Selenium in sediment and food webs of the Tapajós River basin (Brazilian Amazon) and its relation to mercury.

BACKGROUND: We investigated Se levels along the Tapajós River basin - which is an important tributary of the Amazon River - and the possible antagonistic effect of Se in Hg availability. This is the first study to investigate Se transfer from abiotic to biotic compartments and along the food chain in aquatic ecosystems of the Amazon basin. METHODS: Se concentrations were measured in superficial sediment (n = 29), plankton (n = 28) and fishes (n = 121) along two stretches of the Tapajós River basin (Tapup/mi and Taplow), comprising approximately 500 km with different hydrological characteristics. RESULTS: Se concentrations in sediment were significantly higher in the Taplow (345-664 µg kg-1) than in the Tapup/mi (60-424 µg kg-1). The seasonal flooding of the Amazon River probably helps to carry selenium-rich sediment to the Tapajós mouth (Taplow stretch). We suggest that Se in sediment could decrease the bioavailability of Hg resulting in lower MeHg concentrations in fish, as observed in the Taplow (45-934 µg kg-1). Sediment and plankton were positively correlated in relation to their Se concentrations (r = 0.62; p = 0.001) suggesting that sediment can possibly be the main source of Se to plankton. Our data indicate Se uptake by primary consumers, as noted in phytoplankton levels. The decrease of Se concentrations along the food chain was also noteworthy. CONCLUSION: This work elucidates some aspects of Se biogeochemistry in the Amazon basin and shows its importance regarding Hg cycles in aquatic ecosystems.

Concentration and Trophic Transfer of Copper, Selenium, and Zinc in Marine Species of the Chilean Patagonia and the Antarctic Peninsula Area.

Patagonia and Antarctica are biodiverse regions in the Southern Hemisphere, but little is known about the levels of trace elements in marine organisms from these remote coastal ecosystems. In this study, selenium (Se), copper (Cu), zinc (Zn), and stable isotopes of nitrogen (δ15N; relative trophic level) were measured in 36 marine species collected from two locations of the Chilean Patagonia and two locations of the Antarctic Peninsula area to determine whether biomagnification of these trace elements occurs in the food webs. Results indicated that Cu, Se, and Zn levels were slightly lower than those in similar species from elsewhere, and the highest metal levels were found in marine macroinvertebrates compared with fishes. There was evidence of Cu, Se, and Zn biomagnification but only within the lower-trophic-level organisms. When assessing whole food webs, levels of these elements typically decreased from macroinvertebrates to fishes or birds, suggesting lower risks of metal toxicity to higher-level consumers.

Far-reaching cytogenotoxic effects of mine waste from the Fundão dam disaster in Brazil.

On November 2015, one of Brazil's most important watersheds was impacted by the mine waste from Fundão dam collapse in Mariana. The mine waste traveled over 600 km along the Doce River before reaching the sea, causing severe devastation along its way. Here we assessed trace element concentrations and cytogenotoxic effects of the released mine waste. Water samples were collected along the Doce River ten days after the disaster in two impacted sites and one non-impacted site. Sampling points were located hundreds of kilometers downstream of the collapsed dam. Water samples were used for trace element quantification and to run an experiment using Allium cepa to test cytogenotoxicity. We found extremely high concentrations of particulate Fe, Al, and Mn in the impacted sites. We observed cytogenotoxic effects such as alterations in mitotic and phase indexes, and enhanced frequency of chromosomal aberrations. Our results indicate interferences in the cell cycle in impacted sites located hundreds of kilometers downstream of the disaster. The environmental impacts of the dam collapse may not only be far-reaching but also very likely long-lasting, because the mine waste may persist in the Doce River sediment for decades.

Selenium plasma levels in hemodialysis patients: comparison between North and Southeast of Brazil.

