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Chapter-4
Remediation of Heavy Metal Infested Coffee Growing Soils
4.1. Introduction
Accumulation of heavy metals in surface soils and their subsequent effects on
human health and environment is of greater concern in recent years. Mining related
wastes, such as waste rock and tailings represent potential sources of metals that can be
redistributed to the environment by aerial and fluvial transport. In addition, aerial
deposition of smelter emissions has lead to widespread contamination of surface soils at
various locations through out the world. Other industrial sources, such as foundries,
refineries, pesticides, paints and battery manufacturers are also known to be potential
sources o^ A}^\/y metal contamination in soils. Further, extensive use of fertilizers,
(ameliorate! and sew&ge sludge coupled with effluent irrigations has aggravated the
propensity of heavy metal contamination in agricultural soils. Among the metals, lead and
cadmium are of prime concern when they are present in alarming concentrations. Lead is
of specific concern due to its relative abundance at contaminated sitgs and its known
potential to cause adverse health effects in children (Davies,,aila Wixson, 1988) while
cadmium in soil represents a direct contact risk to both hurpan and ecological receptors
due to its relatively high toxicity and plant uptake (AT^©fC 1999)/^
Owing to the widespread distribution of lead and cadmium in soils resulting from
human activities, and the potential human and ecological risks posed by these metals, it
is desirable to develop cost effective remediation strategies for these metals. Metals in
contaminated soils are often present in chemical forms that exhibit varying degrees of
bioavailability to human and ecological receptors. As a result, there has been great
interest (particularly for lead-contaminated soils) for in situ remedial strategies that render
metals less bio-available, so that the metal-contaminated soil no longer represents an
unacceptable exposure risk. The bioavailability of metals in soils to ecological receptors is
often established by directly measuring uptake of metals into the receptor of interest
(e.g., plants or soil invertebrates). However, indirect methods, such as m^surement of
soil pore-water concentrations or diffusive gradients in thin films {D^yiiou et al., 2000) are
gaining acceptance as viable methods to estimate soil metal concentrations that are
115
available for biological uptake. The technologies available for remediation and rectification
are solidification/stabilization, vitrification, electro-kinetic remediation, soil flushing, phyto-
extraction, phyto-stabilization, and chemical stabilization. Each technology has benefits
and limitations, depending on the remedial objectives targeted and on site specific
factors. For example, at large-area sites with low to moderate levels of shallow
contamination, a plant-based (phyto-extraction or phyto-stabilization) or chemical
amendment strategy will be preferred. However, these technologies are often limited to
surface soils with low to moderate contamination. Further, for sites with contamination at
deeper horizons or high levels of contamination, a more aggressive remedial technology
would be efficient..^
In soils cropped to coffee, hitherto the extent of heavy metal contamination being
meager, of all the methods available for remediation, the chemical stabilization appears to
be more appropriate. In this method, application of various ameliorants such as lime,
phosphates, zeolites, apatites, glauconite, iron oxide material, compost have been tried
for remediation. Liming, presumably the most widely known amelioration in agriculture,
which is an age-old practice in coffee cultivation, decreases the mobility of heavy metals.
By virtue of reduced mobility of heavy metals owing to metal hydrolysis and / or co-
precipitation with applied carbonate in soils, consequently their uptake by the plants
would be drastically reduced/
Zeolites are crystalline, hydrated aluminosilicates of alkali and alkaline earth
cations that possess infinite three dimensional crystal structures. It occurs naturally in the
soils and as well could be synthesized in the laboratory. The use of zeolites for pollution
control depends primarily on its ion-exchange capabilities. Among the natural zeolites,
clinoptilolite, chabazite and phillipsite ha^^^^een evaluated as efficient ameliorants for
environmental cleanup (Tsitsishvilli^etal., 1992). Many studies have revealed that there
would be significant reductjpff in heavy metal accumulation in the plants upon application
of zeolites. Miineyev^et al. (1989) opined that soil application of zeolites would reduce Zn
content in barley tissues, and grain as well as Pb and Cd contents in strawberries and
cherries. Gworek (1^^) found significant reduction in the Pb and Cd contents of several
pot grown crops on amending polluted soils with synthetic zeolites. Similarly, Rebedea
116
and Le/p (1994) reported that synthetic zeolites added to a lead/zinc mine spoil and a soil
polluted with Cu and Cd reduced plant uptake of metal in pot s tud ies^
Phosphate salts are capable of immobilizing Pb in soils due to the low solubility of
lead orthophosphate complexes. Further Zn and Cd were precipitated upon application of
phosphatic compounds. Further, humus in the organic matter with enormous retention
capacity was found to attenuate most of the heavy metals under favourable conditions.
Other soil constituents such as the hydrous oxides of Al, Fe and Mn are known to retain
metals in soils. The enhanced sorption of metals by hydrous oxides may be attributed to
metal binding througjn^specific adsorption. The efficacy of hydrous iron oxide examined by
Mench et ai.'-f1^4) revealed substantial decrement of Cd and Pb contents in rye grass
besides stabilization of these metals in highly polluted %Q\\^^
Phyto-availability of the metals in soils depends on the form in which they are
present. Transformation of the accumulated metals depends mainly on the soil properties
like pH, organic matter content, clay type, CEC, CaCOs, oxides and hydroxides of Fe and
Mn. Based on primary accumulation mechanisms in soils and sediments, heavy metals
can be assorted into six categories: (i) water soluble, (ii) exchangeable, (iii) carbonate
bound, (iv) oxide bound, (v) organically bound and (vi) residual fractions (K^&h^fn et al.,
2007). Some of the forms are easily available for the plant uptake, while some are
available with slight difficulty where as some are unavailable and may become available
in course of^time as a result of natural processes taking place in the soil environment
(Forstp^r, 1985). Considering the mere total content of heavy metal is insufficient to
assess the impact of the contaminant as geochemical forms of heavy metals in soil are
dynamic and their solubility is bound to influence their bioavailability.^
A large number of extractants have been used to assess plant available trace
elements (Gupta and,Afen, 1993; He and^^ngh, 1993). Single extractants like weak
replacement of ion salts (MgCb, CaCl2, and NH4NO3), dilute solutions of either weak
acids (acetic acid) or strong acids (HCI, HNO3) and chelating agents (DTPA, EDTA) have
been tried. These single extractants either are able to release the metals that are
associated with exchange sites on the soil solid phase or form complexes with the free
metal ions in the solution; thereby reducing the activities of the free metal ion in solution^
117
Hence these extractants give only an indication about the total bioavailable metals in the
soil but do not represent the different geochemical forms of the metal. Unfortunately, most
available extractants are less specific than desired. Hence, more than one target site may
be attacked or the release from the target site may be less than the relevant^
Selective sequential extraction procedures have been commonly used for studying
the metal mobility and availability in soils. It involves treatment of soil with a series of
reagents in order to partition the trace element content. Improved phase specificity
is the claimed advantage of this method over the juie of single extractant. Numg r̂ous
extraction schemes have been described (Gupta and Chen, 1975; Stovei>efal., 1976;
Tessier etaf, 1979; Shumap'^87,
Clevengerand Mu\\\nsy^82)/^
With soil quality playing an important role and one of the prime prerequisites in
food production and quality, especially in certain export oriented products like coffee, it is
essential to employ the most efficient and cost effective remediation techniques for
contaminants in soils. To meet this challenge, a laboratory study was conducted to
evaluate the remediation of metals Wby several widely available soil ameliorants such as
lime, zeolites, phosphates fertilizers and compost with the following objectives;
(i) To determine the influence of ameliorants on the chemical form and bioavailability of
heavy metals and
(ii) To compare the efficacy of selected ameliorants as metal stabilizers in metal
induced contaminated soils.
