Field persistence studies on pendimethalin residues in onions and soil after herbicide postemergence application in onion cultivation

Abstract

Field studies were undertaken to evaluate the fate of pendimethalin residues in spring and dry onions, after postemergence application of the herbicide in a clay soil onion planting in central Greece, at rates of 1.32 and 2.0 kg of active ingredient (ai)/ha. Residues were determined with capillary GC-ECD after onion extraction with 2-propanol/toluene and extract cleanup in a AgNO3-coated alumina column; the recovery of pendimethalin from spiked onions was found to be 82-99% and the limit of determination 0.007 mg/kg. Pendimethalin residues were found to decline rapidly, and it was estimated that 7 days after the treatment only half of the initial concentrations remained for both the low recommended dose (LRD) and the high recommended dose (HRD) experiments. In all cases the residues in dry bulb onion were well below the lowest maximum residue limit (MRL) set by European countries, which is 0.05 mg/kg. Residues in spring onions at harvest time were also below this level when treated at the LRD and were only slightly above in case of the HRD. The pendimethalin concentration in planting soil for the investigated period declined with half-lives of 37 and 39 days for the LRD and the HRD experiments, respectively.