INTRODUCTION: Patients with chronic kidney disease present selenium (Se) plasma deficiency which is an essential trace element with important biological functions and, the best known biological role is attributed to its presence in the antioxidant enzyme, glutathione peroxidase (GPx). The Se content of foods depends on soil and some authors have suggested that Amazon soil (North Brazilian region) has high Se concentrations when compared to other regions of Brazil. OBJECTIVE: The objective of this work was to compare the Se status in hemodialysis (HD) patients from North and Southeast of Brazil. METHODS: Thirty-eight patients from Southeast region (22 men and 16 women, 15% diabetic, 53.5 ± 26.4 yrs) were compared to 40 patients from North region (28 men and 12 women, 22.5% diabetic, 63.5 ± 11.9 yrs). Se in plasma was determined through atomic absorption spectrophotometry with hydride generation. RESULTS: The plasma Se levels in patients from Southeast region were significantly lower (17.5 ± 11.9 µg/L) when compared to patients from the North (37.1 ± 15.8 µg/L) (p < 0.001). However, both patient groups presented low Se plasma levels when compared to recommended values (60- 120 µg/L). There was no correlation between plasma Se levels and analyzed parameters. CONCLUSION: We concluded that patients from North (Amazon) region present higher plasma Se levels when compared to the patients from Southeast of Brazil. However, independently of the region, HD patients presented Se deficiency.

Mercury and selenium in tropical marine plankton and their trophic successors.

Selenium (Se), mercury (Hg) and methylmercury (MeHg) were determined in microplankton (⩾25µm), crustacean muscle tissue, in the muscle and liver of two fish species and tissues of a dolphin from a bay in the Brazilian Southeast coast. Differences were found between the fish and dolphin muscle and hepatic concentrations. Liver showed the highest concentrations of Se and Hg. Positive biotransference of MeHg from source to consumer was observed for all interactions, demonstrating that MeHg biomagnified along the food web. The pelagic food chain has the highest biomagnification potential when compared to the benthic system. A large excess of Se in relation to Hg was observed in all tissues. The muscle and liver of the predator species, the dolphin and the carnivorous fish, presented similar MeHg. The predator species presented similar MeHg to Hg (% MeHg) ratios in muscle tissues (∼100%), whereas dolphin showed lower hepatic% MeHg (18) than the carnivorous fish (69%). Iliophagous fish presented the lowest % MeHg in tissues. Fish showed a positive relationship between hepatic MeHg and Se, whereas % MeHg did not change with increasing Se:Hg molar ratios in liver. Dolphins showed a significant inverse relationship between hepatic MeHg and Se and the % MeHg and Se:Hg ratios. This suggests a strong antagonistic effect of Se on MeHg assimilation and accumulation in this species. Probably, the differences observed among Hg as MeHg and Se and on the effect of Se on MeHg assimilation and accumulation in all marine species are related to the physiological differences between dolphins and fish.

Brazil nut (Bertholletia excelsa, H.B.K.) improves oxidative stress and inflammation biomarkers in hemodialysis patients.

Cumulative evidence indicates that oxidative stress and inflammation frequently occurs in patients undergoing maintenance hemodialysis (HD) and as a result of overproduction of reactive oxygen species (ROS) and a decrease of antioxidant defenses such as selenium (Se). Previous studies in our laboratory showed that the supplementation of 1 unit of Brazil nut (the richest known food source of Se) a day during 3 months is effective to improve Se status and increase glutathione peroxidase (GPx) levels in HD patients. The aim of this study was to evaluate the effect of Brazil nut supplementation on oxidative stress and inflammation markers in HD patients. Forty HD patients from Rio de Janeiro, Brazil were studied. All patients received one nut per day for 3 months. The Se plasma levels and GPx, 8-isoprostane, 8-hydroxy-2-deoxyguanosine (8-OHdG), and cytokine (TNF-α and IL-6) levels and lipid profile were determined before and after 3 months of supplementation. The plasma Se and GPx activity increased, while cytokines, 8-OHdG, and 8-isoprostane plasma levels decreased significantly after 3 months supplementation. HDL-c levels increased and LDL-c levels decreased significantly. These data suggest that the consumption of only one Brazil nut per day during 3 months was effective to reduce the inflammation, oxidative stress markers, and the atherogenic risk, thereby increasing the antioxidant defenses in HD patients. Our results indicate that Brazil nut as Se source plays an important role as an anti-inflammatory and antioxidant agent in HD patients.

