In Situ Understanding of the Effect of Manure on the Availability of Sulfonamide Antibiotics in Soils Using DGT

In this study, the effects of manure on the availability of sulfonamide antibiotics (SAs) in soils were explored in situ by the Diffusive gradients in thin films (DGT) technique. Five antibiotics, including sulfadiazine (SDZ), sulfamethoxazole (SMX), sulfamethazine (SMZ), sulfachloropyridazine (SCP), and sulfadimethoxine (SDM), were selected as target compounds. Results showed that the manure application to soil could reduce the antibiotic availability indicated by DGT. DGT measurement (CDGT) showed good correlations with the soil solution concentrations (Cd). Manure application can suppress the fluxes of SAs from the soil to the soil solution. Using the DGT-induced soil/sediment flux model (DIFS), the labile pool size (Kdl), the rate constants (k1, k-1) of adsorption and desorption and response time (Tc) of SAs in soils were obtained. The addition of manure increased extractable fraction, labile pool size (Kdl) and k1 but decreased k-1. Together with the nonlinear relationship between DGT fluxes and the reciprocal of diffusive layer thickness (Δg), these findings suggested that the release of SAs from soil particles into the soil solution is thermodynamically and kinetically limited, and the manure application could enhance this limitation. This study offers insight into antibiotic availability in soils caused by manure application.

Competitive adsorption behavior of typical heavy metal ions from acid mine drainage by multigroup-functionalization cellulose: qualitative and quantitative mechanism

In response to Cd, Pb, and Cu pollution in acid mine drainage (AMD), a multigroup cellulose material (TCIS) containing thiol (-SH), carboxyl (-COOH), and imine (-C = N) groups was prepared through oxidation and grafting reactions. At pH 5, the maximum Cd(II), Pb(II), and Cu(II) adsorption performances of TCIS were 53.60, 120.6, and 36.01 mg/g, respectively. In the binary system, the interaction between metal ions was mainly inhibited by competitive adsorption. Cu(II) exhibited the most fierce inhibitory effect and had a relatively stable adsorption performance. In the ternary system, the adsorption order was Cu(II) > Cd(II) > Pb(II). In density functional theory (DFT) calculations, we combined the molecular electrostatic potentials, binding energies, differential charges, and total potentials to illustrate the competitive behavior of metal ions at different binding sites. Moreover, X-ray photoelectron spectroscopy (XPS) and DFT analysis revealed that the adsorption process of TCIS was dominated by the above functional groups, which caused competitive adsorption among Cd(II), Pb(II), and Cu(II).

Kinetics and Mechanism of Degradation of Reactive Radical-Mediated Probe Compounds by the UV/Chlorine Process: Theoretical Calculation and Experimental Verification

The UV/chlorine process, by combining chlorination with UV irradiation, has been recently considered as a highly efficient advanced oxidation process (AOP) technology in water treatment. Nitrobenzene (NB), benzoic acid (BA), and p-chlorobenzoic acid (pCBA) are widely used as model probe compounds in the UV/chlorine system to calculate the second-order rate constants of the specific radical reaction with target contaminates by a competitive kinetics method. A comprehensive understanding of probe compounds' reaction mechanism with reactive radicals is critical for investigation of the UV/chlorine reaction system. Here, we evaluated the radical-mediated reaction kinetics and mechanism of NB, BA, and pCBA in the UV/chlorine process using theoretical calculations and experimental studies. The main reactive radicals ^•OH, ^•ClO, and ^•Cl in the UV/chlorine process for the initial reaction with NB, BA, and pCBA can be explained by H-abstraction and addition pathways. The ΔE ^0,≠ values for the ^•OH reaction with NB, BA, and pCBA were in the range of 5.0-8.0, 3.7-8.2, and 3.4-8.2 kcal mol^-1, respectively. The ΔE ^0,≠ values for ^•ClO and ^•Cl reactions with these three probe compounds were higher than those of ^•OH, indicating slower ^•ClO- and ^•Cl-initiated reactions than that of the ^•OH-initiated reaction. The theoretically calculated radical-mediated reaction kinetic rate constants (k _CP ^C) for NB, BA, and pCBA were 4.58 × 10^-3, 1.28 × 10^-2, and 1.6 × 10^-2 s^-1, respectively, which was consistent with the experimentally determined pseudo-first-order rate constant (k _CP ^RR) in the UV/chlorine process. Interestingly, theoretical calculations showed that ^•ClO and ^•Cl played an important role in subsequent reactions of NB-OH radicals, converting to hydroxylated and chlorinated products, which were further confirmed by experimental products' identification. The findings from this study indicated that quantum chemistry calculations provide an effective means to investigate the reaction kinetics and mechanism of chemicals in the UV/chlorine process.