Response Surface Optimization of an Extraction Method for the Simultaneous Detection of Sulfamethoxazole and 17ß-Estradiol in Soil.

Antibiotics and hormones widely exist in fertilizers and manures, which are excessively used in agriculture and animal husbandry. Considering their potential harm to the environment and human health, the detection of antibiotics and hormones has become a necessity. However, current methods find it difficult to simultaneously extract and detect antibiotics and hormones in soil and to maintain a high level of accuracy and a low cost. In this study, a straightforward, convenient, and simultaneous extraction and detection method of a representative antibiotic (sulfamethoxazole, SMZ) and hormone (17ß-Estradiol, E2) in soil has been established. Ultrasound-assisted extraction (UAE) was used in the pretreatment process and high-performance liquid chromatography with the ultraviolet detector (HPLC-UV) method was then chosen in the detection process. By means of single factors and response surface experiments, optimal extraction conditions were a 41-mL buffer solution (pH 4.27) mixed with 1 g of soil sample, an ultrasonication time of 36 min, an ultrasonication temperature of 25 °C, and two extraction cycles. The detection limits of 0.3-10 µg/kg and quantification limits of 1-30 µg/kg have been obtained. Finally, the optimized simultaneous extraction and detection method was validated by three different real soil samples with recoveries ranging from 79.49% to 86.47%.

The investigation of influencing factors on the degradation of sulfonamide antibiotics in iron-impregnated biochar-activated urea-hydrogen peroxide system: A QSAR study.

Iron-impregnated biochar-activated urea-hydrogen peroxide (FB-activated UHP) is a potential in-situ technology for simultaneously reducing soil sulfonamide antibiotic contaminants and improving soil fertility. To better understand the degradation of sulfonamide antibiotics by FB-activated UHP, a two-dimensional quantitative structure-activity relationship (2D-QSAR) model based on quantum chemical parameters and a three-dimensional QSAR (3D-QSAR) model based on molecular force field were developed to investigate the factors influencing the removal efficiencies (Re%). The optimal 2D-QSAR model was Re%= 0.858-8.930 E-5 EB3LYP-0.175 f(+)x with the evaluation indices of R2= 0.732, q2= 0.571, and Qext2= 0.673. The given 2D-QSAR model indicated that the molecular size (EB3LYP) and Fukui index with respect to nucleophilic attack (f(+)) were intrinsic factors influencing Re%. Three degradation pathways were subsequently proposed based on the f(+) distribution. Compared to the 2D-QSAR model, the developed 3D-QSAR model exhibited a better predictive ability, with the evaluation indices of R2= 0.989, q2= 0.696, and SEE= 0.001. The analysis of field contribution rates suggested that electrostatic field (48.2%), hydrophobic field (25.3%), and hydrogen-bond acceptor field (12.7%) were the main factors influencing Re%. These findings generated critical information for evaluating the degradation mechanisms/rules and provided theoretical bases for initially estimating the Re% of sulfonamide antibiotics undergoing FB-activated UHP process.

Degradation of BTEXS with stable and pH-insensitive iron-manganese modified biochar from post pyrolysis.

An efficient iron-manganese modified biochar (FMBC) was successfully synthesized as a heterogeneous Fenton-like catalyst through easy post-modification and applied for degradation of benzene, toluene, ethylbenzene, xylene isomers (ortho, para, and meta), and styrene (BTEXS) in the presence of H2O2. The catalyst was characterized by Brunauer-Emmett-Teller method, scanning electron microscopy, and X-ray photoelectron spectrometry. The effects of H2O2 concentration, FMBC dose, and initial pH on BTEXS degradation were also investigated. Results showed that degradation efficiency of FMBC for individual BTEXS varied from 83.05% to 94.12% in 3 h. Kinetic analysis showed that a first-order kinetic model with respect to BTEXS concentration could be used to explain the BTEXS degradation for FMBC/H2O2 system. The degradation reaction was more suitable in a wide pH range (3-10) than those in previous studies, thereby overcoming the low-efficiency problem of conventional Fenton reaction at high pH. Moreover, the doses of FMBC and H2O2 are a crucial factor affecting BTEXS degradation. Radical scavenger experiments revealed that ∙OH, ∙O2-, and 1O2 participated in the degradation process, and ∙OH was the major contributor. The synthesized catalyst is durable with stable BTEXS removal efficiency after seven consecutive cycles. The removal efficiency of BTEXS by FMBC in produced water reached 93.23% in 12 h, indicating FMBC has practical value.