Mercury and selenium biomagnification in a Brazilian coastal food web using nitrogen stable isotope analysis: a case study in an area under the influence of the Paraiba do Sul River plume.

Mercury (Hg), selenium (Se) and nitrogen (δ(15)N) stable isotope were assessed in a tropical food web of Rio de Janeiro's north coast. Isotopic data on muscle suggest a difference related to this parameter along the food web; where top-predators (cetacean and voracious fish) displayed heavier δ(15)N over the entire food web. Both top-predators presented similar δ(15)N values. Cetacean displayed higher Hg and lower Se than voracious fish. Five trophic positions (TP) were found in relation to primary consumer as baseline, ranging from 2.0 to 4.0. Positive relationships were found between trace-element and δ(15)N. The slope of regression equations (0.11 for Se and 0.21 for Hg) and food web magnification factors (2.4 for Se and 5.4 for Hg) showed that Hg presented higher rate of increase over the food web. Simultaneous measurements of trace-elements and ecological tracers emphasize the importance of TP into the trophic structure and distribution of Hg and Se throughout the food web.

Selenium and mercury in widely consumed seafood from South Atlantic Ocean.

The growing ingestion of predatory fish by humans has increased their exposure to toxic chemicals. Mercury (Hg) is an exogenous and harmful trace-element that accumulates in all marine organisms. Selenium (Se) is nutritionally important as a micronutrient, but is potentially harmful at intakes above 1mg per day. Se:Hg molar ratios in excess of 1:1 are thought to counteract the adverse effects of Hg, protecting against Hg toxicity. Evaluation of the health risk posed by Hg exposure from seafood consumption requires concurrent consideration of Se content in the same individuals. This study evaluated the Se and Hg concentrations in the edible tissues of 652 individual samples of commonly consumed varieties of carnivorous and planktivorous fish, squid, mussel, shrimp and crab collected from south-eastern Brazil. The Se:Hg molar ratios showed significant variation among and within tropical seafood. All organisms presented Se concentration in muscle of less than 2.0µgg(-1), the maximum allowed selenium concentrations. Only seven individuals of a carnivorous fish species presented Hg in muscle above the maximum permissible limit of 0.5µgg(-1) established by WHO and Brazilian legislation for human consumption of most aquatic species. These same individuals also showed Se:Hg molar ratio of less than 1:1. Se:Hg molar ratios were found to decline with increasing fish length, potentially reducing Se-dependent protection. As a result of their rich Se, low Hg contents and Se:Hg molar ratios exceeding 1:1, nearly all species included in this study provide benefits for human consumption. Two popular seafoods in the region, the carnivorous fish Centropomus undecimalis (common snook) and Micropogonias furnieri (Atlantic croaker), had the most favorable Se:Hg molar ratio values of 33 and 21, respectively. Among the invertebrates, Xiphopenaeus kroyeri (seabob shrimp) and Loligo sanpaulensis (squid) had the most favorable Se:Hg molar ratio values, higher than 20. A selenium health benefit value based on the absolute amounts and relative proportions of Se and Hg in seafood was proposed as a more comprehensive seafood safety criterion.

Mercury-selenium relationships in liver of Guiana dolphin: the possible role of Kupffer cells in the detoxification process by tiemannite formation.

Top marine predators present high mercury concentrations in their tissues as consequence of biomagnification of the most toxic form of this metal, methylmercury (MeHg). The present study concerns mercury accumulation by Guiana dolphins (Sotalia guianensis), highlighting the selenium-mediated methylmercury detoxification process. Liver samples from 19 dolphins incidentally captured within Guanabara Bay (Rio de Janeiro State, Brazil) from 1994 to 2006 were analyzed for total mercury (THg), methylmercury (MeHg), total organic mercury (TOrgHg) and selenium (Se). X-ray microanalyses were also performed. The specimens, including from fetuses to 30-year-old dolphins, comprising 8 females and 11 males, presented high THg (0.53-132 µg/g wet wt.) and Se concentrations (0.17-74.8 µg/g wet wt.). Correlations between THg, MeHg, TOrgHg and Se were verified with age (p<0.05), as well as a high and positive correlation was observed between molar concentrations of Hg and Se (p<0.05). Negative correlations were observed between THg and the percentage of MeHg contribution to THg (p<0.05), which represents a consequence of the selenium-mediated methylmercury detoxification process. Accumulation of Se-Hg amorphous crystals in Kupffer Cells was demonstrated through ultra-structural analysis, which shows that Guiana dolphin is capable of carrying out the demethylation process via mercury selenide formation.

