanding of the surfactant-enhanced biodegradation of HOCs at the gene level, and the proposed pathway should be further validated in the future.

The speciation of soil organic pollutants is of great importance for risk assessment and contaminant remediation, however, only few studies have attempted to develop a speciation scheme for a facilitated risk assessment. This paper postulates a pragmatic speciation scheme for the fractionation of soil polycyclic aromatic hydrocarbons (PAHs) that could correlate with their bioavailabilities, and the aim was to develop a reliable sequential ultrasonic extraction scheme that could differentiate PAHs into four fractions with different environmental relevance. We also investigated the key factors to the fraction distribution of PAHs, as well as the relationship between bioavailability of PAHs and their fractions.Four representative PAHs were spiked into two soils and the distribution of PAH fractions was measured over a period of 90 to 210 days. The reliability of the sequential ultrasonic extraction method was cross-examined by an isotope experiment. The key factors to the fraction distribution, including aging time and properties of soil and PAH, were tested using ultrasonic extraction. The correlation between four fractionated PAHs and their bioavailabilities was assessed with a semipermeable membrane device (SPMD)-assisted desorption assay that mimics the bioconcentration of PAHs.Soil PAHs were speciated into water-soluble-, organic acid-soluble-, organically bound-, and residual fractions via sequential ultrasonic extraction. The water-soluble- and organic acid-soluble fractions, which approximated the total PAHs estimated by SPMD, corresponded to the most bioavailable portions. The latter ones decreased significantly during aging. In contrast, the residual fraction, which limits the effectiveness of remediation, increased during aging following methanolic saponification. The concentrations of water-soluble-, organic acid-soluble-, and organically bound fractions are negatively correlated with the soil organic matter content and the partition coefficient between octanol and water (Kow) of pollutantsThe bioavailability of soil PAHs can be mimicked by a sequential chemical extraction protocol developed in this study. This speciation scheme can be readily used for studying the environmental fate and risk of PAHs, providing us with better rationales in selecting remediation strategies of soil contaminated with PAHs based bioavailability.

Bioremediation of hydrophobic organic compounds (HOCs) contaminated soils involves several physicochemical and microbiological interfacial processes among the soil-water-microorganism interfaces. The participation of surfactants facilitates the mass transport of HOCs in both the physicochemical and microbiological interfaces by reducing the interfacial tension. The effects and underlying mechanisms of surfactants on the physicochemical desorption of soil-sorbed HOCs have been widely studied. This paper reviewed the progress made in understanding the effects of surfactant on microbiological interfacial transport of HOCs and the underlying mechanisms, which is vital for a better understanding and control of the mass transfer of HOCs in the biodegradation process. In summary, surfactants affect the microbiological interfacial behaviors of HOCs during three consecutive processes: the soil solution-microorganism sorption, the transmembrane process, and the intracellular metabolism. Surfactant could promote cell sorption of HOCs depending on the compatibility of surfactant hydrophile hydrophilic balance (HLB) with cell surface properties; while the dose ratio between surfactant and biologic mass (membrane lipids) determined the transmembrane processes. Although surfactants cannot easily directly affect the intracellular enzymatic metabolism of HOCs due to the steric hindrace, the presence of surfactants can indirectly enhanced the metabolism by increasing the substrate concentrations.

