O presente trabalho tem por objetivo analisar o efeito do metilmercúrio na retina de peixe tropical Hoplias malabaricus (Traíra) através de baixas doses agudas. As intoxicações foram realizadas, por meio de injeção intraperitoneal, nas doses de 0,01, 0,05, 0,1 e 1,0 g/g, com um período de quinze dias de depuração do MeHg. Após o término do período de depuração, os olhos foram enucleados e as retinas isoladas foram fixadas em PFA 4% por 3 horas. As retinas foram conservadas, até o momento do uso (ou por no mínimo 9 horas), em tampão PB 0,1M a 4ºC. Após os procedimentos imunohistoquímicos para marcação de células bipolares do tipo ON com estratificação na sublâmina b da CPI, as retinas foram aplanadas para confecção de montagens planas para a análise quantitativa de células bipolares ON imunorreativas a proteína cinase C _. A análise quantitativa das células da camada de células ganglionares (CCG) também foi realizada. Células da CCG foram coradas pela técnica de Nissl, as retinas foram aplanadas em lâminas gelatinizadas e submetidas a uma bateria de desidratação (com diferentes concentrações alcoólicas) e coloração, utilizando cresil violeta como corante. Estas análises foram realizadas em 3 ou 4 retinas para cada dose testada. Análises idênticas foram realizadas nas retinas controle. Todas as retinas foram dividas nos quadrantes dorsal, ventral, nasal, temporal e em centro e periferia. Campos foram fotografados por toda a retina com intervalos de 1 mm, com auxilio do programa Axio Vision por meio de uma câmera digital e um microscópio acoplados a um computador. Os campos amostrados foram contados com o auxilio do programa NIH Scion Imagem 2.0. A densidade média de células foi estimada para cada retina e os grupos intoxicados foram comparados com o grupo controle (Teste T-student). A partir dos dados de densidade celular, mapas de isodensidade foram confeccionados, além de permitir estimar o poder de resolução teórico da acuidade visual de cada um dos animais experimentais utilizados para análise de células da CCG a partir da densidade máxima de células. Evidenciamos que as baixas doses agudas testadas não causam diminuição na densidade célular de células bipolares ON e células da CCG, comparado ao grupo controle. Não houve reduções significativas na densidade de células para ambos os tipos celulares analizados em nenhuma das regiões retinianas nas doses de MeHg testadas. Assim, a intoxicação de MeHg por baixas doses agudas não alterou o poder de resolução teorio da acuiade visual dos animais testados / This study aims to examine the effects of low acute doses of methylmercury (MeHg) on the retina of the tropical fish Hoplias malabaricus (Thraira). Four levels of MeHg intoxication were induced by intraperitoneal injection of doses of either 0.01, 0.05, 0.1 or 1.0 g MeHg/g of body weight, followed by a fifteen day period of depuration of MeHg. After the depuration period, the eyes were harvested, and the retinas were isolated and fixed in 4% paraformaldehyde for 3 hours. The retinas were then stored (for at least for 9 hours) in 0.1 M sodium phosphate PB buffer at 4°C until the time of analysis. ON bipolar cells in sublamina b of the inner plexiform layer immunoreactive to protein Kinase C_ were immunohistochemically labeled, and the retinas were flattened to make whole mounts for quantitative analysis of ON bipolar cell densities. Quantitative analysis of cells in the retinal ganglion cell layer (GCL) was also performed. GCL cells were Nissl stained, and the retinas were flattened on gelatinized slides and subjected to another battery of dehydration (with different alcohol concentrations) and staining using cresyl violet. These analyses were carried out in 3 or 4 retinas for each dose tested. Identical analyses were performed on the control retinas. All retinas were divided into regions: dorsal, ventral, nasal, temporal, center and periphery. Sample retinal fields were photographed throughout the retina at intervals of 1 mm, with a digital camera attached to a microscope using Axio Vision software coupled to a computer. ON bipolar and GCL cells within the fields were counted with the help of the NIH Scion Image 2.0 software. The average density (mm2) of both types of cells was estimated for each retina and the data from each of the four MeHgintoxicated groups were compared with the control group values (Student t-test). From the density data we derived isodensity maps, permitting us to estimate the theoretical resolving power (maximum visual acuity) of each of the experimental animals used from the maximum density of cells in the ganglion cell layer. We showed that low acute doses of MeHg/g do not decrease cell densities of either ON bipolar cells or cells in the GCL, compared to controls. There were no significant decreases in cell density (counts) for either cell type in any of the retinal regions, for any of the MeHg doses tested. Thus, acute low-dose MeHg intoxication did not degrade the estimates of the animals theoretical resolving power

