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This study presents a 35-year record of total mercury (Hg) concentrations in the detritivore fish Prochilodus nigricans (Curimatã) and the carnivore Cichla pleiozona (Tucunaré), two of the most widely distributed, ecologically important and consumed fish species in the upper Madeira River Basin in the Western Brazilian Amazon. Fish samples from the major Madeira River and marginal lakes and tributaries were compared. Irrespective of site, Hg concentrations were higher in the carnivore fish compared to the detritivore. Hg concentrations increased 5-fold in C. pleiozona in the past three decades, whereas they remained relatively constant in P. nigricans when analyzing the entire 35-year period. When analyzed separately, fish in the main river and marginal lake and tributaries presented the same pattern of Hg variation, with a significant increase in Hg concentrations in the carnivore and in the detritivore in marginal lakes and tributaries but not in the main river. This was in line with the increase in methyl-Hg production in tributaries, mostly associated with deforestation in the past decade in the basin. Although an increase in direct emissions from artisanal gold mining also occurred in the past decade, this caused virtually no impact on fish Hg concentrations, suggesting atmospheric emission and deposition in forests and further export to water systems as an intermediate link with fish Hg concentrations.

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Scutes present very complex morphologies with different growth rates at different areas of the carapace that can change the accumulation process of essential and non-essential metals. To infer the effects of morphology and growth on Hg concentrations in scutes, we mapped them in the carapace of one individual of four species of sea turtles sampled along the Brazilian coast. The results showed that Hg concentrations were higher in the vertebral scutes of Chelonia mydas and Eretmochelys imbricata suggesting variation in growth rates of different carapace areas since the vertebral area is the first to develop prior to costal areas. Caretta caretta and Lepidochelys olivacea did not show differences between carapace areas. The preliminary data from this pilot study indicate that vertebral scutes may be suitable for monitoring Hg in C. mydas and E. imbricata, since they reflect longer exposure period. A species-to-species comparison of Hg concentrations is not possible due to the small number of sampled individuals, nevertheless, E. imbricata showed remarkably lower Hg concentrations compared to the other three species. Further studies are required for all four species, with a larger number of individuals, preferentially of varying life stages, due to the unknown effects of different diets, Hg exposure, and migration histories.

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In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary's biological resources.

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Due to global warming, in the northeastern semiarid coastal regions of Brazil, regional and global drivers are responsible for decreasing continental runoff and increasing estuarine water residence time, which promotes a greater mobilization of bioavailable mercury (Hg) and allows increasing fluxes and/or bioavailability of this toxic trace element and an acceleration of biogeochemical transformation of Hg. In this work, an application of dendrochemistry analysis (annular tree rings analysis) was developed for the reconstruction of the historical pattern of mercury contamination in a contaminated area, quantifying chronological Hg contamination trends in a tropical semiarid ecosystem (Ceará River Estuary, northeastern coast of Brazil) through registration of mercury concentration on growth rings in specimens of Rhizophora mangle L. and using the assessment in sediments as a support for the comparison of profiles of contamination. The comparison with sediments from the same place lends credibility to this type of analysis, as well as the relationship to the historical profile of contamination in the region, when compared with local data about industries and ecological situation of sampling sites. In order to evaluate the consequences of the described increase in Hg bioavailability and bioaccumulation in aquatic biota, and to assess the biological significance of Hg concentrations in sediments to fish and wildlife, muscle and liver from a bioindicator fish species, S. testudineus, were also analyzed. The results of this work reinforce the indicators previously described in the semiarid NE region of Brazil, which showed that global climate change and some anthropogenic factors are key drivers of Hg exposure and biomagnification for wildlife and humans. Considering the Hg concentration present in the top layers of sediment (~20 cm around 15 to 20 years) with the outer layers in the tree ring cores and in the sediment's cores from Pacoti estuary and the Ceará estuary, overall the data indicate an increase in mercury in recent years in the Hg surface sediments, especially associated with the fine sediment fraction, mainly due to the increased capacity of small particles to adsorb Hg. There was revealed a positive and significant correlation (p < 0.05) between Hg trends in sediments and Hg trends in annular tree rings. This shared Hg pattern reflects local environmental conditions. The Hg concentration values in S. testudineus from both study areas are not restrictive to human consumption, being below the legislated European limit for Hg in foodstuffs. The results from S. testudineus muscles analysis suggest a significant and linear increase in Hg burden with increasing fish length, indicating that the specimens are accumulating Hg as they grow. The results from both rivers show an increase in BSAF with fish growth. The [Hg] liver/[Hg] muscles ratio >1, which indicates that the S. testudineus from both study areas are experiencing an increase in Hg bioavailability. Possible climate-induced shifts in these aquatic systems processes are inducing a greater mobilization of bioavailable Hg, which could allow an acceleration of the biogeochemical transformation of Hg.

