Molecular fractionation of Zn, Cu, Cd and Pb in the midgut gland of Helix pomatia L.

Specimens of Helix pomatia were fed lettuce enriched with Zn, Cu, Cd and Pb for 30-35 days, after which time the distribution of the four metals in the midgut gland was studied by centrifugation, ion exchange and gel chromatography. In control snails the distribution between the soluble and particulate fraction of the midgut gland is relatively uniform, with a ratio of approximately 3:1 for Cu, Cd and Pb, and of 1:1 for Zn. However, after metal-loading about two-thirds of total Zn and Pb appears in the particulate fraction whereas little change in relative distribution is observed with Cu and Cd. After ion exchange chromatography of the supernatant both Cd and Zn eluted in one distinct peak, Cu in two peaks, whereas Pb seemed to be distributed unspecifically throughout the elution volume. If ion exchange is followed by gel chromatography, Zn, Cu and Cd are found associated with from one to four molecular species, ranging in mol. wt from 1000 to greater than 20,000, whereas no complex was found for Pb. The molecular patterns are specific for each of the three metals and there are some specific shifts in abundance, usually involving one molecular fraction, if control snails are compared with metal-loaded snails.