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Treatment with biosolids affects soil availability and plant uptake of potentially toxic elements
Agriculture, Ecosystems and Environment 109 (2005) 360–364 www.elsevier.com/locate/agee
Short communication
Treatment with biosolids affects soil availability and plant uptake of potentially toxic elements R.S. Lavado *, M.B. Rodrı´guez, M.A. Taboada Facultad de Agronomı´a, Universidad de Buenos Aires, Av. San Martı´n 4453, C1417DSE Buenos Aires, Argentina Received 8 June 2004; received in revised form 7 March 2005; accepted 29 March 2005
Abstract Sewage sludge can be applied to soils without treatment or after biological treatments. We hypothesized that non-digested biosolids have more available potentially toxic elements (PTE) than digested ones. To test the hypothesis six field experiments with maize (Zea mays L.) were carried out on farms located in Buenos Aires province, Argentina. Treatments were non-digested or digested biosolids and controls. Cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were determined with ICP/ES in the used biosolids; in soils (EDTA extractable and total concentration) and in maize (grains and straw). Total Cr, Cu, Ni and Zn, and EDTA extractable Cu and Zn were significantly higher in soils treated with non-digested biosolids. The concentration of Cd, Cr, Cu and Zn in maize plants and Cd concentration in grains were significantly higher in the non-digested biosolid treatment. Soils receiving non-digested biosolids, exhibited higher PTE crop availability in general terms. This fact partially supports the proposed hypothesis. In the non-digested treatments, Cd, one of the most hazardous PTE, was significantly higher in maize plants and grains. # 2005 Elsevier B.V. All rights reserved. Keywords: Biosolids; Potentially toxic elements (PTE); Maize; Elements soil availability; Sewage sludge
1. Introduction Sewage sludge is a valuable source of nutrients for crops. However, mainly due to the occurrence of pathogenic organisms and potentially toxic elements (PTE), this product has different restraints. Therefore, the use of sewage sludge in agriculture is strictly * Corresponding author. Tel.: +54 11 4524 8022; fax: +54 11 4524 8076. E-mail address: [email protected] (R.S. Lavado).
regulated in most countries. There are several treatments but, according to sewage sludge quality they are applied to soils in the following way: (i) without any previous treatments or only subjected to physical procedures (non-digested biosolids) and (ii) after physical and biological treatments (digested biosolids). Chemical, thermal and other treatments are beyond our scope. Digestion processes decreases the pathogenic organism population and the light, volatile, organic compounds (biosolid stabilization) but PTE remain. Their accumulation in soils and crops is of
0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.03.010
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
great concern because of the potential risk on food quality, crop phytotoxicity and environmental damage in general (Mc Laughlin et al., 2000). Different properties of biosolids and their reaction to soils are affected by the chosen treatment. For example, different types of biosolids can affect nitrogen evolution in soils (i.e. Cogger et al., 2004), but their incidence on the availability of soil PTE contents is not widely known (i.e. Basta and Sloan, 1997; Gardiner et al., 1995). When biosolids are applied to soils their own physical–chemical properties determine whether the metals can be liberated or precipitated. The sewage sludge matrix is a major adsorptive medium for PTE in sludge-treated soils (Hooda and Alloway, 1993). Organic matter, clay, Mn and Fe amorphous oxides play a key role in the availability of PTE in soils. In anaerobically digested biosolids, the binding mechanisms of some TE rely mainly on aminoacid functional groups (Artola et al., quoted by Krogmann et al., 1998). Kaschl et al. (2002) found that strong Cd-binding groups include proteinaceous ligands. Among soil-related factors affecting PTE bioavailability, pH is the most important one (Basta and Sloan, 1997). At the same time, several authors emphasized that PTE chemical forms can be changed by organic matter mineralization when biosolids are applied to soils. It may result in large changes in the bindings of PTE. Other authors believe metals remain biologically inert because of inorganic bonds (Stacey et al., 2001). Biosolid composting tends to decrease PTE concentrations and availability (Bragato et al., 1998; Kaschl et al., 2002). We hypothesized that PTE plant availability is lower when digested biosolids are applied to soils, than when non-digested biosolids are applied. This could be caused by a higher level of interaction between EPT and the organic and inorganic biosolid matrix during digestion. To test this hypothesis, we quantified the availability of six PTE in soils and its uptake by maize (Zea mays L.) in soils, which had received digested or non-digested biosolids.
