Full text
| |
| Author(s): |
Guacira de Figueiredo Eufrasio Pauly
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | São Vicente. 2023-05-05. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Biociências. São Vicente |
| Defense date: | 2023-03-31 |
| Advisor: | Denis Moledo de Souza Abessa |
| Abstract | |
The rupture of the Fundão dam, of the responsibility of Samarco/BHP, on the afternoon of November 5, 2015, released more than 50 million m³ of iron mining tailings. It was considered the worst environmental disaster in the history of Brazil so far. Initial data obtained from several studies indicate an immediate rise on the levels of metals in the Doce River Basin, but contradictory results for acute and chronic toxicity using some classic models. Thus, studies evaluating the effects at lower biological levels are required. This study aimed to evaluate the biological effects associated with the contamination of water and sediments of the Rio Doce Basin in the area affected by the rupture of the Fundão dam (MG), in order to generate data on the acute, chronic effects and subchronic effects resulting from contamination by metals, thus estimating potential ecological risks. For this, water and sediment samples were collected at different periods after the rupture and chemically analyzed, and the geochemical and enrichment indices were calculated. Concomitantly, acute toxicity tests were carried out with neonates of Daphnia similis or D. magna, exposed to water and sediment (i.e. sediment water interface) samples. 5 organisms were exposed in 4 replicates of each sample for 48 hours, and then the survivors were counted. Tests were also carried out with adult organisms of Corbicula fluminea, collected in the Ribeira de Iguape river (SP) and exposed to sediments, in flask containing about 4 cm of sediment, 1 L dilution water and 10 organisms. The test system was maintained at 25°C and a photoperiod of 12:12 (light-dark), under aeration. After 14 days, the organisms were sacrificed, and the soft tissues were removed. The bioaccumulation of metals was analyzed, as did the biomarkers glutathione reduction (GSH), glutathione-S-transferase (GST), glutathione peroxidase (GPx), lipoperoxidation (LPO), DNA damage, acetylcholinesterase activity (AChE) and metallothionein (MT). Finally, chronic toxicity tests with embryos of Danio rerio exposed to water samples were performed. Healthy fertilized eggs were obtained and transferred to 24-well microplates containing 2ml of water samples, and observed every 24 hours under an electronic microscope, for checking the coagulation, pigmentation of body and eyes, formation of somites, detachment of the tail, hatching, and lethality. The results obtained revealed high levels of metals in water and sediments in samples collected immediately after the dam collapse, with a reduction of concentrations over time. The geochemical indices demonstrated absence or moderate contamination, with high levels of Mn enrichment in the upper Doce River, according to the EF values. Occasional toxicity was observed in 19 Daphnia ssp., but not correlated with the measured metals. Important bioaccumulation (BAF>1) for Zn in C. fluminea was observed, yet this element was not related with the mining tailings. The results of biomarkers were not directly related to the contamination by the mining tailings. Despite the metal concentrations above the legislation, no difference was observed regarding the control and negative effects on D. rerio embryos exposed to water samples. This study evidences that the bioavailability of metals was limited in the Rio Doce basin, with implications for the environmental restoration processes, at least in the freshwater environments affected by the tailings. (AU) | |
| FAPESP's process: | 18/23279-4 - 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) |
| Grantee: | Guacira de Figueiredo Eufrasio Pauly |
| Support Opportunities: | Scholarships in Brazil - Doctorate |