Rhizoremediation of an historical contaminated site in Brescia (Italy): comparing the current emission of PCBs and PCDD/F to air from soil and other sources

Among the national priority polluted sites, the SIN Brescia Caffaro is located in a mid size city Brescia, (200,000 inhabitants) in northern Italy. The site derived from the activity of the former Caffaro s.p.a., a chemical factory among the largest former polychlorinated biphenyls (PCBs) producer in Europe, which produced such chemicals for more than 50 years up to mid 80’. About 100 Ha of agricultural areas were contaminated by a mix of Persistent Organic Pollutants (POPs, mostly PCBs, dioxins, furans) and heavy metals (Hg, As) in variable concentrations, often exceeding the safety values. Such concentrations are orders of magnitude higher than the typical background anthropogenic values. Since the city of Brescia is located within an industrial district where current emission and secondary sources of POPs are also present (incinerators, smelters, etc.), this site represents a challenging case to evaluate the prevalence of a source over another and select the type of remediation activities. Concentrations of PCBs (more than 80 congeners) and PCDD/Fs in soil were measured averaging samples taken at surficial and deeper layers in 45 points located in the contaminated agricultural areas (totalling about 100 Ha). Concentrations of PCBs and PCDD/Fs were then used in the SoilPlus model (a multilayered dynamic multimedia fugacity model including a two layer dynamic air compartment) to predict hourly air concentrations of selected congeners and dioxin/furan classes for an entire simulation year. Such concentrations were compared to PCB and PCDD/F air concentrations measured in Brescia in five different areas at different seasonal intervals. Principal component analysis showed that calculated PCB fingerprints in air overlap with the measured ones, with seasonal concentrations varying accordingly (the predicted winter concentrations are closer to the measured), confirming that volatilization from soil determines current concentrations. The situation is different for PCDD/F where only furans seem more correlated with soil emissions, showing that dioxin sources are recent. A comparison of soil PCB fingerprints with Aroclor fingerprints confirms that the present congener mixture is mostly of highly chlorinated congeners, while PCDD/F fingerprints confirm the prevalence of furans.Such information is crucial to evaluate the impact and potential remediation effectiveness of rhizoremediation in presence of old and current sources