-
- Sunday, June 1, 2003
- Impacts of Irrigation with Water Containing Heavy Metals on Soil and Groundwater – A Simulation Study
- Published at:Water, Air, & Soil Pollution, Volume 146, Numbers 1-4 / June, 2003
IMPACTS OF IRRIGATION WITH WATER CONTAINING HEAVY
METALS ON SOIL AND GROUNDWATER – A SIMULATION STUDY
MOHAMMED M. AL-SUBU
∗, MARWAN HADDAD, NUMAN MIZYED and
INAYA MIZYED
An-Najah National University, Nablus, Palestine, via Israel
(
∗author for correspondence, e-mail: [email protected])
(Received 26 October 2000; accepted 19 December 2002)
Abstract.
This research work intended to study the impacts of irrigation water containing various
levels of copper, lead, and zinc on adsorption capacity of soil packed in 4
plastic columns and
obtained from two locations around the city of Nablus: Salem (A) and Deir Sharaf (B). Results of
simulation experiments showed an increase in the copper, lead, and zinc concentrations in soil and
in leachate with increasing the amount of metal in irrigation water. Copper, lead, and zinc concentrations
increased also with soil depth and duration of application. The results also indicate that the self
purification of both soils was highly affected by physical factors, i.e. the intermittent application of
irrigation water to the soils in the columns caused soil wetting and drying cycles which resulted in
the formation of cracks in shrinked soils specially in the top half of the columns. Crack formation is
common in such clay soils due to the climatic conditions (Mediterranean type: dry summers and wet
winters) and type of clay minerals in the soil. Thus, short circuiting of water through cracks results
in moving contaminants fast and deep in the soil profile.
Keywords:
groundwater, heavy metals, irrigation water, leachate, mediterranean climate, soil pollution
1. Introduction
Generally, wastewater is a liquid waste that is removed from residential, institutional
and commercial establishments. Contaminants of domestic wastewater are
categorized as: Disease causing microorganisms, essential plant nutrient elements,
dissolved minerals and toxic chemicals and biodegradable organic matter (Manahan,
1990). Discharging raw wastewater to the environment causes pollution
problems, therefore, the treatment of wastewater is essential to enhance overall
water availability and conserve water resources (Aziz
et al., 1996; Moatgomery,
1988).
Urban wastewater collection practices in Palestine are such that many small
industries are located within municipal boundaries and drain their wastewater into
the municipal systems. Due to scarcity of fresh water, farmers use raw wastewater
in irrigation (Haddad, 1990, 1993). The long term use of land application as
a disposal method of raw wastewater and/or sludge may result in limiting soils
agricultural ability to produce (Martin Edward, 1991).
Several studies were conducted on the toxicity of urban wastewater in Palestine
and on its impacts on groundwater, plants and soils (Haddad, 1994; Radi
et al.,
1988; Environmental Protection, 2000; Haddad, 2000). The reported heavy metal
concentrations of wastewater in Palestine range from 0 to 2075 mg L
−1for zinc,
0 to 10 mg L
−1 for copper, and from 0 to 15 μg mL−1for lead (Environmental
Protection, 2000; Haddad, 2000; Haddad
et al., 1999). Zinc has the highest level
due to the fact that galvanized steel tanks mounted on the roofs of buildings and
houses are used in Palestine for water supply storage.
In conventional wastewater treatment, considerable portions of heavy metals
remain in the treated effluent if special advanced treatment is not conducted. Thus,
long term effects of irrigation with wastewater might include pollution of ground
water and soil with heavy metals such as: Pb, Cu and Zn ions (Lebourg
et al., 1998).
Other impacts of treated wastewater in agriculture include the health impacts of
possible contamination of crops by pathogenic bacteria and heavy metals (Farid
et
al
., 1993).
There is a rapidly growing awareness of the threat to water resources caused by
highway drainage and sewage effluents. Some of the most significant contaminants
are heavy metals such as copper, zinc and lead (Farid
et al., 1993; Selim and
Iskandar, 1992; Laxen and Harrison, 1977; Chatzoudis and Rigas, 1998; Mendoza
et al
., 1996).
