Most of the industrial, urban and sewage discharges are released into the La Plata River, Argentina without any previous treatment. However, few works have investigated the extent of metal contamination. The aim of this study was to assess the levels of cadmium, copper, lead and zinc in liver and gills of adults Prochilodus lineatus collected from three sampling stations along the coast of the La Plata River: Berazategui, Berisso and Atalaya (from north to south). Samplings were performed during 2002 and 2004. Berazategui and Berisso were located nearby the main ducts that discharge the urban and domestic waste disposal from the cities of Buenos Aires and La Plata, respectively. The third station, Atalaya, was free of sewage discharges. Levels of cadmium and copper in liver were always higher than those found in gills. Instead, for lead and zinc, high levels were observed either in liver or gills, depending on the sampling station and the sampling period. In both tissues, the concentrations of metals did not differ significantly between male and female fish. In liver samples, the concentrations of cadmium, copper and zinc tended to increase from north to south. Instead, the levels of lead followed an opposite pattern. No clear tendencies were observed in gill samples. The data may be useful as reference levels of metal contaminants in P. lineatus, the most important fish species in the La Plata River system.

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The effects on red blood cells of a single sublethal dose of Pb of 100 mg kg-1 administrated to adult Bufo arenarum were studied. The blood d-aminolevulinic acid dehydratase (d-ALAD) activity, the red blood cell (RBC) osmotic fragility (OF), and the hematocrit (Hct) were measured in control and lead poisoned toad. The enzyme d-ALAD is considered as a specific biomarker for human and animals lead exposure. In Bufo, lead also provoked a significant decrease in the d-ALAD activity without changes in the Hct. OF test was used to compare the impact of Pb on the extent of the RBC hemolysis produced by osmotic stress. Experimental data (absorbance of solubilized hemoglobin and [NaCl]) were fitted to the Orcutt et al. equation (1995) that allows a precise characterization of the parameters involved in OF. In blood from injected toads, the OF resulted significantly reduced. These changes were interpreted as a consequence of alterations in the composition and conformation of the RBC membrane due to Pb, as it was described for human erythrocytes.

The effects of sublethal doses of lead (as acetate) on blood parameters of adult male Bufo arenarum were studied. Toads received one single injection with 10, 25, 50 or 100 mg/kg of body weight, equivalent to approximately 1/90-1/10 of the 120 h-LD50; seven days after the injections, the hematocrit and the blood delta-aminolevulinic acid dehydratase (ALAD) activity were measured. Hematocrit of lead-injected animals did not exhibit significant changes respective to controls that received sodium acetate (range 29.8-38.8%). Blood lead concentrations were positively and significantly correlated with the injected metal doses. Blood ALAD activity declined proportionately to the doses of the metal as well as to its whole blood concentration. Because of its sensitivity and specificity, it was concluded that the activity of delta-ALAD may be adopted as a reliable biomarker of Bufo arenarum experimental lead intoxication.