Abstract
Utilization of treated wastewater (TWW) for agricultural purposes has grown over the past few years because of limited available water resources. This study was performed to assess the long-term irrigation of treated wastewater from the Wadi-Musa region on the accumulation of heavy metals in soil and their uptake and translocation to various parts of olive trees. Fifteen year old trees that had been grown and irrigated with treated wastewater resources since their establishment were used in this study. Irrigation water, soil, and plant samples (root, stem bark, leaves, fruits) were collected and chemically analyzed for their heavy metal content. Accumulation of heavy metals in irrigation water and soil were found to be within the acceptable range for the safe use of treated wastewater according to the standards of the WHO. However, long-term and continuous irrigation with TWW resulted in significant accumulation of heavy metals in plant parts when compared to their levels in irrigation water and soil. Uptake of metals was consistent among plant parts with the highest concentrations for Fe, Mn, Pb and Zn, and the lowest concentrations for Ni, Cr and Cd. Assessment of the bioaccumulation factor (BFC) and translocation factors (TF) of heavy metals into different plant parts indicated selective absorption and partitioning of these heavy metals into different plant parts. High BCF values were observed for Fe, Cu and Ni in roots and fruits, and Fe, Mn, Cd and Pb in leaves. Translocation factors of metal ions were variable among plant parts. Fruits had the highest TF for Cu, Cd and Zn metals, and the lowest for Mn and Fe, while leaves have the highest TF for Fe, Zn and Mn and the lowest for Cd and Pb. The results of this study indicate that olive trees are heavy metal accumulators, caution should be considered in long-term use of TWW and periodic assessment of possible hazards, especially on fruits and oil quality is required.
Highlights
Analysis of effluents indicated that irrigation water pH, EC and biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), sodium adsorption ratio (SAR) and total coliforms count (MPN/100 mL) lie within the standards of Jordan Standards and Metrology Organization [38], and the safe use of treated wastewater for irrigation by the World Health Organization [39]
The composition of heavy metals in irrigation water and soil samples are shown in Tables 3 and 4, respectively
No significant amounts of copper and manganese were detected in the treated wastewater (TWW) used for irrigation (Table 3)
Summary
Uptake of heavy metals by plants from polluted water or soil might contaminate the food chain for both humans and animals Heavy metals such as Cu, Cd, Cr, As, Pb and Ni were reported in olive oil in Cyprus at concentrations that can cause significant health hazards [33]. Spanish table olives were reported to contain significant levels of Cd, Co, Cr, Li, Ni, Pb and Sr [34] In this perspective, olive trees are considered important heavy metal bioaccumulators in different plant parts for Cu, Pb and Zn [31]. The fate of heavy metals in soils, and their absorption and bioaccumulation in olive plants in response to long-term irrigation with TWW effluents, Horticulturae 2021, 7, x FOR PEER REVIEW of 13 plants in the Wadi- Musa region. Of uptake and partitioning of selected heavy metals in olive trees
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