Reduction of arsenic bioavailability by amending seven inorganic materials in arsenic contaminated soil

Journal of Integrative Agriculture 2015, 14(7): 1414–1422 Available online at www.sciencedirect.com

ScienceDirect

RESEARCH ARTICLE

Reduction of arsenic bioavailability by amending seven inorganic materials in arsenic contaminated soil SUN Yuan-yuan1, 3, LIU Rong-le2, ZENG Xi-bai1, LIN Qi-mei3, BAI Ling-yu1, LI Lian-fang1, SU Shi-ming1, WANG Ya-nan1 1

Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences/Key Laboratory of Agro-Environment, Ministry of Agriculture, Beijing 100081, P.R.China 2 Graduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, P.R.China 3 College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, P.R.China

Abstract Seven inorganic amendment materials were added into arsenic (As) contaminated soil at a rate of 0.5% (w/w); the materials used were sepiolite, red mud, iron grit, phosphogypsum, ferrihydrite, iron phosphate, and layered double oxides (LDO). Plant growth trials using rape (edible rape, Brassia campestris L.) as a bio-indicator are commonly used to assess As bioavailability in soils. In this study, B. campestris was grown in a contaminated soil for 50 days. All of the inorganic amendments significantly inhibited the uptake of As by B. campestris. Following soil treatment with the seven aforementioned inorganic ammendments, the As concentrations in the edible parts of B. campestris were reduced by 28.6, 10.5, 8.7, 31.0, 47.4, 25.3, and 28.8%, respectively, as compared with the plants grown in control soil. The most effective amendment was ferrihydrite, which reduced As concentration in B. campestris from 1.84 to 0.97 mg kg–1, compared to control. Furthermore, ferrihydrite-treated soils had a remarkable decrease in both non-specifically sorbed As and available-As by 67 and 20%, respectively, comparing to control. Phosphogypsum was the most cost-effective amendment and it showed excellent performance in reducing the water soluble As in soils by 31% and inhibiting As uptake in B. campestris by 21% comparing to control. Additionally, obvious differences in As transfer rates were observed in the various amendments. The seven amendment materials used in this study all showed potential reduction of As bioavailability and influence on plant growth and other biological processes still need to be further explored in the long term. Keywords: arsenic, amendment, bioavailability, Brassia campestris L.

1. Introduction Received 12 May, 2014 Accepted 22 September, 2014 SUN Yuan-yuan, Tel: +86-10-82106009, E-mail: sunoo126@163. com; Correspondence ZENG Xi-bai, Tel: +86-10-82105612, E-mail: [email protected]; LIN Qi-mei, Tel: +86-10-62892502, E-mail: [email protected] © 2015, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(14)60894-7

Soils with contaminant levels that exceed level II of the Chinese Environmental Quality Standard for Soil (GB 15618–1995) (MEP 1995) are generally considered as ‘contaminated’ soils. Using this level as the criterion for classification, several researchers have estimated that at present 10-20% of the soils in the cropland areas of China are contaminated (Chen et al. 2006; Zeng et al. 2007;

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

Zhou et al. 2011). It should be noted that there are high risk cropland areas where the heavy metal content in soils dramatically exceeds the levels used in the basic classification of contamination. The soils in some of these high risk areas exceed level III of GB 15618–1995 (MEP 1995) and are thus considered to threaten the safety of agricultural production. The largest ore deposits of the arsenic sulfide mineral realgar in Asia are found near in Shimen, Hunan Province, China. As a result of a long history of realgar mining, the arsenic (As) content in soils surrounding the mining areas of Shimen severely exceed safe levels (Zeng et al. 2013). Adding to this problem is the fact that a large proportion of the soils in this area used for intensive crop production. Zeng et al. (2007) analyzed As concentrations in vegetable samples collected from different regions all over China and found that 44.2% of samples contained As; 9.2% of the samples had As levels that exceeded Chinese food safety restrictions. Clearly, a notable portion of the vegetables, grain, and roots produced in China are contaminated with As. Because of this problem, efforts to reduce the bioavailability As in contaminated soils used for crop production have become urgent and these efforts are now considered to be critically important for improving food safety in China. The use of soil amendments to reduce As bioavailability is considered to have high potential for success and to be a feasible measure in many crop production areas (Hartley and Lepp 2008; Simón et al. 2010). Numerous amendments have been tested in soils that are contaminated with heavy metals (Pena et al. 2006; Hartley and Lepp 2008; González-Núñez et al. 2012; Sun et al. 2013). Iron and aluminum bearing materials such as goethite, ferrous sulphate, layered double oxides (LDO) are commonly selected as soil amendments for their high capacity to adsorb arsenates. Sun and Doner (1998) reported that goethite significantly reduced As toxicity in contaminated soils. Warren et al. (2003) found that ferrous sulfate reduced lettuce As concentration by 12.4-39% at two As contaminated sites. Our previous findings showed that Mg/Al-layer doubled oxides (LDO) can efficiently adsorbe As in solution (Sun et al. 2011). Iron phosphate had adsorption capacities of 0.28 and 0.13 mmol g–1 for As(III) and As(V), respectively, and have thus been considered for potential in situ use (Lenoble et al. 2005). Sepiolite, which has both a large specific surface area and a high cadmium (Cd) adsorption capacity, has recently been considered as a cost-effective material for remediating Cd-contaminated soil (Xu et al. 2003; Liang et al. 2011; Sun et al. 2013). Various industrial by-products such as red mud, iron grit, and phosphogypsum have been used to remediate soils contaminated with heavy metals. In short-term laboratory and field studies, red mud (RM) proved to be highly effective at reducing heavy metal mobility in contaminated soils