Mercury and selenium in a top-predator fish, Trichiurus lepturus (Linnaeus, 1758), from the tropical Brazilian Coast, Rio de Janeiro.

Muscular mercury and selenium were assessed in a voracious fish from three Brazilian coastal areas with different environmental conditions. Mercury was higher in specimens from Ilha Grande Bay (0.35 ± 0.17 µg g(-1)) than in cutlassfish from Guanabara Bay (0.30 ± 0.15 µg g(-1)) and Buzios coast (0.13 ± 0.08 µg g(-1)), respectively. No difference was found regarding selenium among these areas. Mercury was positively correlated with fish length and size intervals (sub-adult, small and large adult), suggesting that larger and older fish bioaccumulated more mercury. A large excess of molar selenium in relation to mercury was observed.

Effect of Brazil nut supplementation on plasma levels of selenium in hemodialysis patients: 12 months of follow-up.

BACKGROUND: Large amounts of reactive oxygen species are produced in hemodialysis (HD) patients, and, at higher concentrations, reactive oxygen species are thought to be involved in the pathogenesis of cardiovascular disease. It has been proposed that selenium (Se) may exert an antiatherogenic influence by reducing oxidative stress. The richest known food source of Se is the Brazil nut (Bertholletia excelsa, family Lecythidaceae), found in the Amazon region. OBJECTIVE: The objective of this work was to determine if Se plasma levels in HD patients submitted to a program of supplementation during 3 months with 1 Brazil nut by day could be sustained after 12 months. METHODS: A total of 21 HD patients (54.2 ± 15.2 years old; average time on dialysis, 82.3 ± 51.6 months; body mass index, 24.4 ± 3.8 kg/m(2)) from the RenalCor Clinic in Rio de Janeiro, Brazil, were followed up 12 months after the supplementation study ended. The Se plasma levels were determined by atomic absorption spectrophotometry with hydride generation. RESULTS: The Se Plasma levels (17.3 ± 19.9 µg/L) were below the normal range (60 to 120 µg/L) before nut supplementation, and after 3 months of supplementation, the levels increased to 106.8 ± 50.3 µg/L (P < .0001). Twelve months after supplementation, the plasma Se levels decreased to 31.9 ± 14.8 µg/L (P < .0001). CONCLUSIONS: The data showed that these patients were Se deficient and that the consumption of Brazil nut was effective to increase the Se parameters of nutritional status. Se levels 12 months after the supplementation period were not as low as presupplementation levels but yet significantly lower, and we needed to motivate patients to adopt different dietary intake patterns.

Pulmonary function and histological impairment in mice after acute exposure to aluminum dust.

