Proper Mode of Using Rice Straw Biochar To Treat Cd-Contaminated

Subscriber access provided by SUNY PLATTSBURGH

Article

A proper mode of using rice straw biochar to treat Cd-contaminated irrigation water in mining regions based on a multi-years in-situ experiment Qiuwen Chen, Jianwei Dong, Qitao Yi, Xiaoli Liu, Jianyun Zhang, and Zhaoxia Zeng ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00761 • Publication Date (Web): 13 May 2019 Downloaded from http://pubs.acs.org on May 13, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

A proper mode of using rice straw biochar to treat Cd-contaminated irrigation water in mining regions based on a multi-years in-situ experiment Qiuwen Chen†a,b *, Jianwei Dong†a,b, Qitao Yib, Xiaoli Liuc, Jianyun Zhanga *, Zhaoxia Zengd a

State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing

Hydraulic Research Institute, Nanjing 210029, China b

Center for Eco-Environmental Research, Nanjing Hydraulic Research Institute, No. 34

Hujuguan, Nanjing 210029, China c

College of Resources & Environment, Hunan Agricultural University, No. 1 Nongda Road,

Changsha 410128, China d

Institute of Subtropical Agriculture, Chinese Academy of Sciences, No. 644 Yuanda 2nd

Road, Changsha 410125, China †

Authors contributed equally to the paper.

*

Corresponding authors: Tel./Fax +86 25 85829765, [email protected] (Q. Chen); Tel./Fax

+86 25 85828007, [email protected] (J. Zhang)

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Biochar has been widely used for immobilizing heavy metals in soils due to its favorable sorption capacity. Previous investigations on heavy metal immobilization in waters by biochar are conducted in laboratory. Knowledge about the long-term effects of in-situ biochar application on water bodies contaminated by heavy metals remains scarce. In this research, biochar was derived from cadmium (Cd)-accumulated rice straw. A 35-d laboratory simulation and a three-year field enclosure experiment were carried out to assess the impacts of biochar application on Cd behavior in water-sediment system of a historically Cd-contaminated irrigation pond. Results indicated that the pH of sediment and overlying water increased with biochar addition in both the lab and field experiments. The rice-straw biochar transformed the Cd in sediments from the exchangeable to residual fraction, because biochar addition increased the pH values and organic matter contents in sediment, leading to the sorption, sequestration and passivation of Cd by sediment. The Cd concentration in overlying water decreased with the increase in biochar addition, and it continuously decreased with repeated annual application. Overall, for long-term effects of biochar addition on soluble Cd concentrations, the repeated annual addition of 2% biochar exhibited better performance than repeated annual addition of 1% biochar and one-time addition of 6% biochar. This study provided a proper mode of utilizing rice-straw biochar to treat Cd-contaminated irrigation water in mining regions. Keywords: Cd contamination; Irrigation pond; Overlying water; Sediment; Biochar


Page 2 of 30

Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Heavy metals released from anthropogenic activities (e.g., mineral exploitation and waste release) have contaminated many water bodies worldwide 1,2, giving rise to a hot issue of heavy metal contamination in water-sediment systems. In the aquatic environment, heavy metals are often preferentially associated with surface sediments, and cannot be removed effectively by biodegradation. Once sediment resuspension occurs, heavy metals can enter the overlying water, further impacting local water quality and ecological safety

1-3.

Therefore, in-situ remediation of sediment polluted by heavy

metals is essential. Sewage or wastewater is often used for irrigation because it contains valuable nutrients and organic matter for plants. However, sewage irrigation also worsens the quality of farmland due to possible heavy metal contamination 4. Of particular concern, water ponds in mining areas, which contain heavy metals, are frequently used for irrigation purposes

5,6.

Bansal 7 reported higher concentrations of cadmium (Cd) in soil

under sewage irrigation than fields irrigated by underground water. In China, almost 20% of total cultivated lands are Cd-tainted 8. Therefore, the long-term effects of sewage irrigation on heavy metal concentrations in soil, plants and even groundwater should be assessed due to the potential impact on ecological and human health 9. Thus, how to reduce dissolved heavy metals in irrigation water is an urgent issue. Being a useful biomass pyrolysis product, crop straw biochar has been considered as a type of renewable bioenergy, avoiding the loss of a valuable resource and environmental pollution10,

11.

It is also an environmental-friendly functional material

used for water and soil remediation. It is a well-known heavy metal modifier due to its favorable immobilization properties (e.g., microporous structure, high pH and cation exchange capacity (CEC)) 10. Biochar has a strong adsorption affinity for heavy metals



Page 4 of 30

and can influence speciation and bioaccumulation of heavy metals in polluted soils 12,13. Previous studies have indicated that the addition of biochar can be beneficial for carbon sequestration and heavy metal immobilization in soils due to its highly resistant properties

14,15.

However, few studies have investigated the effects of biochar surface

addition on Cd behavior in overlying water and surface sediment in static water bodies (e.g., reservoir/lakes/ponds) used for irrigation but contaminated by heavy metals. Several researchers have investigated the remediation effects of biochar on contaminated soils. For example, the short-term application of biochar showed a reduction in rice grain Cd content of 90%

16.

Cao et al.

17

found that dairy-manure

biochar was effective in immobilizing both atrazine and lead (Pb) and effectiveness was enhanced with the increase in incubation time and biochar rates. Beesley and Marmiroli 18

reported that the addition of biochar significantly decreased the arsenic (As) and

copper (Cu) concentrations in the porewater of soils. These studies highlight the potential of biochar as a unique amendment for immobilization of both heavy metal and organic contaminants in contaminated soils. Based on lab simulations, some researchers have studied the removal and immobilization of heavy metals in aqueous solution by biochar

11,19-20.

