Accumulation of heavy metals in the franciscana ( Pontoporia blainvillei ) from Buenos Aires Province, Argentina

Marine mammals accumulate heavy metals in their tissues at different concentrations according to trophic levels and environmental conditions. The franciscana ( Pontoporia blainvillei ) is a small coastal species inhabiting the marine and estuarine areas of the Southwestern Atlantic Ocean. Its diet includes numerous species of small fish, squid and crustaceans. The aims of this study were to (i) assess the heavy metal concentration and burden distribution in different franciscana age classes and sex, and to (ii) evaluate both the accumulation processes and the transplacental transference of zinc, cadmium, copper and total mercury. Heavy metal concentrations (wet weight) were determined in eighteen dolphins by Atomic Absorption Spectrophotometry (AAS), by the cold vapour technique (mercury) or with air/acetylene flame (cadmium, zinc and copper). Liver showed the highest concentrations of mercury (max. 8.8 mg/g), zinc (max. 29.7 mg/g) and copper (max. 19.0 mg/g), whereas the highest cadmium concentrations (max. 6.7 mg/g) were found in kidney. Adults contained the highest concentrations for all heavy metals, followed by juveniles and calves in decreasing order, suggesting an age-related accumulation. No differences (p<0.05) were found between sexes within each age class. Organ burden distribution followed the same pattern for all metals and age classes: liver tissues contained maximum burdens. Mercury concentrations were higher than those of cadmium in both foetuses and newborns; and neither metal could be detected in the foetus. The analysed data suggested differences in the placental transference between metals, being significant for mercury and almost null in the case of cadmium. We can conclude that franciscana accumulates heavy metals and, due to its coastal distribution, it may be considered as a biomonitor of its environment.

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