2. Materials and methods Field experiments were carried out on farms located in San Antonio de Areco County, north of Buenos Aires province, Argentina (388580 1000 S, 508310 5500 W). There
361
were two sets of three consecutive experiments each one. In one of them (from 1995/1996 to 1997/1998), treatments were the control and non-digested biosolids at doses of 16 tonnes (dry matter)/(ha year) and for the other set (from 1996/1997 to 1999/2000), treatments were the control and digested biosolids at doses of 16 tonnes (dry matter)/(ha year). All the experiments were designed with three replications. Biosolids were provided by Aguas Argentinas S.A., the great Buenos Aires water operator, from their Southeast Treatment Plant (non-digested biosolid) or North Treatment Plant (digested biosolid). Crop management was the same in all experiments. The crop sequence was maize–wheat– maize. Some maize cultivars and weather conditions differed in some experiments. All soils were Typic Argiudolls. The average composition are within the standard characteristics of those soils of the Pampas: pH, 6.1 0.26; organic carbon (g kg1), 19.3 4.80; available P (mg kg1), 26.8 8.24; total nitrogen (g kg1), 1.7 0.42; clay content (%), 28.5 4.93; silt content (%), 48.5 8.25; sand content (%), 23.0 4.09; cation exchange capacity (cmc kg1), 30.3 5.37. At the time of the third maize harvest, three samples of top soil (0–0.30 m depth) per plot were taken in each set of experiments. Maize grains and straw were sampled from 1 m long in three rows per plot sampled. Soils and maize samples from each plot were homogeneously mixed and each composite sample was analyzed. Soil samples were extracted with EDTA or digested with a 1–1–1 mix of hydrochloric, perchloric and nitric p.a. acids (McGrath and Cunliffe, 1985); plant samples were digested with perchloric and nitric acid. Cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were determined in extracts, by inductively coupled argon plasma emission spectrometry (ICPES/ES) using a Baird 20/70 equipment. A composite biosolid sample was taken in each experiment, digested with acids, like soils, and analyzed with ICPES/ES. Biosolid, soil and plant analyses were checked against standard reference materials. Grain yields were recorded. Mean values and their standard deviations were calculated for maize yields and nutrient concentrations. The effects of biosolids treatments were evaluated by ANOVA. Significant different means were separated using LSD test ( p < 0.05). The digested and non-digested biosolids treatments were
362
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
compared with separate controls because they were applied in different moments.
3. Results and discussion Most soil properties were not significantly affected after biosolid application. Among them, cation exchange capacity; exchangeable potassium, magnesium, calcium and sodium; organic carbon and total nitrogen contents (data not shown). Soil pH values at the start and the end of the experiments were not affected by biosolids treatment. Conversely, concentration of nitrates, available phosphorus and sulfur increased (Table 1). The crop yield increased due to biosolid application (Table 2) but yields varied among experiments, mainly because rainfall differences between years. The annual average rainfall was 1147 mm 238, with no drought period during the study period. Table 3 shows some components and PTE concentration in both types of biosolids. Some differences between them can be related to the treatments, such as organic carbon and nitrogen concentration. Similar total Cd, Cu, Pb and Zn concentrations were found but Cr and Ni were higher in non-digested biosolids. Those differences cannot be attributed to the treatment, but the origin of sewage sludge: the plant, which performs only physical separation, is located in a more industrialized area. Anyway, no samples exceeded local limits for biosolid agricultural usage (Argentine Federal Law 071/2001), which was based on local data and USEPA regulations. Total and EDTA extractable PTE concentrations in soils are shown in Table 4 Control soils showed no differences in both biosolid treatments. Cr, Cu, Ni and Zn total concentration were higher in soils treated with non-digested biosolids. Higher concentrations of total Cr and Ni could be expected from the biosolids composition. Conversely, the behavior of total concentrations of soil Cu and Zn was unexpected. Table 1 Average concentration of nitrates, available sulfur and available phosphorus in soils before and after biosolids (mg kg1) Nutrient
Nitrates
Available S
a
Available P
Before application 48.63 25.83 10.80 6.09 42.00 25.55 After applicationa 75.03 37.67 30.41 10.79 87.63 29.89 a
Data are means (standard deviation, n = 18).
