The points located in the Canal do Cunha basin reveal higher
concentrations of Pb in water during both seasons (rainy and
dry) compared with points located along Guanabara Bay. These
results are attributed to two mechanisms: salinity and physical
dynamics (mixing), which tend to generate a gradient in concentrations
with decreasing values toward the ocean (Sinex and
Helz, 1981).
The concentrations of Pb in water are significantly lower than
the concentrations of Pb in sediment; this result is most likely
due to the substantial load of organic materials received by the
Canal do Cunha basin and Guanabara Bay and the high percentage
of fine aggregates found in the sediment, which promotes metal
adsorption and does not contaminate the water or reach the food
chain.
Fig. 7 shows the concentration of Cu in the water and sediment.
Considering the spatial variation of Cu, the concentrations were
higher at points located along the Canal do Cunha basin than at
points located on the western side of Guanabara Bay.