Understanding the phyto-interaction of heavy metal oxide bulk and nanoparticles: evaluation of seed germination, growth, bioaccumulation, and metallothionein production.

Bilal Ahmed,Javed Musarrat,Almas Zaidi,Asfa Rizvi,Mohammad Saghir Khan

doi:10.1039/c8ra09305a

Abstract

The fast-growing use of nano-based products without proper care has led to a major public health concern. Nanomaterials contaminating the environment pose serious threat to the productivity of plants and via food chain to human health. Realizing these, four vegetable crops, radish, cucumber, tomato, and alfalfa, were exposed to varying concentrations of heavy metal oxide (TiO2, ZnO, Al2O3 and CuO) submicron or bulk (BPs) and nanoparticles (NPs) to assess their impact on relative seed germination (RSG), seed surface adsorption, root/shoot tolerance index (RTI/STI), bioaccumulation, and metallothioneins (MTs) production. The results revealed a clear inhibition of RSG, RTI, and STI, which, however, varied between species of metal-specific nanoparticles and plants. SEM and EDX analyses showed significant adsorption of MONP agglomerates on seed surfaces. The concentration of metals detected by EDX differed among vegetables. Among the metals, Al, Cu, Ti, and Zn were found maximum in alfalfa (12.46%), tomato (23.2%), cucumber (6.32%) and radish (21.74%). Of the four metal oxides, ZnO was found most inhibitory to all vegetables and was followed by CuO. The absorption/accumulation of undesirable levels of MONPs in seeds and seedlings differed with variation in dose rates, and was found to be maximum (1748–2254 μg g−1 dry weight) in ZnO-NPs application. Among MONPs, the uptake of TiO2 was minimum (2 to 140 μg g−1) in radish seedlings. The concentration of MTs induced by ZnO-NPs, ZnO-BPs, and CuO-NPs ranged between 52 and 136 μ mol MTs g−1 FW in vegetal organs. Conclusively, the present findings indicated that both the nanosize and chemical composition of MONPs are equally dangerous for vegetable production. Hence, the accumulation of MONPs, specifically ZnO and CuO, in edible plant organs in reasonable amounts poses a potential environmental risk which, however, requires urgent attention to circumvent such toxic problems.

Highlights

Nano-technological advancements on the one hand have great potential in many environmental and industrial applications, while on the other hand they raise serious concerns over the use of NPs due to environmental problems.[1]
To the ever-increasing demands, it is likely that the production of metal oxide nanoparticles (MONPs) which was just 0.27 million tons in 2012 will increase to 1.663 million tons by 2020.5 Of the total production, 8–28%, 0.4– 7.0%, and 0.1–1.5% MONPs are expected to accumulate in the soil system, water and atmosphere, respectively, a er production, application, and discharge.[5]
Seeds were exposed to NPs and bulk counterparts (BPs) of TiO2, ZnO, Al2O3, and CuO in two sets of experiments – (i) seeds (N 1⁄4 30) from each plant species were soaked in 0.05, 0.5, 2, and 5 mg mlÀ1 of NPs and BPs prepared in distilled water (DDW) for 12 h and kept on a rotatory shaker (150 rpm) at 25 Æ 2 C

Summary

Introduction

Nano-technological advancements on the one hand have great potential in many environmental and industrial applications, while on the other hand they raise serious concerns over the use of NPs due to environmental problems.[1] Among various NPs, metal oxide nanoparticles (MONPs) for example, ZnO, CuO, TiO2, Al2O3, ZrO2, Fe2O3, Ag2O, CeO2 and NiO are widely used in many industries such as cosmetics, energy production, paints, textiles, and rocket fuels, and in biomedical applications.[1,2] Apart from these, MONPs have been applied in agriculture practices as nano-fertilizers and in protecting plants from pathogens.[3,4] Due to the ever-increasing demands, it is likely that the production of MONPs which was just 0.27 million tons in 2012 will increase to 1.663 million tons by 2020.5 Of the total production, 8–28%, 0.4– 7.0%, and 0.1–1.5% MONPs are expected to accumulate in the soil system, water and atmosphere, respectively, a er production, application, and discharge.[5] Once deposited in soil either through nano-products such as fertilizers, insecticide, and pesticides[1,4] or from other sources, the MONPs may become toxic to bacteria, plants, animal, and human cells.[6,7,8,9] Despite these, the understanding on lethality of MONPs is still limited and requires special attention to better understand the consequences of MONPs on crop production.[10] in this context, a very few attempts have been made to assess the biological impacts of NPs in controlled laboratory conditions with single species of model organisms, which are essential to elucidate the interaction mechanism of NPs.[11]

Methods

Results

Conclusion