Table 2 Maize straw and grain biomass production at harvest time (kg ha1) Treatment
Strawa
Grainsa
Control Non-digested biosolid Control Digested biosolid
7328.00 1521.90 7843.50 1720.17 6504.11 1568.86 7120.39 1665.72
5540.00 1063.70 7375.00 1395.00 5698.40 1260.45 6445.51 1142.23
a
Data are means (standard deviation, n = 18).
EDTA extractable Cu and Zn were significantly higher in non-digested treated soils. The concentration of Cd, Cr, Cu and Zn in maize straw was higher in non-digested biosolid treatments. In grains biomass only Cd concentrations were significantly higher, in the non-digested biosolids treatment (Table 3). Nickel and Pb did not show any difference either in plants or grains in any of the treatments. Although there were no differences in soil total or EDTA extractable Cd, plants absorb more Cd in the non-digested treatment. Furthermore, Cd was the only PTE, which was significantly higher in grains in that treatment. Because of soil analysis did not show influence of biosolid treatment on Cd availability, our results agreed with Candelaria and Chang (1997). On the other hand, also agreed with results of Logan et al. (1997) as maize accumulated more Cd in plant biomass and grain in the non-digested treatment. Although soil pH is a significant parameter in PTE solubility (Basta and Sloan, 1997) it is difficult to ascertain its effect on PTE availability in present Table 3 Average concentration of Cu, Zn, Cr, Pb, Cd and Ni in the studied biosolids (dry matter basis) Biosolid properties
Non-digested
Digested
pH Organic carbon (g kg1) N (g kg1) C/N ratio Cu (mg kg1) Zn (mg kg1) Cr (mg kg1) Pb (mg kg1) Cd (mg kg1) Ni (mg kg1)
6.2 0.7 334.2 4.3 21.2 0.3 15.7 1.8 350.3 85.61 1723.5 502.21 205.6 80.82a 292.7 178.56 4.0 2.72 135.5 55.07a
6.5 0.6 291.3 2.1 35.4 0.2 8.2 0.7 374.0 40.97 1737.3 300.08 115.4 19.78b 372.1 169.88 3.6 1.70 30.6 10.55b
Some components and potentially toxic elements in the studied biosolids (dry matter basis). a Data are means (standard deviation, n = 3). b Different letters mean significant differences between treatments at LSD test (P < 0.05).