Although the sorption properties of biochar in soils and aqueous

solutions are well known, insight on biochar-metal interactions in water-sediment systems remains elusive. In particular, the long-term effect of biochar application on heavy metals in real aquatic environments is little reported, but deserves insightful investigation. In this study, an irrigation pond in a mining area was selected to study the mechanisms of Cd immobilization by biochar through lab simulation and in-situ field container experiments. We hypothesized that application of biochar could reduce Cd concentration in water and increase Cd immobilization in surface sediment of irrigation


Page 5 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ponds, the same as it functions in agricultural soils. As the biochar was derived from Cd-polluted rice straw, this study provides a novel way to deal with polluted rice straw and contaminated water bodies simultaneously. MATERIALS AND METHODS Study site The selected irrigation pond (N27°50′1.3″, E113°02′8.4″) was located in the typical industrial city of Zhuzhou in the Hunan Province of China (Fig. 1). The area is identified as “Demonstration Zone for Comprehensive Treatment of Heavy Metal Pollution” because of the high average Cd concentration of 0.99 mg·kg-1 in field rice 21, which is about five times of the national food limits for Cd (0.2 mg·kg-1) 22. The pond was severely contaminated by both waste discharge from a small electroplating factory, which was closed in 2007, and metal-bearing atmospheric deposition originating from adjacent Pb and Zn smelting plants. The mean exchangeable and total Cd concentrations in the 0–15-cm surface sediment of the pond were 2.75 ± (0.91) and 21.9 ± (2.37) mg·kg-1, respectively (Table 1). The mean soluble Cd concentration in the overlying water reached 13.1 ± (4.01) μg·L-1, significantly higher than the irrigation water standard of 5.0 μg·L-1

23.

The mean pH values of the overlying water and surface

sediment were 6.62 ± (0.39) and 7.28 ± (0.53), respectively. According to the results reported by Zhao et al.

24,

the irrigation water with a concentration of 13.1 μg·L-1

contributed approximately 78% of Cd inputs to the double-rice cropping systems in Southern China. Therefore, removal of Cd from the polluted irrigation water has great practical significance.



Page 6 of 30

Figure 1 Study site and view of the studied irrigation pond (Cd concentrations in field rice in each city were obtained from Williams et al. 21).

Biochar preparation Rice straw from Cd-contaminated paddy fields in the study area was collected, chipped and pyrolyzed under oxygen-limited conditions in a pyrolysis muffle furnace reactor in the laboratory. The temperature of the pyrolysis process was slowly and continuously increased from 25 °C at steps of 10 °C per min to 500 °C. The ash content was measured according to the standard method for wood-based activated carbon of China (GB/T 12496.3-1999). The protonation and charge distribution of the biochar surface were analyzed using pH and zeta potential measurements, as described in Jin et al.

25

These measurements were conducted in triplicate. Scanning electron microscope (SEM) imaging analysis was conducted using a HITACHI S4800 SEM (Tokyo, Japan) to observe the morphological properties of the biochar (Fig. S1 in supporting information (SI)). Elemental (C, H, N and O) analysis was performed using an elemental analyzer (Vario ELIII, Elementar, Germany). Biochar derived from rice straw has a high pH value of 10.5 and CEC of 36.1 cmol·kg-1 (Table 1), indicating a strong buffer capacity to acidic environments

26.

The characteristics of biochar obtained in this study were 6 ACS Paragon Plus Environment

Page 7 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


consistent with those derived from crop straw obtained previously

27-29.

The mean Cd

content in the biochar (0.78 ± 0.38 mg·kg-1) was much less than the Cd level (21.9 ± 2.37 mg·kg-1) in the surface sediment of the studied pond. Compared to the sorption capacity of Cd (28 mg·kg-1) by this biochar, the Cd sequestration of the biochar during preparation was negligible. Table 1 Properties of rice straw biochar derived at 500 °C, straw feedstock and sediment. Straw

Biochar

Sediment

feedstock

(RBC500)

(0–15 cm)

pH

10.5

7.28

Yield/%

41.2

Ash content/%

9.97

CEC/cmol·kg-1

36.1 ± 1.96

Total Cd/mg·kg-1

0.471

Exchangeable Cd /mg·kg-1

0.78 ± 0.38

21.9 ± 2.37

0.083 ± 0.01

2.75 ± 0.91

Organic matter/g·kg-1

21.8

C/%

37.5

N/%

0.88

H/%

18.8

O/%

3.09

K/mg·g-1

47.7

P/mg·g-1

0.69

Simulation experiment of Cd immobilization in laboratory Prior to field application, simulation experiments were conducted in the lab to test the effectiveness of biochar on immobilizing Cd. The surface sediment in the selected irrigation pond was collected by a stainless-steel grab sampler in July 2013. The wet sediment was packed into a series of beakers (0.4 m diameter × 0.5 m height) to a depth of 15 cm. Overlying water collected from the same irrigation pond was then added to 7 ACS Paragon Plus Environment


Page 8 of 30

the beakers to a depth of 15 cm. The water-sediment systems were stabilized over 10 d to reach equilibrium. According to Kumpiene et al.

