15 research outputs found

    Aplicação de protótipo de microscópio de baixo custo como estratégia para o ensino de ciências e conscientização ambiental

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    Practical science classes are important methodological resources for teaching-learning process. However, many Brazilian public schools have poor laboratory structure, which hampers the development of practical activities. This extension project aimed to report the development of an interdisciplinary pedagogical strategy covering contents of biology, optics and environmental education, through the construction and application of a microscope prototype, made with low-cost and reusable electro-electronic materials. One hundred and twenty-six students from public elementary schools participated in the project. Workshops were held with theoretical and dynamic classes covering: i) a theoretical and dynamic class addressing concepts about cell, microscope physics and environmental education (solid and electro-electronic waste, recycling and reuse of waste, separation, and accountability), ii) a practical activity with the construction of a microscope prototype with recycled and reusable electronics and iii) evaluative questionnaire. The activity was based on the Sustainable Development Goals (SDGs - ONU), aiming at a quality education and responsible consumption and production. Besides, it was based on the concept of observation and experimentation as a didactic strategy for assimilating information. The results indicated an improvement in the students‚Äô understanding of the concepts of waste and cell, as well as the operation of a microscope, confirming that the activity improved the teaching-learning process. The low cost and easy operable prototype can improve the infrastructure of the schools, besides being an interesting tool to distance education.Aulas pr√°ticas de ci√™ncias s√£o importantes recursos metodol√≥gicos no processo ensino-aprendizagem dos alunos. No entanto, muitas escolas p√ļblicas brasileiras possuem escassa estrutura laboratorial, o que dificulta o desenvolvimento de atividades pr√°ticas. Este projeto de extens√£o teve como objetivo relatar o desenvolvimento de uma estrat√©gia pedag√≥gica interdisciplinar, abrangendo diversas √°reas no ensino de Ci√™ncias, como conceitos de educa√ß√£o ambiental, citologia e √≥ptica, por meio da constru√ß√£o e aplica√ß√£o de um prot√≥tipo de microsc√≥pio, confeccionado com materiais eletroeletr√īnicos reutiliz√°veis, e outros de baixo custo. Participaram do projeto cento e vinte seis alunos, de escolas p√ļblicas do ensino fundamental. Foram ministradas oficinas compostas por: a) aula te√≥rica e din√Ęmica abordando conceitos sobre a c√©lula, f√≠sica do microsc√≥pio e educa√ß√£o ambiental (res√≠duos s√≥lidos e eletroeletr√īnicos, reciclagem e reutiliza√ß√£o de res√≠duos, separa√ß√£o e responsabiliza√ß√£o), b) aula pr√°tica com constru√ß√£o de prot√≥tipo de microsc√≥pio e c) question√°rio avaliativo. A atividade foi fundamentada nos Objetivos de Desenvolvimento Sustent√°vel (ODS - ONU), visando √† educa√ß√£o de qualidade e consumo e produ√ß√£o respons√°veis, assim como na observa√ß√£o e experimenta√ß√£o como estrat√©gia did√°tica para a obten√ß√£o e assimila√ß√£o de informa√ß√Ķes. Os resultados indicaram melhora na compreens√£o, por parte dos estudantes, de conceitos relacionados aos res√≠duos, c√©lulas e funcionamento de um microsc√≥pio, confirmando a contribui√ß√£o da atividade na melhoria do processo ensino‚Äďaprendizagem de ci√™ncias e conscientiza√ß√£o ambiental. O prot√≥tipo, por ser de baixo custo e de f√°cil opera√ß√£o, pode aprimorar a infraestrutura de ensino das escolas, al√©m de ser uma ferramenta interessante para auxiliar no ensino √† dist√Ęncia

    Effect of a temperature rise on metal toxicity for the aquatic biota: a systematic review

