2000 Volume 10 Issue 3 Pages 541-547
Soil samples with high total zinc concentrations (41 to 15200mg kg-1), collected near a mine, were investigated for Zn speciation after taking the extracts from water-saturated soil samples, (described below as“soil solution”), in order to clarify the forms of Zn adversely affecting soil bacteria. The zinc speciation was estimated using an equilibrium thermodynamic computer model, SOILCHEM. The effects of Zn on soil bacteria were evaluated by an indicator: the Zn tolerance level of the bacterial community, shown as IC50. In all samples, more than 80% of total Zn was present as free ion in the soil solutions. The Zn tolerance levels of the bacterial community were dependent on the Zn ion activities with the high square of correlation coefficients (γ2=0.610, p<0.01), but had no relationship with the total zinc concentrations in the soils. The results showed that the high Zn ion activities in the soils led to the development of the Zn tolerance levels of the bacterial community. IC50 was also correlated with the amounts of chloride, nitrate, and sulfate complexes of Zn in the soil solutions.
