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International Journal of Phytoremediation Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/bijp20
Effects of Surface-Modified NanoScale Carbon Black on Cu and Zn Fractionations in Contaminated Soil a
a
Jie-min Cheng , Yu-zhen Liu & Han-wei Wang
a
a
College of Population Resources and Environment , Shandong Normal University , Jinan , China Accepted author version posted online: 25 Aug 2013.Published online: 10 Sep 2013.
Click for updates To cite this article: Jie-min Cheng , Yu-zhen Liu & Han-wei Wang (2014) Effects of Surface-Modified Nano-Scale Carbon Black on Cu and Zn Fractionations in Contaminated Soil, International Journal of Phytoremediation, 16:1, 86-94, DOI: 10.1080/15226514.2012.759530 To link to this article: http://dx.doi.org/10.1080/15226514.2012.759530
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International Journal of Phytoremediation, 16:86–94, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1522-6514 print / 1549-7879 online DOI: 10.1080/15226514.2012.759530
EFFECTS OF SURFACE-MODIFIED NANO-SCALE CARBON BLACK ON CU AND ZN FRACTIONATIONS IN CONTAMINATED SOIL
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Jie-min Cheng, Yu-zhen Liu, and Han-wei Wang College of Population Resources and Environment, Shandong Normal University, Jinan, China Cu contamination soil (547 mg kg–1) was mixed separately with the surface-modified nanoscale carbon black (MCB) and placed in the ratios (w/w) of 0, 1%, 3%, and 5% in pots, together with 0.33 g KH2 PO4 and 0.35 g urea/pot. Each pot contained 20 ryegrass seedlings (Lolium multiflorum). Greenhouse cultivation experiments were conducted to examine the effect of the MCB on Cu and Zn fractionations in soil, accumulation in shoot and growth of ryegrass. The results showed that the biomass of ryegrass shoot and root increased with the increasing of MCB adding amount (p < 0.05). The Cu and Zn accumulation in ryegrass shoot and the concentrations of DTPA extractable Cu and Zn in soil were significantly decreased with the increasing of MCB adding amount (p < 0.05). The metal contents of exchangeable and bound to carbonates (EC-Cu or EC-Zn) in the treatments with MCB were generally lower than those without MCB, and decreased with the increasing of MCB adding amount (p < 0.05). There was a positive linear correlation between the Cu and Zn accumulation in ryegrass shoot and the EC-Cu and EC-Zn in soil. The present results indicated the MCB could be applied for the remediation the soils polluted by Cu and Zn. KEY WORDS: surface-modified nano-scale black carbon, Cu and Zn fractionations, soil, ryegrass
INTRODUCTION Carbon black (CB) is a product of biomass or fossil fuel under incomplete combustion. The particle size of CB is partially in the nanometer range with average values between 20 and 300 nm from different sources (Nowack and Bucheli 2007) and with functional group such as carboxyl, phenolic hydroxyl and carbonyl (Liu 2002). However, such CB often shows higher adsorption capacity of organic compounds(Cornelissen and Gustrafsson 2004)and lower adsorption capacity of metal ions (Fan et al. 2001). Most of surfacemodified carbon adsorbents (MCAs) were prepared by oxidation of activated carbon with HNO3 which has shown good adsorption abilities of Cu and Cd (Zhou et al. 2010). The contents of heavy metals taken up by plants from soils depend on the available metals to plants rather than the total content in soil (Yang et al. 2011). Zheng and Liu (2008) added 750 kg lime per hectare into heavy metals contamination soil and the available Cu, Pb, Cd, and As to plants decreased 21.1%, 48.6%, 11. 6%, and 27.7% and then the uptake
Address coresspondence to Jie-min Cheng, College of Population Resources and Environment, Shandong Normal University, Jinan, 250014 China. E-mail: [email protected] 86
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of Cu, Pb, Cd, and As by mustard decreased 22.3%, 50.0%, 23.1%, and 44.0% respectively. Wang(2009)added 1%, 3%, and 5% MCA modified with HNO3 into the red earth and the available Cu decreased 47.26%, 72.0%, and 80.9% and available Zn decreased 3.0%, 17.7%, and 43.6% respectively. The decrease of metals availability to plants may be an effective method of remediation heavy metal pollution soil. Heavy metals, once in the soil, may become non-soluble or unavailable to plants through precipitation, absorption, complexation, and other reactions with organic and inorganic soil components. The proportion of soluble or non-soluble metals may depend on the characteristic, concentration and residence time of metal contaminant and soil conditions (Young et al. 2000). Tessier et al. (1979) divided the species of metals in sediment or soil into the five parts of exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to organic matte and residual. Shuman (1985) divided them into the eight parts of soluble, exchangeable, bound to carbonates, loose bound to organic matter, bound to manganese oxides, fast bound to organic matter, bound to iron oxides and bound to mineral. Leleyter and Probst (1999) divided them into the eight parts of soluble, exchangeable, bound to carbonates, bound to amorphous iron and manganese oxides, bound to crystal iron and manganese oxides, bound to organic matte and residual. Most of studies showed that the species of soluble and exchangeable metals in soil were available to plants. Their proportions in total metal in soil were important to available and toxic to plants (Allen et al. 1980). The major objective of the present study is to investigate the effect of the modified nano-scale carbon black (MCB) used as an amendment for Cu-contaminated or Zncontaminated soils on metal fractionations in soil by cultivation experiment and to find the relationship between the metal uptake by plant and the metal fractionations in soil. It will provide a proof for an application of the MCB in remediation metal contaminated soils.
