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The mining waste discharged in the bay of Portmán, in Murcia, analyzed in the ALBA Synchrotron (14/02/2019)

The Bay of Portmán is one of the most serious cases of environmental impact due to the dumping of mining waste in Europe.

For 40 years more than 60 million tons of waste were discharged directly into the sea, from the treatment of minerals extracted from the Sierra Minera de Cartagena, which literally filled the bay with sludge rich in heavy metals.

Since 2014, the Consolidated Research Group in Marine Geosciences at the University of Barcelona is investigating Portman Bay.

Now, they have taken samples of these sediments in the ALBA.

The synchrotron light allows them to obtain unpublished information about contamination by heavy metals such as arsenic.

Few people know the Bay of Murcia Portman, where there was one of the largest coastal ecological impacts of mining activity in Europe.

The figures speak for themselves: the Peñarroya company mine poured more than 60 million tons of mining waste into the sea through a 2km pipeline located west of the bay.

Over the years the bay was completely invaded by a mountain of artificial sediments.

The line of the beach advanced 600m and the trail of the discharges reached 12km offshore.

Since the 90s there is no mining activity in Portman but the accumulated waste is still there.

Now, samples of these have reached the ALBA Synchrotron, in Cerdanyola del Vallès, to be analyzed.

The story begins aboard the oceanographic ship Ángeles Alvariño, from where the Consolidated Research Group in Marine Geosciences of the University of Barcelona took samples of the sediments and mining residues under the sea.

"Until now, studies have been carried out basically on the emerged part of the Portman waste," says Marc Cerdà, a doctoral student from the Department of Earth and Ocean Dynamics and a member of the research group.

"We extract material by drilling the seabed with up to 4m tubes and obtain sediment samples in columns."

The analysis of these sediments confirms that they contain arsenic from the minerals of the mine, such as arsenopyrite, and that it is found in different oxidation states.

That is to say, that this arsenic has undergone chemical transformations such as oxidation, which can affect its mobilization and release by dissolution in the water column.

The researchers questioned the degree to which these processes occurred, since "until now almost nothing was known about this," explains Josep Roqué, a professor in the Department of Mineralogy, Petrology and Applied Geology at the UB.

"We are interested in characterizing these mining waste accurately to reconstruct the geochemical processes of alteration of the arsenic-bearing minerals and from there, define the availability in the marine ecosystem of this toxic element," he adds.

Under the light of the synchrotron

To know exactly the geochemical processes that take place in the residues of Portmán, samples of these sediments were first characterized in a non-destructive way in the CORELAB laboratory of the UB.

Afterwards, they have been analyzed in the ALBA Synchrotron, in the CLAESS light line.

Its technique is X-ray spectroscopy, that is, the sample is illuminated with synchrotron light and, detecting the energy it emits and absorbs, it can be deduced what chemical elements form it and in what oxidation state they are.

The samples of the sediments, which contain arsenic, have been prepared under a protocol specially designed with CLAESS scientists, who support researchers from the research centers that come to use the synchrotron.

The analysis under controlled conditions of the sediments allows us to study them as they are found in the bay and, therefore, obtain faithful results.

"CLAESS allows us to take measures under controlled conditions, without exposing the samples to the atmosphere to avoid the risk of oxidation.If we just want to know the oxidation state of the elements in situ, we can not allow them to be altered during their analysis", explains Carlo Marini, line scientist.

In addition, CLAESS also allows to detect the chemical elements in the samples although its concentration is very low.

"It is the first time we analyze such a problem with these powerful tools and we are obtaining unpublished information that was not known about Portman," they note.

The researchers hope to find for the first time valuable clues to know the distribution, mobility and availability of arsenic in the marine ecosystem and, therefore, to evaluate their potential effects on the natural environment and biodiversity of the coastal coast in Murcia.

According to Miquel Canals, head of the Research Group, "Portmán is an exceptional case study on which we still have more questions than answers despite having advanced a lot in the knowledge of its stability, structure and composition, all of them crucial aspects for planning the remediation tasks and, as far as possible, rehabilitation of the bay. "

What remains of "Portus Magnus": a reference for the study of discharges to the sea

Portman was already an important site for the Carthaginians and the Romans, who called him Portus Magnus.

Now, Portman is no longer an important port, he only remembers where he was in the middle of the mining sediments.

At present, there is a rehabilitation project for the bay that aims to eliminate 10 million tons of waste and push the coastline back 300m inwards.

In spite of everything, Portmán could serve as a reference being a case study of the impacts of mining discharges to the sea.

Currently, for example, there is talk of underwater mining: extractions at 3000m depth in the oceans to bring minerals to the surface.

So, events like Portman's are very interesting to see what could happen in cases where there are large spills and processed minerals in the sea.

Source: Agencias

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