Plant assisted bioremediation of a PCB hystorically contaminated area in Southern Italy

Phytoremediation comprises a set of technologies (e.g. plant assisted bioremediation, phytoextraction, phytostabilisation) based on some specific plant capabilities directly or indirectly promoting contaminant removal. Bioremediation of contaminated sites is in line with environmental sustainability and with so called Green Remediation. It means "the practice of considering all environmental effects of remedy implementation and incorporating options to maximize the net environmental benefit of cleanup actions". Phytoremediation or more properly plant assisted bioremediation provides a relatively low cost, environment friendly treatment for many multi contaminated areas. In this work, the results of the first 14th months of poplar-assisted bioremediation of a historically PCB contaminated area in Southern Italy is reported. The Monviso clone was selected for its tested capability to promote hexachlorocyclohexane degradation in another CNR field study. The area investigated has been used for several decades as an unsupervised waste disposal tip and it is contaminated as well as PCBs by heavy metals. Six hundred poplar cuttings (Monviso clone) were planted in an area of 785 m2 previously fertilized with compost. After 14 months, of plant cuttings, soils, roots and leaves of selected target trees were analysed in order to identify PCBs and heavy metals contamination (HM). Chemical investigations were conducted before and after poplar planting using GC-MS and ICP-MS instruments, respectively. At the same time, the abundance, cell viability and dehydrogenase activity (DHA) of the autochthonous microbial community were assessed to investigate microorganisms' role in the reclamation processes. The comparison of the initial chemical analysis of the contaminated area with those performed 14 months after the poplar cutting planting, makes it possible to show: -a general decrease in most of PCB congeners in all soil samples analysed and in no case was the legal limit (60 ppb) exceeded. Trace concentrations of PCBs were found in roots and leaves (their amount was always below the legal limits). -HMs, which were initially found as widespread contaminants and at concentrations generally higher than the legal limits, had by 14 months after the poplar-cuttings planting drastically decreased at all the sampling points. Zn, Cd, Se and Sn were detected in leaf and root samples of the target tree investigated. The HM plant bioconcentration factor (BAF, considering roots and leaves) and translocation factor (TF) suggest that poplars are also able to partially phytoextract and phytostabilise HMs. Microbial results show an significant improvement in microbial activity. In fact microbial DHA increased in all samples analysed 14 months after the poplar-cuttings planting, although it maintained different values at the different sampling points. Overall experimental results suggest an improvement in soil quality in terms of decreasing of PCB and HM contamination, increasing in microbial activity and in organic carbon content, particularly evident in the rhizosphere. Further sampling are foreseen in order to continue monitoring PCB and HM contamination in soil and vegetal parts and to investigate on the microbial structure and activity.