Plant-microbe interactions in a PCB contaminated soil in the presence of Medicago sativa and compost

Polychlorinated biphenyls (PCBs) are persistent pollutants (POPs), exclusively manufactured for industrial applications. Although their production and use was banned almost all over the world more than 30 years ago, they are still commonly found in many ecosystem compartments owing to their high persistence. They are complex technical mixtures of about 30-60 congeners (e.g. Apirolio, produced in Italy and used for electrical transformers). Their biotic degradation can occur through aerobic and anaerobic microbial processes, by metabolism or co-metabolism (where microorganisms need other sources of carbon and energy and the transformation of pollutants occurs as a concurrent process), but the poor contaminant bioavailability and the requirement for an inducer may hinder microbial degradation. These problems may be overcome through processes based on the interactions between plants and their associated rhizobacteria (Bioassisted phytoremediation or rhyzoremediation). Plant may help the contaminant removing, releasing exudates that may serve as growth substrates for the rhizospheric bacteria. Multitudes of soils are considered degraded for both contamination and low organic matter content; in this case, the remediation of contaminated soil by planting and compost addition are essential for improving soil quality. In particular, selected plant species, which are able to promote microbial community activity through the formation of a thick rhizosphere and, consequently, to enrich soil in nutrient content, together with the compost addition can be a useful green remediation technique for promoting contaminant degradation. In order to investigate the interactions between plants and autochthonous microorganisms in the rhizosphere, soil samples were collected from a PCB contaminated area and used for greenhouse microcosm experiments in the presence of the forage species Medicago sativa and/or in the presence of Apirolio and municipal solid waste (MSW) compost. Microbiological and chemical analyses were carried out at different times in order to evaluate the changes in the structure and function of microbial populations in relation to the different experimental conditions.