The extractants used in each step and the sediment fractions targeted are
summarized in Table 1. The procedure was conducted by the extraction
of 0.5 g of dried, fine sediment in 50 mL polypropylene centrifuge
tubes. Following each extraction, the mixtures were centrifuged at
3000 rpm for 20 min; the supernatant was decanted and stored in
clean centrifuge tubes at 4 ?C until analysis. The residue from each
extraction step was washed with 10 mL DDW and mechanically
shaken for 15 min at 30 rpm. After shaking, the residue was centrifuged
at 3000 rpm for 20 min and the supernatant discarded.