Seasonal variations in dissolved heavy metals in the Keritis river, Chania, Greece

Abstract

Agrochemicals, geochemical structure and industrial wastes create a potential source of heavy metal pollution in the aquatic environment. The porpuse of this study was to investigate the seasonal variations in five heavy metals (Cu, Zn, Cd, Pb and Cr) in the surface water of the Keritis river, one of the most important rivers in Chania, Greece. The surface water samples were colloected at 8 sampling sites in the Keritis river system. Seven sampling campaigns were carried out in each site in a 1-year period, during August 2004 to July 2005. Heavy metals were determined by using flame and furnace Atomic Absorption Spectrometry. Ancillary data included water temperature, pH and electric conductivity. Significant variations were observed between the warm period (May to September) and the wet period (October to April), for the studied metals. Heavy metal concentrations were sufficiently higher in warm period than in wet period. The average concentrations in wet and warm period were: Cu (0.88 μg l-1; 6.62 μg l-1), Cd (0.005 μg l-1; 0.019 μg l-1), Pb (0.28 μg l-1; 2.59 μg l-1), Cr (1.44 μg l-1; 3.25 μg l-1), and Zn (4 μg l-1; 39 μg l-1), respectively. The relative variability followed the order: Zn>Pb>Cu>Cd>Cr. The seasonal variations may be due to either anthropogenic causes, such as agricultural practices, especially the use of fertilizers and biocides or wastewater discharge, or natural causes, such as water temperature, pH, redox condition, or river flow. The water pH was lower in warm period than in wet period. The concentrations of Cu, Zn, Cd, Pb and Cr were found to be positively related to the water pH in both periods. The water temperature was higher in the warm period and no strong, but remarkable correlations were found between the heavy metal concentrations and the temperature values for the warm and the wet period. Also, there was found no correlation between the heavy metal concentrations and the electrical conductivity.