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Aquatic humic substances (AHS) are defined as an important components of organic matter, being composed as small molecules in a supramolecular structure and can interact with metallic ions, thereby altering the bioavailability of these species. To better understand this behavior, AHS were extracted and characterized from Negro River, located near Manaus city and Carú River, that is situated in Itacoatiara city, an area experiencing increasing anthropogenic actions; both were characterized as blackwater rivers. The AHS were characterized by 13 C nuclear magnetic ressonance and thermochemolysis GC-MS to obtain structural characteristics. Interaction studies with Cu (II), Al (III), and Fe (III) were investigated using fluorescence spectroscopy applied to parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy with Fourier transform infrared spectroscopy (2D-COS FTIR). The AHS from dry season had more aromatic fractions not derived from lignin and had higher content of alkyls moities from microbial sources and vegetal tissues of autochthonous origin, while AHS isolated in the rainy season showed more metals in its molecular architecture, lignin units, and polysacharide structures. The study showed that AHS composition from rainy season were able to interact with Al (III), Fe (III), and Cu (II). Two fluorescent components were identified as responsible for interaction: C1 (blue-shifted) and C2 (red-shifted). C1 showed higher complexation capacities but with lower complexation stability constants (K ML ranged from 0.3 to 7.9 × 10 5 ) than C2 (K ML ranged from 3.1 to 10.0 × 10 5 ). 2D-COS FTIR showed that the COO - and C-O in phenolic were the most important functional groups for interaction with studied metallic ions., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Due to the visible abundance of plastic improperly disposed of in the environment, the number of investigations has increased worldwide in different water bodies and biota. Despite this, studies of contamination by microplastics in freshwater environments in the Amazon are scarce. This study investigated microplastic contamination in sediment samples of bathing areas in the Central Amazon, in Itacoatiara, Amazonas, Brazil. A total of 202 microplastic particles were recorded in the five investigated areas that are used for recreation. These results indicate no significant difference in the number of microplastic particles among the establishments; however, the size of the microplastic particles differed significantly between the establishments. Both blue and red microplastic particles were recorded, with blue particles being the most abundant. The microplastic particles were in the form of fibers and fragments. The number of microplastic particles was significantly different between the areas within and adjacent to the bathing areas, though the size of the microplastic particles was not significantly different in the areas within and adjacent to the bathing areas. There was no significant correlation in the establishments in regard to their frequency of use and contamination (number of microplastic particles). This is the first study that indicates the anthropogenic impacts associated with microplastic contamination in recreation areas within the Amazon Forest, an area considered by the world to be of vital importance for conservation. The results of this study indicate that microplastics are present in these bathing areas of the Central Amazon and that contamination in areas used for recreation may be significantly higher than in areas not used for this purpose., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Mercury is an element with potential risk to fish and those who consume it. Thus, this study aimed to determine the levels of total mercury (THg), carry out a health risk assessment related to the consumption of the freshwater stingrays Potamotrygon motoro , and determine the physical and chemical properties of the water where stingrays occur. Stingrays of the species P. motoro were obtained from the Amazon River, and samples of the animals' musculature were collected to determine THg levels. Risk assessment was conducted using pre-established formulas of estimated monthly intake (EMI), maximum monthly intake rate (IRmm), and hazard quotient (HQ). Three population scenarios were evaluated, considering both sexes and differences between rural and urban areas. There was no relationship between weight and THg concentration nor between total length and THg concentration. Higher EMI values were observed in rural children; for the IRmm, male children had the lowest consumption levels. For the hazard quotient, there was a similarity between the three age groups when comparing the male and female sexes. In addition, the representatives of the rural area always had lower values than the urban area. Freshwater stingrays, like other elasmobranchs, can be crucial animal species because they act as sentinels in studies that assess harmful chemicals like mercury.

