Pensiri
Akkajit
ab,
Thomas
DeSutter
c and
Chantra
Tongcumpou
*ad
aCenter of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University, Bangkok, Thailand 10330. E-mail: pensiri.a@hotmail.com; tchantra@chula.ac.th
bInternational Postgraduate Programs in Environmental Management, Chulalongkorn University, Phathumwan, Bangkok, Thailand 10330. E-mail: pensiri.a@hotmail.com
cDepartment of Soil Science, North Dakota State University, 214 Walster Hall, P.O. Box 7680, Fargo, ND 58108-6050, USA. E-mail: thomas.desutter@ndsu.edu
dEnvironmental Research Institute, Chulalongkorn University, Phathumwan, Bangkok, Thailand 10330. E-mail: tchantra@chula.ac.th; Fax: +66 2218 8210; Tel: +66 2218 8138
First published on 12th November 2013
The effects of three sugarcane waste-products from an ethanol production plant on the fractionation of Cd and Zn in high Cd and Zn contaminated soil and metal accumulation in sugarcane (Saccharum officinarum L.) were studied, using the BCR sequential extraction and aqua regia extraction procedures. A pot experiment was performed for 4 months with four treatments: no-amendments (control), boiler ash (3% w/w), filter cake (3% w/w) and a combination of boiler ash and vinasse (1.5% + 1.5%, w/w). The results showed that all treatments reduced the most bioavailable concentrations of Cd and Zn (BCR1 + 2) in soils (4.0–9.6% and 5.5–6.3%, respectively) and metal uptake (μg) in the aboveground part of the sugarcane (up to 62% and 54% for Cd and Zn, respectively) as compared to the control. No visual symptoms of metal toxicity and no positive effect on the biomass production of sugarcane were observed. Both Cd and Zn were accumulated mainly in the underground parts of the sugarcane (root > shoot ≥ underground sett > leaf; and root > underground sett > shoot > leaf, respectively) and the translocation factors were below 1, indicating low metal uptake. The results suggested that even though sugarcane waste-products insignificantly promote sugarcane growth, they can be used in agriculture due to the low metal accumulation in sugarcane and the reduction in metal bioavailability in the soil.
Environmental impactWaste utilization of sugarcane waste-products generated from ethanol production processes as soil amendments on agricultural land for metal stabilization and agricultural purposes provides benefits in terms of waste recycling, in situ metal stabilization, and agricultural productivity. An understanding of sugarcane waste-products as soil amendments and soil constituents would be useful for developing management practices within this particular area of waste management, along with the protection of the environment from heavy metal translocation. Therefore, in-depth investigation and long term studies are necessary to determine the validity and feasibility of these waste-products before applying them to real field sites to ensure the experimental results. |
Based on the above considerations, the use of waste-products as a soil amendment might be an alternative suitable option for the reclamation of contaminated soils through reducing metal bioavailability by in situ stabilization and improving soil quality. Numerous waste-products have been widely studied and used as soil amendments and immobilizing agents.3–5 The effects of sugarcane waste-products as a soil amendment on the Cd and Zn bioavailability in soils were studied previously with 3% (w/w) amendment application in a pot experiment.2 The results showed a reduction in the exchangeable fraction of Cd (BCR1) in the amended soils (2.3% to 4.7% and 9.4% to 39.9% in low and high Cd contaminated soils, respectively), as compared to the non-amended soils. In addition, the effects of sugarcane waste-products on sugarcane growth and its metal uptake in low Cd and Zn contaminated soil (less than 5 mg Cd per kg soil) were further studied.6 The results showed a positive effect on biomass production, however, no significant reduction of metal accumulation in the plants was observed.