Though copper is not a cumulative systemic poison, large dose (>100 mg) of
copper are harmful to humans and might cause central nervous system disorder,
failure of pigmentation of hair and adverse effects on Fe-metabolism that results
in liver damage. Excess copper may also be deposited in the eyes, brain, skin,
pancreas and myocardium (McAnally
et al., 1997). Lead is a cumulative poison to
humans. Its major effects are impairment of hemoglobin and porphyries synthesis.
Zinc cause muscular weaknesses and pain, irritability and nausea (AWWA, 1990).
In Palestine, the availability of renewable water resources to maintain various
human needs is poor and scarcity is accelerating with time. Therefore, alternative
water resources development options such as brackish water desalination and the
reuse of treated wastewater is gaining much importance at present. The use of these
options is expected to be obligatory with time.
The present work aims to conduct a column study to simulate Pb, Cu and Zn
ions adsorption on soil and in leachate from two locations near the city of Nablus
in order to recommend if these soils are suitable for wastewater application, based
on simulation results.
2. Methodology
All chemicals were Analytical Grade reagents, deionized water was used for preparation
and dilution of metal solutions. All bottles and other containers (except
columns) were treated with 1 M HNO
3solution before being washed with de
ionized water and dried.
2.1. E
XPERIMENTAL SETUP
The experimental setup consisted of 20 PVC columns, 4
in diameter and 2 m long.
Soil samples from the top 100 cm layer soil were collected from the two locations
near Nablus city, Salim (A) and Deir Sharaf (B), before winter 1998. Small stones
(if any) were removed by hand from soil samples and 19 kg of soil was mixed and
then placed in each column in layers of 10 cm.
To allow drainage flow freely without eroding soil from columns, a thin layer
of gravel and sand was placed in the lower end of the column, with a plastic mesh
screen at the bottom of the column. A plastic container was placed under each
column to collect drainage water.
For each soil, three treatments were carried out. These treatments represent
simulation of irrigation for 2, 10 and 20 yr periods in triplicates. Two other columns
were used as blanks. Rainwater was simulated for the blanks by applying 250 mL
of rainwater to each column as needed.
2.2. W
ATER AND HEAVY METALS APPLICATIONS
To each column, a solution containing known combinations of Pb
2+, Cu2+and
Zn
2+was added. The concentration of each metal was estimated based on following
(Table I):
1. Average rainfall, evapotranspiration, crop irrigation requirements and leaching
in Nablus area.
2. Volume of irrigation water = 1025 mm (m
3/dunum), assuming fruit trees will
be planted in these areas.
3. Volume of leaching water = 403 mm (m
3/dunum). Considering the column
volume, the volume of irrigation water for simulation was 8.05 L per column
per year.
2.3. W
ATER APPLICATION
Two, 10 and 20 yr were selected for simulation to study short, medium and long
terms’ effects of simulation. Details are found in Table I.
2.4. H
EAVY METAL APPLICATION
Metal solutions were prepared from their nitrate salts and stored in polyethylene
bottles.
The amount of heavy metals applied in irrigation was based on the maximum allowable
limit by FAO (10, 5 and 10 mg L
−1 for Zn2+, Cu2+ and Pb2+, respectively)
(FAO, 1980). Details are shown in Table I.
TABLE I
Water and heavy metal application in both soils
a
Description Years
1 2 10 20
Depth of irrigation water (mm) 1025 2050 10250 20500
Depth of leachate water (mm) 403 806 4030 8060
Volume of irrigation water (L/column) 8.05 16.1 80.5 161
Volume of leachate water (L/column) 3.17 6.34 31.7 63.4
Weight of zinc added to each column (mg) 80.5 161 805 1609
Weight of copper added to each column (mg) 40.25 80 402 805
Weight of lead added to each column (mg) 80.5 161 805 1609
Duration (from 28-12-1998 to 23-4-1999 8-5-1999 19-5-1999
a
Humidity was 49–69% and pan evaporation was 2.4–7.8 mm day−1.
2.5. L
EACHATE
Water leaching from the columns drained into the plastic containers under the
columns. To illuminate evaporation of drainage water, the containers were covered
by plastic sheets. Depth of drainage water in the collection containers was monitored
and when it reach about 10–15 cm (this depth equals the height of the small
layer of gravel and sand in the bottom of each column), water was collected and
transferred into storage containers. Storage containers were polyethylene bottles of
4 L in volume. To each storage bottle, 10 mL of 1 M HNO
3has been added.
