Comparisons of metal accumulation and excretion kinetics in earthworms ( Eisenia fetida) exposed to contaminated field and laboratory soils

Abstract

The uptake and excretion kinetics of cadmium, copper, lead and zinc were studied for Eisenia fetida exposed to mixtures of these metals in field and OECD artificial soil. Body burdens in worms exposed to all contaminated soils increased over the duration of the experiment. Highest accumulation rates were for worms exposed to the most polluted soils. Pronounced differences were found in the uptake and excretion patterns for essential and non-essential elements (particularly in field soils). For cadmium and lead (non-essential), an equilibrium plateau was not reached during the uptake study and slow excretion was found on transfer of worms to clean soil. For copper and zinc (essential), fast initial uptake was followed by equilibrium after only a few days exposure. Rapid excretion was found after transfer to clean soil, with half-lives of less than 1 day for both metals. A previous study of the effects of metals on worms exposed in OECD and field soils had indicated a higher toxicity in the artificial medium. Thus, in the present study, it was anticipated that greater toxicity would be reflected by increased body burdens for worms in OECD soil. This was, however, not the case. Explanations are given that might account for the fact that the greater toxicity in OECD soil is not invariably accompanied by higher metal burdens. These include the presence of high concentrations of very toxic and highly available ions in laboratory tests and potential differences in the importance of soluble and total metal concentration for determining toxicity and body burdens.