Monitoring of pesticide residues in a cotton crop soil

This paper reports on the residues of methyl parathion (O,O-dimethyl O-4-ni trophenyl phosphorothioate), trifluralin (alpha, alpha, alpha-trifluoro-2,6 -dinitro-N,N-dipropyl-p-toluidine), endosulfan [(1, 4, 5, 6, 7, 7-hexachlor o-8, 9, 10-trinorborn-5-en-2, 3-ylenebismethylene) sulfite] and dimethoate (O, O-dimethyl S-methylcarbamoylmethyl phosphorodithioate) in a cotton crop soil. Soil samples (0-15 cm) were collected at different periods from the cotton crop farm and subjected to Soxhlet extraction. The extracted materia l was analysed after clean-up by a HP5890 II gas chromatograph equipped wit h a Ni-63 electron-capture detector (ECD-Ni-63) and fitted with a 25m x 0,2 mm i.d. fused silica capillary column [Ultra-2 (5% phenylmethyl polysiloxan e)]. The recoveries of the pesticide residues from the spiked control soil were determined after Soxhlet extraction and C-18 cartridges clean-up by us ing radiotracer techniques with the corresponding C-14- pesticides. The res ults show that in the cotton crop soil the pesticide residues under study w ere present in the range of 0.1 to 0.4 mg.kg(-1). Endosulfan was found to b e rapidly degraded in the soil and formed a sulfate metabolite.