Environ Sci Pollut Res (2015) 22:4654–4659 DOI 10.1007/s11356-014-3711-0
RESEARCH ARTICLE
Phosphate enhances uptake of As species in garland chrysanthemum (C. coronarium) applied with chicken manure bearing roxarsone and its metabolites Lixian Yao & Lianxi Huang & Zhaohuan He & Changming Zhou & Guoliang Li & Xiancai Deng
Received: 26 June 2014 / Accepted: 9 October 2014 / Published online: 21 October 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Roxarsone (ROX), a world widely used feed organoarsenic additive in animal production, can be excreted as itself and its metabolites in animal manure. Animal manure is commonly land applied with phosphorous (P) fertilizer to enhance the P phytoavailability in agriculture. We investigated the accumulation of As species in garland chrysanthemum (C. coronarium) plants fertilized with 1 % (w/w, manure/soil) chicken manure bearing ROX and its metabolites, plus 0, 0.05, 0.1, 0.2, 0.4, and 0.8 g P2O5/kg, respectively. The results show that As(III) was the sole As compound in garland chrysanthemum shoots, and As(III) and As(V) were detectable in roots. Elevated phosphate level supplied more As(V) for garland chrysanthemum roots through competitive desorption in rhizosphere, leading to significantly enhanced accumulation of As species in plants. As(III) was the predominant As form in plants (85.0∼90.6 %). Phosphate could not change the allocation of As species in plants. Hence, the traditional practice that animal manure is applied with P fertilizer may inadvertently increase the potential risk of As contamination in crop via the way ROX → animal → animal manure → soil → crop.
Keywords Roxarsone . Animal manure . Phosphorous fertilizer . As species . Phytoavailability
Responsible editor: Philippe Garrigues L. Yao (*) : X. Deng College of Natural Resources and Environment, South China Agricultural University, Wushan, Tianhe, Guangzhou 510642, China e-mail: [email protected] L. Huang : Z. He : C. Zhou : G. Li Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
Introduction Since roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) can promote growth, inhibit parasites, and improve feed efficiency, it has been world widely used as a safe and excellent feed organoarsenic additive in animal production for decades (Chapman and Johnson 2002). For example, approximately 70 % of broiler production units uses ROX in the USA (Chapman and Johnson 2002), and 23 % of chicken feed is amended with ROX in Guangdong, China (Yao et al. 2013a). While animal is fed with ROX, the major As compounds in manure include ROX and its metabolites such as 3-amino-4hydro-phenylarsonic acid (3-AHPA), 4-hydro-phenylarsonic acid (4-HPA), As(V), As(III), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and unknown As compounds (Garbarino et al. 2003; Jackson and Bertsch 2001; Rosal et al. 2005; Yao et al. 2009). It has been found that some of ROX metabolites (DMA, As(III), and As(V)) can be accumulated in vegetables fertilized with chicken manure (CM) bearing ROX and its metabolites (Yao et al. 2013b; Yao et al. 2009). The potential environmental and public health risks associated with organoarsenic use in animal feeds have been reviewed by Silbergeld and Nachman (2008); however, the potential risk of As contamination in crop via the way ROX → animal → animal manure → soil → plant is still in underestimation. Animal manure is traditionally applied together with phosphorous (P) fertilizer to enhance the P bioavailability via competitive adsorption between phosphate and organic acids generated from animal manure, which has been recommended for decades in China (Zhang 1988). On the other hand, the extractable As compounds including ROX, As(V), As(III), MMA, and DMA in mineral surface increase with increased phosphate level (Jackson and Miller 2000); therefore, we suppose that the uptake of ROX and its metabolites in crops
Environ Sci Pollut Res (2015) 22:4654–4659
might increase when animal manure bearing ROX and its metabolites is land applied together with P fertilizer. This work aims to identify whether combined phosphate supply affects the uptake, transport, and distribution of As species in garland chrysanthemum plants grown in soils amended with CM containing ROX and its metabolites (4HPA, As(V), As(III), MMA, DMA, etc.). We hope this work will contribute to evaluating the potential risks of ROX and its metabolites to human by food chain.
