Phytotoxicity of silver nanoparticles on Vicia faba: Evaluation of particle size effects on photosynthetic performance and leaf gas exchange.

Nanotechnology is an emerging field in science and engineering, which presents significant impacts on the economy, society and the environment. The nanomaterials' (NMs) production, use, and disposal is inevitably leading to their release into the environment where there are uncertainties about its fate, behaviour, and toxicity. Recent works have demonstrated that NMs can penetrate, translocate, and accumulate in plants. However, studies about the effects of the NMs on plants are still limited because most investigations are carried out in the initial stage of plant development. The present study aimed to evaluate and characterize the photochemical efficiency of photosystem II (PSII) of broad bean (Vicia faba) leaves when subjected to silver nanoparticles (AgNPs) with diameters of 20, 51, and 73 nm as well as to micrometer-size Ag particles (AgBulk). The AgNPs were characterized by transmission electron microscopy and dynamic light scattering. The analyses were performed by injecting the leaves with 100 mg L-1 aqueous solution of Ag and measuring the chlorophyll fluorescence imaging, gas exchange, thermal imaging, and reactive oxygen species (ROS) production. In addition, silver ion (Ag+) release from Ag particles was determined by dialysis. The results revealed that AgNPs induce a decrease in the photochemical efficiency of photosystem II (PSII) and an increase in the non-photochemical quenching. The data also revealed that AgNPs affected the stomatal conductance (gs) and CO2 assimilation. Further, AgNPs induced an overproduction of ROS in Vicia faba leaves. Finally, all observed effects were particle diameter-dependent, increasing with the reduction of AgNPs diameter and revealing that AgBulk caused only a small or no changes on plants. In summary, the results point out that AgNPs may negatively affect the photosynthesis process when accumulated in the leaves, and that the NPs themselves were mainly responsible since negligible Ag+ release was detected.

Cytotoxic and genotoxic effects of silver nanoparticles on meristematic cells of Allium cepa roots: A close analysis of particle size dependence.

The use of silver nanoparticles (AgNPs) in commercial products has increased significantly in recent years. However, findings on the toxic effects of the AgNPs are still limited. This paper reports an investigation on the cytotoxic and genotoxic potential of the AgNPs on root cells of Allium cepa. Germination (GI), root elongation (REI), mitotic (MI), nuclear abnormality (NAI), and micronucleus index (MNI) were determined for seeds exposed to various AgNPs diameters (10, 20, 51, and 73 nm) as well as to the silver bulk (AgBulk) (micrometer-size particles) at the concentration of 100 mg·L-1. Transmission electron microscopy (TEM) provided the particle size distribution, while dynamic light scattering (DLS) was used to get the hydrodynamic size, polydispersity index, and zeta potential of the AgNPs. Laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma/optical emission spectrometry (ICP OES) were applied for quantifying the AgNPs content uptake by roots. Silver dissolution was determined by dialysis experiment. Results showed that the AgNPs penetrated the roots, affecting MI, GI, NAI, and MNI in meristematic cells. Changes in these indicators were AgNPs diameter-dependent so that cytotoxic and genotoxic effects in Allium cepa increased with the reduction of the particle diameter. The results also revealed that the AgNPs were the main responsible for the cytotoxicity and genotoxicity since negligible silver dissolution was observed.

Environmental evaluation of flocculation efficiency in the separation of the microalgal biomass of Scenedesmus sp. cultivated in full-scale photobioreactors.

In this paper the environmental evaluation of the separation process of the microalgal biomass Scenedesmus sp. from full-scale photobioreactors was carried out at the Research and Development Nucleus for Sustainable Energy (NPDEAS), with different flocculants (iron sulfate - FeCl3, sodium hydroxide - NaOH, calcium hydroxide - Ca(OH)2 and aluminum sulphate Al2(SO4)3, by means of the life cycle assessment (LCA) methodology, using the SimaPro 7.3 software. Furthermore, the flocculation efficiency by means of optical density (OD) was also evaluated. The results indicated that FeCl3 and Al2(SO4)3 were highly effective for the recovery of microalgal biomass, greater than 95%. Though, when FeCl3 was used, there was an immediate change in color to the biomass after the orange colored salt was added, typical with the presence of iron, which may compromise the biomass use according to its purpose and Al2(SO4)3 is associated with the occurrence of Alzheimer's disease, restricting the application of biomass recovered through this process for nutritional purposes, for example. Therefore, it was observed that sodium hydroxide is an efficient flocculant, promoting recovery around 93.5% for the ideal concentration of 144 mg per liter. It had the best environmental profile among the compared flocculant agents, since it did not cause visible changes in the biomass or compromise its use and had less impact in relation to acidification, eutrophication, global warming and human toxicity, among others. Thus, the results indicate that it is important to consider both flocculation efficiency aspects and environmental impacts to identify the best flocculants on an industrial scale, to optimize the process, with lower amount of flocculant and obtain the maximum biomass recovery and decrease the impact on the extraction, production, treatment and reuse of these chemical compounds to the environment. However, more studies are needed in order to evaluate energy efficiency of the process coupled with other microalgal biomass recovery technologies. In addition, studies with natural flocculants, other polymers and changes in pH are also needed, as these are produced in a more sustainable way than synthetic organic polymers and have the potential to generate a biomass free of undesirable contaminants.

Determination of the biodiesel content in diesel/biodiesel blends: a method based on fluorescence spectroscopy.

Blends of biodiesel and diesel are being used increasingly worldwide because of environmental, economic, and social considerations. Several countries use biodiesel blends with different blending limits. Therefore, it is necessary to develop or improve methods to quantify the biodiesel level in a diesel/biodiesel blend, to ensure compliance with legislation. The optical technique based on the absorption of light in the mid-infrared has been successful for this application. However, this method presents some challenges that must be overcome. In this paper, we propose a novel method, based on fluorescence spectroscopy, to determine the biodiesel content in the diesel/biodiesel blend, which allows in loco measurements by using portable systems. The results showed that this method is both practical and more sensitive than the standard optical method.