A represa Billings é o maior reservatório de água que abastece o estado de São Paulo. Está localizada na bacia do Alto Tietê na região metropolitana de São Paulo, em uma área de proteção ambiental. Contudo, desde o início da sua inundação, vem sofrendo sérias agressões ambientais. Entre elas, o fluxo de entrada de água do rio Pinheiros, usado para controle de enchentes na região metropolitana de São Paulo. A constante entrada de contaminantes na represa se torna preocupante, considerando que, no seu entorno, há diferentes tipos de assentamentos, entre os quais de famílias de pescadores, que usam estas águas sem tratamentos convencionais para consumo doméstico e pesca artesanal para subsistência. Portanto, este estudo teve como objetivo realizar uma avaliação temporal dos níveis de metais presentes na água e em tecidos dos peixes da represa, correlacionando estes valores com o fluxo de entrada de água do rio Pinheiros e do índice pluviométrico na região. Durante o período de um ano, cerca de 800 indivíduos, dentre as principais espécies de peixes consumidas na região Geophagus brasiliensis (acará), Hoplias malabaricus (traíra), Tilapia rendalli (tilápia) e Astyanax ssp (lambari), de sete pontos de pesca, foram coletadas e analisados. Amostras de águas foram coletadas em 13 pontos sugeridos pelos pescadores locais. Considerando cada espécie de peixe analisada, os níveis de metais estão na mesma ordem de magnitude, independentemente da região de captura. Os níveis de Cr, em cerca de 60% dos acarás, 98% dos lambaris, 67% dos traíras e 100% de tilápia não atenderam ao limite estabelecido pela ANVISA. Cu e Hg, em todas as amostras atenderam aos limites estabelecidos pela legislação nacional. A inserção das águas do rio Pinheiros claramente afeta a qualidade da água da represa. As regiões mais contaminadas são: Pedreira, Margem do Bororé, Alvarenga, Barragem Taquacetuba, Casa Caída e Ilha do Biguá. Observou-se também que 100% de amostras não atendem ao limite estabelecido pelo CONAMA; para Cu, Mn, Ni, cerca de 50% não cumprem o limite estipulado para Cd e 20% para Zn. Em linhas gerais, observou-se que esta inserção altera todo o regime natural da represa, mas que ainda assim é possível absorver a contaminação recebida. / The Billings Dam is the largest reservoir of water that supplies in the state of São Paulo. It is part of the Alto Tiete basin, which is located in the metropolitan region of São Paulo in an environmentally protected area. In spite of that, since the beginning of its flooding, several environmental aggressions were observed. Among them the inflow of water from Pinheiros river, used to control floods in the metropolitan region of Sao Paulo .The constant input of contaminants in the dam becomes worrisome, considering that, in its surroundings, there are different kinds of settlements, among them families of fishermen, who use these waters without conventional treatments for domestic consumption and artisanal fishing for livelihood. Therefore, this study aimed to carry out a temporal evaluation of metal levels present in dam\'s water and fish tissue, correlating these values with the water input flow of Pinheiros River and pluviometric index in the region. During a period of one year, circa of 800 individuals among the main consumed fish species in the region Geophagus brasiliensis (acará), Hoplias malabaricus (traíra), Tilapia rendalli (tilápia) e Astyanax ssp (lambari), from seven fishing places were collected and analysed. It was also collected water from thirteen places chosen by local fishermen. Considering each fish specimen analyzed, the levels of metals are in the same order of magnitude regardless of the region of capture. The levels of Cr in circa of 62% of acarás, 98% of lambaris, 67% of traíras and 100% of tilapia do not meet the limit stipulated by ANVISA. Cu and Hg, in all samples meet the limits set by national legislation. The Pinheiros river water clearly affects the quality of dam\'s water. The most contaminated regions were: Pedreira, Margem do Bororé, Alvarenga, Barragem Taquacetuba, Casa Caída and Ilha do Biguá. It was observed that 100% of samples do not meet the limits established for water quality by CONAMA for Cu, Mn and Ni, 50% do not meet the limit for Cd and 20% for Zn . In general, we can observe the entry of to the waters of Pinheiros River during operation of the flotation system and even during the flood control changes the whole natural scheme of the dam, although the dam still manages to absorb the contamination that is received.