2.6. M
ETALS IN SOIL
Metal concentrations in each soil were measured before treatment. After simulation
was finished, soil was evacuated from the PVC column, which was cut into three
pieces or 4 cross sections at 10, 67, 133 and 200 cm heights. Each soil patch was
dried and the metal ions were extracted from a given weight using NH
4Ac/EDTA
solutions. The extracts were then analyzed for Pb, Zn and Cu ions. Extractable ions
were determined as this research is concerned with the amounts adsorbed on soil
surfaces which could be a fraction of total amounts of metals in the soil. Adsorbed
metals influence plant and environment as they interact with soil solution and plant
roots.
2.7. S
OIL ANALYSIS
Soils were analyzed for chloride, carbonate, sodium, potassium, magnesium, calcium,
copper, zinc, lead, phosphorus, total dissolved salts (TDS), organic matter
content and pH according to standard procedure (Laboratory Manual, 1992; Reeve,
1994). Concentrations of chlorides, sodium, potassium, magnesium and copper
were determined in soil extracts. Concentrations of zinc, lead and copper were
determined from extracts by NH
4Ac/EDTA.
Moisture content, particle size distribution, bulk density and specific gravity of
soils were also measured following standard methods (Das Braja Soil Mechanics,
1941).
2.8. I
NSTRUMENTATION
Analysis of Cu, Zn, and Pb were carried out by atomic absorption spectrophotometry
using Atomic Absorption Spectrophotometer VIDEO 11, which was calibrated,
using supplied standards, prior to each use. Electrical conductivity was
measured using Conductivity Meter 4010 instrument. pH was recorded using a
Corning pH Meter Model 12.
3. Results and Discussion
3.1. C
HEMICAL ANALYSIS
Results of soil chemical analysis are shown in Table II. The concentration of total
dissolved solids (TDS) and electrical conductivity readings were low for both soils,
which indicate that neither soil is saline (FAO, 1980; McNeal
et al., 1982). It also
indicate that the average precipitation in the area of 600 mm yr
−1is sufficient with
time to wash salts from soil especially that both soils showed low sodicity and good
permeability, in spite of soil clay nature.
The conductivity readings are supported by the low concentration found for
calcium, magnesium, potassium, sodium, copper, zinc, lead, phosphorous chlorides
and nitrates. For all cations and anions tested, the found concentration was below
the acceptable limits of agricultural soil.
The relatively high percentage composition of calcium carbonates in soil (13–
20%) is attributed to the fact that parent materials of these soils were originated
from rocks rich in calcium carbonates such as limestone and dolomite. The soil pH
(7–8) and the high buffer capacity make soils suitable for most plants, as the nutrient
availability of most macronutrient is high at this pH, though some micronutrient
such as iron and manganese demand more acidic soil.
The low sodicity resulting from low sodium carbonate content indicates that
both soils were not alkaline (pH < 8.3) (Schwab
et al., 1993). The high calcium
carbonate content and the low exchangeable sodium on the surfaces of these soils
result in the formation of highly stable aggregates with suitable permeability and
hence good drainage ability (Sposito, 1989).
TABLE II
Chemical and physical analysis of soil
Type of analysis Salim Deir Sharaf
Electric conductivity of soil extract (mmho cm
−1) 1.2 1.3
Total dissolved solids for soil extracts (mg g
−1) 3.84 4.16
Soil extract pH 7.29 7.11
Chlorides in soil extract (
μg g−1) 87.5 175
Calcium and magnesium in soil extract (meq L
−1)a11.5 10
% Organic matter content 2 12
Phosphorous in soil extract (
μg g−1) 460 240
Potassium in soil extract (
μg g−1) 140 180
Sodium in soil extract (
μg g−1) 1140 880
% CaCO
313.75 20
Copper extracted by NH
4Ac/EDTA (μg g−1) 4.84 2.52
Zinc extracted by NH
4Ac/EDTA (μg g−1) 2.86 1.24
Lead extracted by NH
4Ac/EDTA (μg g−1) 2.66 0.94
% Moisture content 9.4 8.5
Specific gravity (gm cm
−3)2.6 2.7
Bulk density (gm cm
−3) 1.7 1.8
% Silt 43.2 41.6
% Clay 37.6 35.6
% Sand 19.2 22.8
Soil texture Clay loam Clay loam
a
5.0 g dry soil was extracted with 100 mL NH4Ac (1 N).