30

and Liu et al. 31, the addition of

0.2%–4% biochar can improve soil quality effectively. In this study, biochar with a total amount of ~1.7 kg was applied across the water surface at concentration doses of 1%, 2% and 6% (w biochar / w 0–15 cm sediment), expressed as treatments B1, B2 and B6, respectively (Table 2). In addition, a control group (CK) was established without the addition of biochar. Biochar was added to the beakers through uniform surface application with a sieve (the same diameter with beakers) and was added once for each treatment. Overlying water samples in the beakers were collected using a syringe and needle on days 1, 7, 14, 21, 28 and 35 after biochar addition. Each sample was filtered through a 0.45-μm nylon membrane and then acidified to pH 1–2 using HNO3 for further analysis. Final experimental sediments were collected with a stainless-steel grab sampler on the last day to determine Cd concentrations and their different fractions.

Table 2 Biochar treatments at different concentrations and amounts in laboratory and field experiments Field experiment

Total addition amount

Biochar

Lab

addition rate

simulation

2014

2015

2016

CK

0%

0%

0%

0%

0%

0%

0%

B1

1%

1%

1%

1%

1%

1%

3%

B2

2%

2%

2%

2%

2%

2%

6%

B6

6%

6%

6%

0%

0%

6%

6%

Treatment

Lab

Field

simulation experiment

Enclosure experiment of Cd immobilization in field The in-situ field experiment was carried out from 2014 to 2016 to further test and verify 8 ACS Paragon Plus Environment

Page 9 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the long-term effects of biochar on Cd immobilization in both overlying water and surface sediment. A field container was constructed with a PVC column (Φ 60 cm). The volume of the surface water in the container was ~0.4 m3. The container was inserted into sediment to a depth of 30 cm and extended above the water surface to a height of 50 cm. There was no exchange of surface water between the container and outside. A stainless-steel tube was wedged on either side of the container to provide support. Biochar was added annually according to the B1 and B2 treatments in mid-March, and once according to the B6 treatment in mid-March of 2014 (Table 2). The total addition amount of biochar was approximately 5.4 kg. All the prepared biochar was collected together and homogenized fully with a stir bar in a vat. Biochar was evenly distributed with sieves (Φ 60 cm) through stirring and oscillating. The water/sorbent ratio (g·L-1) ranged from 1.0~6.0, which was consistent with the common ratios (1-10 g·L-1) of others 20,32. After biochar addition, the surface water samples from the field containers were collected to a depth of 20 cm with 0.5 L polyethylene plastic bottles in the middle of each month from March to December 2014 to 2016. The pH values of the water samples were measured on site using a pH meter (PHS3C). The sediment samples in the containers were collected carefully in mid-December in 2014 to 2016 using an improved gravity columnar sediment sampler (Φ 60 mm). All samples were transported to the laboratory and stored at 4 °C before analysis. Samples collected in each year were analyzed immediately after taking. Analysis of Cd in overlying water and sediment Porewater samples (50 ml) were collected at 5 cm below the surface sediment with a soil moisture sampler, and then filtered through 0.45-μm syringe-driven filters. Pre-weighed 0.45-μm cellulose acetate membranes were used to filter the overlying



Page 10 of 30

water samples. Each filtered water sample was transferred into a 50-ml centrifuge tube and then acidified immediately using HNO3 (1:1 V/V) to pH ≤2.0. The dissolved heavy metal concentrations in the water phases were determined by a graphite furnace atomic absorption spectrometer (GFAAS) (GTA120, Varian, USA). To determine Cd concentrations in sediment, the sediment samples were ground homogeneously and sieved though a 100-mesh sieve. The samples (1 g) were then added to Teflon beakers with 2 ml of HF, 3 ml of HClO4, and 3 ml of HNO3. After 30 min, the samples were processed using a microwave digestion system (DigiBlock EHD36, China). An atomic absorption spectrophotometer (TAS-990, Beijing Puxi Instrument Factory, Beijing, China) was used to measure Cd concentrations. Different fractions of Cd in the sediment samples (0.50 g) were analyzed by applying the sequential extraction procedures proposed by Tessier et al.

33.

Consequently, five Cd fractions were identified through five sequential extraction steps, including the exchangeable (F1, readily active and bioavailable), carbonate-bound (F2), bound to Fe-Mn oxide (F3), bound to organic matters (F4) and the residual (F5, not active or bioavailable for plants and microorganisms) fractions, as detailed in Table S1 in SI. The soluble Cd in the overlying water collected from both the lab-scale and field experiments and the solutions of each fraction in sediment were analyzed using flame atomic absorption spectroscopy (GTA120, Varian, USA). Quality assurance/quality control The detection limit for GFAAS was 1 μg·L-1 for Cd. The coefficient of determination for the standard curve was higher than 0.99. National standard reference samples (sediment GBW07403) were used for quality control of sediment samples, and the results coincided well with the reference values, with standard deviations of 0.05). The pH in sediment increased in B2 in 2015 when 2% biochar was added a second time, whereas the pH increased in B1 in 2016 when 1% biochar was added a third time (Fig. 4). It is worth noting that the effectiveness of treatment B6 gradually decreased without the repeated addition of biochar (Fig. 3b). Interesting, the Cd concentration in the overlying water in all biochar addition treatments showed less fluctuation than that in the control. 10 CK pH in sediment

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 30

B1

B2

B6

9 8 7 6 2014

2015 Year

2016

Figure 4 Impacts of biochar treatment on sediment pH values in in-situ field application. Different letters above blocks mean significant differences between treatments (P < 0.05) within a single year.