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The green turtle (Chelonia mydas) is known to present an herbivorous diet as an adult; however, juveniles may have an omnivore habit, and these changes in food preference may affect the uptake and accumulation of pollutants, such as mercury (Hg). In order to better understand the influence of this ontogenetic shift on Hg accumulation, this study evaluates the concentrations of total mercury (THg), methyl mercury (MeHg), and stable isotopes of carbon and nitrogen (δ13C and δ15N) in a group of juveniles of the green turtle. Tissue samples (liver, kidney, muscle, and scutes) were sampled from 47 turtles stranded dead on the coast of Bahia, NE, Brazil, between 2009 and 2013. The turtles analyzed showed a size range of 24.9-62.0 cm and an average of 36.4 ± 7.2 cm of curved carapace length. The scutes showed to be a viable method for Hg monitoring in the green turtles. The concentrations of THg and MeHg decreased with increasing size. The isotope values of δ15N and δ13C did not show a clear relationship with the size, suggesting that the green turtles used in our work would be occupying similar trophic levels, and foraging habitat.

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The present study intends to assess the metal pollution of a eutrophic coastal lagoon, analyzing the long-term and actual metal content in surface sediments, suspended particles, aquatic macrophyte and fish species, and the loads emitted from natural processes and anthropogenic sources, including the relative emission of domestic untreated sewage. Distribution indicated contamination of suspended particles with Cd and the predominance of Pb in the bioavailable form in surface sediments which may explain Cd and Pb contamination in fish. Domestic untreated sewage was an important source of Cu and due to the lagoon's management, this source may be increasing the metal content in the lagoon's surface sediments. Soil loss, atmospheric deposition and solid waste disposal also contributed to metal inputs to the lagoon. Extensive contamination has been prevented by the lagoon's management such as sandbar opening. Metal retention within the watershed soils reduce the effective metal transference and lagoon pollution.

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The present study has evaluated temporal and spatial mercury trends based on surficial sediment samples and 210Pb-dated sediment profiles. The obtained results show that there are areas close to the main bay's tributary rivers where the Hg content has doubled during the last 15 years and regions where it has decreased by a factor of 2, mainly the area close to the navigation channel, which is submitted to periodic dredging. In the inner part of the bay, the most contaminated region, mercury shows a strong association with sulfide. In the same region, based on the 210Pb results, it was possible to calculate the yearly increment on the Hg concentration in the surface sediment, 0.62 µg kg-1 y-1 to 0.29 µg kg-1 y-1, according to the distance to the bay's main tributary rivers.

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This study evaluates the influence of environmental and biological factors upon the mercury (Hg) concentrations in the aquatic fauna in the Lower Jaguaribe River Basin (LJRB) - NE, Brazil. Two campaigns conducted in 2015 in the fluvial (FDA) and in the marine-dominated (MDA) areas resulted in 830 organisms from 16 species collected (nine of finfish and seven of invertebrates). Among the invertebrates, the highest Hg concentration occurred in the crab Callinectes bocourti (201 ng g-1), while among the finfish the highest concentration was found in the ladyfish Elops saurus (109 ng g-1), both carnivorous and of high trophic level (TL). Intra-specific comparison showed significant higher Hg concentrations in individuals captured in the MDA. Also, Hg bioaccumulation rate in the shrimp Litopenaeus vannamei was much higher in the MDA. These results, point to a concomitant control of Hg bioavailability by physical-chemical variables along the estuarine gradient of the LJRB.