MATERIALS AND METHODS Modification of Nano-scale Carbon Black A commercial nanoscale carbon black (CB) with particle size of 20–70 nm was purchased from Jinan Carbon Black factory, Shandong Province, China. The CB used in this study was mostly soot without char, charcoal, and obtained by the coal tar fuel. This carbon black was further oxidized with 65% HNO3 for modification by refluxing 10 g of carbon black with 150 ml HNO3 (65%) in a conical flask at 110◦ C for 120 min. The modified nano-scale carbon black (MCB) was filtered, washed with deionized water until ◦ the pH up to 5.5 and finally dried in a vacuum oven at 110 C for 24 h. The specific surface areas of the MCB determined by the BET method in a Micrometrics Accusorb 2100 E were 1259 m2 g−1. Compared with the CB, the MCB has a more negative zeta potential and more functional groups resulted in an increasing surface cation exchange and complexation capacity (Zhou et al. 2010).
Collection of Soil Samples and Preparation A red soil of plough layers (0–20 cm) development on the Quaternary red clay was sampled from near metal smelters, Guixi (Jiangxi Province, China). The soil sample was
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air-dried and sieved (2 mm mesh). The general properties of the soil was pH 3.99, cation exchange capacity (CEC) 9.29 cmol·kg–1, organic matter (OM) 26.6 g·kg–1, clay content up to 40%, Cu 547 mg·kg–1, Zn 70 mg·kg–1,Pb 41 mg·kg–1, and Cd 1.9 mg·kg–1.
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Experimental Design and Procedures The MCB of 0, 1%, 3%, and 5% were added into soil, mixed thoroughly; and placed into pots (1.5 kg per pot). For each pot, 0.33 g urea and 0.35 g K2 HPO4 were added as fertilizer and mixed thoroughly. There were three replicates for each treatment, with 12 pots in total. All pots were adjusted regularly to 70% of field water capacity using deionized water. Twenty well-germinated ryegrass seeds (Lolium multiflorum) (obtained from Academy of Agricultural Sciences Research in Jiangsu Province, PR China) were sowed into each pot. The plants were harvested after a growth period of 8 weeks. At the end of the experiment, the shoot and root were separated, washed, and weighed after adhering water was removed with filter paper. Dry weights of roots and shoots were determined after drying at 70◦ C overnight, before grinding to pass 0.25 mm sieve. Soil subsamples were air-dried and ground to pass through a 1-mm sieve.
Analytical Methods The air-dried soil samples were tested for pH (using a pH meter, 10 g soil in 10 ml 0.01 M CaCl2 ), organic matter (wet combustion method, using H2 SO4 -K2 Cr2 O7 ), available Cu and Zn (by DTPA [pH = 7.3] extraction); and total Zn, Cu, Pb, and Cd (by HNO3 HClO4 -HF extraction), followed by atomic absorption spectrophotometry (AAS). Cu and Zn contents of ryegrass were also determined using AAS after digestion with HNO3 -HClO4 (Shi 1996). The distribution of Cu and Zn in various fractions in the soils at the end of the incubation period was also analyzed. The fractions were tested using the sequential extraction procedures described by European Community Bureau of Reference (Ure et al. 1993), with modifications: (1) exchangeable Cu and Zn and bound to carbonates Cu and Zn (EC-Cu or EC-Zn): extracted with 0.11 mol·L–1 acetic acid; (2) Cu and Zn bound to iron and manganese oxides (RD-Cu or RD-Zn): extracted with 0.1 mol·L–1 NH2 OH-HCl (pH 2.0); (3) Cu and Zn bound to organic matte (OD-Cu or OD-Zn): extracted by oxidizing the organic matter with 8.8 mol·L–1 H2 O2 (pH 2.0) followed by 1 mol·L–1 NH4 OAc extraction; (4) residual fraction of Cu and Zn (RS-Cu or RS-Zn): extracted by 10 ml HF + 2 ml HClO4 . Cu and Zn brought into solution were measured by AAS.
Statistical Analyses The comparison uses ‘Fully Factorial (M) ANOVA’ (SYSTAT) was used to determine the difference between treatments. In a column, means with the same letter were not significantly different at p > 0.05 in different treatments. The relationships between the uptake of metals by ryegrass shoot and the concentrations of DTPA-extractable, and metal fractions in soil were analyzed using the general linear model available in SPSS (Armitage and Berry 1994).
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RESULTS Ryegrass Shoot and Root Biomass Adding MCB increased significantly the biomass of ryegrass shoot and root, and they increased with the increasing of MCB adding amount (Fig. 1). Comparing with non-MCB, ryegrass shoot and root biomass increased 71.6%, 172.8% and 413.2%, and 49.1%, 220.1%, and 435.6% at the MCB adding ratios (w/w) of 1%, 3%, and 5%, respectively.
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Cu and Zn Accumulation in Ryegrass Shoot The Zn or Cu accumulations in the ryegrass shoot decreased with the increasing of the MCB (Fig. 1). Comparing with non-MCB, the Cu and Zn accumulations in the ryegrass shoot were significantly different (p < 0.05) when the MCB addition was more than 3% and 1%. The Zn accumulation in the shoot was more than the Cu. The Cu absorption coefficients (the takeup of plant/the total content of soil) of ryegrass shoot were all lower than 1.0, and were 0.08, 0.05, 0.05, and 0.04 at the MCB adding ratios (w/w) of 0, 1%, 3%, and 5% respectively. The Zn absorption coefficients were higher than 1.0, and were1.82, 1.56, 1.41, and 1.32 respectively. The results indicated that ryegrass shoot was with enrichment of Zn, but not Cu.