Materials and methods Soil, CM, and plant The soil used was collected at the 0–25 cm depth, typical of lateritic red soil from the Crop Experiment Station of the Guangdong Academy of Agricultural Sciences located in Guangzhou, southern China. Prior to use, the soil was airdried, ground to pass through a 2-mm sieve, and well mixed. The fresh CM was taken from an intensive chicken farm located in Huizhou City, Guangdong Province, in southern China, where ROX was used in the chicken feed. The fresh manure was composted for a month, then air-dried with removal of impurities, and passed through a 2-mm sieve. The soil and CM used in this study were same as those used in our previous work (Yao et al. 2013b). The detectable As species in the soil included As(V) (1.48±0.03 mg/kg) and As(III) (0.08±0.0 mg/kg), with the total As of 7.3 mg/kg. The composted CM contained ROX (1.58±0.31 mg/kg), 3-AHPA (0.35±0.14 mg/kg), As(V) (20.49±0.38 mg/kg), As(III) (2.96 ±0.05 mg/kg), MMA (1.72±0.23 mg/kg), DMA (2.99± 0.15 mg/kg), and unknown As species, with the total As of 58.3 mg/kg. The other basic properties of soil and CM could be seen in the previous work (Yao et al. 2013b). A popular leafy vegetable garland chrysanthemum (Chrysanthemum coronarium), purchased from Guangzhou Vegetable Institute, was used. Experimental design A pot experiment in garland chrysanthemum was carried out in a greenhouse. The experiment was designed with five treatments and four replications. The five fertilization treatments were 0, 0.05, 0.1, 0.2, 0.4, and 0.8 g P 2 O 5 (NaH2PO4·2H2O, AR)/kg plus 1 % CM (w/w, manure/soil), respectively, and abbreviated as P0, P1, P2, P3, and P4. The combined use levels of phosphate and CM are based on the greatly different use rates of P fertilizer and animal manure, while these two fertilizers are applied together by different farmers in practice. Phosphate and CM were mixed with 7.5 kg soil thoroughly and then put into a PVC pot (17 cm in height and 24 cm in diameter). The soil moisture was kept at
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approximately 70 % field water holding capacity for 10 days by adding deionized water, then 20 seeds of garland chrysanthemum were sown, with five seedlings kept in each pot eventually. Sample collection and preparation Before sowing, one soil sample was gathered vertically from the surface to the bottom in each pot. After sampling, the hole was filled with the soils in each pot, and then the seeds were sown. The shoots and roots of garland chrysanthemum were harvested separately with stainless steel scissors at 47 days after seeding, washed with tap water, and then rinsed with deionized water. The fresh weight of plants was recorded, followed by immediate lyophilization (Alpha 1–4/LD-plus, Christ), and the dry weight was recorded as well. The lyophilized plant samples were pulverized to a fine powder for total P, total As, and As speciation analysis. Soils adhered to the roots of garland chrysanthemum in each pot were collected as a soil sample when harvested. All the soil samples were lyophilized immediately, then ground and well mixed for As speciation analysis. Chemical analysis Soil, CM, and plant samples were digested with concentrated HNO3 + H2SO4 + HClO4, and the total As was determined by hydride generation-atomic fluorescence spectrometer (HGAFS, AFS8130, Jitian, Beijing). Two reference materials GBW07408 and GBW07602 were used to assure the analysis quality for soil, CM, and plant samples, with the recoveries of 97∼114 %. The As compounds in soil and manure samples were extracted as follows: Approximately 1.0 g soil or 0.2 g manure sample was placed into a Teflon vessel, and 10 mL of mixture of NaH2PO4/H3PO4 (9:1) (0.1 mol/L PO43−) was added, kept in 55 °C water bath for 10 h, and sonicated for 20 min and then centrifuged at 4,000 r/min for 10 min and the supernatant was collected. The residue was extracted twice with 5 mL 0.1 mol/L PO43− and all the extracts were combined. The extracts were transferred to a 20-mL volumetric flask and diluted to 20 mL by adding ultrapure water, then filtered through a 0.22-μm membrane for As species analysis. As species were separated by liquid chromatography (LC, 20AT, Shimadzu, Japan), then detected by HG-AFS (8× dual channel system/SAP10-8130 speciation analysis, Jitian, Beijing). The operating conditions of LC coupled with HG-AFS were presented in Table 1. As species in plant samples were prepared as follows: Approximately 0.25 g sample was placed into a Teflon vessel, 10 mL ultrapure water was added, and kept in 55 °C water bath for 10 h, then sonicated for 20 min, centrifuged for 10 min at 4,000 r/min, and the supernatant was collected.
