**4. Heavy metals in soils amended with sewage sludge**

#### **4.1. Total concentration**

**State City As Cd Co Cr Cu Fe Hg Mn Mo Ni Pb Se Zn Reference** 

mg kg–1

SP Barueri 28.4 385.0 784.3 238.6 152.8 1568.5 [68]

SP Barueri 16.0 386.0 534.0 286.0 171.0 1649.0 [68]

SP Barueri 664.0 228.0 268.0 152.0 1800.0 [69]

SP Barueri 551.0 294.0 595.0 371.0 3810.0 [69]

SP Barueri 660.0 257.0 360.0 180.0 2328.0 [69]

SP Barueri 719.0 263.0 354.0 171.0 1745.0 [69]

880 Environmental Risk Assessment of Soil Contamination

SP Barueri 627.0 287.0 350.0 155.0 2354.0 [69]

SP Barueri <1.0 12.8 12.2 823.8 1058.0 54181 429.0 <0.01 518.4 364.4 2821.0 [70]

SP Barueri <1.0 9.5 5.0 1071.0 1046.0 32500 335.0 <0.10 483.0 233.0 3335.0 [70]

SP Barueri <1.0 9.4 9.3 1297.2 953.0 37990 418.9 <0.01 605.8 348.9 3372.0 [70]

SP Barueri 11.0 808.0 722.0 222.0 231.0 186.0 2159.0 [71]

SP Barueri 10.0 736.0 690.0 194.0 297.0 173.0 2930.0 [71]

SP Barueri 8.0 798.0 998.0 206.0 299.0 169.0 2474.0 [71]

SP Barueri 8.0 798.0 998.0 206.0 299.0 169.0 2474.0 [71]

SP Barueri 20.3 477.7 754.1 355.3 155.8 1926.9 [72]

**Table 2.** Heavy metals in sewage sludge samples used in experiments conducted in Brazil.

SP Franca <1.0 3.3 5.0 633.8 239.8 33793 349.3 <0.01 54.7 199.6 1230.0 [71]

SP Franca <1.0 2.0 4.9 1325.0 259.0 31700 267.0 <0.10 74.0 118.0 1590.0 [71]

SP Franca <1.0 2.1 4.8 1230.0 240.9 24176 232.5 <0.01 72.4 140.5 1198.0 [71]

SP Franca 3.3 29.0 284.5 572.6 184 730.0 2.8 56.6 77.3 1028.3 [73]

SP Franca 2.0 102.0 204.0 18883 243.0 69.0 100.0 1279.0 [74]

SP Franca 1.5 41.3 34.8 43.8 [75]

SP Franca 1.5 41.3 34.8 43.8 [75]

SP Franca 1.5 41.0 34.3 42.4 [75]

SP Franca 1.6 41.7 35.2 45.3 [75]

SP Franca 98.0 42224 242.0 9.8 127.0 1868.0 [76]

SP Jundiaí <0.10 5.8 149.3 284.1 <0.10 676.8 <0.10 41.8 283.1 <0.10 1364.8 [77]

SP Jundiaí <0.01 6.6 188.5 864.8 <0.01 693.3 <0.01 35.4 206.6 <0.01 1738.1 [77]

SP Jundiaí 4.2 14.0 277.7 304.1 1.1 9.8 65.6 201.6 1.8 1869.9 [78]

SP Piracicaba <0.02 207.2 192.9 30295 173.0 <0.01 107.6 943.4 [79]

RJ Rio de Janeiro 0.8 47.0 60.0 82.0 217.0 [80]

SP São Paulo 791.0 38000 315.0 322.0 1888.0 [81]

SP São Paulo 975.0 44000 423.0 401.0 2904.0 [81]

SP São Paulo 1148.0 41000 479.0 459.0 3326.0 [81]

SP São Paulo 989.0 84000 223.0 1240.0 4035.0 [81]

**Statistics** 

Minimum (mg kg–1) 4.2 0.8 4.8 41.0 47.0 184 1.1 60.0 2.8 34.3 42.4 1.8 217.0

Maximum (mg kg–1) 4.2 28.4 29.0 1325.0 1148.0 84000 1.1 730.0 9.8 1240.0 371.0 1.8 4035.0

**Limits (mg kg–1)** 

†Technical Norm # P4.230/1999 of CETESB (Environmental Agency of the State of São Paulo).

‡Resolution # 375/2006 of CONAMA (Brazilian National Environment Council).

