RESIDUES OF PARAQUAT AND LINURON IN AN ORGANIC SOIL AND THEIR UPTAKE BY ONIONS, LETTUCE AND CARROTS

Abstract

Paraquat (1,1′-dimethyl-4,4′-bipyridinium dichloride) and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] were applied to an organic soil, as spray treatments, at rates of 1.12 and 2.24 kg/ha, and 2.24 and 4.48 kg/ha, respectively. The persistence of the herbicides and their residues in lettuce (foliage), onions (root), and carrots (foliage and root) at harvest time were studied under field conditions. Proportionately more residues persisted in the soil from the higher rates of application of paraquat (2.24 kg/ha) and linuron (4.48 kg/ha). About 83–86% of the initial amounts of paraquat and 59–74% of the linuron remained in the soil 4 mo after application. Furthermore, about 50% of the paraquat was recovered from the treated soil 15 mo after application, whereas only about 20% of the linuron was recovered at the end of the same period. Carrots grown in this soil did not absorb detectable (>0.005 ppm) amounts of linuron, while onions and lettuce grown 12 mo after application absorbed the herbicide in various amounts. At the lower rate of application (2.24 kg/ha) linuron residue in onions was 0.014 ppm and that from the higher application rate (4.48 kg/ha) was 0.046 ppm. Lettuce had about 0.009 ppm residue, irrespective of the rate of application. Onions and lettuce grown on paraquat-treated soil had low residue levels (0.001–0.011 ppm). The study demonstrates the potential of paraquat and linuron residues to persist in organic soil, and their uptake by vegetable crops.