Abstract
The application of untreated sewage sludge to cropland in water-deficient areas is common practice. A study was conducted to investigate the transfer of trace elements from sewage sludge to tomato crop and the potential health risk to humans. Two types of sewage sludge, ISS (I-9 Sector wastewater treatment plant, Islamabad) and WSS (Water and Sanitation Authority wastewater treatment plant, Faisalabad), were applied at 0.5%, 1.0%, and 1.5% w/w and compared with control (without any amendment). The test crop was tomato (Lycopersicon esculentum). Results revealed that the ECe of soil was increased by these treatments with respect to all application levels. The levels of Pb (lead) and Zn (Zinc) solubility in soil were increased about 46- and 28-fold by the application of ISS at 1.5% and 16- and 22-fold by the application of WSS at 1.5%, respectively. The highest shoot biomass was recorded with 0.5% level of WSS, while higher rates (1.0% and 1.5%) of both ISS and WSS showed significant (p < 0.001) decline in shoot biomass production, and the lowest SFW was recorded with the addition of ISS at 1.5% application rate (a significant reduction of 44%) compared to control. The pore water analysis and correlation depicted that dissolved organic carbon (DOC) controlled the release of Zn and Pb. The PLI (value < 1) indicated that the overall pollution of trace metals in the investigated samples was absent, but the Igeo and CF showed the contamination potential for Cd, Cu, and Ni was moderate to strong. DIM and HRI analysis suggested that the tomato was safe for human consumption. The HRI values for all trace metals were below the permissible limit (HRI = 1) described by USEPA-IRIS. It was concluded that a lower rate of both sewage sludge types produces more biomass and less accumulation of trace metals in the test crop.
Highlights
Disposal of wastes and pollutants generated by human activities directly into the environment is posing a serious threat to the ecosystem
The results revealed that both Daily Intake of Metals (DIM) and Health Risk Index (HRI) values for all trace metals increased for soil treated with sewage sludge in a dose-additive manner irrespective of the origin of sewage sludge (Table 5)
The HRI values for all trace metals were below the permissible limit (HRI = 1) described by United States Environmental Protection Agency (USEPA)-IRIS
Summary
Disposal of wastes and pollutants generated by human activities directly into the environment is posing a serious threat to the ecosystem. Domestic waste, sewage treatment plants, the production of crude matter, general services, and many other human activities are polluting various environmental compartments. Recycling and reusing the waste materials is arguably an environmentally and economically sustainable option. Sewage sludge (SS) is known to be rich in essential nutrients (nitrogen and phosphorus), organic matter [2,3,4], and trace elements that are beneficial for plant growth and better yield [5,6]. Pakistan is a developing country and has no functional secondary and tertiary
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