This article was downloaded by: [University of Kent] On: 22 April 2014, At: 04:22 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
International Journal of Phytoremediation Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/bijp20
The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil P. Alvarenga
a d
, A. de Varennes
b c
& A. C. Cunha-Queda
b d
a
DCTA—Instituto Politécnico de Beja, Escola Superior Agrária , Rua Pedro Soares , Beja , Portugal b
DQAA—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal c
CEER—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal d
UIQA—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal Accepted author version posted online: 03 Jan 2013.Published online: 24 Sep 2013.
To cite this article: P. Alvarenga , A. de Varennes & A. C. Cunha-Queda (2014) The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil, International Journal of Phytoremediation, 16:2, 138-154, DOI: 10.1080/15226514.2012.759533 To link to this article: http://dx.doi.org/10.1080/15226514.2012.759533
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
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International Journal of Phytoremediation, 16:138–154, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1522-6514 print / 1549-7879 online DOI: 10.1080/15226514.2012.759533
THE EFFECT OF COMPOST TREATMENTS AND A PLANT COVER WITH AGROSTIS TENUIS ON THE IMMOBILIZATION/MOBILIZATION OF TRACE ELEMENTS IN A MINE-CONTAMINATED SOIL P. Alvarenga,1,4 A. de Varennes,2,3 and A. C. Cunha-Queda2,4 Downloaded by [University of Kent] at 04:22 22 April 2014
1
DCTA—Instituto Polit´ecnico de Beja, Escola Superior Agr´aria, Rua Pedro Soares, Beja, Portugal 2 DQAA—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal 3 CEER—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal 4 UIQA—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal A semi-field experiment was conducted to evaluate the use of mixed municipal solid waste compost (MMSWC) and green waste-derived compost (GWC) as immobilizing agents in aided-phytostabilization of a highly acidic soil contaminated with trace elements, with and without a plant cover of Agrostis tenuis. The compost application ratio was 50 Mg ha–1, and GWC amended soil was additionally limed and supplemented with mineral fertilizers. Both treatments had an equivalent capacity to raise soil organic matter and pH, without a significant increase in soil salinity and in pseudo-total As, Cu, Pb, and Zn concentrations, allowing the establishment of a plant cover. Effective bioavailable Cu and Zn decreased as a consequence of both compost treatments, while effective bioavailable As increased by more than twice but remained as a small fraction of its pseudo-total content. Amended soil had higher soil enzymatic activities, especially in the presence of plants. Accumulation factors for As, Cu, Pb, and Zn by A. tenuis were low, and their concentrations in the plant were lower than the maximum tolerable levels for cattle. As a consequence, the use of A. tenuis can be recommended for assisted phytostabilization of this type of mine soil, in combination with one of the compost treatments evaluated. KEY WORDS: mine-contaminated soil, metal(loid)s, assisted phytostabilization, green waste-derived compost, municipal solid waste compost, Agrostis tenuis
INTRODUCTION The exploitation of mineral resources in Portugal is ancient, dating back to the Roman occupation. The intensive activity that took place at some mine districts produced large amounts of waste rock and tailings, containing high concentrations of metals and
Address correspondence to Paula Alvarenga, Instituto Polit´ecnico de Beja, Escola Superior Agr´aria, Rua Pedro Soares, 7801-902 Beja, Portugal. E-mail: [email protected]
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metalloids, which were simply deposited in the surrounding areas (Oliveira et al. 2002; Matos and Martins 2006). The erosion of the spoil heaps by wind and water resulted in permanent pollution of nearby terrestrial and aquatic ecosystems, resulting in large areas where soils are highly enriched in potentially toxic trace elements (TE), with a low pH, poor nutritional conditions and a scarce vegetation (Oliveira et al. 2002; Matos and Martins 2006; ´ Alvarez-Valero et al. 2008; Alvarenga et al. 2012). Among the different remediation options for lands impacted by mining activities, one of the most realistic, environmentally-sound and cost-effective is in situ remediation, using amendments to reduce the bioavailability of TE and to restore the ecological function of the sites (Vangronsveld, Assche, and Clijsters 1995; Bleeker et al. 2002; Brown et al. 2003; Mench et al. 2003; Adriano et al. 2004; de Varennes and Cunha-Queda 2005; Clemente, Almela, and Bernal 2006; Alvarenga et al. 2008, 2009a, 2009b; Lopareva-Pohu et al. 2011; Park et al. 2011). The application of amendments to mine contaminated soils may be advantageous, because they can modify TE behavior, conditioning their mobilization/immobilization, restricting their bioavailability to plants, their leaching potential, and their toxicity (Vangronsveld et al. 1995; Adriano et al. 2004; P´erez-de-Mora et al. 2006a, 2006b; Clemente et al. 2006; Wang and Mulligan 2006; Hartley and Lepp 2008; Alvarenga et al. 2008, 2009a, 2009b; Kidd et al. 2009; Park et al. 2011). This strategy of soil rehabilitation can be classified as assisted phytostabilization, aided phytostabilization or simply phytostabilization, and has been suggested by several authors as strategically important for abandoned mining areas (Mendez and Maier 2008; Alvarenga et al. 2008, 2009a, 2009b; Kidd et al. 2009; P´erez-de-Mora et al. 2011). Assisted phytostabilization of contaminated soils endeavors the in situ immobilization of trace elements through the simultaneous use of soil amendments and the development of a sustainable plant cover (Kidd et al. 2009; P´erez-de-Mora et al. 2011). However, contradictory effects have been reported for metal(loid) mobility as a response to different organic amendments and alkaline materials (Mench et al. 2003; Clemente et al. 2010). In fact, the application of organic and/or inorganic amendments to soils affected by mining activities to correct acidity, increase organic matter content and improve the overall nutritional status, which should promote the immobilization of TE can, in some cases, lead instead to their mobilization. That might be the case when the soil is simultaneously