DTPA-extractable Concentrations of Zn and Cu in Soil At the end of incubation experiment, the concentrations of DTPA-Cu and DTPA-Zn in soils were significantly decreased with the increasing of MCB (p < 0.05) (Fig. 3). Compared with non-MCB, the concentrations of DTPA-Cu decreased 31.34%, 60.98%, and 71.17% when the MCB was added at ratios of 1%, 3%, and 5%, and the concentrations of DTPA-Zn decreased 20.24%, 35.76%, and 44.05% respectively. The DTPA-Cu or DTPA-Zn was not significantly different between the treatments of 3% and 5% MCB.
Figure 1 Influence of MCB on biomass of ryegrass shoot and root. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p < 0.05 in different treatments.
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Figure 2 Influence of MCB amendment on Cu and Zn concentration of ryegrass shoot. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
Cu and Zn Fractions in Soil The results presented in Table 1 showed the Cu and Zn fractions in soil by sequential extraction method of BCR. The EC-Cu and EC-Zn were 128–154 mg·kg–1 and 7–9 mg·kg–1. The RD-Cu and RD-Zn were 4–7 mg·kg–1 and 2–3.5 mg·kg–1. The OD-Cu and OD-Zn were 30–45 mg·kg–1 and 2–9 mg·kg–1. The RS-Cu and RS-Zn were 355–372 mg·kg–1 and 41–46 mg·kg–1. The data in Figure 4 showed the percentages of Cu and Zn fractions of the total metal in soil. The EC-Cu, RD-Cu, OD-Cu, and RS-Cu were about 23.9% ∼ 28.1%, 0.84% ∼ 1.3%, 5.8% ∼ 7.8%, and 65.0% ∼ 68.9% of total Cu in soil respectively. The EC-Zn, RD-Zn, OD-Zn, and RS-Zn were about 11.7% ∼ 14.8%, 1.7 ∼ 3.2%, 3.9% ∼ 17.1%, and 69.5% ∼ 78.7% of total Zn in soil respectively. The percentage of EC-Cu was higher than that of EC-Zn, and the percentage of RS-Cu was lower than that of RS-Zn.
Figure 3 Bioavailability of Cu and Zn during the culturation experiments in soil. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
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Table 1 Cu and Zn fractions in soil Fraction (mg·kg–1) Treatments Cu
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Zn
CK 1%OCB 3%OCB 5%OCB CK 1%OCB 3%OCB 5%OCB
EC
RD
OD
RSl
153.64 ± 3.88 a 136.11 ± 0.73 b 128.46 ± 6.74 b 130.81 ± 2.47 b 8.76 ± 0.32 a 8.63 ± 0.39 ab 7.91 ± 0.53 b 6.99 ± 0.47 c
6.05 ± 0.25 a 4.37 ± 0.69 b 4.60 ± 1.12 ab 6.90 ± 0.90 c 1.66 ± 0.36 bc 1.87 ± 0.21 ab 2.50 ± 0.16 a 1.00 ± 1.06 bd
31.76 ± 0.54 d 33.68 ± 1.24 c 36.94 ± 1.00 b 42.48 ± 1.26 a 2.29 ± 1.07 b 2.14 ± 0.92 b 3.14 ± 1.58 b 10.2 ± 2.50 a
355.55 ± 4.17 c 372.84 ± 0.20 b 377.00 ± 9.52 a 366.81 ± 1.31 bc 46.59 ± 1.75 ac 46.66 ± 0.32 a 41.75 ± 2.27 bc 41.51 ± 3.09 c
The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT).In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
The metal contents of exchangeable and bound to carbonates in the treatments of adding MCB were generally lower than those of non-MCB, and decreased with the increase of MCB. The metal contents of bound to iron and manganese oxides were higher generally than those of non-MCB, and increased with the increase of MCB. There was no clear trend of the metal content of bound to organic matte and residual with the increase of MCB. The percentage of EC-Cu was higher than that of EC-Zn, and RS-Cu was lower than RSZn. The percentages between RD-Cu and RD-Zn, between OD-Cu and OD-Zn were not significantly different. The Interrelation Coefficient between Cu or Zn Fractions in Soil and Cu or Zn Accumulation in Ryegrass Shoots There was a positive linear correlation between the Cu or Zn accumulation in shoots and the EC-Cu or EC-Zn in soil, and a negative linear correlation between Cu or Zn accumulation in shoots and the OD-Cu or OD-Zn in soil (p < 0.01). There was no correlation
Figure 4 The percent of Cu or Zn fractions of the total metal in soil. EC-Exchangeable and bound to carbonates, RD-Bound to iron and manganese oxides, OD-Bound to organic matte and RS- Residual.
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between the Cu or Zn accumulation in shoots and the RD-Cu or RD-Zn in soils. There was a negative linear correlation between the Cu accumulation in shoot and RS-Cu in soil (p < 0.05), and a positive linear correlation between the Zn accumulation in shoot and RS-Zn in soil (p < 0.01) (Table 2).