There were no significant differences in the total Cd concentration in sediments among treatments of B1, B2, B6, and control (Fig. S3 in SI). Compared to the results obtained in the lab-scale experiment (Fig. 5), the in-situ three-year field application of 14 ACS Paragon Plus Environment

Page 15 of 30

biochar treatment on the polluted irrigation pond had a remarkable impact on Cd speciation (Fig. 6). A higher concentration of biochar resulted in a greater Cd immobilization in sediments (P < 0.05). Compared to the one-time addition in treatment B6, the repeated annual addition in B1 and B2 reduced the exchangeable fraction of Cd after each application. The residual fraction in treatment B6 contributed 70.8% to total Cd in samples collected in December 2014, and remained 72.0% and 71.5% in 2015 and 2016, respectively. The residual fractions in treatment B2 contributed 63.3%, 66.3% and 75.7% to total Cd in samples collected in December 2014, 2015 and 2016, respectively. These results above indicated that treatment B6 exhibited less durative effects of Cd immobilization than treatment B2. The once-a-year addition in B1 showed less impact on Cd speciation, whereas treatment B2 transformed the unstable Cd fraction into the residual fraction, which accounted for 75.7% of total Cd in December 2016 (Fig. 6). 18 Cd concentration (mg kg -1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CK

B1

B2

B6

15 12 9 6 3 0 F1

F2

F3 Speciation of Cd

F4

F5

Figure 5 Different fractions of Cd in sediment after 35 d of biochar treatment for lab simulation experiments. (F1: exchangeable fraction; F2: carbonate-bound fraction; F3: Fe-Mn oxide fraction; F4: organic/sulfide fraction; F5: residual fraction)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Cd distribution (%) -


Exchangeable Organically bound 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% CK B1 B2 B6 2014

Page 16 of 30

Carbonate bound Residual

Fe-Mn oxides bound

CK B1

CK B1 B2 2016

B2 B6 2015 Field treatment

B6

Figure 6 Different fractions of Cd in irrigation pond sediment under different biochar treatments in in-situ field application. (CK, B1, B2, and B6 represent the treatments of control, 1% addition, 2% addition, and 6% addition of biochar.)

DISCUSSION Impact of biochar on soluble Cd in overlying water Previous research has reported on the sorption of organic contaminants and heavy metals in soils by biochar

17,19,34,35.

Bian et al.

36

reported that biochar can significantly

reduce extractable Cd in contaminated paddy fields. To date, the removal efficiency and mechanism of heavy metals by biochar in real water bodies are little known, as most relevant studies conducted in aqueous solutions are based on laboratory simulations (e.g., pot experiments)

11,12, 19,37.

However, it is important to understand the long-term

effectiveness of metal stabilization by biochar in real water bodies to determine practical applications of this remediation technology

38.

In this study, a long-term

biochar application experiment on contaminated irrigation ponds was conducted, with


Page 17 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the long-term effects of biochar addition on Cd pollution in the ponds then investigated. As shown in Fig. 2a and Fig. 3b, all three treatments (1%, 2%, and 6% biochar addition) reduced the soluble Cd concentrations in the overlying water with a linear downtrend in both the lab simulation and field experiment. Sorption of Cd on biochar was accompanied by the release of Ca2+, Mg2+, K+ and Na+ into the overlying water 32. Ion strength did have influences on Cd sorption, and the Cd reduction in overlying water was mainly attributed to ion exchange, especially Ca2+ and Mg2+ 39. However, the total Cd sorption amount was usually larger than the increase of these cations in the overlying water, indicating that in addition to ion exchange, other processes (e.g., electrostatic attraction and surface complexation) also affect the Cd sorption. The zeta potential of biochar was negative and ranged from -37 mV to -44 mV when pH values ranged from 6.5 to 7.5, which might promote stronger electrostatic interaction between biochar and Cd ion. In the lab simulation, the soluble Cd concentration in the overlying water decreased with the increase in biochar amount. It seemed that more addition amount of biochar would be better in the short-term from our lab simulation result. However, according to the results obtained in the long-term field experiment, a similar pattern to the lab simulation was found only during the first year of application (Fig. 3b). During the second- and third-year applications, biochar was added again in the B1 and B2 treatments, and the soluble Cd concentrations in the overlying water decreased significantly. The soluble Cd concentrations in B2 during second- and third-year applications were comparable to and lower than the Cd concentrations in B6, respectively (Fig. S2 in SI). For example, the soluble Cd concentration in B2 decreased significantly from 7.09 µg·L-1 (average of the first-year application) to 3.94 (average of the second-year application) to 2.92 µg·L-1 (average of the third-year application). During the second- and third-year applications, the soluble Cd concentration in B2 was



the lowest among the three treatments (Fig. S2 in SI). Thus, repeated addition of 2% biochar each year performed better than the one-time addition of 6% biochar. The accumulation of Cd in crops is positively related to Cd concentration in irrigation water

10,40;

therefore, the removal of Cd from polluted irrigation water has

received growing attention. Application of biochar combined with organic fertilizer is a typical method for soil remediation

41.

In this study, we suggested a new approach to

remove Cd from farmland. The surface application of biochar in irrigation water in the laboratory and field experiments effectively decreased the concentration of soluble Cd in the overlying water (Fig. 2a and Fig. 3b), suggesting that Cd in the overlying water could be sorbed by biochar particles, which subsequently settled in the irrigation pond. This indicated that in addition to the immense and sustainable potential of enhancing soil carbon sequestration, rice straw-derived biochar could be used to effectively mitigate Cd-contaminated irrigation water. Mechanisms of biochar effects on pH values and Cd speciation in sediment Bioavailable Cd in sediment includes soluble Cd in porewater and the bioavailable (exchangeable and carbonate-bound) fraction of sediment. The addition of biochar significantly reduced soluble Cd in sediment porewater (Fig. S4 in SI). Furthermore, the percentage of bioavailable Cd in sediment decreased with the increase of biochar addition, as shown in Fig. 6. However, there was no significant difference in total Cd concentrations of sediment among the three-year application for all treatments (P > 0.05). This result indicated that biochar derived from rice straw transformed the exchangeable Cd fraction into residual forms in the sediment of the heavily contaminated irrigation pond. Unlike the sorption of organic contaminants by biochar, the mechanisms of biochar interaction with heavy metals include ion exchange, (co-)precipitation and electrostatic attraction 37,39.


