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.

Aging characteristics of degradable and non-biodegradable microplastics and their adsorption mechanism for sulfonamides.

As emerging pollutants, microplastics (MPs) and antibiotics (ATs) became a research hotspot in recent years. To evaluate the carrier effect of degradable and non-biodegradable MPs in the aquatic environment, the adsorption behaviors of polyamide (PA) and polylactic acid (PLA) towards two sulfonamide antibiotics (SAs) were investigated. Both chemical and photo-aging were used to handle the virgin MPs. Compared with PA, PLA was aged more drastically, showing the obvious grooves, notches and folds. However, due to the higher temperature during chemical aging, the tiny KPLA (PLA aged by K2S2O8) particles were agglomerated and the specific surface area was reduced to nearly 95 %. For PA, the oxidation of chemical aging was stronger than photo-aging. After aging, the hydrophilicity and polarity of MPs increased. In the adsorption experiments, the adsorption capacity of PA towards SAs was 1.7 times higher than that of PLA. Aging process enabled the adsorption capacity of PLA increased 1.22-3.18 times. Overall, the adsorption capacity of sulfamethoxazole (SMX) by both MPs was superior to sulfamerazine (SMR). These results would help to understand the carrier effects and potential ecological risks of MPs towards co-existing contaminants.

New insights into adsorption mechanism of pristine and weathered polyamide microplastics towards hydrophilic organic compounds.

The widespread coexistence of hydrophilic organic compounds and microplastics (MPs) in the environment has greatly increased their associated environmental problems. To evaluate the potential carrier effect of oxygen-containing MPs on coexisting pollutants, adsorption behaviors of four hydrophilic organic compounds (benzoic acid, sulfamethoxazole, sulfamerazine and ciprofloxacin) on MPs (pristine and weathered polyamide (PA)) were studied in the aquatic environment. The results showed that the surface morphology, size, oxygen content, molecular structure, surface charge and crystallinity of PA were changed after weathering, and the weathering degree of PA treated with heat-activated potassium persulfate was the highest. The main adsorption mechanisms included hydrogen bonding, hydrophobic interaction, charge-assisted hydrogen bonding, and electrostatic interaction. Hydrogen bonding and hydrophobic interaction contributed to the adsorption, while electrostatic interaction weakened the adsorption under the specific pH conditions. The formation of charge-assisted hydrogen bonding (CAHB) was also verified through pH influence experiments, and this force can overcome the electrostatic repulsion. The high adsorption of KPA (PA weathered by K2S2O8) under alkaline conditions was well explained by the formation of homonuclear CAHB due to the increase of oxygen-containing functional groups compared to the other three PA. Additionally, weathering did not always enhance the adsorption of hydrophilic organic compounds on PA, which was related to the changes in surface charge, crystallinity and hydrophilicity of PA. Overall, the physical and chemical properties (e.g., specific surface area, oxygen content, molecular structure) of PA after weathering and its trend of adsorption were different from other oxygen-free MPs in this study. This work can provide basic data for environmental risk of MPs and contribute to clarify and understand the processes of oxygenated MPs in the aquatic environment.