## 4 Discussion
### Bioremediation of Non-Essential Toxic Elements Using Selected Indigenous Microbes
The increase in SOC post-irrigation with TWW might have also contributed to the low bioavailability of non-essential toxic elements, thus affecting the low bioremediation reported in this study, since soil organic matter can adsorb cations [58]. As such, the increase in soil pH and SOC reported in this study might have reduced the bioavailability of non-essential toxic elements to indigenous microbes, thus resulting in a low bioremediation efficiency of selected indigenous microbes. The increase in EC following the bioremediation process, reported in Table 4, is an interesting observation as only distilled water was added to the soils. The increase in EC following the bioremediation process might have been caused by impurities in distilled water, most likely from storage containers during the 12-week bioremediation process, or the increase in EC might be due to metals released as by-products of bioremediation. In this case, this study will contradict the results obtained by [PERSON] [19], who stated that the products of bioremediation are harmless to the crop, as an increased EC in soils can be harmful to crops. The decline in the concentration of essential elements in soils inoculated with selected indigenous microbes, as shown in Table 5, suggests that the indigenous microbes used essential elements to remediate contaminated soils. Since microbes use the essential elements to carry out their ecological functions, the decline in essential elements in the control soils is due to a consortium of soil microbes, as the soils used for bioremediation were not pasteurized. The high decline in K in inoculated soils suggests that the indigenous microbes used more K compared to N and P. The role of potassium in microbes includes the activation of intracellular enzymes, pH regulation, and osmoregulation [59]. Nevertheless, all essential elements are crucial for a successful bioremediation process. [PERSON] et al. [60] reported that adding nutrients to the soil improved bioremediation. Recent studies, have argued that native microbes are naturally better adapted to contaminated soils, and bio-stimulation could enhance their in situ remediation efficiency. [PERSON] et al. [61] concluded that the indigenous microbes are limited by N and P, and the addition of these nutrient could improve bioremediation. [PERSON] et al. [62] isolated _Pseudomonas aeruginosa_, _Klebsiella edwardsii_, and _Enterobacter cloace_ from soils contaminated with heavy metals and reported that the _P. aeruginosa_ had the highest bioremediation potential among the three microbes, with a Cd and Pb removal efficiency of 59% and 34% at 50 mg/L and 300 mg/L, respectively. In contrast, the addition of a carbon source led to _K. edwardsii_ having the highest bioremediation potential amongst the three indigenous microbes with an 80%and 92% remediation efficiency. The selected indigenous microbes that are tolerant to toxic elements used in this study are mostly pathogenic; as such, their bioremediation potential is hindered by their drawback of adversely affecting public health security. The indigenous microbe _S aureus_ is associated with several clinical manifestations such as skin and soft tissue damage, pneumonia, dermatitis, and urinary tract infections [63]. Intestinal infections such as diarrhoea and extraintestinal infections such as urinary and respiratory tract infections are associated with _E. coli_[64]. Meanwhile, _P. aeruginosa_ can cause chronic infection in individuals with a compromised immune system, especially amongst individuals with ventilator-associated pneumonia, cystic fibrosis, and burn wounds [64; 65; 66; 67]. These selected indigenous microbes have the potential to be used as a remediation strategy due to the decrease in the concentration of toxic elements reported in Table 3. However, these microbes can negatively affect public health security; thus, more research should be conducted to ensure the safe usage of these microbes for the remediation of soils contaminated with toxic elements.