Page 18 of 30

Page 19 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The properties of soil/sediment changed after biochar addition. The application of biochar can increase the CEC and pH of soil/sediment as well as their negative surface charge

10.

The reduction in Cd activity and mobility can be partially attributed to the

increase in pH values in soil/sediment 43, leading to the sorption of Cd by soil/sediment due to negative surface charge of sediment particles

44,45.

Surface application and

sedimentation of biochar can gradually increase pH in sediments, as previously reported in soils with biochar addition 46. The mobility of heavy metals in sediment was largely influenced by the pH of the sediment 36,39. In this study, the pH of the biochar was 10.5, well within the range (5.9–12.3) observed for similar biochar materials

39.

Thus, the

biochar used here was alkaline and therefore induced immobilization of heavy metals and mobilization of oxyanions. Results showed that the B1 treatment significantly increased the pH in sediment at the third addition (accumulative addition amount of biochar: 3%); B2 treatment significantly increased the pH in sediment at the second addition (accumulative addition amount of biochar: 4%); and treatment B6 significantly increased the pH in sediment with the single addition (6%) (Fig. 4). This demonstrated that, during field application when the accumulative biochar amount reached 3% or more (≥3.0 g·L-1 of water/sorbent ratio), treatment significantly increased the pH in sediment. The five fractions of Cd in the sediment indicated different potential for bioavailability, following the order of exchangeable (F1) > carbonate (F2) > Fe/Mn oxide (F3) > organic (F4) > residual (F5). Fractions of heavy metals changed with environmental factors, which had important implications for the in-situ immobilization of Cd 3. Biochar addition significantly improved the stabilization of Cd by transforming the exchangeable fraction into the residual fraction (Fig. 6) with the increase in sediment pH (Fig. 4). The addition of biochar also increased the content of organic matter in sediment, leading to passivation and sequestration of Cd in sediment. The



similar results were also found by Walker et al.

42

Moreover, the effects of Cd

stabilization were enhanced by increasing biochar addition through annually repeated patterns. Treatment of rice straw from farmland polluted by heavy metals in mining areas is a challenging issue, as the direct tillage of contaminated straw into farmland may increase the ecological risk of releasing bioavailable forms of heavy metals 47. This study provided insight into reusing and recycling rice straw to control the ecological risks of heavy metal pollution from irrigation in mining areas, which offered a proper mode for treating rice straw and irrigation water systems contaminated by heavy metals. Influencing mechanisms of biochar on Cd in water-sediment systems The partitioning coefficient (KP, L·Kg-1) of Cd between overlying water and sediment phases in field application could be expressed as 𝐾𝑃 = 𝐶𝑆𝑥 ― 𝑖 𝐶𝑊𝑥 ― 𝑖 × 1000, where CSx-i is the annual average Cd concentration in the sediment (µg·g-1); CWi is the annual average Cd concentration in the overlying water (µg·L-1); and x-i is the ith addition of biochar in treatment x (x = B1, B2, or B6). There were no significant differences in the KP values in the control during the three years (Fig. S5 in SI), indicating that Cd in this static water body reached apparent equilibrium. Cd is non-biodegradable and persistent in the environment (Gul et al., 2015). In the control, Cd only existed in the overlying water and sediment phases, whereas Cd in B1, B2 and B6 existed in three phases: i.e., overlying water, sediment and biochar. In this study, the sorption capacity of sediment for Cd (~22 mg/kg) was higher than the measured sorption capacity of biochar for Cd (6~29 mg/kg) for all treatments. Once the biochar was added to these systems, the balance was disturbed, and redistribution of Cd occurred in the overlying water, sediment and biochar. Ion-exchange followed by surface complexation is proposed as the dominant mechanism responsible for Cd immobilization by biochar derived from rice-straw. In this study, half of Cd in biochar were in the residual form (Fig. S6 in SI), 20 ACS Paragon Plus Environment

Page 20 of 30

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


thus the adsorbed-Cd by biochar was stabilized further during the ageing of biochar. Biochar has a high sorption capacity for soluble Cd in water

37,

thus the KP values

increased with the increase in biochar addition (Fig. S5 in SI). For treatment B6, one-time biochar addition at a large concentration (6%) reduced the Cd concentration in the overlying water immediately and dramatically. Although, reduction of Cd adsorption by biochar was not found during the ageing of biochar in treatment B6 within three-year application, the Cd concertation in the overlying water increased slightly from 2014 to 2016 (Fig. 3b). The deposited biochar formed a new “layer” upon the surface sediment, thus the transport trend of Cd from sediment to the overlying water was partially blocked by this new biochar “layer”. However, this blocking was weakened due to the slow ageing of biochar during three-year application. Therefore, the exchangeable Cd contents in sediment increased from 0.99 mg·kg-1 during the first year to 1.57 mg·kg-1 during the third year (Fig. 6). As shown in Table 2, the accumulative total biochar amount after the second addition in B2 was 4%, which was lower than that (6%) for treatment B6. However, the KP value of the former was higher than that of the latter, consistent with the slightly lower Cd concentration in overlying water after the second addition of biochar in B2 (Fig. 3b). The sorption sites on biochar particles in B6 may be covered by each other due to the high density of biochar particles at one-time addition. Thus, the biochar absorption efficiency for treatment B6 was lower than that for treatment B2 after the second addition of biochar. The second addition of biochar in B2 could still adsorb Cd from the overlying water based on the new equilibrium among the three phases (overlying water, sediment and biochar) after the first addition. Therefore, the repeated addition of 2% biochar each year performed better than the one-time addition of 6% biochar. Thus, this study demonstrated that the influence of biochar on heavy metal bioavailability varied not only with application



