Non-toxicity of nano alumina: A case on mung bean seedlings

Wide use of Al₂O₃ nanoparticles (NPs) leading to their possible escape into environment and their interaction with living organisms demands immediate attention. We evaluated impact of nanoparticulate (Al₂O₃-NPs) and ionic (Al³⁺) forms of aluminium on early seedling growth of Vigna radiata. While Al³⁺ inhibited growth of seedlings, Al₂O₃-NPs did not affect it negatively. Unlike enhancement in proline, malondialdehyde and H₂O₂ levels in roots and shoots induced by Al³⁺, these stress markers remained unaltered by Al₂O₃-NPs. No signs of membrane damage were recorded in roots of seedlings raised in presence of Al₂O₃-NPs; this was witnessed from insignificant electrolyte leakage and Evans blue uptake. Activities of antioxidant enzymes, i.e., superoxide dismustase, catalase, guaiacol peroxidase in root and shoot were enhanced by Al³⁺. However, they were unaffected by Al₂O₃-NPs. Al³⁺ enhanced levels of non-protein thiols, phenolics and ascorbate, with no alterations induced by Al₂O₃-NPs. These findings revealed that, Al₂O₃-NPs did not induce oxidative stress in seedlings. Seedlings raised in Al³⁺ showed higher uptake of Al than those grown in Al₂O₃-NPs; Al content was higher in roots. Al was not detected in shoots of seedlings grown in Al₂O₃-NPs. Lower translocation of Al in seedlings raised in Al₂O₃-NPs was due to adsorption/restriction of Al₂O₃-NPs on root surface. Al³⁺ caused ruptures on root epidermis of seedlings and inhibited root-hair formation, whereas no structural damage was caused by Al₂O₃-NPs. Our findings revealed that while ionic Al is highly toxic, nanoparticulate form of Al is non-toxic to growth of V. radiata.