Most of these studies are focused on the potential toxicity of ENPs to plants and both positive and
negative or inconsequential effects have been reported [10]. Among the positive effect reports on plants,
nano-TiO2 was observed to promote the growth of Spinach. [11, 12]. Some research found that Carbon
nanotubes (CNTs) could enhance root growth of onion (Allium cepa) and cucumber (Cucumis sativa) [14].
However, majority of the reports available in the literature indicate phytotoxicity of ENPs. Nano-aluminum
oxide (Al2O3) could inhibit root elongation of corn, cucumber, soybean, cabbage and carrot [14] while nano-
ZnO was reported to be one of the most toxic nanoparticles that could terminate root growth of test plants
(radish, rape, ryegrass, lettuce, corn and cucumber) [15].