Although critical concentrations of Pb
were not found, this metal was always in higher concentration in tested
animals than in the control group. Therefore, it could be important to
further investigation to determine the levels of Pb as well as its
origin in both basins, but especially, in the Mogi-Guaçu. Another
important finding was that there was no correlation between the degree
of anthropogenic impacts and Cd and Pb concentrations. Major impacts
were observed in the Piracicaba than in the Mogi-Guaçu basin, but Cd
and, particularly, Pb concentrations were higher in animals placed in
the Mogi-Guaçu basin, which did not confirm the initial hypotheses. In
addition, we observed larger concentrations of Pb in less impacted
areas of the Piracicaba and Mogi-Guaçu River basins. This fact
suggested that it was not possible to infer about concentrations of
these heavy metals based only in a broad evaluation of human impacts.
The degree of environmental contamination is only one among several
factors that influence metal concentrations in animals. Bioavailability
or specific sources may be responsible for higher concentrations in
apparently less impacted environments.
ACKNOWLEDGEMENTS
This
work was supported by research grants from FAPESP, grant 97/01348-6 and
95/5075-9, and by Esso Brasileira de Petróleo. Our gratitude is
expressed to many friends of the PiraCena project and to Álvaro Costa
for help during the sampling procedures.
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