No abstract

Microplastics (MPs) are an emerging environmental concern. However, vertical transport of MPs remains unclear, particularly in deep reservoirs with thermal stratification (TS). In this study, the vertical variation in MP organization, stability, migration, and the driving factors of the profile in a deep reservoir were comprehensively explored. This is the first observation that TS interfaces in a deep reservoir act as a buffer area to retard MP subsidence, especially at the interface between the epilimnion and the metalimnion. Interestingly, there was a size-selection phenomenon for MP sinking. In particular, the high accumulation of largesized MPs (LMPs; >300 μm) indicated that LMPs were more susceptible to dramatic changes in water density at the TS interfaces. Furthermore, simultaneous analysis of water parameters and MP surface characteristics showed that the drivers of MP deposition were biological to abiotic transitions during different layers, which were influenced by algae and metals. Specifically, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and microscopic Fourier transform infrared analyses implied that the occurrence of metals on the MP surface can promote MP deposition in the hypolimnion. Our findings demonstrated that TS significantly influenced the MP fate in deep reservoirs, and the hotspot of MP exposure risk for vulnerable benthic organisms on the reservoir floor deserves more attention.

The chlorination reaction of aromatic compounds is highly important for the synthesis of pharmaceutical products. As the most common chlorination reagent, chlorine is restricted from undergraduate laboratory experiment training due to its toxicity. In this work, we reported the chlorination of aromatic compounds with chlorine generated from the paired electrolysis of N-chlorosuccinimide. The chlorine in this reaction is produced and consumed in an on-demand manner, ensuring the safety of the reaction, workup, and purification. The reaction is evaluated with 5 undergraduate students with reproducible results and conveys the basic concepts of electrochemical organic synthesis and green synthesis to these students.