SORPTION OF PESTICIDES IN THE SEDIMENT OF THE TEUFELSWEIHER POND (SOUTHERN GERMANY) - I - EQUILIBRIUM ASSESSMENTS, EFFECT OF ORGANIC-CARBONCONTENT AND PH

Sediment adsorption-desorption batch technique studies of seven pestic ides and metabolites with different physiochemical properties, that ha ve been recently applied in agriculture in Germany were performed with sediment samples From the Teufelsweiher pond (area: 3155 m(2), depth: 0.3-1.3 m) in Southern Germany. Sorption kinetics exhibited two pheno mena: an immediate rapid sorption (< 4 h) followed by a slow sorption process over a long period of time (two to four days). Sorption isothe rms could be well described by the Freundlich equation in a nonlinear form (1/n < 1) for all seven compounds. The Freundlich coefficient (K- f) and Freundlich constant (1/n) appeared to be closely related to the physiochemical properties of the compounds. With increasing pesticide hydrophobicity (higher K-ow, lower solubility) their adsorption was s tronger and faster, their desorption much less effective and incomplet e even after a long equilibration time. This hysteresis phenomenon was attributed to both sediment-particle size and organic matter content, which also controlled the pesticide distribution to the particle-size fractions. This distribution exhibited a bimodal behavior: both, the smaller particles (clay, fine silt, < 6.3 mu m) as well as the larger particles (fine sand, 63-200 mu m) showed the most effective sorption of pesticides. In addition, the pH also exhibited a considerable effec t on the sorption behavior of the pesticides. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.