Quantifying the relative contribution of particulate versus dissolved silver to toxicity and uptake kinetics of silver nanowires in lettuce: impact of size and coating

Functionalized high-aspect-ratio silver nanowires (AgNWs) have been recognized as one of the most promising alternatives for fabricating products, with their use ranging from electronic devices to biomedical fields. Given concerns on the safety of AgNWs, there is an urgent need to investigate the relation between intrinsic properties of AgNWs and their toxicity. In this study, lettuce was exposed for either 6 or 18 d to different AgNWs to determine how the size/aspect ratio and coating of AgNWs affect the contributions of the dissolved and particulate Ag to the overall phytotoxicity and uptake kinetics. We found that the uncoated AgNW (39 nm diameter × 8.4 µm length) dissolved fastest of all AgNWs investigated. The phytotoxicity, uptake rate constants, and bioaccumulation factors of the PVP-coated AgNW (43 nm diameter × 1.8 µm length) and the uncoated AgNW (39 nm diameter × 8.4 µm length) were similar, and both were higher than that of the PVP-coated AgNW with the larger diameter(65 nm diameter × 4.4 µm length). These results showed that the diameter of the AgNWs predominantly affected toxicity and Ag accumulation in plants. Particulate Ag was found to be the predominant driver/descriptor of overall toxicity and Ag accumulation in the plants rather than dissolved Ag for all AgNWs tested. The relative contribution of dissolved versus particulate Ag to the overall effects was influenced by the exposure concentration and the extent of dissolution of AgNWs. This work highlights inherent particulate-dependent effects of AgNWs in plants and suggests that toxicokinetics should explicitly be considered for more nanomaterials and organisms, consequently providing more realistic input information for their environmental risk assessment.