118
4.2. Review of Literature
The concept of chemical remediation involves the use of generally unique and
conventional chemical amendments to induce specific chemical reactions within the soil
matrix that render the metal contaminants inert and/or immobile. These remedies involve
lower rates of amendment addition, which do not substantially alter the vital soil properties
such as bulk density, pore distribution, water holding capacity, permeability, volume,
aggregates and structure. Further, upon application of ameliorant to the soil, the
rhizosphere conditions would be modified to favour the growth of crop plants as well as
microbial biotaj/
A substantial amount of research has been conducted to evaluate the potential
efficacy of chemical stabilization technologies for the remediation of lead and cadmium in
soils. Majority of these studies are laboratory investigations particularly evaluating the
effects of phosphate amendments on lead solubility. Phosphate hasjong been known to
be effective at stabilizing lead, as demonstrated by Nria9wt^74). The concept is to
induce the formation of highly insoluble lead phosphate minerals that have a low
bioavailability, mobility and are stable under a variety of environmental conditions {R\pf
et al., 1994). A large body of research has shown that various forms of phosphate
amendments could be effective at stabilizing lead in soils (Berti and Cunrjjngham, 1997;
Boisson et aU
119
potentially be mitigated by the inclusion of iron (as hydrous ferric oxide) with the
phosphate amendment. Another concern is the effect of continual removal of phosphorus
due to plant growth. Hettiaracjaehf^nd Pierzynski (2002) concluded that plant removal of
phosphorus could reduce the effectiveness of phosphorus amendments on lead
bioavailability, unless sufficient excess was applied or if the phosphorus was added in
combination with manganese ox ide^
Other than phosphorus compounds, several amendments have been evaluated to
stabilize lead and cadmium in acidic soils. Municipal bio-solids are a potentially promising
chemical amendment due to their widespread availability and low cost. Condor et al.
(2001) demonstrated that lime-stabilized bio-solids were capable of immobilizing zinc in
smelter-impacted soils and reduced the eco-toxicity of the soils to earthworms. Lime, a
common soil amendment long used in agriculture, induces a rise in soil pH, causing
metals to precipitate as oxides and carbonates. Lime is anticipated to be effective only for
a relatively short period of time before the pH-buffering capacity is depleted; therefore,
repeated applications are often required (VangronsveLd and Cunningham, 1998). Lime
has been shown to be effective at reducing plant uptake of zinc, but mixed results have
been reported for plant uptake of cadmium (KretDspt-^f., 1998; Pierzynski,9rta Schwab,
1993). Lime was fairly ineffective for treatment of high-zinc-content soils from the
Palmerton Zinc Superfund site, unless the lime was combined withjthe high iron bio-solids
and applied as a phyto-stabilization strategy (Li and Chaney/1998). By virtue of reduced
mobility of heavy metals owing to metal hydrolysis and / or co-precipitation with applied
lime in soils, consequently their uptake by the plants would be drastically reduced
(Shuman, 1985; Kabata-Pendias and Pendias,>1-g§2). /^
Effect of application of manure and compost to contaminated soils on zinc
accumulation by Solanum nigrum inoculated with arbuscular mycorrhiza fungi in naturally
contaminated soils has been studied by Marques el-.at:^008). They found that organic
amendment like manure could induce a reduction in the amount of Zn leached through
the soil by about 70 - 80% by the combination of Solanum nigrum and organic
amendments. Jordaiy(^008) has reported the utilization of spent mushroom compost
(SMC) for the re-vegetation of lead - zinc tailings. Reduction of the contaminant
120
concentrations in the SMC treated soil was observed and growth of Lolium perenne was
facilitated in the amended so i l ^
Amendments that provide sorption sites that have a strong affinity for trace metals
have been shown to effectively stabilize lead and cadmium in soils by limiting the
soluble fraction of the metals in the soil matrix. Addition of iron and/or manganese in a
variety of forms (e.g., hydrous oxides, steel shot, steel sludge, furnace slag, and
zero-valent iron) has been shown to be effective at reducing the teachability,
bioaccessibility, and phytoavailability of lead, cadmium, and zinc (pert!' and
Cunningham, 1997; Chen ei-sfC 2000; Chlopecka ajjet^driano, 1997; Hetti^fat'hchi and
Pierzynsl^^02; Kre>8'et al., 1998; MenchjX^\r,^994; PierzypskTand Schwab, 1993;
Sappin-Didtep^ al., 1997; ShumaDr''t?r97). The ability of oxidesp.f Fe and Mn to
attenuate^ejattfc cations has long been demonstrated (Jeripe0968; Shumanĵ J.9S5;
McBrideyf994). The effectiveness of these materials could have been partly due to their
high alkalinity effects in soil and the highest association of metal with iron-manganese
oxide fraction (sp^ecific adsorption), which is pH dependent (Stanton and BLyigef̂ 1967;
Shuman, 1977)^
Zeolites and aluminosilicates have also been demonstrated to have a high
retention capacity for metala^and can be used as stabilizing agents (Boissdn jt.at:7i999a
Chlopecka and Adjjafio, 1997; Edwards, et al., 1999; Garcia-S^hez et al., 1999
Gwor^1992; Lothenbach &i^t^^997: Miinyev et al., 1990; Rebedda and Lepp, 1994
Vangronsveld and Cunningham, 1998). The stabilization of metals by zeolites can be
explained by its ion exchange capability and by its molecular structure. The molecular
structure strictly controls cage size in zeolites, which results in selective rempval of
cations from the soil solution even when present in trace amounts (Bfek, 1974).
Therefore, zeolites were considered as promising amelioraLntXin soils contaminated
especially with metallic cations because of their tendency to either become fixed in the
cage or adsorb on the zeolites surface (Leppert, 1990)^
Chlopecka and Adriano (1996) mimicked \n-siiu stabilization of metals in cropped
soils using several ameliorants. They concluded that lime; iron oxide, zeolites and apatite
file:///n-siiu
121
could significantly reduce the Zn concentration in tissues of 3-week-old maize, in mature
maize tissues (roots, young leaves, old leaves, stems, grain) and barley. The largest
reduction (over 80%) in Zn uptake by all crops was effected by Fe-rich, which was
consistent with the greatest reduction in soil-exchangeable Zn by this ameliorant. Similar
studies on inactivation of Pb conducted by Bertt-^d Cunningham (1997) revealed
significant changes in soil Pb chemistry, leached Pb from soil and Pb measured by a
physiologically based extraction test (PBET) after incorporation of inexpensive
ameliorants. Adhikari and ^ g h (2008) studied the remediation of cadmium pollution in
soils by different amendments using column method. In this study lime, phosphate, city
compost and gypsum were tried at different concentrations. An effective remediation of
Cd was achieved by lime, phosphate and combination of city compost with lime.
Combined application of lime and city compost reduced the movement of Cd in the soil
profile. It appeared that organic matter controls the sorption of Cd in soils and the amount
of Cd sorbed increased with increasing organic carbon content^
Heavy metal adsorption and their distribution upon coal fly ash and sewage sludge
amendment studied by Tripathy et al. (2005) revealed that amendments provided the
additional sorption sites for metals and consequently higher sorption affinity was
observed. Further, they opined that in acid soils with low metal retention capacity
application of amendments like sewage sludge likely to contain heavy metals
necessitates close monitoring of ground water as well as crops owing to high mobility of
metals. Sewage sludge with lower metal concentration and near neutral pH is more
appropriate for agricultural use on wide variety of soils owing to the favourable soil
reaction activating more organic constituents.
In addressing metal-contaminated soils, it is essential to estimate the bioavailability
of the metals that are hazardous. An approach commonly used for studying the mobility of
metals in soils is to use ,selective sequential extraction procedures such as- those
developed by Kashem'et al. (2007) or Tessier et al. (1979) or Shuman (1985).
The procedures, through the use of extractant of increasing strength, estimate the
distribution of metals among the water soluble, exchangeable, carbonate, oxide, organic
and residual fractions. Undoubtedly, the procedure is essentially operational with
122
adequate precautions initiated for specific reactions. It is erroneous to assume that the
nominal forms extracted from soil samples always represent the real situation. Thus,
metals supposedly associated with the carbonate fraction may be extracted with buffered
acetate solution, although soil pH condition may render it highly unlikely that carbonate
actually exist in soil being extracted. In these circumstances, it must be assumed that the
extracted metals are derived from non-carbonate sources that are impossible to specify.
