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Environmental Monitoring and Assessment (2006) 112: 309–326
DOI: 10.1007/s10661-006-1072-y
c
Springer 2006
HEAVY METAL AVAILABILITY IN SOIL AMENDED
WITH COMPOSTED URBAN SOLID WASTES
C. P. JORD
˜
AO
1,∗
,C.C.NASCENTES
2
,P.R.CECON
3
,R.L.F.FONTES
1
and J. L. PEREIRA
2
1
Departamento de Solos, Universidade Federal de Vic¸osa, Vic¸osa, Minas Gerais, Brasil;
2
Departamento de Qu
´
ımica, Universidade Federal de Vic¸osa, Vic¸osa, Minas Gerais, Brasil;
3
Departamento de Inform
´
atica, Universidade Federal de Vic¸osa, Vic¸osa, Minas Gerais, Brasil
(
∗
author for correspondence, e-mail: jordao@ufv.br)
(Received 27 September 2004; accepted 20 January 2005)
Abstract. A study was performed to evaluate the pH and the availability of Zn, Cu, Mn, Pb, and Ni
in soil amended with increasing doses of composted solid wastes, collected in Rio de Janeiro, Rio de
Janeiro State and in Coimbra, Minas Gerais State, Brazil. The influence of the time elapsed between
compost application to the soil and the sampling of the plant growth substrate (soil + compost) for
pH and metal availability analyses was also examined. The availability of heavy metals in the soil,
in the compost and in the substrate was evaluated using DTPA solution for metal extraction. The
increase of the compost doses added to the soil resulted in the increase of the pH in the substrate. The
addition of the compost from the bigger city, Rio de Janeiro, resulted in higher increase in soil pH and
available Zn, Cu, Pb, and Ni levels as compared to the addition of the compost from the smaller city,
Coimbra. Increasing the time elapsed between the compost application to the soil and the sampling of
the mixture resulted in higher available Zn, Cu, Mn, and Pb levels. The addition of the compost from
Rio de Janeiro resulted in substrate metal concentrations in the order Zn > Pb > Ni > Cu > Mn and
for the Coimbra compost the metal concentrations in the substrate was Zn > Pb > Cu > Ni > Mn. The
higher values of pH and available metals obtained for the bigger city were attributed to the greatest
metal contamination of its compost.
Keywords: availability, compost, heavy metal, soil, solid urban waste
1. Introduction
The use of compost in cultivated lands is a world-wide common practice. These
materials are obtained from the decomposition of organic residues and enhance
plant productivity (Ranwa and Singh, 1999; Aguilar et al., 1997). The raw materials
used in the composting processes are animal manure (Adriano, 1986), municipal
wastes such as sewage sludge (Moreno et al., 1996), tree barks (Pinamonte et al.,
1997), and peat (Klock-Moore and Fitzpatrick, 2000), among others. Jord˜ao et al.
(2002) reported that vermicompost enriched with Cu, Cr, Ni, and Zn was used for
plant nutrition in eroded soil. Besides the application in agricultural soils, studies
of Alves and Passoni (1997) have shown the possibility of utilization of municipal
solid waste compost in other activities such as ornamental and urban barbarization
species.
310 C. P. JORD
˜
AO ET AL.
The addition of composts in agricultural soils may: improve the soil aggregation
and structure, which allied to the fertility and other factors result in higher produc-
tivity; increase the soil porosity increasing its capacity of water storage; improve
the soil consistence increasing the exploration of cultivated lands; improve the mi-
cronutrient complexes formation increasing their availability to plants; increase the
soil cation exchange capacity (CEC); increase the soil buffer capacity due to the
addition of colloids and humic substances (Kiehl, 1985).
Despite of the beneficial effects of compost improving the soil fertility and other
soil characteristics, high metal concentrations in this material may be a problem and
limit its utilization. Furthermore, the application of high amounts of vermicompost
from composted urban wastes might cause significant reduction in the soil fungi
activity, which must be taken into account when using these organic amendments
in agricultural systems (S´ainz et al., 1998).
The concentrations of heavy metals in composted urban wastes depends on the
quality of the parent material, as well as on the composting technique utilized, which
is chosen based on the physical characteristics of the raw material (Smith, 1992).
The variability of materials found in wastes from big cities is much larger than that
in wastes from small cities. This might explain the largest compost contamination
produced in very populous cities.
