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Organochlorine pesticides (OCPs) use has been restricted or forbidden in Argentina since 1998 and technical endosulfan is the last currently used OCPs on the soybean-wheat production. As they persist in soil for several years after application, OCPs constitute a source of environmental pollution. This work aims to assess OCPs contamination of groundwater (Gw) and streamwater (Sw) in the Quequén Grande River watershed from south Argentinean Pampas in relation to the hydrogeological characteristics. OCPs were analyzed in Sw, Gw, surface bottom sediments, soils and borehole cutting sediments (Cs) by gas chromatograph-electron capture detector. Pesticide distribution in Cs was dependent on the characteristic of the non-saturated zone. Leached pesticides over 3 m in Cs 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. Endosulfan reaches Gw during application season as well as during flooding events while a retard effect was observed for Sw. Levels of a-and b-isomers were in certain cases above national (7 ng L -1 ) and international (3 ng L -1 ) limits for aquatic biota protection. As the endosulfan sulfate metabolite was present in Gw and Sw and due to its high toxicity, it should be considered in the establishment of water quality criteria for human and environmental protection.

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The Negro River is the most important hydrological system of Patagonia, Argentina, drains a watershed of 140,000 km 2. Its main economic activities are agriculture and industry, representing potential sources of organochlorine compounds (OCCs): organochlorine pesticides (OCPs) and PCBs, respectively. These pollutants are persistent, ubiquitous and hydrophobics and are accumulated in the lipid fraction of biota. Fish are excellent biomonitors of pollution because incorporate COCs from water and through diet, and represent different trophic levels. The aims of the present study were to investigate OCCs levels in wild common carp, Cyprinus carpio (Cyprynidae) focusing on: a) the distribution pattern of OCPs and PCBs in gills, gonads, liver, muscle, and stomach content, b) the potential of common carp as indicator of aquatic OCCs pollution, and c) the evaluation of residues in gills and stomach content to discuss different input pathways of OCCs. HCHs, Chlordanes, DDTs, Endosulfan, Heptachlors, Drines and PCBs were quantified by GC-ECD. The distribution of OCCs (ng.g-1 lipid) was gills> gonads> liver> muscle> stomach content. Endosulfan accounted for 64% of OCCs in gills while, DDTs, PCBs and Chlordanes predominated in the stomach content suggesting the incorporation of more hydrophilic pollutants from the water column and those most persistent and hydrophobic from the diet.

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The Negro River extends from the Andes to the Atlantic Ocean supplying water to several cities and to the most important fruit-bearing productive region of Patagonia. Floodplains from the Upper Valley are artificially irrigated with water delivered from the main channel. Pesticides are increasingly used without strict government control. Dams constructed at the tributary rivers retain sediment and therefore the clean water delivered becomes free of sediment and therefore is able to erode certain levees during high-discharge events. Bedload-transport fraction (sand dunes) increases at the Upper Valley and is fixed at the levees of the Lower Valley by riparian vegetation. This riparian vegetation is dominated by Salix humboldtiana and Schoenoplectus californicus while Spartina sp is abundant at the estuarine marsh area. Organochlorine compounds (OCCs) were measured by GC-ECD including dichlorodiphenyl-trichloroethane (DDT), dichlorophenyl-dichloroethylene (DDE) and dichloro-dyphenyl-dichloroethane (DDD) endosulfans, hexachlorocyclohexanes (HCH) and chlordanes. OCCs were preferentially accumulated at the Upper Valley in relation to the agricultural activities developed. The dominance of DDE and the parental endosulfan can be explained by their past and current use, respectively. PCBs (different congener groups) showed low levels as a consequence of chronic pollution related to the mud fraction. The high concentration in pollutants at the Upper Valley is significantly reduced to the Middle and Lower Valleys due to filtering effects, assumed to be induced by the riparian vegetation. At the estuary, very low OCCs levels were measured probably due to the dilution induced by mesotidal dynamics. The sedimentation rate of the lower floodplain is of 1 mm/year. The bottom of the main channel is dominated by 2D sand dunes. At the inlet, a sandy gravel bank is composed of megaripples 0.5 m high. Tidal currents guarantee the stability of the inlet, and particularly the asymmetric flood-tidal delta. Wave action induces a net longshore sand transport towards the north.