## 3 Results and Discussion  
### Growth, Lignocellulosic Composition and Metal Uptake by Vetiver Grass Grown in Stamp Sand  
The control soil was chosen such that it was similar in texture to that of the stamp sand, but had significantly lower PTM-content, since the sand-like texture of stamp sand highly influences water retention and soil organic matter [36]. Both soils are classified as a sandy loam according to the USDA-NRCS web soil survey. Stamp sand and control soil were characterized prior to the 60-day uptake study (Table 1). Particle size analysis showed that both the stamp sand and control soil had 70% sand content, and their water holding capacities were statistically similar using [PERSON]'s \(t\)-test with \(\alpha\) = 0.05 (Table 1). While stamp sand had more coarse silt (20.3%) when compared to the control soil (5%), the control soil had more clay (15.2%) compared to stamp sand (6.2%). The control soil was more acidic (5.4) compared to the stamp sand (6.8). Stamp sand had high Cu (1551 mg/Kg), Fe (44,830 mg/Kg) and Al (7886 mg/Kg) levels and Toxicity Characteristic Leaching Procedure (TCLP) showed that both Cu and Al had high potential to leach (Table 1). Sequential extraction was done to quantify the operationally-defined forms of Cu, which showed that acid-soluble and reducible fractions of Cu constituted about 20% of the total Cu each, whereas 50% of the Cu was in the residual fraction (silicate \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & Stamp Sand & Control Soil \\ \hline \multirow{6}{*}{Particle Size Distribution} & \% Clay & 6.23 \(\pm\) 2.36 & 15.20 \(\pm\) 0.06 \\  & \% silt & 3.77 \(\pm\) 0.80 & 10.20 \(\pm\) 0.08 \\  & \% Sand Total & 69.74 \(\pm\) 1.28 & 70.81 \(\pm\) 0.09 \\  & \% Sand 1000 \(\upmu\)m & 4.48 \(\pm\) 1.15 & 0 \(\pm\) 0 \\  & \% Sand 500 \(\upmu\)m & 14.45 \(\pm\) 0.95 & 1.29 \(\pm\) 0.05 \\  & \% Sand 400 \(\upmu\)m & 12.06 \(\pm\) 0.16 & 1.70 \(\pm\) 0.02 \\  & \% Sand 250 \(\upmu\)m & 38.76 \(\pm\) 1.45 & 85.75 \(\pm\) 0.03 \\  & \% Course silt & 20.25 \(\pm\) 1.88 & 5.01 \(\pm\) 0.02 \\ \cline{2-3}  & pH & 6.82 \(\pm\) 0.02 & 5.44 \(\pm\) 0.02 \\ \cline{2-3}  & Electrical conductivity (\(\upmu\)S) & 12.7 \(\pm\) 0.21 & 20.9 \(\pm\) 1.23 \\ \cline{2-3}  & Water holding capacity (\% WHC) & 32.12 \(\pm\) 1.44 & 29.7 \(\pm\) 0.01 \\ \cline{2-3}  & Water content (\%) & 22.96 \(\pm\) 2.63 & 46.01 \(\pm\) 0.01 \\ \cline{2-3}  & Organic matter content (\% LOI) & 0.92 \(\pm\) 0.20 & 3.45 \(\pm\) 0.12 \\ \cline{2-3}  & \multirow{2}{*}{Tamm’s Reagent (mg/kg)} & Al & 22.45 \(\pm\) 0.04 & 11.65 \(\pm\) 0.01 \\  & Fe & 89.00 \(\pm\) 0.02 & 93.97 \(\pm\) 0.94 \\ \cline{2-3}  & Cu & 394.32 \(\pm\) 118.18 & 96.55 \(\pm\) 73.43 \\ \cline{2-3}  & \multirow{2}{*}{Toxicity Characteristic Leaching Procedure (mg/kg)} & Fe & 47.20 \(\pm\) 13.94 & 64.20 \(\pm\) 12.69 \\ \cline{2-3}  & & Al & 252.7 \(\pm\) 28.22 & 39.27 \(\pm\) 13.65 \\ \cline{2-3}  & & Cu & 1551 \(\pm\) 28.28 & 27.05 \(\pm\) 9.68 \\ \cline{2-3}  & Total Metal Analysis (mg/kg) & Fe & 44830 \(\pm\) 806.00 & 12212.5 \(\pm\) 333.08 \\ \cline{2-3}  & \multirow{2}{*}{Acid-soluble Extraction (mg/kg)} & Al & 7586.62 \(\pm\) 761.88 & 3777.52 \(\pm\) 558.34 \\ \cline{2-3}  & Acid-soluble & Cu & 397.37 \(\pm\) 3.18 & BDL \\ \cline{2-3}  & Reducible & Cu & 367.00 \(\pm\) 1.18 & BDL \\ \cline{2-3}  & Oxidizable & Cu & 126.60 \(\pm\) 2.94 & BDL \\ \cline{2-3}  & Residual & Cu & 1150.67 \(\pm\) 10.26 & 0.65 \(\pm\) 0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The physical and chemical properties of stamp sand and control soil. Shown as averages from triplicates \(\pm\) standard deviation. Particular to the selection of the control soil was the sand fraction/texture of the soil and the differences in copper concentrations. The % sand fraction of particle size distribution was statistically similar, and the levels of copper were significantly different between soil types using [PERSON]’s \(t\)-test with \(\alpha\) = 0.05.  
bound).