In the present study, we extended the previous work by growing sugarcane in high Cd and Zn contaminated soils (less than 20 mg Cd per kg soil). We evaluated the usefulness of sugarcane waste-products as soil amendments in high Cd and Zn contaminated soil for promoting sugarcane growth, and Cd and Zn in situ stabilization was evaluated by studying the effects of sugarcane waste-products on the bioavailability of the Cd and Zn in the soil and metal uptake by sugarcane. This knowledge must lead to the development of a guideline for using sugarcane waste-products as soil amendments for soil and fertilizer management and for reducing heavy metal contamination in agricultural soils. According to this the following studies were carried out: (1) to investigate the effects of sugarcane waste-products (BA, FC, and VN) from an ethanol production plant as soil amendments on sugarcane growth and for reducing Cd and Zn bioavailability in high Cd and Zn contaminated soil, and (2) to determine the translocation and distribution of Cd and Zn within sugarcane at different growth stages over a time period of 4 months.
The pot experiment was conducted for a period of 4 months. Soil and sugarcane samples were sacrificed and collected monthly on the same sampling dates (from T1 to T4 where T1, T2, T3 and T4 represent the 1, 2, 3 and 4 month growth stages of sugarcane, respectively). In order to constrain the analytical uncertainty of the results, the plants were grown in three different containers for each treatment during the whole experiment, and individual plants were taken from each container at each harvesting period. There were 4 batches of experiments in accordance with the four-month harvesting period. This resulted in a total of 48 experimental pots (3 replications, 4 treatments, and 4 collecting times). Each batch of plants from each container was analyzed independently and the chemical results of the three batches were averaged for each harvesting time.
The whole sugarcane plants were separated into four different parts, including roots, underground setts, shoots and leaves. The aboveground part of the sugarcane represents the leaves and shoots; while the underground part is the summation of the underground setts and roots. Shoot height (cm) was measured from the top of the underground sett to the tip of the longest leaf, and the shoot diameter (cm) was measured in the middle third of the sugarcane stalk. The roots, underground setts, shoots and leaves were oven-dried at 60 °C for 72 h, ground in an agate mortar and their dry weights (g per plant) were recorded.
The pH of the soil and amendments were determined for ratios of 1:
2 and 1
:
5 solid
:
deionized water, respectively. Organic matter (OM), total nitrogen (Total.N), available phosphorous (Avail.P), and exchangeable potassium (Exc.K) were determined using the Walkley–Black method, the Kjeldahl Method, the BrayII method and 1M NH4-acetate extraction, respectively. In this study, total digestion according to the Standard US EPA Method 3052 (1996)7 and the three-step BCR sequential extraction proposed by the Standards, Measurements and Testing programme of the European Union (SM&T)8 including the residual fraction (BCR4) were performed for the soil analysis to determine the total and bioavailable Cd and Zn concentrations, respectively. The roots and underground setts of the sugarcane were determined using aqua regia extraction (3
:
1 ratio of 12 ml HCl and 4 ml HNO3); whereas the shoots and leaves were determined using a mixture of hydrogen peroxide (H2O2) and nitric acid (HNO3) (1
:
3 v/v). The Cd and Zn concentrations in the soil and sugarcane were analyzed using graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS) (AAS-ZEEnit 700 Analytik), respectively. The accuracy of the analytical procedures for total digestion was verified using a soil certified reference material (CRM025-050, RTC) with four replicates. The percent recovery of the sum of the extracted Cd and Zn in all BCR fractions (BCR1, BCR2, and BCR3) plus the residual fraction (BCR4) was compared with the pseudo-total concentration (from aqua regia digestion) for an internal check.
The data were expressed as means with standard deviations (mean ± SD). The statistical analysis was based on one-way analysis of variance (ANOVA) for the comparison of statistical significances between treatments using the SPSS (Statistical Product and Service Solutions) version 17.0 software. The Duncan test at *p < 0.05 was used.