3.2. P
HYSICAL ANALYSIS
Due to the formation of aggregates, sieve analysis was not suitable to determine soil
texture. Therefore, hydrometer analysis was utilized and results are summarized in
Table II.
Soil from both locations was found to contain high clay percentage and classified
as clay loam soil based on textural triangle (Beaton
et al., 1975; Fitzpatrick,
1986). Both sites from which soil was collected are located within alluvial plains
of wadis. The low erosion in these plains and the high annual precipitation allow
the formation of clay. However, medium weathering rates are characteristics of
the environmental conditions of the area in these plains. These conditions result in
forming montmorollinite clay minerals in the area. This could be easily observed
in the Plains of the West Bank and the response of soils there to the weather conditions.
The most common response of such clay minerals is the formation of cracks
in summer (dry weather) and the expansion of soils in winter (wet weather). Depth
of these cracks exceeds 1 m in these soils and might reach several meters in some
deep soil profiles due to the long dry summer which might exceed 6 months. The
soil bulk density is high due to shrinkage and formation of aggregates during the
long months of the dry hot summer season. However, the specific gravity of soil
particles is typical for such soils with calcium carbonates parent materials.
3.3. S
OIL ANALYSIS AFTER SIMULATION
Application of heavy metals was carried out to simulate their impact on soil and
leachate.
The concentrations of metals were analyzed before and after the simulation
experiment and the results are presented in Table III.
Because the industrial zone is located in the eastern side of Nablus City, Soil A
was more polluted with the three heavy metals than in Soil B.
After simulation experiments, soil samples were taken from columns at different
depths (10, 67, 133 and 200 cm), thereafter analyzed for copper, zinc and lead
content (Table III).
For all metals employed in the three terms of treatments, the metal concentration
increased with depth. This could be attributed to one or more of the following
factors:
1. The experimental setup allows better ion exchange between applied solution
and soil particles in the lower part of the column.
2. The applied metal concentrations could be low enough to be washed by the
running water of irrigation.
3. The possibility of short circulating on the walls of the PVC column and through
the soil cracks due to wetting and drying conditions and thus preventing ion
exchange between soil and applied solution in the upper part of the column.
Heavy metals residue was calculated for each element in each column (Table IV).
In all cases, the residue increased with increasing the concentration of metal applied
and simulation period. This indicates that heavy metals application in irrigation
water is accumulative. However, Soil A retained more heavy metals than
Soil B.
Although the present results show an increase in heavy metals concentrations
with depth, the actual increase in the field might be different as a result of different
evapotranspiration rates from different soil layers depending on plant physiology
and distribution of plant roots.
3.4. L
EACHATE ANALYSIS
Figure 1 shows the changes in electrical conductivity of soil with time for the long
term treatment for both soils. The electrical conductivity of soil was enhanced with
duration of treatment whereas salinity decreased.