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DISCUSSIONS Cu and Zn were essential trace elements for plant, and excessive Cu and Zn in soil might inhibit plant growth or even damage (Chu et al. 2004). The total Cu in soil for the greenhouse experiment was 547 mg·kg–1, and the excessive Cu in soil might have an influence on the biomass of ryegrass shoot and root. When the MCB added into the Cu-contaminated soil, which had a negative zeta potential (Zhou et al. 2010) and a surface with hydroxyl groups or carbonyl groups, carboxylic acids and hydroxyl groups (Stafiej and Pyrzynska 2007), the excessive Cu in soil was adsorbed and complexed by the MCB. The transfer of metal ions from soil to shoot was inhibited, and the toxicity of metals to plants reduced. Thereby adding MCB significantly increased the biomass of ryegrass shoot and root, and the biomass increased with the increase of MCB. The plant absorption coefficients of metals indicated the intensity of plant uptake of elements (Yang et al. 2010). The contents of trace elements in herbaceous plants were affected by the species of the plant and the soil environments (Davies 1992; Xu et al. 2005; Wang et al. 2007). Zn was easy to transfer, and the ratio of Zn in the plant and soil was usually higher than 1.3. Cu was hard to transfer, and the ratio of Cu in the plant and soil was mostly lower than 0.08 (Fig. 2). This was the reason the Zn accumulation in shoot was much greater than Cu, though the total Cu in soil was much higher than Zn. While compared with non-MCB, the DTPA-Cu decreased 31.3%, 61.0%, and 71.2% and the DTPA-Zn decreased 20.2%, 35.8% and 44.0% respectively, when the MCB was added at ratios of 1%, 3%, and 5% (Fig. 3). This implied that the passivation of Cu in soil by MCB was easier than Zn. This was the reason that the contents of Cu and Zn in ryegrass shoot were significantly decreased with the increase of MCB, and the reduction of Cu accumulation in ryegrass shoot was greater than Zn. Bioavailability of heavy metals in soil depended on its fractions in soil (Li et al. 2001; Morton-Bermea et al. 2009). The fraction of exchangeable and bound to carbonates was easier to release from soil components, so it was easier available by plant (Wu and Pan 2003). The metal bound to iron and manganese oxides was easier to release under the reducing conditions (Yang et al. 2001), and the metal bound to organic matte under the oxidizing conditions. They had potential toxicity to plants (Rauret et al. 1999). The Table 2 The interrelation coefficient between influence factors and Cu or Zn concentration of ryegrass Cu Fraction EC RD OD RS
Zn
y = a + bx
R
y = a + bx
R
y = −80.01 + 0.81x y = 35.62 −0.81x y = 99.85 −1.90x y = 293.85 −0.71x
0.913∗∗ −0.096 −0.880∗∗ −0.658∗
y = −24.38 + 16.32x y = 103.09 + 2.43x y = 119.37 −2.70x y = −94.20 + 4.57x
0.881∗∗ 0.097 −0.778∗∗ 0.805∗∗
n = 16; r0.05 = 0.576; r0.01 = 0.708
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residual metal was harder to release under natural conditions, and it was almost unavailable to plants (Cong et al. 2009). The percentage of EC-Cu of the total Cu in soil was higher than that of EC-Zn (Fig. 4), so the bioavailability of Cu in soil was higher than that of Zn. There was a positive linear correlation between the Cu or Zn accumulation in ryegrass shoot and the EC-Cu or EC-Zn in soil (p < 0.01) (Table 2), so the metal of exchangeable and bound to carbonates was a supply source to the uptake by plants. The metal contents of exchangeable and bound to carbonates in the treatments of addition MCB were lower than non-MCB, and decreased with the increase of MCB (Table 1), and it was why adding MCB into soil the metals accumulation in ryegrass shoot decreased.
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CONCLUSIONS It could be concluded from the above discussion that the MCB had very good adsorption and complexation properties for the metal ions in soil, and the passivation ability to Cu in soil was stronger than Zn. The MCB could be applied for the remediation of soil polluted by heavy metals (e.g., Cu, Zn). More extensive research was needed to further test under field conditions.
ACKNOWLEDGMENTS The authors would like to thank the National Natural Science Fund Committee, China (41171251) and the Ph.D. Programs Foundation of Ministry of Education of China (20103704110001) for financial support.
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Morton-Bermea E, Hern´andez-Alvarez G, Gonz´alez-Hern´andez F. 2009. Assessment of heavy metal pollution in urban topsoils from the metropolitan area of Mexico City. Journal of Geochemical Exploration 101(3):218–224. Nowack B, Bucheli TD. 2007. Occurrence, behavior and effects of nano particles in the environment. Environ Pollut 150:5–22. Rauret G, Lopez-Sanchez JF, Sahuquillo A. 1999. Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials. Journal of Environmental Monitoring 1:57–61. Shi RH. 1996. The Analytical Methods of Soil Agricultural Chemistry. Beijing (China): Chinese Agricultural Press. Shuman LM. 1985. Fractionation Method for Soil Microelements. Soil Science 140:11–12. Stafiej A, Pyrzynska K. 2007. Adsorption of heavy metal ions with carbon nanotubes. Sep Purif Technol 58:49–52. Tessier A, Campbell P, Bission M. 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 51(7):844–851. Ure AM, Quevauailler PH, Mentau H, Griepink B. 1993. Community Bureau of Reference Information Chemical Analysis Report Eur14763 EN, Commission of the European Communities, Brusselas. Wang C, Fang Y, Wu X. 2007. Absorption Ability of 21 Species of Ornamental Plants on Heavy Metal-Polluted Environments. Protection Forest Science and Technology (Supplement):1–9 Wang H, Wang Y, Cheng J, et al. 2009. Application of modified nano-particle black carbon for the remediation of soil heavy mental pollution. China Environmental Science 29(4):431–436. Wu X, Pan G. 2003. The correlation analysis between the content of heavy metals and the factors influencing the pollution of heavy metals in urban soils in Nanjing city. Acta Pedologica Sinica 40(6):921–929. Xu W, Xiong Z, Wang H. 2005. Effects of Zn stress on nutrient uptake and Zn accumulation in four varieties of ryegrass. Journal of Soil Water Conservation 19(4):32–35, 43. Yang W, Gao Y, Kang Z. 2010. Chemical forms and bioavailability of heavy metals in soil of scenic adjacent to iron ore. Environmental Science and Technology 33(11):82–86. Yang Y, Paterson E, Canpbell C. 2001. Accumulation of Heavy Metals in Urban Soils and Impacts on Microorganisms. Chinese Journal of Environmental Science 22(3):44–48. Yang Y, Zhong R, Nan Z. 2011. Chemical fractions and bioavailability of cadmium and zinc to cole (Brassica campestris L.) grown in the multi-metals contaminated oasis soil, northwest of China. Journal of Environmental Sciences 23(2):275–281. Young SD, Tye A, Carstensen A. 2000. Methods for determining labile cadmium and zinc in soil. Eur J Soil Sci 51:129–136. Zheng X, Liu J. 2008. Effects of different amendments on in situ immobilization of heavy metal pollution soil. Straits Science 18(6):27–28. Zhou D, Wang Y, Wang H. 2010. Surface -modified nano-scale carbon black used as sorbents for Cu(II) and Cd(II). Journal of Hazardous Materials 174:34–39.
