Study On The Bioavailability Of Nanosilver To Rice

Different methods of qualitative and quantitative analysis of AgNP were compared in the study, including the comparison of different methods of separation,digestion, and characterization methods. meanwhile, the bioavailability of AgNP on rice was also investigated, including toxicity, uptake, accumulation and the effect of organic matter on the uptake rate. The results demonstrated that the separation effect of ultracentrifugation was influenced by total Ag concentration in solution. Room temperature digestion(25℃) was a simple and effective digestion method for simple AgNP solution. The hydrodynamic diameter of AgNP obtained through DLS was significantly higher than that of TEM and it was mostly because of the presence of Polyvinylpyrrolidone, which might enlarged the size of AgNP while the Polyvinylpyrrolidone could not be observed by TEM.AgNP could be uptaken and accumulated by rice through root and leaf exposure, and the concentration of AgNP in leaves through leaf exposure was much higher than that of root exposure, but more markedly toxicity to rice by root exposure, for example, when the AgNP exposure concentration was 1 mg/L, the concentration of AgNP in leaves through root exposure was 0.44 mg/kg while the concentration of AgNP was up to 8.40 mg/kg through leaf exposure. The size distribution of AgNP in leaves was also investigated with the aid of single particle inductively coupled plasma mass spectrometry. The size of AgNP after internalized by rice trended to aggregate to 30-40 nm irrespective of exposured Ag forms. In addition, leaves treated with AgNP through leaf exposure were prepared for TEM-EDS analysis. The results confirmed the exist of AgNP with a size range of 30-40 nm, which was in accordance with the results of single particle inductively coupled plasma mass spectrometry. They were much higher than the original size of nanosilver in exposure solution(13.3±3.7 nm). The biomass index showed that AgNP significantly inhibited the growth of rice after exposure, and there was no significant toxic effect through leaf exposure.Decomposed rice straw solution was used as a model organic matter to investigate the effects of NOM on AgNP bioavailability. AgNP uptake rate(0.21 mg/(g·h)—0.03 mg/(g·h)), which was characterized during 4 h exposure, decreased with increasing levels of total organic carbon(TOC, 0 mg/L—20 mg/L); however AgNP uptake rates(~0.03 mg/(g·h)) were comparable when TOC levels were 20 and 80 mg/L respectively. Simultaneously, AgNP dissolution was inhibited(27.5 %—95.5 %) by the decomposed rice straw solution in a dose-dependent manner. This leaded to a reduction in dissolved silver ion concentration in the exposure medium and consequently a lower uptake rate of AgNP. In the meantime, the decomposed rice straw had the potential to promote the aggregation of AgNP, which reduced AgNP uptake. Besides TOC concentrations, molecular weight fractionated NOM had different roles on AgNP uptake rate. Especially, lower molecular weight NOM(<3 KDa) had comparable AgNP uptake rates relative to those pristine NOM, addressing the importance of low molecular weight NOM for AgNP uptake.The results could provide basic data for the study of enrichment and migration of AgNP in plants and the study of biological amplification along the food chain. In addition, it could provid supporting information for the potential risks to higher organisms and human beings.