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.

In Situ Insight into the Availability and Desorption Kinetics of Per- and Polyfluoroalkyl Substances in Soils with Diffusive Gradients in Thin Films.

The physicochemical exchange dynamics between the solid and solution phases of per- and polyfluoroalkyl substances (PFAS) in soils needs to be better understood. This study employed an in situ tool, diffusive gradients in thin films (DGT), to understand the distribution and exchange kinetics of five typical PFAS in four soils. Results show a nonlinear relationship between the PFAS masses in DGT and time, implying that PFAS were partially supplied by the solid phase in all of the soils. A dynamic model DGT-induced fluxes in soils/sediments (DIFS) was used to interpret the results and derive the distribution coefficients for the labile fraction (Kdl), response time (tc), and adsorption/desorption rates (k1 and k-1). The larger labile pool size (indicated by Kdl) for the longer chain PFAS implies their higher potential availability. The shorter chain PFAS tend to have a larger tc and relatively smaller k-1, implying that the release of these PFAS in soils might be kinetically limited but not for more hydrophobic compounds, such as perfluorooctanesulfonic acid (PFOS), although soil properties might play an important role. Kdl ultimately controls the PFAS availability in soils, while the PFAS release from soils might be kinetically constrained (which may also hold for biota uptake), particularly for more hydrophilic PFAS.

Gel Point Suppression in RAFT Polymerization of Pure Acrylic Cross-Linker Derived from Soybean Oil.

Here we report the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylated epoxidized soybean oil (AESO), a cross-linker molecule, to high conversion (>50%) and molecular weight (>100 kDa) without macrogelation. Surprisingly, gelation is suppressed in this system far beyond the expectations predicated both on Flory-Stockmeyer theory and multiple other studies of RAFT polymerization featuring cross-linking moieties. By varying AESO and initiator concentrations, we show how intra- versus intermolecular cross-linking compete, yielding a trade-off between the degree of intramolecular linkages and conversion at gel point. We measured polymer chain characteristics, including molecular weight, chain dimensions, polydispersity, and intrinsic viscosity, using multidetector gel permeation chromatography and NMR to track polymerization kinetics. We show that not only the time and conversion at macrogelation, but also the chain architecture, is largely affected by these reaction conditions. At maximal AESO concentration, the gel point approaches that predicted by the Flory-Stockmeyer theory, and increases in an exponential fashion as the AESO concentration decreases. In the most dilute solutions, macrogelation cannot be detected throughout the entire reaction. Instead, cyclization/intramolecular cross-linking reactions dominate, leading to microgelation. This work is important, especially in that it demonstrates that thermoplastic rubbers could be produced based on multifunctional renewable feedstocks.