1415

(Lombi et al. 2002; Gray et al. 2006; Garau et al. 2007; Castaldi et al. 2009) and in removing As from aqueous solutions (Castaldi et al. 2010; Li et al. 2010). However, little information is available regarding RM’s capacity to fix hazardous anion such as arsenate. Iron grit (steel shots) have been used for As stabilization in contaminated garden soils (Mench et al. 1994). Lidelöw et al. (2007) recorded a 68% reduction of arsenic concentration in pore water following treatment with iron grit. Phosphogypsum (CaSO4·2H2O) is a by-product of the phosphoric acid production industry. Bai et al. (2011) found that adding 20 g kg–1 phosphogypsum to soils markedly decreased As concentrations in maize in a pot trial. While studies of these soil amendments are very promising, little is known about how these materials influence As bioavailability. It is well known that the performance of soil amendments in remediation depends on many factors (Hartley et al. 2004; Hartley and Lepp 2008; Kumpiene et al. 2008). Among these factors, the interactions among soil, heavy metals, plant and the amendments may dominantly control the impacts of soil amendment on heavy metal bioavailability. In particular, the species of plants growing in a given soil is likely to have a marked influence on the remediation performance of soil amendment materials. Brassia campestris L. is a common crop that is grown in southern China; it is an especially popular crop in the areas which surrounds the sampling site of this study. In this study, seven amendments were added into As-contaminated soils and their effects on As bioavailability were assayed using B. campestris as a bioindicator species. The seven amendment materials included industrial by-products (red mud, iron grit, and phosphogypsum), minerals (ferrihydrite and sepiolite), phosphate (iron phosphate), and Al-bearing material (LDO). We hypothesized that the various amendments would differentially impact As bioavailability, and that these differential impacts would affect the amounts of As taken up by B. campestris. The aims were (1) to explore the influence of the seven inorganic materials on As bioavailability; (2) to investigate any changes in the As concentrations in the edible parts of B. campestris in response to 50 days of growth in the various amendments treatment soils; and (3) to screen and finally identify a suitable, practical amendment material that could feasibly be used to reduce As bioavailability in As-contaminated soils.

2. Results 2.1. B. campestris biomass and As concentration Treatment of soils with the various amendments had different impacts on the accumulation of B. campestris dry matter (Fig. 1). Adding LDO resulted in a significant, 16%

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

had a TC of 0.0048, 47% lower than the control. 0.5 mg As kg–1 fresh weight is the maximum levels of As permitted in vegetables in China (GB 2762–2012) (MEP 1995). In this study, although the contents of As in B. campestris did not exceed the limit, it is feasible to compare the abilities of reducing As bioavailability in soils amended with seven inorganic materials.

2.2. Soil mobile As The soil contained tiny amount of water soluble As, 0.55 mg kg–1, 0.3% of the total As in soil (Fig. 2). Despite its low relative abundance, water soluble arsenic is considered

3.5

a

3.0

bc

2.5

bc

bc

d

b cd e

2.0 1.5 1.0 0.5

O LD

gr it gy ps um Fe rri h Iro yd rit n e ph os ph at e ho

Ph o

sp

Iro

n

R M

io lit e

Se p

on

e

0.0

N

decrease in B. campestris dry matter. In contrarst, adding iron phosphate, phosphogypsum, iron grit, RM, or sepiolite significantly enhanced B. campestris dry matter by at least 14%. Growth in soil amended with sepiolite caused the greatest increase in B. campestris dry matter, these plants had 36% more dry matter than the plants grown in the control soil. Treatment of soil with ferrihydrite did not have significant influence on the accumulation of B. campestris dry matter (P<0.01). The As concentration of the edible parts of B. campestris plants grown in the amendment-treated soils were significantly (P<0.01) reduced by 9-53% as compared to the control (Table 1). The largest reduction in plant organ As concentration was observed in the plants grown in soils amended with ferrihydrite; these plants had 53% less As than did the control plants. It is worth noting that amendment of soils with phosphogypsum also caused significant reduction (as much as 31%) in plant organ As concentration. The absorbed quantity of As was quantified by evaluating the As uptake by the B. campestris bioindicator plants grown in soils treated with the various amendment materials; As uptake=Plant dry matter×As concentration. Phosphogypsum, ferrihydrite, iron phosphate, and LDO reduced As uptake by 2.26 to 3.74 μg plot–1. The lowest As uptake value, 2.26 μg plot–1, was observed for plants grown in the ferrihydrite treatment, only 55% of the amount in the control plants. However, amending with red mud or iron grit led to increased As uptake by 4 and 7%, respectively, as compared to the control. Transfer of As was evaluated using ‘transfer coefficients(TC)’: TC=As concentration in crop/Total As concentration in soil. Less than 0.9% of soil As was transferred into B. campestris tissues. The soil amendments significantly decreased the TC value by 0.0048-0.0085. The most drastic effect was detected in the ferrihydrite treatment which