Nevertheless, despite the errors of uncritical acceptance of results from sequential
extraction analysis, the procedure is still widely used because it is a useful first approach
in assessing the likelihood of mobilization and biological uptake of metals from the soil
Chemical stabilization is a relatively new technology particularly as a strategy to
reduce metal bioavailability in soils and thus seems to have limited application at the field
scale. In general, the field tests indicate that chemical amendments have the potential to
be effective in stabilizing lead, zinc, and cadmium in soils thereby reducing the mobility
and bioavailability of these metals. A major focus of research is the potential for the
amendments to reduce the mobility of metals in contaminated sites/ soilsr'
123
4.3. Materials and Methods
The materials used for remediation of heavy metal contaminated soils and the
methods adopted for the study is made available in this chapter. Coffee soils of RV
Nagar, Andhra Pradesh and Balehonnur, Chikmagalur District in Karnataka with
considerable variation in organic carbon, cation exchange capacity as well as oxides of
iron and manganese were used for remediation of lead and cadmium
4.3.1. Soils f . / i rlu4
124
of 0.5 - 2.0 mm with a CEC of 120 cmol kg"̂ and dominant in oxides of silicon (68.3%),
aluminum (13%) and calcium (4.1%) was obtained from Escott Zeolites, Australia. The
agricultural lime with a neutralizing value or calcium carbonate equivalent of 85 per cent
was opted for remediation. The compost with near neutral pH having C: N ratio of 12 was
utilized in the study. The potassium di-hydrogen orthophosphate an analytical reagent
was used as soluble phosphorus source to attenuate heavy metals^
4.3.3. Metal inoculation and remediation
To simulate the contaminated condition in soils, both Pb and Cd were
simultaneously introduced in the form of their respective nitrates. A critical concentration
of 100 ppm of each metal was maintained in two kg soil samples collected from both the
locations of Balehonnur and RV Nagar. Four ameliorants i.e., zeolites, agricultural lime,
potassium di-hydrogen orthophosphate (KH2PO4 AR grade) and compost were blended
with the soil separately at 1.5, 1.0, 0.5 and 1.0 per cent respectively. One absolute control
with no amendment was also maintained. Each treatment was maintained in three
replications and adequate precaution was taken to maintain the moisture content near to
field capacity so, ^s to facilitate amelioration process. Soils spiked with metals and
mieliorates^were incubated at room temperature (= 25 C) for 60 days. Meanwhile, soil
samples from each treatment were drawn at regular intervals of 15 days constituting a
total of four sets of samples. These were sequentially extracted for various forms of Pb
and Cd to assess their mobility and retention pattern in soils^
4.3.4. Sequential extraction
It is essential to estimate the bioavailability of the metals while addressing metal-
contaminated soils to arrive at valid conclusions as far as metal contamination is
concerned. An approach commonly used for studying the mobility of metals in soils is to
use selective sequential extraction procedures such as those developed by Kasfiem and
Singh (2001) or Tessiir et al. (1979) or Shuman (1985). The procedures, with the use of
extractant of increasing strength, estimate the distribution of metals among the water
soluble, exchangeable, carbonate, oxide, organic and residual fractions. A brief summary
125
of the most recent sequential extraction procedure developed by Kash^m and Singh
(2001) was adopted in the current study is highlighted in the following paragraph/^
Two grams of soil, (2 mm sieved) was placed in a 50 ml polycarbonate centrifuge
tube and the following extractions were performed sequentially.
• F1: Soil sample extracted with 20 mL of distilled water for 1 h at 20°C on a rolling
table. -Water soluble (WS) fraction/^
• F2: The residue from F1 extracted with 20 mL of 1 M NH4OAC, pH 7 for 2 h at 20°C
on a rolling table. -Exchangeable (EXC) fraction^
• F3: Residue from the F2 extracted with 20 mL of 1 M NH4OAC, pH 5 for 2 h at 20°C
on a rolling table. -Carbonate (CARB) bound fraction^
• F4: Residue from the F3 extracted with 20 mL of 0.04 M hydroxylamine hydrochloride
(NH2OH.HCI) in 25 per cent acetic acid (v/v) at pH 3, reaction time 6 h in a water bath
at 80°C with occasional shaking. -Oxide (OX) bound fraction^
• F5: Residue from F4 extracted with 15 mL of 30 per cent H2O2 (adjusted pH 2),
reaction time 5.5 h in water bath at 80°C, with occasional shaking. After cooling, 5 mL
of 3.2 M NH4OAC in 20 per cent (v/v) HNO3 was added; sample was shaken on a
rolling table for 0.5 h at 20°C and finally diluted to 20 mL with water. -Organics (OR)
retained tractiori/
• F6: Residue from F5 fraction, extracted with 20 mL of 7 M HNO3, reaction time was 6
h in a water bath at 80°C with occasional shaking. -Residual (RES) fraction
Sequential extraction and analysis were done in triplicate for each sample. Metals
present in different extracts were determined by atomic absorption spectrophotometer
(GBC 932A). The soil pH (1:1 soil water extract) was determined for each sample./
126
4.4. Results and Discussion
Results of remediation studies on heavy metals like lead and cadmium utilising
various ameliorants are briefly discussed in this section. A close perusal of data revealed
a general decrease in the mobile/ bioavailable fraction of lead and cadmium with time.
Further, the quantum of decrease in the bioavailable fraction in soils was hastened by the
application of ameliorants. Between the two metals, more of cadmium remained in the
labile pool compared to that of lead in both the soils. As far as soil vulnerability to the
metal contamination is concerned, the soils of Balehonnur remained more sensitive to
heavy metals compared to that of RV Nagar.̂
As with any remediation, the overall objective of chemical remediation approach
adopted in the current study is to create a final solution that assures protection of human
health and the environment. With scrupulous and scientific adoption of remediation
techniques, the possibilities of transport of contaminants from the polluted soil to the
agricultural products meant for human consumption could be effectively mitigated/^
Sequential extraction protocol not only gives the phytoavailable metal that need to
be effectively bridled to contain the contamination but also provides valuable implications
while selecting an appropriate ameliorant for remediation. In order to reduce the
phytoavailable fraction of a particular metal, the ameliorant should function in such a way
to enhance the non-labile pool constituting oxide bound, organically retained and residual
fractions at the cost of carbonate bound, exchangeable and water soluble fractions
forming labile pool. The ameliorants selected for the current study were found to work in
this particular mode. The zeolites were likely to enhance the oxide bound fraction while
potassium di-hydrogen orthophosphate would enhance residual fractions and similarly,
the compost would enhance the organic bound fractions in the soil. However, the mode of
action of agricultural lime would likely t o ^ both as a conditioner and as an ameliorant
under favourable soil reactions^
In acid soils, application of lime would trigger the activity of pH dependent charges
and in turn enhance the attenuation capacity of the soils. Soil clays saturated with
127
aluminium and hydrogen would be efficiently replaced for metal retention with the lime
application. Usually, the oxides of iron, aluminium and manganese as well as organic
matter are the major constituents likely to be influenced by the application of lime. In
neutral to alkaline conditions, the persistence of applied lime could be assured and the
possibility of metal retention in sparingly soluble carbonate form is bound to occur. This
would be a testimony for lime as an ameliorant besides an effective conditionej^-'^
4.4.1. Ameliorant attenuation efficacy
Distribution of lead among various forms such as water soluble, exchangeable,
carbonate, oxide, organic and residual fractions along with the pH observed over different
intervals in 1:1 soil-water extract of the soils of Balehonnur is depicted in Table 4.10.