The metal plant uptake from soils at high concentrations may result in a great
health risk considering food-chain implications. The absorption by plant roots is
one of the main routes of entrance of heavy metals in the food chain (Jones and
Jarvis, 1981). The food plants, whose exploration system is based on intensive
and continuous cultivation, have great capacity of extracting elements from soils
(Furlani et al., 1978). The cultivation of such plants in contaminated soil represents
a potential risk since the vegetal tissues can accumulate heavy metals. The use of
compost to improve agricultural yield without caring with possible negative effects
might be a problem since the waste composts are most applied to improve soils
used to grow vegetables. Considering the edible part of the plant in most vegetable
species, the risk of transference of heavy metals from soil to humans should be a
matter of concern.
There are established maximum limits of heavy metals in food by the current
Brazilian legislation (Associa¸c˜ao Brasileira das Ind´ustrias da Alimenta¸c˜ao, 1991;
Minist´erio da Sa´ude, 1998). However, there are no available regulations for land
application of compost. Solid urban waste production in Brazil exceeds 230,000
tons per day (O Saneamento, 2000), but information is lacking about the amounts
of compost manufactured in this country. It is reported that in Minas Gerais State
compost production reaches up to 3,200 tons per month (Lelis, 2001).
The total amount of the metals in the soil system has limited significance in
agronomic aspects. More important are the soil metal availability for plant uptake
and its potential for introducing the metals in the food chain. Heavy metals are found
in several geochemical fractions of soils which influence the solubility, mobility
and availability of the metals to plants. The mobility and retention of metals in
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 311
soils depend on complex interactions with the organic and inorganic solid phases
(Brady, 1989).
The availability of heavy metals from the compost added to the soil can be
related to the compost maturity. The total metal content increases during the com-
posting process due to the weight loss caused by the mineralization of the compost.
However, the metal availability is reduced due to the formation of complexes with
humic substances (Garcia et al., 1991).
Another factor affecting metal availability from the compost to plants is the time
elapsed between the application of the compost to the soil and the growth of the
plants. Once the compost is introduced in the soil, the metals present in the compost
are mobilized through the soil fractions.
The determination of bioavailable metals in soils is performed after extraction
with chemical extractants. A suitable chemical extractant should remove the avail-
able forms of an element and show reasonable precision and speed. The DTPA
(diethylenetriamine-pentaacetic acid) is an effective reagent used for predicting the
soil capacity to supply essential nutrients to plants (Mortvedt et al., 1991). It has
been used (DTPA-TEA) as extractant to evaluate metal mobility in flooded soils
(Borges Jr. et al., 2001).
This paper presents the pH measurements and the concentrations of available Zn,
Cu, Mn, Pd, and Ni concentrations in a Brazilian Oxisol amended with composted
urban solid wastes. The composts, collected from a big city and a small city, were
applied to the soil at increasing doses and at different times between the compost
addition to the soil and soil sampling for analysis.
2. Materials and Methods
A pot experiment was carried out using a clayish oxisol from the city of Sete
Lagoas, Minas Gerais State, Brazil. The soil was amended with urban solid waste
composts. The soil was sampled at depth of 20 cm after removing the vegetation,
air-dried and sieved to separate the particles smaller than 4 mm for the physical and
chemical analyses. The substrate (soil + compost) was sieved to separate particles
size smaller than 2 mm for pH determination and metal extraction. Compost samples
were obtained from a Municipal Waste Treatment Plant in Rio de Janeiro (5,850,544
inhabitants), at the State of Rio de Janeiro, and in Coimbra (6,443 inhabitants), at
the State of Minas Gerais, Brazil. The compost samples were air dried and passed
througha2mmsieve.
The pH of the soil, compost samples and substrates (soil + compost) were
measured in deionised water (solid/solution ratio = 1:2.5). Available K and P
were extracted from the soil and compost samples with the Mehlich-1 extractor
(Empresa Brasileira de Pesquisa Agropecu´aria, 1979), while organic carbon was
evaluated by the Walkley-Black method (Gaudette et al., 1974). Exchangeable Ca,
Mg and Al were extracted with 1 mol L
−1
KCl and potential acidity was extracted
312 C. P. JORD
˜
AO ET AL.
with 0.5 mol L
−1
pH 7.0 Ca(OAc)
2
(Empresa Brasileira de Pesquisa Agropecu´aria,
1979). The cation exchange capacity was determined by the summation of ex-
changeable K, Ca, Mg and Al. Particle size distribution in the soil was evaluated
by the pipette method, using 0.1 mol L
−1
NaOH solution as a dispersion agent.
The total organic matter, total nitrogen and moistness contents of the compost sam-
ples were determined by the methods recommended by Kiehl (1985). Total metals
were extracted from the soil and compost samples by digestion with 10 mL of a
HNO
3
/HClO
4
(5:1) mixture, and subsequently with 10 mL of a HF/HClO
4
(5:1).