B. campestris dry matter (g)

1416

Soil amendments

Fig. 1 Brassia campestris L. dry matter in the As-contaminated soil added with different amendments. The bar above each column indicates the standard deviation. RM, red mud; LDO, layered double oxides. The same letter in each column indicates no significant difference at 0.01 level. The same as below.

Table 1 Arsenic concentration and transfer coefficient (TC) from soil to Brassia campestris L. edible part following addition of different amendments into the As-contaminated soil Soil amendments1) None Sepiolite Red mud Iron grit Phosphogypsum Ferrihydrite Iron phosphate LDO 1) 2)

3)

As concentration in B. campestris (mg kg–1 dry matter) 1.84 a 1.31 c 1.64 b 1.68 b 1.28 c 0.97 d 1.37 c 1.31 c

As uptake (μg pot–1)2) 4.13 ab 4.02 ab 4.28 ab 4.40 a 3.26 c 2.26 d 3.74 bc 2.47 d

Arsenic transfer coefficient (TC)3) 0.0090 a 0.0067 cd 0.0085 ab 0.0082 b 0.0067 cd 0.0048 e 0.0069 c 0.0062 d

LDO, layered double oxides. Arsenic uptake=Crop dry matter×As concentration TC value was calculated as follows (Kloke et al. 1984): TC=

As concentration in crop (mg kg–1) Total As concentration in soil (mg kg–1)

The same letters in each row indicate no significant difference at 0.01 level according to Dncun test. The same as below.

1417

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

Soil water soluble As (mg kg–1)

b 0.6

c

c

c d e

0.4

f 0.2

Ph

O

e

LD

ph

Iro

n

ph

os

hy

dr

su

rri Fe

at

ite

m

it os

ph

og

Iro

yp

n

gr

M R

ite ol pi

Se

N

on

e

0.0

Soil amendments

Fig. 2 Water soluble As concentration in the soils amended with different inorganic materials.

12 10 abc AB 8

Before plant grown After plant grown d

ABC cd BC BC bcd

a

a BC e

6

A

ab C

D

4 2

O LD

e at ph

rit e yd Iro

n

ph os

m su Fe

yp

rri h

gr it n

og

Ph os

ph

R

M

0 Iro

More than 45% of As was NH4+ oxalate extractable (F3). The NH4H2PO4 extractable (F2), NH4+ oxalate+ascorbic acid extractable (F4), and the residual As (F5) fractions represented 11 to 14%, 19 to 28%, and 10 to 19% of the total As, respectively. (NH4)2SO4-extractable As (F1) was less than 0.8% of the total. The various soil amendments had diverse impacts on the relative abundances of the particular As fractions (Fig. 4). Ferrihydrite significantly reduced F1, from 0.6 to 0.2%; sepiolite, RM, iron phosphate, and LDO increased F1 by more than 17%. The F2, F3, and F4 fractions were not drastically influenced by the amendments. Iron grit caused a considerable increase in F3 (6%), but a decrease in F4 (30%). All of the amendments enhanced the residual As fraction by at least 0.9%. Red mud treatment caused the largest increase in F5, a 71% increase as compared to untreated soil. The ratio of both F1 and F2 to all the fractions (F1+F2+F3+F4+F5), known as the mobility factor (MF), was reduced in all of the soil amendments, with the exception of sepiolite, in which MF was enhanced by 6% (Table 2). Ferrihydrite, iron grit, and phosphogypsum had greater impacts on MF than did the other amendments.

a

N on Se e pi ol ite

2.3. Soil As fractions

0.8

Soil available As (mg kg–1)

to be one of the more labile fractions of the total As-pool (Ghosh et al. 2004; Femandez et al. 2005). Iron grit, ferrihydrite, phosphogypsum, and LDO all significantly decreased water soluble As by at least 17%. In particular, ferrihydrite treated soil had the lowest water soluble As of 0.28 mg kg–1, only 50% of that of the control. In contrast, sepiolite, iron phosphate, and RM treated soils had more water soluble As than did the control, with increases ranging from 4 to 36%. The highest water soluble As amount, 0.75 mg kg–1, was found in iron phosphate amended soil, which was 36% higher than the control. Available As, defined as the As that can be extracted by NaHCO3 treatment, represents both soluble and exchangeable As. Available As levels are 16 times higher than water soluble As. Amendment with phosphogypsum, iron phosphate, and LDO increased soil available As concentrations by 0.9-6% (Fig. 3). Amendment with the other four materials reduced available As content by between 5–20%. Ferrihydrite treatment in particular resulted in the deepest reduction of available As, 20% lower than the control. B. campestris cultivation generally reduced soil available As content, by a range of 0 to 14%, as compared with the initial, pre-planting values (Fig. 3). Amendment with phosphogypsum, ferrihydrite, iron phosphate, and LDO caused significant reductions of at least 7% compared with the pre-planting values.

