## 3 Results and Discussion
### Analysis of Heavy Metals in Vegetables  
Figure 2a presents the distribution of Cd concentrations in vegetables of the experimental and control groups. Briefly, the Cd concentrations of all vegetables in group 1 ranked in the order: water spinach (2.38 mg/kg) > sweet potato (0.90 mg/kg) > potato (0.18 mg/kg) > sweet potato leaves (0.15 mg/kg) > tomato (0.10 mg/kg). The Cd concentrations in group 2 ranked in the order: water spinach (0.92 mg/kg) > sweet potato (0.86 mg/kg) > sweet potato leaves (0.25 mg/kg) > potato (0.22 mg/kg) > tomato (0.15 mg/kg). A very low Cd concentration was found in all types of vegetable in the control group. Significantly different Cd concentrations were found in all of the investigated vegetables among the three soil contaminant soils, with the results indicating that water spinach becomes the most polluted with Cd as compared to the other vegetables in all experimental groups. \begin{table}
\begin{tabular}{l c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Training Time**} & \multicolumn{6}{c}{**Water Spinets**} & \multicolumn{6}{c}{**Sweet Prudie Leaf**} \\ \cline{2-11} \multicolumn{1}{c}{**(Witch)**} & \multicolumn{1}{c}{**Group 1.Cd**} & \multicolumn{1}{c}{**Group 2.Cd**} & \multicolumn{1}{c}{**Control**} & \multicolumn{1}{c}{**\(p\)-Value**} & \multicolumn{1}{c}{**Group 1.Cd**} & \multicolumn{1}{c}{**Group 2.Cd**} & \multicolumn{1}{c}{**Control**} & \multicolumn{1}{c}{**\(p\)-Value**} \\ \hline
1 st & 0.00 \(\pm\) 0.00 & 1.33 \(\pm\) 1  
The Cu concentrations in group 1 (Figure 2b) were: potato (3.21 mg/kg) > water spinach (2.31 mg/kg) > sweet potato (1.53 mg/kg) > tomato (1.09 mg/kg) > sweet potato leaves (0.85 mg/kg). In group 2, the Cu concentrations ranked in the order: water spinach (5.10 mg/kg) > potato (1.65 mg/kg) > sweet potato (1.60 mg/kg) > sweet potato leaves (0.86 mg/kg) > tomato (0.74 mg/kg). These results show that potato and water spinach were most polluted by Cu among all of the observed vegetables. [PERSON] et al. [39] monitored the heavy metal concentrations in different kinds of vegetables from agricultural fields in neighboring industrial areas in Bangladesh. Cd was found at significant levels in leafy vegetables, tubers, and fruits (0.003-1.60, 0.001-0.71, and 0.001-0.16 mg/kg, respectively), with the Cu concentrations being 0.86-5.80, 0.27-1.60, and 0.46-2.40, respectively. [PERSON] et al. [20] carried out a similar analysis for vegetables in agricultural land near mining areas, showing that the bioaccumulation of heavy metals was significantly higher in leafy than in non-leafy vegetables. This is reflected in our results, where water spinach accumulated abundant Cd as compared to other plants. [PERSON] et al. [40] highlights the potential health risks that are associated with vegetables cultivated in wastewater-contaminated soils, in particular the consumption of leafy vegetables that contain Cd, Cr, Ni, and Pb; and, [PERSON] et al. [41] showed a higher bioaccumulation factor (BAF) for Cd in leaf and root vegetables than in fruit vegetables. Our results were in agreement with those of [PERSON] et al. [39] and [PERSON] et al. [20], and they clearly showed that leafy vegetables are more likely to accumulate heavy metals when compared to other vegetables. [PERSON] et al. [42] reported that, at the lethal concentration of Pb, the barriers in the root endodermis will be broken and cause Pb enter the vascular tissues. That may further affect the mineral nutrition and water balance, inactivate the enzymes activities, change the hormonal status, and then affect the membrane structure and permeability. [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [43] reported that a lower pH influenced the metal uptake by plant, since Cd and Zn are more soluble at decreasing pH. Meanwhile, this may be due to the short growth period and fast growth rate of leafy vegetables, so the osmotic effect and absorption of nutrients from the soil are strong.