Along the aluminum refining process, alumina (Al2O3) constitutes the main source of dust. Although aluminum refinery workers present respiratory symptoms with lung functional changes, no conclusive data about lung function impairment after alumina exposure has been so far reported. We examined the pulmonary alterations of exposure to material collected in an aluminum refinery in Brazil. BALB/c mice were exposed in a whole-body chamber for 1 h to either saline (CTRL, n = 11) or to a suspension (in saline) of 8 mg/m(3) of the dust (ALUM, n = 11) both delivered by an ultrasonic nebulizer. Twenty-four hours after exposure lung mechanics were measured by the end-inflation method. Lungs were prepared for histology. ALUM showed significantly higher static elastance (34.61 +/- 5.76 cmH2O/mL), elastic component of viscoelasticity (8.16 +/- 1.20 cmH2O/mL), pressure used to overcome the resistive component of viscoelasticity (1.62 +/- 0.24 cmH2O), and total resistive pressure (2.21 +/- 0.49 cmH2O) than CTRL (27.95 +/- 3.63 cmH2O/mL, 6.12 +/- 0.99 cmH2O/mL, 1.23 +/- 0.19 cmH2O, and 1.68 +/- 0.23 cmH2O, respectively). ALUM also presented significantly higher fraction area of alveolar collapse (69.7 +/- 1.2%) and influx of polymorphonuclear cells (27.5 +/- 1.1%) in lung parenchyma than CTRL (27.2 +/- 1.1% and 14.6 +/- 0.7%, respectively). The composition analysis of the particulate matter showed high concentrations of aluminum. For the first time it was demonstrated in an experimental model that an acute exposure to dust collected in an aluminum producing facility impaired lung mechanics that could be associated with inflammation.

The relationships between mercury and selenium in plankton and fish from a tropical food web.

BACKGROUND, AIM, AND SCOPE: Selenium (Se) has been shown to reduce mercury (Hg) bioavailability and trophic transfer in aquatic ecosystems. The study of methylmercury (MeHg) and Se bioaccumulation by plankton is therefore of great significance in order to obtain a better understanding of the estuarine processes concerning Hg and Se accumulation and biomagnification throughout the food web. In the western South Atlantic, few studies have documented trace element and MeHg in fish tissues. No previous study about trace elements and MeHg in plankton has been conducted concerning tropical marine food webs. Se, Hg, and MeHg were determined in two size classes of plankton, microplankton (70-290 microm) and mesoplankton (>or=290 microm), and also in muscle tissues and livers of four fish species of different trophic levels (Mugil liza, a planktivorous fish; Bagre spp., an omnivorous fish; Micropogonias furnieri, a benthic carnivorous fish; and Centropomus undecimalis, a pelagic carnivorous fish) from a polluted estuary in the Brazilian Southeast coast, Guanabara Bay. Biological and ecological factors such as body length, feeding habits, and trophic transfer were considered in order to outline the relationships between these two elements. The differences in trace element levels among the different trophic levels were investigated. MATERIALS AND METHODS: Fish were collected from July 2004 to August 2005 at Guanabara Bay. Plankton was collected from six locations within the bay in August 2005. Total mercury (THg) was determined by cold vapor atomic absorption spectrometry (CV-AAS) with sodium borohydride as a reducing agent. MeHg analysis was conducted by digesting samples with an alcoholic potassium hydroxide solution followed by dithizone-toluene extraction. MeHg was then identified and quantified in the toluene layer by gas chromatography with an electron capture detector (GC-ECD). Se was determined by AAS using graphite tube with Pin platform and Zeeman background correction. RESULTS AND DISCUSSION: Total mercury, MeHg, and Se increased with plankton size class. THg and Se values were below 2.0 and 4.8 microg g(-1) dry wt in microplankton and mesoplankton, respectively. A large excess of molar concentrations of Se in relation to THg was observed in both plankton size class and both fish tissues. Plankton presented the lowest concentrations of this element. In fish, the liver showed the highest THg and Se concentrations. THg and Se in muscle were higher in Centropomus undecimalis (3.4 and 25.5 nmol g(-1)) than in Micropogonias furnieri (2.9 and 15.3 nmol g(-1)), Bagre spp (1.3 and 3.4 nmol g(-1)) and Mugil liza (0.3 and 5.1 nmol g(-1)), respectively. The trophic transfer of THg and Se was observed between trophic levels from prey (considering microplankton and mesoplankton) to top predator (fish). The top predators in this ecosystem, Centropomus undecimalis and Micropogonias furnieri, presented similar MeHg concentrations in muscles and liver. Microplankton presented lower ratios of methylmercury to total mercury concentration (MeHg/THg) (34%) than those found in mesoplankton (69%) and in the muscle of planktivorous fish, Mugil liza (56%). The other fish species presented similar MeHg/THg in muscle tissue (of around 100%). M. liza showed lower MeHg/THg in the liver than C. undecimalis (35%), M. furnieri (31%) and Bagre spp. (22%). Significant positive linear relationships were observed between the molar concentrations of THg and Se in the muscle tissue of M. furnieri and M. liza. These fish species also showed significant inverse linear relationships between hepatic MeHg and Se, suggesting a strong antagonistic effect of Se on MeHg assimilation and accumulation. CONCLUSIONS: Differences found among the concentrations THg, MeHg, and Se in microplankton, mesozooplankton, and fishes were probably related to the preferred prey and bioavailability of these elements in the marine environment. The increasing concentration of MeHg and Se at successively higher trophic levels of the food web of Guanabara Bay corresponds to a transfer between trophic levels from the lower trophic level to the top-level predator, suggesting that MeHg and Se were biomagnified throughout the food web. Hg and Se were positively correlated with the fish standard length, suggesting that larger and older fish bioaccumulated more of these trace elements. THg, MeHg, and Se were a function of the plankton size. RECOMMENDATIONS AND PERSPECTIVES: There is a need to assess the role of selenium in mercury accumulation in tropical ecosystems. Without further studies of the speciation of selenium in livers of fishes from this region, the precise role of this element, if any, cannot be verified in positively affecting mercury accumulation. Further studies of this element in the study of marine species should include liver samples containing relatively high concentrations of mercury. A basin-wide survey of selenium in fishes is also recommended.

