Microorganisms as metal sorbents: comparison with other soil constituents in multi-compartment systems

A multi-compartment experimental system (PIGS) was used to study the import ance of microorganisms,for metal distribution in simulated soil systems. Th e influence of pH, solute composition (NaCl and CaCl2) and presence of fulv ic acid on the distribution of zinc, cadmium and mercury among different ph ases in the multi-compartment system was studied, i.e., among bacteria, fun gi and five other solid soil components and a solution phase. Using the mul ti-compartment system combined with a factorial design made it possible to study several soil factors as well as solid soil components simultaneously as well as to estimate interaction effects between soil factors. The microo rganisms accumulated a considerable part (up to 38%) of the metal, despite the fact that they constituted only a minor fraction (0.4 or 1.7%) of the t otal solid mass. In contrast, quartz and feldspar, which together constitut ed 80% of the solid mass, accumulated less than 10%. The fraction associate d with peat was generally large (11-57%) and the other solid components acc umulated intermediate amounts of metal. Solution pH was the single factor t hat had the largest effect on the metal distribution. The effect of pH was less pronounced on fungi than on most other solid components, which indicat es that the relative importance of fungi as metal sorbents increases as pH decreases. Changing solution composition from NaCl to CaCl2 decreased metal sorption to most sorbents except for the microorganisms where an increased accumulation was observed. The combined effects of pH and fulvic acid were considerable in some cases. This study stresses that the microbial sorbent s can respond to changes in the soil solution chemistry in other ways than other solid soil components do. Thus, the microorganism fraction of the sol id phase should not be neglected in metal distribution studies of soil. (C) 1999 Elsevier Science Ltd. All rights reserved.