ENVIRONMENTAL RESTORATION of METALSCONTAMINATED SOILS - CHAPTER 5 potx

The remediation techniques of chemical treatments include adding some chemical material into the polluted soils to reduce the concentration of Cd and Pb in the soil solution, such as lim

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5

Chemical Remediation Techniques for the Soils Contaminated with Cadmium and Lead in Taiwan

Zueng-Sang Chen, Geng-Jauh Lee, and Jen-Chyi Liu

CONTENTS

5.1 Introduction 93

5.2 Materials and Methods 94

5.2.1 The Contaminated Sites 94

5.2.2 Analysis of Basic Soil Properties 95

5.2.3 Treatments in Pot Experiments 95

5.2.4 Bioavailability to Wheat 96

5.2.5 Sequential Fractionation of Heavy Metals in Soils 96

5.2.6 Statistical Analyses 96

5.3 Results and Discussion 96

5.3.1 Cd and Pb Concentration Extracted by Different Reagents in Untreated Soils 96

5.3.2 Changes on the Bioavailability of Cd and Pb after Chemical Treatments 97

5.3.3 Transformation of Chemical Forms of Cd and Pb in the Amended Soils 98

5.3.4 Effect of Chemical Treatments on the Concentration of Cd and Pb Uptake by Wheat 102

5.4 Conclusions 102

Acknowledgments 103

References 103

5.1 Introduction

Soils can be regarded as a major sink of heavy metals that were discharged from different kinds of anthropogenic pollution sources (Nriagu, 1991; Mench et al., 1994) Once heavy metals were released and adsorbed by the soil, most would be persistent because of their fairly immobile nature Cadmium is known to be more mobile and bioavailable than most other heavy metals, but lead is demonstrated to be fairly immobile and unavailable for plant uptake in soil systems Lead deposited on the surface of plant tissue can be of concern (Adriano, 1986)

Many researchers have indicated that agricultural soils contaminated by heavy metals may result in foliar damage, reducing growth yield of crops Heavy metals in soils may

4131/frame/C05 Page 93 Friday, July 21, 2000 4:56 PM

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94 Environmental Restoration of Metals–Contaminated Soils

also be taken up by crops and adversely affect the human health through the food chain (Alloway, 1990)

Several methods have been used to immobilize metals present in contaminated soils One general chemical technique is to apply dolomite, phosphates, or organic matter residues into the polluted soils to reduce the soluble metal concentration by precipitation, sorption,

or complexation (Impents, 1991; Mench et al., 1994; Chen and Lee, 1997) Different soil remediation techniques including engineering, chemical, and biological treatments were proposed and tested to remediate these two contaminated cadmium and lead sites in northern Taiwan (Wang et al., 1989; Chen et al., 1992a; 1992b; Chen, 1994; Chen et al., 1994; Lee and Chen, 1994; Lo and Che, 1994; Wang et al., 1994; Cheng, 1996; Chen and Lee, 1997) Based on economic assessment, engineering and chemical remediation techniques are most efficient and save time for changing the land uses of contaminated sites (Chen et al., 1994) The most effective remediation techniques of the engineering method are removing the polluted surface soils and replacing them with uncontaminated soil Then, the removed contaminated soils can be washed with some chemical extractants or chelating reagents (Chen et al., 1994) The remediation techniques of chemical treatments include adding some chemical material into the polluted soils to reduce the concentration of Cd and Pb in the soil solution, such as lime material, manure or composts, phosphate materials, and hydrous iron and manganese oxides (Mench et al., 1995; Chen and Lee, 1997; Chen et al 1997) The application of lime materials can significantly reduce the solubility of heavy metals in contaminated sites (McBride and Blasiak, 1979; McBride, 1980; Sommers and Lindsay, 1979; Kuo et al., 1985; Liu et al., 1998) Some reports also indicated that the appli-cation of hydrous iron or manganese oxides in contaminated soils could reduce the concen-tration of Cd or Pb in the soil solution (McKenzie, 1980; Kuo and McNeal, 1984; Tiller et al., 1984; Khattak and Page, 1992; Mench et al., 1994) High quantity applications of phosphate

in polluted soils also can reduce the solubility of zinc in the soil solution by precipitation (Bolland et al., 1977; Saeed and Fox, 1979; Barrow, 1987) Some vegetation species, flowers, and trees planted in the polluted soils are also effective in removing the heavy metals from the sites (Lee and Liao, 1993; Lee and Chen, 1994)

The objectives of this chapter are (1) to evaluate the effects of different chemical remedi-ation treatments on the reduction of Cd and Pb soluble in the soils, and (2) to evaluate their bioavailability for wheat grown in the contaminated soils

