Suspected sources of microplastics and nanoplastics: Contamination from experimental reagents and solvents.

There is an increasing concern about the potential effects of microplastics (MPs) and nanoplastics on human health and other organisms. For the separation and detection of MPs, there are various approaches, and the distinct procedures led to different results. However, the presence of MPs in the reagents was not addressed, which could cause false and/or inaccurate results during MPs detection. In this study, the chemical reagents commonly used for the separation and detection of MPs were selected to ascertain whether these reagents introduce MPs. It was shown that a large number of MPs were detected in the reagent and solvent samples. The largest number of MPs (>1 µm) was detected in the KOH reagent, with the abundance of 3070 items/g. The order of MPs abundance in the selected reagents was: KOH > NaCl > CaCl2 > SDS > NaI > H2O2. The types of MPs were the same as the body and stopper of the reagent packaging bottles. MPs size detected in reagent bottles was primarily smaller than 10 µm. The abundance of MPs in the reagents were independent of their purity, however, there was a certain difference in MPs abundance in reagents from different manufacturers. Furthermore, the presence of nanoplastics (< 1 µm) was verified in the reagents through Py-GCMS, with the abundance (39.47-43.01 mg/kg) higher than that of MPs. The obtained results in this study raised specific requirements and cautions for MPs and nanoplastics related research in terms of quality control. Also, this work can facilitate a more accurate assessment of MPs concentrations in the environment.

Role of extracellular polymeric substances in the aggregation and biological response of micro(nano)plastics with different functional groups and sizes.

In this work, the effects of extracellular polymeric substances (EPS) on the aggregation and biological responses of different micro(nano)plastics (MNPs, <1000 µm) were investigated. EPS increased the colloidal stability of PS MPs in NaCl or CaCl2. For the three PS NPs (PS-NH2, PS-COOH, and PS-naked), EPS also enhanced their colloidal stabilities in the presence of NaCl. However, the effect of CaCl2 on the colloidal stabilities of PS NPs in the presence of EPS depended on their surface functional groups. In CaCl2, both Derjaguin-Landau-Verwey-Overbeek theory and molecular bridging explained the interaction between MNPs (both NPs and MPs) and EPS. Laser Direct Infrared and scanning electron microscope imaging showed that opalescent EPS corona formed on PS MPs via intermolecular-bridging by Ca2+, and the critical coagulation concentrations (70 mM in NaCl, 1.5 mM in CaCl2) in EPS were much lower than that for PS NPs (1000 mM for NaCl; 65 mM for CaCl2). PS-NH2 NPs showed the highest increase in the growth of bacteria (Bacillus subtilis), followed by PS MPs and PS-naked NPs, while PS-COOH NPs had no significant effect. Biological response of PS NPs was unaffected by EPS, while EPS further enhanced the positive effects of PS MPs on bacterial growth.