Among these different fractions, invariably the water soluble and exchangeable forms are
considered to be phytoavailable. However, the carbonate bound fractions are also
considered to be phytoavailable depending on the rate of dissolution of carbonates and
the soil reaction. Normally under acidic conditions (pH < 7), existence of calcium
carbonate and retention of metals by it would be a rare phenomenon. Under such
conditions, it must be assumed that the extracted metal (so called carbonate bound
fraction) is derived from non-carbonate sources that are impossible to specify. Further,
this fraction considered to be phytoavailable and cumulated along with water soluble and
exchangeable fractions to arrive at labile or mobile pool of heavy metaL
Sequential extraction of soil samples drawn after 15 days of incubation revealed
the higher efficacy of ameliorants in containing the metal contamination compared to that
of control (Fig 4.10). In this case, cumulated fractions of water soluble, exchangeable and
carbonate bound forms of metal were assigned as phytoavailable and this formed the
very basis for comparison among the ameliorants with respect to their efficacy. Among
the different treatments involving versatile ameliorants, the lowest (12.9%) phytoavailable
lead was observed in the treatment which received KH2PO4 as ameliorant followed by
those of agricultural lime (27.1%), compost (29.3%) and zeolites (30.2%)
128
Table 4.10. Sequential extraction of Pb from lead induced Balehonnur soil at different incubation period after the treatment with different ameliorants
Treatment Lead Fractions (ppm) Total
Pb
Mobile Pool of
Pb, (%)
PH 1:1
Treatment Total
Pb
Mobile Pool of
Pb, (%)
PH 1:1
WS EX CARB OX ORG RES ppm
Mobile Pool of
Pb, (%)
PH 1:1
15 DAYS Control 1.21 5.79 26.25 14.59 7.60 40.96 96.40 34.50 4.4 Zeolite 1.02 5.17 23.55 13.04 9,80 45.78 98.36 30.20 4.5 Lime 1.97 1.73 22.62 14.06 10.40 46.52 97.30 27.10 6.7 KH2PO4 2.17 2.14 8.40 11.47 9.30 65.32 98.80 12.90 5.2 Compost 1.51 5.09 21.99 . 11.85 13.07 43.99 97.50 29.30 4.5 30 DAYS / ( Control 0.59 5.58 25.88 15.91 9.20 38.74 95.90 33.40 4.4 Zeolite 0.92 4.10 16.06 15.14 12.80 48.38 97.40 21.60 4.5 Lime 1.22 1.50 19.78 16.20 14.30 45.30 98.30 22.90 6.7 KH2PO4 1.74 1.86 7.41 13.62 11.40 61.57 97.60 11.30 5.2 Compost 0.84 3.29 19.46, 14.53 17.60 41.18 96.90 24.30 4 .5 . 45 DAYS 7 Control 0.43 2.89 22.30 22.25 12.70 34,98 95.50 26.80 4.5 Zeolite 0.66 3.64 14.10 24.46 13.80 42.04 98.70 18.60 4.4 Lime 0.47 1.43 17,80 18.56 15.20 44.44 97.90 20.10 7.0 KH2PO4 1.00 1.38 6,67 18.82 13.10 57.23 98.20 9.20 5.1 Compost 0.53 2.68 17,20 21.18 18.30 37.01 96.90 21.10 4.5 60 DAYS / Control 0.00 2.65 21,80 23.87 13.40 33.88 95.60 25.60 4.8 Zeolite 0.00 2.57 14,30 26.10 14.70 40.63 98.30 17.20 4.8 Lime 0.40 0.34 18,40 25.53 16.50 36.43 97.60 19.60 7.1 KH2PO4 0.85 0.39 5,55 29.04 14.80 48.17 98.80 6,90 5.4 Compost 0.00 2.24 17,65 26.40 19.80 31.21 97.30 20.40 4.8
WS - water soluble, Ex -Exchangeable, CARB ORG - Organically bound, RES - Residual
Carbonate bound.
However, the treatment not receiving any sort of ameliorant resulted in the highest
(34.5%) phytoavailable lead in the soils. The distribution of Pb into various fractions in
soils receiving no amendments i.e., 'Control' followed the sequence*Residual (42.5%)>'
Carbonate bound (27.2%) > Oxide bound (15.1%) > Organic bound (7.9%) >
Exchangeable (6.0%) > Water Soluble (1.3%) fraction. A similar trend was noticed in all
the treatments but with a lower carbonate bound Pb content in KH2PO4 treatment
compared to others. The range of various fractions in to which Pb speciation was found in
the soils treated with ameliorants was 45.1 - 66.1%, Residual, 8.5 - 23.9% Carbonate
129
bound, 11.6 - 13.3% Oxide bound, 9.4 - 13.4% Organic bound, 1.8 - 5.3% Exchangeable,
and 1.0 - 2.2% Water Soluble. The soil reaction remained acidic in all the treatments and
remained highest (6.7) in case of lime application followed by KH2PO4 (5.2), compost
(4.5) and zeolites (4.5), while the lowest (4.4) was in case of control̂ . '̂-'̂ ^
120
100
80
a 60
f 40 20 ma
Control Zeolite Lime KH2P04 Compost
Amendments
4 I
I Total Pb Available Pb pH
Fig. 4.10. Phytoavailability of lead fraction after 15 days of Incubation
The allocation of lead in to various fractions was quite different in the soils after 30
days of incubation. It was clear from the results that a part of the labile Pb was
transformed into non-labile form over m^time. The Residual fraction of Pb in the soils
receiving ameliorants ranged from 42.5 to 63.1%, Organically bound fraction from 11.7 to
18.2%, Oxide bound fraction from 14.0 to 16.5%, Carbonate bound fraction 7.6 to 20.1%,
Exchangeable fraction from 1.5 to 4.1% and Water Soluble fraction from 0.9 to 1.7% while
the corresponding Pb fractions in 'Control' were 40.4, 9.6, 16.6, 27.0, 5.8 and 0.6%
respectively. The sequence of distribution of lead into various fractions remained very
similar to that on the 15'̂ day after incubation. Fig 4.11 depicts the variation in
phytoavailable Pb with respect to the different amendments after 30 days of Incubation.
Among the various treatments involving competent ameliorants, the lowest (11.3%)
phytoavailable lead was observed in the treatment which received KH2PO4 as ameliorant
followed by those which received zeolites (21.6%), lime (22.9%) and compost (24.3%)^
130
120 _ 100 E 80 o. „ S 60 f 40
20
T 8
Control Zeolite Lime KH2P0^ Compost Amendments iy v
I Total Pb •Available Pb pH
Fig. 4.11. Phytoavailability of lead fraction after 30 days of incubation
However, the treatment not receiving any sort of ameliorant resulted in the highest
(33.4%) phytoavailable lead in the soils. In general, an overall reduction in phytoavailable
Pb over time is evident in all the treatments and also the conspicuous effect of
ameliorants in effectively bridling the contamination is indicated by the results. There was
no appreciable improvement in soil acidity and the measured pH values remained
unchanged in all the treatments over time/^
Control Zeolite Lime KH2P04 Compost Amendments
I Total Pb •Available Pb pH
Fig. 4.12. Pliytoavailability of lead fraction after 45 days of incubation
131
Sequential extraction of soil samples drawn after 45 days of incubation presented
more interesting features indicating gradual decrease in phytoavailable Pb contents with
the lapse of time (Fig 4.12). Among the different treatments involving versatile
ameliorants, the lowest (9.2%) phytoavailable lead was observed in the treatment which
received KH2PO4 as ameliorant followed by those of zeolites (18.6%), lime (20.1%) and
compost (21.1%). It was noticed that, the treatment not receiving any sort of ameliorant
(control) resulted in the highest (26.8%) phytoavailable lead in the soils. Further, there
was no much improvement in soil acidity except in case of lime application where pH
approached neutrality.
After 45 days of incubation, the distribution of applied Pb into different fractions in
the soils receiving amendments was more in non-labile pool compared to that in the
previous two samples drawn at 15 and 30 days after incubation. The Residual fraction of
Pb ranged from 38.2 to 58.3%, Organically bound fraction from 13.3 to 18.9%, Oxide
bound fraction from 19.0 to 24.8%, Carbonate bound fraction 6.8 to 17.8%, Exchangeable
fraction from 1.4 to 3.7% and Water Soluble fraction from 0.5 to 1.0% in soils which
received ameliorants while the corresponding Pb fractions in 'Control' were 36.6, 13.3,
23.3, 23.3, 3.0 and 0.5% respectively. The sequence of distribution of Pb into various
fractions was Residual > Oxide > Carbonate > Organic > Exchangeable > Water Soluble.
The perusal of the results shows that the oxide and organic fractions were enriched with
Pb contents at the cost of other fractions indicating the process of transformation of part
of the labile as well as residual Pb penetrating the structures of oxides and organic
compounds/
The trend of oxide and organic fractions being enriched with Pb at the cost of other
fractions was continued in the soils even after 60 days of incubation (Fig 4.13). Similar
sequence with slightly altered values compared to the previous cases was observed in
these samples. The Residual fraction of Pb ranged from 32.1 to 48.8%, Organically
bound fraction from 15.0 to 20.3%, Oxide bound fraction from 26.2 to 29.4%, Carbonate
bound fraction 5.6 to 18.9%, Exchangeable fraction from 0.3 to 2.6% and Water Soluble
fraction from 0.0 to 0.9% while the corresponding Pb fractions in 'Control' were 35.4, 14.0,
25.0, 22.8, 2.8 and 0.0 % respectively..