5.2 Materials and Methods

5.2.1 The Contaminated Sites

Two rural soils, Chunghsing clayey soil (including sites A and B) and Chaouta sandy soil (including sites C and D), were selected from contaminated sites irrigated with discharged water from chemical plants in northern Taiwan (Chen, 1991) The total area of contami-nated sites in these two regions is about 100 ha

The mean total cadmium concentrations of brown rice and soils in these two sites are 1.49

to 2.99 mg/kg and 4.7 to 378 mg/kg and mean total lead concentrations of brown rice and soils are 1.13 to 8.37 mg/kg and 25.8 to 3145 mg/kg, respectively (Lu et al., 1984; Chen, 1991) These two sites were designated as contaminated sites by the Taiwan government in

1984 because the concentration of Cd in brown rice was higher than the critical health con-centration of Cd of 0.5 mg/kg issued by Department of Health of Taiwan

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Chemical Remediation Techniques for the Soils Contaminated with Cadmium and Lead 95

5.2.2 Analysis of Basic Soil Properties

The particle size distribution of polluted soils was determined by the pipette method (Gee and Bauder, 1986) Soil pH value was determined by a glass electrode in a soil/water ratio

of 1:1 and a soil/1 M KCl ratio of 1:2.5 (McLean, 1982) Total organic carbon content was determined by the Walkley-Black wet combustion method (Nelson and Sommer, 1982) Exchangeable cations (K, Na, Ca, and Mg) and cation exchangeable capacity (CEC) were exchanged by ammonium acetate (pH 7) (Thomas, 1982) The percentage of base saturation (BS%) was calculated by the sum of exchangeable cations divided by CEC The basic soil properties of these four sites are shown in Table 5.1

Based on the databases of the heavy metals in rural soils of Taiwan, sites A and B are only moderately contaminated with Cd, but sites C and D are seriously contaminated with

Cd and Pb The bioavailability concentrations of Cd and Pb in polluted soils were deter-mined by different extraction solutions, such as distilled water by shaking 2 h, 0.1 M HCl

by shaking 1 h (EPA/ROC, 1991), 0.005 M DTPA (pH 5.3) by shaking 1 h (Norvell, 1984), and 0.05 M EDTA (pH 7.0) by shaking 1 h (Mench et al., 1994) Then the extraction solution was filtered with Whatman no 42 filter paper and 0.45 µm Millipore filter paper The con-centrations of Cd and Pb in the extraction solution were determined by flame atomic absorption spectroscopy (Hitachi 180-30 type) Total concentration analysis of Cd and Pb in the polluted soil was digested with concentrated HCl and HNO3 (3:1, v/v) and filtered with Whatman no 42 filter paper and 0.45 µm Millipore filter paper, then the concentrations of

Cd and Pb also determined by flame atomic absorption spectroscopy (Hitachi 180-30 type) (EPA/ROC, 1991)

5.2.3 Treatments in Pot Experiments

Seven chemical treatments were used to compare and evaluate the remediation techniques for soils from the two contaminated sites Five hundred grams of soils were treated as fol-lows and placed in polyethylene pots The treatments included (1) liming with calcium car-bonate to increase soil pH to 7.0, (2) applying high phosphate of 10 g P/500 g soils, (3) applying 2% composts, (4) applying 1% iron oxide, (5) applying 1% manganese oxide, (6) applying 1% zeolite, and (7) maintaining a control treatment Each treatment was repli-cated three times The treated and controlled soils were incubated for 2 months at room temperature and field capacity Wheat (Triticum aestivum) was planted in the treated soils

to evaluate the effectiveness of the chemical treatments on uptake of Cd and Pb Plants were harvested after 1 month

TABLE 5.1

The Physical and Chemical Properties of Four Contaminated Soils

Saturation

From Lee, G J., The Assessment of Remediation Techniques by Chemical Treatments for Soils Contaminated with Cadmium and Lead, Master’s thesis, Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, 1996 With permission

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5.2.4 Bioavailability to Wheat

Several extractants were used to extract the concentration of heavy metals for prediction of bioavailability of metal in the polluted soils (Lakanen and Ervio, 1971; Norvell, 1984) The changes of the bioavailable concentration of Cd and Pb are extracted and evaluated with different extraction reagents including distilled water, 0.1 M Ca(NO3)2 (Mench et al., 1994), 0.05 M EDTA (pH 7.0) (Norvell, 1984), 0.43 M HOAC (Mench et al., 1994), and 0.1 M HCl (EPA/ROC, 1991) Changes in the forms of heavy metals in the polluted soils before and after chemical treatments were used to compare the differences among chemical treatments The extraction solution was filtered by Whatman no 42 filter The concentration of Cd and