Available metals were extracted from the soil, compost samples and soil sub-
strates (soil +compost) with 0.005 mol L
−1
DTPA in 0.01 mol L
−1
CaCl
2
,buffered
at pH 7.3 with 0.1 mol L
−1
TEA (triethanolamine) at a soil/solution ratio of 1:5.
The extractions were performed at room temperature with continuous agitation for
2h(Lindsay and Norvell, 1978).
The procedure for adding lime to the soil has been described elsewhere (Tom´eJr.,
1997). The moistness content of the limed soil was kept close to the field capacity.
The soil sample was incubated during 15 days before starting the application of
the compost to the soil. Individual soil subsamples were amended with compost at
three different doses as follows: 0 ton/ha (control), 35 t ha
−1
(as suggested by the
Comiss˜ao de Fertilidade do Solo do Estado de Minas Gerais (1989), and 70 t ha
−1
(double dose). The procedure was conducted four times in order to obtain different
times (0, 10, 20 and 30 days), elapsed between compost application to the soil and
the collection of the substrate for analysis.
After mixing the compost with the soil, each pot was filled out with 4 dm
3
of the
mixture (soil + compost). The compost/mixture rates to set the treatments were 0
tha
−1
,35tha
−1
, and 70 t ha
−1
(set by adding the compost at the rates of 0 g/pot,
70 g/pot and 140 g/pot, respectively).
During the incubation period, it was added distilled water to the pots to keep the
moistness close to the field capacity.
The concentrations of Zn, Cu, Mn, Pb, Ni, Al, Ca, and Mg were determined by
atomic absorption spectrophotometry. The concentrations of the aforementioned
metals were measured with a Varian atomic absorption spectrophotometer (model
SpectrAA-200), by direct aspiration of the solutions into an air-acetylene or ni-
trous oxide-acetylene flame. Background correction was used for Pb, Zn, and Ni
determinations. For pH measurements a TECNOW pHmeter (model IRIS 7) was
used.
All glassware and materials were cleaned for metal analysis. Certified analytical
grade reagents were used throughout. Blanks were run through all experiments. A
midpoint check standard and calibration blank at the beginning,end and periodically
was analyzed with each group of samples to certify that the instrument calibration
has not drifted. To establish extraction efficiencies, our concurrent analyses of
samples of Standard Sediments (National Institute of Standard & Technology no.
2704) gave the following values, which are within the range of certified values:
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 313
Zn = 447 (438 ± 12), Ni = 44.2 (44.1 ± 3.0), and Cu = 94.5 (98.6 ± 5.0) (in
mg kg
−1
); Al = 6.10 (6.11 ±0.16) and Mg = 1.22 (1.20 ± 0.02) (in g kg
−1
).
In the greenhouse experiment, the treatments were disposed in a factorial outline
2 × 3 × 4, formed by two urban waste compost samples, three doses of compost
(0, 35 and 70 t ha
−1
), and four times of application (0, 10, 20, and 30 days), in a
random block design, with four replications.
Analysis of variance was used and the averages of the qualitative factor (compost
type) were compared by the Tukey’s test at the 5% level of probability.
The soil and compost characteristics are presented in Tables I and II, respectively.
TABLE I
Soil characteristics
pH in H
2
O (1:2.5) 5.10
Organic carbon (%, w/w)
a
4.72
Available P (mg dm
−3
)
b
3.30
Available K (mg dm
−3
)
b
47.00
Exchangeable Al (cmol
c
dm
−3
)
c
1.10
Exchangeable Ca (cmol
c
dm
−3
)
c
1.50
Exchangeable Mg (cmol
c
dm
−3
)
c
0.20
H + Al (cmol
c
dm
−3
)
d
7.80
Sum of the bases (cmol
c
dm
−3
) 1.82
CEC (cmol
c
dm
−3
) 2.92
Base saturation (%) 18.90
Al saturation (%) 37.80
Fe (mg g
−1
) 32.6
e
(0.17)
f
Zn (µgg
−1
) 31.9
e
(0.34)
f
Cu (µgg
−1
) 29.9
e
(0.93)
f
Mn (µgg
−1
) 131
e
(15.7)
f
Pb (µgg
−1
) 21.4
e
(0.47)
f
Ni (µgg
−1
) 9.4
e
(0.07)
f
Cd (µgg
−1
) <0.1
e,g
<(0.1)
f,g
Na (µgg
−1
) 782
e
Sand (%, w/w) 15
Silt (%, w/w) 9
Clay (%, w/w) 76
Texture clayish
a
Walkley-Black method (Gaudette et al., 1974).
b
Mehlich-1 extractant (Embrapa, 1979).
c
1 mol L
−1
KCl exchangeable Ca and Mg.
d
0.5 mol L
−1
pH 7.0 Ca(OAc)
2
extractable acidity.
e
HNO
3
/HClO
4
and HF/HClO
4
mixtures.
f
DTPA/TEA/CaCl
2
solution (Lindsay and Norvell, 1978).
g
Value preceded by < symbol indicate detection limit.