Submitted by Diego Santos (diegosantos@unipampa.edu.br) on 2015-04-10T11:49:39Z No. of bitstreams: 1 111010003.pdf: 1306168 bytes, checksum: 65e96979f53ded7b91f629af13358a87 (MD5) / Made available in DSpace on 2015-04-10T11:49:41Z (GMT). No. of bitstreams: 1 111010003.pdf: 1306168 bytes, checksum: 65e96979f53ded7b91f629af13358a87 (MD5) Previous issue date: 2012-08-20 / O metilmercúrio (MeHg) é um agente tóxico que causa importantes prejuízos à saúde humana e ambiental. Parte desses efeitos está relacionado a sua capacidade de induzir estresse oxidativo. Os mecanismos precisos pelos quais o MeHg leva ao estresse oxidativo ainda não estão bem esclarecidos. Dados na literatura apontam para a participação de selenoproteínas como a glutationa peroxidase e a tioredoxina redutase neste processo. Neste estudo, buscou-se investigar o papel de isoformas de glutationa peroxidase (GPx1 e GPx4) e da tioredoxina redutase (TrxR1) na neurotoxicidade induzida por MeHg em camundongos, focando na atividade e expressão destas proteínas. Nossos resultados mostraram, que o tratamento de camundongos Swiss machos adultos com MeHg (40 mg/L na água de beber) durante 21 dias causa uma diminuição significativa na atividade das enzimas GPx e TrxR no córtex e cerebelo dos animais tratados, em comparação com os controles. Observou-se também uma significativa redução na expressão de GPx1, GPx4 e TrxR1 no cerebelo dos animais tratados, enquanto que no córtex apenas GPx4 e TrxR1 foram afetadas. Concomitantemente a estes resultados, observou-se um aumento significativo na atividade das enzimas antioxidantes SOD, CAT, GR e GST no cerebelo e da CAT no cortex. A expressão de HSP70 foi significativamente aumentada no cerebelo dos animais tratados. Estes dados denotam uma clara resposta celular antioxidante frente aos efeitos tóxicos do MeHg em nosso modelo, reforçando dados da literatura que indicam o estresse oxidativo como um importante mecanismos na neurotoxicidade induzida por este organometal. Além disso, nossos resultados apontam para isoformas de glutationa peroxidase e tioredoxina redutase como importantes alvos moleculares do MeHg e, ao menos, em nosso conhecimento, este é o primeiro estudo demonstrando o papel da GPx4 na neurotoxicidade induzida por este agente tóxico ambiental. Outro objetivo deste trabalho foi investigar os efeitos biológicos do extrato da alga Prasiola crispa(PcE), oriunda do continente Antártico, nos modelos de Drosophila melanogaster e Nauphoeta cinérea. Organismos adaptados a ambientes extremos como a Antártica tendem a apresentarem uma constituição única em termos de metabólitos secundários. Desta forma, estudos que visem à elucidação de efeitos biológicos de organismos oriundos destas regiões tendem a apresentarem relevância do ponto de vista biotecnológico. Nossos dados apontam para um potencial biocida de PcE nos modelos de mosca-da-fruta (Drosophila melanogaster) e barata cinerea (Nauphoeta cinerea), visto que a administração do extrato induziu toxicidade nos dois modelos. A toxicidade em D. melanogaster foi avaliada como percentagem de mortalidade, atividade locomotora (geotaxia negativa) e alterações bioquímicas incluindo atividade acetilcolinesterase (AChE) e marcadores de estresse oxidativo.Também foi investigada a ação cardiotóxica do extrato no modelo de coração semi-isolado de barata cinerea. A administração do extrato(2mg/ml) foi feita por 24 horas e, nas moscas, causou um aumento massivo na mortalidade (aumento de 7,6 vezes em relação ao controle). Também foi observado um aumento significativo na atividade locomotora, indicando uma ação neurotóxica do extrato. A atividade AChE, os níveis de glutationa e formação de hidroperóxido manteve-se inalterada. A atividade da glutationa S-transferase aumentou significativamente após a administração de PcE, já a atividade da catalase diminuiu significativamente em moscas que receberam o extrato. No modelo de coração semi-isolado de barata, foi observado uma diminuição da freqüência cardíaca. A incubação do extrato com DTNB, um forte agente oxidante, bloqueou significativamente o efeito cardiotóxico do extrato, sugerindo que compostos redutores podem ser responsáveis pelo efeito observado. Desta forma, este estudo