Navegando por Autor "Barbosa, Francisco Antônio Rodrigues"

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Algistatic effect of a quinonamethide triterpene on Microcystis novacekii.
(2013) Silva, Fernando César; Guedes, Fernanda Alves de Freitas; Franco, Maione Wittig; Barbosa, Francisco Antônio Rodrigues; Marra, Camila Antunes; Duarte, Lucienir Pains; Silva, Grácia Divina de Fátima; Vieira Filho, Sidney Augusto
Cyanobacteria proliferation represents a problem to water treatment for human consumption supply. Species of the genus Microcystis, commonly found in continental waters, can bloom and produce microcystine and other toxic compounds associated to human and animal poisoning, depending on the nutrient levels present in the water. The use of natural products to control cyanobacteria blooms is promising since they are less harmful to the environment than compounds obtained by organic syntheses. Triterpenes, which are associated with several biological activities, have been isolated from species of the genus Maytenus (Celastraceae), commonly found in Cerrado regions of Brazil. Tingenone is a pentacyclic triterpene that has cytotoxic properties and induces growth inhibition in some microorganisms. In this study, the effects of tingenone isolated from Maytenus gonoclada at distinct concentrations (e.g., 50, 150, 500, 1,500, and 4,500 μg L−1) on the growth rates of Microcystis novacekii was investigated. The algicide activity was verified using M. novacekii cultures growing in ASM1 culture medium at 23 °C and continuous illumination for 96 h. Growth inhibition was monitored by light microscopy and optical density (OD680 nm). The median effective concentration associated to the M. novacekii inhibition growth induced by tingenone was 12.2 μg L−1. The result indicates that tingenone has algicide effect and can be potentially applied in water management for public supply, replacing synthetic algicides.
Determination of methylmercury in sediment and cyanobacteria samples : method validation and application to methylation investigation.
(2018) Mendes, Louise Aparecida; Franco, Maione Wittig; Barbosa, Francisco Antônio Rodrigues; Carvalho, Paula Iannarelli Aires de; Lena, Jorge Carvalho de; Windmöller, Cláudia Carvalhinho
The aim of this work was to validate two methods for methylmercury (CH3Hg+) determination in sediments and cyanobacteria and their application to the Hg methylation study of planktonic organisms in water from a contaminated site in Brazil. Analytical methods for the determination of CH3Hg+ include many steps, and the necessity of adaptation to different matrices is very common and not always easy. In addition, these adaptations require new optimization and validation, which are found in a few articles using the matrix sediments but in none with planktonic organisms. The methods presented here were based on the extraction of CH3Hg+ from these matrices, derivatization, trapping, thermal desorption, GC separation, pyrolysis and detection by AFS (GC-pyro-AFS). The results showed good linearity (0.994) in the range of 0 to 400 pg CH3Hg+ with a repeatability of 3%, an intermediate precision of 8%, a recovery in spiked sample tests in the range of 93 to 129%, and detection limits of 0.04 mg kg 1 for sediments and 1.3 mg kg 1 for cyanobacteria. Certified reference materials showed good recoveries. The method for the cyanobacteria matrix was used for the Hg2+ methylation assay with cultures of cyanobacteria and microalgae isolated from water samples collected in an ancient Hg-contaminated gold mining area in Brazil. The production of CH3Hg+ was detected only in the culture of the microalga Stichococcus species (0.23% of total Hg), indicating its participation in the biotransformation of Hg. The methods can be used as important tools in routine analysis and/or studies of the biogeochemical cycle of Hg.
Diatoms as proxies for environmental change : a paleolimnological investigation of a Shallow Iron Outcrop Lake (Lagoa dos Coutos, Serra do Gandarela, MG).