The determination of the total concentration of heavy metals in soils has been performed with previous extraction of metals from samples using different mixtures of acids. In Brazil, the methods of extraction most widely used are presented in Table 3. Because of the difference in the chemical composition, some of them may produce quite contrasting results. Comparison between the methods HNO3–H2O2–HCl and HClO4–HF shows this contrast. It is observed in Table 4 that concentrations of Cr, Pb and Zn extracted with HNO3–H2O2– HCl were 72 %, 31 % and 62 % lower than concentrations of these metals extracted with HClO4–HF. For Cd, however, the results were not different between the two methods, suggesting that the difference in values between them may depend on the type of metal in question. The contrasting results between these methods are due to extraction differential capacity of the reagent mixtures employed in each of them. The HNO3–H2O2–HCl mix‐ ture does not normally extract metals bound to silicates. On the other hand, hydrofluoric acid contained in the HClO4–HF mixture is able to dissolve silicates and extract metals eventually present in this mineral class. Therefore, concentrations of metals extracted with HNO3–H2O2–HCl tend to be smaller in relation to extraction with HClO4–HF. Thus, it is necessary to standardize the method of extraction of heavy metals to assess the contamina‐ tion of soil amended with sewage sludge.


†United States Environmental Protection Agency. The composition of the extraction methods 3050B and 3051A may vary slightly but it always has HNO3.

**Table 3.** Methods commonly used in Brazil for extraction of heavy metals from soils.

Brazilian official institutions of environment, as CETESB [82] and CONAMA [67], recommend the use of the methods 3050B and 3051A of United States Environmental Protection Agency (USEPA) [83, 84] for extraction of heavy metals in soils amended with sewage sludge. Such methods are not designed to extract fully the metals from the soil, since they normally do not dissolve elements bound to silicates, which are not generally available in the environment,


†Means within a column followed by the same letter are not significantly different according to Tukey test (*p* < 0.05). Values are means of four sewage sludge rates.

Source: Adapted from Nogueira et al. [71].

**Table 4.** Cd, Cr, Pb and Zn extracted by two different methods from a Brazilian Oxisol amended with sewage sludge.

thus without implications for environmental contamination. They extract only elements which could become environmentally available, consequently harmful to living organisms. As the extraction is not fully, the terms pseudototal concentration and total recoverable concentration have recently been employed to designate the concentrations of metals extracted by these official methods, although the use of the term total concentration is still very common. In recent years, many field experiments with sewage sludge were performed in Brazil, particularly in São Paulo state, therefore there are several data on total concentrations of heavy metals in soil which allow studying the risks of contamination pose by agricultural use of the waste. A summary of these experiments is presented below.

Oliveira and Mattiazzo [68] conducted an experiment with sugarcane to test varying rates of sewage sludge applied to an Oxisol for two consecutive years, in which heavy metals were added in different amounts, including rates above the annual maximum rates allowed in São Paulo state by CETESB. The data in Tables 5 and 6 show that there was at least one rate above the annual rate allowed for Cd, Cu, Ni, Pb and Zn, but there was no rate higher than the maximum cumulative rate. In soil, the total concentrations of Cu and Zn (extraction with HCl– HNO3 3+1 in microwave) in layer 0-0.20 m depth increased with increasing sewage sludge rate in two years especially for the higher rates in the second year, indicating a cumulative effect. Cd and Pb were below the LOD of the analytical method (Atomic Absorption Spectrometry– AAS). Ni was detected only in the second year and at the two highest rates of sludge. The addition of metals above the allowed maximum rates increased total concentrations of Cu, Ni and Zn in the second year above the natural concentrations established for São Paulo state (Tables 3 and 7), suggesting that soils receiving high loads of heavy metals by the application of excessive rates of sewage sludge could be contaminated in a short time.

In addition to the possibility of rapidly contaminating the soil with heavy metals, high rates of sewage sludge cause prolonged effect on contamination. Martins et al. [81] observed linear increases in total concentrations of Cu and Zn (extraction with HNO3–HClO 5+1) in a clayey Oxisol in the year of application of sewage sludge single rates which reached maximum of 80 Mg ha–1, being in this rate added quantities of these metals that exceeded the maximum annual limits established for São Paulo state. Four years later, increases were still linear and the concentrations were similar to the first year, indicating that these elements persist in the soil for a long time. In fact, high persistence is a characteristic of heavy metals added to soils [87]. On the other hand, low rates of sewage sludge applied to land do not increase excessively the total concentrations of heavy metals in soils. Oliveira et al. [69] found that the total concentra‐ tions of Cu, Ni, Pb and Zn (extraction with HNO3–H2O2–HCl) in 0-0.20 m layer of an Oxisol cultivated with maize increased after five annual applications of sewage sludge rates up to 10 Mg ha–1 year–1, but the increases did not exceed the limits of these heavy metals allowed in São Paulo state. In the study conducted by Silva et al. [88], the total concentrations of Cu, Ni and Zn (extraction with HCl–HNO3 3+1) in 0-0.20 m layer of a clayey Oxisol cultivated with maize increased in response to rates of sewage sludge from the Barueri and Franca municipalities, but they increased less with Franca sewage sludge, which had lower concentrations of these metals and it was applied at lower rates. Thus, application of low rates of sludge with low concentrations of heavy metals in their composition seems to be a strategy to minimize the excessive accumulation of heavy metals in soils.

