THE DISTRIBUTION AND INTRACELLULAR COMPARTMENTATION OF METALS IN THE ENDOGEIC EARTHWORM APORRECTODEA-CALIGINOSA SAMPLED FROM AN UNPOLLUTED AND A METAL-CONTAMINATED SITE

The tissue distribution of Cd, Cu, Pb, Zn and Ca in the endogeic earth worm Aporrectodea caliginosa living in a non-polluted and a heavy meta l polluted soil was investigated. The tissues of animals from the cont aminated soil contained greater concentrations of Cd, Pb and Zn than t he corresponding tissues of animals from the unpolluted soil. The grea test concentrations of Cd, Pb, Zn, and Ca were primarily accumulated w ithin the posterior alimentary canal (PAC), a tissue fraction which co ntained the greatest proportion of the whole-worm burdens of the respe ctive metals. Cu was distributed fairly evenly in the tissue fractions investigated. The pattern of accumulation for the 'heavy' metals is b roadly similar to that for epigeic earthworms; in contrast, a differen t pattern of tissue accumulation was found for Ca. In animals from the uncontaminated site, the major elemental constituents of the chlorago somes were P, Ca, Zn and S. A significant positive correlation exists between P and Ca within the chloragosomal matrix. These intracellular vesicles are major foci for Pb and Zn accumulation within the PAC, wit h 'excess' metals associated with P ligands within the chloragosome ma trix. The incorporation of Pb and Zn appears to involve the cationic d isplacement of Ca. Such compartmentation appears to prevent disseminat ion of large concentrations of these metals into other earthworm tissu es, and may thus represent a detoxification strategy based on accumula tive immobilization. No intracellular localization of Cd was identifie d in the study, although the Cd concentration in the metalliferous soi ls examined was not exceptionally high. The observations are discussed in the context of a contribution to enhanced understanding of metal e cotoxicology in earthworms by providing baseline data on a little inve stigated ecophysiological group of earthworms. Comparisons of metal di stribution and mechanisms of metal sequestration are made with other e cophysiological groups of earthworms, and the significance of the find ings to biomonitoring and toxicity-testing programmes is considered. ( C) 1998 Elsevier Science Ltd. All rights reserved.