The use of cationic surfactants was proposed to enhance the soil retention of hydrophobic organic contaminants (HOCs). However, due to the complexity of soil composition, the effect of cationic surfactants on the soil sorption of HOCs was limited to a qualitative understanding. To gain further insight into the mechanism of the surfactant and predict its efficiency, a comparative study on the HOCs sorption capacities of the surfactants sorbed on pure typical soil components was investigated.The sorption of cationic surfactant onto five pure typical soil components and the sorption of polycyclic aromatic hydrocarbons (PAHs) by the sorbed surfactant were conducted using batch equilibration methods. Humic acid (HA) and quartz were chosen as the representatives of organic matter and sand, respectively. Montmorillonite, kaolinite, and illite were chosen as representatives of clay minerals.The cationic surfactant sorption capacities of different soil components were of great difference, and the PAH sorption capacities of the surfactant sorbed onto different components were also very different. Aside from the clay minerals, HA was a very active adsorbent for the cationic surfactant, and the sorption mechanism included both adsorption and partition-like processes. For each pure soil component and a certain PAH, a proximately piecewise function was found to describe the relationship of surfactant-normalized PAH distribution coefficient Ksf and the sorption amount of the surfactant on solid Qe-DDPB (R > 0.9). As a result, the sorption of PAHs by different soil components with certain surfactant loading can be estimated.The effect of soil organic matter such as HA could not be ignored when predicting the soil sorption of cationic surfactants. The PAH partition capacities of the sorbed surfactant on HA or clay minerals were very different. However, for each pure soil component, the Ksf value was specifically related with the surfactant loading, which provided a possible means of predicting the efficiency of the cationic surfactant in enhancing the sorption of PAHs onto soils.

Cationic surfactants are common in soils because of their use in daily cosmetic and cleaning products, and their use as a soil amendment for the mitigation and remediation of organic contaminated soils has been proposed. Such surfactant may affect the transfer and fate of organic contaminants in the environment. This study investigated the effect of a cationic surfactant, dodecylpyridinium bromide (DDPB), on the volatilization of polycyclic aromatic hydrocarbons (PAHs) from a paddy soil.The volatilization of PAHs from moist soil amended with different concentrations of DDPB was tested in an open system. The specific effects of DDPB on the liquid–vapor and solid–vapor equilibriums of PAHs were separately investigated in closed systems by headspace analysis.DDPB affects both liquid–vapor and solid–vapor processes of PAHs in soil. At DDPB concentrations below the critical micelle concentration (CMC), movement of PAHs from the bulk solution to the gas–liquid interface appeared to be facilitated by interaction between PAHs and the surfactant monomers adsorbed at the gas–liquid interface, promoting the volatilization of PAHs from solution. However, when DDPB was greater than the CMC, volatilization was inhibited due to the solubilization of PAHs by micelles. On the other hand, the formation of sorbed surfactant significantly inhibited the solid–vapor volatilization of PAHs.The overall effect of the two simultaneous effects of DDPB on liquid–vapor and solid–vapor processes was a decreased volatilization loss of PAHs from soil. Inhibition of PAH volatilization was more significant for the soil with a lower moisture content.

Water chemistry can be a major factor regulating the toxicity mechanism of ZnO nanoparticles (nano-ZnO) in water. The effect of five commonly used aqueous media with various chemical properties on the toxicity of nano-ZnO to Escherichia coli O111 (E. coli) was investigated, including ultrapure water, 0.85% NaCl, phosphate-buffered saline (PBS), minimal Davis (MD), and Luria−Bertani (LB). Combined results of physicochemical characterization and antibacterial tests of nano-ZnO in the five media suggest that the toxicity of nano-ZnO is mainly due to the free zinc ions and labile zinc complexes. The toxicity of nano-ZnO in the five media deceased as follows: ultrapure water > NaCl > MD > LB > PBS. The generation of precipitates (Zn3(PO4)2 in PBS) and zinc complexes (of zinc with citrate and amino acids in MD and LB, respectively) dramatically decreased the concentration of Zn2+ ions, resulting in the lower toxicity in these media. Additionally, the isotonic and rich nutrient conditions improved the tolerance of E. coli to toxicants. Considering the dramatic difference of the toxicity of nano-ZnO in various aqueous media, the effect of water chemistry on the physicochemical properties of nanoparticles should be paid more attention in future nanotoxicity evaluations.