contaminated with metals and metalloids, in particular arsenic (Mench et al. 2003; Clemente et al. 2010; Beesley and Dickinson 2011; Hartley et al. 2010). Arsenic behavior in soil is similar to that of P, since they have chemical similarities, namely they both form insoluble compounds with Al, Fe, and Ca, and they both compete for the same adsorption sites (Adriano 2001). Composts may contain significant amounts of soluble P and release soluble organic acids as more complex organic molecules are degraded (Hartley et al. 2010). As a consequence of soil amendment with composted materials, As mobilization can be enhanced due to the displacement of P by As from organic and inorganic binding sites, and to the increase in dissolved organic matter (Wang and Mulligan 2006; Hartley et al. 2010). Beesley and Dickinson (2011) concluded that non-composted amendments had a lower impact on dissolved organic matter and thus on trace element co-mobility than composted greenwaste, suggesting that the addition of noncomposted materials to remediate urban soils was preferable to composted greenwaste, so as to reduce the risk of mobilizing potentially harmful elements. Previous studies showed that mixed municipal solid waste compost (MMSWC) could be successfully used in the remediation of a highly acidic metal-contaminated mine soil, correcting soil acidity, and increasing soil OM, total N, available P and K to levels that
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improved the establishment of perennial ryegrass. In contrast, a green waste-derived compost (GWC) was not as effective as MMSWC, due to its inability to correct soil acidity, and to its lower contents of N, P and K (Alvarenga et al. 2008, 2009a, 2009b). In fact, the authors reported that N fertilizers and liming materials should be added in addition to GWC, if a vegetation cover were to be established (Alvarenga et al. 2008). The application of both MMSWC and GWC led to a decrease in the level of mobile/effectively bioavailable fractions of Cu, Pb, and Zn, but no attention was paid to As mobilization/immobilization as a consequence of the application of these materials (Alvarenga et al. 2008, 2009a). The current study aims to fulfill those gaps, assessing the effect of MMSWC and GWC, combined with mineral fertilizers and liming materials, as immobilizing agents in the assisted phytostabilization of a soil affected by mining activities. The following parameters were evaluated: soil physicochemical characteristics, trace elements pseudototal and mobile fractions (As, Cu, Pb, and Zn), plant relative growth, trace elements concentration in the plant shoots and soil enzymatic activities. This study may help in the selection of the most appropriate soil treatment for field application in an assisted phytostabilization strategy for those types of mining areas.
MATERIALS AND METHODS Soil and Composts Characterization The mine soil ( 0.05). MMSWC: mixed municipal solid waste compost; GWC: green waste-derived compost; CaO: calcium oxide.
Both treatments led to a significant decrease in the effective bioavailable Cu, more pronounced in the case of the GWC+NPK+CaO application (Table 2). In the case of MMSWC application, despite the fact that the Cu total concentration was similar in the contaminated soil and in the actual organic amendment, the application of this material as Table 2 Effective bioavailable trace elements in the soil with the different treatments: mixed municipal solid waste compost (MMSWC); green waste-derived compost (GWC) + mineral fertilization (NPK) + liming with CaO; not seeded (NS) or seeded (S) (mean ± standard deviation, n = 4).
Control soil MMSWC GWC+NPK+CaO
NS S NS S NS S
As (μg kg–1)
Cu (mg kg–1)
Pb (mg kg–1)
Zn (mg kg–1)
33 ± 10a 35 ± 11a 79 ± 31a 67 ± 26a 145 ± 10b 71 ± 13a
32 ± 5b 32 ± 10b 1.2 ± 0.3a 1.4 ± 0.4a 0.05).
an amendment to the soil was still able to decrease Cu mobility/effective bioavailability in the soil. Only the GWC+NPK+CaO treatment was able to significantly decrease Zn mobility/effective bioavailability in the soil. Although the application of MMSWC seemed to decrease the effective bioavailable Zn (more or less to half the value of the control soil), that difference was not statistically significant, as a consequence of the variability between replicates. The GWC+NPK+CaO treatment led to the most efficient immobilization of Cu and Zn in the soil, perhaps due to the low TE element load of that organic material, in contrast to that of MMSWC. Effective bioavailable Pb was quite low, even in the control soil (≈1% of the total), and was not affected by the compost treatments. The influence of treatments on the As effective bioavailability was the opposite of the one for metals: effective bioavailable As increased more than twice as a consequence of both composts application. It is interesting to note that a higher value was obtained with GWC+NPK+CaO in the presence of A. tenuis, where the soil pH was the highest achieved. This may be the main factor contributing to the increase in the effective bioavailable As fraction. However, the enhanced As mobility could also have been caused by the increase in OM, pointed out by several authors as a main factor contributing to the mobilization of As, or by the increase in available P (Wang and Mulligan 2006; Hartley et al. 2010; Beesley and Dickinson 2011). Despite the increase in As effective bioavailability, this represented only a small fraction of the As pseudo-total content: the As effective bioavailability fraction increased from 0.02 to 0.07% of the As pseudo-total content, emphasizing the low risk of the organic amendment in this soil. Effects on Agrostis tenuis Growth A high phytotoxic effect was observed in the non-amended soil, with negligible plant growth (Fig. 2). Some seeds germinated but the young plants died in a few days. Biomass accumulation was significantly higher in the containers amended with GWC+NPK+CaO, suggesting that the additional application of mineral fertilizers and
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Figure 3 Soil enzymatic activities (mean ± standard deviation, n = 8): (a) dehydrogenase (μg TPF g−1 h−1), (b) β-glucosidase (μmol PNP g−1 h−1); (c) acid phosphatase (μmol PNP g−1 h−1). Columns marked with the same letter are not significantly different (Tukey test, P > 0.05). PNP: p-nitrophenol; TPF: 2,3,5-triphenylformazan; MMSWC: mixed municipal solid waste compost; GWC: green waste-derived compost; CaO: calcium oxide.
