Low-toxic, fluorescent labeled and size-controlled graphene oxide quantum dots@polystyrene nanospheres as reference material for quantitative determination and in vivo tracing

Tracing the entry process of submicrometre plastics in soybean sprouts by leaf-derived fluorescent carbon dots

As a global emerging contaminant, microplastics (MPs) in water or soil can accumulate in vegetables, making them easily ingested through the diet. With excellent and tunable optical properties, carbon dots (CDs) are highly advantageous for tracing the entry process of MPs. Originally, long-wavelength CDs were synthesized from leaf-derived extracts, and fluorescent submicrometer plastics (CDs-MPs) with clean surfaces and concentrated particle sizes were obtained by soap-free microemulsion polymerization. The concentration of CDs-MPs exhibits a significant linear relationship with long-wavelength fluorescence intensity (λEx/λEm: 415/676 nm). Soybean sprouts (SBS), as an important type of food, are susceptible to contamination of MPs due to their soft epidermis and rapidly growing biomass. The results showed that CDs-MPs could be embedded into the cortex of SBS and enter the plant with cell division and elongation, leading to an increase in pore size on the cell wall surface. After entering the root system, CDs-MPs will pass through the Casparian strip and migrate in the vessels. Then, CDs-MPs enter the leaves through vascular bundles, and the distribution and size of epicuticular wax on leaves have changed. Furthermore, SBS showed resistant growth and increased levels of oxidative response when exposed to MPs/CDs-MPs. It is the first study to demonstrate the application of leaf-derived CDs in the prevention of MPs pollution by revealing the migration behavior of submicrometre plastics in SBS.

Toxicity interaction of polystyrene nanoplastics with sulfamethoxazole on the microalgae Chlamydomonas reinhardtii: A closer look at effect of light availability

The coexistence of nanoplastics and antibiotics in the aquatic environment has raised a complicated risk for ecosystems and human health. How the environmental factors e.g., light, regulate the interaction between nanoplastics and antibiotics and the resulting combined toxicity is poorly understood. Here, we investigated the individual and combined toxicity of polystyrene nanoplastics (nPS, 100 mg L¹) and sulfamethoxazole (SMX, 2.5 and 10 mg L^-1) toward the microalgae Chlamydomonas reinhardtii under low (LL, 16 μmol m^-2·s^-1), normal (NL, 40 μmol m^-2·s^-1), and high light (HL, 150 μmol m^-2·s^-1) in terms of cellular responses. Results indicated that the joint toxicity of nPS and SMX commonly exhibited a strong antagonistic/mitigative effect under LL/NL at 24 h, and under NL at 72 h. nPS could adsorb more SMX under LL/NL at 24 h (1.90/1.33 mg g^-1) and under NL at 72 h (1.01 mg g^-1), thereby alleviating SMX toxicity to C. reinhardtii. However, the self-toxicity of nPS had a negative influence on the degree of antagonism between nPS and SMX. The experimental results coupled with computational chemistry further revealed that the adsorption capacity of SMX on nPS was stimulated by low pH under LL/NL at 24 h (∼7.5), while by less co-existing saline ions (0.83 ppt) and algae-derived dissolved organic matter (9.04 mg L^-1) under NL at 72 h. nPS toxicity that was responsible for the toxic action modes was mainly attributed to the shading effect induced by hetero-aggregation and hindrance of light transmittance (>60%), as well as being regulated by additives leaching (0.49-1.07 mg L^-1) and oxidative stress. Overall, these findings provided a critical basis for the risk assessment and management of multiple pollutants in the complex natural environment.