314 C. P. JORD
˜
AO ET AL.
TABLE II
Compost characteristics
Compost of Compost of
Rio de Janeiro Coimbra
pH in H
2
0 (1:2.5) 7.50 6.90
Total organic matter (%, w/w)
a
30.69 33.23
Total carbon (%, w/w) 17.05 18.46
Organic carbon (%, w/w)
b
13.49 13.62
Ntotal (%, w/w)
c
1.46 1.72
Available P (mg dm
−3
)
d
729 570
Available K (mg dm
−3
)
d
1807 1290
Exchangeable Ca (cmol
c
dm
−3
)
e
7.00 9.30
Exchangeable Mg (cmol
c
dm
−3
)
e
1.40 1.50
CEC (cmol
c
dm
−3
) 13.04 14.09
Fe (mg g
−1
) 30.2
f
(0.89)
g
25.4
f
(0.51)
g
Zn (µgg
−1
) 411
f
(101)
g
212
f
(71.4)
g
Cu (µgg
−1
) 90.6
f
(21.9)
g
46.8
f
(7.5)
g
Mn (µgg
−1
) 365
f
(34.9)
g
295
f
(14.6)
g
Pb (µgg
−1
) 101
f
(18.4)
g
36.8
f
(3.8)
g
Ni (µgg
−1
) 23.2
f
(1.47)
g
20.9
f
(0.89)
g
Pb (µgg
−1
) 101
f
(18.4)
g
36.8
f
(3.8)
g
Cd (µgg
−1
) 1.9
f
(0.52)
g
0.65
f
(0.08)
g
Na (mg g
−1
) 11.1
f
2.3
f
Rela¸c˜ao C/N 11.68 10.73
Moisture (%, w/w) 14.10 30.39
a
Ignition at high temperature.
b
Walkley-Black method (Gaudette et al., 1974).
c
Kjeldahl method (Kiehl, 1985).
d
Mehlich-1 extractant (Embrapa, 1979).
e
1 mol L
−1
KCl exchangeable Ca and Mg.
f
HNO
3
/HClO
4
and HF/HClO
4
mixtures.
g
DTPA/TEA/CaCl
2
solution (Lindsay and Norvell, 1978).
3. Results and Discussion
Table III shows the summary of the analysis of variance and the respective coeffi-
cients of variation of pH and metal extractable by DPTA for the soil. The results
have shown that the pH values were significantly affected by all the sources of
variation examined, except for the interaction time × compost.
Significant differences (p < 0.05) were found for the pH values between
the compost samples (Table IV). The differences were observed when applying
70 t ha
−1
in the times of 0, 10 and 30 days; 35 t ha
−1
in each time of application;
and 0 t ha
−1
in the time of 20 days.
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 315
TABLE III
Summary of the variance analysis of pH and metal extractable by DPTA for the soil and its respective coefficients of variation
Mean square
Source of variation
Degree of
freedom pH Zn Cu Mn Pb Ni
Block 3 0.001485 0.043222 0.003903 0.100933 0.0081923 0.000046
Compost 1 0.175107
∗∗
0.797853
∗∗
0.612463
∗∗
58.711870
∗∗
0.633337
∗∗
0.003783
∗∗
Dose 2 1.884444
∗∗
65.606480
∗∗
10.274740
∗∗
12.383290
∗∗
15.932070
∗∗
0.016607
∗∗
Dose × compost 2 0.022770
∗∗
0.300001
∗∗
0.148906
∗∗
21.423470
∗∗
0.197825
∗∗
0.000625*
Time 3 1.462219
∗∗
9.234294
∗∗
4.237401
∗∗
79.123510
∗∗
7.316320
∗∗
0.001838
∗∗
Time × compost 3 0.003279
ns
0.067973
∗
0.014473
∗
1.506119
∗∗
0.025533
∗
0.000802
∗∗
Dose × time 6 0.083051
∗∗
3.206467
∗∗
0.276652
∗∗
4.775285
∗∗
1.324576
∗∗
0.000637
∗∗
Dose × time × compost 6 0.010053
∗∗
0.049201
∗
0.011216
∗
0.410893
∗
0.078131
∗∗
0.000479
∗∗
Error 69 0.001938 0.018398 0.003715 0.148664 0.006958 0.000133
Coefficient of variation (%) 0.77 7.76 3.86 2.72 6.27 14.89
∗
F significant at the 5% level of probability.
