Evaluation of digestion procedures for determining silver in mussels and oysters

Determinations of silver concentrations in mussel and oyster tissue digested with nitric acid were low relative to those measured in undigested tissue analyzed by ultrasonic graphite furnace atomic absorption spectroscopy. Good results were obtained, however, using a mixture of hydrochloric and nitric acids for digestion. Archived NOAA Mussel Watch samples collected in 1986-1993 and originally analyzed following HNO3 or HNO3-HClO4 digestion were reanalyzed with HNO3-HCl digestion in 1995. Results suggest that only 44% of the redeteremined Ag concentrations were within 20% of the original values. Most of the reanalyses yielded higher concentrations, and one-tenth of them were more than 100% higher. Temporal trends in Ag concentrations in the coastal United States have been estimated using the revised data. Statistically significant decreases, mostly in the Northeast have been observed. This is probably an indication of lower Ag discharged in waste waters.