FAO provides answers to soil decontamination

Where pesticides are used and stored there is often spillage and environmental contamination. This is particularly true in countries where large volumes of pesticides are used, for example in locust control operations. The spilled pesticide can remain toxic and noxious for years, blighting the lives of local residents and moving through the environment to poison farmland, water, animals, crops and people who live and work close by.
In Molodo on the Niger River in Mali, spilled pesticides filled the air to such an extent that nobody could work on the site for long without feeling ill. Neighbours and workers close by complained constantly, but to no avail. The owners of the site and the local authorities could do nothing to solve the problem. Mali has several similar sites throughout the country, some close to the region's main source of fresh water, the Niger River, others threatening scarce ground water reserves, while others still render tracts of land, often in built up areas, inaccessible.
FAO was already working with the Government of Mali to help eliminate stockpiles of obsolete pesticides and build capacity to manage agricultural pesticides better. The authorities asked FAO to help solve the problem of the pesticide contaminated sites. Generally such problems are solved by bringing in costly expertise who then commonly recommend costly solutions. Since contaminated soil often involves large volumes, and since Mali is such a large country with contaminated sites separated by hundreds, if not thousands of kilometres, standard solutions would have been far to expensive to implement.
The FAO Pesticides Management Programme sought solutions that could be implemented locally, using available infrastructure and materials. The search led to Wageningen University in the Netherlands, where researchers had developed methodologies for characterization of contaminated sites, and some work had been carried out to manage such sites in the Netherlands. However, the methods had not been tried on pesticides or in Africa.
The FAO-Mali-Wageningen collaboration began in 2007 with site visits to determine whether the approach would work. Having agreed that it should be tried five sites in Mali were selected; each representing different types of contamination and ecological factors such as proximity to water or population centres. Local teams were trained in the methodology for site characterization to identify what the specific risks were, what the land is currently used for and what its use might be in the future, what chemicals were contaminating the site and to what levels of contamination and what types of biological activity were present on the site. All this information forms a package on which decisions for appropriate action can be based.
Appropriate action might range from doing nothing if risks were low and unlikely to increase over time, to complete removal of all contaminated soil and it isolation because risks at the site were high and could not be remedied within a reasonable time scale. At the site in Molodo for example, risks from dieldrin and parathion contamination were deemed to be high, but evidence from ecological surveys and chemical analysis showed that parathion was degrading naturally, while dieldrin remained at the same concentration over time. A decision was made to excavate the site and return a portion of the soil, mixed with organic manure to a small controlled area where the parathion would be degraded over a period of 3 months. The excavated soil is 'land-farmed' in this way in manageable portions until the all of it has gone through this process. This soil, now without parathion was then removed from the 'land-farm' and mixed with ground charcoal to absorb the dieldrin, and isolated in a concrete bunker. Locally produced charcoal was tested in a laboratory and found to be just as effective as costly imported activated carbon. Planting of deep rooted unpalatable vegetation around the original contaminated site prevents any residual contamination from either leaching into the ground when rain falls, or from evaporating into the air. The site has been fenced and signs erected warning people to keep away.
Chemical analysis shows that the parathion in the soil is completely degraded by accelerated microbiological activity, and that dieldrin remains unaffected because it is a particularly stable chemical. The real evidence however, comes from the local population and the mayor of Molodo who express their gratitude for eliminating the overwhelming and ever-present stench of chemicals.
The international workshop on soil remediation that took place in Mali from 22-24 February, 2010, with the participation of ten African countries, not only visited the site in Molodo, but ate their lunch under the shade of a large tree on the site. Participants were told that 18 months ago, they could not have stayed on that site without respiratory protection for more than two minutes, yet here they were enjoying a relaxed meal with no discernable chemical background odour.
Mali, with the help of Wageningen University and the FAO Pesticides Management Programme is showing others how to deal with pesticide contaminated land in an appropriate, cost effective and locally implementable way. Participants in the recent workshop went home with an understanding of how the work can be done, and FAO will continue to help countries to apply these tools to solve a longstanding problem.


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