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    Ecosystems are subject to various stress factors, such as temperature rises due to climate changes and metal disposal. Thermal stress can amplify or mask the effects of metals on aquatic organisms. This study aims to carry out a systematic review on the effects of temperature rises due to climate changes on the toxicity of metals for freshwater organisms. Searches were made in different electronic databases and article selection was based on the following inclusion criteria: concordance with the question of a systematic review; publication in English, Spanish, and Portuguese between 1960 and 2020; and the use of standard methodology. Forty-three articles were included, which were classified with respect to the year and country of publication, test-organisms and metals studied, temperatures tested, and the effects observed. In 80% of the studies analyzed, a temperature rise was responsible for increasing the toxicity of metals for the aquatic organisms. The temperatures studied contemplated the temperature rise predicted by the Intergovernmental Panel for Climate Change at the end of the 21st century. Brazil stood out among the countries for having the greatest number of research studies in this area, although there is still the need for an increase in studies in tropical climate regions. Based on the literature review, it was shown that the metals most studied were copper and cadmium and the test-organisms most used in the research projects were fish. The information obtained from ecotoxicological studies is essential to predict the effects and prevent the risks associated with the metal contamination of aquatic ecosystems due to climate changes.Ecossistemas est√£o sujeitos a diversos estressores, como o aumento da temperatura em raz√£o das mudan√ßas clim√°ticas e do lan√ßamento de metais. O estresse t√©rmico pode amplificar ou mascarar os efeitos dos metais nos organismos aqu√°ticos. Este estudo teve como objetivo realizar uma revis√£o sistem√°tica dos efeitos do aumento da temperatura, associado √†s mudan√ßas clim√°ticas, na toxicidade dos metais para organismos de √°gua doce. Foram realizadas buscas em diferentes bases de dados eletr√īnicas, e a sele√ß√£o dos artigos teve como crit√©rios de inclus√£o: concord√Ęncia com a quest√£o da revis√£o sistem√°tica, publica√ß√£o em ingl√™s, espanhol e em portugu√™s entre 1960 e 2020 e emprego de metodologias padronizadas. Inclu√≠ram-se 43 artigos, que foram classificados com rela√ß√£o ao ano e pa√≠s de publica√ß√£o, organismos-teste e metais estudados, temperaturas testadas e efeitos observados. Em 80% dos estudos analisados, o aumento da temperatura foi respons√°vel por elevar a toxicidade dos metais para os organismos aqu√°ticos. As temperaturas estudadas contemplam o aumento previsto pelo Painel Intergovernamental de Mudan√ßas Clim√°ticas no fim do s√©culo 21. O Brasil destaca-se entre os pa√≠ses com maior n√ļmero de pesquisas nesta √°rea, embora seja necess√°rio o aumento dos estudos em regi√Ķes de clima tropical. Com base na revis√£o bibliogr√°fica, constatou-se que os metais mais estudados foram o cobre e o c√°dmio, e os organismos-teste mais utilizados nas pesquisas foram os peixes. As informa√ß√Ķes obtidas com estudos ecotoxicol√≥gicos s√£o essenciais para a previs√£o dos efeitos e a preven√ß√£o dos riscos associados √† contamina√ß√£o por metais dos ecossistemas aqu√°ticos mediante as mudan√ßas clim√°ticas

    Evaluation of the ecotoxicological effects of metals cadmium and chromium in planktonic organisms

