Characterization of soil health in an Italian polluted site by using microorganisms as bioindicators.

The soil status inside and outside the chemical ACNA factory (Cengio, Italy) has been investigated by assessing chemical and biological parameters. Three sites, two (A and B) located inside the so-called high-risk zone and one (C) outside the factory were considered. Chemical analysis performed in the first metre of depth indicated the presence of inorganic pollution (copper and arsenic) in site A and organic (1,2,3,4-tetrachlorobenzene and 2,4-dichloroaniline) and inorganic (arsenic and mercury) contaminations in site B. Site C did not show any significant contamination and was considered as control. Biological analyses were performed by evaluating functional (substrate utilization pattern and enzymatic activities of the soil extracts) and structural (bacterial population density, composition and structure) diversity of the soil bacterial community as indicator of soil health. Moreover, 20 bacterial strains per site, able to grow on minimal medium added with 2,4-dichloroaniline as sole carbon source, were selected and identified. The metabolic profile of soil extracts, characterized by using Biolog GN MicroPlates, coupled with hierarchical clustering, showed a high similarity between the microbial communities isolated from sites A and B. The highest amounts of enzymatic activities were recorded in site C. Bacterial density in all sites did not differ significantly and a prevalence of r-strategist (fast growing and copiotrophic) bacteria was observed. The composition of the bacterial community showed a higher similarity between sites A andBthan with site C. Only fewbacterial specieswere common to the three sites: as a consequence, a prevalence of bacterial species typically associated to each sitewas observed. The fraction of bacteria able to grow on 2,4-dichloroaniline as sole carbon source on the total culturable bacteria in each sitewas lower than 0.1%. Bacterial identifications were performed by using BiologMicroPlates. By considering the bacterial strains able to grow on minimal medium added with 2,4-dichloroaniline, a higher similarity between sites A and C than with B site was recorded. In conclusion, the presence of different chemical pollutants did not affect the bacterial density but rather the community structure. The characterization of soil chemical properties, metabolic fingerprinting, enzymatic activities and bacterial community structure could be useful tools for the evaluation of the soil health.