Contrasting accumulative patterns of two cationic analogues, Ca and Sr, in ecophysiologically contrasting earthworm species (Aporrectodea longa and Allolobophora chlorotica) from the field

The accumulation of stable strontium and its chemical analogue calcium by two ecophysiologically contrasting species of earthworm (the deep vertical-burrowing 'anecic' Aporrectodea longa and the shallow horizontal-burrowing 'endogeic' Allolobophora chlorotica) was investigated in field populations inhabiting celestite (SrSO4) rich natural soils, using regression and correlation analyses. An increase in soil strontium concentration over a four-orders-of-magnitude range was accompanied by a concomitant increase in tissue strontium burdens of each species. Tissue calcium burdens appeared to be maintained at fairly uniform levels, irrespective of soil calcium concentrations. The contrasting findings suggest that differences exist in the ability of earthworms to physiologically control tissue burdens of these two analogue elements, and this may relate, in part, to differences in the solubility of sequestration products of strontium and calcium. Regressions between body burdens of each metal and tissue dry weight in earthworms indicated that accumulative efficacy for strontium was increased when soil strontium concentrations were extremely high and accompanying soil calcium concentrations were low. Our data also suggest that elevated burdens of strontium appeared to reduce overall tissue calcium burdens to levels below the apparently typical physiological window within populations of earthworms. This study suggests that strontium and calcium accumulation are quantitatively dissimilar, and that strontium accumulation in the tissues of earthworms cannot be predicted simply from the behaviour of calcium despite the fact that the two cations undoubtedly interact competitively for uptake into biological systems. The ecotoxicological implications of these conclusions are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.