Zn, Cd and Hg accumulation by microorganisms, organic and inorganic soil components in multi-compartment systems

A multi-compartment system, PIGS (Partitioning in Geobiochemical Systems), with five compartments was constructed to study metal distribution between soil constituents. Soil microorganisms (Pseudomonas putida, Trichoderma harzianum) were compared with common soil minerals (kaolin and aluminium oxide) and solid organic matter (peat) with respect to their ability to accumulate Zn, Cd and Hg. Experiments were conducted under conditions that are representative of natural soils concerning pH, metal concentration, ionic strength and microbial activity. Different relative amounts of the solid phases were used to approach natural conditions. Results from the PIGS indicated considerable differences in metal distribution between the various solids, and also indicated that for the different solid phases metal distribution was related to variations in pH and ionic strength of the solutions in different ways. The presence of fulvic acid generally decreased metal accumulation by peat and microorganisms around neutral pH. Accumulation by organic compounds (peat), as well as by microorganisms, was substantial under experimental conditions used, i.e. up to more than 40 and 20% of the added metals was accumulated by these components, respectively. In some cases the considerable accumulation of trace metals by the fungus and the bacterium under acidic conditions is of particular interest, since this process may counteract the metal-mobilizing effects of soil acidification. It is evident from our study that microorganisms should not be overlooked when studying metal interactions with soil constituents.