Multiwalled carbon nanotubes in alfalfa and wheat: toxicology and uptake

Abstract

Data on the bioavailability and toxicity of carbon nanotubes (CNTs) in the environment, and, in particular, on their interactions with vascular plants, are limited. We investigated the effects of industrial-grade multiwalled CNTs (75 wt% CNTs) and their impurities on alfalfa and wheat. Phytotoxicity assays were performed during both seed germination and seedling growth. The germinations of both species were tolerant of up to 2560 mg l 21 CNTs, and root elongation was enhanced in alfalfa and wheat seedlings exposed to CNTs. Remarkably, catalyst impurities also enhanced root elongation in alfalfa seedlings as well as wheat germination. Thus the impurities, not solely the CNTs, impacted the plants. CNT internalization by plants was investigated using electron microscopy and two-dimensional Raman mapping. The latter showed that CNTs were adsorbed onto the root surfaces of alfalfa and wheat without significant uptake or translocation. Electron microscopy investigations of internalization were inconclusive owing to poor contrast, so Fe 3 O 4 -functionalized CNTs were prepared and studied using energyfilter mapping of Fe 3 O 4 . CNTs bearing Fe 3 O 4 nanoparticles were detected in the epidermis of one wheat root tip only, suggesting that internalization was possible but unusual. Thus, alfalfa and wheat tolerated high concentrations of industrial-grade multiwalled CNTs, which adsorbed onto their roots but were rarely taken up.

Influence of water soluble carbon dots on the growth of wheat plant

“…Over last few years, there have been extensive studies to understand the influence of nanomaterials on the growth of different types of plants (Khodakovskaya et al 2009;Khodakovskaya et al 2013a, b;Lu et al 2002;Cañas et al 2008;Yang et al 2006;Hong et al 2005a, b;Tan et al 2009;Yuan et al 2011;Khodakovskaya et al 2013a, b;Mahajan et al 2011;Wang et al 2012;Larue et al 2012;Miralles et al 2012;Feizi et al 2012;Tripathi et al 2011;Sonkar et al 2012). Khodakovskaya et al (2009Khodakovskaya et al ( , 2013a demonstrated that at very low doses MWCNT can penetrate the seed coat and enhance the germination of tomato plant.…”

Interactions between engineered nanomaterials and agricultural crops: implications for food safety

“…For example, reduced germinated was noted with nanoparticle ZVI on Hordeum vulgare and Linum usitatissimum seeds at 250 mg/L, NP-ZnO on Zea mays seeds at 2000 mg/L, and CeO 2 on Medicago sativa, Zea mays and Cucumis sativus seeds at 2000 mg/L (Lin and Xing, 2007;LopezMoreno et al, 2010b;El-Temsah and Joner, 2012;Feizi et al, 2012;Ghafariyan et al, 2013). Compared to metal-based ENMs, CNTs were shown to not affect seed germination even at 2000 mg/L (Lin and Xing, 2007;Miralles et al, 2012a). Positive effects on seed germination were reported mainly in TiO 2 and industrial-grade CNTs, particularly on seeds with inherently low germination (Zheng et al, 2005;Miralles et al, 2012a;Feizi et al, 2013).…”

“…However, positive effects were noticed upon NP Au, Fe 2 O 3 , CeO 2 exposure over ion or bulk particle controls, including size-specific effects on root elongation (Barrena et al, 2009;Lopez-Moreno et al, 2010a;Ghodake et al, 2011;Dimkpa et al, 2012;Alidoust and Isoda, 2013;Ghafariyan et al, 2013). Conflicting data in the literature are common for carbon-based ENMs such as graphene, SWCNTs, and MWCNTs (Canas et al, 2008;Begum et al, 2011;Miralles et al, 2012a). More disconcerting than the contradictory findings in the literature is the almost complete lack of mechanistic understanding for the observed plant responses.…”

“…MWCNTs tended to adsorb onto root surfaces and pierce root epidermal tissue. The tubes induce physical damage and therefore stress crop plants without typically being internalized (Miralles et al, 2012a). Surface coating is a second important role in determining the possibility of ENMs uptake.…”

“…Compared to metal-based ENMs, CNTs were shown to not affect seed germination even at 2000 mg/L (Lin and Xing, 2007;Miralles et al, 2012a). Positive effects on seed germination were reported mainly in TiO 2 and industrial-grade CNTs, particularly on seeds with inherently low germination (Zheng et al, 2005;Miralles et al, 2012a;Feizi et al, 2013). Thus, reactive oxygen species (ROS) induced by nano-TiO 2 may have enhanced seed stress resistance and facilitated capsule penetration for water and oxygen intake that enabled more rapid germination (Khot et al, 2012).…”