Harnessing nature to clean up Doñana - scientists recommend a biological solution

An international gathering in Seville of scientists from 14 countries brought together by the European Science Foundation has concluded that a biological approach offers the best long-term solution to last year’s environmental disaster in the Doñana National Park. Despite a massive clean-up operation, involving the disposal of several thousand tons of affected soil and pollutants, the accidental discharge of acid waters and pyritic slurry into the Guadiamar river from the Aznalcóllar mine in April 1998 has left the area of the Doñana National Park in Southern Spain faced with being chronically polluted by heavy metals and arsenic.

The ESF meeting, organised by Victor de Lorenzo of the Consejo Superior de Investigaciones Cientificas and J. Gijs Kuenen of the Delft University of Technology, heard that recent advances in scientists’ understanding of how plants deal with toxic metals and of the chemistry and biology of the element cycles are opening up new possibilities of harnessing nature to deal with toxic spills – a field known as ‘bioremediation’. The natural world is made up of a complex network of cycles, often linked to each other, that are catalysed by a variety of bacteria. Scientists now understand how these cycles transform metals as a function of environmental conditions (pH, redox, aerobic/anaerobic, presence or absence of water etc.). As a result novel technologies are either already available, or under development, to clean up and recycle large volumes of toxic waste.

Preventing similar disasters in the future will involve the development of new methods to avoid the production of toxic wastes in the first place. Meanwhile, in the Doñana park, now that the banks of the river have been physically cleaned, the next big challenge is to get the remaining toxic metals out of the soil. Workshop co-organiser Gijs Kuenen commented: "Ten years ago the advice might have been to dig the soil out, dump it, and replace it by new soil: a nearly impossible task in the case of Aznalcollar. Today, however, it is clear that the immobilisation of the toxic metals is the best option."

First a careful (bio)chemical analysis is necessary to determine the concentration of the toxic metals. Once that is done, immobilisation can be accomplished with special additives such as limestone, special clay types, iron oxides or compost. Tests would need to be undertaken to find out which additives are best suited to the task.

After the toxic metals have been immobilised the river banks should be revegetated by suitable plants, which can help in the immobilisation or in the removal of the remaining non-immobilised metals - a technique known as ‘phytoremediation’. By harvesting the plants such metals can be permanently removed and only the immobilised metals remain. Frequent and long term monitoring (chemical analysis) of the toxic metals will then have to be carried out to identify when unexpected changes occur, and when additional action is needed.

An entirely different problem is the treatment of the toxic sludge in the riverbed. Conditions there are totally different from the air-exposed banks, and hence alternative methods must be employed to overcome the problems of toxic metals in the riverbed-sludge. An immediate measure that should be taken is to make sure that the metals remain immobilised in the mud (sludge) under water. Here the entry of oxygen (air) must be avoided and the best way of doing this is to add organic compounds like wood chips or sawdust, to make sure that all oxygen is consumed at the surface of the mud and that there is a slow production of waste products (H2S) in the mud that keeps the sulfidic metals in an immobilised state.

However, this should only be considered as a temporary solution because the mud may be flushed out during heavy rain. A more permanent fix will require the removal of the toxic mud, remaining behind the dams and in deep pits in the river, even if the metals are kept immobilised by the addition of organic matter.

In addition, the scientists argued that there is an urgent need to develop not yet existing but feasible technologies to deal with otherwise intractable problems such as the pollution of soil with inorganic species of arsenic. According to workshop co-organiser Victor de Lorenzo, this is perhaps the most vicious long-term legacy of the whole spill. "Some particularly toxic chemical substances such as arsenic or mercury need to undergo a series of biotransformations to be converted into less toxic or non-toxic variants," he explains. "Here, advances in modern biotechnology are providing new perspectives to deal with environmental problems which were simply impossible to solve just a few years ago. However, it is necessary to bear in mind that these techniques are very new and therefore cannot be considered as providing 100% guaranteed solutions."

The Workshop ended up by stressing that further research is required to provide the basis for effective decision making. Clean-up decisions will have long term consequences and therefore remediation choices not properly backed up by sound science must be avoided. The scientists expressed their hope that the necessary international and multidisciplinary approaches to the research will materialise in the near term through the European Commission’s Fifth Framework Programme, the ESF’s Groundwater Pollution programme and other international funding schemes.

Ends

Press contacts:

Andrew Smith
Head of Communication and Information, ESF
+33 (0)3 88 76 71 32
or
Dr Victor de Lorenzo
Centro Nacional de Biotecnologica, CSIC, Madrid
+34 91 585 45 36

Notes for editors:

1. The European Science Foundation is the European association of 65 major national funding agencies devoted to scientific research in 22 countries. The ESF assists its member organisations in two main ways: by bringing scientists together in its scientific programmes, networks, exploratory workshops and European research conferences, to work on topics of common concern, and through the joint study of issues of strategic importance in European science policy.

2. While clearly a local tragedy, the Doñana National Park boasts a number of unique features that make this particular pollution incident a disaster of European significance. The area is unique in Europe because of its three complex and closely linked ecosystems (sandy dunes, pine forest, and wetlands), the development of which can be traced back to Roman times. It is home to a rich and varied wildlife and vegetation and it is also an obligatory stopover for many northern European birds during their winter migration. In addition, the park lies within an area of intensive fishing and agriculture, the products of which are marketed across Europe. And even the incident itself had a European dimension as the pollution came from a mine whose origins and owners are not Spanish, but north European.

As a unique site in Europe, responsibility for its protection and conservation cannot be just the duty of local, regional or even national authorities. It is an important part of Europe’s heritage, with an influence way beyond its own boundaries, and anything that affects it is therefore of European concern.

3. ESF Groundwater Pollution programme– the ESF Groundwater Pollution programme was launched in 1997 and aims to serve as a ‘seed corn’ activity to develop long-term multidisciplinary and multinational research collaborations and projects. Its agenda for the next four years was the focus of a major conference in Göteborg, Sweden last November, at which leading European scientists identified priority European research needed to combat the pollution of groundwater by toxic chemicals, radionuclides and excess nutrients

4. ESF exploratory workshops – The Foundation’s limited financial resources are carefully invested in scientific activities that will break new ground, enabling other funding bodies to build on the foundations of our work. One of the cornerstones of this strategy is our system of exploratory workshops. These enable scientists to examine whether an issue should be addressed on a longer-term basis and to form new collaborative links. They provide a useful and responsive mechanism to spearhead scientific advances. As with all the Foundation’s activities, particular attention is paid to complementing rather than duplicating, existing research at a European level.

Issued 12.1.99

For further information contact: Andrew Smith

Category: Media Centre, Press Releases 1999