M. Ledin et al., Microorganisms as metal sorbents: comparison with other soil constituents in multi-compartment systems, SOIL BIOL B, 31(12), 1999, pp. 1639-1648
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.