Total mercury, organic mercury and selenium in liver and kidney of a South American coastal dolphin.

Selenium and total and organic mercury were determined in the liver and kidney of franciscana dolphin (Pontoporia blainvillei) incidentally caught in fishing nets along two Brazilian coastal areas (southeast and south). Regional differences in the concentrations of these contaminants were observed in P. blainvillei. Liver showed the highest organic and total mercury. In general, samples of individuals collected at the southern of Brazil had the highest concentrations of selenium and total and organic mercury. No significant gender differences were observed. Growth stage influenced the accumulation of these contaminants in both organs, and hepatic concentrations increased with the body length, according to the sampling area. Molar mercury and selenium concentrations in liver were significantly correlated, with a Se:Hg ratio close to 4. The among-site differences we found may be related to differences in preferred prey, bioavailability in the marine environment, environmental conditions, or these individuals may belong to distinct populations.

Establishment and analytical quality control of laboratories for Hg determination in biological and geological samples in the Amazon, Brazil

During the past 20 years significant amounts of HG have been released in the Amazonian environment due to goldmining activities. Several Brazilian and foreign research groups have been studying the region, always facing difficulties regarding preservation and transfer of the collected samples from the field to the analytical laboratories. Aiming to solve these problems two high quality Hg analytical laboratories were established in the region. One is located at Fundação Esperança (FE, Santarém, PA), a medical assitance foundation and the other at the Universidade Federal de Rondônia (UNIR), Porto Velho, RO. Their main equipament is: Atomic absorption spectrophotometers for Hg analysis (Klow Injection Mercury System-FIAS 400 with automatic samples-AS90-Perkin Elmer) and a microwave oven digestion system (MDS-2000-CEM). Technicians and researchers were trained in several aspects like environmental and human sampling, digestion methods and Hg analysis for biotic and abiotic materials. This training as well as the installation of the mentioned laboratories were the responsibility of the Universidade Federal do Rio de Janeiro (UFRJ). Intercalibration exercices were performed between several laboratories: Environmental Medicine of Odense University (Denmark), Centre de Toxicologie du Québec, Canada and Occupational Health Sciences (Health-Canada). In the last 18 months the FE laboratory joined the Hg urine analysis intercalibration program of the Laboratory of the Centre of Toxicology in Québec, Canada, reaching accurate results. To date both Amazonian laboratories are able to analyze several different materials: Sediment, soil, fish, urine, hair and blood. The FE laboratory is becoming more specialized in human samples such as urine, blood and hair, wile UNIR laboratory deals with environmental samples such as fish, sediment and soil.