Chemical transformation of copper in some sludge-amended soils

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Chemical transformation of copper in some sludge-amended soilsGeeta Tewari a; Lalit M. Tewari b; Prakash Chandra Srivastava c; Bali Ram d

a Department of Chemistry, b Department of Botany, D.S.B. Campus, Kumaun University, Nainital c

Department of Soil Science, G.B. Pant University of Agriculture and Technology, Pantnagar d Department ofChemistry, B.H.U., Varanasi, India

Online Publication Date: 01 August 2009

To cite this Article Tewari, Geeta, Tewari, Lalit M., Srivastava, Prakash Chandra and Ram, Bali(2009)'Chemical transformation ofcopper in some sludge-amended soils',Archives of Agronomy and Soil Science,55:4,415 — 427

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Chemical transformation of copper in some sludge-amended soils

Geeta Tewaria*, Lalit M. Tewarib, Prakash Chandra Srivastavac and Bali Ramd

Department of aChemistry and bBotany, D.S.B. Campus, Kumaun University, Nainital; cDepartment ofSoil Science, G.B. Pant University of Agriculture and Technology, Pantnagar; dDepartment of

Chemistry, B.H.U., Varanasi, India

(Received 23 June 2008; final version received 4 January 2009)

In a laboratory incubation study, the periodic changes in different chemical fractions ofcopper (Cu) in three sludge-amended soil types (acidic sandy clay loam, neutral clayloam and alkaline clay loam) of varying soil reaction were monitored under fieldcapacity and flooding moisture regime over 16 months. The water soluble andexchangeable fraction of Cu was very low (�1% of total Cu) in all three soil types. Atthe end of incubation (16 months), the sodium acetate extractable (carbonate sorbed)-and residual-Cu fractions transformed into Fe-Mn oxide fraction, irrespective ofmoisture regime in all three soil types. However, the extent of transformation variedamong soils.

Keywords: chemical fractions; metal source; moisture regime; polluted soils; copper

Introduction

Copper (Cu) is an essential plant micronutrient, which is added to agricultural soilsthrough fertilizers, copper-based fungicides (Arias et al. 2004), animal wastes and sewagesludge. Once in the soil, this metal is relatively immobile and can, therefore, persist forlong periods of time (Chaney 1982; Kabata-Pendias and Pendias 1992). High doses ofheavy metals reaching soils through sewage sludge might result in phytotoxic levels in thesoil and undesirable accumulations in the food chain (Chaney 1982). High concentrationof Cu in soils is usually phytotoxic to many agricultural crops and reduced theirproductivity (Poschenrieder et al. 2001). The total Cu content of soil provides only limitedinformation about its potential behavior and bioavailability. In soils, Cu is associated withvarious soil components in different factions, such as water soluble, exchangeable,chelated and complexed forms associated with organic matter, occluded in thesesquioxides and as part of the lattice structure of primary- and secondary-minerals.The intensities of different chemical fractions of heavy metals determine its mobility andavailability to the plants differentially (Kabata-Pendias and Pendias 1992; Singh et al.1997; Han and Banin 1997, 1999, 2000). Water soluble and exchangeable fraction(s) ofheavy metals are mobile and easily available for absorption by plants, while the fractionincorporated into crystalline lattices of clays appears to be relatively inactive in terms ofbioavailability to plants. The other chemical forms could be either relatively available orpoorly available to plants, depending on the actual physico-chemical properties of soil(Sposito et al. 1982; Shuman 1985; Dudka and Chlopecka 1990). Under natural

*Corresponding author. Email: [email protected]

Archives of Agronomy and Soil Science

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conditions, the residual- and oxides bound-fractions of Cu are more abundant pools(Dudka et al. 1990), whereas, in polluted soils, the carbonate-, hydrous oxide-associated-and the residual-fractions tend to increase with time at the expense of the exchangeable-and organic matter bound-fractions (Sposito et al. 1983; McGrath and Cegarra 1992;McLaren and Ritchie 1993).The soil moisture regime affects both soil redox potential and biological activity in soilsand therefore, it is likely to have important bearing on the chemical transformation ofadded heavy metals in soils and may affect the availability of metals to plants (Singhet al. 1997; Singh and Nongkynrih 1999; Kandpal et al. 2003, 2004a, 2004b; Tack et al.2006).Generally, under flooding water regime, Fe and Mn oxides are reduced because oflower redox potential of soil. As a consequence, heavy metals are released andredistribution among the solid phase components occurs (Silviera and Sommers 1977;Han and Banin 1997, 2000). At saturated paste and field capacity moisture regimes,heavy metals added as soluble salts are transformed by an initial fast retention process,followed by a slower long-term distribution process. In both processes, the heavymetals are progressively transformed from labile fractions to less labile fractions (Hanand Banin 1997, 1999).It can be summarized that it is important to elucidate different chemical forms of heavymetals and their transformation in soils amended with sludge to examine their chemicalspeciation and bioavailability. Therefore, the present investigation was undertaken toexamine the chemical transformation of Cu added through sludge in polluted soils ofvarying soil reaction, under both field capacity and flooding moisture regimes.

