A comparison of the seasonal variation of Zn with the remaining
metals reveals that Zn varies from the rainy season to the dry season,
as shown in Fig. 9.
A higher concentration of Zn is detected during the dry season
at collection points GN48, GN50 and CN100. Only GN22 showed
a higher concentration during the rainy season. A study of Guanabara
Bay by Fonseca (2004) showed similar results for Zn.
The spatial concentrations of Zn were influenced by seasonality;
a significant increase was observed during the rainy season at
point GN22, and an increase was observed at collection points
GN48, GN50 and CN100 during the dry season. Studies by the
Financial Evaluation of Ecosystem Management Activities
(FEEMA, 1991) and the Japan International Cooperation Agency
(JICA, 1994) confirmed that industrial waste was a frequent cause
of the contamination. Other contributions of Zn were produced by
atmospheric deposition and corrosion from ship hulls.
The concentration of Zn in the sediment was significantly
higher than the concentration of Zn in water as previously
explained; all metals that were evaluated exhibited similar
behavior.