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
363
Table 4 Total and EDTA extractable concentrations of PTE in soil, and PTE concentrations in grains and straw of maize plants (mg kg1) Soil total
Soil EDTA extractable
Non-digested
Cd Cr Zn Ni Pb Cu
Digested
Non-digested
Control
Applied
Control
Applied
Control
Applied
Control
Applied
0.44 0.04 24.29 3.02a 58.83 3.01a 9.28 1.52a 23.76 1.40 22.28 3.51a
0.50 0.08 31.56 1.42b 63.3 6.45b 13.33 1.78b 20.3 5.45 43.33 3.65 b
0.51. 0.26 11.3 1.75 48.25 19.64 7.03 3.03 17.63 5.45 19.25 7.29
0.50 0.17 13.58 1.25 50.6 21.53 8.48 3.29 22.7 3.62 24.29 10.35
0.07 0.02 0.48 0.30 1.99 0.28a 1.61 0.30 3.63 1.12 2.93 0.87a
0.05 0.02 0.42 0.41 8.94 2.44b 0.65 0.28 4.9 1.25 8.21 1.52b
0.06 0.02 0.38 0.05 2.24 0.52 1.29 0.62 3.64 0.25 2.5 0.23
0.07 0.02 0.46 0.04 5.97 1.64 1.64 0.30 4.76 1.01 4.04 0.61
Straw
Grain
Non-digested
Cd Cr Zn Ni Pb Cu
Digested
Digested
Non-digested
Digested
Control
Applied
Control
Applied
Control
Applied
Control
Applied
0.03 0.01a 0.61 0.07a 32.32 1.15a 0.63 0.35 1.58 0.18 4.75 1.30a
0.50 0.07b 10.66 10.67b 37.95 1.01b 2.4 0.52 1.09 0.60 9.71 1.85b
0.02 0.01 3.55 1.63 12.85 4.11 2.05 0.51 1.35 0.18 3.8 0.20
0.04 0.02 6.34 2.67 16.83 3.27 2.57 0.65 1.00 0.02 5.01 0.19
0.02 0.005a 0,38 0.04 22.04 2.18 0.83 0.23 2.39 0.29 3.62 0.47
0.04 0.01b 0.46 0.03 23.75 2.23 2.00 0.61 4.19 1.37 3.33 0.31
0.01 0.005 0.6 0.09 22.43 1.64 0.75 0.28 1.35 0.31 3.65 0.32
0.01 0.005 1.1 0.01 23.13 4.97 1.43 0.12 2.5 0.23 4.31 0.65
Note: Data are means (standard deviation, n = 18). Different letters mean significant differences between treatments at LSD test ( p < 0.05).
study. The pH differences found in biosolids were not consistent at soil level. The mineralization of sludge organic matter and the consequent release of PTE, on the other hand, cannot be easily related to the differences found in PTE availability and maize accumulation in this short-term study. 4. Conclusion Evidences show that soils which received nondigested biosolids exhibited higher PTE crop availability in general terms. The soil PTE availability and its accumulation in maize tissues partially support the proposed hypothesis. Cd, one of the most mobile PTE, with high environmental impact, was the most remarkable element. No differences in Cd concentration were found among soils but its concentration in maize straw and grains was significantly higher. Acknowledgment This research was performed with a grant from AGUAS ARGENTINAS S.A.—Facultad de Agronomı´a (UBA) agreement.
References Basta, N.T., Sloan, J.J., 1997. Bioavailablility of heavy metals in strongly acidic soils treated with exceptional quality biosolids. J. Environ. Qual. 28, 633–639. Bragato, G., Leita, L., Figliola, A., Nobili, M., 1998. Effects of sewage sludge pre-treatment on microbial biomass and bioavailability of heavy metals. Soil Tillage Res. 46, 129–134. Candelaria, L.M., Chang, A.C., 1997. Cadmium activities, solution speciation and solid phase distribution of Cd in cadmium nitrate and sewage sludge-treated soils systems. Soil Sci. 162, 722–729. Cogger, C.G., Bary, A.I., Sullivan, D.M., Myhre, E.A., 2004. Biosolids processing effects on first and second year available nitrogen. Soil Sci. Soc. Am. J. 68, 162–167. Gardiner, D.T., Miller, R.W., Badamchian, B., Azzari, A.S., Sisson, D.R., 1995. Effect of repeated sewage sludge applications on plant accumulation of heavy metals. Agric., Ecosys. Environ. 55, 1–6. Hooda, P.S., Alloway, B.J., 1993. Effects of time and temperature on the bioavailability of Cd and Pb from sludge-amended soils. J. Soil Sci. 44, 97–110. Kaschl, A., Romheld, V., Chen, Y., 2002. Cadmiun binding by fractions of dissolved organic matter and humic substances from municipal solid waste compost. J. Environ. Qual. 31, 1885– 1892. Krogmann, U., Qu, M., Boyles, L., Martel, J.C., 1998. Biosolids and sludge management. Water Environ. Res. 70, 557–580. Logan, T.J., Lindsay, B.J., Goins, L.E., Ryan, J.A., 1997. Field assessment of sludge metal bioavailability to crops-sludge rate response. J. Environ. Qual. 26, 534–539.