Materials and methods

Soil and sludge samples

Surface (0–15 cm) samples of acidic, neutral and alkaline soils were collected fromVivekananda Laboratory, Almora District, Majhola, *5 km from Moradabad Districthead-quarters and from the Crop Research Centre, Pantnagar, Udham Singh NagarDistrict, India, respectively. General properties of soil samples were determined followingthe procedures outlined by Page et al. (1982). The total metal content of the soils wasdetermined in HF-HClO4 (5:1) digests by atomic absorption spectrophotometry. Theproperties of soil samples used in this study are reported in Table 1.

Table 1. Selected properties of soil samples used in the study.

Soil properties Particle size Acidic soil Neutral soil Alkaline soilTexture range (mm) sandy clay loam clay loam clay loam

Clay (%) 50.002 32.44 32.84 27.84Silt (%) 50.02–0.002 18.00 28.00 28.00Sand (%) 52–0.02 49.56 32.84 44.16pH (1:2) 6.13 7.00 9.57O.C. % 0.94 1.20 0.84% CaCO3 0.39 0.78 2.22C.E.C. (cmol kg71) 11.04 15.75 12.49Field capacity (%) 29.33 27.23 24.28Total Cu (mg kg71 soil) 34.18 24.00 13.68Total Cu (mg kg71 soil)after sludge addition

622.27 655.12 615.15

416 G. Tewari et al.


A bulk sample of sludge was collected from Karula Nala, Moradabad District, India,which received all sewage effluents from local brass industries and the municipality ofMoradabad. The sludge had pH 5.2 in 1:2 suspension, 48 g organic C kg71 and 1.517 gtotal Cu kg71 of sludge on dry weight basis.

Incubation study

Fifteen grams of each soil was taken in a series of 200 ml plastic cups and treated with 10 gsludge (Brofas and Varelides 1997). Treated soils were incubated at field capacity (FC) orcontinuous flooding (maintaining 2.5 cm water level above soil surface) at roomtemperature. The moisture content at field capacity moisture regime was maintainedthroughout the study by adding distilled water to a constant weight. At the end of 1, 2, 4,6, 8, 16, 32 and 48 weeks and finally after 16 months of incubation, three cups of eachtreatment combination were selected. Aliquots (3 g) of moist soil were taken into 50-mlpolycarbonate centrifuge tubes and sequentially extracted, as per the scheme of Ahnstromand Parker (1999).

The following chemical fractions of Cu were obtained:

F1 (Water soluble þ exchangeable, extractable in 0.1 M Sr[NO3]2),F2 (Carbonate bound, extractable in 1 M NaOAc of pH 5.0),F3 (Oxidizable fraction, extractable in 5% NaOCl of pH 8.5),F4 (Reducible fraction, extractable in 0.2M oxalic acid þ 0.2M NH4 oxalate þ 0.1Mascorbic acid, pH 3),F5 (Residual fraction, extractable in HF – HClO4 digest).

Cu content in each fraction was measured by atomic absorption spectrophotometry andthe results were expressed on an oven-dry weight basis. There were three replicates ofsludged soil samples for all estimations, including those for sequential extraction andtreatment (field capacity or flooded) at each time.

Statistical analysis

The data were analyzed using Analysis of Variance (ANOVA) in an asymmetrical twofactorial design to evaluate the contribution to the total variance of time of incubation andmoisture regime. The statistical significance was tested by F-test at p � 0.05.

Results and discussion

Chemical fractions of copper

The concentrations of Cu in different chemical fractions in different soils polluted bysludge under field capacity or flooding water regime are presented in Figure 1 and Table 2.

