Magnesium and the deposition of lead in the shell of three populations of the garden snail Cantareus aspersus

The loss of Pb from snail soft tissues may depend on the excretion of Ca, and involve the mobilization of shell Ca. Most sub-adults in three populations of Cantareus aspersus (syn. Cornu aspersum Mueller) either failed to add, or lost, shell mass on a diet with 250 μg g-1 Pb. Their failure to mineralize shell extensions occurred irrespective of food consumed, time or dietary Mg. Budgets of metals for 36 individuals in each of two populations showed that Ca loss would account for the reduction in shell mass. Lead concentrations were higher in the reduced shells but this may be a consequence of their smaller mass, rather than its cause. In both populations shell reduction correlated with the total mass of Pb assimilated. Any shell growth may have been dependent on the initial Ca reserve in each snail. Differential movement of Mg, Pb and Ca occurred between the shell and soft tissues. - Highlights: → Differential movement of Pb, Ca and Mg occurs in the shells of C. aspersus. → Mg does not affect Pb assimilation but shell Mg and Pb rise on a Pb-dosed diet. → Ca is lost from the shell in most snails, and correlates with total Pb assimilation. → Large initial shell Ca enables some snails to grow shell over 64 days on the diet. → Uptake and toxic response to Pb appears linked to the Ca dynamics of the snails. - Snails losing shell mass on an experimental diet have higher concentrations of shell Pb and Mg, but lose Ca.