Two new predictors combined with quantum chemical parameters for the selection of oxidants and degradation of organic contaminants: A QSAR modeling study.

Oxidation is an attractive treatment method to effectively remove organic contaminants in water. In this study, degradation of 30 organic compounds in different oxidation systems was evaluated, including oxygen (O2), hydrogen peroxide (H2O2), ozone (O3) and hydroxyl radical (HO). First, a quantitative structure-activity relationship (QSAR) model for oxidation-reduction potentials (ORPs) of organics was developed and exhibited a good performance to predict ORP values of organics with evaluation indices of squared correlation coefficient (R2) = 0.866, internal validation (q2) = 0.811 and external validation (Qext2) = 0.669. Four quantum parameters, including f(+)n, f(-)n, EHOMO and EB3LYP dominate the ORP values. Subsequently, a relationship between reaction rates (k) and the difference of ORP for oxidants and organics (ΔEoxi-org) was established, however, which was limited (R2= 0.697). Therefore, two new predictors (slopes and intercepts) are proposed based on the linear relationships between k values and ORPs of oxidants. These new predictors can be applied to estimate the reaction rates and minimum oxidation potential for organic compounds. Afterwards, to express the two predictors, QSAR models were established. The two optimal QSAR models fitted very well with experimental values and were demonstrated to be stable and accurate based on R2 (0.982 and 0.965), q2 (0.950 and 0.950) and Qext2 (0.985 and 0.989). BOx, q(H)+ and q(C)x were main factors influencing the slopes and intercepts. This study developed methods to predict ORPs of organics and established two new predictors to estimate the reaction rates undergoing different oxidation processes, offering new insights into the oxidant selection.

Two-dimensional and Three-dimensional quantitative structure-activity relationship models for the degradation of organophosphate flame retardants during supercritical Water oxidation.

Organophosphate flame retardants (OPFRs) have been increasingly utilized as flame retardants in various fields due to the phasing out of polybrominated diphenyl ethers. To achieve a better understanding of the degradation of OPFRs undergoing supercritical water oxidation (SCWO) process, two-dimensional and three-dimensional quantitative structure-activity relationship (2D-QSAR and 3D-QSAR) models were established to investigate the factors influencing the total carbon degradation rates (kTOC). Results of the QSAR models demonstrated reliable results to estimate the kTOC values, but varied in the influencing factors. Two distinct degradation mechanisms were subsequently proposed based on the distribution of LUMO in molecules for the 2D-QSAR model. CoMFA and CoMSIA methods were applied to develop the 3D-QSAR models. Steric fields were observed to influence kTOC values more than electrostatic fields in the CoMFA model with the contribution rates of 87.2% and 12.8%, respectively. In the CoMSIA model, influence on kTOC values varies between different types of fields with the hydrophobic field being the most influential at 62.1%, followed by the steric field at 25.7% and then the electrostatic field at 10.8%. Results from this study generated critical knowledge of influencing factors on OPFRs degradation and yielded theoretical basis for estimating removal behaviors of OPFRs undergoing SCWO process.

Cow manure-derived biochar: Its catalytic properties and influential factors.