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McGrath, S.P., Cunliffe, C.H., 1985. A simplified method for the extraction of the metals Fe, Zn, Cu, Ni, Cd, Pb, Cr, Co and Mn from soils and sewage sludges. J. Sci. Food Agric. 36, 794– 798. Mc Laughlin, M.J., Hamon, R.E., Mc Laren, R.G., Speir, T.W., Rogers, S.L., 2000. Review: a bioavailability-based rationales
for controlling metal and metalloid contamination of agricultural land in Australia and New Zealand. Aust. J. Soil Res. 38, 1037– 1086. Stacey, S., Merrington, G., MacLaughlin, M.J., 2001. The effect of aging biosolids on the availability of cadmium and zinc in soil. Eur. J. Soil Sci. 52, 313–321.
Short communication
Treatment with biosolids affects soil availability and plant uptake of potentially toxic elements R.S. Lavado *, M.B. Rodrı´guez, M.A. Taboada Facultad de Agronomı´a, Universidad de Buenos Aires, Av. San Martı´n 4453, C1417DSE Buenos Aires, Argentina Received 8 June 2004; received in revised form 7 March 2005; accepted 29 March 2005
Abstract Sewage sludge can be applied to soils without treatment or after biological treatments. We hypothesized that non-digested biosolids have more available potentially toxic elements (PTE) than digested ones. To test the hypothesis six field experiments with maize (Zea mays L.) were carried out on farms located in Buenos Aires province, Argentina. Treatments were non-digested or digested biosolids and controls. Cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were determined with ICP/ES in the used biosolids; in soils (EDTA extractable and total concentration) and in maize (grains and straw). Total Cr, Cu, Ni and Zn, and EDTA extractable Cu and Zn were significantly higher in soils treated with non-digested biosolids. The concentration of Cd, Cr, Cu and Zn in maize plants and Cd concentration in grains were significantly higher in the non-digested biosolid treatment. Soils receiving non-digested biosolids, exhibited higher PTE crop availability in general terms. This fact partially supports the proposed hypothesis. In the non-digested treatments, Cd, one of the most hazardous PTE, was significantly higher in maize plants and grains. # 2005 Elsevier B.V. All rights reserved. Keywords: Biosolids; Potentially toxic elements (PTE); Maize; Elements soil availability; Sewage sludge
1. Introduction Sewage sludge is a valuable source of nutrients for crops. However, mainly due to the occurrence of pathogenic organisms and potentially toxic elements (PTE), this product has different restraints. Therefore, the use of sewage sludge in agriculture is strictly * Corresponding author. Tel.: +54 11 4524 8022; fax: +54 11 4524 8076. E-mail address: [email protected] (R.S. Lavado).
