Ecotoxicological assessment of the highly polluted reconquista river of Argentina

Abstract

The situation of most of the Argentine rivers is very serious due to the amount and range of pollutants, principally as a consequence of industrial development with an inadequate regulatory framework and a deficit of decades in matters of sanitary substructure and waste treatment. Freshwater quality monitoring in Argentina was based on water chemistry and bacteriology, with measurements of only the main variables required for the determination of quality indexes. A multidisciplinary approach considering simultaneous evaluation of a number of factors and processes that in an integrative picture determine its characteristics was poorly developed or lacking. The use of biota for monitoring the aquatic environments has been relatively uncommon compared to abiotic variables. The Reconquista River is a typical lowland watercourse situated in the Buenos Aires Province. Located in a temperate subtropical region, it flows into an international river, Río de la Plata, which is part of the second largest hydrogeographic system of South America, after the Amazon, and the fifth largest in the world. The river receives the output of 80 small tributaries, and one of them, the Morn creek, should be highlighted as it marks the limit between the medium and the lower sections of the river. During the dry season the entire stream is composed of sewage and industrial wastes and known as an open sewer. The river is the second most polluted waterway of Argentina. There is a great variety of industrial activities settled on its basin. Some 10,000 plants, most of them located on the margins of the river, discharge their untreated effluents into the river and use large quantities of water in processing, cooling, and cleaning. Approximately 20% of these industries discharge a total BOD load of approximately 150,000 kg d-1, which is equivalent to an organic loading capacity of 2.5 million population. To monitor water quality of the main course of the Reconquista River, the following principal approaches have been adopted: (a) measurement of approximately 30 physical and chemical variables, (b) determination of biological parameters (phytoplankton and zooplankton abundance, diversity, and community structure, microbiology), (c) acute and prolonged in situ and laboratory toxicity tests with algae, tadpoles, and fish (fry and juveniles) as sentinel organisms, (d) monitoring of alterations in specific physiological and biochemical markers of exposure in fish, and (e) determination of water quality indexes based on the physicochemical profile of the samples. The studies were carried out during a span of 15 years on samples regularly taken in three to five sites covering the length of the river's main bed. The most relevant outcomes of the study can be summarized as follows. Spatial variation of the DO was from 7-8 mg L-1 in S1 down to 0-0.3 mg L-1 in S5, indicating water in Bancalari was in permanent anoxia. COD/BOD ratios oscillated between 11 (in S1) and 4 (in S4-S5), suggesting the presence of important amounts of nonbiodegradable organic matter. The presence of domestic sewage indicators and municipal wastes as chlorides, orthophosphates, inorganic N compounds (NH4+, NO2-, NO3- and phenols were found in all samples, with a clear-cut increase in concentration down river up to values well above MPQs. Total heavy metal concentrations always exceeded widely MPQs established by Argentine law for protection of freshwater life. At all locations organochlorine insecticide levels varied between 40- and 400 fold above legal limits. When considering physicochemical parameters altogether in a spatial and temporal perspective, it becomes evident that there was a progressive but sustained alteration of the water quality downriver, especially after the confluence of the Morn creek, and, that the deterioration increased with time. River water showed an alarming degree of bacterial pollution, which was temporally and spatially highly variable. Environmental physicochemical toxicity data were closely correlated with the results of both acute and sublethal chronic toxicity bioassays. It was concluded that only an integrated analysis of chemical and biological parameters coupled with toxicity tests will offer a realistic view of the state of water quality in the Reconquista River. © 2006 Springer Science+Business Media, Inc.