132
Control Zeolite Lime KH2P04 Compost Amendments
I Total Pb Available Pb pH
Fig. 4.13. Phytoavailability of lead fraction after 60 days of incubation
So with the lapse of time, the retention by oxides and organics has far
exceeded that of carbonates and the sequence of the distribution of Pb into different
fractions is in the order, Residual > Oxide > Organic > Carbonate > Exchangeable >
Water Soluble. Among the different ameliorants, the lowest (6.9%) phytoavailable lead
was observed in the treatment which received KH2PO4 as ameliorant followed by those of
zeolites (17.2%), lime (19.6%) and compost (20.4%). As usual, the treatment not
receiving any sort of ameliorant (control) resulted in the highest (25.6%) phytoavailable
lead in the soils. Further, there was slight improvement in soil acidity with highest pH (7.1)
being recorded in the treatment receiving lime application followed by that of KH2PO4
(5.4), while pH was 4.8 in all the other treatments which received zeolites, compost as
ameliorants and even in the 'control' receiving no ameliorates.
^AyV^r^^fXA^rtJ^'-
Differential allocation of lead among various fractions along with the pH observed
in 1:1 soil-water extract of the soils of RV Nagar is made available in Table 4.12. Under
neutral to alkaline conditions (pH>7), if not occurrence at least persistence of applied
calcium carbonate and retention of metals by it can not be overlooked. Under such
conditions, it must be assumed that the carbonate bound fraction is sparingly soluble and
relatively unavailable to the plants. After foreseeing the potential hazard likely to occur in
133
near future, it is prudent to incorporate the carbonate bound metal with water soluble and
exchangeable fractions to declare the labile or mobile pool of heavy metal^^
Table 4.12. Sequential extraction of Pb from lead induced R V Nagar soil at different incubation period after the treatment with different ameliorants^
Treatment Lead Fractions (ppm) Total Pb
ppm
Mobile Pool of Pb, (%)
PH 1:1 Treatment
WS EX CARB OX ORG RES
Total Pb
ppm
Mobile Pool of Pb, (%)
PH 1:1
15 DAYS Control 1.60 2.04 9.57 8.34 12.39 61.26 95.20 13.9 7.2 Zeolite 1.18 1.88 8.42 7.16 16.59 64.57 99.80 11.5 7.5 Lime 1.20 1.47 8.76 6.75 12.70 65.50 96.38 11.9 8.0 KH2PO4 1.20 1.91 6.86 5.46 12.73 69.04 97.20 10.3 6.9 Compost 1.52 2.15 7.22 8.27 13.84 62.60 95.60 11.4 7.6
30 DAYS f
Control 1.64 1.65 10.89 21.20 15.83 45.09 96.30 14.7 7.3 Zeolite 1.33 1.58 7.79 21.15 16.20 48.25 96.30 11.1 7.5 Lime 1.01 0.83 8.54 21.77 15.70 48.15 96.00 10.8 7.9 KH2PO4 0.59 1.35 7.88 16.70 14.72 56.06 97.30 10.1 6.8 Compost 0.79 1.4 8.31 19.48 18.20 48.60 96.78 10.8 7.6 45 DAYS f ^ Control 1.73 1.34 8.38 24.71 18.50 42.44 97.10 11.8 7.3 Zeolite 1.31 1.24 6.21 25.06 18.64 44.44 96.90 9.0 7.5 Lime 0.95 0.42 8.22/ 26.00 17.35 42.86 95.80 10.0 7.9 KH2PO4 0.27 1.00 5.25 19.51 16.82 53.55 96.40 6.8 6.9 Compost 0.55 1.30 5.55 24.39 20.22 44.79 96.80 7.6 7.6 60 DAYS ( ^ Control 0.66 1.06 8.91 25.30 18.64 40.63 95.20 11.2 7.5 Zeolite 0.10 0.38 7.50 26.26 19.27 43.79 97.30 8.20 7.7 Lime 0.56 0.37 7.69 30.14 19.62 39.42 97.80 8.80 8.1 KH2PO4 0.00 0.28 5.50 28.22 18.94 43.96 96.90 6.00 7.1 Compost 0.28 0.36 5.89 32.25 23.25 35.37 97.40/ 6.70 7.7
\NS - water soluble, Ex -Exchangeable, CARB - Carbonate bound, ORG - Organically bound, RES - Residual
134
Sequential extraction of soil samples drawn after 15 days of incubation revealed
the higher efficacy of ameliorants in containing the metal contamination compared to that
of control (Fig. 4.14). .
Control Zeolite Lime KH2P04 Compost Amendments v V
I Total Pb •Available Pb pH
Fig.4.14. Phyto-availability of lead fraction after 15 days of incubation
Among the different treatments involving versatile ameliorants, the lowest
(10.3%) phytoavailable lead was observed in the treatment which received KH2PO4 as
ameliorant followed by those of compost (11.4%), zeolites (11.5%) and agricultural lime
(11.9%). However, the treatment not receiving any ^oft (of ameliorant resulted in the
highest (13.9%) phytoavailable lead in the soils. In general, the phytoavailable Pb
remained lower in all the treatments compared to those of Balehonnur soils. The soil
reaction remained near neutral to alkaline in all the treatments and remained highest (8.0)
in soil amended with lime followed by compost (7.6), zeolites (7.5) and control (7.2); while
the lowest (6.9) was in case of treatment, which received KH2P04as amendment. A close
perusal of the data on the distribution of applied Pb in the treatments which received
different ameliorants revealed that the retention of lead in general followed the sequence
of residual fraction (64.7 - 71.0%) > organic (13.1 - 16.6%) > carbonate (7.1 - 9.1%) >
oxide (5.6 - 8.7%) > exchangeable (1.5 - 2.2%) > water soluble (1.2 - 1.6%) fractions
indicating a clear dominance of residual fraction. In the 'Control' which received only
applied Pb without any amendment the distribution of Pb in different forms was 64.3% i n ^ ^
135
Residual fraction, 13.0% in Organically bound fraction, 8.8% in Oxide bound fraction,
10.1% in carbonate bound fraction, 2.1% in Exchangeable form and 1.7% in Water
Soluble fraction, y^
The allocation of lead in to various fractions was quite different in the soils after 30
days of incubation. It was clear from the results that a part of the labile Pb constituting
both water soluble and exchangeable forms as well as non-labile Pb exclusively from
residual fraction were transformed to enrich oxide, organic and carbonate retained
fractions. The general sequence for the ameliorant treated soils was slightly modified
compared to the one observed in previous case with slight changes for residual fraction
(50.1 - 57.6%) > oxide (17.2 - 22.7%) > organic (15.1 - 18.8%) > carbonate (8.1 - 8.9%)
> exchangeable (0.9 - 1.6%) > water soluble (0.6 - 1.3%) fractions while these fractions
for the treatment 'control' were 46.8, 22.0, 16.4, 11.3, 1.7 and 1.7% respectively. The
lowest (10.1%) phytoavailable lead was observed in the treatment that received KH2PO4
as ameliorant (Fig 4.15)^^
120 100
f 80 a 60 f 40
20 ttm Control Zeolite Lime (^ KH2P04,€ompost
Amendments •4/'^
8.5
7.5
6.5
5.5
•Available Pb pH
Fig. 4.15. Phyto-availability of lead fraction after 30 days of incubation
Both agricultural lime and compost treated soils recorded similar (10.8%)
phytoavailable metal followed by that which received zeolites (11.1%); while the treatment
not receiving any sort of ameliorant resulted in the highest (14.7%) phytoavailable lead in
the soils. In general overall reduction in phytoavailable Pb over time was evident in all the
treatments except in 'control' indicating conspicuous effect of ameliorants in effectively
!36
bridling the contamination. There was no appreciable improvement in soil acidity as the
measured pH values remained unchanged in all the treatments over time.
Sequential extraction of soil samples drawn after 45 days of incubation presented
more interesting features indicating gradual decrease in phytoavailable Pb contents with
the lapse of time. The general sequence of distribution of Pb in various fractions for the
soils amended with different ameliorants remained same as that on the 30'̂ day after
incubation though the oxide and organic fractions were enriched with Pb contents at the
cost of other fractions. The residual fraction (44.67 - 55.5%) > oxide (20.2 - 27.1%) >
organic (17.4 - 20.9%)> carbonate (5.4 - 8.6%) > exchangeable (0.4 -1.3%) > water
soluble (0.3 - 1.4%) fraction were noted for the different treatments while the respective
fractions for the 'control' treatment were 43.7, 25.4, 19.1, 8.6, 1.4 and 1.8%. Among the
different treatments involving versatile ameliorants, the lowest (6.8%) phytoavailable lead
was observed in the treatment which received KH2PO4 as ameliorant followed by those of
compost (7.6%), zeolites (9.0%) and lime (10.0%).