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    A cont√≠nua entrada de metais pesados nos ambientes aqu√°ticos constitui uma potencial amea√ßa aos ecossistemas naturais devido √† a√ß√£o t√≥xica direta em organismos aqu√°ticos. Nos ambientes aqu√°ticos, os organismos est√£o expostos a metais tanto dissolvidos na √°gua como aqueles presentes na cadeia tr√≥fica. Um maior conhecimento sobre o papel do alimento como rota adicional de exposi√ß√£o a metais ou como um poss√≠vel retentor de sua toxicidade para invertebrados aqu√°ticos √© necess√°rio. Considerando-se a import√Ęncia dos metais na contamina√ß√£o ambiental, bem como a necessidade de melhor entendimento das intera√ß√Ķes desses elementos nos sistemas aqu√°ticos, o presente estudo visou a avaliar a sensibilidade de esp√©cies fitoplanct√īnicas (Selenastrum capricornutum e Microcystis aeruginosa) e de esp√©cies zooplanct√īnicas (Daphnia similis e Ceriodaphnia dubia) aos metais c√°dmio e cromo e os efeitos t√≥xicos desses elementos em tais organismos. O crescimento celular, a concentra√ß√£o de clorofila, o biovolume e o peso seco das algas foram analisados quando as esp√©cies algais foram expostas aos metais por meio de testes de toxicidade aguda. Testes de toxicidade aguda e cr√īnica com o zoopl√Ęncton aos metais tamb√©m foram realizados e o efeito de diferentes densidades algais (alta, m√©dia e baixa) sobre a toxicidade dos metais aos clad√≥ceros foi avaliado. Al√©m disso, algas foram expostas aos metais, oferecidas como alimento a C. dubia e os efeitos t√≥xicos cr√īnicos foram investigados. Os resultados demonstraram que S. capricornutum foi mais sens√≠vel ao c√°dmio e M. aeruginosa foi mais sens√≠vel ao cromo, sendo essa diferen√ßa relacionada √† capacidade das algas para reter os metais. Com o aumento de ambos os metais, houve uma diminui√ß√£o na densidade celular, na taxa de crescimento, na clorofila e no peso seco das algas. A presen√ßa de diferentes densidades de S. capricornutum n√£o alterou significativamente o valor da CE(I)50; 48h aos metais para D. similis, mas a elevada densidade de M. aeruginosa reduziu a toxicidade do c√°dmio para o dafin√≠deo. A alta densidade de alimento (106 c√©ls/mL) influenciou negativamente a reprodu√ß√£o e a sobreviv√™ncia de C. dubia quando exposta a concentra√ß√Ķes subletais dos metais em solu√ß√£o. Alimento exposto √† metais, quando fornecido em alta e em m√©dia densidade, tamb√©m afetou a sobreviv√™ncia e a reprodu√ß√£o dos organismos-teste. Apesar de a √°gua ser uma importante rota de exposi√ß√£o aos metais para os organismos aqu√°ticos, o alimento deve ser considerado uma via de contamina√ß√£o adicional.The continuous input of heavy metals into aquatic systems constitutes a potential threat to natural ecosystems because of the direct toxic action on aquatic organisms. In aquatic ecosystems, the organisms are exposed to dissolved metals in the water as to metals presents in the food chain. A larger knowledge about paper of food as an additional route of exposure to metals or as possible retainer of its toxicity for aquatic organisms is necessary. Considering the importance of metals in contamination of aquatic ecosystems and the need of better understanding of the interactions of those elements in the aquatic ecosystems as well, the aim of this study was to evaluate the sensibility of phytoplankton species (Selenastrum capricornutum and Microcystis aeruginosa) and zooplankton species (Daphnia similis and Ceriodaphnia dubia) to cadmium and chromium metals and the toxic effects of those elements in such organisms. Analysed of cellular growth, chlorophyll concentration, biovolume and dry weight of the algae were carried out when algal species were exposed to metals. Acute and chronic toxicity tests with the zooplankton were also accomplished and the effect of different algal densities (high, middle and low) on toxicity of metals to cladoceran was evaluated. Alga S. capricornutum was exposed to metals, supplied as food to C. dubia and chronic toxicity effects were investigated. The results demonstrated that S. capricornutum was more sensitive to cadmium and M. aeruginosa was more sensitive to chromium, this difference was related the capacity of the algae to retain metals. Cell density, growth rate, chlorophyll and dry weight of the algae were reduced with increase of both metals. The presence of different density of S. capricornutum does not alter the value of EC50 to metals for D. similis, but high density of M. aeruginosa reduced the toxicity of cadmium for daphnid. High food density (106 cells/mL) influenced negatively on reproduction and survival of C. dubia when this organism was exposed to sublethal concentrations of metals in solution. Food exposed to metals, when it was supplied at high and middle density, also affected survival and reproduction of the test organisms. Although the water to be considered a important route of exposure of metals for aquatic organisms, the food should be considered an additional source of toxicity

    Ecotoxicological and limnological studies at the cascade reservoirs in the medium and low Tietê river (SP): a spatial and temporary analyses

