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Cr contamination is a growing concern in the Amazon. Along with the rise of cattle farming in the region, tanneries are becoming more common and threatening environmental quality, since the effluents from this activity are rich in Cr. The objective of this study was to evaluate the seasonal and spatial dynamics of Cr in fish with different feeding habits from Puruzinho Lake, located in the Madeira River basin, also determining the daily intake of Cr associated with the consumption of these fish by the population that lives around the lake. Seasonality and feeding habits directly affected Cr dynamics in fish (p < 0.0001), with medians of Cr concentration ranging between 0.07 mg kg -1 in the species Cichla pleiozona, a carnivorous fish, and 0.62 mg kg -1 in Mylossoma duriventre, a herbivorous fish. The high Cr concentrations in M. duriventre were related to the biodilution effect of Cr in the trophic chain (R 2  = 0.14, p < 0.0001). The consumption of M. duriventre by the population was associated with the highest daily intake of Cr (55.5 μg∙day -1 ), exceeding the recommended limits of Cr intake (35 μg∙day -1 ). However, no harmful effects on health are expected due to the ingestion of Cr through the consumption of fish from Puruzinho Lake. Spatial analysis showed an increasing trend in Cr concentrations along the Madeira River, suggesting that contaminants present in the river are being carried over long distances and are reaching preserved areas of the Amazon., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The increase in global demand for electric energy is reflected in plans to construct numerous hydroelectric dams in South America that can cause chronic ecological impacts if not built and managed correctly. One of the main impacts generated by hydropower dams is the accumulation of Hg chemical species in their reservoir compartments and the downstream transport of these contaminants. Hg circulation in these environments has been studied for 27 years and this review brings a synthesis of the dynamics that are now well established, so that future studies can focus on gaps and inconsistent results in the literature. The topics cover the methylation process of Hg, its transfer along the trophic chain and the impacts downstream from dams. In addition, meta-analyses are used to propose regression models that explain Hg dispersion in environmental compartments of reservoirs, using as predictors morphological, spatial and temporal aspects of these environments., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Damming rivers to generate electricity creates a lentic environment that favors methylmercury (MeHg) formation. Reservoirs in the Amazon are critical environments for MeHg formation, considering its old soils and the use of Hg in gold mining in the region. The objective of this study was to evaluate MeHg accumulation in three environmental compartments (aquatic macrophytes, suspended particulate matter (SPM) and sediment) of the Samuel reservoir (Western Amazon, Brazil), during the low water, ebb and high water hydrological periods, characterizing the dry season, the end of the rainy season and the rainy season, respectively. MeHg concentrations were determined through GC-AFS. The aquatic macrophytes presented higher %MeHg in their roots (up to 12%) compared to their other tissues. This ratio was 1.7 and 5.9 times higher than those observed for SPM and the sediment, but MeHg concentrations were the lowest (0.5-4.5 ng g -1 ) among the three environmental compartments. Contrary, the highest MeHg concentration was observed in SPM (104 ng g -1 ) during the low water period. The MeHg concentration in the sediment profile decreased with increasing depth (0.93-0.48 ng g -1 ) and with decreasing organic matter lability (increasing C:N ratio). In the SPM, on the other hand, MeHg concentration showed a positive association with increasing C:N ratio. We conclude that MeHg dynamics in the SPM are associated with the hydrological periods, with peaks during the low water period. The organic matter lability of the sediments is more limiting to the production of MeHg than the total Hg concentrations., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Bioaccumulation of mercury and methylmercury in fish represents a serious risk to human beings. Extreme climate events like droughts may increase the trophic transfer of contaminants and net methylation of mercury. The present study assessed the influence of the 2014 drought on total mercury and methylmercury levels in fish from the lower Paraiba do Sul river basin. Contaminant levels were compared for Pimelodus fur, Pachyurus adspersus, Pimelodella lateristriga, Oligosarcus hepsetus, and Crenicichla lacustris captured in five sites in 2013 (N = 212) and 2014 (N = 231). The results indicate that levels of contaminants were higher during the drought in most species. Rainfall was weakly and negatively correlated with total mercury levels in most of the species. The weak relationship between these two variables was due to the indirect influence of rainfall on mercury bioaccumulation. In summary, drought increased the levels of two contaminants in fish., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This