Synergistic Effects of Lavandula angustifolia and a Bacterial Consortium on Bioremediation of a Heavy Metal-Contaminated Soil

Heavy metal (HM) contamination represents a significant threat to soil functionality and ecosystem health. The present study aims to assess the efficacy of an integrated bioremediation strategy combining Lavandula angustifolia (lavender) and a four-strain bacterial consortium in restoring a multi-contaminated soil collected from a former industrial site in Southern Italy. Microcosm experiments were conducted over a period of 90 days, including three treatments and a control: a planted condition (PLANT), a bioaugmented condition (BIOAUG), and a combined plant and bioaugmentation condition (PLANT+BIOAUG). The control (HCS) consisted of unplanted and non-bioaugmented soil. Soil physico-chemical parameters (e.g., pH, electrical conductivity, and heavy metal concentrations), plant growth, microbial abundance, and dehydrogenase activity (DHA) were measured at the initial and final experimental time. Finally, a Soil Quality Index (SQI) was applied. The combined treatment (PLANT+BIOAUG) promoted a significant reduction in total Pb and Sn concentrations by 44.7% and 66.9%, respectively. Moreover, a significant increase in soil pH and microbial abundance was observed. Applying the SQI to integrate overall soil data made it possible to highlight the highest quality score (0.73) for this condition. These findings suggest the potential effectiveness of lavender-assisted bioaugmentation as a scalable and multifunctional strategy for remediating heavy metal-contaminated soils, in line with ecological restoration principles.