Organic contaminated soils have become a widespread environmental problem, which may lead to a great threat to the quality of agricultural production and to human health. Physical, chemical, and biological technologies have been employed for the mitigation and remediation of organic contaminated soils. This paper reviews the progress of mitigation and remediation technologies for organic contaminated soils and suggests two different strategies for the mitigation of ’slightly-contaminated’ agricultural soils and the remediation of ‘heavily-contaminated’ soils/sites, respectively. On this basis, directions for future research in this field are suggested.

Enhancing desorption of hydrophobic organic contaminants from soils is a promising approach for the effective remediation of soils contaminated with organic compounds. The desorption efficiency of chemical reagent, such as surfactant, should be evaluated. In this study, the effect of mixed anionic–nonionic surfactants sodium dodecylbenzene sulfonate (SDBS)–Tween 80 on the distribution of polycyclic aromatic hydrocarbons in soil–water system was evaluated.Batch desorption experiments were employed to evaluate the distribution of polycyclic aromatic hydrocarbons (PAHs) and surfactants in soil–water system. PAHs and SDBS were determined by high-performance liquid chromatography, Tween 80 by spectrophotometry, and total organic carbon with a carbon analyzer.Sorption of PAHs to soil was increased at low surfactant concentration due to the effective partition phase on soil formed by sorbed surfactants. The mixture of anionic and nonionic surfactants decreased the sorption of surfactants to soil, increasing the effective surfactant concentration in solution and thus decreasing the sorption of PAHs on soil. Anionic–nonionic mixed surfactant showed better performance on desorption of PAHs from soil than single surfactant. The greatest desorption efficiency was achieved with low proportions of SDBS (SDBS/Tween80 = 1:9).SDBS–Tween 80 mixed surfactant showed the highest desorption rate with low proportion of SDBS, which indicated that the addition of relative low amount of anionic surfactant could significantly promote the desorption efficiency of PAHs by nonionic surfactants. Results obtained from this study did provide useful information in surfactant-enhanced remediation of soil and subsurface contaminated by hydrophobic organic compounds.

Plant lipids were considered as the main storage sites for hydrophobic organic contaminants while carbohydrates were generally underestimated, and the lipid−water partition coefficients (Klip) of contaminants were assumed to be the same as the corresponding octanol−water partition coefficients (Kow). Sorption of five polycyclic aromatic hydrocarbons (PAHs) to ryegrass root and its carbohydrates and lipids was investigated to evaluate the role of carbohydrates and lipids on sorption of organic contaminants to plant. Results revealed that sorption of PAHs to ryegrass root was actually regulated by both carbohydrates and lipids rather than lipids individually, as generally assumed. Kch (carbohydrates−water partition coefficient) and Klip could be estimated with the corresponding Kow values: log Kch = 1.23 log Kow − 2.42 and log Klip = 1.23 log Kow − 0.78. Although the affinity of PAHs for lipids appears to be about 1.64 orders of magnitudes higher than that for carbohydrates, sorption of PAHs to carbohydrates could not be neglected because of its predominant weight fraction in plants (about 98 times of lipids for ryegrass root). An improved model containing integral roles of carbohydrates and lipids was established, which showed excellent accuracy for predicting the sorption of organic contaminants to plants.

Illuminating the factors that influence the organic carbon content normalized sorption coefficient (KocKoc) of organoclays towards hydrophobic organic compounds (HOCs) is meaningful for predicting and optimizing the sorption capacity of organoclay. In this paper, the structures and sorption characteristics towards HOCs of organobentonites synthesized with octadecyltrimethylammonium chloride (OTMAC) and dioctadecyldimethylammonium chloride (DODMAC) were studied in order to further account for the variation of KocKoc. The conformations of bentonite-sorbed OTMA+ and DODMA+ transformed from disorder to order as surfactant loading increasing. The packing densities of DODMA+ aggregates were higher than those of OTMA+ aggregates at low surfactant loadings. At high surfactant loading region (1.0–1.4CEC for OTMA-Bent and 0.5–0.7CEC for DODMA-Bent), similar paraffin-type bilayer arrangements were adopted by sorbed OTMA+ and DODMA+, and their packing densities were close under the same focfoc in dry state organobentonites. It was found that loading forms of surfactant onto bentonite had important effect on the structure of organobentonite in water-saturated state, and further to influence the sorption characteristics of organobentonite towards HOCs. When the loading exceeded 0.8CEC, OTMAC in salt molecule form appeared in the clay interlayer via hydrophobic interaction. The strong hydration of surfactant ammonium heads and the counterions (Cl−) in aqueous system interfered the hydrophobic interaction of the OTMA+ clusters and destroyed the close packing in clay galleries. As a result, the sorption capacity of organobentonite towards HOCs was sharply reduced.The appearance of OTMAC molecules in clay galleries destroyed the close packing of alkyl chains (a), then the sorption capacity of OTMA-Bent was reduced sharply (b).

