Effect of Direct Contact on the Phytotoxicity of Silver Nanomaterials

The increasing use of silver nanomaterials (AgNMs) in consumer products will result in an increased amount entering the environment, where AgNMs were recently found to cause phytotoxicity in the model plant Lolium multiflorum. To better understand the causes of the phytotoxicity, we have designed a new set of experiments to study the effect of AgNM dissolution. Dissolution of AgNMs was measured over a 1-month period to determine if dissolution alone caused phytotoxicity. Very little dissolution was observed over the testing period, suggesting a different mechanism caused the majority of the toxicity. To further confirm this hypothesis, AgNMs were physically separated from the seeds and plants by a dialysis membrane. Toxicity was ameliorated in AgNM-exposed plants, showing that direct contact between AgNMs and plant seeds/roots is a required condition for the observed phytotoxicity in plant models. Probing further, a surface reactivity assay showed increased surface reactivity of silver nanoparticles (AgNPs) and silver nanocubes (AgNCs) corresponded to increased toxicity compared to silver nanowires (AgNMs). The work here can help build the knowledge base regarding shape control of nanomaterials and reducing unintended side effects.