demonstrou os efeitos tóxicos de PcE, em dois modelos de inseto, sugerindo seu potencial como bioinseticida. Os mecanismos precisos relacionados a este efeito ainda necessitam de esclarecimentos, entretanto, alterações em sistemas antioxidantes vitais podem estar envolvidos. / Methylmercury (MeHg) is a toxic agent that causes severe damage to human health and the environment. These effects are related to its ability to induce oxidative stress. The precise mechanisms by which MeHg leads to oxidative stress are not well understood. Data from literature point to the involvement of selenoproteins such as glutathione peroxidase and thioredoxin reductase in this process. In this study, we sought to investigate the role of isoforms of glutathione peroxidase (GPx4 and GPx1) and thioredoxin reductase (TrxR1) in MeHg-induced neurotoxicity in mice, focusing on activity and expression of these proteins. Our results showed that treatment of adult male mice Swiss with MeHg (40 mg / L in drinking water) for 21 days causes a significant decrease in GPx and TrxR enzyme activity in the cerebral cortex and cerebellum of treated animals when compared to controls. We also observed a significant reduction in the expression of GPx1, GPx4 and TrxR1 in the cerebellum of the treated animals, whereas in the cortex only GPx4 and TrxR1 are affected..In parallel, we observed a significant increase in antioxidant enzymes SOD, CAT, GR and GST in the cerebellum and CAT in cortex. HSP70 expression was significantly increased in the cerebellum of the treated animals. These results show a clear antioxidant cell response against the toxic effects of MeHg in our model, reinforcing the literature data indicating oxidative stress as an important mechanism in the neurotoxicity induced by this organometal. Furthermore, our results point to isoforms of glutathione peroxidase and thioredoxin reductase as important molecular targets of MeHg and, at least, to our knowledge, this is the first study demonstrating the role of GPx4 in the neurotoxicity induced by this toxic environmental agent. Another objective of this study was to investigate the biological effects of the extract of the alga Prasiola crispa (PcE), from the Antarctic continent, in the insect models Drosophila melanogaster and Nauphoeta cinerea. Organisms adapted to extreme environments such as Antarctica tend to present a unique composition in terms of secondary metabolites. Thus, studies aimed at elucidating the biological effects of organisms from these areas tend to be relevant in a biotechnological point of view. Our data demonstrates a potential biocide PcE effect in the fruit fly (Drosophila melanogaster) and lobster cockroach (Nauphoeta cinerea), since the administration of the extract induced toxicity in both models. Toxicity in D. melanogaster was assessed as percentage of mortality, locomotor activity (negative geotaxis) and biochemical measurements including acetylcholinesterase (AChE) and markers of oxidative stress. We also investigated the cardiotoxic action of the extract in a cockroach semi-isolated heart model. The administration of the extract (2 mg / ml) for 24 hours toflies, caused a massive increase in mortality (7.6-fold increase compared to control). We also observed a significant increase in locomotor activity, indicating a neurotoxic action of the extract. AChE activity, glutathione levels and the formation of hydroperoxide remained unchanged. The activity of glutathione S-transferase significantly increased after administration of PcE while catalase activity was significantly decreased in flies that received the extract. A significant decrease in heart rate in the cockroach semi-isolated heart model was observed after PcE administration. The incubation of the extract with DTNB, a strong oxidizing agent, significantly blocked the cardiotoxic effect of the extract, suggesting that reducing compounds may be responsible for the observed effect. Thus, this study demonstrated, for the first time, the toxic effects of PcE, in two insect models, suggesting its potential as a bioinsecticide. The precise mechanisms related to this effect still need clarification, however, changes in vital antioxidant systems may be involved.

