For quality assurance, the instruments were calibrated based on a linear four-point calibration curve for each element. Standard calibration curves with an r2 between 0.999 and 0.998 were run
during measurements. Continuing calibration verification was performed by analyzing a standard solution and a blank solution for each of the element at intervals. To verify the quality of the results, matrix spike/matrix spike duplicates were analyzed with each batch of about 10 samples for each element. For each run, a triplicate sample and three blanks were analyzed. An analytical spike recovery was done by adding increasing amounts of a standard solution of each element to an aliquot of the digested sample. A matrix spike recovery of the elements from fish was determined by adding increasing amounts of the solution of each element to known amounts of two different samples. They were all taken through the digestion procedure. The resulting solutions were analyzed for the concentration of the three elements using the appropriate
instrumental method. The accuracy of the analytical method used was evaluated by analysis of certified reference material (CRM), Fish Homogenate IAEA 407 for Hg, Pb and Cd. Four replicates
were performed. All the samples were taken through the digestion procedure. The resultant solutions were analyzed for the elemental concentrations. Precision was determined by conducting
five replicate analyses of some of the samples. All samples were analyzed in duplicate and sometimes in triplicate by the instrument for consistency.