∗∗
F significant at the 1% level of probability.
ns
F Not significant at 5% level of probability.
316 C. P. JORD
˜
AO ET AL.
TABLE IV
Mean values of pH obtained from the application of different times
and doses of compost samples from Rio de Janeiro and Coimbra
Time of application of the compost (in days)
Compost 0 10 20 30
0tha
−1
Rio de Janeiro 5.86a 5.51a 5.37a 5.19a
Coimbra 5.85a 5.50a 5.31b 5.17a
35tha
−1
Rio de Janeiro 5.95a 5.92a 5.93a 5.50a
Coimbra 5.87b 5.73b 5.77b 5.43b
70tha
−1
Rio de Janeiro 6.33a 6.11a 5.99a 5.60a
Coimbra 6.11b 6.00b 5.97a 5.51b
Mean valuesfollowed bythesameletterforeachtimeofapplication
and dose of the compost are not different at the 5% level according
to the Tukey’s test.
The compost from RiodeJaneiro, in general, was more efficient than the compost
from Coimbra to increase the soil pH (Table IV). Urban waste composts have high
concentrations of exchangeable bases which contribute to the increase of the soil
pH (Kiehl, 1985), probably due to the exchange of H
+
ions present in the soil and
the bases released by the compost. It is observed that the Na and K concentrations
in the compost from Rio de Janeiro are greater than those in the compost from
Coimbra, while the Ca and Mg concentrations in both composts are very close
(Table II). Eira and Carvalho (1970) observed the increase of the pH from 5.2 to
5.7 in an oxisol due to the addition of composted municipal solid waste.
The organic components of the compost also influence the increase of soil pH.
Negatively charged organic radicals formed during the organic matter decompo-
sition could retain H
+
ions from the soil, enhancing the pH value. However, in
calcareous soils, 19 months after initial application, organic amendments decreased
soil pH (Zinati et at., 2001). The application of compost to soil can limit the growth
of plants such as lettuce and carrot due to the higher pH and conductivity resulting
from the compost amendment. Furthermore, the increase of metal concentrations in
soils amended with solid waste compost might produce phytotoxic effects in plants
(Costa et al., 1994a; Costa et al., 1997).
For both composts, the increase of the time between compost addition and the
sampling of the substrate for analysis resulted in reduction of the pH value for all
application doses examined (Figure 1, Table IV). The effect occurred even in the
absence of composts, suggesting that the time between the lime addition and the
sampling of the substrate for analysis also influenced the soil pH.
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 317
Figure 1. The relationship between soil solution pH and the time of compost addition at the application
doses in (a) compost of Rio de Janeiro and (b) compost of Coimbra.
The highest pH values were found in soils treated with 70 t ha
−1
of compost at
the zero day time of application, being 6.33 and 6.11 for the compost samples of
Rio de Janeiro and Coimbra, respectively (Table IV).
The pH range wasnot very wide, varying from 5.17 to 6.33 (Table IV). According
to Costa et al. (1997), the application of 90 t ha
−1
of a Rio de Janeiro urban waste
compost into a sandy loam soil resulted in an increase of more than three units
of pH (from 4.75 to 8.85). The application of 60 t ha
−1
of composted municipal
solid waste to soil elevated soil pH to values close to 8.0 (Hernando et al.,1989;
Hern´andez et al., 1992). The increase in soil pH due to compost addition depends
on the soil and the compost characteristics as well as on the dose and time applied.
The best range of soil pH for lettuce yield is between 5.7 and 7 (Malavolta,
1981). In the treatments of soils amended with compost (except those in which the
time between application and sampling was 30 days), the pH values in the substrate
were inside that range (Table IV).
The results of Table III also show that the available Zn concentrations in the
soil were significantly affected by all the sources of variation examined. In the
treatments without compost application (control), the available Zn concentrations
did not differ statistically (Table V).
The substrate with the compost from Rio de Janeiro showed the highest available
Zn concentration, 5.27 µgg
−1
, followed by the substrate with the compost from
318 C. P. JORD
˜
AO ET AL.