To study the relationship of catalytic activity with Fe configuration over bentonite, three kinds of Fe-pillared bentonites were prepared by pillaring the bentonite with different Fe configurations (Fe-polycation, α-Fe2O3 and α-FeOOH). The characteristics of Fe-pillared bentonites were detected by N2 adsorption/desorption, XRF, XRD, FTIR, AFM and UV–vis. Their catalytic activities were compared by discoloration and mineralization of Orange II in the presence of UV light and H2O2. The order of catalytic activity of Fe-pillared bentonites for dye discoloration was α-Fe2O3-pillared bentonite (α-Fe2O3-P-B) > hydroxyl-Fe-pillared bentonite (H-Fe-P-B) > α-FeOOH-pillared bentonite (α-FeOOH-P-B). And that for dye mineralization was α-Fe2O3-P-B = H-Fe-P-B ≫ α-FeOOH-P-B. A possible catalytic mechanism was proposed for surface and solution reactions to discuss the difference in their catalytic activities. The rate constants of UV-Fenton reaction decreased but the catalytic activities of Fe-pillared bentonites for H2O2 became more obvious when the UV light wavelength increased. Furthermore, the reaction activation energy of UV-Fenton reaction was 18.6 kJ mol−1, 20.1 kJ mol−1 and 23.9 kJ mol−1 with catalyst of H-Fe-P-B, α-Fe2O3-P-B and α-FeOOH-P-B, respectively. The results showed that both α-Fe2O3-P-B and H-Fe-P-B were promising catalysts for UV-Fenton system because of its physical and chemical stability and highly catalytic activity.

The effect of anionic-nonionic mixed surfactant (SDBS-TX100) on the uptake of phenanthrene and pyrene by ryegrass in a hydroponic system was studied, and the influence factors including the compositions and concentrations of mixed surfactants and the compounds properties were also discussed. The results showed that SDBS-TX100 mixtures with certain compositions and concentrations could enhance the uptake of phenanthrene and pyrene by ryegrass, which could be attributed to the improved uptake capacity of ryegrass roots for phenanthrene and pyrene. SDBS-TX100 can enhance the uptake of phenanthrene and pyrene by ryegrass in a wider range of surfactant concentrations (0−0.8 mmol/L) in comparison with corresponding single surfactants, and the maximal contents of phenanthrene and pyrene in ryegrass roots were obtained with the concentrations of SDBS-TX100 around the corresponding critical micelle concentrations. The uptake of phenanthrene and pyrene by ryegrass increased with the increasing mole fraction of SDBS in mixed surfactant solutions, and SDBS-TX100 mixture with a mole ratio of SDBS to TX100 at 9:1 had the greatest capacity in enhancing the uptake of phenanthrene and pyrene, at which the corresponding maximal concentrations of phenanthrene and pyrene in ryegrass roots were 216 and 8.16 times those without surfactants, respectively. Results from this study indicate that the anionic-nonionic mixed surfactants (SDBS-TX100) would be a preferred selection for the application of surfactant-enhanced phytoremediation technology to contaminated soils.