International Journal of Phytoremediation Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/bijp20
Effects of Surface-Modified NanoScale Carbon Black on Cu and Zn Fractionations in Contaminated Soil a
a
Jie-min Cheng , Yu-zhen Liu & Han-wei Wang
a
a
College of Population Resources and Environment , Shandong Normal University , Jinan , China Accepted author version posted online: 25 Aug 2013.Published online: 10 Sep 2013.
Click for updates To cite this article: Jie-min Cheng , Yu-zhen Liu & Han-wei Wang (2014) Effects of Surface-Modified Nano-Scale Carbon Black on Cu and Zn Fractionations in Contaminated Soil, International Journal of Phytoremediation, 16:1, 86-94, DOI: 10.1080/15226514.2012.759530 To link to this article: http://dx.doi.org/10.1080/15226514.2012.759530
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
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International Journal of Phytoremediation, 16:86–94, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1522-6514 print / 1549-7879 online DOI: 10.1080/15226514.2012.759530
EFFECTS OF SURFACE-MODIFIED NANO-SCALE CARBON BLACK ON CU AND ZN FRACTIONATIONS IN CONTAMINATED SOIL
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Jie-min Cheng, Yu-zhen Liu, and Han-wei Wang College of Population Resources and Environment, Shandong Normal University, Jinan, China Cu contamination soil (547 mg kg–1) was mixed separately with the surface-modified nanoscale carbon black (MCB) and placed in the ratios (w/w) of 0, 1%, 3%, and 5% in pots, together with 0.33 g KH2 PO4 and 0.35 g urea/pot. Each pot contained 20 ryegrass seedlings (Lolium multiflorum). Greenhouse cultivation experiments were conducted to examine the effect of the MCB on Cu and Zn fractionations in soil, accumulation in shoot and growth of ryegrass. The results showed that the biomass of ryegrass shoot and root increased with the increasing of MCB adding amount (p < 0.05). The Cu and Zn accumulation in ryegrass shoot and the concentrations of DTPA extractable Cu and Zn in soil were significantly decreased with the increasing of MCB adding amount (p < 0.05). The metal contents of exchangeable and bound to carbonates (EC-Cu or EC-Zn) in the treatments with MCB were generally lower than those without MCB, and decreased with the increasing of MCB adding amount (p < 0.05). There was a positive linear correlation between the Cu and Zn accumulation in ryegrass shoot and the EC-Cu and EC-Zn in soil. The present results indicated the MCB could be applied for the remediation the soils polluted by Cu and Zn. KEY WORDS: surface-modified nano-scale black carbon, Cu and Zn fractionations, soil, ryegrass
INTRODUCTION Carbon black (CB) is a product of biomass or fossil fuel under incomplete combustion. The particle size of CB is partially in the nanometer range with average values between 20 and 300 nm from different sources (Nowack and Bucheli 2007) and with functional group such as carboxyl, phenolic hydroxyl and carbonyl (Liu 2002). However, such CB often shows higher adsorption capacity of organic compounds(Cornelissen and Gustrafsson 2004)and lower adsorption capacity of metal ions (Fan et al. 2001). Most of surfacemodified carbon adsorbents (MCAs) were prepared by oxidation of activated carbon with HNO3 which has shown good adsorption abilities of Cu and Cd (Zhou et al. 2010). The contents of heavy metals taken up by plants from soils depend on the available metals to plants rather than the total content in soil (Yang et al. 2011). Zheng and Liu (2008) added 750 kg lime per hectare into heavy metals contamination soil and the available Cu, Pb, Cd, and As to plants decreased 21.1%, 48.6%, 11. 6%, and 27.7% and then the uptake
Address coresspondence to Jie-min Cheng, College of Population Resources and Environment, Shandong Normal University, Jinan, 250014 China. E-mail: [email protected] 86
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of Cu, Pb, Cd, and As by mustard decreased 22.3%, 50.0%, 23.1%, and 44.0% respectively. Wang(2009)added 1%, 3%, and 5% MCA modified with HNO3 into the red earth and the available Cu decreased 47.26%, 72.0%, and 80.9% and available Zn decreased 3.0%, 17.7%, and 43.6% respectively. The decrease of metals availability to plants may be an effective method of remediation heavy metal pollution soil. Heavy metals, once in the soil, may become non-soluble or unavailable to plants through precipitation, absorption, complexation, and other reactions with organic and inorganic soil components. The proportion of soluble or non-soluble metals may depend on the characteristic, concentration and residence time of metal contaminant and soil conditions (Young et al. 2000). Tessier et al. (1979) divided the species of metals in sediment or soil into the five parts of exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to organic matte and residual. Shuman (1985) divided them into the eight parts of soluble, exchangeable, bound to carbonates, loose bound to organic matter, bound to manganese oxides, fast bound to organic matter, bound to iron oxides and bound to mineral. Leleyter and Probst (1999) divided them into the eight parts of soluble, exchangeable, bound to carbonates, bound to amorphous iron and manganese oxides, bound to crystal iron and manganese oxides, bound to organic matte and residual. Most of studies showed that the species of soluble and exchangeable metals in soil were available to plants. Their proportions in total metal in soil were important to available and toxic to plants (Allen et al. 1980). The major objective of the present study is to investigate the effect of the modified nano-scale carbon black (MCB) used as an amendment for Cu-contaminated or Zncontaminated soils on metal fractionations in soil by cultivation experiment and to find the relationship between the metal uptake by plant and the metal fractionations in soil. It will provide a proof for an application of the MCB in remediation metal contaminated soils.