liming material was able to overcome the constraints of the GWC, with low amounts of available nutrients and little neutralizing capacity. Effects on Soil Enzymatic Activities The biochemical status of a soil has often been proposed as an early and sensitive indicator of soil ecological restoration in remediation processes, since many enzymes respond immediately to changes in soil fertility status (P´erez-de-Mora et al. 2005; P´erez-de-Mora
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et al. 2006c; Tejada et al. 2006; Hinojosa et al. 2008). Dehydrogenase is an oxidoreductase enzyme which has been used as a measurement of overall microbial activity, since it is an intracellular enzyme related to the oxidative phosphorylation process (Tabatabai 1994; Caravaca et al. 2005; Gil-Sotres et al. 2005; Izquierdo et al. 2005; Tejada et al. 2006). Soil hydrolases, such as β-glucosidase and phosphatase, related to cycles of C and P, are sensitive indicators of management-induced changes due to their strong relationship with soil organic matter content and quality (Caravaca et al. 2005; Izquierdo et al. 2005; Tejada et al. 2006). Several studies reported increased soil hydrolase activities following the addition of organic materials (Caravaca et al. 2005; P´erez-de Mora et al. 2005; P´erez-de-Mora et al. 2006c; Tejada et al. 2006), and following the revegetation of metal-contaminated soils (Izquierdo et al. 2005; P´erez-de-Mora et al. 2005; P´erez-de-Mora et al. 2006c; Zhang et al. 2006). In this study, amended soil had higher soil enzymatic activities, especially in the containers where plants were grown. However, the differences were only significant in some cases, mainly following the application of MMSWC and in the presence of A. tenuis (Fig. 3). For the dehydrogenase activity (which is a general indicator of microbial activity), both soil compost amendments combined with A. tenuis growth led to a significant increase in the activity of this enzyme in all containers, indicating that the compost treatments were able to improve soil quality. Despite the fact that the differences between containers with plants or with bare soils were not statistically significant (again as a consequence of the variability between replicates), there was an obvious overall tendency for an improvement in soil microbial activity as a consequence of the vegetation cover. Perhaps the time span of our experiment did not allow that differences to be so clear. Results Discussion Using Pearson’s Correlations The strongest correlations were obtained between soil pH and the metal(loid) effective bioavailable fractions (Table 3); effective bioavailable As was highly positively correlated with soil pH (r = 0.81, P < 0.001), whereas the effective bioavailable Cu and Zn were highly negatively correlated with the same soil property (r = –0.85 and r = –0.86, respectively, P < 0.001). This emphasizes the consequence of the acidity correction on the immobilization of metals, and on the mobilization of As. Nevertheless, it is difficult to ascertain from the results of this study which was the main factor(s) responsible for the mobilization of As. In fact, the two other main soil properties that may influence As mobilization, OM content and P (Wang and Mulligan 2006; Hartley et al. 2010; Beesley and Dickinson 2011), were also positively correlated to mobile As, although with lower correlation coefficient values. Although highly significant positive Pearson’s correlations were obtained between soil OM and N, available P and available K, this was expected and these relations were accentuated by the fact that the GWC amended containers also received a basal dressing with those plant nutrients. As for the soil enzymatic activities, the higher correlations were obtained between their values and soil OM and N contents, suggesting a positive effect of those soil properties on the soil microbial activity. In fact, the increase of the soil enzymatic activities seemed to be more influenced by the increase in soil OM than by the concomitant acidity correction: pH(H2 O) was only significantly correlated with dehydrogenase activity (r = 0.59, P < 0.05). Dehydrogenase activity was negatively correlated with mobile Cu and Zn, showing that the immobilization these metals had a positive effect on the overall microbial activity. However,
148
0,15 — — — — — — — — —
NKjeldahl
0,47 0,31 0,84∗∗∗ — — — — — — —
OM
0,80∗∗∗ 0,20 — — — — — — — —
0,79∗∗∗ 0,40 0,91∗∗∗ 0,82∗∗∗ — — — — — —
Available K 0,73∗∗∗ 0,19 0,85∗∗∗ 0,81∗∗∗ 0,89∗∗∗ — — — — —
Available P 0,81∗∗∗ 0,20 0,65∗∗ 0,39 0,73∗∗∗ 0,72∗∗∗ — — — —
Asmobile −0,85∗∗∗ −0,10 −0,87∗∗∗ −0,70∗∗ −0,87∗∗∗ −0,75∗∗∗ −0,59∗∗ — — —
Cumobile 0,04 −0,17 −0,06 −0,02 −0,02 −0,07 −0,11 −0,14 — —
Pbmobile −0,86∗∗∗ −0,01 −0,70∗∗ −0,44 −0,71∗∗∗ −0,59∗∗ −0,66∗∗ 0,85∗∗∗ −0,03 —
Znmobile
0,59∗ 0,39 0,69∗∗ 0,63∗∗ 0,73∗∗∗ 0,46 0,33 −0,80∗∗∗ −0,02 −0,70∗∗
Dehyd
0,28 0,31 0,60∗∗ 0,79∗∗∗ 0,58∗ 0,46 0,09 −0,53 0,20 −0,29
β-gluc
0,40 0,15 0,64∗∗ 0,58∗ 0,47 0,31 0,05 −0,59∗∗ −0,20 −0,46
Acid-Phos
∗ p < 0.05, ∗∗ p < 0.01 and ∗∗∗ p < 0.001; EC: electrical conductivity; OM: organic matter; As mobile , Cumobile , Pbmobile , and Znmobile : effective bioavailable trace elements in the soil; Dehyd: dehydrogenase; β-gluc: β-glucosidase; and Acid-Phos: acid phosphatase activities.
pH(H2 O) EC OM NKjeldahl Available K Available P Asmobile Cumobile Pbmobile Znmobile
EC
Table 3 Pearson correlation coefficients (r) between soil physicochemical properties, metal(loid) mobile/effective bioavailable concentrations and soil enzymatic activities.
