Metals contents in two fishes of different feeding behaviour in the Lower Paraná River and Río de la Plata Estuary

Cd, Cr, Cu and Pb concentrations were measured in the water and these plus Zn were measured in the diet, muscle and liver of the detritivorous fish Prochilodus lineatus and the omnivorous fish Pterodoras granulosus at two sites (Lower Paraná River and Río de la Plata right margin) located upstream and downstream, respectively, from Buenos Aires, an important source of xenobiotics. Cu and Cr concentrations in water were higher in the Río de la Plata coastal waters, while Cd and Pb were below detection limits. The stomach contents of P. lineatus showed a higher metal content at the estuary, attaining concentrations within the range reported for contaminated sediments. However, metals in fish tissue were not higher at the estuary and, except for Cd in liver, were lower than in the organic fraction of the stomach content. Thus, only Cd was accumulated. The P. granulosus diet was composed mainly of river vegetation debris and clams, Corbicula fluminea, at the estuary. Cd, Cu and Pb in liver were higher at the estuary while only Cu was higher in the diet at this site. The different nature of the diet seems associated with a differential bioavailability of its metal content. P. granulosus accumulates Cu at both sites and Cd at the estuary. Both fishes showed higher metal content in liver than in muscle. Cr in liver was below detection limits. No relation was found between metal content and fish size. Overall, metal content in fish tissues were low, except for Cu in P. granulosus and Cd in P. lineatus, similar to those of uncontaminated sites, suggesting that homeostatic mechanisms prevent metal accumulation.