The natural microbial activity in the unsaturated soil is vital for protecting groundwater in areas where high loads of biodegradable contaminants are supplied to the surface, which usually is the case for airports using aircraft de-icing fluids (ADF) in the cold season. Horizontal and vertical distributions of microbial abundance were assessed along the western runway of Oslo Airport (Gardermoen, Norway) to monitor the effect of ADF dispersion with special reference to the component with the highest chemical oxygen demand (COD), propylene glycol (PG). Microbial abundance was evaluated by several biondicators: colony-forming units (CFU) of some physiological groups (aerobic and anaerobic heterotrophs and microscopic fungi), most probable numbers (MPN) of PG degraders, selected catabolic enzymatic activities (fluorescein diacetate (FDA) hydrolase, dehydrogenase, and β-glucosidase). High correlations were found between the enzymatic activities and microbial counts in vertical soil profiles. All microbial abundance indicators showed a steep drop in the first meter of soil depth. The vertical distribution of microbial abundance can be correlated by a decreasing exponential function of depth. The horizontal trend of microbial abundance (evaluated as total aerobic CFU, MPN of PG-degraders, and FDA hydrolase activity) assessed in the surface soil at an increasing distance from the runway is correlated negatively with the PG and COD loads, suggesting the relevance of other chemicals in the modulation of microbial growth. The possible role of potassium formate, component of runway de-icers, has been tested in the laboratory by using mixed cultures of Pseudomonas spp., obtained by enrichment with a selective PG medium from soil samples taken at the most contaminated area near the runway. The inhibitory effect of formate on the growth of PG degraders is proven by the reduction of biomass yield on PG in the presence of formate.

The degree of soil pollutants in the Dunaújváros area has been monitored regularly at 10 sampling points of the town from the upper 0–20 cm and lower 20–40 cm layers of the soils. The quantity of some organic (PAH, TPH) and inorganic (toxic metal) pollutants were determined by GC-MS and ICP analyzation. Microbial status, such as the total cultivable bacteria (CFU) and total catabolic enzyme activity, measured by fluorescein diacetate analysis (FDA) were also estimated. The area of the industrial town could be divided into more and less contaminated regions, although the measured pollutants were far below the estimated permissible limits. However, at some of the more polluted soils even triple amounts of contaminants could be measured compared to the lesscontaminated sites. Among inorganics the Zn microelement reached the highest levels (average is about 100 mg·kg−1 soil), which could be related to the heavy industrial activity. A positive correlation appeared among the organic and inorganic pollutants and also between the pollutants and the measured enzymatic values. The enhanced FDA activity was found at the most contaminated sites preceding the potential “loss of function” on a long-term basis. The fast and reliable microbial parameter could be suggested as further regular monitoring tool.