Soil amendments

Fig. 3 Available As concentration in the soils amended with different inorganic materials.

3. Discussion 3.1. Influence of different amendments on B. campestris growth and As uptake No strong relationship between B. campestris dry matter content and As concentrations in B. Campestris was found in this study. The physical-chemical properties of amendments, such as nutrient elements and pH value, may influence plant growth. After LDO being added, the treated soil pH increased from 7.11 to 7.50 (Table 3), which may result in

1418

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

a decrease in biomass and has been proved in the present study. The Mg and Si in sepiolite may be partially responsible for the significant improved growth of B. campestris (Fig. 1). Similar results were obtained in sepiolite treated soils contaminated by Cd/Pb (Xu et al. 2003; Liang et al. 2011; Sun et al. 2013). Iron phosphate also significantly enhanced rape biomass. This could be explained by the fact that the accompanied phosphate could improve plant

F1

F2

F3

F4

F5

1.0 0.8

a

b

0.6

a

a

a

bc

cd

bc

c

b

a

a

ab

b

b

0.4

c

0.2 0.0 16

a

ab

12

bc

cd

d

d

8 4 0 Relative content (%)

60

bc

45

d

d

c

d

a

d

30 15 0 30 25 20 15 10 5 0

ab

25 20

e

a

b

15

b

3.2. Influence of different amendments on As availability

b

b

c

cd

10

c

d

5 0

e

on

N

S

ite

ol

i ep

M

R

n Iro

it

gr

m

su

p gy

ho

sp

o Ph

growth generally (Yan et al. 2012). The As concentration of B. campestris, grown in the treated soils was significantly lower than control (Table 1), indicating an overall decrease of soil phytotoxicity. Iron oxides are considered to be the most efficient material for As adsorption in soils (Sun and Doner 1998; Hartley et al. 2004; Kumpiene et al. 2008). Ferrihydrite showed the greatest potential to immobilize soil As and attenuate As transfer from soil to plant, and the lowest plant As concentration (0.97 mg kg–1) was found in ferrihydrite treated soil. Numerous studies have been conducted in which sepiolite was used to reduce the availability of Cd/Pb in soils and inhibit Cd/Pb absorption in plants (Xu et al. 2003; Liang et al. 2011; Sun et al. 2013). In this study, we found sepiolite significantly reduced As concentration in B. campestris to 1.31 mg kg–1, equivalent to 19% reduction compared to control. This result demonstrated that sepiolite’s capacity to alleviate As phytotoxicity. Bai et al. (2011) found that adding phosphogypsum (20 g kg–1 soil) markedly decreased As concentrations in maize by 39% comparing to control in a pot trial. Our study also found that 30% reduction of As concentration in B. campestris reduced by phosphogypsum adding. The main composition of phosphogypsum is CaSO4·2H2O. As could combine with calcium (Ca2+) which could alter the charge balance of the adsorbent surface, reduce negative charges, and then form complexes (Hartley et al. 2004; Lopes et al. 2013). Several researchers have reported that As immobilization is might controlled by formation of Ca-As precipitates (Bothe and Brown 1999; Dutré et al. 1999; Vandecasteele et al. 2002). Hence, As phytotoxicity was alleviated in phosphogypsum treated soil.

Fe

e

rit

yd

h rri

n

Iro

te

ha

p os

O

LD

ph

Soil amendments

Fig. 4 The percentage of each fraction in total As from the soil amended with different inorganic materials. F1, (NH4)2SO4extractable As; F2, NH4H2PO4 extractable As; F3, NH4+ oxalate extractable As; F4, NH4+ oxalate+ascorbic acid extractable As; F5, residual As.

A significant correlation (P<0.05) between As concentration in B. campestris (y) and soil available As (x) was observed (y=0.245x-0.573, r=0.717, n=24), indicating that lower soil available As concentration could result in lower plant As uptake. Iron oxides applied to garden soils have shown decreases of as much as 50% in water-extractable As concentrations, together with lower accumulation levels in plant tissues (Mench et al. 1998). The significant decreases of water soluble As and available As concentration were observed in ferrihydrite treated soils (Figs. 2 and 3). The solid-solution distribution coefficient (Kd) of the soils under the eight treatments varied from 264 to 734 l kg–1 (data not shown). Ferrihydrite treated soils presented the highest Kd among all treatments, indicating that ferrihydrite has the strongest ability to immobilize soil As (Lopes et al. 2013). Among the other treatments, LDO was also found to have the ability to decrease the available As concentration, and

1419

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

Table 2 Mobility factor (MF) in the As-contaminated soil added with different amendments Soil amendments MF (%)1) 1)

