Thirty-six days after the beginning of the 2020 school year in Brazil, the Rio de Janeiro state education system began an unprecedented disruptive period due to the COVID-19 crisis, which abruptly affected general educational activities, particularly chemistry teaching. An adaptation to a new paradigm of remote teaching and massive use of online educational technology alternatives was tentatively performed, generating lessons for improving implemented actions. Educational institutions prepared independent teaching strategies to provide remote chemistry classes for a total of nearly 397,700 students who were able to begin or continue chemistry classes. This “snapshot” of a daily-life reality faced by professionals engaged in chemistry education in Rio de Janeiro’s schools identified the following factors that negatively affected the implemented actions: the applied television broadcaster essentially covered only the heavily urbanized region, leaving out rural and impoverished areas; a significant absence of adequate technological equipment (e.g., smartphones, tablets, notebooks) for students; pedagogical limitations of instructors, without sufficient training to use online technologies; and inherent limitations of video classes, which do not adequately substitute for practical learning in chemistry laboratories. Strategy improvements are imperative, considering that students face the challenge of increasingly being protagonists for the organization and management of the teaching–learning process.
A simple, fast and sensitive spectrophotometric method for the simultaneous determination of Cr(III) and Cr(VI) in effluents and contaminated waters using a UV-visible spectrophotometer, which operates with an advanced software for multicomponent analysis, is proposed. The method consists in the complexation of Cr (III) with EDTA and reaction of Cr(VI) with diphenylcarbazide (DPC). Variables, such as pH and colour stability time, were studied. The effect of concomitant ions on the simultaneous Cr(III) and Cr(VI) determination was also investigated. The sums of the chromium species concentrations obtained by the proposed method were compared with the total chromium concentrations found by electrothermal atomic absorption spectrometry. Recoveries of the chromium species between 75 and 136% were obtained for spiked samples. The linear working range for Cr(III) was 0.5 -30 mg L
The soils of the Amazon Region are usually highly weathered and not very fertile. However, in this same region are archeological soils called Amazonian Dark Earth, that have high concentrations of mineral nutrients and stable organic matter. Recently, Certini and Scalenghe proposed that the Anthropocene would have started in 2000 years BP, based on the use of anthropic soils such as Anthropocene Golden Spikes, especially the Amazonian Dark Earth. This study aims to compare the characteristics of Amazonian Dark Earth and Acrisols typical of Central Amazonia and to evaluate the role of these archaeological soils in issues related to the Anthropocene. Although all soils have been recognized as dystrophic, the Amazonian Dark Earth reflect their more complex pedogenesis, in which natural and anthropic processes act together, unlike the Acrisols. In the Anthropocene, Amazonian Dark Earth can be considered as excellent environmental markers indicating the onset and long-term extension of pre-Colombian human activities in the Amazon Region, but lack the stratigraphic characteristics necessary to be considered as adequate Golden Anthropocene Spikes.
resumo Foram comparadas as concentrações de na, K e p em extratos de solos, obtidas por um método de extração convencional, no qual é utilizada uma razão solo:extrator (mehlich-1) de 1:10, com aquelas encontradas utilizando uma razão solo:extrator (mehlich-1) de 1:5. também, foram comparados os resultados obtidos por técnicas de quantificação convencionais, nas quais na e K são quantificados por fotometria de chama e p por espectrofotometria de absorção molecular, com aqueles encontrados por espectrometria de emissão óptica com plasma indutivamente acoplado (iCp oes). Foram analisadas 15 amostras de solo brasileiro. no estudo de repetibilidade aplicado a todos os resultados, os maiores Cvs foram encontrados para p e na, principalmente quando as concentrações dos analitos foram menores (≤ 9 mg dm -3 para p e ≤ 10 mg dm -3 para na). esse fato foi devido provavelmente à heterogeneidade dos extratos, que continham partículas coloidais. Filtração ou centrifugação em vez de decantação dos extratos provavelmente resultaria em menores Cvs. no estudo de reprodutibilidade, realizado para três amostras, foram obtidos resultados não reprodutíveis somente para K em uma amostra. todos os resultados obtidos por iCp oes foram semelhantes aos obtidos por espectrofotometria de absorção molecular uv-vis. e fotometria de chama, indicando que a primeira técnica foi adequada para determinação de na,(1) recebido para publicação em 1 de dezembro de 2009 e aprovado em 27 de outubro de 2011.(2) pesquisador, departamento de Geoquímica, Universidade Federal Fluminense -UFF. outeiro de são João Batista s/n°, Cep 24020-150 niterói (rJ). e-mails: ricardosoaresuff@yahoo.com.br; santelli@geoq.uff.br (3) analista, embrapa solos. rua Jardim Botânico 1024, Cep 22460-000 rio de Janeiro (rJ). e-mail: viviane@cnps.embrapa.br (4) pesquisador, embrapa solos. rua Jardim Botânico 1024, Cep 22460-000 rio de Janeiro (rJ). e-mail: davidcampos@cnps.embrapa.br (5)
Archaeological soils know as Amazonian Dark Earth (ADE) were proposed to be eligible as golden spikes from the beginning of the Anthropocene 2000 years BP (before presente). This hypothesis was highly contested by the international scientific community that pointed out as ADE do not have the necessary geological preservation conditions to serve as golden spikes. One of the main allegations is how ADE is found in natural ecosystems, which are susceptible to natural or anthropic erosion, which would prevent an adequate stratigraphic preservation. Therefore, the objective of this study was to evaluate the stability characteristics of ADE soil aggregates over different fallow periods and to determine if the ADE have a stratigraphic preservation capacity that makes them resistant to rain and mechanical erosion. It was observed that the fallow time did not significantly influence the stability of aggregates of the two evaluated areas and it was observed also that the organic matter of the soil (SOM) did not play a strong role as a cementing agent of the particles due to the oxidic and kaolinite character of these areas. Consequently, a susceptibility to rainfall and anthropic erosion of the ADE was verified, making them unusable as golden spikes from the beginning of the Anthropocene.
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