However, this strategy may be insufficient for Cd. Nogueira et al. [78] observed that application of 10.8 Mg ha–1 of sewage sludge, rate defined to supply 100 % of N required by sugarcane, increased total concentrations of As, Cd, Cu, Ni, Pb and Zn (extraction by Method 3051A – see Table 3) in 0-0.20 m layer of an Ultisol in assessments performed 360 and 720 days after application of the sludge. While the concentrations of As, Cu, Ni, Pb and Zn were well below the limits established by CETESB and CONAMA, the concentration of Cd (0.2 mg kg–1) was relatively close to the limit of CETESB (< 0.5 mg kg–1, Table 7). Although the concentration of Cd has more than double to reach this limit, the fact that the limit is too low cause concern in relation to any increase in Cd concentration due to new applications of sewage sludge. In the work of these authors has been reported for the first time in Brazil the effect of sewage sludge on the accumulation of Se in soil. Se concentration increased from 0.068 to 0.092 mg kg–1 with application of 10.8 Mg ha–1 of sludge, but this increase was below the limit of CETESB (0.25 mg kg–1) and far below the limit of CONAMA (5 mg kg–1).

thus without implications for environmental contamination. They extract only elements which could become environmentally available, consequently harmful to living organisms. As the extraction is not fully, the terms pseudototal concentration and total recoverable concentration have recently been employed to designate the concentrations of metals extracted by these official methods, although the use of the term total concentration is still very common. In recent years, many field experiments with sewage sludge were performed in Brazil, particularly in São Paulo state, therefore there are several data on total concentrations of heavy metals in soil which allow studying the risks of contamination pose by agricultural use of the waste. A

**Table 4.** Cd, Cr, Pb and Zn extracted by two different methods from a Brazilian Oxisol amended with sewage sludge.

HNO3–H2O2–HCl 1.93 a 28.72 b 15.72 b 64.82 b HClO4–HF 1.99 a 104.17 a 23.05 a 171.97 a

†Means within a column followed by the same letter are not significantly different according to Tukey test (*p* < 0.05).

Heavy metal† Cd Cr Pb Zn mg kg–1

Oliveira and Mattiazzo [68] conducted an experiment with sugarcane to test varying rates of sewage sludge applied to an Oxisol for two consecutive years, in which heavy metals were added in different amounts, including rates above the annual maximum rates allowed in São Paulo state by CETESB. The data in Tables 5 and 6 show that there was at least one rate above the annual rate allowed for Cd, Cu, Ni, Pb and Zn, but there was no rate higher than the maximum cumulative rate. In soil, the total concentrations of Cu and Zn (extraction with HCl– HNO3 3+1 in microwave) in layer 0-0.20 m depth increased with increasing sewage sludge rate in two years especially for the higher rates in the second year, indicating a cumulative effect. Cd and Pb were below the LOD of the analytical method (Atomic Absorption Spectrometry– AAS). Ni was detected only in the second year and at the two highest rates of sludge. The addition of metals above the allowed maximum rates increased total concentrations of Cu, Ni and Zn in the second year above the natural concentrations established for São Paulo state (Tables 3 and 7), suggesting that soils receiving high loads of heavy metals by the application

In addition to the possibility of rapidly contaminating the soil with heavy metals, high rates of sewage sludge cause prolonged effect on contamination. Martins et al. [81] observed linear increases in total concentrations of Cu and Zn (extraction with HNO3–HClO 5+1) in a clayey Oxisol in the year of application of sewage sludge single rates which reached maximum of 80 Mg ha–1, being in this rate added quantities of these metals that exceeded the maximum annual limits established for São Paulo state. Four years later, increases were still linear and the concentrations were similar to the first year, indicating that these elements persist in the soil for a long time. In fact, high persistence is a characteristic of heavy metals added to soils [87].

of excessive rates of sewage sludge could be contaminated in a short time.

summary of these experiments is presented below.

