Feeding the soil

Under attack from intensive farming, underground dumps and abandoned industrial sites, Mother Earth is being sorely tested. After financing a few soil remediation projects, Europe has come up with one or two solutions, but will they be enough to revive soils already in their death throes?

Les Dicyrtoma vivent dans le sol. Ils possèdent un appareil saltatoire, appelé la furca, situé sous le ventre, qui leur permet de sauter en cas de danger et d’être ainsi catapultés en l’air. Ils se nourrissent de matières organiques et participent activement à l’équilibre biologique des sols. © LAMS Dicyrtoma are insects that live in soil. They have a saltatory appendage, called the furca, situated on the underside of their belly, which enables them to catapult themselves into the air in the event of danger. They feed off organic matter and play an active part in maintaining the soil’s biological balance. © LAMS

Research conducted by the French Petroleum Institute, a member of the STRESOIL project. © A A Hydraulic fractures are induced in an experimental cell to be treated using steam-injection. © IFP
© IFP B A geological experimental cell containing induced hydraulic fractures is treated using steam injection. © IFP
© IFP C Geological excavation of the experimental cell previously treated using steam injection. © IFP
© IFP D Bioventilation experimental cell in a clay area with induced hydraulic fractures. © IFP
© IFP E Equipment for treating the air extracted from the bioventilation experimental cell (activated carbon filtration). © IFP

On 20 August 2006, the Probo Koala docked at the port of Abidjan. In its hold were 581 tonnes of toxic waste: a cocktail of hydrogen sulphide, caustic soda, phenols and oil. During the night, the refuse was loaded onto trucks and distributed around the city's rubbish dumps. The toll exacted by this massive soil pollution was 10 people dead and 7 000 hospitalised.

One month beforehand the ship-owner had tried to get his problematic consignment treated by an approved disposal firm in the port of Amsterdam, but finally decided against it because of the prohibitive cost.

While this is obviously an extreme case, soil pollution is a worldwide problem that is having some alarming consequences. In March 2008, the organisation Pesticide Action Network Europe(1) measured pesticide levels in 40 wines from Europe, South Africa, Australia and Chile: all the bottles contained traces of pesticide, in some cases... 5 800 times the permitted level in tap water!

Agriculture in the hot seat

Farmers are often accused of contaminating the soil. Some use organic fertilisers and insecticides for no good reason and to excess. And the public authorities know that it is virtually impossible to ban their use without jeopardising harvests.

According to Lydia Bourguignon, an agro - nomist at the French Laboratory for Soil Micro biology Analysis (Laboratoire d'Analyse Microbiologique des Sols, LAMS), the problem goes even deeper. "After several decades of intensive farming, we have reached stalemate. Soils are depleted and have to be drip-fed to support crops." Surprisingly, the cause of soil impoverishment turns out to be excessively heavy farm machinery. This compacts the earth, which prevents oxygen from penetrating the soil, in turn depriving it of its essential nutrients: the micro-organisms that make crops grow.

"The damage doesn't stop there," the scientist adds. "Soil compaction results in rainwater run-off, with soil erosion to boot. In addition, the run-off washes a large proportion of the pesticides and fertilisers into the surrounding rivers. However, alternative cultivation techniques, such as conservation agriculture(2), do exist and have been successfully tested in Brazil and Argentina. They are less expensive and, above all, less harmful to the environment." Lydia Bourguignon also stresses the need for judicious crop selection: "It is high time we remembered that each type of soil has its own specific function. As long as we go on expecting to grow carrots on land more suited to cereals, we will have to put up with using chemical substances to make up for the soil's shortcomings."

Industry - the worst polluter

According to European Environment Agency figures, industrial activities are responsible for 62% of Europe's soil pollution, with the oil sector alone accounting for 14%. Among the most ommon harmful substances are heavy metals 37%), mineral oil (33%), flavouring substances and phenols.

Nonetheless, there is an obligation on European firms to deal with the pollution they cause. Firms bring in consultants to clean up their soil or treat their waste, such as the French Geological Survey (Bureau de Recherches Géologiques et Minières, BRGM). Dominique Darmendrail, hydrogeochemist and scientific adviser at BRGM, describes the progress made in this area: "For more than 20 years, we have been developing pollution control processes based on biological methods of soil remediation or stabilising the offending chemical compounds. For instance, a foundry contacted us to help it to remove phenol from its moulding sand. After several months of research, our laboratories isolated a bacterial consortium capable of degrading phenol. The micro-organisms are cultivated on site and then seeded in the polluted land. The treated sand is then used as ballast for roads."

They also employ chemical stabilisation techniques for heavy metals. "This is how we treat chromate, a mineral compound frequently used by metallurgical firms," explains Dominique Darmendrail. "We inject sodium dithionite into the soil to reduce chrome VI to chrome III. Chrome VI is a toxic form of the compound and, being soluble, is liable to percolate into groundwater, whereas chrome III is non-toxic and not very soluble." Industry - the worst polluter

Prevention and cure

The European Commission has decided to encourage these first steps towards resolving the problem by launching calls for soil remediation projects. Although such calls are all too rare for the experts' liking, they have nevertheless produced results. The STRESOIL and BioMinE projects are two success stories.