pH | OM (%) | Total.N (%) | Avail.P | Exc.K | Cd | Zn | |
---|---|---|---|---|---|---|---|
(mg kg−1) | |||||||
a BA = boiler ash; FC = filter cake; BAV = boiler ash and vinasse (50![]() ![]() |
|||||||
Soil | 6.60 | 2.58 | 0.09 | 11 | 74 | 19 | 914 |
BA | 8.85 | 6.20 | 0.12 | 6964 | 3325 | 0.01 | 60 |
FC | 6.02 | 17.4 | 1.39 | 1041 | 5350 | 0.54 | 163 |
BAV | 6.58 | 15.2 | 0.31 | 4003 | 11![]() |
0.44 | 117 |
As soil pH is one of the most important factors affecting metal speciation and transformation, the soil pH was determined at every sampling period at each sugarcane growth stage (from T0 to T4) (Fig. 1). It was shown that the pH of the treated soils significantly increased (*p < 0.05) with the residence time from the first sampling (T0), with the highest pH occurring at the end of incubation period T4 (+1.0 to +1.5 pH unit increase). Cui et al.9 showed a similar pattern of pH change, with an initial increase followed by a decrease, and then the pH remained constant after incubating soils for a period of 6 months with Indian mustard. The initial increase in pH may be due to the alkaline amendments, which have a high K content that could contribute to an excess of Ca. Organic matter in the amendment materials used in this study may also be released and modify soil pH, depending on the buffering capacity of the soil, the composition of the organic matter and the soil physico-chemical properties.
Treatment | Mean biomass dry weight (g per plant) ± SD | Height (cm) | Diameter (cm) | ||
---|---|---|---|---|---|
Leaf | Shoot | Root | |||
a Mean values ± SD denoted by the same letter in a column indicates no significant difference according to the Duncan test at *p < 0.05. | |||||
Ctrl | 26.9 ± 3.6a | 16.9 ± 4.5a | 11.8 ± 4.4a | 172 ± 9.6a | 1.93 ± 0.21a |
BA | 11.9 ± 10.1a | 13.4 ± 3.8a | 5.80 ± 2.3a | 134 ± 51a | 1.80 ± 0.14a |
FC | 13.1 ± 16.5a | 11.2 ± 10.5a | 4.28 ± 5.2a | 122 ± 39a | 1.23 ± 0.81a |
BAV | 33.1 ± 8.3a | 16.2 ± 2.8a | 11.9 ± 6.2a | 166 ± 3.8a | 2.20 ± 0.10a |
Cd concentration (mg kg−1) in sugarcane | ||||
---|---|---|---|---|
Ctrl | BA | FC | BAV | |
Leaf | 0.3976b | 0.0273a | 0.1678ab | 0.3762b |
Shoot | 0.9349a | 0.7009a | 0.8761a | 0.7813a |
Sett | 0.8121a | 0.8087a | 0.7278a | 0.7488a |
Root | 1.7464ab | 2.2681b | 0.8121a | 0.8323a |
Total-sugarcane* | 0.8362a | 0.8737a | 0.5684a | 0.5975a |
Total-soil** | 12.9a | 12.7a | 12.9a | 13.4a |
TF | 0.06 | 0.07 | 0.04 | 0.04 |
Zn concentration (mg kg−1) in sugarcane | ||||
---|---|---|---|---|
Ctrl | BA | FC | BAV | |
a * = total concentration in sugarcane; ** = total concentration in soil. Values denoted by the same letter in a row indicates no significant difference according to the Duncan test at *p < 0.05. | ||||
Leaf | 30.4a | 27.0a | 26.5a | 26.2a |
Shoot | 104ab | 57.2a | 120b | 91ab |
Sett | 140a | 134a | 135a | 77a |
Root | 222a | 251a | 257a | 168a |
Total-sugarcane* | 95.1a | 117a | 89.3a | 75.1a |
Total-soil** | 520b | 499a | 523b | 527b |
TF | 0.18 | 0.23 | 0.17 | 0.14 |
In addition, Cd and Zn accumulation (μg) in the aboveground and underground parts were determined (Table 4). It was found that the metal uptake of these two metals changed over time; they accumulated more in the underground parts in the first two month (T1 and T2) and then moved up to the aboveground parts at the end of harvesting period (T4). As expected, the total Cd and Zn accumulations (μg) were highest at the end of the pot experiment (T4) due to plant growth and metal accumulation. The metal increase in sugarcane was proposed to result from uptake by plants during the growth period.
