Effects of Flooding and Ferrhydrite on Copper Fractionation in Paddy Soil

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Procedia Environmental Sciences 18 (2013) 135 – 142

2013 International Symposium on Environmental Science and Technology (2013 ISEST)

Effects of flooding and ferrhydrite on copper fractionation in paddy soil Beibei Liua, Dong Qub, Xin Chena, Qinfen Lia, Lixu Penga,* a Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China Environmental Assessment and Risk Analysis Center, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China Danzhou Scientific Observing and Experimental Station of Agro-Environment, Ministry of Agriculture, Danzhou 571737,China b College of Resources and Environment, Northwest A&F University, Yangling 712100, China

Abstract Chemical fraction plays an influential role in solubility and potential bioavailability of heavy metals in soils. Seasonally flooding and iron reduction are significant environmental processes of paddy soil. They may influence the fractionation of cooper (Cu) in paddy soil. In this study, an anaerobic incubation experiment was conducted to simulate the anaerobic environment of flooded paddy soil. The fractionations of native and spiked Cu in paddy soil were determined using a modified sequential extraction procedure (SEP) method. The effects of flooding time on Cu fractions were determined. The effects of ferrihydrite on Cu fractions were also investigated to understand the interaction between Cu contamination and iron reduction process. The results showed that the native Cu in soil were most in the residual and organic matter fractions, but the more available fractions, such as, the exchangeable and carbonates fractions occupied only a little proportion. After flooding, the native Cu in soil released from organic matter fraction and crystalloid ferric oxides fraction, and transferred to the easy extracted fractions, such as, amorphous ferric oxides, carbonates and exchangeable fractions. The spiked Cu was easily absorbed by carbonates and organic matter in soil, but after flooding, the two fractions transferred into ferric oxides fraction, especially amorphous ferric oxides fraction. Similar phenomena were observed after adding ferrihydrite in soil except for the disposal of added 400mg/kg Cu. The process of iron reduction was inhibited significantly by Cu contamination and the inhibition of Cu contamination to iron reduction decreased after adding ferrihydrite. The transformation of Cu fractions had significant relation to the process of iron anaerobic reduction in paddy soil. © ©2013 2013The TheAuthors. Authors.Published Publishedby byElsevier ElsevierB.V. B.V. Selection peer-review under responsibility of Beijing Institute of Technology. Institute of Technology. Selectionand and/or peer-review under responsibility of Beijing Keywords: Paddy soil; Copper fractionation; Ferrihydrite; Flooding; Iron reduction

* Corresponding author. Tel.: +86-898-66969271; fax:+86-898-66969211 . E-mail address: [email protected].

1878-0296 © 2013 The Authors. Published by Elsevier B.V.

Selection and peer-review under responsibility of Beijing Institute of Technology. doi:10.1016/j.proenv.2013.04.018

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1. Introduction The application of pesticides, commercial fertilizers, and sewage sludge as well as air-borne pollution has led to a widespread accumulation of heavy metals in agricultural soils. In recent years, there has been an increasing concentration of heavy metals in agricultural soils in China as the results of the application of fertilizer and compost, wastewater irrigation, and the deposition of industrial pollutants [1]. Copper (Cu) is an essential nutrient element for plant growth and is a toxic heavy metal in excess concentrations. Xu et al. reported that the rice grain yields decreased exponentially and significantly with the increase of soil Cu levels, and more than 60 % of the Cu in grain was accumulated in polished rice [2]. The contamination of the food chain by Cu is detrimental to human and animal health. Therefore, soil Cu concentration and availability are of agricultural and environmental significance. The bioavailability and mobility of heavy metals in soil strongly depend on their physicochemical forms in soils, i.e. chemical fraction or speciation [3, 4]. It is important to understand chemical fractions of Cu in order to assess Cu availability and toxicity to crop plants in a contaminated soil. The sequential extraction procedure (SEP) was proposed by Tessier et al. [5], in which soil heavy metal was operationally fractionated into water soluble, exchangeable, weakly specifically adsorbed, Fe/Mn oxidesbound, organically bound, and residual portions. Seasonally flooding, which is a significant environmental process in paddy soil, could influence soil physical, chemical and biological processes, and then affect the fate of heavy metals [6]. Iron reduction is an important process in paddy soil during flooding [7]. Iron oxides are important heavy metal sinks [8] and heavy metal release is associated with subsequent ferric oxides dissolution [9]. In our former study, it was investigated that Cu had significant effects on iron reduction [10]. There have been more research concerned about the fractionation of Cu in paddy soil [11-13], but a few have studied the dynamic transformation of Cu fraction during flooding and the interaction between Cu contamination and iron reduction process is still unknown. In the present study, an anaerobic incubation experiment as reported by He and Qu (2008) [14] was conducted to simulate the anaerobic environment of flooded paddy soil. The fractionations of native and spiked Cu in paddy soil were determined using the modified SEP method. The effects of flooding time on Cu fractions were determined. The effects of ferrihydrite on Cu fractions were also investigated to understand the interaction between Cu contamination and iron reduction process in paddy soil. 2. Materials and methods 2.1. Sample preparation Soil was taken from drained paddy field after harvesting, in Huilong town, Gonglai city, Sichuan, China. Soil sample was collected from the top 20 cm, removed the plant residual, air-dried, ground, and passed through a 20 mesh nylon sieve. Soil sample was kept in polyvinylchloride bottles at room temperature. The organic matter content in the soil was 48.9 g/kg, the total content of Cu was 35.3g/kg, the pH was 7.34 (in 5 parts H2O to 1 part soil), amorphous iron concentration was 3.08g/kg, and free iron concentration was 11.7g/kg. 2.2. Anaerobic incubation Three gram soil was mixed with sterilized deionized water, Cu (SO4)2 solutions and ferrihydrite solution (5.96 g/kg Fe, 1mL), at a ratio of 1:1 (wt / vol) in a 10 mL sterilized serum bottle. Oxygen was removed by gassing nitrogen into the bottle at a ratio of 2 L/min (1.01×105 Pa) for 1 min. All the bottles

