Factors controlling the heavy metal ion activity in soil contaminated by microplastics with different mulch durations: Partial least squares path model.

Film covers have been widely applied worldwide. However, the effects of long-term plastic film mulching use on heavy metal (HM) activity in soil remain unclear. This study focused on farmland in the upstream part of the Pearl River in China and collected 103 soil samples after 2, 5, and 15 years of plastic film mulching. The main environmental factors controlling microplastics (MPs), plasticizer phthalic acid esters (PAEs), HM pollution characteristics, and HM activity were analyzed. The results showed that Polyethylene (PE) and di(2-ethylhexyl) dicyclohexyl phthalate (DCHP) were the main MPs and PAEs, respectively. The abundance of MPs and the concentrations of free HM ions (Cd, Cu, and Ni) in the soil solution increased with increasing plastic film mulching duration. The Partial Least Squares Path Model (PLS-PM) indicated that after plastic film mulching, soil chemical properties (pH/amorphous Fe) and biological properties (Dissolved organic carbon/ Easily oxidizable carbon/Microbial biomass carbon) were the main controlling factors for free and complexed HM ions (Cd, Pb, Cu, and Ni). These results suggest that, after plastic film mulching, MPs indirectly regulate HM activity by altering soil properties. This study provides a new perspective for the management of MPs and HM activities in agricultural ecosystems.

[Study on the interaction of levofloxacin and MCM-41 by fluorescence spectrum].

The mesoporous molecular sieve MCM-41 was synthesized by hydrothermal method under microwave irradiation and the levofloxacin was encapsulated in the hexagonal ordered channels of MCM-41 using pickling process. The structure and property of MCM-41 and LVFX/MCM-41 were characterized by means of small-angle X-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR), N2 physical adsorption, and thermogravimetric analysis-differential thermal analysis (TGA-DTA). The pore diameter and the specific surface area of the mesoporous molecular sieve MCM-41 synthesized under microwave irradiation were 2.382 nm and 1015 m2 x g(-1) respectively. The fluorescence spectra of MCM-41, LVFX/MCM-41, LVFX (solid) and LVFX (solution) were investigated. The results indicated that there were some visible red shifts in the fluorescence spectrum of the composite of LVFX/MCM-41 as compared with the samples before being encapsulated. It was inferred from the results that hydrogen bonds were formed between levofloxacin and the hydroxy group in the inner pores, and the electron cloud could transfer from the hydroxy group to electro-attracting group. At the same time, the electron cloud could transfer in much larger annulations, and the conjugated system of LVFX was extended because of the new annulations formed, which contributed to the red shifts of the fluorescence spectra. The strong interactions between the LVFX and MCM-41 provided the theory for developing a novel delayed release drug using MCM-41 as the carriers.