TABLE V
Mean values of available Zn, Cu, Mn, Pb, and Ni concentrations
(µgg
−1
) obtained from the application of different times and
doses of the composts from Rio de Janeiro and Coimbra
Time of application of the compost (in days)
Compost 0 10 20 30
Zinc
0tha
−1
Rio de Janeiro 0.22a 0.27a 0.31a 0.35a
Coimbra 0.21a 0.30a 0.34a 0.34a
35tha
−1
Rio de Janeiro 1.33a 1.68a 1.96a 2.60a
Coimbra 1.26a 1.48b 1.71b 2.39b
70tha
−1
Rio de Janeiro 1.89a 2.93a 3.29a 5.27a
Coimbra 1.78a 2.41b 3.10a 4.56b
Copper
0tha
−1
Rio de Janeiro 0.73a 0.92a 1.08a 1.28a
Coimbra 0.71a 0.91a 1.01a 1.16b
35tha
−1
Rio de Janeiro 1.05a 1.46a 1.97a 2.42a
Coimbra 1.03a 1.38b 1.75b 2.26b
70tha
−1
Rio de Janeiro 1.75a 2.05a 2.38a 2.85a
Coimbra 1.37b 1.79b 2.01b 2.60b
Manganese
0tha
−1
Rio de Janeiro 11.05a 11.49a 15.18a 15.83a
Coimbra 10.95a 11.77a 15.47a 16.06a
35tha
−1
Rio de Janeiro 13.85a 14.11a 15.86a 17.01a
Coimbra 11.14b 12.19b 14.73b 15.63b
70tha
−1
Rio de Janeiro 15.40a 15.62a 16.48a 17.41a
Coimbra 11.37b 12.90b 13.10b 15.23b
(Continued on next page)
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 319
TABLE V
(Continued)
Time of application of the compost (in days)
Compost 0 10 20 30
Lead
0tha
−1
Rio de Janeiro 0.45a 0.56a 0.63a 0.74a
Coimbra 0.41a 0.56a 0.60a 0.72a
35tha
−1
Rio de Janeiro 0.97a 1.06a 1.70a 2.22a
Coimbra 0.67b 0.95a 1.65a 2.13a
70tha
−1
Rio de Janeiro 0.98a 1.79a 2.58a 3.26a
Coimbra 0.96a 1.46b 1.88b 2.99b
Nickel
0tha
−1
Rio de Janeiro 0.054a 0.055a 0.056a 0.069a
Coimbra 0.053a 0.055a 0.051a 0.065a
35tha
−1
Rio de Janeiro 0.059a 0.078a 0.106a 0.086a
Coimbra 0.061a 0.068a 0.068b 0.056b
70tha
−1
Rio de Janeiro 0.085a 0.122a 0.139a 0.095a
Coimbra 0.080a 0.094b 0.097b 0.105a
Mean values for each metal followed by the same letter for each
time of application and dose of the compost are not different at the
5% level according to the Tukey’s test.
Coimbra, 4.56 µgg
−1
. These results were obtained from the soils amended with
compost with 70 t ha
−1
, added 30 days before the sampling of the substrate for
analysis (Table V).
The application of the compost from Rio de Janeiro increased the available Zn
concentration from 6 to 15 times, as compared with the control soil, while the range
due to the compost from Coimbra was 6 to 13.4 times (Table V).
Significant differences (p < 0.05) were found for the available Zn concentra-
tion, except for the initial treatment (control) (Table V). In most of the treatments
with compost addition, the available Zn concentration was greater where the com-
post of Rio de Janeiro was used.
The substrate with the compost from Rio de Janeiro showed higher total and
available Zn concentrations than that with compost from Coimbra (Table II). Thus,
the former had a larger potential of increasing the content of available Zn in the
soil than the latter.
320 C. P. JORD
˜
AO ET AL.
The total Zn content, pH, organic matter, adsorption sites and microbial activity
of the soil affect the Zn availability (Alloway, 1993). The soil pH is the most
important factor controlling Zn availability, which decreases with the increase of
the pH (Shuman and Li, 1996). In the soil solution, the decrease of a unit of pH
increases 100 times Zn solubility (Mortvedt et al., 1991).
The final degradation products of the organic matter, i. e., the humic and, mainly,
the fulvic acids, bind Zn
2+
ions forming soluble organic complexes at a wide range
of pH, thus, Zn solubility and mobility in soils are enhanced (Alloway, 1993).
In this work, the enhanced Zn availability was attributed to the pH reduction as
well as to the greater organic matter degradation due to the increase of the incubation
time of the compost with the soil. On the other hand, the increased Zn availability
due to the elevation of the applied doses was attributed to the increase in the total
content of this element in the soil. The addition of urban waste composts to soil
can enhance its heavy metals contents, however, this depends on the origin of the
composts. Costa et al. (1994b) reported enhanced soil available Zn extracted with
the Mehlich-1 solution (HCl 0.05 mol L
−1
plus H
2
SO
4
0.0125 mol L
−1
), in soil
amended with increasing doses of composted urban waste.