amount of biochar, but also with the application mode. Biochar addition should be precisely designed to maximize the reduction in Cd bioavailability in irrigation ponds for sustainable application. Supporting information The following files are shown in the supplementary materials of this article and are available free of charge: Table S1 Sequential extraction procedures for Cd speciation used in this study. Figure S1 SEM image of the rice-straw biochar Figure S2 Cd concentrations in overlying water with different amounts of biochar addition in field application. Figure S3 The Cd concentrations in sediment for all treatments in field application. Figure S4 Variations in soluble Cd concentrations in sediment porewater in treatment B2 for field application. Figure S5 Partition coefficients of Cd between sediment and overlying water under different amounts of biochar addition in field application. Symbols in black, orange, and red represent the log KP values of Cd during the first-year (2014), second-year (2015), and third-year (2016) biochar application in-situ, respectively. Figure S6 Different fractions of Cd in biochar. (F1: exchangeable fraction; F2: carbonate-bound fraction; F3: Fe-Mn oxide fraction; F4: organic/sulfide fraction; F5: residual fraction) ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of China (No. 91547206, No. 51425902, No. 51409101), the Innovation Cluster Fund of Jiangsu province, and the Innovation Cluster Fund of Nanjing Hydraulic Research Institute. We are grateful to Dr. Christine Watts for proofreading the English.


Page 22 of 30

Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Conflicts of interest The authors declare no conflicts of interest. References 1. Akcay, H., Oguz, A., Karapire, C., 2003. Study of heavy metal pollution and speciation in Buyak Menderes and Gediz river sediments. Water. Res. 37, 813–822. DOI: 10.1016/S0043-1354(02)00392-5 2. Peng, J., Song, Y., Yuan, P., Cui, X., Qiu, G., 2009. The remediation of heavy metals contaminated

sediment.

J.

Hazard.

Mater.

161,

633–640.

DOI:

10.1016/j.jhazmat.2008.04.061 3. Dong, J., Xia, X., Zhang, Z., Liu, Z., Zhang, X., Li, H., 2018. Variations in concentrations and bioavailability of heavy metals in rivers caused by water conservancy projects: Insights from water regulation of the Xiaolangdi Reservoir in the Yellow River. J. Environ. Sci. 74,79–87. DOI: 10.1016/j.jes.2018.02.009 4. Liu, W., Zhao, J., Ouyang, Z., Söderlund, L., Liu, G., 2005. Impacts of sewage irrigation on heavy metal distribution and contamination in Beijing, China. Environ. Int. 31, 805–812. DOI: 10.1016/j.envint.2005.05.042 5. Du, Y., Hu, X., Wu, X., Shu, Y., Jiang, Y., Yan, X., 2013. Affects of mining activities on Cd pollution to the paddy soils and rice grain in Hunan province, Central South China. Environ. Monit. Assess. 185, 9843–9856. 6. Razo, I., Carrizales, L., Castro, J., Díaz-Barriga, F., Monroy, M., 2004. Arsenic and heavy metal pollution of soil, water and sediments in a semi-arid climate mining area

in

Mexico.

Water.

Air.

Soil.

Poll.

152,

129–152.

DOI:

10.1023/b:wate.0000015350.14520.c1 7. Bansal, O.P., 2004. Uptake of heavy metals by crop plants. Poll. Res. 23, 501–506. 8. Hu, Y., Cheng, H., Tao, S., 2016. The challenges and solutions for



Page 24 of 30

cadmium-contaminated rice in China: a critical review. Environ. Int. 92, 515–532. DOI: 10.1016/j.envint.2016.04.042 9. Rattan, R.K., Datta, S.P., Chhonkar, P.K., Suribabu, K., Singh, A.K., 2005. Long-term impact of irrigation with sewage effluents on heavy metal content in soils, crops and groundwater—a case study. Agr. Ecosyst. Environ. 109, 310–322. DOI: 10.1016/j.agee.2005.02.025 10. Jiang, J., Xu, R., Jiang, T., Li, Z., 2012. Immobilization of Cu(Ⅱ), Pb(Ⅱ) and Cd(Ⅱ) by the addition of rice straw derived biochar to a simulated polluted ultisol. J. Hazard. Mater. 229-230, 145–150. DOI: 10.1016/j.jhazmat.2012.05.086 11. Kong, H., He, J., Gao, Y., Wu, H., Zhu, X., 2011. Cosorption of phenanthrene and mercury(II) from aqueous solution by soybean stalk-based biochar. J. Agr. Food. Chem. 59, 12116–12123. DOI: 10.1021/jf202924a 12. Tan, Z., Lin, G.S.K., Ji, X., Rainey, T.J., 2017. Returing biochar to fields: A review. Appl. Soil. Ecol. 116, 1–11. DOI: 10.1016/j.apsoil.2017.03.017 13. Yao, Q., Liu, J., Yu, Z., Li, Y., Jin, J., Liu, X., Wang, G., 2017. Three years of biochar amendment alters soil physiochemical properties and fungal community composition in a black soil of northeast China. Soil. Biol. Biochem. 110, 56–67. DOI: 10.1016/j.soilbio.2017.03.005 14. Houben, D., Evrard, L., Sonnet, P., 2013. Mobility, bioavailability and pH-dependent leaching of cadmium, zinc and lead in a contaminated soil amended with

biochar.