However, the treatment not receiving any sort of ameliorant (control) resulted in the
highest (11.5%) phytoavailable lead in the soils (Fig 4.16). Further, there was no
appreciable change in soil reaction in different treatments with the lapse of time./
120 100
? 80 S 60 f 40
20 0 ton
Control Zeolite Lime (KH2P04 Compost Amendments"^^^>i^
8.5
7.5
6.5
5.5
I Total Pb •Available Pb pH
Fig. 4.16. Phyto-availability of lead fraction after 45 days of incubation
137
Similar trend of oxide and organic fractions being enriched with Pb at the cost of
other fractions was continued in the soils even after 60 days of incubation. Sequence
similar to that at 45 days after incubation was obtained with residual fraction
(36.3 - 45.4%) > oxide (27.0 - 33.1%) > organic (19.5 - 23.9%) > carbonate (5.7 -7.9%)
> exchangeable (0.3 - 0.4%) > water soluble (0 - 0.6%) fractions for the ameliorant
treated soils. The soil under the treatment 'Control' recorded 42.7, 26.6, 19.6, 9.4, 1.1 and
0.7% respectively for Residual, Oxide, Organic, Carbonate, Exchangeable and Water
Soluble fractions of Pb. Among the different ameliorants KH2PO4 resulted into the lowest
(6.0%) phytoavailable lead followed by those of compost (6.7%), zeolites (8.2%) and lime
(8.8%) that is depicted in Fig. 4.17. ^
I 80 Q. 60
Control Zeolite Lime i
138
Among the ameliorants, potassium di-hydrogen phosphate (KH2PO4) was found
most efficient in reducing the phytoavailable Pb in both the soils of Balehonnur (Fig 4.18)
and RV Nagar (Fig 4 . 1 9 ) ^
Control
LL Zeolite Lime
Amendments
I Available Pb (15 DAI) ••Available Pb (60 DAI)
Fig.4.18. Temporal variation of phytoavailable Pb wrt ameliorants in Balehonnur soils
16
_ 1 4
XI tt- 10
I 6 10
I' 0. 2 hM
Control Zeolite KH2P04 Lime KH2P0f Compost Amendments
• Available Pb (15 DAI) • Available Pb (60 DAI)
Fig.4.19. Temporal variation of phytoavailable Pb wrt ameliorants in RV Nagar soils
139
In Balehonnur soils, the phytoavallable Pb reduced from 12.9 to 6.9 per cent upon
incubation with KH2PO4 after 15 and 60 days, respectively. Similarly, in RV Nagar soils
the phytoavallable Pb reduced from 10.3 to 6.0 percent after 15 and 60 days,
respectively. Phosphate has long been known to be effective at stabilizing lead, as
demonstrated by Nriagti (1974). The concept is to induce the formation of highly insoluble
lead phosphate minerals that have a low bioavailability and mobility and are stable under
a variety of environmental conditions (Ruby et al., 1994). Current results were
substantiated by the predecessors who have shown that various forms of phosphate
amendments can be effective at stabilizing lead in soils (Berti and Cunningham, 1997
Boisso'n et al., 1999a, b; Chen et al., 1997; Cotter-Howells-fnd Caporn, 1996
Hettiarachchi apd Pierzynski, 2002; Ma^efal., 1993, 1995; Pierzynsl
140
their tendency to either become fixed in the cage or adsorb on the zeolites surface
(Lepp^, 1990y
The conspicuous dual role of agricultural lime as a conditioner as well as
ameliorant was proved in the current studies as evidenced by the impcovement in soil
acidity and retention of metals in the carbonate form. Lime was found a better alternative
next to that of zeolites in reducing the phytoavailable Pb in both the soils of Balehonnur
and RV Nagar. In Balehonnur soils, the phytoavailable Pb reduced from 27.1 to 19.6
percent upon incubation with lime after 15 and 60 days, respectively. Similarly, in RV
Nagar soils the phytoavailable Pb reduced from 11.9 to 8.8 percent after 15 and 60 days,
respectively. These attenuations may be attributed to the fact that by virtue of reduced
mobility of heavy metals owing to metal hydrolysis and / or co-precipitation with applied
lime in soils. Consequ,ently the phytoavailability of heaw^jnetals would be drastically
reduced (Shuman, 1985; Kabata-Pendias and Pendias, 1992). Lime, a common soil
amendment long used in agriculture, induces a rise in soil pH, causing metals to
precipitate as oxides and carbonates. Lime is anticipated to be effective only for a
relatively short period of time before the pH-buffering capacity is depleted; therefore,
repeated applications are often required (Vangronsveld and Strfimngham, 1998).^
'h f ̂ ^ Compost was found a better option in reducing the phytoavailable Pb in both the
soils of Balehonnur and RV Nagar. In Balehonnur soils, the phytoavailable Pb reduced
from 29.3 to 20.4 percent upon incubation with lime after 15 and 60 days, respectively.
Similarly, in RV Nagar soils the phytoavailable Pb reduced from 114 to 6.7»percapt after
15 and 60 days, respectively. Jordan et al. (2008) reports the HreneTicenJ effect of
application of spent mushroom compost (SMC) in reducing the metal contamination from
the lead-zinc contaminated site. Applicafioniof compost and organic manure to soils
naturally contaminated with zinc (^^^^^^3M^ reduce the zinc accumulation by
Solanum nigrum by 40 and 80% respectively as reported by Marques et al. (gD08). The
results of the present study are in agreement with these findings. Condor et al. (2001)
demonstrated that lime-stabilized bio-solids were capable of immobilizing zinc in smelter-
impacted soils and reduced the eco-toxicity of the soils to earthworms. This suggests that
141
the organic amendment in combination witti lime can reduce the phytoavailability of heavy
metals effectively.
In both the soils of Balehonnur and RV Nagar the over all rating of |meliorate§^for
their efficacy in attenuation of lead was in the order of KH2PO4 > Zeolites > Agricultural
lime > Compost^
4.4.2. Cadmium amelioration
Unlike lead, most of the cadmium remained in the labile or phytoavailable pool
despite amelioration in both the soils. The veracity of Cd contamination was higher in the
soils of Balehonnur compared to that of RV Nagai^X
Results pertaining to the assortment of cadmium among various forms such as
water soluble, exchangeable, carbonate, oxide, organic and residual fractions in the soils
of Balehonnur upon incubation for 60 days are made available in Table 4.13. In general,
the phytoavailable Cd fraction reduced with lapse of time. Sequential extraction of soil
samples drawn after 15 days of incubation revealed relatively higher efficacy of
ameliorants with some exceptions in containing the cadmium contamination compared to
that of control (Fig. 4.20). Among the different treatments involving versatile ameliorants,
the lowest (80.8%) phytoavailable cadmium was observed in the treatment which
received agricultural lime as ameliorant followed by that KH2PO4 (81.5%), Zeolite (86.6%)
and compost (86.9%). The maximum phytoavailable Cd (87.2%) was recorded in 'control"
where the soil did not receive any amendment/^
The retention of cadmium in 'Control' followed the sequence of exchangeable
(53.8%) > carbonate (31.1%) > organic (5.8%) > oxide (4.0%) > residual (2.9%) > water
soluble (2.4%) fractions. A similar trend was observed in all the amended soils also
except that for lime. In the agriculture lime amended soil, the sequence was Carbonate
(45.0%) >Exchangeable (35.6%) > Organic (8.6%) >Oxide (6.7%) > Residual (3.9%)>
Water Soluble (0.2%) fraction/'
142
Table 4.13. Sequential extraction of Cd from cadmium induced Balehonnursoil at different incuation period after the treatment with different ameliorants
Treatment Cadmium Fractions (ppm) Total
Cd
Mobile Pool of
Cd, (%)
pH 1:1 Treatment
Total Cd
Mobile Pool of
Cd, (%)
pH 1:1
WS EX CARB OX ORG RES ppm
Mobile Pool of
Cd, (%)
pH 1:1
15 DAYS Control 2.4 53.2 30.7 4.0 5.7 2.9 98.9 87.2 4.4 Zeolite 2.0 52.2 31.0 4.4 5.3 3.5 98.4 86.6 4.5 Lime 0.2 35.0 44.2 6.6 8.5 3.8 98.3 80.8 6.7 KH2PO4 1.7 37.8 38.0 5.7 8.1 3.8 95.1 81.5 5.2 Compost 1.6 45.0 40.1 4.5 5.2 3.3 99.7 86.9 4.5 30 DAYS Control 1.9 45.8 37.6 9.8 2.6 0.5 98.2 86.9 4.4 Zeolite 1.1 37.9 34.8 8.3 3.6 0.4 86.0 85.7 4.5 Lime 0.1 24.9 40.2 10.0 7.0 0.6 82.8 78.7 6.7 KH2PO4 0.5 36.0 31.1 11.0 5.6 0.5 84.8 79.8 5.2 Compost 0.6 39.4 33.5 9.1 2.2 0.5 85.3 86.2 4.5 45 DAYS Control 2.1 45.0 37.3 7.5 1.8 3.9 97.6 86.5 4.5 Zeolite 2.3 37.5 39.4 8.0 1.9 4.0 93.0 85.1 4.4 Lime 1.3 24.9 40.2 9.5 4.3 7.6 87.8 75.6 7.0 KH2PO4 1.8 29.4 34.7 9.0 4.5 5.4 84.8 77.8 5.1 Compost 2.2 40.0 32.5 6.5 2.5 3.3 87.0 85.9 4.5 60 DAYS Control 3.6 40.3 36.5 7.3 1.6 4.0 93.3 86.2 4.8 Zeolite 3.7 32.0 27.3 6.8 1.3 3.2 74.3 84.8 4.8 Lime 0.3 15.3 35.7 11.0 2.4 5.8 70.5 72.8 7.1 KH2PO4 1.9 20.5 30.3 10.7 2.5 4.7 70.6 74.6 5.4 Compost 3.2 38.3 31.1 8.3 2.2 2.2 85.3 85.1 4.8
WS - water soluble, Ex -Exchangeable, CARB - Carbonate bound, ORG - Organically bound, RES - Residual
The sorting of cadmium in to various fractions was quite different In the soils after
30 days of incubation. It is clear from the results that exchangeable and oxide bound
fractions were enriched at the cost of remaining fractions and the general sequence of
distribution of Cd into various fractions was slightly modified compared to the one
observed in previous case with exchangeable (46.6%) > carbonate (38.3%) > oxide
(10.0%) > organic (2.7%) > water soluble (1.9%) > residual (0.5%) fractions for the
treatment 'control'.
