## 3 Results and Discussion
### Bioaccumulation Factor  
Bioaccumulation factors for Pb, Zn, Cu, and Cd were assessed for phytoremediation potential of root, stem, leaves, and intact plant tissues, besides determining associated health risk if consumed for medicinal or forage purposes. Highest accumulation of Cd (1.22 \(\pm\) 0.66) was recorded in root and intact-plant compared to Pb, Cu, and Zn. Our results depicted BAF >1 for Cd in some abandoned sites (i.e., KTH, GTM, SKR, SMR, and PC), indicating plant potential as hyper-accumulator with higher organic matter  
Figure 2: Bio-concentration of Pb, Zn, Cu, and Cd in plants (mg/kg) total dry biomass and its concentration in soil collected from different abandoned habitats in Khyber Pakhtunkhwa, Pakistan. Note: P (Plant), S (Soil), Threshold levels: Pb = 5 mg/kg [43], Zn = 60 mg/kg: Cu = 10 mg/kg [44], Cd = 0.1 mg/kg [45] in plants while for soil while Pb = 8.15 mg/kg, Zn = 44.19 mg/kg, Cu = 8.39 mg/kg [46] and for Cd = 0.31 mg/kg [47]. (**A–D**) (Sub-Figure for Pb, Zn, Cu and Cd, respectively). contents (0.83 \(\pm\) 0.17), despite the high accumulation of Pb in the root (BAF \(>\) 1) in sites like SMR, PC, BKP, TBM, GCD, AMS, and CBS respectively (Table 1). Zn was significantly accumulated in the root and intact plants harvested at AMS and CBS sites, whilst Cu hyperaccumulation was not found in any abandoned site. Additionally, we observed a significant accumulation difference (\(p\) < 0.001) between root and intact-plant for all the sites, except Pb accumulation at the GTM site (\(p\) < 0.45). In contrast, a low accumulation of Zn was recorded at all the abandoned sites except AMS and CBS (BAF \(>\) 1). In contrast, the bioavailability factor for Cu was \(<\)1 at all the sites indicating the poor ability of _X. strumarium_ to accumulate this metal. Generally, BAF \(>\)1 is related to the high mobility of metals in soils, possibly favored by soil physicochemical characteristics, specific plant species metabolism, and metal pollutant characteristics or derivatives, thus making its readily available for absorption by the plants [48; 49; 50; 51; 52]. Our aforementioned results link well with the _X. strumarium_ plant screened with BAF \(>\) 1 for Cd and Pb at roadside areas in Faisalabad-Sargodha [26], while the same opposite low sign pattern for Zn accumulation and its mobility is also clearly depicted. Soil texture plays a crucial role in heavy metal availability for absorption in plant species [48]. In our study, we observed the soil textural pattern as sand (40%) \(>\) silt (33%) \(>\) clay (26%), advocating highly mobilized heavy metals, thereby enhancing its availability for absorption and accumulation in plants as reported by [PERSON] (1979) [53]. This behavior of soil texture with heavy metal absorption seems to be typical as [PERSON] et al., (1996) [54] reported higher availability of Pb and Cu in fine-sand soils and [55] in sandy soils. The same relationship between higher soil sand contents and mobility strength of Cd was also noted by [56]. In other words, increased soil sand contents are correlated with the mobility of heavy metals. Hence, the inland sandy soil texture enhanced these metals' mobility and accumulation extent in _X. strumarium_ in this region. The Khyber Pakhtunkhwa province lies under the most substantial sandy soil influence of the Indus Basin System (IBS), often facing heavy floods in semiarid regions. Hence, even a slight increase in flood frequency particularly in monsoon conditions may enhance sand particles, perhaps increasing mobility and accumulation of heavy metals both in native and exotic plants. Given the importance of low soil organic matter (SOM) for metals availability, the negative relationship between heavy metals availability and mobility in plants is not surprising. Consequently, the availability of Pb and Cd was negatively affected by organic matter contents (Table 1), previously endorsed by [57; 58] in different plant species.