Methods were developed for the determination of methylmercury in natural waters and sediments based on steam distillation and aqueous phase ethylation followed by gas chromatography-atomic fluorescence spectrometry. The methods were shown to be free from measurable artefactual methylation of inorganic mercury and offered improved sample throughput over existing methods. Improvements were made to existing methods for the determination of total mercury in biota, sediments and natural waters and dissolved mercury species in natural waters. These methods were applied to the study of mercury cycling in two remote field sites. The cycling of mercury species was studied in Lake Murray in Western Province, Papua New Guinea, which has been historically noted as a region of high mercury concentrations in fish. Concentrations of methylmercury and total mercury in the water column were found to be variable and consistent with non-contaminated lake systems. Concentrations of methylmercury and total mercury in the sediments were also found to be low, except for in the south of the lake, which was influenced by an intermittent supply of water and sediments with elevated mercury concentrations from the Strickland River. Methylmercury concentrations in the sediments were generally higher in the backwater areas due to littoral processes. The low concentrations of methylmercury in the sediments and waters were inconsistent with other systems previously studied in the northern hemisphere, showing a link between high mercury concentrations in fish and high concentrations of methylmercury in waters or sediments. Therefore, the biota of Lake Murray were studied in order to account for the differences between this and other systems. A study was conducted of the stable isotope ratios of carbon and nitrogen in biota from Lake Murray to elucidate key food-web interactions. This study revealed that the dominant carbon source for fish in the lake is plankton, although algae and macrophytes may also be involved in the food-web. The methylmercury bioaccumulation factors between trophic levels were similar to those measured in temperate systems of the northern hemisphere. The high concentrations of methylmercury, observed in piscivorous fish, were shown to be a consequence of the complex food-web and the number of trophic levels in the food-chains. The cycling of mercury species was studied in Lake Gordon and Lake Pedder in southwest Tasmania, which has recently been identified as being in a region of high mercury concentrations in trout and eels. The concentrations of total mercury were found to be reasonably uniform in the waters of both lakes, spatially and temporally. The concentrations of methylmercury in the waters were seasonally variable, and were consistently lower in Lake Pedder than in Lake Gordon. Dilution of methylmercury concentrations by precipitation direct to the lake surface, probably accounts for the most of the difference in methylmercury concentrations between the lakes. Owing to the long residence time of water in Lake Gordon, this reservoir mixes inputs of water with varying methylmercury concentrations. Concentrations of total mercury and methylmercury in submerged soils were low and depth profiles of mercury species in the water column did not show evidence of a gradient of mercury concentrations due to releases from the sediments. The concentrations of methylmercury observed in the water column are consistent with the concentrations observed in the fish. A budget of the mercury inputs and outputs to Lake Gordon showed that in-lake processes and sources in the catchment areas both contributed significantly to the concentrations of methylmercury in the lake. The methylation of mercury in Lake Gordon appeared to mainly occur in the surface waters (< 10 m) and was not consistent with processes leading to the methylation of mercury at the oxic/anoxic boundary observed in seepage lakes in Wisconsin. The concentrations of total mercury and methylmercury in bogs in the catchment areas of Lakes Gordon and Pedder, were high and governed by the concentration of organic matter in the sediments. The processes involved in the supply of mercury species from the Lake Gordon and Lake Pedder catchments appear to be similar to those in drainage lakes in the temperate and boreal regions of the northern hemisphere. The formation of the Lake Gordon and Lake Pedder reservoirs appears to have had little impact on the mean annual concentrations of methylmercury released to the downstream environment.