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    Entre os diversos impactos nos ecossistemas aqu√°ticos, a constru√ß√£o de reservat√≥rios talvez represente um dos principais agentes modificadores, inserindo altera√ß√Ķes f√≠sicas, qu√≠micas e biol√≥gicas nos sistemas antes e ap√≥s a sua constru√ß√£o. No Brasil, tal impacto tamb√©m √© singular, verificando-se o aproveitamento dos mesmos para a constru√ß√£o de barragens, principalmente as constru√≠das em cascatas (sistemas Paranapanema, Tiet√™ e S√£o Francisco por exemplo), sendo que, neste padr√£o de constru√ß√£o, espera-se, na maioria das vezes, um efeito crescente do controle da qualidade da √°gua, com o primeiro reservat√≥rio mais eutr√≥fico que os demais por sua capacidade de reter materiais provenientes dos principais tribut√°rios. No estado de S√£o Paulo, na regi√£o Sudeste, destacam-se os reservat√≥rios de Barra Bonita, Bariri, Ibitinga, Promiss√£o, Nova Avanhandava, e Tr√™s Irm√£os. Visando avaliar os impactos e contribuir com informa√ß√Ķes para monitorar as condi√ß√Ķes ambientais desses reservat√≥rios, foram realizadas coletas de √°gua e sedimento em quatro per√≠odos distintos (outubro/99, fevereiro, maio e julho/00), em 15 esta√ß√Ķes de coleta, incluindo esta√ß√Ķes nos rios Tiet√™ e Piracicaba e √† montante e √† jusante da barragem de cada um dos seis reservat√≥rios, bem como no rio Bauru (um afluente bastante impactado de toxicidade com amostras de √°gua e sedimento, utilizando-se Daphnia similis (em bioensaios de toxicidade aguda) e Ceriophnia dubia (em bioensaios de toxicidade cr√īnica), an√°lises de metais totais na √°gua e biodispon√≠veis no sedimento, al√©m do monitoramento de vari√°veis limnol√≥gicas (temperatura, pH, condutividade, oxig√™nio, dissolvido, material em suspens√£o, clorofila-a, nutrientes totais e dissolvidos). Os resultados obtidos para as vari√°veis limnol√≥gicas, de modo geral, revelaram diferen√ßas na qualidade de √°gua em rela√ß√£o √†s escalas espacial e temporal (efeitos de fatores climatol√≥gicos e hidrodin√Ęmicos-vaz√£o e tempo ) de reten√ß√£o de √°gua), com elevado aporte de nutrientes pelos rios Tiet√™ e Piracicaba, al√©m da incorpora√ß√£o, da sedimenta√ß√£o e da redu√ß√£o de materiais no reservat√≥rio de Barra Bonita, promovendo a melhoria da qualidade da √°gua nos demais reservat√≥rios, caracterizando assim, as primeiras esta√ß√Ķes como eutr√≥ficas e as demais como mesotr√≥ficas e oligotr√≥ficas. Concentra√ß√Ķes de metais totais de √°gua acima do limite estabelecido pela resolu√ß√£o CONAMA 20/1986 foram encontradas, bem como um aumento da fra√ß√£o biodispon√≠vel. Os ensaios revelaram toxicidade aguda para Dapnhia similis somente nos reservat√≥rios localizados √† justante da barragem de Barra Bonita, o que n√£o seria inicialmente esperado. Tal fato pode estar relacionado √†s entradas difusas de polui√ß√£o ou a presen√ßa de metais no sistema Tiet√™, os quais, no primeiro reservat√≥rio, estariam mais presentes na forma retida em fun√ß√£o de sua maior incorpora√ß√£o (pela maior biomassa e pelo maior tempo de reten√ß√£o), n√£o causando toxicidade aguda aos organismos devido √† parte dissolvida n√£o ser t√£o elevada. Os resultados de toxicidade cr√īnica, por√©m, configuraram um padr√£o diferente, verificando-se toxicidade em ordem decrescente (de Barra Bonita √† Tr√™s Irm√£os), na maioria dos per√≠odos de amostragens, o que demonstra o estado de degrada√ß√£o ambiental nos reservat√≥rios e a necessidade de estudos mais integrados para uma melhor avalia√ß√£o ambiental.Among the several impacts in the aquatic ecosystems, perhaps the construction of reservoirs represents one of the principal modifier agents, inserting physical, chemical and biological alterations in the systems before and after its construction. In Brazil, such impact is also singular, having verified this application for the construction of reservoirs, mainly the ones built in cascades (Paranapanema, Tiet√™ and S√£o Francisco system, for example) and, in that construction pattern, in most cases, a growing effect of the control of the quality of the water is anticipated, with the first reservoir being more eutrophic than the others for its capacity to retain materials that come from the principal tributary. In the southeast of S√£o Paulo States, Barra Bonita, Bariri, Ibitinga, Promiss√£o, Nova Avanhandava and Tr√™s Irm√£os reservoirs stand out. Seeking to evaluate the impacts and contributing with information to evaluate the environmental conditions of those reservoirs, collections of water and sediment were accomplished in four different periods (October/99, February, May and July/00), in 15 sampling stations, including stations in the Tiet√™ and Piracicaba Rivers and at the specified place after and before the line of the dam, from each one of the six reservoirs, as well as the Bauru River (a very impacted tributary of the Bariri Reservoir ). Toxicity bioassays were accomplished with samples of water and sediment using Daphnia similis (in acute toxicity bioassays) and Ceriodaphnia dubia (in chronic toxicity bioassays), analyses of total metals in the water and bioavailable in the sediment, besides the monitoring of limnological variables (temperature, pH, conductivity, dissolved oxygen, material in suspension, chlorophyll-a, total nutrients and dissolved). The results obtained for the limnological variables, in general, revealed differences in the quality of the water in relation to the spatial and temporary scales (effects of climatological factors and hydrodynamic- flowing out and residence time) with high contribution of nutrients from the Tiet√™ and Piracicaba Rivers, besides the incorporation, the sedimentation and the reduction of materials in the Barra Bonita Reservoir, promoting the improvement of the water quality in the other reservoirs, characterizing, in this way, the first stations as eutrophic and the others as mesotrophic and oligotrophic. Concentrations of total metals in the water above the established limit for the resolution CONAMA 20/1986 were found out, and an increase of the fraction bioavailable of metals was verified as well. The bioassays only revealed acute toxicity for Daphnia similis to the points after the Barra Bonita Reservoir, something not initially awaited for. Such fact can be related to the diffuse entrances of pollution or to the presence of metals in the Tiet√™ System, which, in the first reservoir, would be more present in the form retained in function of their largest incorporation (for the largest biomass and for the largest residence time), not causing acute toxicity to the organisms due to the dissolved part not to being so high. However, the results of chronic toxicity, configured a different partem, being verified toxicity in decreasing order (from Barra Bonita to Tr√™s Irm√£os), during most of the samplings periods, which demonstrates the state of environmental degradation in the reservoirs and the need for more integrated studies for a better environmental evaluation