MATERIALS AND METHODS Modification of Nano-scale Carbon Black A commercial nanoscale carbon black (CB) with particle size of 20–70 nm was purchased from Jinan Carbon Black factory, Shandong Province, China. The CB used in this study was mostly soot without char, charcoal, and obtained by the coal tar fuel. This carbon black was further oxidized with 65% HNO3 for modification by refluxing 10 g of carbon black with 150 ml HNO3 (65%) in a conical flask at 110◦ C for 120 min. The modified nano-scale carbon black (MCB) was filtered, washed with deionized water until ◦ the pH up to 5.5 and finally dried in a vacuum oven at 110 C for 24 h. The specific surface areas of the MCB determined by the BET method in a Micrometrics Accusorb 2100 E were 1259 m2 g−1. Compared with the CB, the MCB has a more negative zeta potential and more functional groups resulted in an increasing surface cation exchange and complexation capacity (Zhou et al. 2010).
Collection of Soil Samples and Preparation A red soil of plough layers (0–20 cm) development on the Quaternary red clay was sampled from near metal smelters, Guixi (Jiangxi Province, China). The soil sample was
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air-dried and sieved (2 mm mesh). The general properties of the soil was pH 3.99, cation exchange capacity (CEC) 9.29 cmol·kg–1, organic matter (OM) 26.6 g·kg–1, clay content up to 40%, Cu 547 mg·kg–1, Zn 70 mg·kg–1,Pb 41 mg·kg–1, and Cd 1.9 mg·kg–1.
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Experimental Design and Procedures The MCB of 0, 1%, 3%, and 5% were added into soil, mixed thoroughly; and placed into pots (1.5 kg per pot). For each pot, 0.33 g urea and 0.35 g K2 HPO4 were added as fertilizer and mixed thoroughly. There were three replicates for each treatment, with 12 pots in total. All pots were adjusted regularly to 70% of field water capacity using deionized water. Twenty well-germinated ryegrass seeds (Lolium multiflorum) (obtained from Academy of Agricultural Sciences Research in Jiangsu Province, PR China) were sowed into each pot. The plants were harvested after a growth period of 8 weeks. At the end of the experiment, the shoot and root were separated, washed, and weighed after adhering water was removed with filter paper. Dry weights of roots and shoots were determined after drying at 70◦ C overnight, before grinding to pass 0.25 mm sieve. Soil subsamples were air-dried and ground to pass through a 1-mm sieve.
Analytical Methods The air-dried soil samples were tested for pH (using a pH meter, 10 g soil in 10 ml 0.01 M CaCl2 ), organic matter (wet combustion method, using H2 SO4 -K2 Cr2 O7 ), available Cu and Zn (by DTPA [pH = 7.3] extraction); and total Zn, Cu, Pb, and Cd (by HNO3 HClO4 -HF extraction), followed by atomic absorption spectrophotometry (AAS). Cu and Zn contents of ryegrass were also determined using AAS after digestion with HNO3 -HClO4 (Shi 1996). The distribution of Cu and Zn in various fractions in the soils at the end of the incubation period was also analyzed. The fractions were tested using the sequential extraction procedures described by European Community Bureau of Reference (Ure et al. 1993), with modifications: (1) exchangeable Cu and Zn and bound to carbonates Cu and Zn (EC-Cu or EC-Zn): extracted with 0.11 mol·L–1 acetic acid; (2) Cu and Zn bound to iron and manganese oxides (RD-Cu or RD-Zn): extracted with 0.1 mol·L–1 NH2 OH-HCl (pH 2.0); (3) Cu and Zn bound to organic matte (OD-Cu or OD-Zn): extracted by oxidizing the organic matter with 8.8 mol·L–1 H2 O2 (pH 2.0) followed by 1 mol·L–1 NH4 OAc extraction; (4) residual fraction of Cu and Zn (RS-Cu or RS-Zn): extracted by 10 ml HF + 2 ml HClO4 . Cu and Zn brought into solution were measured by AAS.