To elucidate interactions of neutral organic contaminants (NOCs) with siloxane surfaces (often referred to hydrophobic nanosites) found between cations in 2:1 phyllosilicates, adsorption of aliphatic and aromatic compounds onto both internal and external siloxane surfaces of tetramethylammonium-intercalated bentonite with a cation exchange capacity (CEC) of 108 cmol/kg (108TMA) and its reduced-charge bentonite (CEC = 65 cmol/kg, 65TMA) were investigated. Reduction of the layer charge and saturation of bentonite interlayers with TMA+ modify the interlayer microenvironments, which dramatically promote adsorption of NOCs. Specific mechanisms (i.e., steric restriction and phenyl-effect) control the adsorption of NOCs onto internal siloxane surfaces of TMA+-bentonites from water. The adsorption sites of 108TMA can not provide sufficient space to accommodate NOCs, hence hindering adsorption. Adsorption mechanism on 65TMA varies with solute-loadings, from polarity-selective at low loadings to aromaticity-preferable at high loadings. Significant contribution of phenyl-effect between adsorbed-solutes to aromatics adsorption on 65TMA is found. Solvent polarity effect on the aggregation of TMA+-bentonites and aniline adsorption demonstrated that the contribution of external siloxane surfaces to favor adsorption in n-hexane are actually exploited but generally omitted. These observations provide significant insights into distinguishing different uptake mechanisms as well as the potential means for the rational design of better organic sorbents.

Temperature dependence of naphthalene sorption to four organoclays with different surfactant (CTMA+) packing densities was examined. The results showed that both ΔHoΔHo and ΔSoΔSo increase generally with CTMA+ packing density. For organoclays with a low CTMA+ packing density, the sorption process is driven by both the enthalpy term (ΔHo)(ΔHo) and the entropy term (−TΔSo)(−TΔSo), with values ranging from −4.7 to −7.5 kJmol−1 and −15.9 to −20.8 kJmol−1, respectively. As the CTMA+ packing density increases, the sorption process is driven by the entropy term (from −29.2 to −65.0 kJmol−1) while it is opposed by the enthalpy term (from 7.9 to 40.5 kJmol−1). These results indicate that the enthalpy demand for cavity formation within the surfactant aggregates and the mixing entropy of solute with surfactant aggregates both increase with the surfactant packing density. This means that the surfactant aggregates will form various organic phases as their packing density varies. Controlling the surfactant aggregates within an intermediate packing density range can improve the sorption capacities of the organoclays.A schematic representation for naphthalene molecules partitioning into loosely packed (a) and densely packed (b) surfactant alkyl chain phases.

The influence of structural characteristics of series of surfactant–clay complexes on their sorption capacities toward naphthalene were examined, which presented some novel information about how to improve the sorption capacities of the complexes. It was shown that sorption of naphthalene on these complexes strongly depended on the conformations of the adsorbed surfactants, and the organic carbon normalized sorption coefficient (Koc) value varied in a wide range (5000–20,000 L/kg) with surfactant conformation. That was, Koc value first increased gradually until the maximum and then decreased sharply as the surfactant conformation developed progressively from liquidlike to solidlike (i.e., increasing surfactant packing density and ordering). At low packing density stage the surfactant aggregates have high surface/volume ratio and the attractive forces between surfactant and solute are relatively weak; whereas at high packing density stage interactions between surfactant alkyl chains are strong and more free energy is needed for creating cavities in the surfactant mediums. In both cases the sorption capacities of the complexes are weak. Thereby, the surfactant aggregates can be considered as different partition phases as their conformations changed, which then lead to the variation of Koc value. Controlling the surfactant aggregates within intermediate packing density range can optimize the sorption capacities of the complexes.