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Environ Sci Pollut Res (2015) 22:4654–4659
Table 1 Working conditions of LC-HG-AFS LC
HG-AFS (8× dual channel system/SAP10-8130, Jitian, Beijing)
Plant LC pump: double pump (20AT, Shimadzu, Japan) Column: Phenomenex Reversed C18 (ODS3, 250 mm×4.6 mm i.d., 5 μm) Mobile phase: A: NaH2PO4 (10 mmol/L), TBAB (0.5 mmol/L), CH3OH (3 %, v/v), pH=6.22 B: NaH2PO4 (50 mmol/L), TBAB (0.5 mmol/L), CH3OH (5 %, v/v), pH=6.22 Flow rate, 1.0 mL/min Injection volume, 100 μL Soil and chicken manure LC pump: double pump (20AT, Shimadzu, Japan) Column: Phenomenex Reversed C18 (ODS3, 250 mm×4.6 mm i.d., 5 μm) Mobile phase A: NaH2PO4 (10 mmol/L), TBAB (0.5 mmol/L), CH3OH (3 %, v/v), pH=6.22 B: NaH2PO4 (50 mmol/L), TBAB (0.5 mmol/L), CH3OH (5 %, v/v), pH=6.22 Gradient elution: 0–11 min, 100 % A; 11–20 min, 100 % B; 20–30 min, 100 % A Flow rate, 1.0 mL/min Injection volume, 100 μL
The residue was extracted twice and all the extracts were combined. The extracts were lyophilized, and 5 mL ultrapure water for root or 2 mL for shoot sample was added to dissolve the residue and filtered through a 0.22-μm membrane for LCHG-AFS analysis.
Standards and reagents The reference materials of ROX (97.5 %, Dr. Ehrenstorfer Gmbh, Germany), 3-AHPA (99 %, Sigma-Aldrich, USA), 4HPA (98 %, TCI Tokyo Kasei, Japan), trimethylarsine oxide (98 %, Tri Chemical Laboratories Inc., Japan), trimethylarsine (99 %, Strem Chemicals, USA), and phenylarsonic acid (99 %, Aladdin, USA) were used in this work. The standard stock solutions of As(V) (Na2HAsO4·12H2O, 17.5±0.4 mg/ L), As(III) (Na3AsO3, 75.7 ± 1.2 mg/L), MMA (CH 4 AsNaO 3 ·1.5H 2 O, 25.1 ± 0.8 mg/L), and DMA (C2H6AsNaO2·2H2O, 52.9±1.8 mg/L) were bought from the National Standard Materials Center of China. The stock solutions were stored in the dark at −4 °C. Prior to use, the four stock solutions were diluted to 100, 75.5, 50.2, and 105.8 μg/L, respectively. High-performance liquid chromatography (HPLC) methanol (Burdick & Jackson, USA) and analytical-grade reagents were used in all the experiments. Ultrapure water was prepared with Millipore Milli-Q Academic. The recoveries of standard addition of ROX, 3-AHPA, 4HPA, As(V), As(III), MMA, and DMA for plant, manure, and soil could be seen in the previous report as well (Yao et al. 2013b). The detection limits for ROX, 3-AHPA, 4-HPA,
Oxidant, 2.0 % KBH4/0.5 % KOH Reducer, 2.0 % K2S2O8/0.5 % KOH HCl, 7.0 % (v/v) PMT voltage, 295 V Carrier gas: argon, 400 mL/min Shield gas, 600 mL/min Hcl current, 90 mA (primary)/40 mA (boosted) Oxidant, 2.0 % KBH4/0.5 % KOH Reducer, 2.0 % K2S2O8/0.5 % KOH HCl, 7.0 % (v/v) PMT voltage, 295 V Carrier gas: argon, 400 mL/min Shield gas, 600 mL/min Hcl current, 90 mA (primary)/40 mA (boosted)
As(V), As(III), MMA, and DMA were 9.5, 3.8, 8.4, 4.7, 1.8, 1.9, and 3.6 μg/L. Data and statistics All data were the means of four replications and expressed as mean±standard error. The concentrations of all As compounds were presented as the elemental As. Transfer factors (TFs) of As or P were computed as the ratios of As or P contents (fresh weight) in shoots/As or P contents (fresh weight) in roots of garland chrysanthemum. Data were subjected to ANOVA and LSD (P
RESEARCH ARTICLE
Phosphate enhances uptake of As species in garland chrysanthemum (C. coronarium) applied with chicken manure bearing roxarsone and its metabolites Lixian Yao & Lianxi Huang & Zhaohuan He & Changming Zhou & Guoliang Li & Xiancai Deng