The evaluation of contamination by domestic sewage is relevant in the Amazon region; however, it has neither been well-developed nor accompanied by research or monitoring programs. In this study, caffeine and coprostanol as indicators of sewage were investigated in water samples from Amazonian water bodies that crisscross the city of Manaus (Amazonas state, Brazil) and cover regions with distinct main land uses such as high-density residential, low-density residential, commercial, industrial, and environmental protection areas. Thirty-one water samples were studied based on their dissolved and particulate organic matter (DOM and POM) fractions. Quantitative determination of both caffeine and coprostanol was carried out using LC-MS/MS with APCI in the positive ionization mode. The streams of the urban area of Manaus had the highest concentrations of caffeine (1.47-69.65 μg L -1 ) and coprostanol (2.88-46.92 μg L -1 ). Samples from the peri-urban Tarumã-Açu stream and from the streams in the Adolpho Ducke Forest Reserve showed much lower concentrations of caffeine (20.20-165.78 ng L -1 ) and coprostanol (31.49-120.44 ng L -1 ). Samples from the Negro River showed a wider range of concentrations of caffeine (20.59-873.59 ng L -1 ) and coprostanol (31.72-706.46 ng L -1 ), with the highest values found in the outfalls of the urban streams. Levels of caffeine and coprostanol were significantly positively correlated in the different organic matter fractions. The coprostanol/(coprostanol + cholestanol) ratio proved to be a more suitable parameter than the coprostanol/cholesterol one in low-density residential areas. Proximity to densely populated areas and the flow of water bodies appear to influence the caffeine and coprostanol concentrations, which was observed in their clustering in the multivariate analysis. The results indicate that caffeine and coprostanol can be detected even in water bodies that receive very low domestic sewage input. Therefore, this study revealed that both caffeine in DOM and coprostanol in POM represent viable alternatives for use in studies and monitoring programs even in remote areas of the Amazon, where microbiological analyses are often unfeasible., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In this study, the multi-marker approach was used for the first time with a highly urbanized lake located in the city of Fortaleza, Brazil, to provide a comprehensive view of temporal trends in sources of pollutants and evaluate the relation between the influence of anthropogenic activities and socioeconomic development. Total concentrations of the markers analyzed ranged from 21.0 to 103.8 ng g -1 , 450.2 to 2390.2 ng g -1 , and 233.8 to 9827.3 ng g -1 for ∑ PAHs , ∑ n-alk , and ∑ sterols , respectively. Concentrations and patterns of PAH, AH, and sterol ratio distribution changed over time and may be associated with different episodes in the history of the city of Fortaleza. The marker ratio distribution in the sediment core revealed an overlap of natural and anthropogenic sources, with degraded oil, biogenic inputs, pyrogenic processes, and fecal contamination from humans and animals in the past changing to petroleum fossil inputs and high contamination from sewage in the present day. The distribution of markers and the chronological history of Fortaleza revealed two distinct periods related to human activities during the development of the city. In the first period (prior to the 1950s), the main human activities were animal breeding and the use of biomass for domestic activities, public and cargo transportation, and commercial activities, especially food production. In the second period (after the 1950s), expansion of the city occurred due to the so-called Brazilian economic miracle and the main human activities were industrialization and urbanization processes, involving deforestation, paving, sewage discharge, and petroleum combustion., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The main toxicity mechanism of organophosphate insecticides such as malathion is the acetylcholinesterase enzyme inhibition. However, fish responses to organophosphates may vary depending on the activation of different defense mechanisms as well as the length of exposure. As such, the evaluation of acetylcholinesterase activity, in combination with the evaluation of biotransformation and antioxidants enzymes levels, is useful for indicating damage in fish exposed to this insecticide. Moreover, evaluating mitochondrial activity might evidence how the hierarchic responses occur in relation to the length of time that the fish is exposed. Therefore, the aim of our study is to evaluate whether the length of exposure to malathion differentially affects the biochemical responses of tambaqui. Our hypothesis is that the physiological alterations due to exposure are time dependent. Fish were exposed to sublethal concentrations of the insecticide during 6, 12, 24, 36, and 48 h. Contrary to expectations, there was no acetylcholinesterase activity inhibition during the experiment, which indicates an absence of neurotoxicity. Phase II biotransformation mechanism was activated early, especially in the liver. Oxidative damage was evident in the first hours of exposure and was concurrent with the activation of antioxidant enzymes. Mitochondrial bioenergetics were differentially affected by the length of exposure. The data suggest that the tambaqui regulates mitochondrial respiration differently over time, seeking to maintain homeostasis and ATP demand, and ensures the activation of response mechanisms, thus minimizing oxidative damage and avoiding the neurotoxicity of malathion., (Copyright © 2021. Published by Elsevier B.V.)

Roundup® (RD) is a glyphosate-based herbicide used to control weeds in agriculture, and fishponds. In the Amazon, hypoxia is a natural phenomenon in flooded areas. Beyond the challenge of hypoxia, fish need to cope with the use of pesticides as RD that increases in the aquatic environment through the leaching of agricultural areas, and in aquaculture fish tanks. Thus, there is a need to better understand the combined effects of hypoxia and RD contamination for aquatic biota. The aim of this study was to investigate the effects of Roundup® (RD) and subsequent acute hypoxia in the gene expression, genotoxicity, histological and physiological responses of Colossoma macropomum. Fish were individually exposed to four different treatments during 96 h: normoxia (N), hypoxia (H), RD plus normoxia (NRD), and RD plus hypoxia (HRD) (RD concentration represents 75% of LC 50 - nominal concentration 15 mg L -1 to C. macropomum). HRD fishes presented down-regulation of hif-1α gene and ras oncogene, while NRD fish presented overexpression of ras; no difference occurred in hif-1α gene expression in both normoxia treatments. The glutathione-S-transferase and catalase activities increased in HRD fish liver compared to NRD. Otherwise, there was no difference in lipoperoxidation (LPO) between all treatments. Genetic Damage Index, measured throughout comet assay in erythrocytes of all treatments, presented similar values, excepted by fish exposed to NRD. As regard as hypoxic exposure, hypoxic fish presented significantly lower values, compared to HRD fishes. An increase in liver histological injuries occurred in H and HRD fish groups. In conclusion, we may affirm that C. macropomum is sensitive concerning RD contamination and that this sensitivity increases when combined with hypoxia., (Copyright © 2019 Elsevier Inc. All rights reserved.)