Endosulfan is an organochlorine pesticide widely used in Southwest China. In this paper, the adsorption and desorption characteristics of endosulfan in two typical agricultural soils (latosol and lateritic red soil) in this area were studied. The results showed that Langmuir isothermal equation could well describe the adsorption thermodynamic characteristics of endosulfan in latosol and lateritic red soil, and the maximum adsorption capacities of α-endosulfan were 0.186 and 0.209 mg/g, while those of β-endosulfan were 0.140 and 0.148 mg/g, respectively. Endosulfan adsorption in the two soils was an exothermic physicochemical process, but dominated by physical process. The adsorption kinetic characteristics of endosulfan in the two soils could be well described by second-order kinetic equation, and the initial rate constants were 0.228 and 0.325 mg/(g min) for α-endosulfan, while those were 0.119 and 0.125 mg/(g min) for β-endosulfan, respectively. The adsorbed endosulfan in the two soils was difficult to be desorbed into the liquid phase, and showed weak desorption hysteresis. These results implied that endosulfan could be firmly adsorbed by the two soils, and their adsorption and desorption abilities may be related to the contents of soil clay and organic matter.

•The water level fluctuation zone of the Three Gorges Reservoir is a redox rotation area.•The accumulation of elemental sulfur appeared both in sulfate reduction and sulfide re-oxidation.•Methylmercury content in soil/sediment is positively correlated with elemental sulfur content during the flooding period.•Methylmercury during the flooding period may be fixed by pyrite.The water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) in China experiences a drying and wetting rotation every year, and the water level induced redox variation may influence inorganic sulfur speciation and mercury methylation. In this work, a simulative flooding and drying experiment and a sulfate added flooding experiment were conducted to study this topic. The results showed that sulfate was reduced from the 10th d during the flooding period based on the detected sulfide in water and the increased elemental sulfur (S0) in sediment. Sulfate reduction and sulfide re-oxidation led to the increase of S0 contents with the maximal values of 1.86 and 0.46 mg kg−1 during the flooding and drying period, respectively. Methylmercury (MeHg) content in sediment displayed a rising trend (0.16–0.28 μg kg−1) in the first 40 d during the flooding period, and then declined from 0.28 to 0.15 μg kg−1. A positive correlation between MeHg content and S0 content in soil (r = 0.53, p < 0.05) was found during the flooding period, and a positive but not significant correlation between the percent of MeHg in THg (%MeHg) and S0 content (r = 0.85, p = 0.08). In sulfate added flooding simulation, MeHg content in sediment did not increase with the sulfate concentration increasing. The increased pyrite in high-sulfate treatment may fix mercury through adsorption process. This study demonstrated that inorganic sulfur species especially S0 and chromium reducible sulfur (CRS) play an important role on mercury methylation in the WLFZ of the TGR.Download high-res image (973KB)Download full-size image

An amperometric nitrite sensor modified with multi-walled carbon nanotubes (MWCNTs) and poly(toluidine blue) (PTB) on glassy carbon electrode was constructed. The surface morphology of the composite- modified electrode was characterized by scanning electron microscopy, and the electrochemical response behavior and electrocatalytic oxidation mechanism of nitrite were investigated by cyclic voltammetry. The high surface-to-volume ratio of MWCNTs and PTB brings the electrochemical sensing unit and nitrite in full contact. This renders the electrochemical response extremely sensitive to nitrite. Under the optimal measurement conditions and a working voltage of 0.73 V (vs. SCE), a linear relationship is obtained between the oxidation peak current and nitrite concentration in the range of 39 nM–1.1 mM, and the limit of detection is lowered to 19 nM (at an S/N ratio of 3). The sensor was successfully applied to the determination of nitrite in greenhouse soils.

