Populations of the marine molluscan bivalve Dosinia exoleta in Galicia
(northwest Spain) present lead (Pb) concentrations above the limit for human consumption.
Accordingly, its collection for human consumption was forbidden since 2008. The high
bioaccumulation of Pb in this species is surprising given that Pb concentrations are not
very high in its environment and that other bivalve infaunal species inhabiting the same
areas do not show such high Pb contents. This study reports the discovery and description
of extracellular granules present in the kidney tubule lumina of this species. Large
granules (20−200 μm) mainly composed of calcium phosphate represent
between 50% and 75% of the dry weight of the kidneys. Metal analysis revealed that from 78
to 98% of the Pb body burden was present in the kidney, and from 87% to 92% of this Pb
within the kidney was contained in metal rich granules. Most of the zinc in these bivalves
was also found to be associated with these kidney granules, while other metals, such as
copper and cadmium, were associated with other kidney fractions. This study confirms that
the high Pb concentrations observed in D. exoleta, and the relationship
of Pb concentration with individual size, are due to the inclusion of Pb in kidney
granules that accumulate in the kidney lumen over the course of the bivalve’s life.