Cd | Metal uptake (μg) | |||||||
---|---|---|---|---|---|---|---|---|
T1 | T2 | T3 | T4 | |||||
Aboveground | Underground | Aboveground | Underground | Aboveground | Underground | Aboveground | Underground | |
Ctrl | 0.752 | 4.07 | 3.64 | 4.04 | 13.5 | 8.73 | 26.8 | 24.9 |
BA | 0.299 | 5.49 | 2.56 | 7.36* | 13.2 | 7.54 | 10.2* | 18.9 |
FC | 0.018 | 4.33 | 8.38 | 5.23 | 17.1 | 9.65 | 13.7* | 7.29* |
BAV | 0.553 | 11.6* | 7.84 | 6.14 | 23.6 | 9.76 | 25.2 | 15.4* |
Zn | T1 | T2 | T3 | T4 | ||||
---|---|---|---|---|---|---|---|---|
a Note: * = The mean value is significantly different compared to the Ctrl, according to the Duncan test at *p < 0.05. | ||||||||
Ctrl | 66 | 650 | 388 | 1171 | 1767 | 1723 | 2489 | 3324 |
BA | 27 | 841 | 366 | 824 | 1939 | 1503 | 1156* | 2661 |
FC | 42 | 702 | 1016 | 1189 | 2142 | 1468 | 1645 | 1766 |
BAV | 58 | 1757 | 1142 | 1719 | 2216 | 1380 | 2298 | 2797 |
Moreover, the results showed that the addition of 3% (w/w) BA or FC was effective in reducing Cd uptake in the aboveground part of the sugarcane at the end of the pot experiment, showing a 62.7% and 53.7% reduction, respectively, compared to the Ctrl (Table 4). However, no significant difference in Zn uptake (*p < 0.05) was observed in this study, except with the BA treatment.
Treatment | BCR1 + 2 Cd concentration (mg kg−1) | ||||
---|---|---|---|---|---|
T0 | T1 | T2 | T3 | T4 | |
Ctrl | 26.8 ± 2.2b | 14.3 ± 1.3a | 4.96 ± 0.8a | 5.32 ± 0.3b | 3.54 ± 0.1a |
BA | 16.5 ± 5.5ab | 11.7 ± 1.4a | 4.80 ± 0.4a | 4.64 ± 0.2a | 3.30 ± 0.2a |
FC | 24.3 ± 2.2ab | 13.9 ± 1.2a | 4.61 ± 0.2a | 4.69 ± 0.3a | 3.40 ± 0.3a |
BAV | 19.2 ± 5.3a | 14.3 ± 1.3a | 5.27 ± 0.5a | 4.78 ± 0.3ab | 3.20 ± 0.4a |
Treatment | BCR1 + 2 Zn concentration (mg kg−1) | ||||
---|---|---|---|---|---|
T0 | T1 | T2 | T3 | T4 | |
a Mean values ± SD denoted by the same letter in a column indicates no significant difference according to the Duncan test at *p < 0.05. | |||||
Ctrl | 647 ± 67b | 404 ± 38b | 64 ± 2.1ab | 182 ± 6.0a | 128 ± 6.6a |
BA | 223 ± 169a | 333 ± 10a | 63 ± 1.1a | 180 ± 6.1a | 120 ± 2.4a |
FC | 526 ± 20b | 402 ± 43b | 63 ± 0.8a | 174 ± 6.4a | 121 ± 8.6a |
BAV | 468 ± 145b | 415 ± 27b | 66 ± 1.4b | 182 ± 4.4a | 120 ± 6.9a |
According to the results, reductions in the most bioavailable Cd and Zn concentrations (BCR1 + 2) (mg kg−1) at the end of the experiment (T4) were observed with BA, FC and BAV (not significant difference), and ranged from 4.0–9.6% and 5.5–6.3%, respectively. Two hypotheses can explain this phenomenon. Firstly, the direct effect of amendment addition of raising the pH of the treated soils throughout the experiment (Fig. 1). The precipitation of metal hydroxides and carbonates may cause metals to be less mobile in this study. Secondly, the binding of metals to the added amendments, which are known to be rich in metal binding sites, could occur. The results from this study clearly revealed that the pH increase, caused by the addition of amendments, had a major role in reducing the metal bioavailability in soils and thus its uptake by sugarcanes.
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