Chemosphere

92,

1450–1457.

DOI:

10.1016/j.chemosphere.2013.03.055 15. Park, J.H., Choppala, G., Lee, S.J., Bolan, N., Chung, J.W., Edraki, M., 2013. Comparative sorption of Pb and Cd by biochars and its implication for metal immobilization

in

soils.

Water.

Air.

Soil.


Poll.

224,

1711.

DOI:

Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10.1007/s11270-013-1711-1 16. Bian, R., Chen, D., Liu, X., Cui, L., Li, L., Pan, G., Xie, D., Zheng, J., Zhang, X., Zheng, J., 2013. Biochar soil amendment as a solution to prevent Cd-tainted rice from China: results from a cross-site field experiment. Ecol. Eng. 58, 378–383. DOI: 10.1016/j.ecoleng.2013.07.031 17. Cao, X., Ma, L., Gao, B., Harris, W., 2009. Dairy–manure derived biochar effectively sorbs lead and atrazine. Environ. Sci. Technol. 43, 3285–3291. DOI: 10.1021/es803092k 18. Beesley, L., Marmiroli, M., 2011. The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar. Environ. Pollut. 159, 474–480. DOI: 10.1016/j.envpol.2010.10.016 19. Lu, H., Zhang, W., Yang, Y., Huang, X., Wang, S., Qiu, R., 2012. Relative distribution of Pb2+ sorption mechanisms by sludge-derived biochar. Water. Res. 46, 854–862. DOI: 10.1016/j.watres.2011.11.058 20. Xu, X., Cao, X., Zhao, L., Wang, H., Yu, H., Gao, B., 2013. Removal of Cu, Zn, and Cd from aqueous solutions by the dairy manure-derived biochar. Environ. Sci. Pollut. R. 20, 358–368. DOI: 10.1007/s11356-012-0873-5 21. Williams, P.N., Lei, M., Sun, G., Huang, Q., Lu, Y., Deacon, C., Meharg, A.A., Zhu, Y.G., 2009. Occurrence and partitioning of cadmium, arsenic and lead in mine impacted paddy rice: Hunan, China. Environ. Sci. Technol. 43, 637–642. DOI: 10.1021/es802412r 22. Ministry of Health, 2017. National food safety standard-maximum levels of contaminants in food (GB 2762-2017). Beijing, China. 23. Ministry of Agriculture, 2005. Standards for irrigation water quality (GB5084-2005). Beijing, China.



24. Zhao, F., Ma, Y., Zhu, Y., Tang, Z., McGrath, S.P., 2014. Soil contamination in China: current status and mitigation strategies. Environ. Sci. Technol. 49(2), 750– 759. DOI: 10.1021/es5047099 25. Jin, J., Li, S., Peng, X., Liu, W., Zhang, C., Yang, Y., Han, L., Du, Z., Sun, K., Wang, X., 2018. HNO3 modified biochars for uranium (VI) removal from aqueous solution, Bioresource Technol. 256, 247–253. DOI:10.1016/j.biortech.2018.02.022 26. Gul, S., Whalen, J.K., Thomas, B.W., Sachdeva, V., Deng, H.Y., 2015. Physico-chemical properties and microbial responses in biochar-amended soils: mechanisms and future directions. Agr. Ecosyst. Environ. 206, 46–59. DOI: 10.1016/j.agee.2015.03.015 27. Kloss, S., Zehetner, F., Dellantonio, A., Hamid, R., Ottner, F., Liedtke, V., Schwanninger, M., Gerzabek, M.H., Soja, G., 2012. Characterization of slow pyrolysis biochars: effects of feedstocks and pyrolysis temperature on biochar properties. J. Environ. Qual. 41, 990–1000. DOI: 10.2134/jeq2011.0070 28. Xu, D., Zhao, Y., Sun, K., Gao, B., Wang, Z., Jin, J., Zhang, Z., Wang, S., Yan, Y., Liu, X., Wu, Feng., 2014. Cadmium adsorption on plant- and manure-derived biochar and biochar-amended sandy soils: Impact of bulk and surface properties. Chemosphere 111, 320-326. DOI: 10.1016/j.chemosphere.2014.04.043 29. Zornoza, R., Moreno-Barriga, F., Acosta, J.A., Muñoz, M.A., Faz, A., 2016. Stability, nutrient availability and hydrophobicity of biochars derived from manure, crop residues, and municipal solid waste for their use as soil amendments. Chemosphere 144, 122–130. DOI: 10.1016/j.chemosphere.2015.08.046 30. Kumpiene, J., Lagerkvist, A., Maurice, C., 2008. Stabilisation of As, Cr, Cu, Pb and Zn in soil using amendments - a review. Waste. Manage. 28, 215–225. DOI: 10.1016/j.wasman.2006.12.012