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it is difficult to determine whether microbial activity responded more to decreased metal mobility or to general soil improvement, since those properties changed concomitantly. The same circumstance was pointed out by Kumpiene et al. (2009); these authors suggested that further research is needed to unambiguously determine whether the soil biochemical endpoints respond more to decreased metal mobility or to the general soil fertility. Alvarenga et al. (2012) selected soil OM as the most important factor affecting the activity of the microbial community.
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Results Discussion Using Multivariate Exploratory Techniques A PCA was performed on the results with the exception of pseudo-total metal content, EC, and Pb mobile/effective bioavailable concentration because those soil characteristics were not affected by the treatments and were not correlated with any other variable, as calculated by the Pearson’s correlation coefficients (Table 3). Samples were also clustered according to the results obtained from the hierarchical cluster analysis (linkage distance < 0.55). Loadings, which resulted from PCA, were only significant for the first two principal components, PC1 and PC2; PC1 explained 67% and PC2 explained 18% of the total variance. Soil pH, OM, NKjeldahl , available P, available K and dehydrogenase activity had large loading coefficients on PC1 (>0.700), all with positive values, while Cu and Zn mobile/effective bioavailable concentrations were significantly correlated with PC1, but with negative values (Fig. 4). The PCA showed the effectiveness of soil remediation, with an inverse correlation between those two groups of variables. The incorporation of the organic residues shifted the amended soil samples to the right (G, GP, M, and MP are located on the positive section of PC1), relative to the unamended soil (C and CP are located on the negative section of PC2). However, PC1 was not able to separate the amended soils samples, showing that both treatments were equivalent in their capacity to correct raise soil pH, OM, NKjeldahl , available P, available K and dehydrogenase activity, while decreasing Cu and Zn mobile/effective bioavailable concentrations. β-glucosidase activity had a large loading coefficient on PC2 (>0.700), with a positive value. This seems to be the only soil property with the ability to discriminate between the treatments: the soil samples amended with GWC and not seeded (G) were located in the negative section of PC2, while the soil samples amended with MMSWC and seeded with A. tenuis (MP) were located in the positive section of PC2. The Uptake of Trace Elements by A. tenuis Trace elements concentrations in the plant were not significantly different when both soil amendments were applied (Table 4). Metal concentration guidelines can be used to help evaluate metal toxicity issues that may arise during phytostabilization (e.g., domestic animal toxicity limits) as cattle and other wildlife may consume these plants. In this experiment, TE concentrations in the plant were lower than the maximum tolerable level for cattle (National Research Council 2005). Zinc was the only metal with concentrations within the range that can be considered as excessive or toxic to plants (Kabata-Pendias and Pendias 2001). However, the plants had a healthy aspect in all the amended containers. The accumulation factors (AF), i.e. the ratio of the metal(loid) concentration in the shoot to the pseudo-total metal(loid) concentration in the soil, were calculated. Ideally,
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Table 4 Trace elements concentrations in A. tenuis shoots with the different soil treatments: mixed municipal solid waste compost (MMSWC); green waste-derived compost (GWC) + mineral fertilization (NPK) + liming with CaO; and accumulation factors (AF) for trace elements (mean±standard deviation, n = 4)
Plant shoot concentration (mg kg–1)
MMSWC
Cu
Pb
Zn
1.4 ± 0.1a
12 ± 6a
8 ± 2a
287 ± 99a
1.3 ± 0.4a 0.007 5–20
10 ± 4a 0.04 20–100
8.5 ± 0.3a 0.03 30–300
189 ± 31a 0.3 100–400
30
40
100
500
AF: accumulation factor = metal concentration in shoot tissue/total metal concentration in the soil; Concentrations refer to a dry weight basis; aKabata-Pendias and Pendias (2001); bNational Research Council (2005). Means in a column marked with the same letter are not significantly different Tukey test, P > 0.05).
2.0
β-gluc MP1
1.5
MP2
MP3 GP1
0.5
0.0
-0.5
Cumobile, Znmobile
CP2 CP4
C2 CP1C3 C4CP3 C1
GP2
M1
GP4 M3 M4
M2
GP3
-1.0
pH, OM, NKejldahl, Pavail, Kavail, Dehyd
MP4 1.0
PC2 (18%)
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GWC+NPK+CaO AF (n = 8) Plant leaf tissue concentrations excessive or toxica Maximum tolerable level for cattleb
As
-1.5 G1 G3 G2G4 -2.0
-2.5 -2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
PC1 (67%)
Figure 4 Combined plot of scores and loadings on PC1 versus PC2. The most important parameters for the definition of the two components are shown on the edge of each axis, indicating the direction in which the value of the parameter increases. Samples were clustered according to the results obtained from the hierarchical cluster analysis (linkage distance
International Journal of Phytoremediation Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/bijp20
The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil P. Alvarenga
a d
, A. de Varennes
b c
& A. C. Cunha-Queda
b d
a
DCTA—Instituto Politécnico de Beja, Escola Superior Agrária , Rua Pedro Soares , Beja , Portugal b
DQAA—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal c
CEER—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal d
UIQA—Instituto Superior de Agronomia, TU Lisbon , Tapada da Ajuda , Lisboa , Portugal Accepted author version posted online: 03 Jan 2013.Published online: 24 Sep 2013.
