Accumulation of heavy metals in Jordanian soils irrigated with treated wastewater threatens agricultural sustainability. This study was carried out to investigate the environmental fate of Zn, Ni, and Cd in calcareous soils irrigated with treated wastewater and to elucidate the impact of hydrous ferric oxide (HFO) amendment on metal redistribution among soil fractions. Results showed that sorption capacity for Zarqa River (ZR1) soil was higher than Wadi Dhuleil (WD1) soil for all metals. The order of sorption affinity for WD1 was in the decreasing order of Ni > Zn > Cd, consistent with electrostatic attraction and indication of weak association with soil constituents. Following metal addition, Zn and Ni were distributed among the carbonate and Fe/Mn oxide fractions, while Cd was distributed among the exchangeable and carbonate fractions in both soils. Amending soils with 3% HFO did not increase the concentration of metals associated with the Fe/Mn oxide fraction or impact metal redistribution. The study suggests that carbonates control the mobility and bioavailability of Zn, Ni, and Cd in these calcareous soils, even in presence of a strong adsorbent such as HFO. Thus, it can be inferred that in situ heavy metal remediation of these highly calcareous soils using iron oxide compounds could be ineffective.
Jordan is considered as one of the world’s poorest nations in renewable water resources with a per capita share of less than 148 m3 annually, far below the absolute water scarcity level of 500 m3/capita/year [
The largest treatment plant in Jordan is Khribet As-Samra Waste Stabilization Ponds (KS) located 30 km north east of the capital Amman, which provides 70% of all treated wastewater generated in the country [
One method of controlling metal mobility is the application of iron oxide-based amendments to the soil which may be a cost effective, “in situ” approach to restore contaminated soils and wastewaters [
Although heavy metal content in soils irrigated with KS wastewater has been reported, no study so far has investigated heavy metal sorption characteristics, fractions, and environmental fate in these soils. If agriculture is to remain a viable and sustainable option in the area using KS treated wastewater, it is imperative that measures can be ensured to control metal mobility, availability, and possible transfer to the food chain. In this study, we aim at evaluating the environmental fate of Zn, Ni, and Cd in characteristic semidesert calcareous soils irrigated with treated wastewater by investigating the
The soils in this study were collected from fields irrigated with treated wastewater (TWW) discharged from Khirbet As-Samra plant (KS) (Figure
Map of the study area showing the location of investigated soils irrigated with treated wastewater from Khirbet As-Samra effluent along the Zarqa River, Jordan.
On the basis of irrigation water quality, the study area can be divided into two regions: the first includes areas irrigated along Wadi Dhuleil where the water used is treated wastewater only, and the second includes areas irrigated along Zarqa River where treated wastewater is seasonally blended with surface water. Soils collected from these two zones are henceforth referred to as WD (Wadi Dhuleil) and ZR (Zarqa River) soils. Three composite samples were taken from each zone (WD and ZR) at depths of 0–20, 20–40, and 40–60 cm. Soils were air dried, ground to pass a 2 mm sieve, and stored in clean polyethylene bottles prior to analysis. Soils were analyzed for particle-size distribution using hydrometer method [
Total elemental analysis was determined using Atomic Absorption Spectroscopy (AAS) (AAnalyst 700, Perkin-Elmer Inc.,USA) after digestion with HNO3-HCl according to the USEPA 3050-B method [
Sorption isotherms of Zn, Ni, and Cd were constructed for WD1 and ZR1 soils, each representing a distinct area in terms of irrigation water quality. Isotherms were obtained by adding 30 mL of varying concentrations of metal solution to 50 mL centrifuge tubes containing 0.5 g of soil. Solutions of Zn, Ni, and Cd were prepared from salts of Zn(NO3)2, Cd(NO3)2, and Ni(NO3)2, respectively. Initial concentrations (
The distribution of Zn, Ni, and Cd among soil fractions was investigated in WD1 and ZR1 soils at two initial metal concentrations (1280 and 3200 mg kg−1) and in presence or absence of 3% HFO. Initially, 1.0 g of soil was weighed in 50 mL centrifuge tubes and a portion of the tubes was amended with 3% (w/w) HFO while another remained nonamended. Then, 32 mL of 40 mg L−1 or 100 mg L−1 Zn, Cd, or Ni solution was added to the tubes giving 1280 and 3200 mg kg−1, respectively. Tubes were shaken for 1 week until equilibration was reached, centrifuged to separate the liquid from the solid phase, and filtered, and the supernatant was acidified using 0.1 M HNO3. Equilibrium concentrations (
Analysis of variance statistical analysis was performed using SPSS 17 (SPSS, Inc. Chicago, IL) and comparison of means was undertaken using
Table
Chemical and physical properties of Wadi Dhuleil (WD) and Zarqa River (ZR) soils at 0–20 cm depth.
