MOBILITY AND DISSIPATION STUDIES OF METRIBUZIN, ATRAZINE AND THEIR METABOLITES IN PLAINFIELD SAND USING FIELD LYSIMETERS

Mobility and persistence of metribuzin (Lexone DF) and its metabolites (deaminated, DA; diketo, DK; deaminated-diketo, DADK) were studied using 75-cm x 15-cm filed lysimeters packed with Plainfield sand, and subjected to two moisture regimes (rainfall, supplementary watering). Atrazine was applied to all lysimeters as an internal reference. Each lysimeter set consisted of 24 lysimeters, divided into two moisture treatments of six pairs each. Effluent was monitored for metribuzin, DA, DK, DADK, atrazine and desthylatrazine. Selected core pairs were sectioned (7 x 10 cm) and analyzed to determine mobility and persistence for each chemical at weeks 1, 2, 4, 8, 12, and 21. No chmemical moved more than 30 cm, nor were they detected in the effluent of cores receiving rainfall. In cores receiving supplementary watering, substantial amounts of metribuzin moved more than 30 cm by week 2 and eluted on 21 occasions throughout the study. The DADK and DK were much more mobile than metribuzin in the lysimeters, eluting more frequently than metribuzin. Metribuzin and metabolites were considerably more mobile than either atrazine or desethylatrazine in Plainfield sand. Metribuzin disappearance closely followed first-order kinetics with t1/2 values of 3.08 and 2.04 weeks, respectively, for the rainfall and supplementary watering treatments. The primary degradation pathway for metribuzin was through the DK intermediate rather than the DA intermediate.