Pb was determined by the atomic adsorption spectrophotometer (Hitachi 180–30 type) The harvested samples of wheat were dried at 60°C for 2 days and digested with concen-trated sulfuric acid mixed with perchloric acid The concentration of Cd and Pb in the digestion solution was determined by atomic adsorption spectrophotometer

5.2.5 Sequential Fractionation of Heavy Metals in Soils

To evaluate chemical forms of heavy metals in treated contaminated soils, a sequential extraction technique based on the method of Mench et al (1994) was used Briefly, the sequential fraction procedure was performed in four steps with the assumption that the four chemical forms of metals existing in the contaminated soils were (1) water soluble, exchangeable, weakly bounded to organic matter, carbonate fractions, extracted with 0.11 M acetic acid (HOAC) and shaken for 16 h; (2) occluded Fe or Mn oxide fraction, extracted with 0.1 M hydroxyl ammonium chloride (HONH3Cl) and shaken for 16 h; (3) organically bound and sulfide fraction, extracted with 1 M ammonium acetate and shaken for 16 h; and (4) structurally bound in residual fraction, digested in 3:1 v/v 12 M

HCl and 14 M HNO3 (aqua regia) All extracts were stored in polyethylene tubes and retained at 4°C for analysis The concentration of Cd and Pb in these fractions of soils was determined by atomic absorption spectrophotometer

5.2.6 Statistical Analyses

The analysis of variance and significant differences of concentration of Cd and Pb in the dif-ferent chemical treatments for four polluted soils was performed by SAS (SAS, 1982) The statistical significance was defined at p <0.10

5.3 Results and Discussion

5.3.1 Cd and Pb Concentration Extracted by Different Reagents in Untreated Soils

The concentrations of Cd and Pb in these four contaminated soils extracted with different extraction reagents are shown in Table 5.2 Results indicated that the most serious contam-inated site was site D with sandy soils showing the highest concentration of Cd (18.6 mg/kg) and Pb (611 mg/kg) (Table 5.2) For the clayey soils, site A is a more seriously pol-luted site (5.47 mg/kg total Cd and 39.2 mg/kg total Pb) than site B

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5.3.2 Changes on the Bioavailability of Cd and Pb after Chemical Treatments

An index of the bioavailability of heavy metals in these polluted soils can be evaluated by different extractants, such as distilled water, 0.1 M Ca(NO3)2, 0.05 M EDTA (pH 7.0), 0.43 M

HOAC, and 0.1 M HCl Results of pot experiments in these soils indicate that the decreas-ing sequences for different chemical materials to reduce the extraction concentration of Cd

in these polluted soils are, at first, calcium carbonate, manganese oxide, or zeolite, and then composts based on the concentration extracted by EDTA (p <0.10); there are no effects on the other chemical treatments (Table 5.3) These results support some other papers that indicated that the application of lime materials can significantly reduce the solubility of Cd

in soil solutions (McBride and Blasiak, 1979; Sommers and Lindsay, 1979; McBride, 1980; Christensen, 1984; Kuo et al., 1985; Mench et al., 1994; Liu et al., 1998) These results also support results that the application of hydrous iron or manganese oxide materials can sig-nificantly reduce the solubility of Cd in the soil solutions (McKenzie, 1980; Kuo and McNeal, 1984; Tiller et al., 1984; Fu et al., 1991; Khattak and Page, 1992; Mench et al., 1994; Lee, 1996) In this study of Taiwan polluted sites, control of soil pH is a key factor to control the extractability (or bioavailability) of Cd in clayey or sandy polluted soils

The decreasing sequence of different methods to reduce the extraction concentration of Pb

in these polluted soils consists of manganese oxide, calcium carbonate, or zeolite based on the concentration extracted by Ca(NO3)2 or HOAC (p <0.10), and there are no effects for the other chemical treatments (Table 5.4) These results support the results that the application

of lime materials can significantly reduce the solubility of Pb in the soil solutions of contam-inated sites (McBride and Blasiak, 1979; McBride, 1980; Sommers and Lindsay, 1979; Kuo et al., 1985; Mench et al., 1994; Lee, 1996) These results also support results that the application

of hydrous iron or manganese oxide materials can significantly reduce the solubility of Pb

in the soil solutions (McKenzie, 1980; Kuo and McNeal, 1984; Tiller et al., 1984; Khattak and Page, 1992; Mench et al., 1994; Lee, 1996) These results also support results that the appli-cation of zeolite can significantly reduce the solubility of Pb in the soil solutions (Gworek, 1992) In this study of Taiwan polluted soils, application of hydrous manganese

TABLE 5.2

Cd and Pb Concentration in Soils Extracted by Different Single Solutions for Four Contaminated Soils before Chemical Treatments

(mg/kg)

Cd

Pb

located at Tatan contaminated site ND: not detectable.

