Study warns of new risks of Samarco dam collapse

In the first conclusive evaluation after the dam collapse researchers show the damage caused by tailings in the marine zone. Threats to the Abrolhos Bank increased.

Elmano Augusto / elmano.cordeiro@icmbio.gov.br

The monitoring of the mining tailings from the Samarco dam in the coastal and marine zone of Espírito Santo and southern Bahia needs to be maintained and improved, since the level of contamination, although apparently decreasing, still raises great concern. Mud flow, which is concentrated on the seabed, continues northward along the coast and poses a strong threat to the environmental health of the Abrolhos Bank, the largest coral reef formation in the South Atlantic.

These are some of the conclusions reached by oceanologist Adalto Bianchini, of the Federal University of Rio Grande (FURG), physicist Heitor Evangelhista, of the State University of Rio de Janeiro (UERJ), and geologist Alex Bastos, of the Federal University of Espírito Santo (UFES). They presented the results of the three expeditions to evaluate the impacts of the mud in the region of the mouth of the Rio Doce on Wednesday (21) to the Chico Mendes Institute for Biodiversity Conservation (ICMBio) in Brasilia. It is the first conclusive study on the damages caused to the marine zone after the rupture of the dam, the biggest environmental tragedy in the history of Brazil.

Contamination

Following the collapse of the Samarco dam in the Bento Rodrigues district of Mariana (MG) and the arrival of the mud at the mouth of the Doce river in November 2015, the ICMBio and its partners promoted three expeditions to the coastal area affected by the disaster to verify the degree of contamination – the first was in January, the second in April and the third in December 2016. The work was supported by the ship of the National Center for Research and Conservation of Southern and Southeastern Marine Biodiversity (CEPSUL), a unit of the Institute.

During the excursions, samples were collected from surface of the water and the seabed, and from marine animals and other living organisms. The laboratory tests initially detected a high degree of contamination by heavy metals and chemical elements – iron, nickel, copper, zinc, aluminum, manganese, chromium, arsenic, among others – that diminished as the mud spreads. Nevertheless, the damage was not little, as the study reveals.

According to the researchers, between the first and third shipments, there was a considerable reduction in the presence of phytoplankton, zooplankton, ichthyoplankton and benthos in the water samples and substrate of the seabed. These organisms are at the base of the food chain and their absence compromises the balance of the entire marine ecosystem of the region.

Stress

According to the researchers, the coastal area affected by the tailings, which stretches for hundreds of miles from the mouth of the Doce River, is environmentally six times more “stressed” than normal. In this case, it is advisable to maintain the ban on fishing, especially trawling, which turns over the seabed and can cause “recontamination”.

Commenting on the threats to the Abrolhos region, which is a national marine park, the researchers have admitted the presence of iron “microparticles” in the water samples collected in the region, which may be a sign that the tailing mud is approaching. However, according to them, it is still not possible to say “strictly” that the archipelago was hit by the contamination.

Given this situation, they recommended the maintenance of the monitoring throughout the region affected by the tailings, with the inclusion of new and more precise evaluation measures. It is only then, the researchers said, that it will be possible to have a more effective control on the evolution of the contamination process and to know for sure if the impact already caused to the environment is “acute”, that is, short term and reversible, or “chronic” , that is, definitive and without solution.

Fonte: ICMBio

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