Beibei Liu et al. / Procedia Environmental Sciences 18 (2013) 135 – 142

were sealed with butyl rubber cover and aluminum cap and then incubated at 25°C in the dark. The treatments were as follows, 0 mg/kg Cu, 100 mg/kg Cu, 400 mg/kg Cu, 0 mg/kg Cu + ferrihydrite, 100 mg/kg Cu + ferrihydrite, 400 mg/kg Cu + ferrihydrite. There are 3 replications per treatment for each incubation period. 2.3. Determination of ferrous iron Three vials were randomly selected from each treatment at day 0, 2, 6, 13, 21 and 31d of the incubation. Each vial was shaken vigorously to homogenize and then a 0.4 mL aliquot was removed from each culture and transferred to a screw top plastic tube containing 4.6 mL 0.5mol/L HCl. The samples were extracted for 24 h at 25 °C and then passed through a 0.22 m filter. Ferrous iron (Fe (II)) in the filtrate was determined using the ferron colorimetric method [15, 16]. 2.4. Fractionation and determination of Cu Fractionation of Cu in soil was determined by SEP method which was modified according to the reference [5]. Briefly, 1.6ml soil suspensions were taken from the serum vials, and extracted as follows: (i) exchangeable fraction (Exc-): 1.6 mL soil suspension was placed in a centrifuge tube and extracted at 25 °C for 1 h with 10 mL of 1 mol/L Mg(NO3)2 at pH 7.0 with continuous agitation; (ii) carbonates bound fraction (Carb-): the residue from (i) was leached at 25 °C with 10 mL of 1 mol/L NaOAc-HOAc at pH 5.0 for 4 h with continuous agitation; (iii) manganese oxides bound fraction (MnOx-): the residue from(ii) was extracted at 25 °C with 10 mL 0.1 mol/L NH2OH·HCl (pH 5.0), shook for 4 h; (iv) organic matter bound fraction (O.M.-): 5 mL distilled water was added to the residue from (iii) to disperse soil, then 10 mL 30% H2O2 were added, and heated at 85 °C with continuous agitation, then cooled when nearly dried, and then disposal the residue again with 10 mL 30% H2O2, heated to nearly dry, extracted with 1 mol/L Mg(NO3)2 after cooled (the method was the same as exchangeable fraction); (v) amorphous ferric oxides bound fraction (AFe-): 20 mL of 0.2 mol/L (NH4)2C2O4 - 0.2 mol/L H2C2O4 (pH 3.0) was added to the residue from (iv), shook 4 h at dark; (vi) crystalloid ferric oxides bound fraction (CFe-): 20 mL of 0.2 mol/L (NH4)2C2O4 + 0.2 mol/L H2C2O4 + 0.1 mol/L ascorbic acid (pH 3.0) was added to the residue from(v), heated at 96 °C for 1 h; (vii) Residual fraction (Res-): the residue from (vi) was digested with a HClO4 + H2SO4 + HNO3 mixture. The concentrations of Cu in the extracts were determined using an airacetylene flame atomic absorption spectrophotometer (AAS) Perkin-Elmer Model 800. Standard solutions were prepared from 1000 mg/L Cu stock solution. 2.5. Data analysis and Quality Control The content of each copper fraction was calculated as fractionation coefficient which is the ratio of the content of each metal fraction to the total metal contents. Before any analysis was performed, all glasswares used were acid-washed to avoid any possible contamination. The sum of all extraction steps for Cu had been calculated and compared with the total concentration of Cu. Therefore, the method was acceptable since satisfactory recoveries which were 102.5% to 125.2%. 3. Results 3.1. Cu fractionation in paddy soil Fig. 1 shows the fractionations of native and spiked Cu in paddy soil. The native Cu in soil were

