RESIDUALITY AND DISSIPATION OF THE FUNGICIDE MANEB FROM TWO PANAMANIAN AGRICULTURAL SOILS.

Abstract

Residue levels of maneb in two panamanian soils under outdoor conditions were monitored from august 1993 to december 1994. Soils sampled at IDIAP's experimental subcenters in El Coco and Cerro Punta, Republic of Panama, were air dried and sieved prior to conditioning under a local environment near the laboratory al Tocumen. Hard-PVC cylinders (54) containing 1 kg soil each were treted with maneb C-14 labelled and Maneb 80 WP in an experimental design of divided parcels with nine blocks and three replicates. The maneb concentration in soil was 642 µg/kg, soil and the total activity applied to each soil was 214.1 KBq. Samples in triplicate were collected at days 0, 1, 20, 52, 84, 173, 299, 360 and 487 days after treatment. Results of the radiometric analysis revealed a rapid dissipation for maneb from both soils; dissipation was more rapid in the soil from Cerro Punta. The half-life was in the range of 20 days. Dissipation occurred mainly during rainy season. After a year of the application maneb residues in soil were 11-13% of the original added amount and have low significance. Residues at this time are no-extractable (bound) residues. It is concluded that the application of maneb in recomended dosage and at a low frecuency has no residual risk for the soil under local conditions. Leaching of residues to lower soil layers was not observed.