Comparisons are drawn between microbial communities of forest soils in the north-taiga subzone at various stages of their contamination with pollutants from iron-ore production. Investigations were made in cowberry pine stands located 5 to 114 km south-east of the Kostomuksha ODM (the gradient totals 8 sites).

The major soil pollutants in the studied area were sulphur, iron, nickel, chromium, zink accumulated in considerable amounts in the pine stand litter in the 5-km zone from the pollution source. No strict relation between the content of these elements as well as of manganese, cobalt, cadmium and lead in the sample plots' litter and the distance from the mill was found.

The degree of soil biogenicity after 11-13 years of the mill's operation was also little related to the distance from the mill. As of the thirteenth year of the ODM operation the sites formed the following sequence in order of decreasing total number of bacteria (km from the mill): 5>63>33>114>22>85>27>16. The effect of microbial activity stimulation by pollutants in the impact zone recorded in the first ten years of observations reduced, but the traces of microflora suppression have not yet been found here. Microbial communities generally preserved the features typical for forest soils of the north-taiga subzone.