Sources of variation in the assimilation of lead by a common gastropod sentinel Cantareus aspersus

Abstract

The assimilation efficiency of Pb was measured in the candidate sentinel Cantareus aspersus, to assess its capacity to consistently represent the bioavailability of Pb. Three populations were compared from habitats with different levels of toxic and essential metals. For each, 36 snails were fed a laboratory diet with known concentrations of Pb, Ca and Mg over 64days. Lead bioavailability was measured as the percentage assimilation by the soft tissues (mass in tissues as a fraction of that consumed), and its variation was assessed between populations, exposure periods, dietary Mg and replicates. The indicated bioavailability was consistent over time and Pb consumed, but differed between populations and diets. Population differences were due, in part, to their different growth rates: soft tissue growth was positively correlated with Pb mass and, in the most rapidly growing populations, this accounted for more than 40% of the variation in soft tissue Pb. Populations did not differ in their consumption of Pb, but the highest Mg diet induced higher food consumption and a reduced assimilation of Pb. Tissue growth determines retention and contributes to the variation in the bioavailability indicated by these populations, as do essential metals in the diet. Such variability has important implications for monitoring programmes using resident populations of sentinels to map the bioavailability of toxic metals or integrate a pollution signal over time.