Lead Deposition in the Shell of the Bivalve, Mya arenaria: an Indicator of Dissolved Lead in Seawater

Abstract

A strong correlation is observed between the lead content of the shell of the bivalve, Mya arenaria, and dissolved Pb in the seawater in which it grows. Three intertidal sites populated with Mya were selected for study and monitored at least once per month for dissolved Pb during 1988 and 1989. Organisms were collected at the end of the growing season of each year and the most recent annual growth increment was analysed for Pb. A comparison of lead concentrations in shells to seasonally averaged dissolved Pb determined at each of these sites yields a linear relationship described by: Pb shell(nmol g -1) = (9·99 ± 1·18)Pb water(nmol kg -1)-0·05 r = 0·97 Lead in the shell of Mya is concentrated by a factor of 10000 relative to seawater making it a sensitive indicator for ambient Pb concentrations. The Pb content of shells excavated from middens left by Indians inhabiting the Boston Harbor islands and radio-carbon dated to be 1600 years old, suggest that pre-industrial dissolved Pb concentrations in Boston Harbor were 24 ± 8 pmol kg -1. Present day concentrations are 25-50 times higher.