Surface and groundwater pollution by organochlorine compounds in a typical soybean system from the south Pampa, Argentina

Abstract

Organochlorine pesticides (OCPs) use have been restricted or forbidden in Argentina since 1998; being technical endosulfan the last currently OCPs used on the soybean-wheat production. Since they persist in soil for several years after application, OCPs constitute a source of environmental pollution. This work aims to assess the contamination of groundwater (Gw) and streamwater (SW) by OCPs in a typical agricultural area from the south of Argentinean Pampas, the Quequén Grande river watershed, in relation with the hidrogeologycal characteristics. OCPs were analyzed in Sw, Gw, surface sediments (SS) and sediment from saturated and non-saturated zone by GC-ECD. Pesticide distribution in sediment wells was dependent on the characteristic of the non-saturated zone. Leached pesticides until 3 meters showed the pattern: HCHs = endosulfan > chlordanes > DDTs, and from 3 to 6 m heptachlor was the main group as a consequence of the past use of this compound in the area, mainly on potato crops. These profiles agree with water table variations that allows the movement of pesticides, particularly for the less hydrophobic. Endosulfan reaches Gw during application season while a retard effect was observed for Sw. Levels of α- and β-isomers were in certain cases above the limit for aquatic biota protection (7 ng L-¹). Endosulfan sulfate metabolite was at higher levels than parental compounds. Considering its high toxicity we recommend to include it in the establishment of water quality criteria for human and environment protection, since its occurrence in water resources represent a risk for human being and environment.