Received: 26 June 2014 / Accepted: 9 October 2014 / Published online: 21 October 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Roxarsone (ROX), a world widely used feed organoarsenic additive in animal production, can be excreted as itself and its metabolites in animal manure. Animal manure is commonly land applied with phosphorous (P) fertilizer to enhance the P phytoavailability in agriculture. We investigated the accumulation of As species in garland chrysanthemum (C. coronarium) plants fertilized with 1 % (w/w, manure/soil) chicken manure bearing ROX and its metabolites, plus 0, 0.05, 0.1, 0.2, 0.4, and 0.8 g P2O5/kg, respectively. The results show that As(III) was the sole As compound in garland chrysanthemum shoots, and As(III) and As(V) were detectable in roots. Elevated phosphate level supplied more As(V) for garland chrysanthemum roots through competitive desorption in rhizosphere, leading to significantly enhanced accumulation of As species in plants. As(III) was the predominant As form in plants (85.0∼90.6 %). Phosphate could not change the allocation of As species in plants. Hence, the traditional practice that animal manure is applied with P fertilizer may inadvertently increase the potential risk of As contamination in crop via the way ROX → animal → animal manure → soil → crop.
Keywords Roxarsone . Animal manure . Phosphorous fertilizer . As species . Phytoavailability
Responsible editor: Philippe Garrigues L. Yao (*) : X. Deng College of Natural Resources and Environment, South China Agricultural University, Wushan, Tianhe, Guangzhou 510642, China e-mail: [email protected] L. Huang : Z. He : C. Zhou : G. Li Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
Introduction Since roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) can promote growth, inhibit parasites, and improve feed efficiency, it has been world widely used as a safe and excellent feed organoarsenic additive in animal production for decades (Chapman and Johnson 2002). For example, approximately 70 % of broiler production units uses ROX in the USA (Chapman and Johnson 2002), and 23 % of chicken feed is amended with ROX in Guangdong, China (Yao et al. 2013a). While animal is fed with ROX, the major As compounds in manure include ROX and its metabolites such as 3-amino-4hydro-phenylarsonic acid (3-AHPA), 4-hydro-phenylarsonic acid (4-HPA), As(V), As(III), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and unknown As compounds (Garbarino et al. 2003; Jackson and Bertsch 2001; Rosal et al. 2005; Yao et al. 2009). It has been found that some of ROX metabolites (DMA, As(III), and As(V)) can be accumulated in vegetables fertilized with chicken manure (CM) bearing ROX and its metabolites (Yao et al. 2013b; Yao et al. 2009). The potential environmental and public health risks associated with organoarsenic use in animal feeds have been reviewed by Silbergeld and Nachman (2008); however, the potential risk of As contamination in crop via the way ROX → animal → animal manure → soil → plant is still in underestimation. Animal manure is traditionally applied together with phosphorous (P) fertilizer to enhance the P bioavailability via competitive adsorption between phosphate and organic acids generated from animal manure, which has been recommended for decades in China (Zhang 1988). On the other hand, the extractable As compounds including ROX, As(V), As(III), MMA, and DMA in mineral surface increase with increased phosphate level (Jackson and Miller 2000); therefore, we suppose that the uptake of ROX and its metabolites in crops
Environ Sci Pollut Res (2015) 22:4654–4659
might increase when animal manure bearing ROX and its metabolites is land applied together with P fertilizer. This work aims to identify whether combined phosphate supply affects the uptake, transport, and distribution of As species in garland chrysanthemum plants grown in soils amended with CM containing ROX and its metabolites (4HPA, As(V), As(III), MMA, DMA, etc.). We hope this work will contribute to evaluating the potential risks of ROX and its metabolites to human by food chain.
