# Remediation Opportunities for Arsenic-Contaminated Gold Mine Waste
## 4 Phytoremediation
### Identified Plant Species  
Identifying plant species that bioaccumulate, hyperaccumulate, or stabilise As is vital for phytoremediation and has been widely studied (Table 4) [98]. It is stated that to confirm a As hyperaccumulating species, the above ground biomass must accumulate >1000 mg/kg of arsenic [120; 121; 122; 123]. The first As hyperaccumulator was discovered by [PERSON] et al. [14]; the Chinese brake fern, _Peteris vittata_, grew on chromatated copper-arsenate-contaminated soil. The fronts of _P. vittata_ contained 1442-7526 mg/kg of As, and contaminated soil had As  
Figure 3: Phytoextraction and phytostabilisation mechanisms for phytoremediation of potentially toxic elements in soil. Orange arrows show direction of potentially toxic element uptake [31; 59; 73; 82; 88; 89; 90; 91; 113].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Techniques** & **Characteristics** & **References** \\ \hline Phytoextraction & Arsenic uptake in above ground biomass. & [14; 108] \\  & Immobilising As in the rhizosphere to & \\ Phytostabilisation & prevent leaching into water and & [13; 16] \\  & bioavailability. & \\ Phytovolatilisation & Plant uptakes As through the xylem and & \\  & transforms As to a less toxic and volatile & \\  & form. Plant then releases As emissions. & \\ Rhizodegradation & Microbial community in the rhizosphere & \\  & degrade organic contaminants. & \\ Rhiziltration & Filtering of groundwater, surface water, & \\  & and wastewater with plant roots. & [82; 112] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Phytoremediation techniques and characteristics.  
concentrations ranging from 18.8 to 1603 mg/kg [14]. _P. vittata_ growing on uncontaminated soil (0.47-7.56 mg/kg, As) was also analysed, and fronds bioaccumulated 11.8-64.0 mg/kg of As [14]. In general, the expected bioaccumulation of As on uncontaminated soil is 3.6 mg/kg, almost half the bioaccumulation reported for _P. vittata_[14]. The search for additional As hyperaccumulators is currently underway, and reports have identified _Pteris umbrosa_ as a possible candidate [98; 124]. A study by [PERSON] et al. [124], aimed to identify additional _Pteris_ species for As hyperaccumulating characteristics. _P. vittata, Pteris cretica, Pteris longifolia_, and _P. umbrosa_ were exposed to 0-500 mg/kg of As and results showed similar As hyperaccumulating capabilities to those displayed by _P. vittata_[124]. For example, both _P. vittata_ and _P. umbrosa_ were efficient in bioaccumulating As in their fronds, 57.1 \(\pm\) 9.0% and 56.8 \(\pm\) 4.8%, respectively, a characteristic essential for phytoextraction [125]. Pteris species are fern plants typically found in rainforests, along coasts, dry regions, and tropical and subtropical landscapes [126]. The habitat of _P. umbrosa_ is the east coast of Australia, which might have implications for phytoextraction in non-coastal and arid to semi-arid regions such as Bendigo, a gold mining town in regional Victoria [98]. Hyper/accumulating plant species currently identified for As are primarily fern species, which have specific climate requirements; this causes concern for their use in phytoremediation projects for gold mine waste locations [16]. Fern species are unsuitable for arid to semi-arid climates, which are the common environments for gold mining towns. There is a need to identify plant species for phytoremediation projects that are compatible with arid to semi-arid climates, such as tussock grasses, and conducting studies with site-specific soil.