Background and Aim: insecticides are widely used for protecting of agriculture and stored products. Organophosphorus insecticides are used more than other pesticides in agriculture. Therefore the residue of these insecticides in environment such as water may be hazardous to human health. Golestan Province is one of the important agricultural zones in north of Iran. In this area, azinphosmetyl and diazinon widely used for pest control. Garaso and Gorganrood are two important rivers of Golestan Province, which are exist in the near of agricultural lands and gardens, and therefore exposed to insecticides pollutions. Determination of this organophosphorus pesticide residue in water of rivers is important in this area.

Materials and Methods:This is a cross-sectional study, was performed for 1 year, during May 2006 to March 2007. In this research 152 samples from two rivers was sampling and tested. Water sampling from 3 detemined stations in among rivers was performed. azinphosmetyl and diazinon extracted from water samples with used of methylene chloride and acetone and so clean up and concentration phase was done. High performance Thin Layer Chromatography (HPTLC) was used for quantity and quality assay of insecticides.

Results:The residue of Diazinon and Azinphosmetyl in summer is significantly different from others seasons (P<0.05). The most of azinphosmetyl and diazinon residue was determined in summer. Three other seasons (spring, autumn and winter) are not significantly different in azinphosmetyl and diazinon residue (P>0.05). The means of azinphosmetyl residue in Garaso and Gorganrood in summer was 14.56ppm (±SD= 10.59) and 14.9(±11.67), respectively. The means of diazinon in Garaso and Gorganrood in summer was 22.4ppm (±18.62) and 6.74(±6.89), respectively.

Conclusion: The diazinon residue in spring and summer was more than allowed standard limitation in both rivers (Garaso and Gorganrood). But azinphosmetyl residue only in summer in Garaso river was more than allowed standard limitation.