Insecticide residues in cotton crop soil

Dimethoate, monocrotophos, triazophos, deltamethrin, cypermethrin and endos ulfan were applied to a cotton crop soil located at Nurpur village, Punjab, India. The insecticides were applied sequentially at recommended dosages i n cotton fields by foliar application in 1995, 1996 and 1998. Soil samples were collected from the cotton crop farms and extracted with acetone. The e xtracted material was analysed by a gas liquid chromatograph (GLC) equipped with an Ni-63 electron-capture detector (ECD-Ni-63). Recovery data was obt ained by fortifying soil with insecticide. The average recoveries from the fortified soil samples were 76-92% for organophosphorous compounds and 90-9 8% for synthetic pyrethroids and organochlorines. The results showed that t he insecticide residues under study were present in the range of 1.16 to 41 .97 ng g(-1), d.wt.soil. The pattern of dissipation of the insecticides use d was similar for the duration of the crop. Half lives of the insecticides ranged from 7 to 22 days. Except endosulfan none of the other insecticides used were leached below 15 cm. Endosulfan was found to be rapidly degraded in the soil and formed a sulfate metabolite. Persistence and dissipation pa ttern in soils with history of exposure to the insecticide compared to non- history soils were similar.