Microorganisms are the most numerous organisms in the soil biological fraction. Their population and metabolic relations are affected by environmental changes, such as pollutant deposition on and movement into the soil. The aim of this work was to assess the soil microbial activity in a Pb mining and metallurgy plant, in Adrianópolis (PR), to determine soil biological quality indicators. The soil (layers 0 to 5 and 5 to 10 cm) was sampled once at five locations four times (May, September, November and January),approximately, 62 years after mining activity and 12 after the activity was stopped. The total Pb and Zn content in the soil was determined through inductively coupled plasma - atomic emission Spectrometry (ICP-AES), after microwave digestion of the soil samples with concentrated HF, HNO3 and 30 % (v/v) H2O2. To extract the heavy metals in bioavailable form, a boiling HNO3 0.5 mol L-1 solution was used. The following soil microbial parameters were estimated: Total Bacteria (TB); Sporulating Bacteria (SB); percentage of Sporulating Bacteria comparing to TB; Fungi; correlation between fungi and TB; Microbial respiration; Microbial Biomass; Microbial Carbon percentage compared to the soil total organic C; Metabolic quotient. Three methods were used to the statistical data analysis: (a) differentiation of the sites trough Principal Component Analysis (PCA); (b) establishment of an Environmental Quality Index (EQMI) based on microbiological parameters; and (c) simple correlation analysis. The the heavy metal effect microorganisms was minimized by the high soil fertility. However, in the month with the most unfavorable climatic conditions for the microorganisms (May - lowest temperatures), soils with the highest Pb showed reduced microorganism population and microbial activity, which means that under these conditions bacteria and fungi were good soil quality indicators. The highest SB proportion in the most Pb contaminated soils in the coldest month (0.95I correlation to May) can be interpreted as a resistance mechanism of these organisms. The environment microbial quality index (EMQI) in the 0 to 5 cm layer was more efficient than PCA in distinguishing locations with heavy metal contamination: the values decreased in the opposite sense to the increase in the soil Pb. However, in the 5 to 10 cm layer PCA was more efficient to this purpose.
biological indicators; environmental contamination; heavy metals