In this study, two generic haptens of phthalate esters (PAEs) were synthesized by introducing spacer arms with different lengths at the meta-position of an ester group of dimethyl phthalate (DMP). Immune and coating antigens were prepared by coupling the haptens with bovine serum albumin (BSA) and ovalbumin (OVA), respectively. Polyclonal antibodies against two immunogens were obtained, and their sensitivities and specificities were examined by enzyme-linked immunosorbent assay (ELISA). Under the optimal experimental conditions, the IC50 values of eight PAEs were obtained in the range of 17.12–102.57 ng mL−1 with the limits of detection (LODs) around 0.012–0.042 ng mL−1. The prepared polyclonal antibody with a higher titer displayed a broad cross-reactivity in the range of 16.69–83.84% for the other seven PAEs (except DMP). The average recoveries of PAEs at the spiked levels of 0.5, 1.0 and 10.0 ng mL−1 ranged from 63.9% to 103.6% with relative standard deviations (RSDs) below 11.32%, which was consistent with gas chromatography-mass spectrometry (GC-MS). The developed ELISA method was successfully applied to determine multiple PAEs in greenhouse soils.

Microbial degradation has been commonly used to remedy endosulfan-contaminated soil. However, this technique is limited by low degradation efficiency with high toxic metabolite. This work investigated the photodegradation efficiencies of endosulfan in soil with the elution of surfactants and revealed the kinetic characteristics of photocatalytic degradation with two strategies, i.e., surfactant elution followed with photocatalytic degradation, and simultaneous elution and photocatalytic degradation.The endosulfan-contaminated soil, photocatalyst (nitrogen-doped anatase TiO2), and three eluents composed of Tween 80, SDS, and Na2SiO3 were prepared, respectively. The degradation efficiencies of endosulfan in soil were examined by the photocatalyst under visible-light irradiation with two strategies, i.e., surfactant elution followed with photocatalytic degradation, and simultaneous elution and photocatalytic degradation. The kinetic characteristics of photocatalytic degradation of endosulfan in soil were studied at certain time intervals.The XRD, X-ray photoelectron spectroscopy, and UV–vis diffuse reflection spectra revealed that nitrogen was doped into TiO2 lattice, and the optical absorption of nitrogen-doped TiO2 shifted toward visible-light region. The residual ratios of α-, β-endosulfan in soil eluates obviously decreased with the irradiation time increasing and could not be detected at 240 min; this process could be well described by first-order kinetic model, and the half-lives of α-, β-endosulfan were 43.0–71.7 and 51.1–85.3 min, respectively; the concentrations of endosulfan sulfate showed a trend of increase, decrease, and till complete degradation. For simultaneous elution and photocatalytic degradation, the residual ratios of α-, β-endosulfan in soil were 0.21–0.25, 0.41–0.43 at 120 h with eluent 1 to eluent 3 treatments, respectively; the degradation process of endosulfan in soil-aqueous systems could be well described by four-parameter biphasic first-order kinetic model.Endosulfan in the soil eluates could be completely degraded at 240 min under visible-light irradiation and could be described by pseudo first-order kinetic equation. The degradation process of endosulfan in soil-aqueous systems obeyed four-parameter biphasic first-order kinetic model. As an intermediate of photocatalytic degradation, endosulfan sulfate could be rapidly degraded. It was concluded that surfactant elution followed with photocatalytic degradation was more effective than simultaneous elution and photocatalytic degradation.

Animal tissue samples were extracted with ethyl acetate or alkalized ethyl acetate, and purified with MCX or LC-18 solid-phase extraction columns, and the matrix effects (ME%) in the simultaneous determination of four fenicol antibiotics including chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA) were studied by ultra performance liquid chromatography-tandem mass spectrometry. ME% for FFA in swine muscle and casings extracted by ethyl acetate with LC-18 column cleanup were 11.1% and 10.4%, and in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with MCX column cleanup ME% were 8.1% and 16.1%, respectively, showing strong signal suppression; while ME% for FF in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with LC-18 column cleanup were 148.5% and 146.9%, and in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with MCX column cleanup were 234.3% and 150.9%, showing strong signal reinforcement. Deuterated chloramphenicol-d5 could only be used as an internal standard to eliminate matrix effects for CAP determination. It may be that the most effective method to eliminate matrix interference in the simultaneous determination of the four analytes is quantified by using matrix-matched solutions. Under the optimum conditions of sample pretreatment and quantitative analysis, the decision limits (ccα as specified in European Directive 2002/657/EC) for FFA, TAP, CAP and FF in swine muscle were determined to be 0.4, 0.05, 0.02 and 0.02 μg kg−1, and 0.5, 0.1, 0.04 and 0.03 μg kg−1 in casings; the detection capabilities in swine muscle were determined to be 0.7, 0.09, 0.05 and 0.05 μg kg−1, and 1.2, 0.19, 0.12 and 0.07 μg kg−1 in casings, respectively.