The Cu availability in the soil was significantly affected by all the sources of
variation examined (Table III). Based on the times between compost addition and
substrate sampling, in general, the increase of the doses of the compost from Rio
de Janeiro enhanced the Cu concentration (Table V). The greatest Cu concentration
was 2.85 µgg
−1
,inthe soil amended with 70 t ha
−1
of compost, 30 days before
the sampling of the substrate for analysis. Businelli et al. (1996) reported that in a
calcareous soil amended with 30 and 90 t ha
−1
of compost the Cu concentration was
enhanced in corn grain, although it remained within the range normally found in
this vegetable. Calcareous soils amended with municipal solid wastes can increase
growth and yield of vegetables with negligible increases in Zn, Mn and Cd levels as
shown in the work of Ozoreshampton et al. (1994) with tomato and squash crops.
Karam et al. (1998) reported significant increase in soil metal concentrations as
the soil was amended with municipal solid waste at different rates, whereas Gigliotti
et al. (1996) observed significant increases in Cu, Zn, Pb, and Cr concentrations in
clay-loam calcareous soil amended with urban waste compost.
In sandy soil treated with different rates of municipal solid waste compost,
AbdelSabour and ElSeoud (1996) found heavy metals concentrations in the seeds
below the threshold for phytotoxicity occurrence.
The application of the composts from Rio de Janeiro and Coimbra increased
the available Cu concentration almost 3 times in the substrate, as compared with
the control (0 t ha
−1
)(Table V). For the compost from Coimbra, the addition of
70 t ha
−1
after 30 days of incubation resulted in the greatest availability of Cu (2.60
mg g
−1
)(Table V). Studying the total and DTPA extractions for determination of
available Zn and Cu in intensively cultivated soils, Reyzabal et al. (2000) found
70% of the Zn in the surface layers was in unavailable forms and almost 50% of
the Cu was in available forms.
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 321
Haque et al. (2000) found significant correlation between the EDTA and DTPA-
extraction methods for micronutrient determination in soils and the amounts ex-
tracted were in the order: Mn > Fe > Cu > Zn. The amounts of Cu extracted by
DTPA or EDTA represent the fraction available for plant uptake. According to Al-
loway (1993), the physicochemical forms of trace metal associations in the available
fraction include the metal in soil solution and part of that adsorbed in the solid phase.
High levels of extracted metals with DTPA can be due to the dissolution of metal
precipitates (carbonates, hydroxides and phosphates) caused by microbial activity
that changes soil pH and gaseous composition; to the oxidation of metal sulphides
to sulphates; and to the metal release from organic matter (Lake et al., 1984).
The forms of Cu in soil solution (as complexes or in the ionic forms) as well as
the absorbed forms in the soil are available for plants while the Cu forms present
in oxides and organic compounds are relatively unavailable (Malavolta, 1994).
The increase in the soil pH reduces Cu availability (Andrade et al., 1975) and
the humic acids constitute a relevant fraction in the organic matter to bind Cu in
insoluble forms (Knezek and Ellis, 1980). In sewage sludge, most of the copper
is associated with the humic fraction, while Zn and Cd are more associated to the
precipitate fractions and to the fulvic acids (Holtzclaw et al., 1978).
According to Lagerweff et al. (1977), the metal-chelates stability constants tend
to have the decreasing order: Cu > Pb > Zn > Cd. Therefore, the increase of the
available Cu concentration in soil solution is much smaller that for Zn, due to,
mainly, the formation of insoluble complexes with humic acids.
DTPA plays an important role in metal extraction in soil. It has suitable stability
constants for complex formation with Fe, Zn, Cu, and Mn simultaneously (Lindsay
and Norvell, 1978). However, information about the use of DTPA for extracting
metals to determine availability to plants in soils amended with compost is still
scarce.
Significant differences (p < 0.05) were found for the available Cu concentration
in the treatments that were used compost samples from Rio de Janeiro and Coimbra
(Table V). In general, the application of doses of 35 and 70 ton/ha of the compost
from Rio de Janeiro caused a greater Cu availability in the soil as compared to that
for the Coimbra compost. Similar to the observation for Zn, this was due to the
higher total and available metal concentrations in the compost from Rio de Janeiro
(Table II).
The available Mn concentrations in the soil were significantly affected by all the
sources of variation examined (Table III). Both time (between compost addition
and substrate sampling) and doses applied resulted in increased concentration of
available Mn (Table V). The highest concentration of this element was 17.41 µgg
−1
,
in the soil amended with 70 t ha
−1
of compost added 30 days before the sampling
of the substrate for analysis.
