Silver nanoparticle (AgNPs) toxicity is related to nanoparticle interaction with the cell wall of microorganisms and plants. This interaction alters cell wall conformation with increased reactive oxygen species (ROS) in the cell. With the increase of ROS in the cell, the dissolution of zero silver (Ag0) to ionic silver (Ag+) occurs, which is a strong oxidant agent to the cellular wall. AgNP interaction was evaluated by transmission electron microscopy (TEM) on Lactuca sativa roots, and the mechanism of passage through the outer cell wall (OCW) was also proposed. The results suggest that Ag+ binds to the hydroxyls (OH) present in the cellulose structure, thus causing the breakdown of the hydrogen bonds. Changes in cell wall structure facilitate the passage of AgNPs, reaching the plasma membrane. According to the literature, silver nanoparticles with an average diameter of 15 nm are transported across the membrane into the cells by caveolines. This work describes the interaction between AgNPs and the cell wall and proposes a transport model through the outer cell wall.

The advancement of nanotechnology has increased use of nanoparticles in industrial scale. Among the most used nanoparticles are those silver-based. Large-scale use can raise levels of these nanoparticles in aquatic environments, which, in turn, presents potential risks to aquatic organisms and ecosystems, causing undesired environmental impacts. To evaluate the potential risk of the silver nanoparticles (AgNPs) interaction with plants, seeds of Lactuca sativa L. (Asteraceae) were exposed to different concentrations of AgNPs (12.5, 25, 50, 100 ppm), using the percentage of germinated seeds and morphological changes in the root as toxicity criterion. Only at the maximum concentration of AgNPs (100 ppm), there is a negative effect on root growth in relation to the positive control (distilled water). These negative effects may be related to the production of reactive oxygen species (ROS) caused by the dissolution of Ag0 in Ag+. Other concentrations had a positive effect on root growth, although not significant. Scanning electron microscopy (SEM) images showed morphological changes in the root surface exposed to the concentration of 100 ppm of AgNPs, resulting in root deformation. The accumulation of silver nanoparticles (AgNPs) was observed using transmission electron microscopy (TEM). AgNPs were found in the vacuoles, cell wall, middle lamella and cytoplasm, individualised or forming agglomerates. These results broaden our understanding of the safe levels of nanoparticle use and its impact on the environment. In addition, the nanoparticles used in this study can be used in new product development, since the observed maximum safe amount.

The effects of ultrasound processing parameters on the extraction of antioxidative enzymes and a toxicity assessment of cashew apple bagasse puree were investigated. Ultrasound directly affects the formation of reactive oxygen species such as H₂O₂, and consequently, superoxide dismutase, catalase, and ascorbate peroxidase activities. S.O.D. activity increased up to 280% after U.S. processing at 75 W/cm², 1:3 bagasse: water ratio, and 10 min compared to non-processed bagasse. Therefore, the effect of ultrasound in delaying browning could be correlated to the enhanced antioxidant enzyme activity and decrease in peroxidase activity. At center point conditions (226 W/cm², 1:3 bagasse: water ratio; 6 min), a decrease of 20% and 50% on POD and PPO activities was observed, respectively. No significant acute toxicity or protective effect was observed in unprocessed and sonicated cashew apple bagasse. Although cashew bagasse processed at 75 W/cm² prevented nauplii death after 24 h of exposure, this data cannot assure the protective effect once the number of dead nauplii on 100 μg/mL was similar. However, these data indicate a possible protective effect, especially in higher cashew bagasse concentrations. The results suggest that sonicated cashew apple bagasse puree, a coproduct obtained from a traditional valued fruit in Brazil, may be used as a source of antioxidative enzymes, which further has great importance in therapeutics.