2.4. Digestion procedure
The fish samples were digested for total mercury determination by an open flask procedure which was developed by Akagi and Nishimura (1991). In this digestion method, 0.5 g of homogenized fish sample was weighed into 50 mL volumetric digestion flask,and 1 mL distilled H2O, 2 mL HNO3:HCIO4 (1:1 v/v) and 5 mL H2SO4 were added in turns. The mixture was then heated at a temperature of 200 ± 5 C for 30 min. The sample solution was then
cooled and diluted to 50 mL with double distilled water.