Water soluble and exchangeable (Cu-F1) fraction

Statistical analysis reveals that the mean content of Cu-F1 fraction was highest in acidicsoil, followed by neutral and alkaline soils. Such patterns could be anticipated in view of aprofound effect of equilibrium pH and proportion of coarse soil fraction (sand %) offeringlower number of adsorption sites on the concentration of water-soluble and exchangeable

Archives of Agronomy and Soil Science 417


Figure 1. Changes in the concentration of different chemical fractions of Cu in different soilspolluted by sewage sludge under field capacity and flooding water regime (W ¼ week; M ¼ month;F.C. ¼ field capacity; exch. ¼ exchangeable; extr. ¼ extractable; Org. ¼ organically).



Table2.

(a)Concentrationofdifferentchem

icalpoolsofcopper

insoilspollutedbysludgeincubatedunder

fieldcapacity

andfloodingmoisture

regim

e(M¼

Moisture

regim

e,T¼

Tim

eofincubation).

Tim

einterval

Acidic

soil

Neutralsoil

Alkalinesoil

F.C.

Flooding

� xF.C.

Flooding

� xF.C.

Flooding

� x

Exchangeable

Cufraction(C

u-F

1)

T1W

7.63

8.75

8.19

7.79

5.85

6.82

2.30

1.95

2.12

T2W

6.48

4.94

5.71

7.67

3.96

5.82

2.23

1.28

1.75

T4W

7.98

8.42

8.20

7.75

2.79

5.27

2.61

1.33

1.97

T6W

9.06

4.19

6.62

5.99

1.34

3.66

1.73

0.80

1.26

T8W

7.18

4.44

5.81

2.68

1.88

2.28

2.47

0.75

1.61

T16W

2.03

3.71

2.87

1.48

1.83

1.65

0.68

0.59

0.63

T32W

1.05

2.84

1.94

0.63

1.45

1.04

0.52

0.47

0.49

T48W

2.35

3.54

2.95

1.17

2.90

2.03

0.32

0.01

0.16

T16M

2.98

8.54

5.76

2.24

4.27

3.25

0.41

0.01

0.21

Av.

5.19

5.48

5.34

4.15

2.92

3.54

1.47

0.80

1.13

Effects

MT

MX

TM

TM

XT

MT

MX

TSEM

0.15

0.31

0.31

0.07

0.14

0.14

0.04

0.09

0.09

LSD

(p�

0.05)

0.43

0.89

0.89

0.20

0.40

0.40

0.11

0.26

0.26

NaOAcextractable

Cufraction(C

u-F

2)

T1W

194.46

119.94

157.20

90.66

100.65

95.65

159.08

151.18

155.13

T2W

183.10

153.60

168.35

98.86

108.10

103.48

185.16

183.60

184.38

T4W

200.30

192.30

196.30

57.59

98.50

78.05

113.13

179.26

146.20

T6W

195.27

236.89

216.08

86.15

107.12

96.63

105.19

162.28

133.73

T8W

193.37

177.98

185.68

49.53

101.16

75.34

184.79

172.93

178.86

T16W

130.52

175.05

152.79

29.65

74.79

52.22

103.08

116.99

110.04

T32W

78.09

88.62

83.35

45.56

48.41

46.98

82.23

100.60

91.41

T48W

125.26

109.74

117.50

78.08

77.67

77.88

133.70

147.04

140.37

T16M

79.81

88.01

83.91

54.07

76.43

65.25

74.44

95.45

84.94

Av.

153.35

149.12

151.24

65.57

88.09

76.83

126.75

145.48

136.12

Effects

MT

MX

TM

TM

XT

MT

MX

TSEM

0.72

1.53

1.53

0.25

0.53

0.53

0.80

1.69

1.69

LSD

(p�

0.05)

NS

4.39

4.39

0.72

1.52

1.52

2.29

4.85

4.85

(continued)



Table

2.

(Continued

).

Tim

einterval

Acidic

soil

Neutralsoil

Alkalinesoil

F.C.

Flooding

� xF.C.

Flooding

� xF.C.

