Aranyos, Tibor

Füleky, György

Makádi, Marianna

Orosz, Viktória

Tomócsik, Attila

European Chemical Bulletin

University of Debrecen Electronic Archive

Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 480
TOXIC ELEMENTS IN THE SEWAGE SLUDGE – SOIL – PLANT 
CHAIN 
Attila Tomócsik[a]*, Viktória Orosz[a], Tibor Aranyos[a], Marianna Makádi[a] and 
György Füleky[b] 
 
Paper was presented at the 4th International Symposium on Trace Elements in the Food Chain, Friends or Foes, 15-17 November, 2012, 
Visegrád, Hungary 
 
Keywords: sewage sludge compost, agriculture, toxic element, sandy soil 
According to statistical data the amount of sewage sludge does not increase as it was prognosed some years ago. Although this is a positive
effect, we have to solve the problem of recycling of the sewage sludge. The appropriate chemical composition of municipal sewage sludge
compost is suitable for nutrient supply in the agriculture. The small-plot experiment with sewage sludge compost was started in the spring
of 2003. Three doses of compost (9, 18, 27 t ha-1) and a control treatment were used in the experiment. The small-plot experiment was re-
treated in the fall of 2006 and 2009. In the composting process bentonite, rhyolite and wheat straw were used as additives for improving the
quality of the compost. Our purpose was to stabilize or increase the fertility of sandy soil and contribute to the reduction of environmental
pollution. In the plot experiment there were three test plants: triticale, maize and pea. These three plants were sawn in crop rotation. We
examined the concentration of nickel (Ni) and zinc (Zn) in two soil layers, 0-30 and 30-60 cm in 2008-2009 years. We could not observe
toxic effects on the test plants. The aim of the experiment was to investigate whether the application of sewage sludge compost cause
hazardous accumulation of toxic elements in the soil and plants. 
 
 
* Corresponding Authors 
Fax: (+36)-42-496-009  
E-Mail: tomocsik@agr.unideb.hu 
[a] Research Institutes of University of Debrecen, H-4400 
Nyíregyháza, Westsik Vilmos u. 4-6. 
[b] Szent István University, Department of Soil Science and 
Agricultural Chemistry, H-2103 Gödöllő, Páter Károly u. 1. 
 
Introduction 
Sewage sludge is an organic waste which usually contains 
high levels of nitrogen and phosphorous as well as 
significant concentrations of micronutrients 1,2. The use of 
sewage sludge in soil has very beneficial effects on the 
quantity and availability of nutrients, on the restoration of 
structural stability of the soil and on resistance against soil 
erosion 3,4. 
Composting offers an effective method for treating 
sewage sludge by stabilizing organic matter, reducing odour, 
and killing human pathogens and weed seeds by the heat 
generated 5,6. The products can be used as soil conditioner to 
improve soil physical properties by increasing soil organic 
matter content. In this way the water holding capacity and 
aggregate stability are increased, but soil bulk density is 
reduced7. Sewage sludge compost also represents a source 
of nitrogen (N), phosphorus (P), potassium (K) and trace 
elements such as zinc (Zn), copper (Cu) and molybdenum 
(Mn) for plant growth8. 
However, the presence of toxic elements in composts is 
the main cause of adverse effects on animal and human 
health, transmitted through the food chain from soil, 
groundwater and plants9. 
The sewage sludge contains toxic elements within an 
organic matrix. This may lead to the increased solubility of 
some of the metals (due to the formation of soluble organic 
complexes) or to their immobilization and subsequent 
reduced possibility of being assimilated by the plant10. 
Consequently, exact analyzing the contents of toxic 
elements in composts is very important for the routine 
monitoring and risk assessment and regulation of 
environmental protection. 
In the present study, we aimed to measure toxic element, 
such us nickel (Ni) and potential toxic element, like zinc 
(Zn). During the experiment we would like to follow the 
movement of toxic elements in the food chain. 
Experiments 
Experimental design 
The small-plot experiment was established in spring, 2003 
at the Research Institute of CAAES of University of 
Debrecen, at the town of Nyíregyháza, located in the NE 
part of Hungary. It was re-treated in 2006, when the field 
experiment was re-arranged and the size of plots was 
enlarged.  
The size of small-plots was 19 x 36 meters. The 
experiment was done in five replications on sandy soil. Our 
compost fills the requirements of the Agricultural Ministry 
Order of 36/2006 (V.18.). The compost includes 40% 
sewage sludge, 25% straw, 30% rhyolite and 5% bentonite. 
These materials have good effects on light textured sandy 
soils especially when they are mixed with organic material 
 
Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 481
(e.g. sewage sludge). The compost was applied at 9, 18, 27 t 
ha-1 doses, ploughed into the 0-30 cm soil layer before 
sowing. The effect of the applied compost on triticale (x 
Triticosecale Wittmack), maize (Zea mays) and pea. (Pisum 
sativum L.) was studied.  
Toxic elements of plant samples were measured after 
harvesting. In the case of triticale and maize the toxic 
elements content of grain was measured. The toxic element 
content of pea plants were measured in its three parts (root, 
straw + pods and grain). Composite soil samples were 
mixed from 5 subsamples in each plot from 0-30 and 30-60 
cm soil layers after harvesting of all test plants. 
The applied compost 
In the Table 1 can be seen the important parameters of the 
applied compost 
Table 1. Main characteristics of the applied compost 
Parameter  Value 
pH (H2O 1:10) 7.2 
Dry matter content [m/m% raw matter]  54 
Organic matter content [m/m % dry matter]  26 
Total N-content [m/m% dry matter]  1.68 
Total P2O5-content [m/m% dry matter]  0.7 
Total K2O-content [m/m% dry matter]  0.4 
As (mg kg-1) 5.26 
Cd (mg kg-1) 0 
Co (mg kg-1) 0 
Cr (mg kg-1) 21.96 
Cu (mg kg-1) 149.7 
Hg (mg kg-1) 1.42 
Ni (mg kg-1)] 12.09 
Pb (mg kg-1) 23.33 
Se (mg kg-1) 2.51 
 
