Is drainage water representative of root zone leaching of pesticides?

06-12-2005

In connection with the reassessment of the mobility of glyphosate, doubts have been raised over whether pesticide concentrations measured in drains are also representative of the concentrations leached from the root zone to drain depth between drains.

Or, in other words, does the concentration of pesticides measured in drains give a true and fair picture of the annual, flux-averaged concentration found at a depth of approximately one meter?

The Geological Survey of Denmark and Greenland (GEUS) and the Danish Institute of Agricultural Sciences (DIAS) have jointly carried out an extensive survey of the existing scientific literature, which, so far, does not include an in-depth study of this issue. The report's conclusions are thus based on a collection of studies, each describing elements of the above issue.

On the porous loamy soils typically found in Denmark, drainage water concentrations are deemed to be representative of the levels leached from the root zone to drain depth. On very well-drained soils and on heavy clay soils the use of drainage water as an indicator of leaching levels is more problematic. On these soils, leaching levels can be either overestimated or underestimated, depending on local conditions.

Used critically, and incorporating the hydrological and geological aspects (as in the Danish Pesticide Leaching Assessment Programme), the authors believe that pesticide concentrations in drainage water can be used as a measure of the concentrations leached from the root zone to drain depth between drains.

The results are available from the report "Is drainage water representative of root zone leaching of pesticides?" and can be obtained from GEUS or downloaded from www.pesticidvarsling.dk.

For further information please contact:
Head of research unit Ole H. Jacobsen, DIAS, tel.: +45 8999 1761
Scientist Jeanne Kjær, GEUS. Tel.: +45 38 14 23 33.