    Cadmium and Chromium Toxicity to Pseudokirchneriella subcapitata and Microcystis aeruginosa

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    The toxicity of cadmium and chromium to Pseudokirchneriella subcapitata and Microcystis aeruginosa was evaluated through algal growth rate during 96h exposure bioassays. Free metal ion concentrations were obtained using MINEQL(+) 4.61 and used for IC50 determination. Metal accumulations by the microorganisms were determined and they were found to be dependent on the concentration of Cd2+ and Cr6+. IC50 for P. subcapitata were 0.60 mu mol L-1 free Cd2+ and 20 mu mol L-1 free Cr6+, while the IC50 values for M. aeruginosa were 0.01 mu mol L-1 Cd2+ and 11.07 mu mol L-1 Cr6+. P. subcapitata accumulated higher metal concentrations (0.001 - 0.05 mu mol Cd mg(-1) dry wt. and 0.001 - 0.04 mu mol Cr mg(-1) dry wt) than the cyanobacteria (0.001 - 0.01 mu mol Cd mg(-1) dry wt and 0.001 - 0.02 mu mol Cr mg(-1) dry wt). Cadmium was more toxic than chromium to both the microorganisms.National Research Council (CNPq) [140156/2002-0]State of Sao Paulo Research Aid Foundation (FAPESP) [10417/2002

    Evaluation of the ecotoxicological effects of metals cadmium and chromium in planktonic organisms