In the composted sewage sludge there were nitrogen (N), 
phosphorus (P) and potassium (K), which are useful for 
enhancing the available nutrients content of soil. The toxic 
elements content of compost was low therefore it is good for 
agricultural utilization. In the applied compost amount of 
nickel was under the limit value determined by the 
Agricultural Ministry Order of 36/2006 (V.18.). 
Chemical and statistical analysis 
The Zn and Ni content of soil and plant samples were 
measured according to the MSZ –08-0012/16-87. Briefly, 
the samples were digested with cc. HNO3 : H2O2 and after 
filtering, the heavy metal contents of solutions were 
measured by using an ICP-OES emission spectrometer. 
Statistical significance (P<0.05) of the differences was 
determined by one-way ANOVA and Tukey’s multiple 
range test. Statistical analysis was performed with SPSS 
13.0., with five replications.  
Results and Discussion 
Toxic elements in the soil 
The utilization of sewage sludge in agriculture may cause 
to get a certain amount of toxic elements into the soil. This 
could result in the contamination of soil and plants by toxic 
elements. In our data reveal the fate of Zn and Ni in the 
sewage sludge-soil-plant chain. 
The heavy metal content in soils comes from two sources: 
first, from the natural heavy metal content of soil and on the 
other hand, as a result of soil pollution. The measurable 
concentration of the micronutrients in the soil usually 
increases when the amount of heavy metals entering into the 
soil is higher than their leached or utilized quantity11.  
In the Table 2 the Ni and Zn concentrations of soil of the 
three test plants measured in 2008 are shown. The Ni and Zn 
content of the soil were below the 40 and 200 mg kg-1 limit 
in all treatments in this year. Concentration of Zn was 
increased after the treatments in the upper 0-30 cm soil layer, 
but this increase was not statistically significant. The 
measured Zn concentrations were around 30 mg kg-1. In 
Canada12 various crop responses were measured to a mixed 
municipal solid waste compost and the fate of certain metals 
associated with compost were examined. Plant and soil 
samples were collected after the compost application to 
analyse for content of Arsenic (As), Cupper (Cu), Zn, 
Mercury (Hg) and Lead (Pb). The research results showed 
that the compost slightly increased the heavy metal 
concentrations of the soil. The amount of Ni did not increase 
in the top soil under triticale. 
 Similar results were found when sea weeds compost was 
applied (leaves of beached Posidonia oceanica were used), 
which had high concentrations of heavy metals. Except of 
Ni, they measured higher heavy metal concentrations in soil 
samples amended with compost than in the control ones. 
The low concentration of Ni in soluble and exchangeable 
form explains its low mobility and biological activity 13. 
Toxic elements content of soil samples measured in 2009 
can be seen in Table 3. Ni concentrations of soil samples 
were similar in both soil layers (7.35 – 10.09 mg kg-1) in 
2009 and neither was above the 40 mg kg-1 threshold limit. 
The compost treatment did not increase its concentration. 
Low increase of Zn concentration in all treatments was 
found in the top soil samples collected from green pea’s 
plots. On the contrary a researcher14 observed significantly 
higher levels of Zn, manganese (Mn) and Cu in soil 
amended with compost at a rate of 19 t ha-1 but their applied 
compost had high heavy metal content (Zn: 566 mg kg-1, 
Mn: 176 mg kg -1 and Cu: 226 mg kg -1).  
Concentrations of measured elements were under the limit 
value (Ni: 40 and Zn: 200 mg kg-1). 
Toxic elements in the test plants 
Pea (Pisum sativum L.) 
In Table 4 presents the ratio of toxic elements content in 
different parts of pea in the sewage sludge compost 
treatment. The amount of Ni measured in the pea grain yield 
was slightly higher than the plants growing in unpolluted 
sites  but  among  the  treatments  the   differences   are    not  
Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 482
significant. The amount of Zn was higher in the grain yield 
compared to other two parts of the plants in the year 2008 
and 2009. Due to the 18 and the 27 t ha-1 treatment the Zn 
concentration increased in different parts of the plants. In 
2009 the amount of Zn increased only in the 9 and 27 t ha-1 
treatments compared to the control plots, while the Zn 
concentrations measured in the 18 t ha-1 treatments were 
similar to the control ones.  
 
Table 2. Nickel and zinc content in two layers of soil under test plants in the sewage sludge compost experiment in 2008 
Ni (mg kg-1) Zn (mg kg-1) 
0-30 cm 30-60 cm 0-30 cm 30-60 cm 
 Plant 
  
Dose of compost 
(t ha -1) 
Mean S.D. Mean S.D. Mean S.D. Mean S.D. 
control 4.724 6.364 9.116 1.648 33.84 2.64 29.22 1.13 
9 4.230 5.649 9.274 1.494 35.26 1.79 28.40 1.54 
18 4.280 5.588 8.295 0.246 36.76 4.29 28.45 1.39 
Triticale 
27 4.058 5.065 10.768 3.353 35.48 4.97 29.36 1.81 
          
control 0.065 0.055 9.860 1.120 32.53 2.29 28.46 1.11 
9 3.878 5.236 9.380 1.176 33.04 2.17 29.17 0.32 
18 4.118 5.110 9.393 0.405 34.98 2.33 29.42 2.51 
Maize 
27 3.908 4.917 9.394 0.973 35.96 1.35 29.24 1.81 
          
control 0.123 0.037 10.478 1.100 32.15 7.48 26.88 1.28 
9 3.828 4.808 10.010 1.174 36.46 10.37 31.64 6.85 
18 3.746 4.974 9.862 2.059 33.94 3.57 27.84 2.85 
Green pea 
27 4.894 6.488 9.584 1.741 33.40 1.78 27.80 1.98 
approved limit1 (mg kg-1) 40 200 
1 (50/2001. Government regulation). There was not significant difference among treatments, according to the Tukey’s test 
(p>0.05) 
 