(2016) Leibowitz, Zachary William; Leite, Mariangela Garcia Praça; Sant'Anna, Eneida Maria Eskinazi; Cassino, Raquel Franco; Leite, Mariangela Garcia Praça; Delício, Maria Paula; Barbosa, Francisco Antônio Rodrigues
Os sedimentos lacustres fornecem registros de condições físicas, químicas e biológicas passadas dos lagos e seus ambientes circundantes. Muitos estudos paleolimnológicos utilizam diatomáceas como objetos de investigação devido à sua sensibilidade a condições limnológicas e por possuírem uma parede celular de sílica que permanecem bem preservadas ao longo do tempo. No entanto, o conhecimento autoecológico das espécies é requisito fundamental para o sucesso completo das investigações. Embora estudos sobre diatomáceas no Brasil remontem ao século XIX, os mais recentes estão concentrado nos estados da região Sul e de São Paulo. A geoquímica de sedimentos de lagos, assim como as diatomáceas, também podem fornecer informações sobre mudanças passadas, no entanto, é importante ressaltar que estes podem sofrer mudanças pós-deposicionais. Uma maneira de entender melhor a geoquímica de sedimentos é usar procedimentos de extração padrão (PEPs). Para estudar as diatomáceas, as alterações limnológicas passadas e a geoquímica de um lago temporário raso (Lagoa dos Coutos) foram coletados dois testemunhos de 10 cm de comprimento das zonas central e litorânea, os quais foram divididos em intervalos de 1 cm. A partir daí, os sedimentos foram processados e analisados a cada centímetro para identificação das diatomáceas, mudanças na assemblia de espécies de diatomáceas, pH, nitrogênio, matéria orgânica e idade de radiocarbono. Também realizou-se um BCR® PEP harmonizado de 3 passos e uma digestão total no seu resíduo, tendo sido analisadas as concentrações de numerosos elementos utilizando-se um ICP-OES. Foram identificadas 22 espécies de diatomáceas, 4 como novos registros para Minas Gerais, 1 como um novo registro para o Brasil, 5 como cf. e, para 3 espécies não foram encontrados correspondentes semelhantes na literatura. A análise das diatomáceas nos sedimentos desta lagoa só foi possível para o testemunho do litoral, embora tenham sido observadas mudanças, a falta de conhecimento autoecológico impossibilitou interpretações significativas. Com base no limitado conhecimento autoecológico das diatomáceas encontradas, sugere-se que o lago permaneceu oligotrófico e ácido desde pelo menos 7550 anos cal AP. O padrão de fracionamento geoquímico entre os pontos mostrou que uma maior parte da concentração elementar total foi encontrada na fração residual do testemunho central em relação ao testemunho do litoral. Com algumas exceções, o core central também apresentou concentrações mais altas de quase todos os elementos analisados em comparação com o core do litoral. A dissolução de sílica no ponto central foi observada em diatomáceas e em análises mineralógicas.
Forest–lake ecotones in a tropical forest : terrestrial invertebrate inputs to lakes decrease with forest distance.
(2022) Dolabela, Bárbara Martins; Costa, Fernanda Vieira da; Pinto, Victor Diniz; Lopes, Isabela; Bezerra Neto, José Fernandes; Barbosa, Francisco Antônio Rodrigues; Ribeiro, Sérvio Pontes
1. Ecotones between tropical forests and lakes compose an ecosystem intercon- nection with a high abundance of terrestrial invertebrates, which represent an outstanding resource for the aquatic fauna. However, there is still little quantita- tive information on tropical forest contribution in terms of invertebrate inputs into lacustrine systems and the factors controlling this flux. 2. To quantify the terrestrial invertebrate contribution into tropical lakes, we se- lected six lakes located in the Atlantic rainforest, south-eastern Brazil, and used pan traps placed in the lakeshore. We focused on total abundance, biomass, and richness of insect orders. To assess the influence of forest and lake morphom- etry on terrestrial invertebrate inputs into lakes, we measured the forest–lake distance and considered the morphometric characteristics of each lake. 3. Distance from forest negatively affected the invertebrate biomass reaching the lakes. The dissimilarity across different ecotones also increased with distance from the forest. Perimeter-to-area ratio negatively affected the invertebrate abundance, suggesting that more dendritic lakes receive more invertebrates from the forest. 4. We estimated that annually, on average 21 tons of terrestrial invertebrates fall into the studied lakes, representing a massive food resource for the aquatic eco- system. Hence, if the distance from the forest increases due, for instance, to se- vere drought or deforestation, it will create an herbaceous environment unable to provide such a quantity of insects to the water ecosystems, compromising aquatic and terrestrial trophic webs dynamics.