Novel insights into the joint phytotoxicity of nanoplastics and silver ions at environmentally relevant concentrations: a dual aggregation-induced emission bioimaging approach

Nanoplastics (NPs) act as carriers of heavy metals and pose toxicity to aquatic organisms due to their affinity for heavy metals; however, the particular role of NPs in this joint toxicity remains unclear. Using a dual aggregation-induced emission (AIE) bioimaging technique, we quantitatively visualized AIE luminogen-incorporated polystyrene NPs (AIENPs) and metallic Ag+ in Chlamydomonas reinhardtii, aiming to elucidate the toxic mechanisms of coexposed NPs and Ag+. AIENPs with 40 nm and 80 nm diameters, namely, 40AIENPs and 80AIENPs, were prepared and subjected to UV irradiation to mimic natural aging processes. Toxicity results indicated that 40AIENPs and 80AIENPs cocultured with Ag+ altered the phytotoxicity of Ag+ in two distinct ways. The phytotoxicity of Ag+ was intensified by coexposure with 40AIENPs but was alleviated by coexposure with 80AIENPs. Bioimaging results indicated that coexposure with aged 40AIENPs resulted in 1.63 +/- 0.04-1.74 +/- 0.10-fold higher internalization of Ag+ than individually exposed Ag+ (normalized based on the exposed Ag concentration), resulting in more Ag+ localization at the apical zones and cell surface. Although coexposure with differently aged 80AIENPs resulted in an increase of 1.17 +/- 0.09-1.35 +/- 0.04-fold in the accumulation of Ag+, the efficiency of Ag+ internalization decreased by 1.01 +/- 0.02-1.04 +/- 0.02-fold, which is attributed to a larger amount of Ag+ being adsorbed onto the cell surface. Mechanistic results indicated that when coexposed with differently aged 40AIENPs, the generation of reactive oxygen species increased and the photosynthetic activities of the algal cells decreased. These effects were different from those observed when coexposed with Ag+ in the presence of 80AIENPs. This study differentiates the bioaccumulation, biodistribution, and biological responses of Ag+ when coexposed with NPs, emphasizing the significant influence of NP sizes and aging degrees. Nanoplastics (NPs) act as carriers of heavy metals and pose toxicity to aquatic organisms due to their affinity for heavy metals; however, the particular role of NPs in this joint toxicity remains unclear.