143
120
100
E «° S 60 •a O 40
20
0
b Control Zeolite Lime
Amendments
8 7 6 5
- 4 T 3
2 1 0
X a.
I Totaled [Available Cd PH
Fig. 4.20. Phyto-availability of cadmium fraction after 15 days of incubation
The agriculture lime treated soil had the higher carbonate bound fraction (48.6%)
than the exchangeable fraction (30.1%) followed by oxide (12.1%), organic (8.5%),
residual (0.7%) and water-soluble fractions (0.1%) while the soils under other
amendments followed the pattern exhibited by the treatment 'control'. Coming to the
various treatments involving competent ameliorants, the lowest (78.7%) phytoavailable
cadmium was observed in the treatment which received agricultural lime as ameliorant
followed by those of KH2PO4 (79.8%), Zeolites (85.7%), compost (86.2%) and control
(86.9%) as depicted in Fig. 4 . 2 1 ^
Fig. 4.21. Phiyto-availability of cadmium fraction after 30 days of incubation
144
Sequential extraction of soil samples drawn after 45 days of incubation presented
more interesting features indicating gradual decrease in phytoavailable Cd contents with
the lapse of time. It is evident from the results that the oxide, organic and residual
fractions were enriched with Cd contents at the cost of other fractions. The distribution
sequence of the Cd fractions sequence remained very similar to that observed on the 30"̂
day after incubation with exchangeable (46.1%) > carbonate (38.2%) > oxide (7.7%) >
residual (4.0%) > water soluble (2.2%) > organic (1.8%) fractions for 'Control'. Among the
different treatments involving versatile ameliorants, the lowest (75.6%) phytoavailable Cd
was observed in the treatment which received agricultural lime as ameliorant followed by
KH2PO4 (77.7%), zeolites (85.1%) and compost (85.9%) while the highest (86.5 %) was
reported in the 'control' as shown in Fig. 4 . 2 2 ^
120 T 8 100 -
£- 80 ^
a 60 'b-frVb -fa^ 4 ^ 0 40 20 iDXl | > 3 0 ' ^ ' ^ ' ^ ^ J ^ i 0
Control Zeolite Lime (KH2P04 ̂ Compost Amendments ^ • ^ j l / ' ^
^ H Total Cd ^ ^ Available Cd — -pH j
Fig. 4.22. Phyto-availability of cadmium fraction after 45 days of incubation
The typical trend of oxide fraction being enriched with Cd was continued in the
soils even after 60 days of incubation. The sequence of distribution of Cd in various
fractions was exchangeable (43.2%) > carbonate (39.1%) > oxide (7.8%) > residual
(4.3%) > water - soluble {3.9%) > organic (1.7%)) for the 'Control'. Except for lime and
KH2PO4 treated soils, the similar trend was observed. The carbonate fraction dominated
the exchangeable fraction in soils treated with lime and KH2PO4. Among the different
145
treatments involving versatile ameliorants, the lowest (72.8%) phytoavailable cadmium
was observed in the treatment which received agricultural lime as ameliorant followed by
KH2PO4 (74.6%), Zeolites (84.8%) and Compost (85.1%). 'Control', which did not receive
any amendment, recorded the highest phytoavailable Cd (86.2%) as shown in Fig. 4.23.
100 J J 8
iitifirl'i' Control Zeolite Lime Q KH2P04 ICompost
Amendments~V"*»^
^ H Total Cd ^ B i Available Cd pH
Fig. 4.23. Phyto-availability of cadmium fraction after 60 days of incubation
Differential allocation of cadmium among various fractions observed in the soils of
RV Nagar is made available in Table 4.14. In general, the phytoavailable Cd fractions
were lower in all the treatments compared to those of Balehonnur soils. The data
obtained from sequential extraction of the samples corresponding to the 15 days after
incubation revealed that the retention of cadmium in various fractions followed the
sequence of exchangeable (43.5%) > carbonate (36.5%) > organic (9.0%) > residual
(6.2%) > oxide (4.5%) > water soluble (0.3%) in the soil under the treatment 'Control',
which did not receive any amendment/'
The soils receiving Zeolites and agricultural lime as amendments had higher
carbonate fractions than the exchangeable fraction while the soils treated with KH2PO4
and compost exhibited portioning sequence similar to that of 'Control'. The variation in
phytoavailable Cd in soil samples drawn after 15 days of incubation with respect to the
different ameliorants is presented in Fig. 4.24/
146
Table 4.14: Sequential Extraction of Cd from cadmium induced R V Nagar soil at different incubation period after the treatment with different ameliorants
^
Treatment Lead Fractions (ppm) Total
Cd
Mobile Pool of Cd, (%)
PH 1:1
Treatment Total Cd
Mobile Pool of Cd, (%)
PH 1:1 WS EX CARB OX ORG RES ppm
Mobile Pool of Cd, (%)
PH 1:1
15 DAYS Control 0.3 38.5 32.3 4.0 8.0 5.5 88.6 80.2 7.2 Zeolite 0.2 27.9 29.5 4.4 10.4 5.6 78.0 73.8 7.5 Lime 0.1 23.5 35.3 6.1 8.3 4.9 78.2 75.3 8.0 KH2PO4 0.2 39.7 30.2 5.8 9.2 5.1 90.2 77.7 6.9 Compost 0.2 31.7 29.6 4.5 10.8 5.9 82.7. 74.4 ,- 7.6 30 DAYS c r r—
Control 0.5 36.8 38.9 14.5 4.9 0.9 96.5 79.0 7.3 Zeolite 0.3 22.7 33.9 19.2 4.8 0.9 81.8 69.6 7.5 Lime 0.2 21.1 42.1 15.8 6.0 1.1 86.3 73.5 7.9 KH2PO4 0.4 30.9 35.3 15.9 4.8 0.8 88.1 75.6 6.8 Compost 0.4 22.0 35.4 16.6 4.8 1.1 80.3 , 72.0 , 7.6 45 DAYS
147
Control Zeolite Lime fKHaPO^ Compost Amendment
I Total Cd I Available Cd pH
Fig. 4.24. Phyto-availability of cadmium fraction after 15 days of incubation
The ameliorating efficacy of the different ameliorants used after/1h^30 days of
incubation is depicted In Fig 4.25. The lowest (69.6%) phytoavailable cadmium was
observed in the treatment which received zeolites as amellorant followed by compost
(72.0%), agriculture lime (73.5%), and KH2PO4 (75.6%). Obviously, the treatment not
receiving any sort of amellorant (control) resulted in the highest (79.0%) phytoavailable
cadmium in the soils. In general, overall reduction In phytoavailable Cd over time was
evident in the treatments that received zeolites and compost as amendments
The sorting of cadmium In to various fractions was quite different in the soils after
30 days of Incubation. The results showed that enriching of oxide and carbonate bound
fractions at the cost of remaining fractions had taken place. The sequence of distribution
of Cd in to various forms was slightly modified compared to the one observed for samples
drawn after 15 days of incubation. The distribution of Cd in to various forms for the
'Control' sample was in the order, carbonate bound (40.3%) > exchangeable (38.1%) >
oxide bound (15.0%>) > organic bound (5.1%) > residual (0.9%) > water-soluble (0.5%).
