Levels of heavy metals (chromium, copper, lead and cadmium) in water and sediments of the lower Salado River (Argentina) are presented and compared to Canadian and Argentinian environmental standards. Measurement of metal levels was performed using atomic absorption spectroscopy. In order to interpret analytical results, one way ANOVA, hierarchical cluster analysis and correlations were used. Geoaccumulation Index was used as a measure of metal pollution in sediments. There were differences between the accumulation of metals in sediments and water and the control sampling site. Heavy metals, especially chromium, copper and lead, appear to be an important problem to these freshwater environments.

The main factors determining the geochemical fate of copper in urban freshwaters affected by raw sewage discharges were investigated in this work. Water samples from the Iraí and Iguaçu rivers were collected monthly during a 1-year period at two points located upstream and downstream from the city of Curitiba, in Brazil. Results revealed that raw sewage discharges from the heavily urbanized area caused an enhancement of humic-coated suspended solids in the Iguaçu River. In these waters copper is predominantly associated with the humic-coated particles whereas in the Iraí River copper was found primarily in the aqueous phase. The transfer of copper from the aqueous to the solid phase changed its physical speciation along the watercourse. Thus, aspects related to the overall transport of trace metals in watercourses become an important issue to be considered in further studies concerning the effect of sewage discharges on the geochemical speciation and fate of trace metals in urban rivers.

Masu salmon Oncorhynchus masou masou divides into two life histories after a year of life in the river, the sea-run form and the fluvial form. Since salmons are anadromous, the sea-run form salmons are known to pollute the river sediments during spawning migration. In this study, we have studied the accumulation of organochlorines in the fluvial form as well as the sea-run form, and discussed their differences. In order to elucidate the accumulation patterns of organochlorines in both the fluvial and sea-run form masu salmons, the concentrations of organochlorines were determined in the muscle of both life histories. The organochlorines in the sea-run form were 7 to 21 times higher than those of fluvial form. Since salmons are semelparous, the carcasses of polluted sea-run form pollute the river sediments. The trans-nonachlor/trans-chlordane (N/C) ratio in the fluvial form (1.93) was significantly lower than that of sea-run form (23.8). This indicates that the fluvial form is polluted by comparatively newly input chemicals. These results suggest that sea-run form masu salmons have the potential to pollute the river sediments secondarily as vectors, but from the difference in N/C ratio between the two forms, the fluvial fish does not seem to be polluted by those organochlorine compounds of sea-run fish origin yet.