Page 26 of 30

Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


31. Liu, S., Qi, X., Han, C., Liu, J., Sheng, X., Li, H., Luo, A., Li, J., 2017. Novel nanosubmicron

mineral-based

soil

conditioner

for

sustainable

agricultural

development. J. Clean. Prod. 149, 896–903. DOI: 10.1016/j.jclepro.2017.02.155 32. Zhang, F., Wang, X., Yin, D., Peng, B., Tan, C., Liu, Y., Tan, X., Wu, S., 2015. Efficiency and mechanisms of Cd removal from aqueous solution by biochar derived from water hyacinth (Eichornia crassipes). J. Environ. Manage. 153, 68–73. 33. Tessier, A, Campbell, P.G.C., Blesson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 7, 844–851. DOI: 10.1021/ac50043a017 34. Melo, L.C., Puga, A.P., Coscione, A.R., Beesley, L., Abreu, C.A., Camargo, O.A., 2016. Sorption and desorption of cadmium and zinc in two tropical soils amended with sugarcane-straw-derived biochar. J. Soil. Sediment. 16, 226–234. DOI: 10.1007/s11368-015-1199-y 35. Uchimiya, M., Lima, I.M., Thomas Klasson, K., Chang, S.C., Wartelle, L.H., Rodgers, J.E., 2010. Immobilization of heavy metal ions (CuII, CdII, NiII, and PbII) by broiler litter-derived biochars in water and soil. J. Agr. Food. Chem. 58, 5538– 5544. DOI: 10.1021/jf9044217 36. Bian, R., Joseph, S., Cui, L., Pan, G., Li, L., Liu, X., Zhang, A., Rutlidge, H., Wong, S., Chia, C., Marjo, C., Gong, B., Munroe, P., Donne, S., 2014. A three-year experiment confirms continuous immobilization of cadmium and lead in contaminated paddy field with biochar amendment. J. Hazard. Mater. 272, 121–128. DOI: 10.1016/j.jhazmat.2014.03.017 37. Harvey, O.R., Herbert, B.E., Rhue, R.D., Kuo, L.J., 2011. Metal interactions at the biochar-water interface: energetics and structure-sorption relationships elucidated by flow sorption microcalorimetry. Environ. Sci. Technol. 45, 5550–5556. DOI:



Page 28 of 30

10.1021/es104401h 38. Ahmad, M., Rajapaksha, A.U., Lim, J.E., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S.S., Ok, Y.S., 2014. Biochar as a sorbent for contaminant management in soil and water: a review. Chemosphere 99, 19–33. DOI: 10.1016/j.chemosphere.2013.10.071 39. Han, L., Sun, H., Ro, K.S., Sun, K., Libra, J.A., Xing, B., 2017. Removal of Antimony (III) and Cadmium (II) from Aqueous Solution using Animal Manure-derived Hydrochars and Pyrochars, Bioresource. Technol. 234, 77–85. DOI: 10.1016/j.biortech.2017.02.130 40. Liu, K., Lu, J., He, W., Zhang, H., Cao, Y., Dai, Y., 2015. Major factors influencing cadmium uptake from the soil into wheat plants. Ecotox. Environ. Safe. 113, 207– 213. DOI: 10.1016/j.ecoenv.2014.12.005 41. Li, J., Xu, Y., 2015. Immobilization of Cd in paddy soil using moisture management and

amendment.

Environ.

Sci.

Pollut.

R.

22,

5580–5586.

DOI:

10.1007/s11356-014-3788-5 42. Walker, D. J., Clemente, R., Bernal, M. P., 2004. Contrasting effects of manure and compost on soil pH, heavy metal availability and growth of Chenopodium album L. in a soil contaminated by pyritic mine waste. Chemosphere, 57(3), 215–224. DOI:10.1016/j.chemosphere.2004.05.020 43. He, Y., Huang, D., Zhu, Q., Wang, S., Liu, S., He. H., Zhu, H., Xu, C., 2017. A three-season field study on the in-situ remediation of Cd-contaminated paddy soil using lime, two industrial by-products, and a low-Cd-accumulation rice cultivar. Ecotox. Environ. Safe. 136, 135–141. DOI: 10.1016/j.ecoenv.2016.11.005 44. Chen, D., Guo, H., Li, R., Li, L., Pan, G., Chang, A., Joseph, S., 2015. Low uptake affinity cultivars with biochar to tackle Cd-tainted rice – A field study over four rice


Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


seasons in Hunan, China. Sci. Total. Environ. 541, 1489–1498. DOI: 10.1016/j.scitotenv.2015.10.052 45. Naidu, R., Bolan, N.S., Kookana, R.S., Tiller, K.G., 1994. Ionic-strength and pH effects on the sorption of cadmium and the surface charge of soils. Eur. J. Soil. Sci. 45, 419–429. DOI: 10.1111/j.1365-2389.1994.tb00527.x 46. Jones, D.L., Rousk, J., Edwards-Jones, G., DeLuca, T.H., Murphy, D.V., 2012. Biocharmediated changes in soil quality and plant growth in a three year field trial. Soil. Biol. Biochem. 45, 113–124. DOI: 10.1016/j.soilbio.2011.10.012 47. Zhan, F., Chen, J., Qin, L., Wang, J., Li, Y., 2016. Effects of applying Cd/Pb contaminated maize stalks on growth and nutrient and Cd and Pb content of faba bean. Journal of Agro-Environment Science 35, 661–668. (in Chinese with English abstract)



TOC

Synopsis Repeated annual addition of biochar derived from rice-straw is a more proper approach to sustainable application to treat Cd-contaminated irrigation water than one-time addition.


Page 30 of 30

Proper Mode of Using Rice Straw Biochar To Treat Cd-Contaminated

Recommend Documents