To cite this article: P. Alvarenga , A. de Varennes & A. C. Cunha-Queda (2014) The Effect of Compost Treatments and A Plant Cover with Agrostis tenuis on the Immobilization/Mobilization of Trace Elements in a Mine-Contaminated Soil, International Journal of Phytoremediation, 16:2, 138-154, DOI: 10.1080/15226514.2012.759533 To link to this article: http://dx.doi.org/10.1080/15226514.2012.759533
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
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This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
International Journal of Phytoremediation, 16:138–154, 2014 C Taylor & Francis Group, LLC Copyright ISSN: 1522-6514 print / 1549-7879 online DOI: 10.1080/15226514.2012.759533
THE EFFECT OF COMPOST TREATMENTS AND A PLANT COVER WITH AGROSTIS TENUIS ON THE IMMOBILIZATION/MOBILIZATION OF TRACE ELEMENTS IN A MINE-CONTAMINATED SOIL P. Alvarenga,1,4 A. de Varennes,2,3 and A. C. Cunha-Queda2,4 Downloaded by [University of Kent] at 04:22 22 April 2014
1
DCTA—Instituto Polit´ecnico de Beja, Escola Superior Agr´aria, Rua Pedro Soares, Beja, Portugal 2 DQAA—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal 3 CEER—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal 4 UIQA—Instituto Superior de Agronomia, TU Lisbon, Tapada da Ajuda, Lisboa, Portugal A semi-field experiment was conducted to evaluate the use of mixed municipal solid waste compost (MMSWC) and green waste-derived compost (GWC) as immobilizing agents in aided-phytostabilization of a highly acidic soil contaminated with trace elements, with and without a plant cover of Agrostis tenuis. The compost application ratio was 50 Mg ha–1, and GWC amended soil was additionally limed and supplemented with mineral fertilizers. Both treatments had an equivalent capacity to raise soil organic matter and pH, without a significant increase in soil salinity and in pseudo-total As, Cu, Pb, and Zn concentrations, allowing the establishment of a plant cover. Effective bioavailable Cu and Zn decreased as a consequence of both compost treatments, while effective bioavailable As increased by more than twice but remained as a small fraction of its pseudo-total content. Amended soil had higher soil enzymatic activities, especially in the presence of plants. Accumulation factors for As, Cu, Pb, and Zn by A. tenuis were low, and their concentrations in the plant were lower than the maximum tolerable levels for cattle. As a consequence, the use of A. tenuis can be recommended for assisted phytostabilization of this type of mine soil, in combination with one of the compost treatments evaluated. KEY WORDS: mine-contaminated soil, metal(loid)s, assisted phytostabilization, green waste-derived compost, municipal solid waste compost, Agrostis tenuis
INTRODUCTION The exploitation of mineral resources in Portugal is ancient, dating back to the Roman occupation. The intensive activity that took place at some mine districts produced large amounts of waste rock and tailings, containing high concentrations of metals and
Address correspondence to Paula Alvarenga, Instituto Polit´ecnico de Beja, Escola Superior Agr´aria, Rua Pedro Soares, 7801-902 Beja, Portugal. E-mail: [email protected]
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metalloids, which were simply deposited in the surrounding areas (Oliveira et al. 2002; Matos and Martins 2006). The erosion of the spoil heaps by wind and water resulted in permanent pollution of nearby terrestrial and aquatic ecosystems, resulting in large areas where soils are highly enriched in potentially toxic trace elements (TE), with a low pH, poor nutritional conditions and a scarce vegetation (Oliveira et al. 2002; Matos and Martins 2006; ´ Alvarez-Valero et al. 2008; Alvarenga et al. 2012). Among the different remediation options for lands impacted by mining activities, one of the most realistic, environmentally-sound and cost-effective is in situ remediation, using amendments to reduce the bioavailability of TE and to restore the ecological function of the sites (Vangronsveld, Assche, and Clijsters 1995; Bleeker et al. 2002; Brown et al. 2003; Mench et al. 2003; Adriano et al. 2004; de Varennes and Cunha-Queda 2005; Clemente, Almela, and Bernal 2006; Alvarenga et al. 2008, 2009a, 2009b; Lopareva-Pohu et al. 2011; Park et al. 2011). The application of amendments to mine contaminated soils may be advantageous, because they can modify TE behavior, conditioning their mobilization/immobilization, restricting their bioavailability to plants, their leaching potential, and their toxicity (Vangronsveld et al. 1995; Adriano et al. 2004; P´erez-de-Mora et al. 2006a, 2006b; Clemente et al. 2006; Wang and Mulligan 2006; Hartley and Lepp 2008; Alvarenga et al. 2008, 2009a, 2009b; Kidd et al. 2009; Park et al. 2011). This strategy of soil rehabilitation can be classified as assisted phytostabilization, aided phytostabilization or simply phytostabilization, and has been suggested by several authors as strategically important for abandoned mining areas (Mendez and Maier 2008; Alvarenga et al. 2008, 2009a, 2009b; Kidd et al. 2009; P´erez-de-Mora et al. 2011). Assisted phytostabilization of contaminated soils endeavors the in situ immobilization of trace elements through the simultaneous use of soil amendments and the development of a sustainable plant cover (Kidd et al. 2009; P´erez-de-Mora et al. 2011). However, contradictory effects have been reported for metal(loid) mobility as a response to different organic amendments and alkaline materials (Mench et al. 2003; Clemente et al. 2010). In fact, the application of organic and/or inorganic amendments to soils affected by mining activities to correct acidity, increase organic matter content and improve the overall nutritional status, which should promote the immobilization of TE can, in some cases, lead instead to their mobilization. That might be the case when the soil is simultaneously contaminated with metals and metalloids, in particular arsenic (Mench et al. 2003; Clemente et al. 2010; Beesley and Dickinson 2011; Hartley et al. 2010). Arsenic behavior in soil is similar to that of P, since they have chemical similarities, namely they both form insoluble compounds