Marine sediment was digested according to USEPA [11]. 1 g of dried sediments was digested in 10 ml of 8 M nitric acid over a hot plate at
92- 95 oC for 10 min. After cooling, 5 mL of concentrated nitric acid was added with continuous heating for 30 min. Deionized water (2 mL) and 30% hydrogen peroxide (3 mL) were added: the digested sediment was then heated until bubbles disappeared. Hydrochloric acid