regulated in most countries. There are several treatments but, according to sewage sludge quality they are applied to soils in the following way: (i) without any previous treatments or only subjected to physical procedures (non-digested biosolids) and (ii) after physical and biological treatments (digested biosolids). Chemical, thermal and other treatments are beyond our scope. Digestion processes decreases the pathogenic organism population and the light, volatile, organic compounds (biosolid stabilization) but PTE remain. Their accumulation in soils and crops is of
0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.03.010
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
great concern because of the potential risk on food quality, crop phytotoxicity and environmental damage in general (Mc Laughlin et al., 2000). Different properties of biosolids and their reaction to soils are affected by the chosen treatment. For example, different types of biosolids can affect nitrogen evolution in soils (i.e. Cogger et al., 2004), but their incidence on the availability of soil PTE contents is not widely known (i.e. Basta and Sloan, 1997; Gardiner et al., 1995). When biosolids are applied to soils their own physical–chemical properties determine whether the metals can be liberated or precipitated. The sewage sludge matrix is a major adsorptive medium for PTE in sludge-treated soils (Hooda and Alloway, 1993). Organic matter, clay, Mn and Fe amorphous oxides play a key role in the availability of PTE in soils. In anaerobically digested biosolids, the binding mechanisms of some TE rely mainly on aminoacid functional groups (Artola et al., quoted by Krogmann et al., 1998). Kaschl et al. (2002) found that strong Cd-binding groups include proteinaceous ligands. Among soil-related factors affecting PTE bioavailability, pH is the most important one (Basta and Sloan, 1997). At the same time, several authors emphasized that PTE chemical forms can be changed by organic matter mineralization when biosolids are applied to soils. It may result in large changes in the bindings of PTE. Other authors believe metals remain biologically inert because of inorganic bonds (Stacey et al., 2001). Biosolid composting tends to decrease PTE concentrations and availability (Bragato et al., 1998; Kaschl et al., 2002). We hypothesized that PTE plant availability is lower when digested biosolids are applied to soils, than when non-digested biosolids are applied. This could be caused by a higher level of interaction between EPT and the organic and inorganic biosolid matrix during digestion. To test this hypothesis, we quantified the availability of six PTE in soils and its uptake by maize (Zea mays L.) in soils, which had received digested or non-digested biosolids.
2. Materials and methods Field experiments were carried out on farms located in San Antonio de Areco County, north of Buenos Aires province, Argentina (388580 1000 S, 508310 5500 W). There
361
were two sets of three consecutive experiments each one. In one of them (from 1995/1996 to 1997/1998), treatments were the control and non-digested biosolids at doses of 16 tonnes (dry matter)/(ha year) and for the other set (from 1996/1997 to 1999/2000), treatments were the control and digested biosolids at doses of 16 tonnes (dry matter)/(ha year). All the experiments were designed with three replications. Biosolids were provided by Aguas Argentinas S.A., the great Buenos Aires water operator, from their Southeast Treatment Plant (non-digested biosolid) or North Treatment Plant (digested biosolid). Crop management was the same in all experiments. The crop sequence was maize–wheat– maize. Some maize cultivars and weather conditions differed in some experiments. All soils were Typic Argiudolls. The average composition are within the standard characteristics of those soils of the Pampas: pH, 6.1 0.26; organic carbon (g kg1), 19.3 4.80; available P (mg kg1), 26.8 8.24; total nitrogen (g kg1), 1.7 0.42; clay content (%), 28.5 4.93; silt content (%), 48.5 8.25; sand content (%), 23.0 4.09; cation exchange capacity (cmc kg1), 30.3 5.37. At the time of the third maize harvest, three samples of top soil (0–0.30 m depth) per plot were taken in each set of experiments. Maize grains and straw were sampled from 1 m long in three rows per plot sampled. Soils and maize samples from each plot were homogeneously mixed and each composite sample was analyzed. Soil samples were extracted with EDTA or digested with a 1–1–1 mix of hydrochloric, perchloric and nitric p.a. acids (McGrath and Cunliffe, 1985); plant samples were digested with perchloric and nitric acid. Cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were determined in extracts, by inductively coupled argon plasma emission spectrometry (ICPES/ES) using a Baird 20/70 equipment. A composite biosolid sample was taken in each experiment, digested with acids, like soils, and analyzed with ICPES/ES. Biosolid, soil and plant analyses were checked against standard reference materials. Grain yields were recorded. Mean values and their standard deviations were calculated for maize yields and nutrient concentrations. The effects of biosolids treatments were evaluated by ANOVA. Significant different means were separated using LSD test ( p < 0.05). The digested and non-digested biosolids treatments were
362
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
compared with separate controls because they were applied in different moments.