From Lee, G J., The Assessment of Remediation Techniques by Chemical Treatments for Soils Contaminated with Cadmium and Lead, Master’s thesis, Graduate Institute of Agricultural Chemistry, National Taiwan Uni-versity, Taipei, 1996 With permission

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oxides is also another key factor to control the extractability (or bioavailability) of Pb in clayey or sandy polluted soils

5.3.3 Transformation of Chemical Forms of Cd and Pb in the Amended Soils

The changes of sequential fractions of Cd and Pb in soils B and D after chemical treatments in

2 months are shown in Figure 5.1 and 5.2 (the results of site A and site C are not shown here)

TABLE 5.3

Cadmium Concentrations Extracted by Single Extractant for Four Soils Treated with Different Chemical Materials

Cd Concentrations in Single Extraction Solution

(mg/kg)

Site A after 2 Months

Site B after 2 Months

Site C after 2 Months

Site D after 2 Months

different FO: iron oxides; MO: manganese oxides; ND: not detectable.

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Results from sequential fractionations of metals indicate that Cd in polluted soil B can be transformed to Fe-, Mn-bound, or residual forms from soluble forms after these chemical treatments (Figure 5.1), but Pb in polluted soil D can be transformed to Fe- and Mn-bound forms, or organic compound bound forms from soluble or residual forms after these chem-ical treatments (Figure 5.2) These results also indicate that Cd and Pb in the available (or soluble) form in the contaminated soils can be significantly transformed into fixed (or unavailable) forms after these chemical treatments, especially when treated with man-ganese oxide, lime material, or zeolite applied with 1% of these materials (p < 0.10)

TABLE 5.4

Lead Concentration Extracted by Different Single Solution for Four Soils Treated with Different Chemical Materials

Pb Concentrations in Single Extraction Solution

(mg/kg)

Site A after 2 Months

Site B after 2 Months

Site C after 2 Months

Site D after 2 Months

(p <0.10) Treatments: FO: iron oxides; MO: manganese oxide; Liming: applying calcium carbonate to increase soil pH to 7.0; ND: non-detectable.

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FIGURE 5.1

The distribution of Cd in different soil fractions in soil B treated in 1 month (a) and in 2 months (b).

a

b

100

80

60

40

20

0

Oxides

Mn Oxides

Treatments

100

80

60

40

20

0

Residual Fraction Organically Bound and Sulphide Fraction Fe- and Mn-Bounded Form

Exchangeable, Organic Matter Weakly Bounded and Carbonate Form 4131/frame/C05 Page 100 Friday, July 21, 2000 4:56 PM

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FIGURE 5.2

The distribution of Pb in different soil fractions in soil D treated in 1 month (a) and in 2 months (b).

b

a

100

80

60

40

20

0

100

80

60

40

20

0

Oxides

Mn Oxides

Treatments

Residual Fraction Organically Bound and Sulphide Fraction Fe- and Mn-Bounded Form

Exchangeable, Organic Matter Weakly Bounded and Carbonate Form 4131/frame/C05 Page 101 Friday, July 21, 2000 4:56 PM

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5.3.4 Effect of Chemical Treatments on the Concentration of Cd and Pb Uptake

by Wheat

The concentration and total uptake of Cd and Pb in wheat species (Triticum aestivum) grow-ing in the chemical treatments are shown in Tables 5.5 and 5.6 Results indicated that con-centrations of Cd in the leaves of wheat for different chemical treatments in these four soils, except treatment of iron oxide, were all significantly lower than that of control treatment (p <0.10) But there is not any effect on the concentration of Cd in the leaf of wheat when the concentration ranged from 70 to 115 mg/kg in very serious Cd polluted sandy soils Tables 5.5 and 5.6 also showed that only manganese oxide treatment can significantly reduce the concentration and total uptake of Pb in the leaf of wheat growing in sandy or clayey polluted soils, even in the soils A and B in which the concentrations of Pb are close

to background level

5.4 Conclusions

Results indicate that the chemical forms of Cd and Pb in the polluted soils can be trans-formed to unavailable forms from available forms after these chemical treatments Appli-cations of manganese oxides, calcium carbonate, and zeolite slightly reduced the concentration of Cd and Pb extracted from contaminated soils and also reduced the con-centration and uptake of Cd and Pb in the tested wheat species

TABLE 5.5

Cd and Pb Concentrations in Wheat Growing in Four Soils with Different Chemical Treatments

(mg/kg dry weight)

Cd

Pb

different FO: iron oxides; MO: manganese oxides.

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