Carbaryl and monocrotophos residues in cottonseed products. Part of a coordinated programme on isotopic tracer-aided studies of chemical residues in cotton seed, feed, oil and related products

Cotton plants of Deltapine variety were treated with carbaryl (naphthyl-1-14C), (6.7 mg/plant) three times at two week intervals. Seeds were collected at maturity and 14C-residues were determined in the oil and cake by standard procedures. 14C-carbaryl and/or metabolite residues were 0.42 and 0.15 mg/kg in the crude oil and cake respectively. Parallel studies were conducted with spectrophotometric techniques using p-nitrobenzene diazonium fluoborate as chromogenic agent. Applications were made three times at a rate of 14 mg/plant. Residues in the crude oil and cake were found to be 0.83 and 0.04 mg/kg respectively. The higher residue level in the oil - compared to the radiometric technique - probably relates to higher application rates. Cotton plants of Deltapine variety were treated with (N-methyl-14C) monocrotophos (0.09 mg/plant) three times at two week intervals, as recommended for agricultural practice. Seeds were collected at maturity and standard procedures for extraction, clean-up and paper and thin-layer chromatography were adopted for the ultimate determination of residues in seed, oil and cake. Parallel experiments, using spectrophotometric techniques, were made for comparison. 14C-residues of monocrotophos and/or metabolites in cottonseed, crude oil and cake were found to be 0.06, 0.12 and 0.05 mg/kg respectively. Corresponding data obtained by non-nuclear techniques were 0.18, 0.42 and 0.15 mg/kg respectively. The discrepancy between the two sets of results may be related to different rates of application: 0.3 mg and 0.09 mg/plant for non-nuclear and radiometric techniques respectively. Among the major metabolites identified in the cottonseed were dimethyl phosphate and O-desmethyl monocrotophos. N-demethylated monocrotophos and sugar conjugates were also identified