Statistical Analyses The comparison uses ‘Fully Factorial (M) ANOVA’ (SYSTAT) was used to determine the difference between treatments. In a column, means with the same letter were not significantly different at p > 0.05 in different treatments. The relationships between the uptake of metals by ryegrass shoot and the concentrations of DTPA-extractable, and metal fractions in soil were analyzed using the general linear model available in SPSS (Armitage and Berry 1994).
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RESULTS Ryegrass Shoot and Root Biomass Adding MCB increased significantly the biomass of ryegrass shoot and root, and they increased with the increasing of MCB adding amount (Fig. 1). Comparing with non-MCB, ryegrass shoot and root biomass increased 71.6%, 172.8% and 413.2%, and 49.1%, 220.1%, and 435.6% at the MCB adding ratios (w/w) of 1%, 3%, and 5%, respectively.
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Cu and Zn Accumulation in Ryegrass Shoot The Zn or Cu accumulations in the ryegrass shoot decreased with the increasing of the MCB (Fig. 1). Comparing with non-MCB, the Cu and Zn accumulations in the ryegrass shoot were significantly different (p < 0.05) when the MCB addition was more than 3% and 1%. The Zn accumulation in the shoot was more than the Cu. The Cu absorption coefficients (the takeup of plant/the total content of soil) of ryegrass shoot were all lower than 1.0, and were 0.08, 0.05, 0.05, and 0.04 at the MCB adding ratios (w/w) of 0, 1%, 3%, and 5% respectively. The Zn absorption coefficients were higher than 1.0, and were1.82, 1.56, 1.41, and 1.32 respectively. The results indicated that ryegrass shoot was with enrichment of Zn, but not Cu.
DTPA-extractable Concentrations of Zn and Cu in Soil At the end of incubation experiment, the concentrations of DTPA-Cu and DTPA-Zn in soils were significantly decreased with the increasing of MCB (p < 0.05) (Fig. 3). Compared with non-MCB, the concentrations of DTPA-Cu decreased 31.34%, 60.98%, and 71.17% when the MCB was added at ratios of 1%, 3%, and 5%, and the concentrations of DTPA-Zn decreased 20.24%, 35.76%, and 44.05% respectively. The DTPA-Cu or DTPA-Zn was not significantly different between the treatments of 3% and 5% MCB.
Figure 1 Influence of MCB on biomass of ryegrass shoot and root. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p < 0.05 in different treatments.
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Figure 2 Influence of MCB amendment on Cu and Zn concentration of ryegrass shoot. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
Cu and Zn Fractions in Soil The results presented in Table 1 showed the Cu and Zn fractions in soil by sequential extraction method of BCR. The EC-Cu and EC-Zn were 128–154 mg·kg–1 and 7–9 mg·kg–1. The RD-Cu and RD-Zn were 4–7 mg·kg–1 and 2–3.5 mg·kg–1. The OD-Cu and OD-Zn were 30–45 mg·kg–1 and 2–9 mg·kg–1. The RS-Cu and RS-Zn were 355–372 mg·kg–1 and 41–46 mg·kg–1. The data in Figure 4 showed the percentages of Cu and Zn fractions of the total metal in soil. The EC-Cu, RD-Cu, OD-Cu, and RS-Cu were about 23.9% ∼ 28.1%, 0.84% ∼ 1.3%, 5.8% ∼ 7.8%, and 65.0% ∼ 68.9% of total Cu in soil respectively. The EC-Zn, RD-Zn, OD-Zn, and RS-Zn were about 11.7% ∼ 14.8%, 1.7 ∼ 3.2%, 3.9% ∼ 17.1%, and 69.5% ∼ 78.7% of total Zn in soil respectively. The percentage of EC-Cu was higher than that of EC-Zn, and the percentage of RS-Cu was lower than that of RS-Zn.
Figure 3 Bioavailability of Cu and Zn during the culturation experiments in soil. The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT). In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
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Table 1 Cu and Zn fractions in soil Fraction (mg·kg–1) Treatments Cu
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Zn
CK 1%OCB 3%OCB 5%OCB CK 1%OCB 3%OCB 5%OCB
EC
RD
OD
RSl
153.64 ± 3.88 a 136.11 ± 0.73 b 128.46 ± 6.74 b 130.81 ± 2.47 b 8.76 ± 0.32 a 8.63 ± 0.39 ab 7.91 ± 0.53 b 6.99 ± 0.47 c
6.05 ± 0.25 a 4.37 ± 0.69 b 4.60 ± 1.12 ab 6.90 ± 0.90 c 1.66 ± 0.36 bc 1.87 ± 0.21 ab 2.50 ± 0.16 a 1.00 ± 1.06 bd
31.76 ± 0.54 d 33.68 ± 1.24 c 36.94 ± 1.00 b 42.48 ± 1.26 a 2.29 ± 1.07 b 2.14 ± 0.92 b 3.14 ± 1.58 b 10.2 ± 2.50 a
355.55 ± 4.17 c 372.84 ± 0.20 b 377.00 ± 9.52 a 366.81 ± 1.31 bc 46.59 ± 1.75 ac 46.66 ± 0.32 a 41.75 ± 2.27 bc 41.51 ± 3.09 c
The comparison uses “Fully Factorial(M)ANOVA”(SYSTAT).In a column, means with the same letter are not significantly different at p > 0.05 in different treatments.