with Al, Fe, and Ca, and they both compete for the same adsorption sites (Adriano 2001). Composts may contain significant amounts of soluble P and release soluble organic acids as more complex organic molecules are degraded (Hartley et al. 2010). As a consequence of soil amendment with composted materials, As mobilization can be enhanced due to the displacement of P by As from organic and inorganic binding sites, and to the increase in dissolved organic matter (Wang and Mulligan 2006; Hartley et al. 2010). Beesley and Dickinson (2011) concluded that non-composted amendments had a lower impact on dissolved organic matter and thus on trace element co-mobility than composted greenwaste, suggesting that the addition of noncomposted materials to remediate urban soils was preferable to composted greenwaste, so as to reduce the risk of mobilizing potentially harmful elements. Previous studies showed that mixed municipal solid waste compost (MMSWC) could be successfully used in the remediation of a highly acidic metal-contaminated mine soil, correcting soil acidity, and increasing soil OM, total N, available P and K to levels that
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improved the establishment of perennial ryegrass. In contrast, a green waste-derived compost (GWC) was not as effective as MMSWC, due to its inability to correct soil acidity, and to its lower contents of N, P and K (Alvarenga et al. 2008, 2009a, 2009b). In fact, the authors reported that N fertilizers and liming materials should be added in addition to GWC, if a vegetation cover were to be established (Alvarenga et al. 2008). The application of both MMSWC and GWC led to a decrease in the level of mobile/effectively bioavailable fractions of Cu, Pb, and Zn, but no attention was paid to As mobilization/immobilization as a consequence of the application of these materials (Alvarenga et al. 2008, 2009a). The current study aims to fulfill those gaps, assessing the effect of MMSWC and GWC, combined with mineral fertilizers and liming materials, as immobilizing agents in the assisted phytostabilization of a soil affected by mining activities. The following parameters were evaluated: soil physicochemical characteristics, trace elements pseudototal and mobile fractions (As, Cu, Pb, and Zn), plant relative growth, trace elements concentration in the plant shoots and soil enzymatic activities. This study may help in the selection of the most appropriate soil treatment for field application in an assisted phytostabilization strategy for those types of mining areas.
MATERIALS AND METHODS Soil and Composts Characterization The mine soil ( 0.05). MMSWC: mixed municipal solid waste compost; GWC: green waste-derived compost; CaO: calcium oxide.
Both treatments led to a significant decrease in the effective bioavailable Cu, more pronounced in the case of the GWC+NPK+CaO application (Table 2). In the case of MMSWC application, despite the fact that the Cu total concentration was similar in the contaminated soil and in the actual organic amendment, the application of this material as Table 2 Effective bioavailable trace elements in the soil with the different treatments: mixed municipal solid waste compost (MMSWC); green waste-derived compost (GWC) + mineral fertilization (NPK) + liming with CaO; not seeded (NS) or seeded (S) (mean ± standard deviation, n = 4).
Control soil MMSWC GWC+NPK+CaO
NS S NS S NS S
As (μg kg–1)
Cu (mg kg–1)
Pb (mg kg–1)
Zn (mg kg–1)
33 ± 10a 35 ± 11a 79 ± 31a 67 ± 26a 145 ± 10b 71 ± 13a
32 ± 5b 32 ± 10b 1.2 ± 0.3a 1.4 ± 0.4a 0.05).
an amendment to the soil was still able to decrease Cu mobility/effective bioavailability in the soil. Only the GWC+NPK+CaO treatment was able to significantly decrease Zn mobility/effective bioavailability in the soil. Although the application of MMSWC seemed to decrease the effective bioavailable Zn (more or less to half the value of the control soil), that difference was not statistically significant, as a consequence of the variability between replicates. The GWC+NPK+CaO treatment led to the most efficient immobilization of Cu and Zn in the soil, perhaps due to the low TE element load of that organic material, in contrast to that of MMSWC. Effective bioavailable Pb was quite low, even in the control soil (≈1% of the total), and was not affected by the compost treatments. The influence of treatments on the As effective bioavailability was the opposite of the one for metals: effective bioavailable As increased more than twice as a consequence of both composts application. It is interesting to note that a higher value was obtained with GWC+NPK+CaO in the presence of A. tenuis, where the soil pH was the highest achieved. This may be the main factor contributing to the increase in the effective bioavailable As fraction. However, the enhanced As mobility could also have been caused by the increase in OM, pointed out by several authors as a main factor contributing to the mobilization of As, or by the increase in available P (Wang and Mulligan 2006; Hartley et al. 2010; Beesley and Dickinson 2011). Despite the increase in As effective bioavailability, this represented only a small fraction of the As pseudo-total content: the As effective bioavailability fraction increased from 0.02 to 0.07% of the As pseudo-total content, emphasizing the low risk of the organic amendment in this soil. Effects on Agrostis tenuis Growth A high phytotoxic effect was observed in the non-amended soil, with negligible plant growth (Fig. 2). Some seeds germinated but the young plants died in a few days. Biomass accumulation was significantly higher in the containers amended with GWC+NPK+CaO, suggesting that the additional application of mineral fertilizers and
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Figure 3 Soil enzymatic activities (mean ± standard deviation, n = 8): (a) dehydrogenase (μg TPF g−1 h−1), (b) β-glucosidase (μmol PNP g−1 h−1); (c) acid phosphatase (μmol PNP g−1 h−1). Columns marked with the same letter are not significantly different (Tukey test, P > 0.05). PNP: p-nitrophenol; TPF: 2,3,5-triphenylformazan; MMSWC: mixed municipal solid waste compost; GWC: green waste-derived compost; CaO: calcium oxide.