TABLE III
Concentrations of copper, zinc and lead in soil at different depths at the end of simulation
period
Column Residue concentration in soil batches (
μg g−1) Total
Lower Middle Upper (mg)
Cu
2 yr Salim 11.111.07 3.630.46 3.450.12 115.149.77
D. Sharaf 10.000.07 2.030.16 2.250.08 90.481.53
10 yr Salim 37.610.47 4.450.58 3.570.59 288.979.84
D. Sharaf 36.490.77 3.030.74 2.670.84 267.2713.6
20 yr Salim 81.610.81 5.031.13 4.500.82 577.1811.70
D. Sharaf 78.670.19 3.381.02 2.830.55 53057 9.38
Zn
2 yr Salim 19.890.36 1.670.22 1.800.16 147.9 2.91
D. Sharaf 17.410.99 0.990.41 0.840.34 121.9 5.07
10 yr Salim 93.941.35 2.040.15 1.870.27 619.7 9.91
D. Sharaf 91.291.05 1.300.05 1.090.15 593.3 5.93
20 yr Salim 181.331.85 4.150.06 2.290.22 1189.2 13.43
D. Sharaf 170.137.99 1.850.49 1.430.17 1089.2 21.25
Pb
2 yr Salim 18.610.99 2.510.08 2.290.05 148.2 5.8
D. Sharaf 17.750.62 1.750.66 1.370.17 132.2 8.1
10 yr Salim 90.690.72 3.530.08 3.040.17 615.9 4.79
D. Sharaf 88.970.71 2.030.24 1.590.30 586.4 1.40
20 yr Salim 184.600.53 5.570.81 3.360.26 1225.7 6.89
D. Sharaf 176.6411.29 2.750.32 2.090.30 1149.4 68.52
The amount of heavy elements in leachate (Table IV) was also dependent on the
simulation period as expected. However, no significant difference in the amount of
heavy elements was found in leachate from the two soils. This could result from
similar physical and chemical characteristics of the two soils. Therefore their selfpurification
capacities are also similar. The threat to groundwater, if happens, will
rather depend on the hydrogeological characteristics of the two areas.
Mass balance of metal requires that the added amount in irrigation water plus
that present initially in soil, should equal to the metal residue in soil plus that in
TABLE IV
Mass balance of copper, zinc and lead
Actual Mass balance calculations
Initial Applied Leachate Residue
(mg) (mg) (mg) (mg)
Cu
2 yr Salim 115.14 91.96 80.00 2.21 169.75
D. Sharaf 90.48 47.88 80.00 3.25 124.64
10 yr Salim 288.97 91.96 402.00 38.45 455.51
D. Sharaf 267.27 47.88 402.00 39.43 410.45
20 yr Salim 577.18 91.96 805.00 45.12 845.23
D. Sharaf 537.57 47.88 805.00 46.61 806.27
Zn
2 yr Salim 147.9 54.37 161 1.01 214.36
D. Sharaf 121.9 23.55 161 1.41 183.14
10 yr Salim 619.7 54.37 805 17.07 842.30
D. Sharaf 593.3 23.55 805 18.12 810.43
20 yr Salim 1189.2 54.37 1609 66.33 1597.0
D. Sharaf 1098.2 23.55 1609 82.32 1550.2
Pb
2 yr Salim 148.2 50.578 161 0.61 210.96
D. Sharaf 132.2 17.805 161 1.01 177.80
10 yr Salim 615.9 50.578 805 19.08 836.49
D. Sharaf 586.4 17.805 805 19.67 805.88
20 yr Salim 1225.7 50.578 1609 33.18 1623.1
D. Sharaf 1149.4 17.805 1609 34.26 1592.5
leachate (Table IV). The difference between the amount of metal found by mass
balance calculations and that found experimentally in soil, especially for two years
treatment could be explained by one or more of the followings:
1. Precipitation of metal ions as insoluble salts.
2. Adsorption of heavy metals on the columns’ surfaces.
3. The variation in temperature during the experimental period.
Figure 1.
Electric conductivity (mmho cm−1) of the leachate versus date of experiment for the 20 yr
term treatment.
4. Conclusions
The two soils were found to have similar chemical and physical properties and thus
showed similar response to simulation experiments.
The nature of metal, soil properties and the metal loading level affected redistribution
of metals in soil. The three metals used showed cumulative effect on soil
and in leachate, and thus the possibility of groundwater contamination does exist.
The concentrations of these elements and other heavy metals should be reduced as
much as possible and industrial waste should be either separated or treated before
dumped in domestic wastewater.
The clay nature of soils and their high content of montmorollinites were responsible
for the formation of large and deep cracks due to wetting and drying
weather conditions. As a result, cation exchange between soil and running solution
was not allowed which reduces self-purification capacity of soil. Continuous
monitoring of wastewater, soil and groundwater qualities are essential for any
sustainable reuse of wastewater in Palestine.
Acknowledgements
Authors are thankful to An Najah N. University for financial support of the present
work.
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Water, Air, & Soil Pollution, Volume 146, Numbers 1-4 / June, 2003
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