The similar trend was noticed in all the amended soils also.
Sequential extraction of soil samples drawn after 45 days of incubation
indicated gradual decrease In phytoavailable Cd contents with the lapse of time. It was
evident from the results that the oxide, organic and residual fractions were enriched with
Cd contents at the cost of other fractions. Samples drawn from the treatment which did
148
not receive any ameliorant (control) exhibited a sequence of distribution of Cd into various
fractions which was similar to that observed for the samples drawn after 30 days of
incubation i.e., carbonate (40.4%) > exchangeable (36.9%) > oxide (13.4%) > organic
(7.2%) > residual (1.6%) > water soluble (0.6%) fractions. Though the quantities varied,
the distribution pattern of Cd into various fractions was similar in 'control' as well as
amended soils/
ikm 8.5 8 7.5 7 I
^ 6.5 a-- 6 ' 5.5 f 5
Control Zeolite Lime KH^P04 Compost Amendments P L f - ^ * -I 5 Control Zeolite Lime KH2P04 Compost
Amendmenta^V?' sjy ^IHTotal Cd c : i3 Available Cd pH
Fig. 4.26. Phyto-availability of cadmium fraction after 45 days of incubation
149
The sequential extraction of the soils from 'Control', sampled after 60 days of
incubation showed an increase in carbonate bound, oxide bound and organically bound
Cd fractions over those in the 45"̂ day sampled soils. The general sequence of
distribution of Cd into different fractions was carbonate (41.6%) > exchangeable (35.3%)
> oxide (14.2%) > organic (7.9%) > residual (0.8%) > water soluble (0.2%) fractions for
'Control' and all other amended soils except that for zeolites amended soils. The zeolites
amended soils showed slightly higher carbonate bound Cd fraction over the
exchangeable form. Lowest (65.1%) phytoavailable cadmium was observed in the
treatment which received zeolites as ameliorant followed by compost (67.8%), agricultural
lime (69.1%) and KH2PO4 (73.4%). Highest (77.1%) phytoavailable cadmium was
recorded in the treatment (control) not receiving any sort of ameliorant (Fig. 4.27)^
100
I 60 Q.
^ 4 0 +
" 20 +
Control Zeolite Lime ^$H2P04 Amendments
I Total Cd I Available Cd pH
Fig. 4.27. Phyto-availability of cadmium fraction after 60 days of incubation
In general, chemical amelioration with agriculture lime was efficient for reducing
the phyto-available cadmium concentrations for soils with pH < 7 while Zeolite was
efficient in bringing down the contamination levels of Cd in soils with higher pH (>7). As
far as cadmium attenuation with agricultural lime as an ameliorant is concerned the
phytoavailable Cd reduced from 80.8 to 72.8 percent in Balehonnur soils over a period of
15 to 60 days after incubation (Fig. 4.28)^^^
150
J 85
1 70
Control Zeolite V h l
Lime , KH2P04^ Compost Amendments 'V__JB^ ' -^ '
Fig.4.28. Temporal variation of phytoavailable Cd wrt ameliorants in Balehonnur soils
Cadmium immobilization with lime may be attributed to tlie metal hydrolysis and /
or co-precipitation with applied lime in soils. Consequently the phytoayailability of heavy
metals would be drastically reduced (ShLupaffT 1985; KabatShPendias and Pendias,
1992). Similar results where lime has been found to be effective at reducing plant uptake
of zinc, but mixed results have been reported for plant uptake of cadmium (Krebs et-al-T
1998; Pierzyn^kr^nd Schwab, 1993).^^
KH2PO4 as an ameliorant could reduce the phytoavailability of Cd from 81.5 to
74.6% in these soils. As reported by different workers Cd was precipitated upon
application of phosphate compounds (Brude^pld et al., 1963; lngrajjj.^t al., 1992; Xy-and'
Schwar tz^ 994) and generally, the precipitation reactions were of lower magnitude
entirely dependent on prevailing soil conditions as well as sufficiency of gestation period.
The similar reactions might have resulted in lower attenuation of c a d m i u m ^
In the soils of R V Nagar phytoavailable cadmium content was reduced from 73.8
to 65.0% in Zeolites treated soil followed by Compost which resulted into a reduction of
phytoavailable Cd from 74.4 to 67.8% during the same period of incubation (Fig. 4 .29 ) . ^
151
^ 90 -1
^ 85
^ 80 .
i 75
^ 70 TO
o % 65 ^ 60 ^
L h k ^ Compost
^ 90 -1
^ 85
^ 80 .
i 75
^ 70 TO
o % 65 ^ 60 ^ Control Zeolite Lime /KH2F04
Amendments — v ' ' v ^ ^ Compost
^ 90 -1
^ 85
^ 80 .
i 75
^ 70 TO
o % 65 ^ 60 ^
• Available Cd (15 DAI) • Available Cd (60 DAI)
^ Compost
Fig.4.29. Temporal variation of phytoavailable Cd wrt ameliorants in R V Nagar soils
Present results are well supported by the previous works where zeolites and
aluminosilicates have been demonstrated to have a high retention capacity for metals and
can be used as stabilizing agents (Boisson'et al., 1999a; Chlopecl
152
The efficacy in attenuation of lead by the amelioratives was in the order of
KH2PO4 > Zeolites > Agricultural lime > Comoost fpr.bpth the soils of Balehonnur and RV
Nagar. However, the sequence of(^mellorate^ varied in attenuating cadmium in both the
soils. In Balehonnur soils the sequence with Lime > KH2PO4 > Zeolites > Compost was
effective in amelioration of cadmium while a slightly different sequence was observed for
that in R V Nagar soils with Zeolites > Compost > Lime > KH2P04^
Summary
Soils cropped to coffee receive heavy doses of chemical fertilizers, rock
phosphates and processed municipal sewage wastes and thus likely to be contaminated
with heavy metals like lead and cadmium metals. These metals when present in excess in
soils are bio-available and also can be leached to nearby water sources causing potential
toxicity to(pante)and/or animals. This study evaluated the possibilities of remediation by
means of chemical amendment approach to immobilize these potentially dangerous
elements in soils thereby decreasing their availability to plants. A soil incubation study for
over 60 days was carried out in two different coffee soils (pH 5.6 and 7.2) by amending
them with Potassium di-hydrogen orthophosphate, agricultural lime, zeolite and compost^
It was found that all these chemical amendments were effective in stabilizing lead
and cadmium metals in coffee soils with different efficacies. Potassium di-hydrogen
orthophosphate was the most effective chemical in attenuating lead in coffee growing
soils followed by Zeolite, agricultural lime and compost. In the case of cadmium,
agricultural lirne was superior to other amendments in moderately acidic soils (pH-5.6)
while Zeolite^ was found to be more effective in slightly higher pH (7.2) soils in
attenuating cadmium. All the amendments reduced the bioavailability of both lead and
cadmium. Chemical reaction between the phosphate and lead possibly resulted in the
formation of lead pyromorphites similar to highly insoluble lead phosphates thereby
decreasing its bioavailability in soils. The carbonate content in the agricultural lime also
seemed to play a key role in the chemical stabilization of both lead and cadmium in the
soils and helped consequently in decreased availability of these metals,/