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.

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.

RESUMO. O processo de industrialização e o crescimento acelerado da população mundial que ocorreu nas últimas décadas colocaram em risco diversos ecossistemas, em especial os aquáticos, que tiveram contato com numerosas substâncias químicas potencialmente tóxicas. Estudos de ecotoxicidade com organismos sensíveis a pequenos desequilíbrios ambientais são estudados de forma crescente com o objetivo de testar substâncias que poderiam representar efeitos tóxicos no organismo humano. Dentro deste grupo, destacam-se os pequenos cnidários do gênero Hydra. Por possuir uma série de características favoráveis, este grupo se consolidou como organismo-teste frente a diversos tipos de espécies. Este trabalho de revisão teve o propósito de reunir as informações mais relevantes sobre a importância dos testes de ecotoxicidade e as vantagens e desvantagens da utilização de espécies do gênero Hydra em tais estudos.Palavras chave: Bioensaios, ecotoxicologia, hydra, organismo-teste Hydra (Cnidaria, Hydrozoa) as a model in ecotoxicity studies: Review ABSTRACT. The industrialization process and the accelerated growth of the world population that it happened in the last decades put in risk several ecosystems, especially the aquatic ones that had contact with numerous potentially toxic chemical substances. Ecotoxicity studies with organisms sensitive to small environmental imbalances are increasingly being studied with the aim of testing substances that could represent toxic effects on the human body. Within this group, the small cnidarians of the genus Hydra stand out. By having a series of favorable characteristics, this group consolidated as test organism in front of several species types. This review work had the purpose of gathering the most relevant information about the importance of the tests of ecotoxicity and the advantages and disadvantages of the use of species of the genus Hydra in such studies.Keywords: Bioassays, ecotoxicology, hydra, test organism Hydra (Cnidaria, Hydrozoa) como modelo en estudios de ecotoxicidad: Revisión RESUMEN. El proceso de industrialización y el crecimiento acelerado de la población mundial que ha ocurrido en las últimas décadas han puesto en riesgo diversos ecosistemas, en particular los acuáticos, que han tenido contacto con numerosas sustancias químicas potencialmente tóxicas. Los estudios de ecotoxicidad con organismos sensibles a pequeños desequilibrios ambientales se estudian de forma creciente con el objetivo de probar sustancias que podrían representar efectos tóxicos en el organismo humano. Dentro de este grupo, se destacan los pequeños cnidarios del género Hydra. Por poseer una serie de

No abstract