liming material was able to overcome the constraints of the GWC, with low amounts of available nutrients and little neutralizing capacity. Effects on Soil Enzymatic Activities The biochemical status of a soil has often been proposed as an early and sensitive indicator of soil ecological restoration in remediation processes, since many enzymes respond immediately to changes in soil fertility status (P´erez-de-Mora et al. 2005; P´erez-de-Mora
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et al. 2006c; Tejada et al. 2006; Hinojosa et al. 2008). Dehydrogenase is an oxidoreductase enzyme which has been used as a measurement of overall microbial activity, since it is an intracellular enzyme related to the oxidative phosphorylation process (Tabatabai 1994; Caravaca et al. 2005; Gil-Sotres et al. 2005; Izquierdo et al. 2005; Tejada et al. 2006). Soil hydrolases, such as β-glucosidase and phosphatase, related to cycles of C and P, are sensitive indicators of management-induced changes due to their strong relationship with soil organic matter content and quality (Caravaca et al. 2005; Izquierdo et al. 2005; Tejada et al. 2006). Several studies reported increased soil hydrolase activities following the addition of organic materials (Caravaca et al. 2005; P´erez-de Mora et al. 2005; P´erez-de-Mora et al. 2006c; Tejada et al. 2006), and following the revegetation of metal-contaminated soils (Izquierdo et al. 2005; P´erez-de-Mora et al. 2005; P´erez-de-Mora et al. 2006c; Zhang et al. 2006). In this study, amended soil had higher soil enzymatic activities, especially in the containers where plants were grown. However, the differences were only significant in some cases, mainly following the application of MMSWC and in the presence of A. tenuis (Fig. 3). For the dehydrogenase activity (which is a general indicator of microbial activity), both soil compost amendments combined with A. tenuis growth led to a significant increase in the activity of this enzyme in all containers, indicating that the compost treatments were able to improve soil quality. Despite the fact that the differences between containers with plants or with bare soils were not statistically significant (again as a consequence of the variability between replicates), there was an obvious overall tendency for an improvement in soil microbial activity as a consequence of the vegetation cover. Perhaps the time span of our experiment did not allow that differences to be so clear. Results Discussion Using Pearson’s Correlations The strongest correlations were obtained between soil pH and the metal(loid) effective bioavailable fractions (Table 3); effective bioavailable As was highly positively correlated with soil pH (r = 0.81, P < 0.001), whereas the effective bioavailable Cu and Zn were highly negatively correlated with the same soil property (r = –0.85 and r = –0.86, respectively, P < 0.001). This emphasizes the consequence of the acidity correction on the immobilization of metals, and on the mobilization of As. Nevertheless, it is difficult to ascertain from the results of this study which was the main factor(s) responsible for the mobilization of As. In fact, the two other main soil properties that may influence As mobilization, OM content and P (Wang and Mulligan 2006; Hartley et al. 2010; Beesley and Dickinson 2011), were also positively correlated to mobile As, although with lower correlation coefficient values. Although highly significant positive Pearson’s correlations were obtained between soil OM and N, available P and available K, this was expected and these relations were accentuated by the fact that the GWC amended containers also received a basal dressing with those plant nutrients. As for the soil enzymatic activities, the higher correlations were obtained between their values and soil OM and N contents, suggesting a positive effect of those soil properties on the soil microbial activity. In fact, the increase of the soil enzymatic activities seemed to be more influenced by the increase in soil OM than by the concomitant acidity correction: pH(H2 O) was only significantly correlated with dehydrogenase activity (r = 0.59, P < 0.05). Dehydrogenase activity was negatively correlated with mobile Cu and Zn, showing that the immobilization these metals had a positive effect on the overall microbial activity. However,
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0,15 — — — — — — — — —
NKjeldahl
0,47 0,31 0,84∗∗∗ — — — — — — —
OM
0,80∗∗∗ 0,20 — — — — — — — —
0,79∗∗∗ 0,40 0,91∗∗∗ 0,82∗∗∗ — — — — — —
Available K 0,73∗∗∗ 0,19 0,85∗∗∗ 0,81∗∗∗ 0,89∗∗∗ — — — — —
Available P 0,81∗∗∗ 0,20 0,65∗∗ 0,39 0,73∗∗∗ 0,72∗∗∗ — — — —
Asmobile −0,85∗∗∗ −0,10 −0,87∗∗∗ −0,70∗∗ −0,87∗∗∗ −0,75∗∗∗ −0,59∗∗ — — —
Cumobile 0,04 −0,17 −0,06 −0,02 −0,02 −0,07 −0,11 −0,14 — —
Pbmobile −0,86∗∗∗ −0,01 −0,70∗∗ −0,44 −0,71∗∗∗ −0,59∗∗ −0,66∗∗ 0,85∗∗∗ −0,03 —
Znmobile
0,59∗ 0,39 0,69∗∗ 0,63∗∗ 0,73∗∗∗ 0,46 0,33 −0,80∗∗∗ −0,02 −0,70∗∗
Dehyd
0,28 0,31 0,60∗∗ 0,79∗∗∗ 0,58∗ 0,46 0,09 −0,53 0,20 −0,29
β-gluc
0,40 0,15 0,64∗∗ 0,58∗ 0,47 0,31 0,05 −0,59∗∗ −0,20 −0,46
Acid-Phos
∗ p < 0.05, ∗∗ p < 0.01 and ∗∗∗ p < 0.001; EC: electrical conductivity; OM: organic matter; As mobile , Cumobile , Pbmobile , and Znmobile : effective bioavailable trace elements in the soil; Dehyd: dehydrogenase; β-gluc: β-glucosidase; and Acid-Phos: acid phosphatase activities.