The effect of fish consumption on the risk of cardiovascular disease has been extensively studied. Omega-3 fatty acids present in fish, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been found to have beneficial effects through several mechanisms. In addition, selenium, an antioxidant, may be protective. Fish also represents the main human exposure source to the pollutant methylmercury (MeHg), which is associated with elevated cardiovascular risk in previous studies. The aim of this thesis was to evaluate whether MeHg is associated with the risk of myocardial infarction (MI) or stroke, whether EPA+DHA or selenium (Se) have protective associations, and if the overall association between fish consumption and risk of stroke or MI is detrimental or protective. A prospective incident case-control study design was used to study effects on stroke or MI. Three hundred and sixty-nine cases with twice as many matched controls were included in the study on stroke, while 431 cases with 499 controls participated in the MI study, all from the Northern Sweden Health and Disease Study. The data was collected from health examinations of the population from 1986 until 1999. Also, time trends in burdens of mercury (Hg), lead (Pb) and cadmium (Cd) in erythrocytes (Ery) from 1990 to 1999 were examined. The food frequency questionnaire (FFQ) used in the case-control studies was correlated with measurements of fatty acids in erythrocyte membranes as biomarkers of intake. In this northern Swedish population, levels of Ery-Hg and Ery-Pb decreased during the 1990´s, but Ery-Cd decreased only in smoking men. No significant associations were found between Ery-Hg or levels of EPA+DHA and the risk of stroke. Men reporting fish consumption &gt;3 meals/week had an elevated risk of stroke. In the MI study, higher levels of Ery-Hg were associated with lower risk of MI. No clear associations were found for reported fish consumption, levels of EPA+DHA or Ery-Se. The validated FFQ has a fair reliability in estimating intake of fatty acids EPA and DHA. However, the low variation in fish consumption in the general population in combination with different versions of the FFQ (with pre-defined, multiple choice alternatives) decreased the reliability of self-reported fish consumption in the case-control studies on risk of stroke or MI. In conclusion, MeHg has no harmful association regarding the risk of stroke or MI in this population with generally low exposure levels. The protective association regarding risk of MI is probably due to Ery-Hg being a biomarker for consumption of fish, a source of other beneficial nutrients. Thus, in this population the benefits of the nutrients in fish appear to overcome the potential harm of MeHg. The finding of elevated stroke risk related to high fish consumption in men will be investigated further. / PHIME; Public health impact of long-term, low-level mixed element exposure in susceptible population strata

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Les thiols et le sélénium peuvent jouer un rôle important dans la méthylation du mercure des environnements aquatiques. Pour démontrer la présence des thiols et du sélénium et leur relation avec le mercure dans certains écosystèmes d'eau douce québécois, une campagne d’échantillonnage fut réalisée durant l’été 2010, dans le parc national du Mont-Tremblant (Laurentides, Québec). Il existe une corrélation significative entre le sélénium et le mercure total dans l’eau des lacs du parc. Cependant, les concentrations de sélénium sont très faibles dans les lacs, les étangs de castor et les ruisseaux. Par ailleurs, les lacs du parc national du Mont-Tremblant ont des concentrations relativement élevées de méthylmercure avec une moyenne de 0,33 ng L-1 et des maximums allant jusqu’à 3,29 ng L-1. Les étangs de castor peuvent aussi être considérés comme des lieux de contamination au méthylmercure, avec une concentration moyenne de 0,95 ng L-1. Toutefois, la présence d’une colonie de castors sur le bassin versant d’un lac ne semble pas influencer les concentrations de mercure que l’on y retrouve. Deux thiols sont détectables dans l’eau de surface des Laurentides, soit le glutathion et l’acide thioglycolique. La concentration de ce dernier thiol est corrélée significativement avec celle du mercure total et du méthylmercure. Les thiols peuvent jouer un rôle important dans les processus de méthylation en favorisant le transport du mercure inorganique à l’intérieur des bactéries sulfato-réductrices. Afin de mieux comprendre l’action antagoniste entre le sélénium et le mercure, des études devraient être réalisées au niveau des tissus des organismes vivants dans ces zones pauvres en sélénium. / Thiols and selenium may influence mercury methylation in aquatic environments. To demonstrate the occurrence of both elements with mercury in selected aquatic systems of Quebec, a sampling campaign was conducted during the summer of 2010 in Mont-Temblant national park (Laurentians, Quebec). There is a significant correlation between selenium and total mercury in surface water. However, concentrations of selenium are very low in lakes and beavers ponds. In addition, the park’s lakes have a relatively high concentrations of methyl mercury with an average of 0,33 ng L-1 and maximum values up to 3,29 ng L-1. Beaver ponds can also be considered hotspots of methylmercury contamination, with an average concentration of 0,95 ng L-1. However, the presence of a colony of beavers in the watershed of a lake does not appear to influence the levels of mercury in that lake. Two species of thiols are present in the surface water of the Laurentian ecosystems: glutathione and thioglycolic acid. The latter is significantly correlated with total mercury and methyl mercury. Thiols may play an important role in the methylation process by promoting the transport of inorganic mercury within the sulfate-reducing bacteria. To better undestand the antagonistic action between selenium and mercury, more research should be conducted in the tissue of organisms living in areas of low concentration of selenium to know if they are protected against mercury toxicity.