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Monitoring phosphorus (P) concentration in water and sediments in the Castanhão reservoir, under intensive aquaculture, in Northeastern Brazil showed internal process to dominate P cycling following a reduction of reservoir volume due to an extended drought period. A strong negative correlation between soluble reactive phosphorus in surface waters (SRPs) with the reservoir volume results from diminishing dilution capacity; bottom water SRP showed no significant correlation with volume and imply SRP remobilization to surface layers. Total suspended solids (TSS) showed a significant correlation with chlorophyll-a, suggesting change primary productivity following SRP enrichment of surface waters and living cells dominating the TSS. As a result, eutrophication, as established by a trophic state index, was triggered in the reservoir probably enforced by intensive fish farming effluents, whose nutrients accumulated in bottom waters and which became available due to breaking of the thermocline. Since low rainfall periods are typical of the semiarid region and tend to be more frequent and stronger due to climate change, multiple use of reservoirs in NE Brazil should be reevaluated.

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This study establishes regional background levels and upper thresholds (geochemical baseline) for Zn, Cu, Pb, Cr, Mn, and Fe from surface samples and profiles taken in 16 sedimentary environments of the Parnaíba River Delta estuary, NE-Brazil. Three approaches were applied to evaluate metal contamination: normalization to Fe, statistical analysis and sediment quality guidelines or environmental assessment criteria (TEL-PEL). Metal concentrations in sediments ranged from 2.4 to 31 mg Zn kg(-1), 1.5 to 48 mg Cu kg(-1), 1.3 to 28 mg Pb kg(-1), 1.5 to 38 mg Cr kg(-1); 145 to 1,356 mg Mn kg(-1), and 0.3% to 2.5% for Fe. All metals showed positive correlations with the <0.63 µm sediment fraction, indicating a significant association with rich lithogenic sources of iron oxide-hydroxides. Results suggest a low probability of adverse effects to the local aquatic biota. The background values of the area were lower than those reported for other areas of the northeastern coast of Brazil.

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Ribeira Bay is located approximately 130 km south of the city of Rio de Janeiro and receives discharges of liquid effluent from the Angra dos Reis nuclear power plant (NPP) site, where two pressurized water reactors are located. To test whether the presence of anthropogenic radionuclides in sediments in Ribeira Bay could be correlated to the NPP operations, we sampled seven sediment cores and determined accumulation rates and chronologies. Only one sediment core did not exhibit a superficial mixing layer; this sample was used for dating purposes. Cesium-137 and (207)Bi were observed in this sediment profile, but their presence was associated with atmospheric fall-out rather than the nearby NPP. The exponential decay of (210)Pb concentration with sediment layer depth was verified below a superficial mixing layer for all other sediment cores. Calculated accumulation rates ranged from 1.2 mm y(-1) in the inner bay to 6.2 mm y(-1) close to its entrance.

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The analytical scanning electron microscope (SEM) has been used to determine the presence and distribution of atomic elements in mineralogy. However, the detection of light elements such as carbon is difficult to obtain with standard energy-dispersive X-ray spectrometry (EDS) and usual proceedings for SEM. This study proposes a new protocol to detect calcium carbonate by SEM/EDS using sediments from the Jaguaribe River estuary, NE Brazil, as a model. Handmade gold mounting discs (Au stubs) were used as sample support and samples were adhered with inexpensive glue (Loctite Super_Bonder) or directly disposed on the Au stubs. CaCO(3) and NaCl for chemical analysis were used as control and counterproof to the carbon adhesive tape. Control salts EDS analyses indicate that the method was efficient to detect light elements. Sediments obtained from different depths in the core sampled at the Jaguaribe River estuary consist of particles and aggregates with diverse morphology that covers a wide range of particle or aggregate size. Morphology and dimensions were similar for all core depths. Analysis of samples disposed on gold mounting disc without glue showed that sediment bulk particles usually presented small particles adhering on the surface. Clay minerals were predominant but silica was also often identified. Calcium was a trace element in a small number of sediment bulk particles. Biological and non-biological calcium carbonates, including nanoparticles, were identified in all core depths. X-ray emitted from Au stub did not interfere in the CaCO(3) EDS analysis. Calcium carbonate particles from sediments were identified using this novel approach.