None 13.9 b

Sepiolite 14.7 a

Red mud 13.4 b

Iron grit 12.5 c

Phosphogypsum 12.5 c

MF value was calculated based on the following equation (Salbu et al. 1998): MF=

Ferrihydrite 12.0 c (F1+F2)

(F1+F2+F3+F4+F5)

Iron phosphates 13.4 b

LDO 13.3 b

×100%

Table 3 Soil pH value in the soils amended with different inorganic materials Soil amendments pH before plant grown pH after plant grown

None 7.11 b 7.47 c

Sepiolite 7.09 bc 7.61 b

Red mud 7.19 b 7.71 a

Iron grit 6.95 bc 7.49 c

Phosphogypsum 6.79 c 7.27 d

Ferrihydrite Iron phosphates LDO 6.92 bc 6.82 c 7.50 a 7.47 c 7.49 c 7.75 a

Table 4 Total heavy metal concentrations (mg kg–1) of amendments used in this study Chemical parameters Cd Cu Pb As Si (%) Al (%) Fe (%) Mg (%) Ca (%)

Sepiolite 0.04 1.90 7.47 0.40 17.86 0.76 0.20 13.07 15.43

Red mud 0.12 51.37 67.43 30.76 7.83 14.28 5.02 0.54 10.89

Iron grit 0.01 59.45 36.85 60.12 3.54 0.73 59.65 0.18 0.75

Phosphogypsum 0.06 3.00 2.31 2.14 2.24 0.28 0.22 0.17 25.52

Ferrihydrite 0.03 0.22 74.7 0.05 0.06

Iron phosphates LDO 0.03 0.48 9.36 3.88 1.42 2.96 2.75 0.27 1.37 0.06 0.28 40.00 26.68 0.12 1.44 34.00 0.21 0.25

-, not determined.

this decrease could be attributed to an important property of LDO, which is its ability to restructure the original layered structure of LDO after adsorption of various anions (Lü et al. 2006; Sun et al. 2011). A standard sequential extraction procedure was used to investigate the distribution of As among different soil pools and to explore how the different fractions of As influence the available As. In this study, As in the untreated soils was primarily associated with amorphous and crystalline Fe oxides (F3 and F4). In ferrihydrite treated soils, the proportion (>69%) of As in F3 and F4 fractions were higher than that in the other treatments, while As in F1 and F2 fractions were generally lower (12%). The results indicated that ferrihydrite facilitated As transfer from F1+F2 to F3+F4, videlicet As transfer from labile As pool to more stable As pool, which resulted in a decrease of As availability in ferrihydrite treated soils. Sepiolite addition increased F1+F2 in the soil, which resulted in a highest MF value of sepiolite comparing with other amendments. However, As in plants grown on sepiolite treated soils reduced significantly comparing with control. This phenomenon may be related to rhizosphere effect. The content of active ion oxide in sepiolite treated soil was the lowest, 26.3 mg kg–1 (data not shown). Plant roots would release reductive or chelate compounds to enhance the uptake of Fe under Fe-deficiency conditions. This process might facilitate the transfer of As to another binding form, and

would likely enhance the availability of As (Fitz and Wenzel 2002). In RM and iron grit treated soils, the residual As (F5) which is generally considered to be insoluble and less available for plant uptake were significantly enhanced by 76 and 51% reduction comparing to untreated soil, respectively. Consistent results were also obtained by Garau et al. (2011), which indicated that RM addition was able to increase the residual fraction significantly, approximately 4 times higher than control. Hartley and Lepp (2008) also found that iron grit addition redistributed As to the residual fraction (50% higher than control). In general, application of amendments could provide extra binding surface of As, which may lead to a translocation of As from more mobile/available fraction to more stable fraction, and induce a decrease of available As concentration, thereby inhibit As uptake by B. campestris.

4. Conclusion The application of amendments to As-contaminated soil was investigated with the aim of reducing the bioavailability and potential food chain transfer of As. Compared with the control, B. campestris grown in soils which were treated with amendment materials had reduced As concentrations in edible parts and consistent increases in biomass, with the exception of LDO treatment. In situ remediation techniques

1420

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

can be useful for the rehabilitation of As contaminated soils. Ferrihydrite inhibited B. campestris As uptake by decreasing the liable fraction of As (F1). Iron grit converted soil As to the more stable forms of the F3 and F5 fractions. Sepiolite, RM, and phosphogypsum redistributed soil As to the residual fraction. The main tactic used to immobilize soil As with amendments is to redistribute soil As from a liable fraction to a stable fraction. Using the three related parameters (TC, Kd, MF) as a basis for selection, ferrihydrite was the most efficient amendment tested. Additionally, by-products like phosphogypsum and RM both showed good capacities to remediate soil As. Phosphogypsum was the most cost effective amendment. Although by-products seem to be a low-cost treatment and the reuse of such materials can be considered as a benefit, it must be taken into consideration that there are risks related to the release of chemical impurities from these materials. Thus, the use of by-product amendments in sensitive environments should be avoided. Caution is required in the use of soil amendments; we only partially understand (1) the chemical properties and mechanisms of amendments in soils; (2) the ecological consequences the use of each amendment material; and (3) the potential for deleterious remobilization of components of these amendment materials in the future. More long-term studies will enable better understanding of the possible changes in amendment and contaminant mineralogy and speciation over time.

