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.
Coconut water is widely consumed and appreciated due its sensory, nutritional, and functional characteristics. Despite being widely consumed, this beverage has a short shelf life that can be improved through processing technologies including nonthermal technologies. Although this processing is promising, it also can generate toxic bioactive compounds of natural and synthetic origin. Their safety has been long discussed, and concern for human food security is now clearly manifested by warnings added on products labels. The aim of this work was to evaluate the toxic and the protective effect of natural and processed coconut water by non-thermal technologies against oxidative stress in brine shrimp (Artemia salina). For acute toxicity test, A. salina nauplii instar II were exposed to different concentrations and ozone-processed (OTCW), plasma-processed (PTCW), and ultrasound-processed (UTCW) coconut water. The non-processed sample was the negative control. By the end of experiment (48 h), dead nauplii were counted and investigated under optical and electron microscopy. The protective effect was evaluated against H 2 O 2 and morphological changes were also investigated. Coconut water treated with plasma and ultrasound was not toxic to Artemia salina nauplii at 10, 100, or 1000 μg mL −1 ; however, ozone-treated artificial seawater caused a mild toxicity to nauplii exposed to 1000 μg mL −1 . All coconut water samples, included untreated samples, presented protective effect against oxidative stress caused by H 2 O 2 reaching levels of 87.5% protection compared to control (24 h of experiment).
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 15nm 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.
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