Parameter | Unit | Soil sample | |||||
---|---|---|---|---|---|---|---|
WD1 | WD2 | WD3 | ZR1 | ZR2 | ZR3 | ||
Particle size | SL | SL | SL | SL | SL | SL | |
pH | 8.4 | 8.3 | 8.4 | 8.3 | 8.6 | 8.2 | |
EC | dS m−1 | 2.1 | 3.2 | 2.2 | 3.7 | 3.0 | 2.2 |
CEC | cmol kg−1 | 19.4 | 20.7 | 21.1 | 22.3 | 17.2 | 20.3 |
ESP | % | 8.9 | 9.2 | 2.6 | 9.9 | 1.8 | 3.9 |
OM | % | 2.0 | 1.1 | 2.1 | 1.6 | 1.0 | 2.1 |
CaCO3 | % | 33.1 | 32.5 | 36.1 | 40.6 | 61.6 | 22.3 |
Fe | % | 0.56 | 0.63 | 0.58 | 0.51 | 0.51 | 0.53 |
Ca | mg kg−1 | 2759.1 | 2891.1 | 5508.8 | 3549.0 | 2421.3 | 5051.4 |
Mg | mg kg−1 | 552.6 | 594.3 | 178.8 | 737.1 | 175.5 | 475.2 |
Na | mg kg−1 | 398.0 | 439.7 | 125.6 | 509.2 | 70.0 | 181.2 |
K | mg kg−1 | 42.3 | 49.9 | 29.4 | 26.9 | 36.8 | 31.9 |
Fe | mg kg−1 | 3.6 | 3.6 | 3.5 | 3.7 | 3.9 | 3.5 |
|
mg kg−1 | 18.7 | 37.0 | 18.6 | 14.8 | 31.6 | 43.0 |
|
mg kg−1 | 35.0 | 37.0 | 43.5 | 87.2 | 39.6 | 94.8 |
Table
Total elemental content of WD and ZR soils at depths of 0–20, 20–40, and 40–60 cm.
Metal | Soil sample | Critical valuesa | ||||||
---|---|---|---|---|---|---|---|---|
Depth | WD1 | WD2 | WD3 | ZR1 | ZR2 | ZR3 | ||
cm | mg kg−1 | |||||||
Zn | 0–20 | 60.1 | 65.7 | 74.7 | 61.7 | 69.3 | 66.2 | 70–400 |
20–40 | 55.9 | — | 71.2 | 63.0 | 67.0 | 62.5 | ||
40–60 | 60.1 | — | — | 63.1 | 69.7 | — | ||
|
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Cd | 0–20 | 1.8 | 1.9 | 2.0 | 2.5 | 4.0 | 2.8 | 3–8 |
20–40 | 1.7 | — | 2.1 | 2.6 | 3.6 | 3.3 | ||
40–60 | 1.6 | — | — | 2.4 | 4.3 | — | ||
|
||||||||
Ni | 0–20 | 43.9 | 42.6 | 46.3 | 36.5 | 40.7 | 39.1 | 100 |
20–40 | 41.8 | — | 43.7 | 38.5 | 40.5 | 37.2 | ||
40–60 | 45.2 | — | — | 46.4 | 40.7 | — | ||
|
||||||||
Cu | 0–20 | 18.8 | 19.1 | 20.7 | 18.0 | 26.7 | 18.9 | 60–125 |
20–40 | 17.5 | — | 20.7 | 18.6 | 23.1 | 18.3 | ||
40–60 | 18.8 | — | — | 18.3 | 23.6 | — | ||
|
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Pb | 0–20 | 25.7 | 25.1 | 23.8 | 31.2 | 29.0 | 27.1 | 100–400 |
20–40 | 23.5 | — | 25.5 | 31.1 | 25.2 | 28.3 | ||
40–60 | 23.7 | — | — | 30.0 | 28.6 | — |
Figure
Adsorption isotherms of Zn, Cd, and Ni in WD (a) and ZR (b) soils. The solid lines represent modeled adsorption data.
Equilibrium concentrations of Zn, Ni, and Cd produced satisfactory fits to both Freundlich and Langmuir models as indicated by
Parameters of Langmuir and Freundlich isotherms for sorption of Zn, Cd, and Ni in WD1 and ZR1 soils.
Metal ion | Soil | Freundlich model | Langmuir model | ||||
---|---|---|---|---|---|---|---|
|
|
|
|
|
| ||
Zn | WD1 | 2247.3 | 0.35 | 0.94 | 3028.8 | 4.61 | 0.94 |
ZR1 | 3164.6 | 0.42 | 0.94 | 3476.9 | 5.72 | 0.95 | |
|
|||||||
Cd | WD1 | 1711.6 | 0.29 | 0.93 | 2370.7 | 10.00 | 0.92 |
ZR1 | 2933.6 | 0.63 | 0.98 | 4580.9 | 1.64 | 0.99 | |
|
|||||||
Ni | WD1 | 2295.6 | 0.27 | 0.96 | 2462.2 | 28.40 | 0.91 |
ZR1 | 2033.4 | 0.30 | 0.98 | 2692.0 | 5.89 | 0.93 |
Figure
Relative distribution of Zn, Cd, and Ni in WD1 and ZR1 soils amended or nonamended with 3% hydrous ferric oxide (HFO). Mean values followed by the same letter within a column are not different at
Figures
Distribution of Zn, Ni, and Cd in WD1 soil with and without HFO amendment following addition of 1280 mg kg−1 ((a), (c), and (e)) and 3200 mg kg−1 ((b), (d), and (f)) of metal solution. Mean values followed by the same letter within a column are not different at
Distribution of Zn, Ni, and Cd in ZR1 soil with and without HFO amendment following addition of 1280 mg kg−1 ((a), (c), and (e)) and 3200 mg kg−1 ((b), (d), and (f)) of metal solution. Mean values followed by the same letter within a column are not different at
The results revealed that metals were mainly associated with the mobile fraction of soils, indicating the high potential mobility and bioavailability of these metals. This is consistent with the electrostatic attraction of metals in WD1 soils as indicated earlier. The strong association of Cd with the carbonate fraction has been reported in calcareous soils, attributed to its precipitation in the form of CdCO3 or by replacing Ca in calcite crystals, which explains the results presented here [
Sorption isotherm data showed that between the 2 TWW-impacted calcareous soils (WD and ZR) examined, the ZR1 soil had higher affinity for Zn, Ni, and Cd than WD1 soil as indicated by the Langmuir sorption capacity,
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors gratefully thank The University of Jordan, Deanship of Academic Research, for funding this research under Grant no. 49/2011-2012.