5. Materials and methods 5.1. Soil The used As-contaminated soil (0-20 cm) was collected from a farm adjacent to an arsenic mining in Shimen, Hunan Province. The air-dried soil was passed through 2 mm for pot test and 0.15 mm for chemical analysis. The dominant minerals measured by X-ray powder diffraction analysis were quartz, muscovite and clinochlore. The soil contained organic matter 28.70 g kg–1, total nitrogen 1.63 g kg–1, total phosphate 0.87 g kg–1, total potassium 17.10 g kg–1, the cation exchange capacity (CEC) 10.50 cmol kg–1, total arsenic 195.42 mg kg–1, available arsenic 8.99 mg kg–1 and pH 7.36.

5.2. Amendments The acidity of sepiolite and iron (III) phosphates obtained from Dazhi Thermal Insulation Company and Guangxi Bimobi Technology Company, China, were pH 8.66 and pH 3.09 respectively. Iron grit from steel factory (metal powders and granules), red mud from CHINALCO (China), phosphogypsum from Kailin Group had pH values of 8.43,

11.12, and 2.13 respectively. Both ferrihydrite and layered double oxides (LDO) were prepared in our laboratory using the method of Wu and Zeng (2011) and Sun et al. (2013) had pH 6.80 and pH 11.59, respectively. The total heavy metal concentration of amendments were shown in Table 4.

5.3. Pot test Portions of soil, each 800.00 g, were mixed with a certain amount of NH4Cl, KH2PO4, and K2SO4 fertilizer, containing 0.15 g N kg–1, 0.18 g P2O5 kg–1, 0.12 g K2O kg–1. The soils were then amended with none as CK and with seven materials of sepiolite, red mud, iron grit, phosphogypsum, ferrihydrite, iron phosphate and LDO, at a rate of 0.5% w/w. Following thoroughly mixing, the soils in plastic pots (16 cm in diameter, 20 cm height) were homogenized at a greenhouse for 2 wk. Twenty rape seeds (Brassia campestris L.) were sown in each pot and maintained four similar seedlings after 7 d. Each amendment had three pots. The edible parts of B. campestris were harvested by cutting to the soil surface after 50 d. Both fresh biomass and dry matter were determined for calculating both fresh yield and dry matter, respectively. The oven-dried samples, firstly denatured enzymes at 105°C for 15 min and the oven-dried at 75°C for 3 d, were ground in a mechanical sample grinder and stored in polyethylene self-sealed bags prior to As analysis. The soils were collected, air-dried and sieved for As fraction assay.

5.4. Analytical methods Soil pH was determined with a pH meter at 1:2.5 ratio of soil to deionized water. The CEC was measured with 1 mol L–1 pH7.0 ammonium acetate saturation method. Soil organic matter was determined by a volumetric method of potassium permanganate oxidation (Lu 1999). Water soluble As was extracted with deionized water at 1:10 ratio of soil to water (Ettler et al. 2007; Száková et al. 2009). Available As content was extracted with 0.5 mol L–1 NaHCO3 (Woolson et al. 1971). Total As was digested with acid in aqua regia (NY/T 1221.11-2006) and then measured with atomic fluorescence spectrometry (HG-AFS 9120, Jitian Instrument Co., Beijing detection limit <0.02 µg L–1 As). Arsenic fractionations were analyzed by the method of Wenzel et al. (2001). Five sequential steps were assumed to extract non-specifically adsorbed As (F1), specifically adsorbed As (F2), As associated with amorphous and poorly-crystalline hydrous oxides of Fe and Al (F3), As associated with well-crystallized hydrous oxides of Fe and Al (F4), and residual As (F5), respectively. Plant samples were digested and then measured according to the method of GB/T 5009.11-2003 (MOH 2003).

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

5.5. Statistical analysis All the analyses were performed in triplicates. One-way analysis of variance (one-way ANOVA) was carried out to compare the significance of the means. Duncan post hoc test (P<0.01) was given if the significance was lower than P-values (P<0.01).

Acknowledgements The author acknowledges the financial support of the National Natural Science Foundation of China (41171255), and the National Scientific and Technology Program during12th Five-Year Plan period, China (2012BAD14B02).

