The existing system of management and development of irrigation and drainage without consideration of the ecological danger have led to disruption of the ecosystem balance and change it function. The existence of many rivers draining into the Caspian Sea, and uncontrolled utilization of pesticide toxicants, are one of major concern regarding the water resources in the north provinces of Iran. A study have been done for measuring of Organochlorine and Organophosphorus pesticides in nine rivers of the Caspian Sea basin in Mazandaran and Golestan Provinces which include Haraz, Babolroud, Talar, Tajan, Siahroud, Gharahsoo, Nekaroud, Gorganroud and Atrak from April 2005 to March 2006. Samples analyzing revealed that Phosphorous toxin are observed frequently in aquatic ecosystems especially in summer and autumn. Diazinon as a phosphorous pesticide almost was found in all rivers during the year and its concentration is somewhat more than others. On the other hand, chlorinated pesticides are observed frequently in spring and especially in summer, but are not found in winter at all. Due to the vast expansion of agricultural fields in the study area, these contaminants are leached by rainfall, irrigation and drainage activities and then are conducted to the rivers and finally into the Caspian Sea.
Key words: Caspian sea, pesticides, Mazandaran, Golesatan.
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