Flooding

� x

OrganicallyboundCufraction(C

u-F

3)

T1W

44.94

46.64

45.79

30.54

35.42

32.98

29.19

9.55

19.37

T2W

52.70

55.60

54.15

73.73

42.82

58.28

35.23

10.23

22.73

T4W

12.79

10.43

11.61

19.05

10.99

15.02

12.56

15.94

14.25

T6W

58.57

45.75

52.16

38.24

46.51

42.37

21.05

17.89

19.47

T8W

14.05

21.80

17.92

14.37

14.17

14.27

19.70

15.46

17.58

T16W

47.80

44.62

46.21

31.99

37.85

34.92

22.90

22.23

22.56

T32W

19.24

19.40

19.32

11.18

13.62

12.40

15.57

20.88

18.23

T48W

35.29

32.70

33.99

20.18

22.45

21.31

29.35

34.55

31.95

T16M

60.95

34.87

47.91

34.38

29.57

31.97

19.63

28.30

23.97

Av.

38.48

34.64

36.56

30.40

28.15

29.28

22.80

19.45

21.12

Effects

MT

MX

TM

TM

XT

MT

MX

TSEM

0.25

0.52

0.52

0.42

0.89

0.89

0.18

0.39

0.39

LSD

(p�

0.05)

0.72

1.49

1.49

1.20

2.55

2.55

0.52

1.12

1.12



Table2.

(b)Concentrationofdifferentchem

icalpoolsofcopper

insoilspollutedbysludgeincubatedunder

fieldcapacity

andfloodingmoisture

regim

e(M¼

Moisture

regim

e,T¼

Tim

eofincubation).

Tim

einterval

Acidic

soil

Neutralsoil

Alkalinesoil

F.C.

Flooding

� xF.C.

Flooding

� xF.C.

Flooding

� x

Fe-Mnbound(reducible)Cufraction(C

u-F

4)

T1W

165.48

141.49

153.48

192.52

188.87

190.69

112.56

126.40

119.48

T2W

186.46

208.75

197.60

247.53

240.48

244.01

210.95

215.77

213.36

T4W

368.89

229.61

299.25

327.45

286.56

307.01

280.35

215.94

248.14

T6W

310.62

232.95

271.78

267.87

253.07

260.47

258.59

249.84

254.21

T8W

182.74

126.68

154.71

108.82

205.05

156.93

254.90

200.00

227.45

T16W

244.02

233.21

238.61

172.51

227.28

199.89

211.80

186.02

198.91

T32W

269.53

302.80

286.17

287.08

320.45

303.76

279.41

340.34

309.88

T48W

336.98

269.47

303.23

355.67

353.96

354.82

344.71

289.59

317.15

T16M

405.88

373.30

389.59

410.78

411.56

411.17

401.22

428.94

415.08

Av.

274.51

235.36

254.93

263.36

276.36

269.86

261.61

250.31

255.96

Effects

MT

MX

TM

TM

XT

MT

MX

TSEM

1.74

4.12

4.12

1.30

2.76

2.76

1.59

3.37

3.37

LSD

(p�

0.05)

4.99

11.82

11.82

3.73

7.92

7.92

4.56

9.66

9.66

ResidualCufraction(C

u-F

4)

T1W

276.00

371.71

323.86

360.25

350.98

355.61

479.64

493.68

486.66

T2W

259.77

265.63

262.70

253.96

286.41

270.18

349.19

371.88

360.54

T4W

98.56

247.74

173.15

269.91

282.91

276.41

374.11

370.30

372.20

T6W

114.99

168.75

141.87

283.51

273.73

278.62

396.21

351.95

374.08

T8W

291.16

357.60

324.38

506.37

359.51

432.94

320.89

393.63

357.26

T16W

264.14

231.92

248.03

446.14

340.01

393.07

444.31

456.94

450.63

T32W

320.60

274.86

297.73

337.31

297.84

317.57

405.04

320.48

362.76

T48W

188.63

273.05

230.84

226.67

224.78

225.72

274.68

311.58

293.13

T16M

138.89

183.79

161.34

180.28

159.94

170.11

287.07

230.05

258.56

Av.