References Bai L H, Zhang S Y, Zhang N M, Xia Y S, Wang Y S, Jiang R, Zhao H. 2011. Effect of different phosphogypsum addition levels and mycorrhizal inoculation on growth and phosphorus, sulfur and arsenic uptake by maize plants (Zea mays L). Acta Scientiae Circumstantiae, 31, 2485–2492. (in Chinese) Bothe J V, Brown P W. 1999. Arsenic immobilization by calcium arsenate formation. Environmental Science Technology, 33, 3806–3811. Castaldi P, Melis P, Silvetti M, Deiana P, Garau G. 2009. Influence of pea and wheat growth on Pb, Cd, and Zn mobility and soil biological status in a polluted amended soil. Geoderma, 151, 241–248. Castaldi P, Silvetti M, Enzo S, Melis P. 2010. Study of sorption processes and FT-IR analysis of arsenate sorbed onto red muds (a bauxite ore processing waste). Journal of Hazardous Materials, 175, 172–178. Chen T B, Song B, Zheng Y M, Huang Z C, Lei M, Liao X Y. 2006. A survey of lead concentrations in vegetables and soils in Beijing and their health risk. Scientia Agricultura Sinica, 39, 1589–1597. (in Chinese) Dutré V, Vandecasteele C, Opdenakker S. 1999. Oxidation of arsenic bearing fly ash as pretreatment before solidification. Journal of Hazardous Materials, 68, 205–215. Ettler V, Mihaljevič M, Šebek O, Nechutný Z. 2007. Antimony availability in highly polluted soils and sediments: A comparison of single extractions. Chemosphere, 68, 455–463. Fernandez P, Sommer I, Cram S, Rosas I, Gutiérrez M. 2005. The influence of water-soluble As (III) and As (V) on dehydrogenase activity in soils affected by mine tailings. Science of The Total Environment, 348, 231–243. Fitz W J, Wenzel W W. 2002. Arsenic transformations in the soil-rizosphere-plant system: Fundamentals and potential application to phytoremediation. Journal of Biotechnology, 99, 259–278. Garau G, Castaldi P, Santona L, Deiana P, Melis P.

1421

2007. Influence of red mud, zeolite and lime on heavy metal immobilization, culturable heterotrophic microbial populations andenzyme activities in a contaminated soil. Geoderma, 142, 47–57. Garau G, Silvetti M, Deiana S, Deiana P, Castaldi P. 2011. Long-term influence of red mud on As mobility and soil physico-chemical and microbial parameters in a polluted sub-acidic soil. Journal of Hazardous Materials, 185, 1241–1248. Ghosh A K, Bhattacharyya P, Pal R. 2004. Effect of arsenic contamination on microbial biomass and its activities in arsenic contaminated soils of Gangetic West Bengal, India. Environment International, 30, 491–499. González-Núñez R, Alba M D, Orta M M, Vidal M, Rigol A. 2012. Remediation of metal-contaminated soils with the addition of materials -Part II: Leaching tests to evaluate the efficiency of materials in the remediation of contaminated soils. Chemosphere, 87, 829–837. Gray C W, Dunham S J, Dennis P G, Zhao F J, McGrath S P. 2006. Field evaluation of in situ remediation of a heavy metal contaminated soil using lime and red-mud. Environmental Pollution, 142, 530–539. Hartley W, Edwards R, Lepp N W. 2004. Arsenic and heavy metal mobility in iron oxide-amended contaminated soils as evaluated by short- and long-term leaching tests. Environmental Pollution, 131, 495–504. Hartley W, Lepp N W. 2008. Effect of in situ soil amendments on arsenic uptake in successive harvests of ryegrass (Lolium perenne cv Elka) grown in amended As-polluted soils. Environmental Pollution, 156, 1030–1040. Kumpiene J, Lagerkvist A, Maurice C. 2008. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments -A review. Waste Management, 28, 215–225. Lenoble V, Laclautre C, Deluchat V, Serpaud B, Bollinger J C. 2005. Arsenic removal by adsorption on iron(III) phosphate. Journal of Hazardous Materials, 123, 262–268. Li Y R, Wang J, Luan Z K, Liang Z. 2010. Arsenic removal from aqueous solution using ferrous based red mud sludge. Journal of Hazardous Materials, 177, 131–137. Liang X F, Xu Y M, Wang L, Sun G H, Qin X, Sun Y. 2011. Insitu immobilization of cadmium and lead in a contaminated agricultural field by adding natural clays combined with phosphate fertilizer. Acta Scientiae Circumstantiae, 31, 1011–1018. (in Chinese) Lidelöw S, Ragnvaldsson D, Leffler P, Testfaildet S, Maurice C. 2007. Field trials to assess the use of iron-bearing industrial by-products for stabilization of chromated copper arsenatecontaminated soil. Science of The Total Environment, 387, 68–78. Lombi E, Zhao F J, Zhang G Y, Sun B, Fitz W, Zhang H, MaGrath S P. 2002. In situ fixation of metals in soils using bauxite residue: chemical assessment. Environmental Pollution, 118, 435–443. Lopes G, Guilherme L R G, Costa E T S, Curi N, Penha H G V. 2013. Increasing arsenic sorption on red mud by phosphogypsum addition. Journal of Hazardous Materials,