3. Results and discussion Most soil properties were not significantly affected after biosolid application. Among them, cation exchange capacity; exchangeable potassium, magnesium, calcium and sodium; organic carbon and total nitrogen contents (data not shown). Soil pH values at the start and the end of the experiments were not affected by biosolids treatment. Conversely, concentration of nitrates, available phosphorus and sulfur increased (Table 1). The crop yield increased due to biosolid application (Table 2) but yields varied among experiments, mainly because rainfall differences between years. The annual average rainfall was 1147 mm 238, with no drought period during the study period. Table 3 shows some components and PTE concentration in both types of biosolids. Some differences between them can be related to the treatments, such as organic carbon and nitrogen concentration. Similar total Cd, Cu, Pb and Zn concentrations were found but Cr and Ni were higher in non-digested biosolids. Those differences cannot be attributed to the treatment, but the origin of sewage sludge: the plant, which performs only physical separation, is located in a more industrialized area. Anyway, no samples exceeded local limits for biosolid agricultural usage (Argentine Federal Law 071/2001), which was based on local data and USEPA regulations. Total and EDTA extractable PTE concentrations in soils are shown in Table 4 Control soils showed no differences in both biosolid treatments. Cr, Cu, Ni and Zn total concentration were higher in soils treated with non-digested biosolids. Higher concentrations of total Cr and Ni could be expected from the biosolids composition. Conversely, the behavior of total concentrations of soil Cu and Zn was unexpected. Table 1 Average concentration of nitrates, available sulfur and available phosphorus in soils before and after biosolids (mg kg1) Nutrient
Nitrates
Available S
a
Available P
Before application 48.63 25.83 10.80 6.09 42.00 25.55 After applicationa 75.03 37.67 30.41 10.79 87.63 29.89 a
Data are means (standard deviation, n = 18).
Table 2 Maize straw and grain biomass production at harvest time (kg ha1) Treatment
Strawa
Grainsa
Control Non-digested biosolid Control Digested biosolid
7328.00 1521.90 7843.50 1720.17 6504.11 1568.86 7120.39 1665.72
5540.00 1063.70 7375.00 1395.00 5698.40 1260.45 6445.51 1142.23
a
Data are means (standard deviation, n = 18).
EDTA extractable Cu and Zn were significantly higher in non-digested treated soils. The concentration of Cd, Cr, Cu and Zn in maize straw was higher in non-digested biosolid treatments. In grains biomass only Cd concentrations were significantly higher, in the non-digested biosolids treatment (Table 3). Nickel and Pb did not show any difference either in plants or grains in any of the treatments. Although there were no differences in soil total or EDTA extractable Cd, plants absorb more Cd in the non-digested treatment. Furthermore, Cd was the only PTE, which was significantly higher in grains in that treatment. Because of soil analysis did not show influence of biosolid treatment on Cd availability, our results agreed with Candelaria and Chang (1997). On the other hand, also agreed with results of Logan et al. (1997) as maize accumulated more Cd in plant biomass and grain in the non-digested treatment. Although soil pH is a significant parameter in PTE solubility (Basta and Sloan, 1997) it is difficult to ascertain its effect on PTE availability in present Table 3 Average concentration of Cu, Zn, Cr, Pb, Cd and Ni in the studied biosolids (dry matter basis) Biosolid properties
Non-digested
Digested
pH Organic carbon (g kg1) N (g kg1) C/N ratio Cu (mg kg1) Zn (mg kg1) Cr (mg kg1) Pb (mg kg1) Cd (mg kg1) Ni (mg kg1)
6.2 0.7 334.2 4.3 21.2 0.3 15.7 1.8 350.3 85.61 1723.5 502.21 205.6 80.82a 292.7 178.56 4.0 2.72 135.5 55.07a
6.5 0.6 291.3 2.1 35.4 0.2 8.2 0.7 374.0 40.97 1737.3 300.08 115.4 19.78b 372.1 169.88 3.6 1.70 30.6 10.55b
Some components and potentially toxic elements in the studied biosolids (dry matter basis). a Data are means (standard deviation, n = 3). b Different letters mean significant differences between treatments at LSD test (P < 0.05).