216.97

263.89

240.43

318.26

286.23

302.25

370.13

366.72

368.42

Effects

MT

MX

TM

TM

XT

MT

MX

TSEM

1.92

4.07

4.07

1.66

3.52

3.52

2.19

4.94

4.64

LSD

(p�

0.05)

5.51

11.67

11.67

4.76

10.09

10.09

NS

14.17

13.31

NS¼

Notsignificantatp5

0.05.



fraction of Cu in soils. Reddy et al. (1995) also observed increased availability andmobility of metal ions in soil solution with a decreased soil pH. The mean content of Cu-F1 fraction was higher under field capacity compared to flooding moisture regime, possiblydue to higher acidity maintained under the former moisture regime and also the fasterdecomposition of organic matter in an oxic environment. With submergence, soil pHshifted towards neutrality and therefore a relatively lower mean content of Cu-F1 fractioncould be anticipated under saturated, compared to field capacity moisture regime. Soilsubmergence has been reported to decrease Cu availability in soils, owing to theprecipitation of Cu as sulfide under reducing conditions (Dutta et al. 1989; Singh andNongkynrih 1999). The content of Cu-F1 fraction decreased significantly with incubationtime in all three soils. This could be attributed to fixing of Cu on soil minerals due to agingeffects (Tagami and Uchida 1998; Jalali and Khanlari 2008).

NaOAc extractable (Cu-F2) fraction

The mean concentration of Cu-F2 fraction was highest in acidic soil, followed by alkalineand then neutral soil. The highest concentration of sodium acetate extractable Cu in acidicsoil could be ascribed to release of Cu from other fractions which failed to release Cu atthe previous extraction step and also from the sodium acetate soluble fraction of soilorganic matter. The mean concentration of Cu-F2 fraction was also higher under fieldcapacity in acidic soil compared to flooding, while the reverse was true for the neutral andalkaline soils. Considerable adsorption of metal onto soil carbonates in non-flooded soilmight decrease metal availability (Navrot and Ravikovitch 1969). The content of Cu-F2 inall soils also declined significantly with increasing incubation time.

Organically bound (oxidizable) (Cu-F3) fraction

The mean content of Cu-F3 fraction was highest in acidic soil followed by the neutral andthen alkaline soils. The mean content of Cu-F3 fraction was higher under field capacitythan flooding, especially, in both acidic and alkaline soils. The concentration of thisfraction also declined with time, especially in the alkaline and neutral soils, but increasedin acidic soil. The data were significant at p � 0.05.

Iron and Mn oxide bound (Cu-F4) fraction

Generally, the mean content of Cu-F4 fraction was highest in neutral soil followed byalkaline and acidic soils. The mean concentration of Cu-F4 fraction was higher under fieldcapacity than under flooding, especially in the acidic and alkaline soils, but the reverse wastrue for neutral soil. Generally, under normal redox ranges prevalent in agriculture, Cudoes not undergo redox reactions, but it could be co-precipitated with Fe-Mn hydrousoxides (Matagi et al. 1998). The concentration of Cu-F4 fraction increased with incubationtime with some in between fluctuations, but at the end of incubation period (16 months)the highest value was recorded.

Residual (Cu-F5) fraction

Generally, the mean content of Cu-F5 fraction was highest in alkaline soil followed byneutral and then acidic soils. The mean content of Cu-F5 fraction was higher under fieldcapacity in neutral soil, compared to submergence. However, the reverse was true for



acidic soil. Under field capacity moisture regime, the higher content of this fractionsuggested irreversible sorption of this metal on silicates (Lindsay and Norvell 1969). Anincrease in the content of residual fraction of Cu especially, in acidic soil, could be due topromoted hydrolysis of trace metals on the surface of silicate layers with a concomitantrelease of protons causing lesser exchange of adsorbed metals. The mean concentration ofthis fraction was initially higher, but later decreased during incubation.

Changes in percent distribution of different chemical fractions of copper

Changes in the percent distribution of different chemical fractions of Cu in the non-polluted and polluted soils before incubation are shown in Figure 2 (2a, 2b, respectively).Originally in these soils, Cu was largely present in Fe-Mn oxide bound- and residual-fractions. In order to evaluate the relative distribution of different chemical fractions of Cuin soils receiving sludge, the percent distribution of various chemical fractions of the metalafter incubation under field capacity and flooding moisture regimes was calculated anddepicted in Figure 3.Total soil Cu concentration increased in all sludge-amended soils; from 34.18–622.27 mgkg71 in acidic soil, from 24.00–655.12 mg kg71 in neutral soil and from 13.68–615.15 mgkg71 in alkaline soil. Total and extractable soil Cu concentrations have been reported toincrease when soil was amended with Municipal Solid Waste (MSW) compost (Zheljazkovand Warman 2004; Walter et al. 2006; Zhang et al. 2006). The most abundant Cu fractionsin the treated soils were the non-residual fractions (70.85–73.97%). Among non-residualfractions, the Fe-Mn oxide bound fraction was dominant (38.84–46.24%), possibly owingto co-precipitation of added Cu with Fe and Mn oxides present in soil. In soils, Fe and Mnoxides exist as discrete particles or as coatings on other particles and have also beenreported to be excellent scavengers for heavy metals, both in natural and polluted soils(Kuo et al. 1983; Xian and Shokohifard 1989). However, Fe-Mn oxides are unstable under