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    A cont√≠nua entrada de metais pesados nos ambientes aqu√°ticos constitui uma potencial amea√ßa aos ecossistemas naturais devido √† a√ß√£o t√≥xica direta em organismos aqu√°ticos. Nos ambientes aqu√°ticos, os organismos est√£o expostos a metais tanto dissolvidos na √°gua como aqueles presentes na cadeia tr√≥fica. Um maior conhecimento sobre o papel do alimento como rota adicional de exposi√ß√£o a metais ou como um poss√≠vel retentor de sua toxicidade para invertebrados aqu√°ticos √© necess√°rio. Considerando-se a import√Ęncia dos metais na contamina√ß√£o ambiental, bem como a necessidade de melhor entendimento das intera√ß√Ķes desses elementos nos sistemas aqu√°ticos, o presente estudo visou a avaliar a sensibilidade de esp√©cies fitoplanct√īnicas (Selenastrum capricornutum e Microcystis aeruginosa) e de esp√©cies zooplanct√īnicas (Daphnia similis e Ceriodaphnia dubia) aos metais c√°dmio e cromo e os efeitos t√≥xicos desses elementos em tais organismos. O crescimento celular, a concentra√ß√£o de clorofila, o biovolume e o peso seco das algas foram analisados quando as esp√©cies algais foram expostas aos metais por meio de testes de toxicidade aguda. Testes de toxicidade aguda e cr√īnica com o zoopl√Ęncton aos metais tamb√©m foram realizados e o efeito de diferentes densidades algais (alta, m√©dia e baixa) sobre a toxicidade dos metais aos clad√≥ceros foi avaliado. Al√©m disso, algas foram expostas aos metais, oferecidas como alimento a C. dubia e os efeitos t√≥xicos cr√īnicos foram investigados. Os resultados demonstraram que S. capricornutum foi mais sens√≠vel ao c√°dmio e M. aeruginosa foi mais sens√≠vel ao cromo, sendo essa diferen√ßa relacionada √† capacidade das algas para reter os metais. Com o aumento de ambos os metais, houve uma diminui√ß√£o na densidade celular, na taxa de crescimento, na clorofila e no peso seco das algas. A presen√ßa de diferentes densidades de S. capricornutum n√£o alterou significativamente o valor da CE(I)50; 48h aos metais para D. similis, mas a elevada densidade de M. aeruginosa reduziu a toxicidade do c√°dmio para o dafin√≠deo. A alta densidade de alimento (106 c√©ls/mL) influenciou negativamente a reprodu√ß√£o e a sobreviv√™ncia de C. dubia quando exposta a concentra√ß√Ķes subletais dos metais em solu√ß√£o. Alimento exposto √† metais, quando fornecido em alta e em m√©dia densidade, tamb√©m afetou a sobreviv√™ncia e a reprodu√ß√£o dos organismos-teste. Apesar de a √°gua ser uma importante rota de exposi√ß√£o aos metais para os organismos aqu√°ticos, o alimento deve ser considerado uma via de contamina√ß√£o adicional.The continuous input of heavy metals into aquatic systems constitutes a potential threat to natural ecosystems because of the direct toxic action on aquatic organisms. In aquatic ecosystems, the organisms are exposed to dissolved metals in the water as to metals presents in the food chain. A larger knowledge about paper of food as an additional route of exposure to metals or as possible retainer of its toxicity for aquatic organisms is necessary. Considering the importance of metals in contamination of aquatic ecosystems and the need of better understanding of the interactions of those elements in the aquatic ecosystems as well, the aim of this study was to evaluate the sensibility of phytoplankton species (Selenastrum capricornutum and Microcystis aeruginosa) and zooplankton species (Daphnia similis and Ceriodaphnia dubia) to cadmium and chromium metals and the toxic effects of those elements in such organisms. Analysed of cellular growth, chlorophyll concentration, biovolume and dry weight of the algae were carried out when algal species were exposed to metals. Acute and chronic toxicity tests with the zooplankton were also accomplished and the effect of different algal densities (high, middle and low) on toxicity of metals to cladoceran was evaluated. Alga S. capricornutum was exposed to metals, supplied as food to C. dubia and chronic toxicity effects were investigated. The results demonstrated that S. capricornutum was more sensitive to cadmium and M. aeruginosa was more sensitive to chromium, this difference was related the capacity of the algae to retain metals. Cell density, growth rate, chlorophyll and dry weight of the algae were reduced with increase of both metals. The presence of different density of S. capricornutum does not alter the value of EC50 to metals for D. similis, but high density of M. aeruginosa reduced the toxicity of cadmium for daphnid. High food density (106 cells/mL) influenced negatively on reproduction and survival of C. dubia when this organism was exposed to sublethal concentrations of metals in solution. Food exposed to metals, when it was supplied at high and middle density, also affected survival and reproduction of the test organisms. Although the water to be considered a important route of exposure of metals for aquatic organisms, the food should be considered an additional source of toxicity

