Biological remediation technologies are an environmentally friendly approach for the treatment of polluted soils.
This study evaluated through a pot experiment four bioremediation strategies: a) natural attenuation,
b) phytoremediation with alfalfa (Medicago sativa L.), c) bioaugmentation with Pseudomonas aeruginosa and
d) bioaugmentation-assisted phytoremediation, for the treatment of a co-contaminated soil presenting moderate
levels of heavy metals (Cu, Pb and Zn at 87, 100 and 110 mg kg−1 DW, respectively) and petroleum hydrocarbons
(3800 mg kg−1 DW). As demonstrated by plant biomass and selected physiological parameters alfalfa plants
were able to tolerate and grow in the co-contaminated soil, especially when soil was inoculated with
P. aeruginosa, which promoted plant growth (56% and 105% increase for shoots and roots, respectively) and appeared to alleviate plant stress. The content of heavy metals in alfalfa plants was limited and followed the order:
Zn N Cu N Pb. Heavy metals were mainly concentrated in plant roots and were poorly translocated, favouring their
stabilization in the root zone. Bioaugmentation of planted soil with P. aeruginosa generally led to a decrease of
plant metal concentration and translocation. The highest degree of total petroleum hydrocarbon removal was obtained for bioaugmentation-assisted phytoremediation treatment (68%), followed by bioaugmentation (59%),
phytoremediation (47%) and natural attenuation (37%). The results of this study demonstrated that the