Effects, uptake, and translocation of aluminum oxide nanoparticles in lettuce: A comparison study to phytotoxic aluminum ions.

The widespread use of aluminum oxide nanoparticles (Al 2 O 3 NPs) unavoidably causes the release of NPs into the environment, potentially having unforeseen consequences for biological processes. Due to the well-known issue of Al phytoxicity, plant interactions with Al 2 O 3 NPs are cause for concern, but these interactions remain poorly understood. This study investigated the effects of Al 2 O 3 NPs on lettuce (Lactuca sativa L.) to elucidate the similarities and differences in plant growth responses when compared to those of Al ions. Seed germination, root length, biomass production, and uptake of Al and nutrients were measured from hydroponically-grown lettuce with varying concentrations of Al 2 O 3 NPs (0, 0.4, 1, and 2 mg/mL) or AlCl 3 (0, 0.04, 0.4, and 1 mg/mL). The Al 2 O 3 NPs treatments had a positive influence on root elongation, whereas AlCl 3 significantly reduced emerging root lengths. While 0.4 mg/mL Al 2 O 3 NPs promoted biomass, 1 and 2 mg/mL showed a 10.4% and 17.9% decrease in biomass, respectively, when compared to the control. Similarly, 0.4 and 1 mg/mL AlCl 3 reduced biomass to 22.3% and 9.96%, respectively. Both treatments increased Al uptake by roots linearly; however, translocation of Al 2 O 3 NPs into shoots was limited, whereas translocation of AlCl 3 increased with increasing treatment concentration. Further, Al 2 O 3 NPs adsorbed on the roots serve as adsorbents for macronutrients, promoting their absorption and uptake in plants, but not micronutrients. Calcium uptake was the most inhibited by AlCl 3. A new in vivo imaging technique, with elemental analysis, confirmed that Al 2 O 3 NPs were assimilated as particles, not ions, suggesting that the observed phytotoxicity is not due to Al ions being released from the NPs. Thus, it is concluded that Al 2 O 3 NPs pose less phytoxicity than AlCl 3 , primarily due to NPs role on stimulated root growth, significant adsorption/aggregation on roots, limited lateral translocation to shoots, and increased uptake of macronutrients. Unlabelled Image • The Al 2 O 3 NPs aggregated onto root serve as adsorbents for plant macronutrients. • Al 2 O 3 NPs help enhance uptake of plant macronutrients, but reduce micronutrients. • In vivo images of Al 2 O 3 NPs in tissue indicate NPs are assimilated as particles. • Al 2 O 3 NPs possess a lower potential than Al ions to translocate in shoots. • Al 2 O 3 NPs do not undergo biotransformation after being taken up by roots. [ABSTRACT FROM AUTHOR]