Limpet mucus as a depuration route and potential biomonitor

Metal granules have previously been found in the mucus trails of gastropods. We hypothesised that such metals could be a marker of environmental pollution and that mucus may constitute a depuration route. We investigated this using limpets from sites in north-east England. Mucus production generally showed a significant logarithmic correlation with flesh dry weight of limpet but there was an up to 4-fold inter-site variation. Mucus production did not vary in any systematic way with metal content of either mucus or flesh. X-ray microanalysis revealed that Ca, Cl, S, K, P, Si, Mg and Fe were widely distributed in mucus across sites. Aluminium, Cr, Cu, Mo and Ni were also detected, but at lower frequencies. Ion chromatography analysis of metals in mucus (Cd, Co, Cu, Ni, Pb, Zn) indicated that Pb was dominant. In general, metals with levels > 10 mu g g(-1) were found at sites close to the polluted Tees estuary. In limpet flesh, the dominant metal was Fe and again metal levels were generally highest close to the Tees. Where comparisons can be made, metal levels in mucus were typically higher (by up to 2000x) than those in the flesh. Metal levels in mucus showed little correlation with flesh dry weight or with metal levels in limpet flesh. The high levels of Pb and other metals in mucus, relative to the flesh, may suggest that mucus functions as a depurator, animals releasing as much Pb per day in mucus as is stored within the flesh. Mucus has the potential for use as a non-destructive biomonitor that allows for repeat and instantaneous measurements.