    Ecotoxicological and limnological studies at the cascade reservoirs in the medium and low Tietê river (SP): a spatial and temporary analyses

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    Entre os diversos impactos nos ecossistemas aqu√°ticos, a constru√ß√£o de reservat√≥rios talvez represente um dos principais agentes modificadores, inserindo altera√ß√Ķes f√≠sicas, qu√≠micas e biol√≥gicas nos sistemas antes e ap√≥s a sua constru√ß√£o. No Brasil, tal impacto tamb√©m √© singular, verificando-se o aproveitamento dos mesmos para a constru√ß√£o de barragens, principalmente as constru√≠das em cascatas (sistemas Paranapanema, Tiet√™ e S√£o Francisco por exemplo), sendo que, neste padr√£o de constru√ß√£o, espera-se, na maioria das vezes, um efeito crescente do controle da qualidade da √°gua, com o primeiro reservat√≥rio mais eutr√≥fico que os demais por sua capacidade de reter materiais provenientes dos principais tribut√°rios. No estado de S√£o Paulo, na regi√£o Sudeste, destacam-se os reservat√≥rios de Barra Bonita, Bariri, Ibitinga, Promiss√£o, Nova Avanhandava, e Tr√™s Irm√£os. Visando avaliar os impactos e contribuir com informa√ß√Ķes para monitorar as condi√ß√Ķes ambientais desses reservat√≥rios, foram realizadas coletas de √°gua e sedimento em quatro per√≠odos distintos (outubro/99, fevereiro, maio e julho/00), em 15 esta√ß√Ķes de coleta, incluindo esta√ß√Ķes nos rios Tiet√™ e Piracicaba e √† montante e √† jusante da barragem de cada um dos seis reservat√≥rios, bem como no rio Bauru (um afluente bastante impactado de toxicidade com amostras de √°gua e sedimento, utilizando-se Daphnia similis (em bioensaios de toxicidade aguda) e Ceriophnia dubia (em bioensaios de toxicidade cr√īnica), an√°lises de metais totais na √°gua e biodispon√≠veis no sedimento, al√©m do monitoramento de vari√°veis limnol√≥gicas (temperatura, pH, condutividade, oxig√™nio, dissolvido, material em suspens√£o, clorofila-a, nutrientes totais e dissolvidos). Os resultados obtidos para as vari√°veis limnol√≥gicas, de modo geral, revelaram diferen√ßas na qualidade de √°gua em rela√ß√£o √†s escalas espacial e temporal (efeitos de fatores climatol√≥gicos e hidrodin√Ęmicos-vaz√£o e tempo ) de reten√ß√£o de √°gua), com elevado aporte de nutrientes pelos rios Tiet√™ e Piracicaba, al√©m da incorpora√ß√£o, da sedimenta√ß√£o e da redu√ß√£o de materiais no reservat√≥rio de Barra Bonita, promovendo a melhoria da qualidade da √°gua nos demais reservat√≥rios, caracterizando assim, as primeiras esta√ß√Ķes como eutr√≥ficas e as demais como mesotr√≥ficas e oligotr√≥ficas. Concentra√ß√Ķes de metais totais de √°gua acima do limite estabelecido pela resolu√ß√£o CONAMA 20/1986 foram encontradas, bem como um aumento da fra√ß√£o biodispon√≠vel. Os ensaios revelaram toxicidade aguda para Dapnhia similis somente nos reservat√≥rios localizados √† justante da barragem de Barra Bonita, o que n√£o seria inicialmente esperado. Tal fato pode estar relacionado √†s entradas difusas de polui√ß√£o ou a presen√ßa de metais no sistema Tiet√™, os quais, no primeiro reservat√≥rio, estariam mais presentes na forma retida em fun√ß√£o de sua maior incorpora√ß√£o (pela maior biomassa e pelo maior tempo de reten√ß√£o), n√£o causando toxicidade aguda aos organismos devido √† parte dissolvida n√£o ser t√£o elevada. Os resultados de toxicidade cr√īnica, por√©m, configuraram um padr√£o diferente, verificando-se toxicidade em ordem decrescente (de Barra Bonita √† Tr√™s Irm√£os), na maioria dos per√≠odos de amostragens, o que demonstra o estado de degrada√ß√£o ambiental nos reservat√≥rios e a necessidade de estudos mais integrados para uma melhor avalia√ß√£o ambiental.Among the several impacts in the aquatic ecosystems, perhaps the construction of reservoirs represents one of the principal modifier agents, inserting physical, chemical and biological alterations in the systems before and after its construction. In Brazil, such impact is also singular, having verified this application for the construction of reservoirs, mainly the ones built in cascades (Paranapanema, Tiet√™ and S√£o Francisco system, for example) and, in that construction pattern, in most cases, a growing effect of the control of the quality of the water is anticipated, with