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mainly in the residual and organic matter fractions, which were 26.9% and 24.3% of total Cu in the soil respectively, then were the amorphous ferric oxide fraction and crystalloid ferric oxide fraction, which were 15.4% and 15.4% of the total soil Cu respectively, while the exchangeable, manganese oxide and carbonate fractions were little, which were 7.71%, 5.24% and 5.13% of the total soil Cu respectively. When added 100mg/kg Cu in the soil, the of carbonates and organic matter fractions Cu were increased significantly than the native Cu, which were 33.3% and 38.5% of the total soil Cu respectively. The carbonate fraction Cu was increased to 52.5% of the total soil Cu when the concentration of the added Cu increased to 400 mg.kg-1. It indicated that the carbonates and organic matter played important roles for absorption of Cu in soil.

Cu Fraction Coefficient (%)

100 80

ExcCarbMnOxO.M.AFeCFeRes-

60 40 20 0

Native Cu

+100 mg/kg Cu +400 mg/kg Cu

Fig. 1. Fractionations of native and spiked Cu in paddy soil.

3.2. Effect of flooding time on Cu fractionation

CarbCFe-

MnOxRes-

O.M.-

80 60 40 20 0

0

2

6 13 21 Flooding Time (d)

(a)

30

100 80 60 40 20 0

0

2

6

13

Flooding Time (d)

(b)

21

30

Cu Fraction Coefficient (%)

ExcAFe-

100

Cu Fraction Coefficient (%)

Cu Fraction Coefficient (%)

Fig.2 shows the fractionations of native and spiked Cu in paddy soil during flooding. It can be seen that the fractionations of native and spiked Cu in paddy soil were changed significantly with flooding. For the native Cu, the organic matter fraction rapidly decreased after 13 d flooding and then maintained approximately at a level of 5.60 %. The crystalloid ferric oxides fraction decreased about 3.93%. While the amorphous ferric oxides fraction increased obviously with an increment of 12.2 % after 30 d flooding. The exchangeable and carbonates fractions also had a little increased with flooding. It indicated that the native Cu in the paddy soil released from organic matter fraction and crystalloid ferric oxides fraction, and transferred to the easy extracted fractions, such as, amorphous ferric oxides, carbonates and exchangeable fractions with flooding.

100 80 60 40 20 0

0

2

6 13 21 Flooding Time (d)

(c)

Fig. 2. Fractionations of native and spiked Cu in paddy soil at different flooding times. (a) native Cu, (b) 100mg/kg Cu, (c) 400 mg/kg Cu.

30

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The spiked Cu was mainly in the carbonates and organic matter fractions. After 30 d flooding, Cu of the two fractions both decreased significantly. Such as, for the treatment of added 100 mg/kg Cu, the carbonates fraction decreased of 30.3 % and the organic matter fraction decreased of 36.1 % after flooding. The manganese oxides fraction also had a little decrease after flooding. In contrast, the amorphous ferric oxides fraction increased of 62.3 % and crystalloid ferric oxides fraction increased of 6.28 % after flooding. The exchangeable fraction increased after 6 d flooding, and then decreased to the initial content after 30 d flooding. The residual Cu had no obvious change. The similar transformation of the fractions of Cu in paddy soil with flooding was observed for the treatment of added 400 mg/kg Cu. The results indicated that the spiked Cu was easily absorbed by carbonates and organic matter in soil, but after flooding, the two fractions transferred into ferric oxides fraction, especially amorphous ferric oxides fraction. 3.3. Effect of ferrihydrite on Cu fractionation Fig. 3 shows the fractionations of native and spiked Cu in paddy soil added ferrihydirte at different flooding times. Comparing Fig. 3 with Fig. 2, it can be seen that, for the native Cu and spiked 100 mg/kg Cu, added ferrihydrite in soil had no obvious effect on the transformation of Cu fractions with flooding. However, for the disposal of added 400 mg/kg Cu in soil, the increments of the Cu of amorphous ferric oxides and crystalloid ferric oxides fractions after 30 d flooding which were 71.9 % and 6.79 %, were significantly higher than those of without added ferrihydrite, which were 47.0 % and 5.52 %. MnOxRes-