Figure 2. Distribution of Cu in 2 (a) different non-polluted soils, 2 (b) soils polluted with sludgebefore incubation.



submerged and low Eh conditions (Tessier et al. 1979). With the application of MSWcompost, the highest increase in Cu content has been reported in the organically-boundfraction, a fraction temporarily unavailable to plants (Zheljazkov andWarman 2004). Onlya small percentage of Cu existed as soluble and exchangeable fraction (�1%) in the sludgeamended soils. On average, the percent distribution of different Cu fractions followed theorder: F4 4 F5 4 F2 4 F3 4 F1.Application of sludge significantly increased NaOAc extractable and organically-boundfractions of soil Cu. This might be because organic matter and in situ formed CaCO3 in thesewage sludge act as a source of Cu and a major adsorbent for this metal, respectively. Theresults of this study were consistent with the results of Sims and Kline (1991) and Moreraet al. (2001), who also reported that with sewage sludge application, the organically-boundfraction of Cu increased.After one week of incubation, however most Cu was present in the carbonate bound-, Fe-Mn oxide bound- and residual-fractions. Earlier studies also revealed that the Fe-Mnoxide bound and NaOAc extractable fractions were the major solid phases of Cu in thesoil amended with sludge, sulfate salts and Cu-enriched manure, or contaminated minetailings (Mullins et al. 1982; Payne et al. 1988; Chlopecka 1993; McLaren and Ritchie1993).After long-term incubation (16 months), changes in the Cu content were similar underboth moisture regimes. In all soils, NaOAc (sodium acetate) extractable- and residual-Cu

Figure 3. Changes of different chemical pools of Cu in acidic, neutral and alkaline soil polluted bysludge under (a) field capacity (FC) and (b) flooding water regime.



transformed into Fe-Mn oxide bound fraction. Han and Banin (1997, 1999) and Han et al.(2001) examined the possible pathway of transformation of added Cu after one year ofincubation under saturated, field capacity and wetting-drying cycle moisture regimes andfound that Cu transferred from EXC (exchangeable) fraction into ERO (easily reducibleoxide fraction) and RO (reducible oxide fraction), from EXC into OM (organic matterbound) fractions and from EXC and CARB (carbonate bound) fractions into the RO,OM, ERO and RES (residual) fractions, respectively.

Changes of overall lability of Cu in soils under different moisture regimes

Statistical Analysis of changes in overall lability of Cu with time in polluted soils underdifferent moisture regimes is shown in Figure 4. According to Han and Banin (2000), metalfractions among solid-phase components could be grouped as readily labile (exchangeablefraction), potentially labile (carbonate-bound and organically-bound fractions) and lesslabile (Fe-Mn oxide bound and residual fraction) fractions. In sludge-amended soils,redistribution took place from the potentially labile to less labile Cu fraction in all soils.Generally, the field capacity moisture regime maintained higher Cu availability thanflooding. Among soils, the extent of transformation was highest in acidic soil followed byalkaline and neutral soils.

Figure 4. Changes in overall lability of Cu in acidic, neutral and alkaline soil polluted by sludgeunder (a) field capacity (FC) and (b) flooding water regime.



Conclusions

Application of sewage sludge increased the total Cu content in all soils. The percentage ofthe total Cu content in the water soluble and exchangeable fraction was very low (�1%) insludge-amended soils. The solubility of Cu as the extractable fraction could signify lowsolubility, and therefore, low availability to crop plants, since the readily soluble forms areregarded as the most bioavailable. After 16 months of incubation, irrespective of themoisture regime, there was a decrease in the residual- and NaOAc extractable-fractionswith an increase in Fe-Mn oxide bound-fraction (temporarily unavailable to plants).The soil moisture regime strongly influences the transformation of Cu added throughsludge in the soils. Compared to flooding, field capacity moisture regime encouragedhigher Cu reactivity and transformation into poorly labile fractions, especially in acidicsoil.

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Chemical transformation of copper in some sludge-amended soils

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