Residues of aldicarb in oranges: a unit-to-unit variability study.

Residues of aldicarb and its sulphoxide and sulphone oxidative metabolites in individual Navelino orange trees were determined at several time intervals after soil application of TEMIK 10G at 200 g formulated material per tree. Analysis was by HPLC with postcolumn derivatization giving average recoveries of 98% for aldicarb (RSD 6%), 34% for aldicarb sulphoxide (RSD 5%) and 77% for aldicarb sulphone (RSD 5%). Lowest calibrated levels (LCLs) were 0.02 mg/kg for aldicarb and aldicarb sulphone and 0.04 mg/kg for aldicarb sulphoxide. At the recommended preharvest interval (PHI) of 120 days no detectable residues of any compound, including the parent compound, were found in and of the samples analysed. In mature fruits (PHI of 88 days) detectable residues at the LCL for aldicarb sulphoxide and 0.03 or 0.04 mg/kg for aldicarb sulphone were found in only three of the 18 samples analYsed. In immature fruits detectable residues of aldicarb sulphoxide at concentrations ranging between 0.04 (LCL) and 0.51 mg/kg were detected in 70 out of 88 samples analysed, while residues of aldicarb sulphone at concentrations 0.02 (LCL) to 0.8 mg/kg were detected in 73 out of 88 samples. Indicative variability factors for sulphoxide and sulphone were estimated for immature fruits.