Beyond conventional endpoints: evaluation of toxic effects in Danio rerio and Corbicula fluminea associated with water and sediments contaminated by the mining tailings released after the rupture of the Fundão Dam, at Rio Doce (ES - MG)

Abstract

The Breakage of the Fundão Dam, situated on the Rio Doce Hydrographic Basin, in November 5th 2015, released more than 50 x 106 m3 of tailings from iron mining and was considered the worst environmental disaster in the history of Brazil. The direct consequences of the disaster were varied, and involved the spread of the muddy residues along the hydrographic basin, reaching the coast and marine zones. The residues have high concentrations of metals, thus they have potential to cause toxic effects on the biota and long-term ecological risks, which would be associated with the bioaccumulation and throphic transfer of metals. The first results reported are conflicting, with respect to the acute and chronic toxicity for some classical biological models; this scenario evidences the need of evaluating the effects at lower biological levels, such as biochemical, developmental, genotoxic and cellular, which may be capable of responding to subtle exposures. This study aims to evaluate the biological effects associated with the contamination of the water and sediments of the Rio Doce Basin, along the area affected by the rupture of the Fundão Dam (MG/ES), and generate data on the chronic and subchronic effects resulting from metal contamination. To achieve that, the toxicity of water samples to embryos of the zebrafish Danio rerio will be evaluated, and the effects will be related with the concentrations of metals. The chronic and subchronic effects on the bivalve Corbicula fluminea will be also assessed, from the exposure to sediments and the analysis of biochemical biomarkers. This study will consider sets of samples collected in different moments after the disaster, which are stored in the laboratory; additionally, we intend to collect more samples during 2019, in order to have a temporal trend on the contamination and its effects. Fertilized eggs of D. rerio will be obtained from laboratory cultured broodstock (in aquariums of 20 liters) and transferred to well microplates with capacity of 2 ml containing the Rio Doce water samples. The eggs will be observed every 24 hours in microscope, for the following endpoints: coagulation of fertilized eggs, heartbeat rate, pigmentation of body and eyes, formation of somites, tail detachment, hatching and lethality. The bivalve C. fluminea will be used in whole-sediments tests: adult individuals will be collected in the Ribeira de Iguape River and acclimatized in laboratory. Then, four replicates per sample will be prepared, by the introduction of about 4 cm of sediment from Rio Doce and clean water in 2 litter polyethylene vessels, and the addition of five animals in each vessel. The test system will be maintained at 25 ° C and photoperiod of 12:12 (light - dark) under aeration. At the end of seven days of exposure, organisms will be sacrificed by thermal shock, and the gills and digestive glands will be extracted for biochemical and chemical analyzes. The following biomarkers will be used: metallothioneins, glutathione-S-transferase, lipid peroxidation (LPO), DNA damage, reduced glutathione (GSH), acetylcholinesterases (Ache), carbonilated/oxidized proteins (PCO), and cell death signaling by caspases' activity. Chemical analyzes of the water, sediment and soft tissue samples of C. fluminea will be conducted by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), in collaboration with the partner research institutions. Results of each endpoint will be analyzed for distribution (normality) and variance homogeneity, followed by one-way Analysis of Variance (ANOVA). Results of bioaccumulation will analyzed through multiple regressions, using the concentrations of each element in the sediments and soft tissues of C. fluminea. Finally, the chemical and ecotoxicological data will be integrated by the use of multivariate analysis, such as Principal Component Analysis (PCA) and cluster analysis (CA). (AU)