Sorption and Desorption Characteristics of Tylosin in Three Louisiana Soils

Aged polyamide microplastics enhance the adsorption of trimethoprim in soil environments

Microplastics (MPs) in the environment typically age. However, the influence of aged MPs on the adsorption of antibiotics in soil remains unknown. In this study, the adsorption behavior of trimethoprim (TMP) on soil and soil containing aged polyamide (PA) was investigated using batch and stirred flow chamber experiments. The adsorption of TMP on the tested soil with and without PA was fast, with the k_a values ranging from 50.5 to 55.6 L (mg min)^-1. The adsorption of TMP on aged PA was more than 20 times larger than that on the tested soil, which resulted in an "enrichment effect." Furthermore, aged PA altered the pH of the reaction system, thereby enhancing the adsorption of TMP. Consequently, the K_d values of TMP for soil, soil containing 5%, and 10% aged PA were 5.64, 12.38, and 23.65 L kg^-1, respectively. The effect of aged PA on the adsorption of TMP on soil depended on pH values. However, TMP adsorption on soil containing 10% aged PA was constantly higher (p < 0.01) than that on soil with NaCl concentrations ranging from 0 to 50 mmol L^-1. These findings provide new insights into the effect of environmental MPs on the fate and transport of antibiotics in soil environments.

Modeling the sorption of Ni(II) and Zn(II) by Mn oxide-coated sand: Equilibrium and kinetic approaches

The behavior of metal cations in oxide-dominated systems is controlled by sorption reactions, which in turn depend on pH. Descriptions of such reactions are of interest for contaminant monitoring or remediation efforts; however, widely used isotherms such as Freundlich or Langmuir neglect the effect of pH and are therefore limited in their applicability. Two pH-dependent isotherms and their kinetic analogs were developed and evaluated regarding their ability to describe equilibrium and time-dependent sorption of Ni and Zn by Mn oxide-coated sand (MOCS). The sorption of Ni and Zn by MOCS at pH 4.0, 5.5, and 7.0 was investigated using batch equilibration and stirred-flow techniques. The affinity of MOCS for either metal cation was highly pH dependent, with greater affinity at higher pH. Both isotherms described the batch data well. Flow interruption during stirred-flow experiments indicated that chemical nonequilibrium existed between solution and sorbed phases of both Ni and Zn and that such nonequilibrium was greater with increasing pH. Both kinetic models provided good descriptions of the solution data from stirred-flow experiments and correctly captured the effect of pH on chemical nonequilibrium. These models offer simple alternatives to surface complexation approaches and are expected to be easily applied to describe equilibrium and time-dependent sorption of a wide range of metal cations by variably charged minerals or oxide-coated media.

Effective extraction of tylosin and spiramycin from fermentation broth using thermo-responsive ethylene oxide/propylene oxide aqueous two-phase systems

Recyclable aqueous two-phase systems with thermo-responsive phase-forming materials have been employed to separate macromolecules; however, these systems have achieved very limited separation efficiency for small molecules, such as antibiotics. In this study, aqueous two-phase systems composed of the ethylene oxide/propylene oxide copolymer and water were developed to extract alkaline antibiotics from the fermentation broth. In the aqueous two-phase systems with an ethylene oxide ratio of 20 and propylene oxide ratio of 80, the partition coefficients of tylosin and spiramycin reached 16.87 and 20.39, respectively, while the extraction recoveries were 70.67 and 86.70%, respectively. Coupled with mechanism analysis, we demonstrated the feasibility of extracting alkaline antibiotics using this aqueous two-phase system, especially for 16-membered macrolide antibiotics. The molecular dynamic simulation was employed to visualize the process of dual-phase formation and the partition behavior of antibiotics in an aqueous two-phase system. The dynamic simulation revealed the binding energy between the antibiotic and ethylene oxide/propylene oxide copolymers, which provides a simple indicator for screening suitable antibiotics in aqueous two-phase systems. Our recyclable aqueous two-phase systems provide a robust approach for the extraction of 16-membered macrolide antibiotics with ease of operation and high recovery rates, which is appropriate for large-scale extraction in the fermentation industry.