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River management has altered the land-sea transport of water, sediments, and chemical compounds with profound impacts on the structure of continental and costal ecosystems. Understanding riverine transport across modified watersheds allow for better assessment of the influence of river management on material fluxes to coastal waters. Here, we assess the quantitative and qualitative aspects of mercury (Hg) transport across a modified watershed by diversion of Paraíba do Sul River waters into Sepetiba Bay, Brazil. We measured concentrations and speciation of Hg in water samples collected at sites within the modified watershed. These data, together with water discharge and sediment load from numerical models and measurements were used to estimate mass balances. In the Sepetiba watershed, mercury is mainly associated with suspended sediments (90%) and therefore Hg flux displayed the characteristic trend of downstream reduction due to trapping efficiency of particulate load by successive reservoirs. The mass balance suggests that the major source of mercury to Sepetiba Bay is the erosion of soil-derived particles from the drainage basin rather than mercury diverted from Paraíba do Sul River watershed.

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This work presents quality control results on the mercury concentrations in different environmental (river sediments, forest soils, river suspended matter and fish) and human samples from the lower Madeira River, Amazon sampled between 2001 and 2003, about 15-20 years after the nearly cessation of gold mining activities in the region, which reached its peak in the late 1980s. The study aimed to compare mercury concentrations in these environmental samples with those reported by other authors during the gold rush of the Madeira River Basin. Today, in the Madeira River the releases of mercury register a sudden reduction due the gold price fall in the international trade. However, about 100 t of Hg were released to the atmosphere and to aquatic systems in the region during the gold rush. The present survey shows that notwithstanding the reduction of Hg emissions to the Madeira River Basin from gold mining proper, concentrations in fish and humans are similar to those measured during the gold rush. Reduction in Hg concentrations is restricted to areas close to old point sources and only for abiotic compartments (air and sediments). Remobilization of Hg from bottom sediments plus re-emission from soils due to land use changes are probably responsible for keeping high Hg concentrations in biological samples.

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Dissolved gaseous Hg, reactive Hg, total dissolved Hg and particulate Hg concentrations were measured in samples of majors tributaries of the Sepetiba Bay, SE Brazil (Itimirim, Itinguçu, Guarda, Guandu, São Francisco and Ita rivers), in dry and rainy seasons. The average Hg concentrations found varied from 0.02 to 0.18 ng L(-1) for dissolved gaseous Hg, from 0.1 to 18.1 ng L(-1) for reactive Hg, from 0.1 to 66.6 ng L(-1) for total dissolved Hg and from 0.3 to 250 ng L(-1) for particulate Hg. During the rainy season, a decrease in the dissolved Hg concentrations and an increase in the particulate Hg concentrations was observed. Positive correlations were found between the reactive Hg and the total dissolved Hg concentrations (r = 0.99), between the particulate Hg and TSS concentrations (r = 0.82) and between total Hg and particulate Hg concentrations (r = 0.95). The instantaneous Hg fluxes varied among rivers from 0.02 to 412 microgs(-1) for total dissolved Hg and from 0.03 to 12,572 microgs(-1) for particulate Hg. The log Kd varied from 3.76 to 6.43 and showed a significant increase in rainy season following an increase in particulate Hg and a decrease in dissolved Hg concentrations. These results suggest that erosion and runoff are the major pathways of Hg transport to rivers and eventually to Sepetiba Bay.

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