This research examines the feasibility of synthesizing inorgano–organo composites based on bentonite-silylated pillared interlayered clays (SPILCs) by pre-pillaring of bentonite with the Keggin ion (hydroxyaluminum polycation) and then silylating with alkylchlorosilanes. The results of organic carbon content analysis, FTIR, XRD, and DTA/TG indicated that the silyl group can be successfully grafted to the inner surface of pillared interlayered clays (PILCs) through reaction with the OH groups of the pillars and the d-spacing of synthesized PILCs and SPILCs were almost the same. SPILCs have both the higher organic carbon content relative to original bentonite and PILCs and the better surface and pore properties relative to surfactants-modified organobentonites. A comparison of the modifier demand of SPILCs and CTMAB-bentonites indicated that the silylation of PILCs was a modifier-economized process for organically modification of bentonite. The heat-resistant temperature of SPILCs, 508 °C for OTS-Al-PILC and 214 °C for TMCS-Al-PILC, are more excellent organobentonites. Unlike the partition-predominated sorption mechanisms of organobentonites, both adsorption and partition are important components of sorption mechanism of SPILCs. The VOC sorption capacity of SPILCs is approximately same with that of organobentonites and the hydrophobicity of SPILCs is superior to that of PILCs.The mechanism for the formation of SPILCs is generally a two-step process: (1) pre-pillaring of bentonite with the Keggin ion, and (2) silylating PILC with alkylchlorosilanes.

Simultaneous sorption of organic compounds and phosphate from water by inorganic–organic bentonites (IOBs) was investigated, which would contribute to the treatment of contaminated water containing both of these contaminants. A series of IOBs were synthesized by intercalating bentonite with both cetyltrimethyl ammonium bromide (CTMAB) and hydroxy-aluminum at their various ratios, and the obtained materials had large basal spacing, low surface area and high organic carbon contents. Sorption experiments with phenol, p-chlorophenol, 2,4-dichlorophenol, 2-naphthol, nitrobenzene, p-nitrotoluene or naphthalene together with phosphate demonstrated that IOBs could simultaneously remove organic compounds and phosphate from water, due mainly to the partition and ligand exchange mechanism, respectively. The sorption capacity of IOBs with organic compounds was retained as those of organobentonites, and the removed amount were in the range of 42–98% for the tested organic compounds. In addition, the removal efficiency of phosphate by IOBs is higher than that by the corresponding hydroxy-aluminum pillared bentonites, and more than 98% phosphate were removed at the initial concentration of 20 mg/L (calculated as P). The coexisting organic compounds had little influence on the sorption of phosphate to IOBs under the experimental conditions. Thus, IOBs could be promising sorbents for simultaneous removal of organic compounds and phosphate from water.

The role and contribution of siloxane surface and exchanged organic cations on sorption process of organic contaminants is critical for the designing of high efficient organoclay adsorbents. In this study, organobentonites were synthesized using hexamethonium bromide (HM) and tetramethyl ammonium bromide (TMA). And their structures and sorption characteristics for phenol were examined. It was suggested that HM molecules lay parallel to the silicate planes, and were isolated from each other in the interlamellar surfaces. Sorption of phenol by HM-Bent and TMA-Bent were dominanted by adsorption process. At low phenol concentrations, adsorption capacity of phenol on 30HM-Bent is higher than that on 60TMA-Bent, while it is lower at high phenol concentrations. The adsorption capacity of phenol on HM-Bent increased with increasing HM loading under 0.40CEC (cationic exchanged capacity), but which decreased when HM loading over 0.40CEC. The observed results suggested that in HM-Bent, the exposed siloxane surface was the effective adsorption sites for phenol, while the organic cations contributed to enhancing hydrophobic environment and the affinity for organic contaminants.

