Biochemical changes and bioaccumulation of manganese in Astyanax lacustris (Teleostei: Characidae).

Major tailings dam failures have occurred recently around the world and resulted in severe environmental impacts, such as metal contamination. Manganese is a metal highly associated with mining activities, largely detected in mining dam collapses. This metal is considered necessary for different organisms, but it can be toxic and cause oxidative stress and genetic damage in fishes. In this study, we investigated the toxic effects of manganese on Astyanax lacustris, by exposing the fish individually to different concentrations of this metal (2.11, 5.00, and 10.43 mg/L) for 96 h. To assess the effects of manganese, we used biochemical biomarkers (glutathione S-transferase, catalase, and acetylcholinesterase enzyme activity) and the manganese bioaccumulation in different tissues (liver and gills). The obtained data showed that only at concentrations of 5.00 mg/L and 10.43 mg/L the activity of glutathione S-transferase differed significantly. Additionally, the acetylcholinesterase activity in the brain tissue was inhibited. The highest level of manganese bioaccumulation was observed in the liver and branchial tissue. Overall, we concluded that high concentrations of manganese may cause physiological changes in Astyanax lacustris.

Multiple biomarkers response of Astyanax lacustris (Teleostei: Characidae) exposed to manganese and temperature increase.

The present study aimed to evaluate the toxicity of Mn (6.65 mg/L) at different exposure times (96 h, 7, 14, and 21 days) and evaluate its possible toxic effects on the fish Astyanax lacustris through multi-biomarkers and the maximum critical temperature (CT Max). The results show an increase in the Mn accumulation (liver and gills) with increasing exposure time. The glutathione S-transferase (GST) activity showed differences in the group exposed to Mn for 96 h compared to the group exposed for 21 days. The acetylcholinesterase (AChE) activity increased in the fish exposed for 7 days compared to the control group. On the other hand, no genotoxic changes were observed. The CT Max showed that the loss of equilibrium of 50% of the fish occurs at a temperature of 39ºC, with and without the Mn presence. Furthermore, the catalase gene expression (oxidative stress) did not show alterations.

Do Manganese and Iron in Association Cause Biochemical and Genotoxic Changes in Oreochromis Niloticus (Teleostei: Cichlidae)?

The present study aimed to evaluate the toxicity of the association between Fe and Mn in Oreochromis niloticus through genotoxic (micronucleus test and comet assay) and biochemical (CAT and GST enzymes) assays. The tested treatments were T1 = control group (without metal addition), T2 = 2.60 mg L-1 of Fe + 0.2 mg L-1 of Mn, and T3 = 4.40 mg L-1 of Fe + 3.49 mg L-1 of Mn, during 96-h bioassays. All animals exposed to the metals showed a significant increase in erythrocyte micronucleus frequency and DNA damage. The hepatic GST activity increased two times in animals exposed to T3 compared to the control group. The results indicate that Fe + Mn caused genotoxic and biochemical changes in exposed fish. Therefore, excess metals in ecosystems, even those essential for organisms, can be dangerous for the local biota due to the risk associated with high concentrations of these metals.

Metal bioaccumulation and its genotoxic effects on eggs and hatchlings of giant Amazon river turtle (Podocnemis expansa).

The aim of this study was to assess whether possible metal contamination in the sediment of the nests of giant Amazon river turtle, Podocnemis expansa, could contaminate eggs and hatchlings, triggering genotoxic damage. Therefore, sediments of P. expansa nests from two sites in the Brazilian Amazon were evaluated, with the first being collected at Araguaia River and the second at Crixás-Açu River. Newly hatched offspring, eggs, and sediments were collected from the beaches of these two rivers and the quantification of metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Pb, and Zn) was carried out by atomic absorption spectroscopy. All targeted metals were found in both sediment and P. expansa biological samples collected on the beaches presenting higher concentrations in the sediment of Crixás-Açu River. Metals found in the eggshells before nesting and in the egg contents were maternally transferred. Moreover, augmented concentration of metals led by metal transfer from the nests sediments were detected in the eggshells after nesting (ENH) and in the newly hatched offspring (H). Probably this metal relocation to the newly hatchlings augmented the frequency of micronuclei in their blood, presenting 15.25‰ in hatchling found in Crixás-Açu River beaches and 10‰ in newly hatched animals from Araguaia River beaches. These results indicate the occurrence of maternal transfer of metals (essential or not) to the eggs in testudines as well as a transference from the sediments to the nesting eggs, triggering genotoxic effects on the hatchlings.

