Contaminated soil

Obsolete pesticides are often improperly stored. Liquid pesticides can leak out of corroded drums into the soil and groundwater and end up polluting local lakes and rivers. The wind can spread pesticide powders over a wide area.

Once pesticides enter soil they spread at rates that depend on the type of soil and pesticides, moisture and organic matter content of the soil and other factors. A relatively small amount of spilled pesticides can therefore create a much larger volume of contaminated soil. For example, approximately 30 tonnes of pesticides buried on a site in Yemen in the 1980s contaminated over 1500 tonnes of soil.

Obviously, this can pose a serious health and environmental threat to nearby communities.

A complex process

Cleaning up contaminated water and soil is a desirable part of any obsolete pesticide disposal operation. But dealing with contaminated soil is a costly, technically complex and difficult task. Limited funds for cleanup usually focus first on removal of the source of contamination (the pesticides themselves) and decontamination of soil and water is generally addressed on the basis of risk analysis when additional funds are available.

Every site is different. First the extent of the contamination and the impact on the local environment must be determined. This requires an understanding of the chemical properties of the pesticides. Often the pesticides are unknown and samples must be analysed.

Depending on the results of the chemical analysis and risk assessment, there are three basic ways of dealing with contaminated soil and water:
■ removing the contamination by excavating the soil and pumping-up of groundwater;
■ containing the contamination by covering contaminated soil with buildings, asphalt or another impermeable layer, and preventing contaminated groundwater from flowing downstream;
■ preventing human contact with the contamination by covering the contamination with clean soil, fencing-off contaminated areas and closing contaminated wells.

The costs

Removing contamination is more expensive than containing it, which in turn is more expensive than taking protective measures. But it ends the problem once and for all. Containment and protective measures are effective only for as long as they are maintained and their proper maintenance may be difficult to ensure over a long period of time.

The FAO Programme has published a reference manual for assessing soil contamination to assist developing countries to make sound decisions about how to deal with the problem in the most cost-effective manner. FAO is also working to develop cost effective methods for dealing with pesticide contaminated soil in developing countries.