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Soil Needs Decades to Recover from a Spill

05 November 2010 Plataforma SINC

Twelve years after the spillage at Aznalcóllar (Spain), a team led by the National Museum of Natural Science (NMNS-Spanish National Research Council) states that the soil affected has recovered "reasonably well". Their study of nematodes (microscopic soil worms that are indicators of the biological state of soil) confirmed the "enormous" impact of heavy metals and is useful for predicting the effect of the red mud spillage in Hungary.

One month ago, a spillage of red mud with toxic material from the aluminium holding pond in the city of Kolontar devastated the west of Budapest (Hungary) and reached the Danube. The immediate consequences were the loss of ten human lives and the destruction of houses and crops. In Spain, the Aznalcóllar spillage in 1998 affected the fauna in the soil of Doñana and exterminated several species. Some nematodes disappeared in the first few months after the disaster.

"The abundance and diversity of these animals was affected immediately, but in the long term, the nematodes themselves did not suffer any irreparable damage," the main author of the study and researcher at the NMNS (SNRC) in Madrid Alfonso Navas told SINC.

The study, published recently in Nematropica, compared samples from the unpolluted and polluted areas. According to the results, the diversity and maturity of nematodes was "significantly" lower in the polluted area than in the unpolluted area. "Nickel and Copper appear to be the most toxic metals for the nematode community," Navas added.

"The issue is not whether or not the nematodes disappear, because that is impossible, but whether the nematode fauna, which plays a biological role and recycles organic matter, has suffered damage and also whether the soil has felt the effects of the spill", the researcher specified. "It could take tens of years for the soil to recover," the expert added.

"An impact such as a spillage of this type affects soil structure. Even though it can recover in the long term, the immediate function of the micro fauna is altered for decades", Navas insists. The direct impact of such spillages is also coupled with the fact that majority contain heavy metals.

According to the researchers, Aznalcóllar has been "restored in exemplary fashion", a process that began with a determined and rapid response on behalf of the SNRC and the Regional Government of Andalucía".

However, "some of that soil is still affected by heavy metals, although there is no reason to dramatise because they have been immobilised by physical and chemical corrective measures", Navas indicated. According to the researcher, the surroundings of the Doñana National Park were also used for mining, where "there were already a large number of heavy metals".

The Largest Ecological Disaster in Hungary

On the 4th of October, the Hungarian aluminium holding pond in the city of Kolontar ruptured sending toxic red mud into at least 40km2 of the West of Budapest. Houses, farms, crops and human lives were lost. The "extraordinary" fertility of the plains of the Danube was also affected. "It is highly likely that this area will not be able to be used to grow crops for a long time," Navas said.

Furthermore, "in Hungary, action was not taken as efficiently or quickly as was to be expected, as in Aznalcóllar, and toxic pollutants have probably reached a much greater depth than was the case in Spain", the expert stated.

The "advantage" of the Spanish spillage is that a mud crust was formed which saw pollutants remain on the surface, therefore making it possible to remove them mechanically. In Hungary "it was not hot enough for such a crust to form and the content of the spillage percolated into the soil", the scientist said.

If heavy metals filter into the soil, "biodiversity is reduced and the productivity of the soil, in both physical and nutritional terms, is noticeably affected. Without the biological natural components of the soil, the latter is not moved or aired and therefore becomes compact over time," Navas indicated.

The Spanish biologist believes Aznalcóllar could serve as a model for how to act in Hungary. The nematodes and earthworms play a "fundamental" role because they accelerate the cycle of nutrients and see to it that the latter interchange. "Without the micro fauna, the roots of plants asphyxiate and do not grow, leading to a reduction in the (agricultural and forest) fertility of the soil," Navas concludes.

Attached files

  • El vertido de Aznalcóllar de 1998 afectó a la fauna de los suelos de Doñana y exterminó a varias especies. Foto: CSIC.

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