the first reservoir being more eutrophic than the others for its capacity to retain materials that come from the principal tributary. In the southeast of S√£o Paulo States, Barra Bonita, Bariri, Ibitinga, Promiss√£o, Nova Avanhandava and Tr√™s Irm√£os reservoirs stand out. Seeking to evaluate the impacts and contributing with information to evaluate the environmental conditions of those reservoirs, collections of water and sediment were accomplished in four different periods (October/99, February, May and July/00), in 15 sampling stations, including stations in the Tiet√™ and Piracicaba Rivers and at the specified place after and before the line of the dam, from each one of the six reservoirs, as well as the Bauru River (a very impacted tributary of the Bariri Reservoir ). Toxicity bioassays were accomplished with samples of water and sediment using Daphnia similis (in acute toxicity bioassays) and Ceriodaphnia dubia (in chronic toxicity bioassays), analyses of total metals in the water and bioavailable in the sediment, besides the monitoring of limnological variables (temperature, pH, conductivity, dissolved oxygen, material in suspension, chlorophyll-a, total nutrients and dissolved). The results obtained for the limnological variables, in general, revealed differences in the quality of the water in relation to the spatial and temporary scales (effects of climatological factors and hydrodynamic- flowing out and residence time) with high contribution of nutrients from the Tiet√™ and Piracicaba Rivers, besides the incorporation, the sedimentation and the reduction of materials in the Barra Bonita Reservoir, promoting the improvement of the water quality in the other reservoirs, characterizing, in this way, the first stations as eutrophic and the others as mesotrophic and oligotrophic. Concentrations of total metals in the water above the established limit for the resolution CONAMA 20/1986 were found out, and an increase of the fraction bioavailable of metals was verified as well. The bioassays only revealed acute toxicity for Daphnia similis to the points after the Barra Bonita Reservoir, something not initially awaited for. Such fact can be related to the diffuse entrances of pollution or to the presence of metals in the Tiet√™ System, which, in the first reservoir, would be more present in the form retained in function of their largest incorporation (for the largest biomass and for the largest residence time), not causing acute toxicity to the organisms due to the dissolved part not to being so high. However, the results of chronic toxicity, configured a different partem, being verified toxicity in decreasing order (from Barra Bonita to Tr√™s Irm√£os), during most of the samplings periods, which demonstrates the state of environmental degradation in the reservoirs and the need for more integrated studies for a better environmental evaluation

    Effects of interactions between algal densities and cadmium concentrations on Ceriodaphnia dubia fecundity and survival

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    The influence of different densities of the algae Pseudokirchneriella subcapitata on the chronic toxicity of cadmium to Ceriodaphnia dubia was investigated. The importance of algal cells as a source of metal to zooplankton was studied by exposing P. subcapitata cells to free cadmium ions and supplying the algae as food to C. dubia. The results of a bifactorial analysis (metal versus food levels) showed that metal toxicity to zooplankton was dependent on food level. Significant toxic effects on the fecundity and survival of C. dubia were observed at low metal concentrations with high algal density. Algae contaminated with Cd2+ were less toxic to cladoceran than was the Cd2+ in solution. Green algae retained cadmium and released low metal concentration in the test medium. We concluded that algal cells are an important route of exposure to metal and a factor that has an appreciable influence on the expression of metal toxicity to daphnids. (C) 2007 Elsevier Inc. All rights reserved.National Research Council (CNPq)[140156/2002-0]Sao Paulo State Research Support Foundation (FAPESP)[10417/2002
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