digested by nitric acid and perchloric acid (2:1) on a
hotplate until the solution became clear. Cu, Zn, Cd
and Pb concentrations in the water were determined
by the extraction method (APHA, 1998) using an
atomic absorption spectrophotometer (AAS, Perkin
Elmer 2380). Plankton and fish samples were
prepared for heavy metal analysis according to the
method described by Kalay et al. (1999).