Materials and methods Soil, CM, and plant The soil used was collected at the 0–25 cm depth, typical of lateritic red soil from the Crop Experiment Station of the Guangdong Academy of Agricultural Sciences located in Guangzhou, southern China. Prior to use, the soil was airdried, ground to pass through a 2-mm sieve, and well mixed. The fresh CM was taken from an intensive chicken farm located in Huizhou City, Guangdong Province, in southern China, where ROX was used in the chicken feed. The fresh manure was composted for a month, then air-dried with removal of impurities, and passed through a 2-mm sieve. The soil and CM used in this study were same as those used in our previous work (Yao et al. 2013b). The detectable As species in the soil included As(V) (1.48±0.03 mg/kg) and As(III) (0.08±0.0 mg/kg), with the total As of 7.3 mg/kg. The composted CM contained ROX (1.58±0.31 mg/kg), 3-AHPA (0.35±0.14 mg/kg), As(V) (20.49±0.38 mg/kg), As(III) (2.96 ±0.05 mg/kg), MMA (1.72±0.23 mg/kg), DMA (2.99± 0.15 mg/kg), and unknown As species, with the total As of 58.3 mg/kg. The other basic properties of soil and CM could be seen in the previous work (Yao et al. 2013b). A popular leafy vegetable garland chrysanthemum (Chrysanthemum coronarium), purchased from Guangzhou Vegetable Institute, was used. Experimental design A pot experiment in garland chrysanthemum was carried out in a greenhouse. The experiment was designed with five treatments and four replications. The five fertilization treatments were 0, 0.05, 0.1, 0.2, 0.4, and 0.8 g P 2 O 5 (NaH2PO4·2H2O, AR)/kg plus 1 % CM (w/w, manure/soil), respectively, and abbreviated as P0, P1, P2, P3, and P4. The combined use levels of phosphate and CM are based on the greatly different use rates of P fertilizer and animal manure, while these two fertilizers are applied together by different farmers in practice. Phosphate and CM were mixed with 7.5 kg soil thoroughly and then put into a PVC pot (17 cm in height and 24 cm in diameter). The soil moisture was kept at
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approximately 70 % field water holding capacity for 10 days by adding deionized water, then 20 seeds of garland chrysanthemum were sown, with five seedlings kept in each pot eventually. Sample collection and preparation Before sowing, one soil sample was gathered vertically from the surface to the bottom in each pot. After sampling, the hole was filled with the soils in each pot, and then the seeds were sown. The shoots and roots of garland chrysanthemum were harvested separately with stainless steel scissors at 47 days after seeding, washed with tap water, and then rinsed with deionized water. The fresh weight of plants was recorded, followed by immediate lyophilization (Alpha 1–4/LD-plus, Christ), and the dry weight was recorded as well. The lyophilized plant samples were pulverized to a fine powder for total P, total As, and As speciation analysis. Soils adhered to the roots of garland chrysanthemum in each pot were collected as a soil sample when harvested. All the soil samples were lyophilized immediately, then ground and well mixed for As speciation analysis. Chemical analysis Soil, CM, and plant samples were digested with concentrated HNO3 + H2SO4 + HClO4, and the total As was determined by hydride generation-atomic fluorescence spectrometer (HGAFS, AFS8130, Jitian, Beijing). Two reference materials GBW07408 and GBW07602 were used to assure the analysis quality for soil, CM, and plant samples, with the recoveries of 97∼114 %. The As compounds in soil and manure samples were extracted as follows: Approximately 1.0 g soil or 0.2 g manure sample was placed into a Teflon vessel, and 10 mL of mixture of NaH2PO4/H3PO4 (9:1) (0.1 mol/L PO43−) was added, kept in 55 °C water bath for 10 h, and sonicated for 20 min and then centrifuged at 4,000 r/min for 10 min and the supernatant was collected. The residue was extracted twice with 5 mL 0.1 mol/L PO43− and all the extracts were combined. The extracts were transferred to a 20-mL volumetric flask and diluted to 20 mL by adding ultrapure water, then filtered through a 0.22-μm membrane for As species analysis. As species were separated by liquid chromatography (LC, 20AT, Shimadzu, Japan), then detected by HG-AFS (8× dual channel system/SAP10-8130 speciation analysis, Jitian, Beijing). The operating conditions of LC coupled with HG-AFS were presented in Table 1. As species in plant samples were prepared as follows: Approximately 0.25 g sample was placed into a Teflon vessel, 10 mL ultrapure water was added, and kept in 55 °C water bath for 10 h, then sonicated for 20 min, centrifuged for 10 min at 4,000 r/min, and the supernatant was collected.
