Determination of Some Selected Heavy Metals in Fish and Water Samples from Hawassa and Ziway Lakes

Abstract

Samples of Tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) were collected from Hawassa and Ziway Lakes during March 1-20 of 2003 E.C. The moisture content of freeze-dried body of the fish collected from six sites ranged between 62.6% and 86.6% (m/m). An optimal procedure required 12 mL mixture of HNO 3 , HClO 4 , and H 2 O 2 (3:2:1, respectively) to mineralize powdered samples in open refluxed digestion vessels: 0.5 g of the fish body. The concentrations of 3 toxic elements in the body of the fish determined by flame atomic absorption spectrophotometer varied, respectively, (mg of element/kg of fish); Cd = 0.4 -1.85, Pb = 0.05 -0.5 and Hg = 0.07 -0.096. The concentration of those three heavy metals in water samples was also determined similarly by FAAS varied, respectively, as (mg of element/L of water sample); Cd = 0.06 -0.66, Pb = 0.28 -0.36 and Hg = 0.5 -0.74. Application of the statistical t-test on heavy metal elements data has shown that there was a significant difference between the mean concentrations of Hg in water samples from the two Lakes. There is no significant difference between fish as well as water sample of the two lakes for the other metals.