Role of the microbial consortium Enzyveba in the bioremedation of diesel and HiQ diesel-contaminated soils.

Diesel fuels spills from pipeline ruptures, underground storage tanks leaking or tanker over turning determine remarkable amounts of diesel fuel hydrocarbons released on areas often dedicated to agricultural activities. As a consequence of their massive production and use as fuel for transportation, they have become one of the most common source of organic pollutants. They generally consist of a complex mixture of linear, branched and cyclic alkanes and aromatic compounds. The biodegradation of such a complex mixture of hydrocarbons usually requires the cooperation of different microorganisms. Such consortia of microorganisms are often absent in the majority of freshly contaminated soils or sites, which do not undergo microbial decontamination promptly. Therefore, the application of unspecified, naturally established complex consortia of microorganisms, such as those occurring in domestic or agro-industry sludge, manure or compost, which generally carry a high diversity of bacteria and fungi along with a variety of essential nutrients, able to sustain survival and colonization of allocthonous microbes in the inoculated biotope, might enhance the bioremediation of diesel-oil mixed contaminated soil. On the other hand, current legislation on the restoration of contaminated sites in some European Countries encourages the employment of some of such sources of microflora, and in particular those obtained from the microbial decomposition/stabilization of “adequate quality organic materials” from municipal wastes, in the biological restoration of contaminated soils and sites (see, as an example, the Italian D. Lgs. No. 152/2006). Enzyveba, a partially characterized complex consortium of not-adapted microorganisms developed through prolonged stabilization of high quality organic wastes produced by Marcopolo Engineering SpA (Cuneo, Italy), was recently found to be able to markedly intensify the aerobic remediation of actual sites aged PAH- and PCB-contaminated soil by acting as a source of both exogenous specialized microorganisms and nutrients. In the present study, the biodegradability of two commercial diesel fuels, i.e., Diesel and HiQ Diesel, spiked to an agricultural soil at 10 g kg-1 was studied under aerobic slurry-phase conditions in the absence and in the presence of Enzyveba, through an integrated chemical-microbiological-ecotoxicological monitoring procedure. A quite similar hydrocarbon composition was displayed by Diesel and HiQ Diesel, which were found to be both extensively and almost completely biodegraded (90%) under all conditions after 4.5 months of treatment. The low initial toxicity, monitored with the animal Folsomia candida mortality test and the plant Lepidium sativum inhibition shoot elongation test, was removed at the end of treatment. The addition of Enzyveba resulted in a higher availability of cultivable specialized bacteria and fungi in the reactors but this only resulted in a slight intensification of soil bioremediation, probably because the pristine soil was rich of microorganism able to degrade diesel fuel. A faster biodegradation of hydrocarbons and a more rapid and extensive depletion of initial ecotoxicity were generally observed in the soil reactors spiked with HiQ Diesel with respect to those spiked with Diesel probably for its content of additives capable of improving hydrocarbons bioavailability.