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Environ Sci Pollut Res (2015) 22:4654–4659
Table 1 Working conditions of LC-HG-AFS LC
HG-AFS (8× dual channel system/SAP10-8130, Jitian, Beijing)
Plant LC pump: double pump (20AT, Shimadzu, Japan) Column: Phenomenex Reversed C18 (ODS3, 250 mm×4.6 mm i.d., 5 μm) Mobile phase: A: NaH2PO4 (10 mmol/L), TBAB (0.5 mmol/L), CH3OH (3 %, v/v), pH=6.22 B: NaH2PO4 (50 mmol/L), TBAB (0.5 mmol/L), CH3OH (5 %, v/v), pH=6.22 Flow rate, 1.0 mL/min Injection volume, 100 μL Soil and chicken manure LC pump: double pump (20AT, Shimadzu, Japan) Column: Phenomenex Reversed C18 (ODS3, 250 mm×4.6 mm i.d., 5 μm) Mobile phase A: NaH2PO4 (10 mmol/L), TBAB (0.5 mmol/L), CH3OH (3 %, v/v), pH=6.22 B: NaH2PO4 (50 mmol/L), TBAB (0.5 mmol/L), CH3OH (5 %, v/v), pH=6.22 Gradient elution: 0–11 min, 100 % A; 11–20 min, 100 % B; 20–30 min, 100 % A Flow rate, 1.0 mL/min Injection volume, 100 μL
The residue was extracted twice and all the extracts were combined. The extracts were lyophilized, and 5 mL ultrapure water for root or 2 mL for shoot sample was added to dissolve the residue and filtered through a 0.22-μm membrane for LCHG-AFS analysis.
Standards and reagents The reference materials of ROX (97.5 %, Dr. Ehrenstorfer Gmbh, Germany), 3-AHPA (99 %, Sigma-Aldrich, USA), 4HPA (98 %, TCI Tokyo Kasei, Japan), trimethylarsine oxide (98 %, Tri Chemical Laboratories Inc., Japan), trimethylarsine (99 %, Strem Chemicals, USA), and phenylarsonic acid (99 %, Aladdin, USA) were used in this work. The standard stock solutions of As(V) (Na2HAsO4·12H2O, 17.5±0.4 mg/ L), As(III) (Na3AsO3, 75.7 ± 1.2 mg/L), MMA (CH 4 AsNaO 3 ·1.5H 2 O, 25.1 ± 0.8 mg/L), and DMA (C2H6AsNaO2·2H2O, 52.9±1.8 mg/L) were bought from the National Standard Materials Center of China. The stock solutions were stored in the dark at −4 °C. Prior to use, the four stock solutions were diluted to 100, 75.5, 50.2, and 105.8 μg/L, respectively. High-performance liquid chromatography (HPLC) methanol (Burdick & Jackson, USA) and analytical-grade reagents were used in all the experiments. Ultrapure water was prepared with Millipore Milli-Q Academic. The recoveries of standard addition of ROX, 3-AHPA, 4HPA, As(V), As(III), MMA, and DMA for plant, manure, and soil could be seen in the previous report as well (Yao et al. 2013b). The detection limits for ROX, 3-AHPA, 4-HPA,
Oxidant, 2.0 % KBH4/0.5 % KOH Reducer, 2.0 % K2S2O8/0.5 % KOH HCl, 7.0 % (v/v) PMT voltage, 295 V Carrier gas: argon, 400 mL/min Shield gas, 600 mL/min Hcl current, 90 mA (primary)/40 mA (boosted) Oxidant, 2.0 % KBH4/0.5 % KOH Reducer, 2.0 % K2S2O8/0.5 % KOH HCl, 7.0 % (v/v) PMT voltage, 295 V Carrier gas: argon, 400 mL/min Shield gas, 600 mL/min Hcl current, 90 mA (primary)/40 mA (boosted)
As(V), As(III), MMA, and DMA were 9.5, 3.8, 8.4, 4.7, 1.8, 1.9, and 3.6 μg/L. Data and statistics All data were the means of four replications and expressed as mean±standard error. The concentrations of all As compounds were presented as the elemental As. Transfer factors (TFs) of As or P were computed as the ratios of As or P contents (fresh weight) in shoots/As or P contents (fresh weight) in roots of garland chrysanthemum. Data were subjected to ANOVA and LSD (P