•Thiamphenicol and florfenicol can be effectively removed with the MWCNTs modified electrode.•The removal process of the two antibiotics could be described by pseudo first-order kinetic model.•Electrocatalytic reduction is promising to remove low-concentration antibiotics in wastewater.•The reduction pathways of the two antibiotics may include dehalogenation and carbonyl reduction.The electrocatalytic reduction of thiamphenicol (TAP) and florfenicol (FF) was investigated with multi-walled carbon nanotubes (MWCNTs) modified electrode. MWCNTs was dispersed in pure water with the assistance of dihexadecyl phosphate (DHP), and then modified on glassy carbon electrode (GCE). The electrocatalytic reduction conditions, such as bias voltage, supporting electrolyte and its initial pH, and the initial concentrations of TAP and FF, were also optimized. The experimental results indicated that the removal efficiencies of 2 mg L−1 TAP and FF in 0.1 M NH3·H2O-NH4Cl solution (pH 7.0) reached 87% and 89% at a bias voltage of −1.2 V after 24 h electrocatalytic reduction, respectively. The removal process could be described by pseudo first-order kinetic model, and the removal rate constants of TAP and FF were obtained as 0.0837 and 0.0915 h−1, respectively. The electrocatalytic reduction products of TAP and FF were identified by liquid chromatography-tandem mass spectrometry (LC–MS/MS), and the possible reduction mechanisms were preliminarily analyzed. Electrocatalytic reduction is promising to remove low-concentration TAP and FF in wastewater with the MWCNTs modified electrode, and may cut down their toxicity through dehalogenation and carbonyl reduction.Low-concentration thiamphenicol and florfenicol can be efficiently removed by electrocatalytic reduction through dehalogenation and carbonyl reduction.Download high-res image (109KB)Download full-size image

Animal tissue samples were extracted with ethyl acetate or alkalized ethyl acetate, and purified with MCX or LC-18 solid-phase extraction columns, and the matrix effects (ME%) in the simultaneous determination of four fenicol antibiotics including chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA) were studied by ultra performance liquid chromatography-tandem mass spectrometry. ME% for FFA in swine muscle and casings extracted by ethyl acetate with LC-18 column cleanup were 11.1% and 10.4%, and in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with MCX column cleanup ME% were 8.1% and 16.1%, respectively, showing strong signal suppression; while ME% for FF in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with LC-18 column cleanup were 148.5% and 146.9%, and in swine muscle extracted by ethyl acetate and alkalized ethyl acetate with MCX column cleanup were 234.3% and 150.9%, showing strong signal reinforcement. Deuterated chloramphenicol-d5 could only be used as an internal standard to eliminate matrix effects for CAP determination. It may be that the most effective method to eliminate matrix interference in the simultaneous determination of the four analytes is quantified by using matrix-matched solutions. Under the optimum conditions of sample pretreatment and quantitative analysis, the decision limits (ccα as specified in European Directive 2002/657/EC) for FFA, TAP, CAP and FF in swine muscle were determined to be 0.4, 0.05, 0.02 and 0.02 μg kg−1, and 0.5, 0.1, 0.04 and 0.03 μg kg−1 in casings; the detection capabilities in swine muscle were determined to be 0.7, 0.09, 0.05 and 0.05 μg kg−1, and 1.2, 0.19, 0.12 and 0.07 μg kg−1 in casings, respectively.