An efficient solid catalyst, hydroxyl-Fe-pillared bentonite (H-Fe-P-B), was successfully developed for photo-assisted Fenton reaction. The characteristics of the catalyst were detected by N2 adsorption/desorption, X-ray fluorescence spectroscopy (XRF), X-ray powder diffraction (XRD), UV–vis absorption spectra (UV–vis) and atom force microscopy (AFM). The catalytic activity of H-Fe-P-B was evaluated in discolouration and mineralization of Orange II in UV-Fenton system. The effects of pH, Orange II concentration, UV light wavelength and temperature on Orange II degradation were studied in detail. It was found that the catalytic activity of H-Fe-P-B for H2O2 came from Fe-polycations between bentonite sheets rather than Fe3+ or Fe2+ in tetrahedral or octahedral sheets of bentonite. As the leaching of iron from the H-Fe-P-B after treatment was negligible, the H-Fe-P-B exhibited a high catalytic activity and good long-term stability in multiple runs in the discolouration and mineralization of Orange II. Because of the strong surface acidity, the H-Fe-P-B acted as not only catalyst but also solid acid in UV-Fenton system, as a result, almost 100% colour removal and 95% TOC removal of 0.2 mM Orange II could be obtained at 40 and 120 min even if the initial pH of solution was as high as 9.0. These results implied that the H-Fe-P-B was a promising catalyst for UV-Fenton system.

The purpose of this work is to synthesize a new type of bentonite sorbent that can simultaneously remove both organic compounds and phosphate from water. Inorganic-organic bentonites (Al-CTMAB-Bent) were synthesized by modifying bentonites with both AlCl3 and cetyltrimethyl ammonium bromide (CTMAB). Simultaneous sorption of aqueous phenanthrene and phosphate onto Al-CTMAB-Bent was examined. Removal rates of phenanthrene and phosphate from water reached 96.3% and 90.2%, respectively, at their respective initial concentrations of 1 mg/L and 5 mg/L and the added amount of Al-CTMAB-Bent was 1.25 g/L. The residual turbidity of the Al-CTMAB-Bent suspension decreased 81.4% compared to that of organobentonite suspension after a 1 h settling time. Thus, inorganic-organic bentonite can be used to treat wastewater containing both organic pollutants and phosphate.

This paper put forward a microwave irradiation method to effectively prepare organbentonite, which aims to decrease time-consuming and energy-intensive in preparation of organobentonite by convention. The optimal conditions for preparing organobentonite by microwave (MOB) were studied. The mechanism of organobentonite prepared by microwave was proposed. Characteristics of MOB and organobentonite prepared by convention (COB) were compared in detail. An ideal amount of cetylpyridinium chloride (CPC) used for preparation of organobentonite was 1.0 times of cation exchange capacity (CEC) of bentonite. The optimal microwave irradiation time was 2 min. The preparation reaction time for organobentonite was decreased from several hours by convention to only a few minutes by microwave, which confirms that microwave method is very effectively for preparing organobentonite. XRD and atomic force microscopy (AFM) showed that the CPC moles have entered into interlayer spacing of bentonite. Comparing with natural bentonite, the intense endothermic peaks in differential thermal analysis (DTA)/Thermogravimetry (TG) curves of COB and MOB drifted to low temperature zone. Comparing with COB, the interlayer spacing of MOB was raised and the organic carbon content of MOB was increased 32.5% by microwave, which benefit to the sorption of organic compounds onto MOB from water.

Losses of surfactants through sorption to soils/sediments, especially to clay minerals, by various chemical interactions such as sorption and precipitation threaten the success of surfactant in enhancing remediation of contaminated soil and groundwater. In this study, the behavior of mixtures of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) sorbed to a montmorillonite saturated with calcium (Ca-montmorillonite) was investigated, and compared with that of individual surfactants. It is shown that the amounts of both TX-100 and SDBS sorbed to Ca-montmorillonite are significant. However, the amount of either TX-100 or SDBS sorbed can be decreased and minimized when they are mixed with each other. Mixed micelle formation, which causes negative deviation of critical micelle concentrations (CMCs) from the ideal, is responsible for the decrease in sorbed TX-100 and sorbed SDBS in their mixtures. Because of their ability to minimize their amounts sorbed and thus enhance their active concentrations, as observed in mixed TX-100 and SDBS systems, mixed anionic–nonionic surfactants exhibit potential advantages in the area of enhanced soil and groundwater remediation.

