Comparison of the Leaching Behaviour of Alachlor and its Metabolites Under Field and Laboratory Conditions

Abstract

The aim of the investigation was to evaluate whether the results of field studies and those obtained from soil column experiments are comparable in order to describe leaching behaviour of pesticides. The fate of Alachlor and its metabolites 2,6-diethylaniline and 2-chloro-2',6-diethylacetanilide are described in this paper. Field leaching study and laboratory soil column experiments carried out with the formulated herbicide LASSO® gave similar results. Applied Alachlor remained mostly in the top 10 cm soil layer representing a limited mobility. Very small amounts of Alachlor in ground and percolated water indicated only a slight leaching potential. The calculated half-life of 15 days and 90% loss after 335 days demonstrate a remarkable persistence of alachlor. Only 2-chloro-2',6'-diethylacetanilide but not 2,6-diethylaniline was detected in soil and percolated water. It is still uncertain if these residues originate from the formulated product or result partially from metabolism. Column experiments with the same soil carried out under undisturbed conditions are a simple alternative to field studies and allow quantitative estimations. The column experiments support the assumption that most of the alachlor that cannot be found after application is not lost by wind drifting or volatilization but due to formation of bound residues.