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os efeitos tóxicos do metil-mercúrio (MeHg) em seres humanos vêm sendo amplamente discutidos, a partir de episódios de contaminação devida a ingestão frequente de peixe contaminado, em Minamata, no Japão, ou ao consumo de pão preparado com cereais tratados com fungicidas a base de metil-mercúrio, no Iraque, indicando que o metil mercúrio pode afetar o sistema nervoso central. A população ribeirinha na região do Pantanal, Brasil, é dependente do peixe, como principal fonte de alimentos e proteínas. Naquela região, o resultado de décadas de mineração de ouro, em pequena escala, foi a contaminação de muitos sistemas aquáticos com mercúrio. Consequentemente, muitas espécies de peixes possuem níveis de MeHg relativamente altos. O objetivo deste trabalho foi avaliar o nível de exposição ao MeHg entre a população ribeirinha do Pantanal. No primeiro artigo, apresentam-se os resultados da validação do método recordatório de 24 horas auto-referido, utilizando-se, como padrão-ouro, o método da pesagem, tendo-se verificado que há aproximadamente um erro de 30% ao estimar a quantidade de peixe consumido por aquela população. Um erro deste pode ser importante em se tratando do consumo de peixes carnívoros, os quais apresentam altos teores de mercúrio. No segundo artigo, ao analisar a associação entre o status neurocognitivo e a concentração de mercúrio no cabelo da população acima, os resultados indicaram que adultos expostos ao metil-mercúrio, através do consumo de peixe, podem ter déficits importantes nas medidas do desempenho neurocomportamental, sem alterações detectáveis no humor ou afetividade. Os efeitos mais importantes do mercúrio, entre os indivíduos analisados, foram detectados nos testes de velocidade e destreza da coordenação motora fina, na inibição da resposta na busca visual, e em tarefas de atenção. No terceiro artigo, considerando-se as associações observadas na concentração de mercúrio no cabelo com alguns desfechos dos testes neuro-psicológicos aplicados, calculou-se a dose-marcadora (BMD) e o limite inferior do intervalo de confiança do BMD (BMDL). Os resultados da dose marcadora e da dose de referência provisória são concordantes com os resultados estimados pelas agências de saúde internacionais.

Methylmercury (MeHg) is a potent neuro and nephrotoxicant in several animal species including humans, particularly during their development. The purpose of this study was to investigate the effects of aqueous seed extract of Syzygium cumini (L.) Skeels (Scc) on the acute MeHg treatment in neonatal rats. Neonatal rats (P2) received orally a single dose of MeHg (10 mg/kg) and also two doses of Scc. After two days, the effects of this treatment were investigated in the cerebral cortex, hippocampus, kidney, liver and urine samples of rats. We observed that N-Acetyl-β-d-glucosaminidase (NAG) activity in the kidney and urine was higher in MeHg-group when compared with the control group. Similarly, the lipid peroxidation levels were higher in the liver and kidney as well as the Adenosine deaminase (ADA) activity increased in the hippocampus, kidney and liver. These results indicate that increased NAG and ADA activities, as well as thiobarbituric acid reactive species (TBARS) levels may play a critical role in MeHg nephrotoxicity. The most relevant finding in our investigation was that acute MeHg treatment in neonatal rats caused liver and renal impairment and Scc was able to prevent such effects. It appears that mechanisms related to scavenging activity of Scc could be involved with its protection effect. Key words: Methylmercury; Syzygium cumini; N-Acetyl-β-d-glucosaminidase; rat; adenosine deaminase / O metilmercúrio (MeHg) é um agente tóxico potente tanto para o sistema nervoso central como para o renal. Provoca danos nos seres humanos e em ratos, particularmente durante o estágio de desenvolvimento. Neste estudo, ratos em desenvolvimento (P2) receberam uma dose única de MeHg (10 mg/kg), por via oral e/ou duas doses do extrato aquoso de sementes de Syzygium cumini (L.) Skeels (Scc). Após dois dias (P4), foram investigados os efeitos deste tratamento no córtex cerebral, hipocampo, rim, fígado e urina. Observamos que a atividade da N-acetil-β-d-glicosaminidase (NAG) nos rins e na urina foi maior no grupo que recebeu MeHg, quando comparado com o grupo controle. Da mesma forma, os níveis de peroxidação lipídica foram maiores no fígado e rim e a atividade da adenosina deaminase (ADA) encontrou-se elevada no hipocampo, rins e fígado, nos ratos tratados com MeHg. Estes resultados indicam que o aumento da atividade da NAG e da ADA, bem como os níveis das espécies reativas ao ácido tiobarbitúrico (TBARS), desempenham um papel importante como marcadores de nefrotoxicidade causada pelo MeHg. Assim, o achado mais relevante na nossa investigação foi a de que o tratamento agudo com MeHg em ratos neonatos pode provocar nefrotoxicidade e a administração do Scc pode reverter estes efeitos provavelmente devido as propriedades antioxidantes de Scc.