Seasonal changes in metal levels (Cu, Pb, Cd, Zn and Ca) within the grey field slug, Deroceras reticulatum, living in a highly polluted habitat

Slugs (Deroceras reticulatum) (Muller)) were collected from a disused Pb/Zn mine site for a period encompassing 3 years. The analysis of whole body replicates, collected monthly for a period of one year, demonstrated a large variability in metal concentrations for each of the five metals (Cu, Pb, Cd, Zn and Ca) analysed. Nevertheless, a number of significant monthly differences in metal levels were found, the most regular being for Ca, and the least regular for Cu. Significant differences in metal body burdens were also found between slugs collected during the same month, but in consecutive years. The presence of such large and irregular variability greatly restricts the potential value of terrestrial slugs as biomonitors of heavy metal contamination.