HEAVY-METALS IN SEDIMENTS FROM THE PARAGUAY RIVER - A PRELIMINARY-STUDY

The first results ever obtained on heavy metal concentrations (Fe, Mn, Cr, Cu, Zn and Pb) in the Paraguay River surface sediments are presen ted. Samples collected at 11 locations, along a distance of 570 km, be tween the cities of Bahia Negra and Alberdi in Paraguay, for six diffe rent periods between November 1991 and 1993, were analyzed. The Paragu ay sediments appeared to have features of an unpolluted river even tho ugh significant amounts of domestic and industrial effluents are disch arged near the river channel. The relative heavy metal enrichment in s ediments between Bella Vista and Asunci6n, caused by local domestic se wage and industrial outfalls, is less than for the shale standard valu es. The heavy metal content of the sediments exhibited seasonal variat ions. Enhanced organic matter content and biochemical oxygen demand of the river load in winter caused most likely a retainment of the heavy metals in a dissolved state. Consequently, the sediments deposited in the winter were relatively depleted in these elements. (C) 1998 Elsev ier Science B.V.