In recent years, much attention has been focused on developing heterogeneous catalyst for Fenton or photo-Fenton process to reuse the catalyst and avoid the possible pollution caused by the metal ions in the solution. Through cation exchange reaction, hydroxyl-Fe pillared bentonite (H-Fe-P-B) was successfully prepared as a solid catalyst for UV-Fenton process. Compared with raw bentonite, the content of iron, interlamellar distance and external surface area of H-Fe-P-B increased remarkably. Heterogeneous UV-Fenton catalytic degradation of azo-dye Acid Light Yellow G (ALYG) was investigated in aqueous using UVA (365 nm) light as irradiation source. The effects of H2O2 concentration, catalyst dosage, initial pH and temperature on degradation of ALYG were studied in detail. The results demonstrated that the H-Fe-P-B had high catalytic activity. In optimal operation conditions, more than 98% discoloration and 65% TOC removal of 50 mg/L ALYG could be achieved after 120 min treatment. The iron leaching rates of H-Fe-P-B were all below 0.6% in multiple runs in the degradation of ALYG, which indicated that the heterogeneous catalyst had long-term stability and activity. Another advantage of this catalyst was its strong surface acidity, which made the range of pH for heterogeneous UV-Fenton system extended from 3.0 to 9.0. The results indicated that the H-Fe-P-B was a promising catalyst for heterogeneous UV-Fenton system.

Simultaneous sorption of organic compounds and phosphate from water by inorganic–organic bentonites (IOBs) was investigated, which would contribute to the treatment of contaminated water containing both of these contaminants. A series of IOBs were synthesized by intercalating bentonite with both cetyltrimethyl ammonium bromide (CTMAB) and hydroxy-aluminum at their various ratios, and the obtained materials had large basal spacing, low surface area and high organic carbon contents. Sorption experiments with phenol, p-chlorophenol, 2,4-dichlorophenol, 2-naphthol, nitrobenzene, p-nitrotoluene or naphthalene together with phosphate demonstrated that IOBs could simultaneously remove organic compounds and phosphate from water, due mainly to the partition and ligand exchange mechanism, respectively. The sorption capacity of IOBs with organic compounds was retained as those of organobentonites, and the removed amount were in the range of 42–98% for the tested organic compounds. In addition, the removal efficiency of phosphate by IOBs is higher than that by the corresponding hydroxy-aluminum pillared bentonites, and more than 98% phosphate were removed at the initial concentration of 20 mg/L (calculated as P). The coexisting organic compounds had little influence on the sorption of phosphate to IOBs under the experimental conditions. Thus, IOBs could be promising sorbents for simultaneous removal of organic compounds and phosphate from water.

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke of 12 commercial brand cigarettes were determined in a simulated chamber of 20.25 m3 in size. The total concentrations of 17 PAHs (∑PAHs) in the chamber were 3500 and 1152 ng/m3 in vapor phase and particulate phase, respectively. In vapor phase, the yield of naphthalene (NA) appeared to be the most abundant (2462 ng/cig) followed by fluorene (FLUOR) and acenaphthylene (ACY), while the yield of benzo[ghi]perylene (BP) was the most abundant (259.7 ng/cig) in particulate phase followed by phenanthrene (PHEN) and FLUOR. The proportion of PAHs in particulate phase increased with increasing molecular weight. PAHs with two to six rings accounted for 40.2%, 35.3%, 11.7%, 7.6%, 5.2% of ∑PAHs, respectively. There was no obvious correlation between PAHs, benzo[a]pyrene (BaP) concentrations in tobacco smoke and smoking tar contents, nicotine contents. With the source fingerprint of PAHs in tobacco smoke, NA could be regarded as the marker of tobacco smoke source because of its largest contribution to ∑PAHs (40.2%), followed by FLUOR (12.7%) and ACY (9.8%). Further study indicated that more than 80% of BaP in indoor air of resident homes in Hangzhou was from tobacco smoke.