# Bioremediation Methods for the Recovery of Lead-Contaminated Soils: A Review
## 3 Phytoremediation
### Phytoremediation Capability of Plants in Spiked Soils  
Many phytoremediation studies [40; 41; 42] were performed under controlled experimental conditions in soils spiked with lead solutions or powder to assess the restoration capacity of selected plants. For this purpose, [PERSON] et al. [43] investigated the phytoextraction ability of sunflower, in particular _Helianthus annuus_ species, to remove lead and cadmium from soil. An air-dried loamy sandy soil was collected from Burnley campus garden (Melbourne University, Australia) and mixed 1:1 (_v_/_v_) with perlite. Seeds of sunflower were sown on this mixed soil and, after two weeks, they were treated with solutions containing different concentrations of lead aimed to evaluate the effect of an increasing level of pollutant exposure on plant growth. Total content of lead was measured by AAS after digestion with aqua regia and a mixture of HCl/HNO\({}_{3}\) (for soil and plant's shoots and roots, respectively). Growth and biomass production dropped owing to the high concentrations of Pb. Pb content in roots increased more than in shoot as metal concentration in the soil rose. However, _H. annuus_ exhibited a BF \(<\) 1 and so cannot be considered an accumulator.  
_Catharanthus roseus_ was studied by [PERSON] et al. [30] for lead and nickel phytoremediation. Again, plants were grown in pots filled with garden soil watered with metals solutions and the uptake was estimated after 20 days. After harvesting, washing, and drying, plants were digested with a mixture of HCl/HNO\({}_{3}\) and metals content was analyzed in AAS. Results showed that _C. roseus_ behaves as a lead accumulator in roots (BF \(>\) 1 and TF \(<\) 1) and is therefore useful for phytostabilization treatments.  
Compared to grasses and other smaller plants, trees have the advantage of having deeper roots that allow them to reach deeper layers of soil. Within this framework, [PERSON] [19] studied the appropriateness of three trees (_Acacia saligna_, _Eucalyptus rostrate_, and _Conocarpus erectus_) for phytoremediation. Three-month-old seedlings were transplanted in plastic pots containing soil mixed with a fine powder of PbCl\({}_{2}\). Roots of the tree species seemed to be more resistant to heavy metal pollution than shoots, since the above-ground biomass was strongly reduced after treatment with a high concentration of metal. _A. saligna_ was the most tolerant, as no significant alterations of the plant biomass were observed. Among the stress indicators, the lowest RWC was reported for _A. saligna_ shoots and roots, while the chlorophyll pigments did not seem to undergo alterations.  
Both _A. saligna_ and _E. rostrata_ accumulated Pb mainly in roots (TF \(<\) 1), while _C. erectus_ did so mainly in shoots (TF \(>\) 1). Moreover _A. saligna_ showed a metal content in its biomass higher than that of the other two plants. Although higher concentrations of lead were found in roots of _A. saligna_ and _E. rostrata_, significantly high concentrations were also measured in the above-ground tissues; these, together with absence of reduction in the biomass, support these plants as possible Pb hyperaccumulators.