The metal contents of exchangeable and bound to carbonates in the treatments of adding MCB were generally lower than those of non-MCB, and decreased with the increase of MCB. The metal contents of bound to iron and manganese oxides were higher generally than those of non-MCB, and increased with the increase of MCB. There was no clear trend of the metal content of bound to organic matte and residual with the increase of MCB. The percentage of EC-Cu was higher than that of EC-Zn, and RS-Cu was lower than RSZn. The percentages between RD-Cu and RD-Zn, between OD-Cu and OD-Zn were not significantly different. The Interrelation Coefficient between Cu or Zn Fractions in Soil and Cu or Zn Accumulation in Ryegrass Shoots There was a positive linear correlation between the Cu or Zn accumulation in shoots and the EC-Cu or EC-Zn in soil, and a negative linear correlation between Cu or Zn accumulation in shoots and the OD-Cu or OD-Zn in soil (p < 0.01). There was no correlation
Figure 4 The percent of Cu or Zn fractions of the total metal in soil. EC-Exchangeable and bound to carbonates, RD-Bound to iron and manganese oxides, OD-Bound to organic matte and RS- Residual.
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between the Cu or Zn accumulation in shoots and the RD-Cu or RD-Zn in soils. There was a negative linear correlation between the Cu accumulation in shoot and RS-Cu in soil (p < 0.05), and a positive linear correlation between the Zn accumulation in shoot and RS-Zn in soil (p < 0.01) (Table 2).
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DISCUSSIONS Cu and Zn were essential trace elements for plant, and excessive Cu and Zn in soil might inhibit plant growth or even damage (Chu et al. 2004). The total Cu in soil for the greenhouse experiment was 547 mg·kg–1, and the excessive Cu in soil might have an influence on the biomass of ryegrass shoot and root. When the MCB added into the Cu-contaminated soil, which had a negative zeta potential (Zhou et al. 2010) and a surface with hydroxyl groups or carbonyl groups, carboxylic acids and hydroxyl groups (Stafiej and Pyrzynska 2007), the excessive Cu in soil was adsorbed and complexed by the MCB. The transfer of metal ions from soil to shoot was inhibited, and the toxicity of metals to plants reduced. Thereby adding MCB significantly increased the biomass of ryegrass shoot and root, and the biomass increased with the increase of MCB. The plant absorption coefficients of metals indicated the intensity of plant uptake of elements (Yang et al. 2010). The contents of trace elements in herbaceous plants were affected by the species of the plant and the soil environments (Davies 1992; Xu et al. 2005; Wang et al. 2007). Zn was easy to transfer, and the ratio of Zn in the plant and soil was usually higher than 1.3. Cu was hard to transfer, and the ratio of Cu in the plant and soil was mostly lower than 0.08 (Fig. 2). This was the reason the Zn accumulation in shoot was much greater than Cu, though the total Cu in soil was much higher than Zn. While compared with non-MCB, the DTPA-Cu decreased 31.3%, 61.0%, and 71.2% and the DTPA-Zn decreased 20.2%, 35.8% and 44.0% respectively, when the MCB was added at ratios of 1%, 3%, and 5% (Fig. 3). This implied that the passivation of Cu in soil by MCB was easier than Zn. This was the reason that the contents of Cu and Zn in ryegrass shoot were significantly decreased with the increase of MCB, and the reduction of Cu accumulation in ryegrass shoot was greater than Zn. Bioavailability of heavy metals in soil depended on its fractions in soil (Li et al. 2001; Morton-Bermea et al. 2009). The fraction of exchangeable and bound to carbonates was easier to release from soil components, so it was easier available by plant (Wu and Pan 2003). The metal bound to iron and manganese oxides was easier to release under the reducing conditions (Yang et al. 2001), and the metal bound to organic matte under the oxidizing conditions. They had potential toxicity to plants (Rauret et al. 1999). The Table 2 The interrelation coefficient between influence factors and Cu or Zn concentration of ryegrass Cu Fraction EC RD OD RS
Zn
y = a + bx
R
y = a + bx
R
y = −80.01 + 0.81x y = 35.62 −0.81x y = 99.85 −1.90x y = 293.85 −0.71x
0.913∗∗ −0.096 −0.880∗∗ −0.658∗
y = −24.38 + 16.32x y = 103.09 + 2.43x y = 119.37 −2.70x y = −94.20 + 4.57x
0.881∗∗ 0.097 −0.778∗∗ 0.805∗∗
n = 16; r0.05 = 0.576; r0.01 = 0.708
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residual metal was harder to release under natural conditions, and it was almost unavailable to plants (Cong et al. 2009). The percentage of EC-Cu of the total Cu in soil was higher than that of EC-Zn (Fig. 4), so the bioavailability of Cu in soil was higher than that of Zn. There was a positive linear correlation between the Cu or Zn accumulation in ryegrass shoot and the EC-Cu or EC-Zn in soil (p < 0.01) (Table 2), so the metal of exchangeable and bound to carbonates was a supply source to the uptake by plants. The metal contents of exchangeable and bound to carbonates in the treatments of addition MCB were lower than non-MCB, and decreased with the increase of MCB (Table 1), and it was why adding MCB into soil the metals accumulation in ryegrass shoot decreased.
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CONCLUSIONS It could be concluded from the above discussion that the MCB had very good adsorption and complexation properties for the metal ions in soil, and the passivation ability to Cu in soil was stronger than Zn. The MCB could be applied for the remediation of soil polluted by heavy metals (e.g., Cu, Zn). More extensive research was needed to further test under field conditions.
ACKNOWLEDGMENTS The authors would like to thank the National Natural Science Fund Committee, China (41171251) and the Ph.D. Programs Foundation of Ministry of Education of China (20103704110001) for financial support.
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