Twelve years ago there was a spillage of pyritic sludge from a mine at Aznalcóllar, in the Doñana National Park in Spain, where four million cubic meters of acidic water and one million cubic meters of waste material containing high levels of toxic compounds contaminated more than 4,500 hectares of the rivers Agrio and Guadiamar and the land around them. Now, 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 occurred west of Budapest in 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 study published 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," said first author Alfonso Navas of the National Museum of Natural Science to Servicio de Información y Noticias Científicas (SINC). "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.
"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."
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."
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".
Aznalcóllar, in the Doñana National Park, 1998 sludge disaster. Credit: SNRC
The Largest Ecological Disaster in Hungary
On October 4th, 2010, 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", he 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".
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."
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.
Citation: A. Navas, P. Flores-Romero, S. Sanchez-Moreno, J. A. Camargo, and E. C. McGawley, 'Effects Of Heavy Metal Soil Pollution On Nematode Communities After The Aznalcollar Mining Spill', Nematropica v40 no 1 (free to read)