Extraction method

Values are means of four sewage sludge rates. Source: Adapted from Nogueira et al. [71].

882 Environmental Risk Assessment of Soil Contamination

The concentrations of heavy metals presented above refer only to the topsoil (0-0.20 m depth). However, deeper and stratified sampling can give an idea of how these metals are distributed among soil layers. Merlino et al. [73] evaluated the concentrations of Cd, Cr and Pb (extraction with HNO3–H2O2–HCl) in the layers 0-0.10, 0.10-0.20 and 0.20-0.40 m of an Oxisol cultivated with maize after 11 years of annual application of sewage sludge rates up to 20 Mg ha–1. The concentrations of Cr and Pb increased only in the 0-0.10 m layer, suggesting accumulation in the superficial layer. There was no effect on the concentration of Cd. In another study, there was also no effect on total concentrations of Cd, Cr, Ni and Pb (extraction with HNO3–H2O2– HCl) in the layers 0-0.10, 0.10-0.20, 0.20-0.30, 0.30-0.40 e 0.40-0.50 m depth of a clayey Oxisol after four annual applications up to 15 Mg ha–1 year–1 to supply nitrogen (N) for sugarcane [75]. In contrast, Oliveira and Mattiazzo [89] observed significant increases in total concentrations of Zn (extraction with HCl–HNO3 3+1 in microwave) until the layer of 0.40-0.60 m of an Oxisol amended with relatively high rates of sewage sludge (> 30 Mg ha–1 year–1) for two consecutive years and cultivated with sugarcane, suggesting that Zn was leached to layers below the incorporation layer of sludge (0-0.20 m depth). For Cu and Cr, there was no evidence of leaching. It was not possible to assess the mobility of Cd, Ni and Pb in soil, because their concentrations were below the LOD of the analytical method (AAS).


**Table 5.** Rate and total concentration of heavy metals in a Brazilian Oxisol amended with sewage sludge and cultivated with sugarcane


**Sewage sludge rate Cd Cr Cu Ni Pb Zn** 

884 Environmental Risk Assessment of Soil Contamination

**1996/97 1997/98 1996/97 1997/98 1996/97 1997/98 1996/97 1997/98 1996/97 1997/98 1996/97 1997/98 1996/97 1997/98** 

**Rate applied to soil (kg ha–1)**

**Total concentration in soil† (mg kg–1)**

0 0 nd‡ nd 16.57 15.55 17.86 16.87 nd nd nd nd 21.14 20.19

33 37 nd nd 21.56 18.14 19.47 26.17 nd nd nd nd 39.22 50.03

66 74 nd nd 25.30 25.21 27.90 36.39 nd 10.65 nd nd 40.41 77.11

99 110 nd nd 25.59 27.19 30.97 42.85 nd 14.63 nd nd 41.27 97.21

†In the 0–0.20 m soil layer. Digestion of soil samples was performed with HCl + HNO3 (3:1) in a microwave oven.

‡Not detected. Concentration of the metal was below the limit of detection of the analytical method (AAS).

Source: Adapted from Oliveira and Mattiazzo [68].

\_\_\_\_\_\_\_\_\_ Mg ha–1 \_\_\_\_\_\_\_\_\_

cultivated with sugarcane

**Table 5.** Rate and total concentration of heavy metals in a Brazilian Oxisol amended with sewage sludge and

**Table 6.** Loading rates for heavy metals applied by sewage sludge in São Paulo State and Brazil


**Table 7.** Limits for heavy metals in soils from São Paulo State and Brazil

Besides increasing or not be changed, the concentrations of heavy metals can also decrease in response to the application of sewage sludge, as shown in the work of Macedo et al. [92]. Concentrations of Cd, Cr and Pb (extraction with HNO3–H2O2–HCl) were evaluated in the layers 0-0.10, 0.10-0.20 and 0.20-0.40 m of a clayey Oxisol cultivated with maize after 11 years of application of sludge sewage rates up to 20 Mg ha–1 year–1. In general, the application of sewage sludge reduced the concentrations of heavy metals in the surface layers, with decreas‐ ing quite evident for Cd in layer of 0-0.10 m depth. This reduction was not expected since metals were added to the soil. Probably, the heavy metals added and part of those natives may have combined with components of sewage sludge forming highly stable compounds resistant to the attack of the extractant used.
