The Aznalcóllar spill (Seville), which will be 22 years old on April 25, is one of the biggest mining accidents in the world. The fracture of a pond spilled 4.5 million cubic meters of toxic sludge on some 5,000 hectares of agricultural land, the area equivalent to almost four times the city of Cádiz. A study by the Universities of Granada and Almería revealed that, despite regeneration work and after more than two decades, part of the affected area (7%), the closest to the mine, maintains high levels of acidity and heavy metals such as arsenic, lead, copper and zinc. A recent investigation by the universities of Granada, Elche and Tokyo has discovered a weapon against this contamination: the use of compost generated with worms, organic and inorganic waste as well as microorganisms so that the land itself can regenerate. It is a kind of immunotherapy applied to the earth.
“There are things that have not been resolved,” highlights Francisco José Martín, who leads the research by the group of the Department of Edaphology and Agricultural Chemistry of the University of Granada (UGR). And to solve them they have looked at nature itself. “This is the use of organic and inorganic waste from human activities, mainly from agriculture and the extractive industry, to make a “vermicompost” with the action of worms and microorganisms,” explains the researcher.
“The idea is not to massively introduce elements artificially to recreate the soil, but to activate it so that it begins to be colonized by plant species. The rest is done by nature,” says Martín, lead author of the research published in Chemosphere.
Vermicompost, widely used in agriculture and known as “worm humus”, manages to retain heavy metals such as copper, zinc and cadmium and prevent their spread to other soils or aquifers. However, in the course of the investigation, they have detected unwanted effects. “Some elements, such as arsenic or lead, can be enhanced and become more available”, explains the researcher. To avoid this, other agents are added, such as iron oxide from the mine dumps in Alquife (Granada) or sludge generated by polishing and cutting marble in Macael (Almería).
PACO BRIDGES
In this sense, the study will continue with the objective of “expanding the range of residues and microorganisms that generate the desired effect”: activate nature so that it regenerates the soil. This is the case of fungi, especially mycorrhizal fungi, which are symbiotically associated with 80% of land plants.
Japan’s interest
Yasuo Nakamaru, from the Faculty of Bioindustry of the Agricultural University of Tokyo ( Japan). The Japanese interest in Aznalcóllar is that the contaminated area along the Guadiamar riverbed has become, according to Martín, a “natural laboratory” where formulas for “assisted restoration” can be tested.
Japan, like most developed countries, has many areas contaminated by the use of herbicides and pesticides. The very cultivation of rice, basic in the Asian country, presents heavy metals that generated in the fifties a bone disease baptized as Itai-Itai (oh, oh) for the pain it caused. The researcher from Granada plans to continue the research with the Japanese university.
The Aznalcóllar area affected by residual contamination is no longer agricultural land and its use is limited exclusively to a recreational green corridor, but other areas that are in use and contain heavy metals can benefit from the results of this research, which has given hopeful results. “With the appropriate doses and follow-ups, the area could recover 100% in two or three years,” says Martín.
The research has been financed with funds from the research group and from two Projects of the National R&D Plan, the last of which is currently co-directed between the University of Granada and the Zaidín Experimental Station, dependent on the Higher Council for Scientific Research (CSIC). ).
One of the advantages of the analyzed model is the reuse of waste generated by human activity, one of the main objectives of the UGR’s Edaphology and Agricultural Chemistry team. In this sense, the department is also investigating the possibilities of generating “technosols”, artificial soils manufactured specifically to favor the recovery of seriously degraded areas, according to their characteristics.