Monitoring of organochlorine and organophosphorus pesticides in the water of the Reconquista River (Buenos Aires, Argentina).

The Reconquista river is a typical example of the adverse impact of human activity on a watercourse. Approximately 10% of the population of the country is settled on its basin and it receives wastewater discharges from residences and industries. This paper describes the results of the first systematic data for measurement of pesticides in surface water of the river, based on a monthly monitoring program over two-year span. The analyses were performed, in three sampling stations (S1, S2 and S3), along 46 km of its course, following the AOAC methods. Screening included the following pesticides: (a) Organochlorines: alpha, beta and gamma HCH; heptachlor, heptachlor epoxide; aldrin; endrin; dieldrin; op' and pp' DDT; op' and pp' DDE; alpha and gamma chlordane and endosulphan II; (b) Organophosphates: ethyl and methyl parathion; chlorpyrifos and fenitrothion. From the 60 samples analyzed, 35% contained organochlorine pesticides in a concentration higher than the detection limit. Organophosphates were found in no case. Throughout the studied period, DDT and its metabolite DDE were only found in S1 and gamma chlordane in S3; heptachlor was present in 50% of the samples of S2 and in 35% of S3, while HCH isomers were detected in 38% of S2 and 45% of S3 samples. Neither temporal nor spatial trends were found. There was not a relationship between the time of samplings and the fumigation season for farming purposes. At all locations, pesticides levels were found to be between 40 and 400 times higher than the legal limits established for protection of aquatic life.