Analytical Sciences

Abstract − Analytical Sciences, 18(7), 779 (2002).

Monitoring of the Pesticide Diazinon in Soil, Stem and Surface Water of Rice Fields
Alireza GHASSEMPOUR,*  Ali MOHAMMADKHAH,** Fazel NAJAFI,*** and Mohammad RAJABZADEH**
*Chemistry Research Center, Shahid Beheshti University, Evin, Tehran, Iran
**Department of Chemistry, Faculty of Science, University of Guilan, Rasht, Iran
***Department of Biology, Faculty of Science, University of Guilan, Rasht, Iran
Diazinon is an organophosphorus insecticide (OPP) that is used as a pesticide for Chilo suppressalis (WLK) (Lep., Pyralidae) in rice fields. The extraction of diazinon from soil and the stems of rice plants has been carried out by microwave-assisted extraction (MAE) and the results compared with ultrasonic extraction (USE). The best parameters for MAE are hexane-acetone (8:2 v/v) as a solvent, a 2.5 min extraction time, and 20 ml of the solvent volume. Also, surface-water samples of the rice fields were extracted by solid phase extraction (SPE) using a C18 disc. The optimum conditions of SPE were a sample volume of 750 ml, a pH of 7 and high ionic strength of water. The extracted samples were analyzed by gas chromatography-mass spectrometry (GC-MS). The relative standard deviation (RSD) and regression coefficients related to the linearity were <3.5% (n = 5) and 0.99, respectively. The limit of detection (LOD) is 0.1 ng ml-1 with selected ion monitoring (SIM) at 137 m/z. The average recoveries of diazinon in soil and stem samples by MAE and surface-water by SPE were 98% (±3), 94% (±5) and 87% (±3), respectively. In June, the concentration of diazinon in soil and stem samples of the rice plants in Guilan province is high (55 ng ml-1) and in September is low (2 ng ml-1). In surface-water samples, the results are converse. In November, diazinon can not be detected in soil, stem or surface-water samples. Diazinon is degraded to diethylthiophosphoric acid. Also, three microorganism genera (Pseudomonas sp, Flavobacterium sp and Agrobacterium sp) have been found to degrade diazinon in soil and surface water.