is one of the first studies to evaluate the effect of biometric variables (total length and weight), diet, and abiotic matrices (sediment and water column) on the bioaccumulation of methylmercury in tissues (muscle, liver, and gills) of four fish (two carnivore-invertivores, Pimelodus fur and Pachyurus adspersus; one carnivore-piscivore, Oligosarcus hepsetus; and one omnivore, Pimelodella lateristriga) in the lower section of a river in southeastern Brazil. Samples of fish (n = 120), water (n = 5) and sediment (n = 5) were collected at five sites characterized by pollution with mercury due to the use of organomercury fungicides and stream bed gold mining, commonly carried out in that section of the river in the 1980s. The results show that biometric variables are strongly correlated with methylmercury levels in muscle (r = 0.61, p < 0.0005) of P. fur. As a rule, concentrations of total mercury and methylmercury did not vary considerably between the organs of the species of different food habits, because of the environmental conditions in the study area. Despite the low concentrations of mercury in sediments (<0.05 mg kg -1 wet. wt), this compartment is a representative source of this pollutant for the organisms investigated, due to the close contact these animals keep with it in view of the low water columns in that section of the river., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Intrauterine methylmercury exposure and prenatal iron deficiency negatively affect offspring's brain development. Since fish is a major source of both methylmercury and iron, occurrence of negative confounding may affect the interpretation of studies concerning cognition. We assessed relationships between methylmercury exposure and iron-status in childbearing females from a population naturally exposed to methylmercury through fish intake (Amazon). We concluded a census (refuse <20%) collecting samples from 274 healthy females (12-49 years) for hair-mercury determination and assessed iron-status through red cell tests and determination of serum ferritin and iron. Reactive C protein and thyroid hormones was used for excluding inflammation and severe thyroid dysfunctions that could affect results. We assessed the association between iron-status and hair-mercury by bivariate correlation analysis and also by different multivariate models: linear regression (to check trends); hierarchical agglomerative clustering method (groups of variables correlated with each other); and factor analysis (to examine redundancy or duplication from a set of correlated variables). Hair-mercury correlated weakly with mean corpuscular volume (r=.141; P=.020) and corpuscular hemoglobin (r=.132; .029), but not with the best biomarker of iron-status, ferritin (r=.037; P=.545). In the linear regression analysis, methylmercury exposure showed weak association with age-adjusted ferritin; age had a significant coefficient (Beta=.015; 95% CI: .003-.027; P=.016) but ferritin did not (Beta=.034; 95% CI: -.147 to .216; P=.711). In the hierarchical agglomerative clustering method, hair-mercury and iron-status showed the smallest similarities. Regarding factor analysis, iron-status and hair-mercury loaded different uncorrelated components. We concluded that iron-status and methylmercury exposure probably occur in an independent way., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A Teflon dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined variations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17+/-14ngm(-2) h(-1) and 0.9+/-1.9ngm(-2)h(-1), for day and night, respectively), but were similar within the forest site (4.8+/-1.4ngm(-2)h(-1) and 4.4+/-1.8ngm(-2) h(-1) for day and night periods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concentrations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM concentrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture.

Until the 1990s the 1,1,1-trichloro-bis-2,2'-(4chlorophenyl) ethane (DDT) was sprayed in the walls of the house along the Madeira River basin, Brazilian Amazon, a region well known for its large number of malaria cases. In 1910, Oswaldo Cruz described the presence of malaria in 100% of the population living in some localities from the Madeira River basin. Data available in the literature point to the DDT contamination in fishes captured in Madeira River region. Fish is the major source of dietary protein to these people. DDT tends to accumulate in lipid rich tissues and is being eliminated by different events, including lactation. Considering the importance of feeding breast milk to the children, the associated risks of DDT exposure via breast milk intake to children must be assessed. This is the main objective of this work: to analyse the presence of the p,p'-DDT and its metabolites p,p'-DDE and p,p'-DDD in 69 human milk samples and to estimate the intake of DDT and its metabolite in terms of total DDT (total DDT=p,p'-DDE+p,p'-DDD+p,p'-DDT). All the samples showed contamination with DDT and its metabolites ranging from 25.4 to 9361.9 ng of total DDT/g of lipid (median=369.6 ng of total DDT/g of lipid) and 8.7% of the estimated daily intake (EDI), in terms of total DDT, which was higher than the acceptable daily intake proposed by the WHO.