The prevalence of nanomaterials requires a comprehensive study on their biological impacts especially in coastal and estuarine environments where AgNPs are likely to end up. Here, a radio-synthesizing method was employed to trace the behavior of Ag nanoparticles (AgNPs) with two sizes (15 nm and 60 nm) and two coatings (humic acid and citrate) in an estuarine oyster Crassostrea hongkongensis. Through radioactive AgNPs tracing and biokinetic modeling, we for the first time demonstrated the differential uptake mechanisms of different-sized AgNPs in the oysters. Specifically, ingestion of particles dominated the uptake of 60 nm AgNPs, whereas dermal uptake and ingestion contributed equally for 15 nm AgNPs. Surface coating (humic acid vs. citrate) did not significantly affect the uptake of...[ Read more ]

The prevalence of nanomaterials requires a comprehensive study on their biological impacts especially in coastal and estuarine environments where AgNPs are likely to end up. Here, a radio-synthesizing method was employed to trace the behavior of Ag nanoparticles (AgNPs) with two sizes (15 nm and 60 nm) and two coatings (humic acid and citrate) in an estuarine oyster Crassostrea hongkongensis. Through radioactive AgNPs tracing and biokinetic modeling, we for the first time demonstrated the differential uptake mechanisms of different-sized AgNPs in the oysters. Specifically, ingestion of particles dominated the uptake of 60 nm AgNPs, whereas dermal uptake and ingestion contributed equally for 15 nm AgNPs. Surface coating (humic acid vs. citrate) did not significantly affect the uptake of AgNPs by the oysters. The depuration of AgNPs from the oysters was relatively faster than that for the Ag ion. The digestive gland was the key detoxification organ of AgNPs with the greatest loss of Ag by the end of depuration. By coupling high-resolution nanoscale secondary ion mass spectrometry (NanoSIMS) elemental mapping with scanning electron microscope (SEM) ultrastructural characterization, we also successfully visualized the subcellular localization as well as the potential toxicity effects of AgNPs in the oyster gill filaments. Stable isotope tracing method was adopted to investigate the respective uptake and transport mechanisms of differently labeled ¹⁰⁹AgNPs and ¹⁰⁷Ag⁺ ions. We further identified two categories of hemocytes (blood cells) and illustrated their roles in AgNPs transport and sequestration. The integration of morphological and functional aspects of Ag subcellular distribution in different target cells suggested that oysters were equipped with a specialized endo-lysosomal (epithelial cells) or phago-lysosomal system (hemocytes) in regulating the cellular process of AgNPs, during which the lysosome was the most involved organelle and sulfur was the most relevant macronutrient element. In this study, we demonstrated that isotope tracing methods are applicable in both biokinetic modelling (radioactive isotope tracing) and subcellular imaging (stable isotope tracing) of AgNPs, providing reliable methodology for our understanding of bio-nano interactions in natural environments.