## 4 Discussion
### Metal Uptake and Distribution within Plant Organs  
The continuous supply of wastewater has caused considerable changes in physico-chemical properties in soils at Chakera and has ultimately led to enhanced uptake of metal ions by vegetables [36]. It is now well evident that most plants, particularly vegetables, require metals in trace amounts for their nutritional values [37]. As roots are in direct contact with soil to absorb water, dissolved nutrients and trace elements are taken up and finally accumulate in vegetables [38]. Some metal elements like Fe and Mn are less mobile and tend to remain in roots [39]. Furthermore, metals are mostly sequestered in the roots of most horticultural crops [40]. Variations exist in metal contents in plant organs concerning metal distribution, and the metal content in different plant parts is indicative of their presence in waste-polluted soils [41]. However, differential levels of the accumulation of metals have already been reported in a number of vegetables grown on metal-contaminated soils [8]. The tendency of metal accumulation in edible parts of vegetables shows their direct incorporation into the food chain, which poses health risks [42]. In our study, the concentrations of metals were several times higher in tomato plants sampled from the study site, which was supplied with wastewater, than those in the plants grown in a metal-free environment. These results are in line with previous studies reporting similar findings in wastewater-grown vegetables [41].  
In the present study, wastewater irrigation resulted in increased Fe and Pb accumulation in different plant organs of tomato plants as well as tomato fruit. High Pb concentration in tomato plants may be related to the high accumulation of this metal in soil due to industrial activities and vehicular emissions, as well as its possible aerial deposition and absorption. Higher Fe content in tomato plants compared with other micronutrients (Zn and Mn) could be because it accumulates more in plants than any other metal ion [43]. These findings are similar to those of [PERSON] and [PERSON] [44] and [PERSON] and [PERSON] [45], who studied the effect of wastewater irrigation on cauliflower, spinach, maize, and berseem. These researchers found a substantial accumulation of Fe and Pb in different plant tissues of the abovementioned crops. A comparison of the levels of metals found in tomato plants with permissible limits reported by the WHO [46; 47] and Asaolu [48] in plants and edible portions of vegetables (Table 2) showed that, unlike Fe, the levels of Zn, Mn, and Pb were well above the permissible limits. However, a comparison of metals in different plant parts with metal limits revealed that concentrations of Mn and Zn in the roots and leaves were much higher than those in the tomato fruit. Fe and Mn are immobile in plants. As seen in our results, these metals were mostly sequestered in roots and, due to little mobility, caused nonsignificant differences in Endocarp. In contrast to the other metals, a higher Pb concentration was observed in the leaves and fruit of tomato. The results of the present study are analogous to those [PERSON] et al. [2], who reported a similar pattern of metal accumulation in tomato plants. These results are also in agreement with some previous studies that reported elevated concentrations of different metals in edible parts of most food cropssubjected to continuous irrigation with wastewater [20]. The results of the present study also support the findings of other researchers [49; 50] indicating that the accumulation of such metals above permissible limits poses a major health concern in humans.