pH(H2 O) EC OM NKjeldahl Available K Available P Asmobile Cumobile Pbmobile Znmobile
EC
Table 3 Pearson correlation coefficients (r) between soil physicochemical properties, metal(loid) mobile/effective bioavailable concentrations and soil enzymatic activities.
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it is difficult to determine whether microbial activity responded more to decreased metal mobility or to general soil improvement, since those properties changed concomitantly. The same circumstance was pointed out by Kumpiene et al. (2009); these authors suggested that further research is needed to unambiguously determine whether the soil biochemical endpoints respond more to decreased metal mobility or to the general soil fertility. Alvarenga et al. (2012) selected soil OM as the most important factor affecting the activity of the microbial community.
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Results Discussion Using Multivariate Exploratory Techniques A PCA was performed on the results with the exception of pseudo-total metal content, EC, and Pb mobile/effective bioavailable concentration because those soil characteristics were not affected by the treatments and were not correlated with any other variable, as calculated by the Pearson’s correlation coefficients (Table 3). Samples were also clustered according to the results obtained from the hierarchical cluster analysis (linkage distance < 0.55). Loadings, which resulted from PCA, were only significant for the first two principal components, PC1 and PC2; PC1 explained 67% and PC2 explained 18% of the total variance. Soil pH, OM, NKjeldahl , available P, available K and dehydrogenase activity had large loading coefficients on PC1 (>0.700), all with positive values, while Cu and Zn mobile/effective bioavailable concentrations were significantly correlated with PC1, but with negative values (Fig. 4). The PCA showed the effectiveness of soil remediation, with an inverse correlation between those two groups of variables. The incorporation of the organic residues shifted the amended soil samples to the right (G, GP, M, and MP are located on the positive section of PC1), relative to the unamended soil (C and CP are located on the negative section of PC2). However, PC1 was not able to separate the amended soils samples, showing that both treatments were equivalent in their capacity to correct raise soil pH, OM, NKjeldahl , available P, available K and dehydrogenase activity, while decreasing Cu and Zn mobile/effective bioavailable concentrations. β-glucosidase activity had a large loading coefficient on PC2 (>0.700), with a positive value. This seems to be the only soil property with the ability to discriminate between the treatments: the soil samples amended with GWC and not seeded (G) were located in the negative section of PC2, while the soil samples amended with MMSWC and seeded with A. tenuis (MP) were located in the positive section of PC2. The Uptake of Trace Elements by A. tenuis Trace elements concentrations in the plant were not significantly different when both soil amendments were applied (Table 4). Metal concentration guidelines can be used to help evaluate metal toxicity issues that may arise during phytostabilization (e.g., domestic animal toxicity limits) as cattle and other wildlife may consume these plants. In this experiment, TE concentrations in the plant were lower than the maximum tolerable level for cattle (National Research Council 2005). Zinc was the only metal with concentrations within the range that can be considered as excessive or toxic to plants (Kabata-Pendias and Pendias 2001). However, the plants had a healthy aspect in all the amended containers. The accumulation factors (AF), i.e. the ratio of the metal(loid) concentration in the shoot to the pseudo-total metal(loid) concentration in the soil, were calculated. Ideally,
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Table 4 Trace elements concentrations in A. tenuis shoots with the different soil treatments: mixed municipal solid waste compost (MMSWC); green waste-derived compost (GWC) + mineral fertilization (NPK) + liming with CaO; and accumulation factors (AF) for trace elements (mean±standard deviation, n = 4)
Plant shoot concentration (mg kg–1)
MMSWC
Cu
Pb
Zn
1.4 ± 0.1a
12 ± 6a
8 ± 2a
287 ± 99a
1.3 ± 0.4a 0.007 5–20
10 ± 4a 0.04 20–100
8.5 ± 0.3a 0.03 30–300
189 ± 31a 0.3 100–400
30
40
100
500
AF: accumulation factor = metal concentration in shoot tissue/total metal concentration in the soil; Concentrations refer to a dry weight basis; aKabata-Pendias and Pendias (2001); bNational Research Council (2005). Means in a column marked with the same letter are not significantly different Tukey test, P > 0.05).
2.0
β-gluc MP1
1.5
MP2
MP3 GP1
0.5
0.0
-0.5
Cumobile, Znmobile
CP2 CP4
C2 CP1C3 C4CP3 C1
GP2
M1
GP4 M3 M4
M2
GP3
-1.0
pH, OM, NKejldahl, Pavail, Kavail, Dehyd
MP4 1.0
PC2 (18%)
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GWC+NPK+CaO AF (n = 8) Plant leaf tissue concentrations excessive or toxica Maximum tolerable level for cattleb
As
-1.5 G1 G3 G2G4 -2.0
-2.5 -2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
PC1 (67%)
Figure 4 Combined plot of scores and loadings on PC1 versus PC2. The most important parameters for the definition of the two components are shown on the edge of each axis, indicating the direction in which the value of the parameter increases. Samples were clustered according to the results obtained from the hierarchical cluster analysis (linkage distance
