FATE OF [C-14] TERBUTYLAZINE IN SOIL-PLANT SYSTEMS

Lysimeter and laboratory tests were carried out with the C-14-labeled herbicide terbutylazine and a sandy agricultural soil in an application rate of 890 g/ha. The laboratory test in a small plant-soil-ecosystem showed that uptake of residues by maize plants occurred nearly completely by the root pathway. In the lysimeter study small volatilization chambers were placed on the soil of three lysimeters to get information about volatilization and biodegradation to (CO2)-C-14 under outdoor conditions; maize was grown. Volatilization rates were highest at the day of application and then decreased; after 32 days, between 0.30% and 0.36% of the initially applied amount was lost by volatilization. Biomineralization during this time period was between 3.07% and 5.26%. Maize plants took up 0.41% of the applied radioactivity; this C-14 was due to polar metabolites and to unextractable residues and not to unchanged terbutylazine. About 1 year after application of the pesticide, volatilization and biodegradation of terbutylazine and probably of its metabolites were determined again after tilling the soil. Volatilization rates were in the same range as in the first year 30 days after application. (CO2)-C-14-formation was lower and no lag phase could be observed.