Radiotracer Study of the Fate and Persistence of Organic Fungicides Used as Seed Dressing on Grain. Part of a Coordinated Program of Isotopic Tracer Aided Studies of Foreign Chemical Residues in Food. Final Report for the Period 15 September 1972--29 February 1976

摘要

Radiotracer-aided studies were made of the fate and persistence of Thiram, used as a seed dresser, and Ziram, used as a foliar spray, and their effects on soil fertility and plant growth. Thiram applied as a seed dresser had no inhibitory effect on (a) seedling height and rhizosphere microflora of barley, (b) soil microflora, (c) nodulation of cowpea plants. The uptake of exp 35 S radioactivity at 20-day stage was 0.3% of the total applied as exp 35 S thiram. Thiram as such was not present in barley or maize plants at any of the growth stages up to grain formulation but was converted into DDC-glucoside, DDC-alamine, fungicide X and TTCA. The quantity of these decreased in barley and maize with time and were in negligible amounts at grain stage. The sulphur from thiram found its way into sulphur-containing metabolites like protein, amino acids, sulfolipids, etc. Ziram, a foliar spray fungicide was also converted into DDC-conjugates and the amounts of residue were negligible at harvest time both in rice and groundnut. Thiram degraded more rapidly in unsterilized soils than in sterilized soil, thus indicating biodegradation. The fungicide is more persistent in sandy than in laterite and alluvial soils. Microbial degradation of thiram was shown by comparing persistence of exp 35 S thiram in sterilized and unsterilized soils. A Pseudomonas sp. isolated from soil was capable of degrading thiram and ziram and DDC-aminobutyric acid was the major polar metabolite. The appearance of similar degradation products with these dialkyl dithiocarbamates indicated that they have some common metabolic pathway. (Atomindex citation 09:357667)