In a recent study about the effects of 40, 80 and 120 Mg/ha of a composted
solid waste applied on a degraded semiarid shrubland site, Cuevas et al. (2000)
reported an elevation of the concentrations of total Zn, Pb, Cd, Ni in the amended
322 C. P. JORD
˜
AO ET AL.
soil similar to that in the control. These authors emphasized that these increases
were only significant for total Zn, Pb and Cu, while for soil DTPA-extractable Zn
and Cu there was high significance in the amended soil.
Santos et al. (1999) reported enhanced available Mn concentrations in soil
amended with increasing doses of composted urban waste as the extraction was
performed with Mehlich-1 solution. Eneji et al. (2001) reported that the DTPA-
extractable Mn increased in soil amended with chicken manure and swine manure.
In tropical soils, one of the causes of Mn toxicity in plants may be the release
of this element due to the decomposition of the organic matter. However, soils
with high organic matter content may present smaller Mn availability (Lucas and
Knezer, 1972). The DTPA extractable Mn concentration in the soil (Table I) was
higher than that of the Coimbra compost (Table II). The available Mn in the soil from
this region might be retained in the organic matter, thus, the Mn concentration in the
substrate tended to reduce as the compost doses were increased and the incubation
time was greater (Table V). The available Mn concentration in the compost from
Rio de Janeiro was almost 1.4 times greater than that in the compost from Coimbra
(Table II).
The available Pb concentrations in the soil were significantly affected by all the
sources of variation examined (Table III). The application of the compost from Rio
de Janeiro increased 6 times the Pb concentration in the substrate, as compared with
the control (0 t ha
−1
). The highest concentration was 3.26 mg g
−1
Pb with 70 t ha
−1
applied 30 days before the sampling of the substrate for analysis (Table V). In
the treatments with addition of the compost from Coimbra, the Pb concentration
increased around 6 times reaching the highest concentration of 2.99 mg g
−1
, when
70 t ha
−1
were applied 30 days before sampling the substrate for analysis. In contrast
with zinc, the increment of available Pb in the studied soil due to compost addition
was not very high.
Based on the concentrations of available Pb in the composts (Table II) and in
the soil (Table I), the addition of the composts to soil increased the concentration of
Pb in the mixture soil-compost (Table V). The compost that presented the greatest
Pb concentration contributed with the largest increment in the soil.
Significant differences (p < 0.05) were found for the available Pb concentra-
tion in some treatments (10, 20 and 30 days before the collection of substrate for
analysis), mainly in those with application of 70 t ha
−1
compost (Table V).
The available Ni concentration in the soil was significantly affected by all the
sources of variation examined (Table III). The highest available Ni concentration
in the substrate was 0.14 mg g
−1
, with application of 70 t ha
−1
,20days before
sampling (Table V). For the compost from Coimbra, in general, there was small
increase in the concentration of available Ni due to the increase in the time between
compost addition and substrate sampling. The highest value was 0.10 mg g
−1
, with
the application of 70 t ha
−1
,20days before sampling (Table V).
The composts from Rio de Janeiro and Coimbra showed low Ni contents,
23.2 µgg
−1
and 20.9 µgg
−1
, respectively (Table II). Typical Ni concentration
METAL AVAILABILITY IN SOIL AMENDED WITH COMPOST 323
in compost of urban solid waste is 28 µgg
−1
(Aguilar et al., 1997). In general, the
Ni levels in the mixture soil +compost (Table V) were lower than in the composts
(Table II), however, Giusquiani et al. (1992) have shown enhanced levels of Cu,
Zn, Ni, and Cr in soil columns amended with composted urban waste.
Significant differences (p < 0.05) were found for the available Ni concentration
in some treatments, when the studied factor was the compost (Table V). The same
reasons previously discussed regarding the other metals can be used for explain the
significance of this result.
4. Conclusions
The compost from Rio de Janeiro produced, in general, higher increase in soil pH
and available Zn, Cu, Pb, and Ni levels than that of the smaller city, Coimbra.
For both composts, the increase of the time between compost addition and the
collection of the substrate for analysis resulted in the reduction of the pH value
for all application doses examined. In general, the available Zn concentrations
enhanced with the increase of the time of application at the established doses, as
well as with the increase of the doses at the established times.
The findings also showed that the application of composted urban solid wastes to
soil increased the available concentrations of Cu, Pb, and Ni in the soil according to
the increase of the doses of the compost used. However, available Mn was reduced
with the increase of the time or doses. The available concentrations of Zn, Cu, and
Pb in the soil increased according to the increase of the time of application of the
composts.
Acknowledgements
We thank the Brazilian National Research Council (CNPq, Brazil) for the financial
support.
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