CONICET | Buscador de Institutos y Recursos Humanos

The Matanza-Riachuelo, a heavy polluted river, flows into Rio de la Plata estuary, main source of drinking water for Buenos Aires city. The population and industrial activities are concentrated in the lower basin (Riachuelo). This paper seeks to assess the water quality and the behaviour of main river water pollutants in an area close to the Riachuelo mouth. Fourteen sampling sites were selected, nine in the navigation channel of Riachuelo and five following a transect parallel to the estuary shore. Physical, chemical and biological variables were determined in freshwater. Anoxic condition was detected in Riachuelo, the low dissolved oxygen (DO) values, and the presence of thermotolerant coliforms and fecal streptococcus may be attributable to untreated wastewater discharges. Downstream DO increased as total sulfide decreased in the water samples. High COD/BOD ratio detected in Riachuelo samples suggested the presence of non biodegradable organic matter. The inhibitory effect obtained in BOD test indicates the presence of toxic compounds. The concentration of heavy metals in the samples was high, exceeded the guide levels for the protection of aquatic life. The high salts concentrations detected in the mouth of the river could induce a decreasing of suspended particulate matter (SPM). The progressive dilution process and the sedimentation of SPM and heavy metals associated, explains the decrease of metals concentration in the river mouth area. Downstream, the SPM increased probably due to local resuspension processes. The main water pollutants decrease in Rio de la Plata estuary. Nevertheless, as riverine sediments act as carriers and sinks for contaminants, it is necessary to study the distribution of main pollutants also in bed sediments to determine their ecotoxicological potential effects.

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