The scientists working on the STRESOIL project (In Situ STimulation and REmediation of Contaminated Fractured SOILs) are tackling petroleum products that become embedded in the fractures of many types of soil. "It was no easy task," says Frank Haeseler, Project Leader at the French Petroleum institute (Institut Français du Pétrole), who is in charge of biological treatment at STRESOIL. "The whole team meets regularly at the former Kluczewo airbase (PL), where the ground is heavily polluted with kerosene. As in the rest of northern Europe, the soil there consists of glacial till pierced by vertical fractures caused by the movement of glaciers in the distant past. Although the clay strata are highly impermeable to kerosene, this pollutant is able to filter down through the fractures to the sand layers, where it contaminates the groundwater aquifers situated, in the case of Kluczewo, 5-6 metres below."

Two techniques were tested, each of them based on creating horizontal disks of sand in the subsoil to connect the natural vertical fractures together. The first technique consists of injecting water vapour at a temperature of 100°C to flush out the kerosene, which enters the vapour phase and can be recovered in a well before being pumped out. The second, gentler but slower, technique consists of stimulating the micro-organisms already in the soil to intensify kerosene biodegradation. The resulting fractures "aerate" the earth, increasing pollution removal efficiency. "Our project came to an end three months ago, with extremely satisfying results," Frank Haeseler is delighted to say. "Both methods yielded 72 % pollution removal efficiency. Steam injection allows a site to be cleaned up in three months, compared with 12 months for the biostimulation technique although, in the final analysis, the cost is the same for both techniques."

The BioMinE project (BIOtechnology for Metal bearing materials IN Europe) aims to preserve resources by optimising the ecoefficiency of metal recovery methods. "Europe is a big producer of mined metals," says Dominique Morin, researcher at the BRGM and BioMinE Project Coordinator. "Pyrometallurgy is the conventional technique used for separating metals from the surrounding rock. However, the high temperatures that this requires make pyrometallurgy a very energyconsuming technique and the resulting residual gas phase solutions generate hazardous emissions." BioMinE proposes biohydrometallurgy as a replacement or ancillary solution - i.e. micro-organisms are used as catalysts to degrade and dissolve ores. Not only are such structures smaller and more flexible, they are also cheaper and less damaging.

"Although biohydrometallurgy cannot be used on its own at present, this highly promising technique is already yielding financial benefits. Unlike with pyrometallurgy, the biohydrometallurgy process keeps the ores in aqueous solution, which prevents air pollution. The technique also allows the maximum amount of heavy metals contained in rock to be extracted." At present, all the waste from mining activities is stored in basins, each with a capacity of 100 billion tonnes, before finally being buried underground. It is difficult to guarantee 100 % safety at the sites. For instance, there may be a risk of poor impermeability of a storage basin or of secondary external pollution causing new chemical reactions with the metals still present. Dominique Morin concludes: "Reducing the quantity of residual metals helps to reduce the risk of pollution. A determined scientific research effort could result in bioprocesses of dual benefit to manufacturing, in terms of both increased returns and environmental gains."

Consensus in Europe?

Researchers' efforts to develop innovative and effective biological methods are meaningful only if all Europe's polluted sites are classified and if willingness to clean them up is followed by action. Luca Montanarella, head of the European Soil Data Centre (IT), makes no bones about it: "The European Union has virtually no involvement in soil management at present. However, the current stalemate has absolutely nothing to do with a lack of willingness on the part of the Commission or the European Parliament, but rather with a lack of consensus among Member States."

In 2000, a working group was set up to develop a strategy for managing polluted soils. On the basis of its conclusions, in November 2007 the European Parliament adopted a Soil Framework Directive recommending that each Member State should draw up an inventory of polluted sites within a reasonable time frame. "Our proposal was non-binding," says Luca Montanarella, "and we confined ourselves to classifying the sites, while delegating the issue of decontamination to the Member States." In spite of this, five influential Member States opposed the directive: France, Germany, the Netherlands, Austria and the UK (strangely enough all leaders in soil management). Luca Montanarella explains this paradox: "They do not wish to pay for a new system for logging data that they already possess. As the remaining 22 Member States have only patchy information about their soils, they welcome the initiative. We trust that a solution can be found very soon. It would suffice for a country like France to change its mind for the directive to be adopted, although we would prefer to arrive at a general consensus by negotiating the contentious issues."

Marie-Françoise Lefèvre

  1. PAN-EUROPE study: "Message in a Bottle - Results of esticide analysis of 40 bottles of wine bought in the EU"
  2. See the article "Back to Earth", research*eu no 57


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Trusting to nature?

In Europe, natural attenuation is a little-used method for removing soil pollutants. It consists of allowing the micro-organisms naturally present in the earth to get to work, while monitoring soil evolution during the treatment period.

Before implementing the method, its efficiency is validated in the laboratory and the rehabilitation period is estimated by modelling. In certain cases, natural attenuation is highly effective, especially for managing oil storage sites. The process used differs according to whether the pollution is organic or metallic. In the case of organic pollution, the appropriate bacteria degrade the pollutant in situ by gradually reducing its mass. In the case of heavy metals, the micro-organisms cause a chemical modification that results in a less mobile and toxic form of the compound. While it does not reduce the pollution itself, it inhibits its damaging effects.

Natural attenuation produces virtually no waste, requires little above-ground infrastructure, and its rehabilitation costs are lower than for excavation or for seeding allogenic bacteria. However, there is a lengthy rehabilitation period.

Natural attenuation tends to be ruled out beyond a certain absorption period (which the UK has set at 30 years) because it is difficult to guarantee that the conditions conducive to degradation will persist or to avoid all secondary pollution. Lastly, for it to become a credible option, natural attenuation must be encompassed by a protocol (tests, predictive model and monitoring), failing which anybody could claim to be using the method simply by leaving the land to its own devices.


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  • Biomine
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  • Stresoil
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