**4. Conclusion**

toxic elements to sludge solids and soils can limit transfer to roots. Some metals, such as Cr and Pb, have very low solubility in soils and show a particularly strong barrier. Leafy crops tend to have less protection in the uptake of metals in comparison to root crops. Many experiments have shown the metals have lower concentrations in seeds and fruits compared to roots, stems, and leaves. For example, Mo is more concentrated in soybean seeds than in the leaves [24], and Tl concentrations in rapeseed are higher than in the leaves [25]. For slightlymoderately Cd-contaminated soils, the transfer of Cd to the seed of linseed (flax), sunflower, corn, and wheat can be sufficiently high to exceed health standards in some countries [26, 27], whereas Zn uptake by corn (maize) in a multiyear sewage sludge experiment on calcareous

For copper concentration in crops, results for Cu were observed in the long-term field sludge experiments of Hinesly and Hansen [29], Hinesly et al. [30], and Soon et al. [28]. It was observed that Cu concentration increased in maize stover when there was an increase in Cu loading in the soil through sludge application. But interestingly, the increase was not directly proportional to the amount of increased Cu application. Reasons for such behavior are Cu sorption by sludge and soil organic matter and plants' strong physiological barrier to Cu translocation

Because of the complicated nature as to how metals behave in soils especially when they are added through sewage sludge, it is almost impossible to provide generalized guidelines. For any particular situation, various considerations should be given before setting metal application guidelines. Such concentration should include soil physical and chemical properties especially adsorption characteristics, crops to be grown, and usage of grown crops. Contamination of such land by metals should be regarded as irreversible and must be kept to the lowest

To evaluate microbial contamination, multisamples were sent to the Muscat Municipality laboratory from all crops. Different tests were done such as the total aerobic plate count, Coliform bacteria, *Escherichia coli, Staphylococcus aureus, Salmonella* spp., yeast, and mold. No

Same finding was reported by Boswell [32], when he noticed that sewage sludge amendment increased the fruit yield significantly compared to the un-amended control and no toxic or

Water productivity factor can be calculated by comparing water used in this study with plant

of water was used to irrigate all crops, and as it was found in **Figures 6**–**8**, Kala compost gave better yield than NPK treatment, which means that water productivity of Kala compost was

). The same amount

harmful bacteria were found, and according to that all crops can be eaten safely.

production (water productivity = total fruit weight, kg/water applied, m3

soils was within the safe limit [28].

58 Soil Contamination - Current Consequences and Further Solutions

[31].

practicable level [9].

**3.7. Biological analysis**

**3.8. Water productivity**

higher than NPK treatment.

detrimental effects on fescue were noted.

It can be concluded that treated municipal wastes (Kala compost) enriched the agricultural soil by improving soil physiochemical properties. Kala compost was a good conditioner for soil as it supported plants with many elements needed for high yield. Soil and plant chemical analysis did not show any problem of heavy metal accumulation. The application of Kala compost did not cause any environmental and human health problems. Therefore, it is safe to apply treated municipal wastes (Kala compost) in some agricultural crops if good management is practiced. Moreover, it is recommended that long-term records on application of treated municipal wastes (Kala compost) are reviewed, so clear findings can be generalized for future applications.
