Different responses of Chlorella vulgaris to silver nanoparticles and silver ions under modulation of nitric oxide.

Silver nanoparticles (Ag-NPs) are widely used in daily life because of their antibacterial properties. A fraction of Ag-NPs are released into the ecosystem during their production and utilization. The toxicity of Ag-NPs has been reported. However, it is still disputed whether the toxicity is mainly due to the released silver ions (Ag+). In addition, few studies have reported the response of algae to metal nanoparticles under modulation of nitric oxide (NO). In this study, Chlorella vulgaris (C. vulgaris) was used as a model organism to study the toxic effects of Ag-NPs and Ag+ released from Ag-NPs on algae under the modulation of NO. The results showed that the biomass inhibition rate of Ag-NPs (44.84%) to C. vulgaris was higher than that of Ag+ (7.84%). Compared with Ag+, Ag-NPs induced more severe damage to photosynthetic pigments, photosynthetic system II (PSII) performance, and lipid peroxidation. More serious damage to cell permeability led to higher internalization of Ag under Ag-NPs stress. Application of exogenous NO reduced the inhibition ratio of photosynthetic pigments and chlorophyll autofluorescence. Further, NO reduced the MDA levels by scavenging reactive oxygen species induced by Ag-NPs. NO modulated the secretion of extracellular polymers and hampered the internalization of Ag. All these results showed that NO alleviates the toxicity of Ag-NPs to C. vulgaris. However, NO did not improve the toxic effects of Ag+. Our results provide new insights into the toxicity mechanism of Ag-NPs to algae modulated by the signal molecule NO.

Roles of polystyrene micro/nano-plastics as carriers on the toxicity of Pb2+ to Chlamydomonas reinhardtii.

Little information could be consulted on the impacts of micro-plastics as carriers on toxicity of heavy metals, especially for micro-plastics of different sizes. Therefore, this study investigated the adsorption and desorption of Pb2+ on polystyrene plastics with nano- and micro-size (NPs and MPs), and further evaluated the roles of NPs and MPs as carriers on the toxicity of Pb2+ to Chlamydomonas reinhardtii (C. reinhardtii). The results showed that NPs showed higher adsorption capacities and a lower desorption rate for Pb2+ than MPs. The growth inhibitory rates (IR) of mixed and loaded Pb2+ with MPs to C. reinhardtii were 18.29% and 15.76%, respectively, which were lower than that of Pb2+ (22.28%). The presence of MPs decreased the bioavailability of Pb2+ to C. reinhardtii by a competitive adsorption for Pb2+ between MPs and algal cells, and suppressed membrane damage and oxidative stress caused by Pb2+. Maximum IR was observed for the mixture of NPs with Pb2+ (35.64%), followed by Pb2+ loaded on NPs (30.13%), single NPs (26.71%) and Pb2+ (21.01%). The internalization of NPs with absorbed Pb2+ intensified lipid peroxidation. The mixed and loaded microplastics with Pb2+ had more negative effects on C. reinhardtii than the single microplastics. The size-dependent effect was observed in the capacity of heavy metal ions carried by microplastics and the roles of microplastics as carriers on the toxicity of Pb2+. The results showed that the indirect risk of microplastics as 'carriers' could not be ignored, especially for NPs.