O.M.-

100 80 60 40 20 0

0

2

6 13 21 Flooding Time (d)

(a)

30

100 80 60 40 20 0

0

2

6 13 21 Flooding Time (d)

(b)

30

Cu Fraction Coefficient (%)

CarbCFe-

Cu Fraction Coefficient (%)

Cu Fraction Coefficient (%)

ExcAFe-

100 80 60 40 20 0

0

2

6

13

21

30

Flooding Time (d)

(c)

Fig. 3. Fractionations of native and spiked Cu in paddy soil added ferrihydirte at different flooding times. (a) native Cu, (b) 100mg/kg Cu, (c) 400mg/kg Cu.

3.4. Reaction between Cu contamination and iron reduction The Fe(II) concentration in paddy soils with different levels of Cu contamination at different flooding times were determined to investigate the reaction between Cu contamination and iron reduction. The results are shown in Fig. 4. From Fig. 4, it can be seen that the increment and increase rate of Fe(II) concentration in paddy soil during flooding was decreased when added Cu, especially for the disposal of added 400mg/kg Cu. It indicated the process of iron reduction was inhibited significantly by Cu contamination. As shown in Fig. 4 b, the increment and increase rate of Fe(II) concentration in paddy soil during flooding were both increased after adding ferrihydrite. It indicated that the inhibition of Cu contamination to iron reduction decreased after adding ferrihydrite.

-1

-1

9 8 7 6 5 4 3 2 1 0

Fe(II) concentration (mg.g )

Beibei Liu et al. / Procedia Environmental Sciences 18 (2013) 135 – 142

Fe(II) concentration (mg.g )

140

Blank +100mg/kg Cu +400mg/kg Cu 0

5

10 15 20 Flooding Time (d)

(a)

25

30

14 12 10 8 6

Blank +100mg/kg Cu +400mg/kg Cu

4 2 0

0

5

10 15 20 Flooding Time (d)

25

30

(b)

Fig. 4. Fe(II) concentration of paddy soil with different level of Cu contamination at different flooding times. (a) without added ferrihydrite in soil, (b) added ferrihydrite in soil.

4. Discussion Our results indicated a low bioavailability of Cu in the tested paddy soil. The native Cu in paddy soil were mainly in the residual and organic matter fractions, while the more available fractions, such as, the exchangeable and carbonates fractions occupied only a little proportion. But after flooding, the Cu in soil transferred to the easily available fractions. The native Cu in soil released from organic matter fraction and crystalloid ferric oxides fraction, and transferred to amorphous ferric oxides, carbonates and exchangeable fractions after flooding. Iron-reduction has been recognized as an important process in flooded soil. It have been reported that the content of crystalloid ferric oxides decrease, while amorphous ferric oxides significantly increase with flooding, which may be several hundred times than before flooding [17]. That may be the main reason why Cu in paddy soil transformed to amorphous ferric oxides bound fractions after flooding. The release of organic matters bound Cu may have relation to the decomposition of soil organic matter during flooding which may be utilized by anaerobic bacteria [18]. The reduction of manganese oxides is also an important process in flooding soil [19]. In our study, the transformation of manganese oxides bound Cu was not significant probably because the content of manganese oxides bound Cu was little. Comparing the results of native Cu and spiked Cu, it can be seen that for native Cu, the crystalloid ferric oxide bound Cu decreased with flooding, but the opposite phenomenon was observed for spiked Cu. The difference may be explained by the effect of Cu on the anaerobic reduction of iron oxides. It has been believed that the anaerobic reduction of iron oxides is mainly a process of microbial dissimilatory reduction [20, 21]. Heavy metal toxicity was one of the major factors affecting reduction of metalcontaminated hydrous ferric oxides [22, 23]. Our results showed that the process of iron reduction was inhibited significantly by Cu contamination. That may be the main reason of the difference between the transformation of crystalloid ferric oxide bound native and spiked Cu. For the disposal of added 400mg/kg Cu, the content of amorphous ferric oxides bound Cu was increased more than that of the treatment without ferrihydrite. This is available for Cu sequestration in soil, and then to decrease its toxicity on bacteria. That is why the inhibition of Cu on iron reduction decreased after adding ferrihydrite. It also can be observed that during the flooding time, Fe (II) concentration increased rapidly initially, then slowly or came to equilibrium. The turning time was consistent with that of the transformation of Cu fractions in soil. For instance, for the treatment of without adding ferrihydrite, the Fe (II) concentration in soil increased slowly after 13 d flooding (Fig. 4 a), accordingly, the change of fractionation of Cu in soil was slightly (Fig. 2). As shown in Fig. 4 b and Fig. 3, the corresponding flooding time of iron reduction and the transformation of Cu fractions was 6 d. As a result, it can be concluded that the transformation of