1422

SUN Yuan-yuan et al. Journal of Integrative Agriculture 2015, 14(7): 1414–1422

262, 1196–1203. Lu R K. 1999. Analytical Methods for Soil Agricultural Chemistry. China Agricultural Science and Technology Press, Beijing. pp. 22–27. (in Chinese) Lü L, He J, Wei M, Evans D G, Duan X. 2006. Factors influencing the removal of fluoride fromaqueous solution by calcined Mg-Al-CO3 layered double hydroxides. Journal of Hazardous Materials, 133, 119–128. Mench M, Vangronsveld J, Didier V, Clijsters H. 1994. Evaluation of metal mobility, plant availability and immobilization by chemical agents in limed-silty soil. Environmental Pollution, 86, 279–286. Mench M, Vansgrosveld J, Lepp N, Edwards R. 1998. Physico-chemical aspects and efficiency of trace element immobilization by soil amendments. In: Vangronsveld J, Cunningham S, eds., Metal-Contaminated Soils: In Situ Inactivation and Phytorestoration. Springer, Berlin. pp. 151–182. MEP (Ministry of Environmental Protection of the People’s Republic of China). 1995. Environmental Quality Standard for Soils. Standards Press of China, Beijing. pp. 1-3. (in Chinese) MOH (Ministry of Health of the People’s Republic of China). 2003. Determination of Total Arsenic and Abio-Arsenic in Foods. Standards Press of China, Beijing. pp. 71–84. (in Chinese) Pena M, Meng X G, Korfiatis G P, Jing C Y. 2006. Adsorption mechanism of arsenic on nanocrystalline titanium dioxide. Environmental Science Technology, 40, 1257–1262. Simón M, Diez M, González V, García I, Martín F, Haro D S. 2010. Use of liming in the remediation of soils polluted by sulphide oxidation: a leaching-column study. Journal of Hazardous Materials, 180, 241–246. Sun X, Doner H E. 1998. Adsorption and oxidation of arsenite on goethite. Soil Science, 163, 278–287. Sun Y B, Sun G H, Xu Y M, Wang L, Liang X F, Lin D S. 2013. Assessment of sepiolite for immobilization of cadmiumcontaminated soils. Geoderma, 193–194, 149–155. Sun Y Y, Zeng X B, Bai L Y, Wang J J, Li L F, Su S M, Wang Y N, Duan R, Wu C X. 2013. Regulation of exogenous in meadow cinnamon soils by applying layered double oxides and modified red mud. Journal of Agro-Environment Science, 32, 1545–1551. (in Chinese) Sun Y Y, Zeng X B, Bai L Y. 2011. Adsorption of arsenate

from aqueous solution by Mg/Al layered double oxide. Acta Scientiae Circumstantiae, 31, 1377–1385. (in Chinese) Száková J, Tlustoš P, Goessler W, Frková Z, Najmanová J. 2009. Mobility of arsenic and its com pounds in soil and soil solution: The effect of soil pretreatment and extraction methods. Journal of Hazardous Materials, 172, 1244–1251. Vandecasteele C, Dutré V, Geysen D, Wauter G. 2002. Solidification/stabilization of arsenic bearing fly ash from metallurgical industry. Immobilization mechanism of arsenic. Waste Management, 22, 143–146. Warren G P, Alloway B J, Lepp N W, Singh B, Bochereau F J M, Penny C. 2003. Field trials to assess the uptake of arsenic by vegetables from contaminated soils and soil remediation with iron oxides. The Science of the Total Environment, 311, 19–33. Wenzel W W, Kirchbaumer N, Prohaska T, Stingeder G, Lombi E, Adriano D C. 2001. Arsenic fractionation in soils using an improved sequential extraction procedure. Analytica Chimica Acta, 436, 309–323. Woolson E A, Axley J H, Kearney P C. 1971. Correlation between available soil arsenic, estimated by six methods and response of corn (Zea mays L.). Soil Science Society of America Journal, 35, 101. Wu P P, Zeng X B. 2011. Study on arsenate adsorption by synthetic iron and aluminum oxides/hydroxides. China Evironmnetal Science, 31, 603–610. (in Chinese) Xu Y M, Li J X, Dai X H, Yuan Z H. 2003. Effects of in-situ inactivation on behaviour of lead in contaminated soil. Journal of Agro-Environmental Science, 22, 685–688. (in Chinese) Yan X L, Zhang M, Liao X Y, Tu S X. 2012. Influence of amendments on soil arsenic fraction and phytoavailability by Pteris vittata L. Chemosphere, 88, 240–244. Zeng X B, Li L F, Mei X R. 2007. Heavy metal content in soils of vegetable-growing lands in China and source analysis. Scientia Agricultura Sinica, 40, 2507–2517. ( in Chinese) Zeng X B, Xu J M, Huang Q Y, Tang S R, Li Y T, Li F B, Zhou D M, Wu Z J. 2013. Some deliberations on the issues of heavy metals in farmlands of China. Acta Pedologica Sinica, 50, 186–194. (in Chinese) Zhou M, Tan J, Jin W. 2011. Soil pollution: Heavy metals are more toxic than pesticides. [2011-03-02]. http://www. Xinhuanet.com (in Chinese) (Managing editor SUN Lu-juan)