To 5 g of each sample, 10 mL nitric acid was added. These were left overnight for pre-digestion. The samples were then heated using a water bath maintained at 80-100°C for 5 hours, cooled, filtered and filled with distilled water to volume in a 50 mL volumetric flask. The samples were transferred and stored in polyethylene bottles prior to Flame Atomic Absorption Spectrophotometry (FAAS)