Beibei Liu et al. / Procedia Environmental Sciences 18 (2013) 135 – 142

Cu fractions during flooding in paddy soil had significant relation to the process of iron anaerobic reduction. 5. Conclusions From the study, it can be conclude that the fractionation of Cu in paddy soil significantly influenced by flooding time and Cu concentration, and iron reduction process played an important role on the transformation of Cu fractionation during flooding. The native Cu in soil were strongly absorbed by soil and most of the Cu could not be easily extracted, but it transferred to the easy extracted fractions, such as, amorphous ferric oxides, carbonates and exchangeable fractions after flooding. The spiked Cu was easily absorbed by carbonates and organic matter in soil, and after flooding, the two fractions transferred into ferric oxides fraction. The process of iron reduction was inhibited significantly by Cu contamination and the inhibition of Cu contamination to iron reduction decreased after adding ferrihydrite. The transformation of Cu fractions had significant relation to the process of iron anaerobic reduction in paddy soil. Acknowledgements This work was supported by the Fundamental Research Funds for Environment and Plant Protection Institute, CATAS (No. 2012hzs1J008-1, 2011hzs1J001, 1630042012008) and the National Natural Science Foundation of China (No. 41171204). References [1] Jia DA, Zhou DM, Wang YJ, Zhu HW, Chen JL. Adsorption and cosorption of Cu(II) and tetracycline on two soils with different characteristics. Geoderma 2008;146:224 30. [2] Xu JK, Yang LX, Wang ZQ, Dong GC, Huang JY, Wang YL. Toxicity of copper on rice growth and accumulation of copper in rice grain in copper contaminated soil. Chemosphere 2006;62:602 7. [3] Mclaren RG, Clucas LM. Fractionation of copper, nickel, zinc in metal-spiked sewage sludge. J Environ Qual 2001;30:1968 75. [4] Li JX, Yang XE, He ZL, Jilani G, Sun CY, Chen SM. Fractionation of lead in paddy soils and its bioavailability to rice plants. Geoderma 2007;141:174 80. [5] Tessier A, Campbell PGC, Bisson M. Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 1979;5:844 51. [6] Takahashi Y, Minamikawa R, Hattori KH, Kurishima K, Kihou N, Yuita K. Arsenic behavior in paddy fields during the cycle of flooded and non-flooded periods. Environ Sci Technol 2004;38:1038 44. [7] Stumn W, Sulzberger B. The cycling of iron in natural environments: considerations based on laboratory studies of heterogeneous redox processes. Geochim Cosmochim Acta 1992;56:3233 57. [8] Tessier A, Belzile N, Devitre RR, Leppard GG, Fortin D. Metal sorption to diagenetic iron and manganese oxyhydroxides and associated organic matter: narrowing the gap between field and laboratory measurements. Geochim Cosmochim Acta 1996;60:387 404. [9] Cummings DE, Fendorf S, Rosenzweig RF, Caccavo FJr. Arsenic mobilization by the dissimilatory Fe(III)-reducing bacterium Shewanella alga BrY. Environ Sci Technol 1999;33:723 29. [10] Liu BB, Qu D. Effects of different heavy metals on dissimilatory iron reduction. J Northwest A & F Univ (Nat Sci Ed) 2006;34:115 20. (In Chinese) [11] Luo YM, Jiang XJ, Wu LH, Song J, Wu SC, Lu RH, Christie P. Accumulation and chemical fractionation of Cu in a paddy soil irrigated with Cu-rich wastewater. Geoderma 2003;115:113 20. [12] Wu CF, Luo YM, Zhang LM. Variability of copper availability in paddy fields in relation to selected soil properties in southeast China. Geoderma 2010;156:200 06. [13] Abbaspour A. Fractionation of copper in soils as influenced by waterlogging and application of crop residues. Iran J Soil Res 2012;25:295 306.

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