2, Universidad Nacional Autónoma de México, Mexico City, , Mexico
3, Universidad Nacional Autónoma de México, Mexico City, , Mexico
Carbon nanomaterials, including nanodiamond (ND) and carbon nanotubes (CNTs) promise numerous and diverse applications. This makes their production steadily grow, which raised concerns on their potential impact on environmental systems and human health. These concerns resulted in a number of research reports on how ND and CNTs influence the growth, development and functions of different living organisms, with an emphasis on plants of agricultural importance. Unfortunately, the design of an adequate experimental setup is complicated, due to a considerable size of crop plants. As a result, only short-term assays are usually carried out, whereas long-term effects are inevitably overlooked.
Here we describe a new approach for the long-term assays of ND and CNTs phytotoxicity, employing three cactus species Parodia ayopayana, Ferocactus latispinus and Melocactus matanzanus. All of them are small and slow growing plants, which is very convenient for long-term phytotoxicity assays using the substrate volumes as small as tens of milliliters, contrary to the commonly reported experiments with crop species. The experimental setup of choice was a soil-based experiment. It allows for a better match of the real environmental situation, but, on the other hand, does not allow for direct observations of root development in vivo, contrary to the in vitro experiment performed in vertically-oriented Petri dishes on the plant culture medium solidified with the agar, which we reported previously.1 After few-months observations of seedling growth, we concluded that pristine single-walled CNTs (SWNTs; synthesized by arc-discharge process) exhibited the strongest phytotoxic effect as compared to ND, pristine multi-walled CNTs (MWNTs; by CVD) and purified SWNTs, which can be attributed to a considerable fraction of impurities (amorphous carbon, graphitized particles, metal catalyst, etc.). Our results also showed that after first three months of exposure both ND and nanotubes might produce seemingly favorable effect on seedling growth. Nevertheless, this effect can invert after further exposure for one or more months. Therefore, careful evaluation of the possible phytotoxic effects of ND and other nanomaterials must include observations of the exposed plants for several months, whereas shorter, several week-long assays are definitely insufficient and might produce misleading results.
This work was supported by the projects CONACYT-250655 and UNAM DGAPA-IN200516.
(1) V. A. Basiuk, et al., Sci. Adv. Mater., 5, 1337 (2013).