Is the Doce River elutriate or its water toxic to Astyanax lacustris (Teleostei: Characidae) three years after the Samarco mining dam collapse?

In 2015, after the Fundão dam failure, in Minas Gerais State, Brazil, around 50 million cubic meters of sludge from iron mining tailings were discharged into the Doce River. After the dam collapse, surpassing concentrations of metals were observed in the river sediment, which could be harmful to aquatic organisms, including the fishes. The present study aimed to evaluate the toxic effects of both elutriate and water, collected from the Doce River, on Astyanax lacustris three years after the dam failure. A bioassay was carried out through subchronic exposure to Doce River water (E0) and three elutriate concentrations (10, 50 and 100%). Biochemical analyses (CAT, GST, AChE), metal bioaccumulation assays and calculation of the integrated biomarker response index, version 2 (IBRv2) were performed. The outcomes uncovered deleterious consequences on organisms exposed to E0, with AChE inhibition and bioaccumulation of Fe and Mn in both liver and gills. IBRv2 values were more elevated in fishes exposed to E0 for all tissues. Thus, the elutriate was not harmful for the assessed fishes, since complexing agents presented in the sediment, such as goethite and hematite, may have triggered metals' chelation. In this scenario, the elutriate may have acted as a protective agent for the subjected organisms, unlike the Doce River waters, in which contaminants were proven to be hazardous for the aquatic biota.

Genotoxic, biochemical and bioconcentration effects of manganese on Oreochromis niloticus (Cichlidae).

Manganese and iron were found at high concentrations (3.61 mg/L and 19.8 mg/L, respectively) in the water of the Rio Doce after the dams of Fundão and Santarém broke in Mariana/MG (Brazil). These same metals were found in fish and crustacean muscle (15 mg/kg and 8 mg/kg wet weight, respectively) in the specimens collected near the Rio Doce's outfall. Due to the variation in Mn concentration found in the lower Rio Doce, this study aimed to determine the effects of Mn in Oreochromis niloticus, at the concentrations allowed by CONAMA, and in concentrations found in the Rio Doce after the dams broke. The animals were exposed to the following dissolved concentrations: control group (0.0 mg/L), 0.2; 1.5 and 2.9 mg/L manganese for 96 h. In addition, a positive control was conducted, injecting intraperitoneally with cyclophosphamide (at 25 mg/kg). These exposures caused significant erythrocyte micronucleus formation in the organisms exposed to the highest concentration, as well a significant increase in the DNA damage index of erythrocytes from organisms exposed to 1.5 mg/L and 2.9 mg/L treatments. The glutathione S-transferase enzyme activity also showed a significant increase in the liver of the organisms exposed to 2.9 mg/L. However, catalase activity increased significantly in the gills of the animals exposed to all concentrations of manganese that were tested. Manganese bioconcentrated in greater quantities in the liver than the gills. Thus, manganese causes significant damage to genetic material, generates nuclear abnormalities, activates the body's detoxification system and can accumulate in animal tissue.

Effects of the water-soluble fraction of diesel oil (WSD) on the fertilization and development of a sea urchin (Echinometra lucunter).

Considering the high number of accidents with diesel oil spills occurring in the marine ecosystem, toxicity tests aimed at assessing the effects of this pollutant on biota are necessary and urgent. Thus, the present study aimed to evaluate the toxicity of the soluble fraction of diesel oil (WSD) in the fertilization success of gametes and pluteu larvae of the sea urchin Echinometra lucunter. To do this, gametes and embryos were exposed to concentrations of 0% (control group), 0.5%, 1.5% and 2.5% of WSD. The fertilization success of exposed gametes and embryos were reduced significantly when compared to the control group in all tested concentrations. With this finding, it is evident that diesel oil can be significantly promoted in the early and adult life stages of a particular organism, and a better way of evaluating this toxicity is through the analysis of contaminant effects throughout the reproductive cycle of a species.