Zinc sequestration by earthworm (Annelida: Oligochaeta) chloragocytes. An in vivo investigation using fully quantitative electron probe X-ray micro-analysis

The elemental compositions of chloragosome "granules" in the earthworm Lumbricus rubellus living in non-polluted and heavily Zn-polluted soils were determined by fully quantitative electron probe X-ray microanalysis. P, Ca, S and Zn were the major elemental components of the chloragosomes. The in vivo accumulation of Zn by the chloragosomes was accompanied by diminished chloragosomal Ca concentrations. Zn was apparently bound by at least two ligand pools (Pool 1 = uncharacterised; Pool 2 = P-containing ligands, binding approximately 45% and 55% of the Zn, respectively) in the "control" chloragosomes. In Zn-contaminated chloragosomes, most (approximately 70%) was bound by P-containing ligand(s) but some (less than 1%) was also bound by S-containing ligands. It is suggested that the sequestration of Zn in chloragosomes results in the detoxification of the metal by accumulative immobilisation.