The conversion of waste biomass into biochar is considered as a waste disposal alternative, especially because biochar is a low-cost adsorbent for soil contaminants. However, a risk of desorption of contaminants from biochar may lead to secondary pollution. This study investigated the degradation behavior of soil fumigant, 1,3-dichloropropne (1,3-D), on cow manure-derived biochar (CMB) pyrolyzed at five different temperatures from 300 to 700 °C (termed as C-300 to C-700). Results showed that 1,3-D degradation rate was U-shape related to biochar pyrolysis temperature. Four degradation byproducts (NH2CH2CH2CH3OH, CH3CH2NH2, NH2COCONH2, OHCH2COOH) were identified by headspace GC-MS. When biochar humidity improved from 0 to 50% or incubation temperature increased from 20 to 40 °C, the degradation of cis-1,3-D on C-300 improved 24.26% and 35.48%, respectively. The OH concentrations, detected by the terephthalic acid method, were considerably higher for C-300 than that for C-700. Pyrolysis temperature (300-700 °â€¯C) governed biochar physicochemical properties and further affected 1,3-D degradation mechanisms (pH-controlled substitution or OH-restricted oxidation reaction). All these findings showed that CMB can adsorb and degrade 1,3-D, thereby reduce its desorption risk, indicative of the conversion of cow manure into biochar as an effective waste management practice.

Synthesis of a stable magnesium-impregnated biochar and its reduction of phosphorus leaching from soil.

Biochar improves soil fertility and promotes long-term terrestrial carbon sequestration. However, biochar seems not to be stable enough due to physical, chemical and biological reactions. In this study, a novel, stable, and magnesium (Mg)-impregnated biochar was prepared from cow dung and applied to decrease P leaching from soil. XPS, FTIR, XRD, SEM and EDS were used to evaluate the effect of modification and phosphorus(P) sorption on the oxidation resistance of biochar. The results showed that the oxidation resistance of the Mg-impregnated biochar was improved by the formation of MgO on its surface. The soil column experiment indicated that the Mg-impregnated -biochar decreased P loss from leaching by 89.25%. In addition, the available P content of the soil surface layer under Mg-impregnated biochar treatment increased by 3.5-fold relative to that under the control treatment. P sorption also enhanced the oxidation resistance of biochar. The relative contents of CO, CO, and COOH on the surface of P-laden biochar was 20.97% and was lower than those on the surface of biochar without P sorption (33.15%). Oxidation resistance was enhanced by the formation of new MgP crystals, which prevented the oxidation of CC, CC, and CH into CO, CO, and COOH, respectively, by acting as a physical barrier between the biochar surface and oxygen. The results of XRD, SEM and EDS provided evidence for the formation of MgP crystals. Overall, results indicated that the Mg-impregnated biochar can reduce P leaching loss from soil and has enhanced stability.

2D-QSAR and 3D-QSAR simulations for the reaction rate constants of organic compounds in ozone-hydrogen peroxide oxidation.

Synergistic oxidation of ozone (O3) and hydrogen peroxide (H2O2) is an effective water treatment for the elimination of organic pollutants. In this study, 23 organic compounds were conducted to study the reaction rate constants during O3-H2O2 oxidation. Then, two- and three-dimensional quantitative structure-activity relationship (QSAR) models were established to investigate the factors influencing the reaction rate constants by using multiple linear regression method and comparative molecular similarity index analysis (CoMSIA) method, respectively. Both of the two models showed good performance on predicting the reaction rate constants, the associated statistical indices of 2D-QSAR and 3D-QSAR models were R2 = 0.898 and 0.952, q2 = 0.841 and 0.951, Qext2 = 0.968 and 0.970, respectively. But varied in the influence factors, as for the 2D-QSAR model, three quantum chemical parameters, included dipole moment, the largest change of charge in each atom during the nucleophilic attack, the maximum positive partial charge on a hydrogen atom linked with a carbon atom affected the reaction rate. While in the 3D-QSAR model, the electrostatic field played the most important role in evaluating the reaction rate with the contribution of 35.8%, followed by hydrogen bond acceptor and hydrophobic fields with the contribution of 24.9% and 23.2%, respectively. These two models provided predictive tools to study the influencing factors for the degradation of organics and might potentially be applied for estimating the removal properties of unknown organics in O3-H2O2 oxidation process.