R.S. Lavado et al. / Agriculture, Ecosystems and Environment 109 (2005) 360–364
363
Table 4 Total and EDTA extractable concentrations of PTE in soil, and PTE concentrations in grains and straw of maize plants (mg kg1) Soil total
Soil EDTA extractable
Non-digested
Cd Cr Zn Ni Pb Cu
Digested
Non-digested
Control
Applied
Control
Applied
Control
Applied
Control
Applied
0.44 0.04 24.29 3.02a 58.83 3.01a 9.28 1.52a 23.76 1.40 22.28 3.51a
0.50 0.08 31.56 1.42b 63.3 6.45b 13.33 1.78b 20.3 5.45 43.33 3.65 b
0.51. 0.26 11.3 1.75 48.25 19.64 7.03 3.03 17.63 5.45 19.25 7.29
0.50 0.17 13.58 1.25 50.6 21.53 8.48 3.29 22.7 3.62 24.29 10.35
0.07 0.02 0.48 0.30 1.99 0.28a 1.61 0.30 3.63 1.12 2.93 0.87a
0.05 0.02 0.42 0.41 8.94 2.44b 0.65 0.28 4.9 1.25 8.21 1.52b
0.06 0.02 0.38 0.05 2.24 0.52 1.29 0.62 3.64 0.25 2.5 0.23
0.07 0.02 0.46 0.04 5.97 1.64 1.64 0.30 4.76 1.01 4.04 0.61
Straw
Grain
Non-digested
Cd Cr Zn Ni Pb Cu
Digested
Digested
Non-digested
Digested
Control
Applied
Control
Applied
Control
Applied
Control
Applied
0.03 0.01a 0.61 0.07a 32.32 1.15a 0.63 0.35 1.58 0.18 4.75 1.30a
0.50 0.07b 10.66 10.67b 37.95 1.01b 2.4 0.52 1.09 0.60 9.71 1.85b
0.02 0.01 3.55 1.63 12.85 4.11 2.05 0.51 1.35 0.18 3.8 0.20
0.04 0.02 6.34 2.67 16.83 3.27 2.57 0.65 1.00 0.02 5.01 0.19
0.02 0.005a 0,38 0.04 22.04 2.18 0.83 0.23 2.39 0.29 3.62 0.47
0.04 0.01b 0.46 0.03 23.75 2.23 2.00 0.61 4.19 1.37 3.33 0.31
0.01 0.005 0.6 0.09 22.43 1.64 0.75 0.28 1.35 0.31 3.65 0.32
0.01 0.005 1.1 0.01 23.13 4.97 1.43 0.12 2.5 0.23 4.31 0.65
Note: Data are means (standard deviation, n = 18). Different letters mean significant differences between treatments at LSD test ( p < 0.05).
study. The pH differences found in biosolids were not consistent at soil level. The mineralization of sludge organic matter and the consequent release of PTE, on the other hand, cannot be easily related to the differences found in PTE availability and maize accumulation in this short-term study. 4. Conclusion Evidences show that soils which received nondigested biosolids exhibited higher PTE crop availability in general terms. The soil PTE availability and its accumulation in maize tissues partially support the proposed hypothesis. Cd, one of the most mobile PTE, with high environmental impact, was the most remarkable element. No differences in Cd concentration were found among soils but its concentration in maize straw and grains was significantly higher. Acknowledgment This research was performed with a grant from AGUAS ARGENTINAS S.A.—Facultad de Agronomı´a (UBA) agreement.
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