The impact of silver nanoparticles on plant physiology

Engineered nanoparticles (ENPs) are increasingly being exploited in a whole range of applications and products due to their novel physicochemistry. Hence it is inevitable that ENPs will enter the environment at an increasing rate over the coming years. The consequential impact following interaction between ENPs with plants and soil microbial communities is of great concern given that they play fundamental roles in the environment and food production. In this study, the impact of capped silver nanoparticles (cAg NPs) on terrestrial (Arabidopsis thaliana and Vicia faba) and aquatic (Lemna minor) plants was investigated. In addition, due to the important role of bacteria in plant survival and growth, this study also assessed the effect of cAg NPs on plant-associated soil microbial community structure. cAg NPs demonstrated varied toxicity towards plants and the associated soil microbes. Whilst the aquatic plants and soil microbial communities investigated in this study were not affected by cAg NPs up to 100 mg/L, for the terrestrial plants evaluated here, cAg NPs above 12 mg/L (specifically 50 and 100 mg/L) demonstrated differential toxic responses. Based on the results of this study, it is clear that concentration, exposure method, released ions, plant species, light intensity and growth mediums are key factors that influence the toxicity of cAg NPs. Although the cAg NP concentrations applied in this study are not yet environmentally relevant, with continued and uncontrolled commercial production of Ag NPs and/or in the event of spillage, such concentrations could occur in the environment in the future. Chlorophyll fluorescence and gas exchange are valuable techniques for analysing the toxicity of ENPs on plants, due to their rapid and reliable results. Further studies in the interactions between plants and Ag NPs are urgently needed and would benefit from the use of different application methods such as aerosolization.