Table 3. Nickel and zinc content in two layers of soil under test plants in the sewage sludge compost experiment in 2009 
 Plant Ni (mg kg-1) Zn (mg kg-1) 
0-30 cm 30-60 cm 0-30 cm 30-60 cm 
  
 Dose of compost 
(t ha -1) 
Mean S.D. Mean S.D. Mean S.D. Mean S.D. 
control 8.256 1.177 8.294 0.275 21.857 2.547 21.971 2.703 
9 7.924 0.734 8.992 0.816 22.201 2.172 21.989 1.370 
18 7.761 1.130 8.616 1.576 22.137 1.726 19.755 4.213 
Triticale 
27 8.058 0.377 7.994 1.623 22.580 2.325 20.258 5.766 
          
control 8.510 1.528 10.099 1.228 20.082 1.423 20.270 5.449 
9 9.625 3.265 9.411 2.593 23.016 4.989 22.221 9.451 
18 8.322 1.680 8.381 2.760 20.941 1.057 17.681 3.592 
Maize 
27 7.703 1.617 8.390 1.729 20.673 0.989 17.249 3.363 
          
control 8.203 1.297 8.346 2.680 22.677 2.779 20.359 3.167 
9 8.503 1.454 8.509 0.426 23.665 3.686 22.375 1.463 
18 8.034 1.308 7.356 2.572 24.137 2.708 21.104 4.664 
Green pea 
27 8.161 1.511 7.845 3.304 27.806 3.471 19.502 4.702 
approved limit1 (mg kg-1) 40 200 
1 (50/2001. Government regulation) There was not significant difference among treatments, according to the Tukey’s test 
(p>0.05) 
 
Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 483
Zn content in maize
in unpolluted plants: 25-150 mg kg-1
0,0
10,0
20,0
30,0
40,0
control 9 18 27
Dose of compost (t ha-1)
m
g 
kg
-1 2008
2009
Ni content in maize
in unpolluted plants: 0.1-5  mg kg-1
-3,0
0,0
3,0
6,0
9,0
12,0
control 9 18 27
Dose of compost (t ha-1)
m
g 
kg
-1
 
Table 4. Nickel and zinc concentrations in different parts of pea in the sewage sludge compost experiment 
Ni, mg kg-1 Zn, mg kg-1 
2008 2009 2008 2009 
  
  
Dose of 
compost  
(t ha -1) 
Mean S.D. Mean S.D. Mean S.D. Mean S.D. 
control 33.58 23.25 15.08 5.25 20.52 8.24 26.33 6.23 
9 32.87 23.47 14.25 7.64 15.26 11.77 29.16 6.72 
18 36.39 30.23 5.77 2.69 22.24 12.18 22.87 9.07 
Root 
27 52.40 51.23 3.64 1.47 23.88 8.10 32.59 5.66 
           
control 1.75 1.03 12.48 7.33 13.04 5.14 25.29 3.66 
9 2.59 2.75 20.88 15.83 15.04 2.70 21.45 3.81 
18 1.61 1.24 33.30 30.31 13,60 2.57 24.27 4.99 
Straw + 
Pods 
27 1.71 0.71 25.52 18.45 19.10 8.11 24.78 6.93 
           
control 12.36 8.87 7.92 3.48 48.27 11.13 46.91 5.27 
9 7.61 5.34 5.55 2.52 43.99 20.87 44.72 7.73 
18 8.69 3.22 2.38 0.94 51.08 4.20 45.15 4.11 
Grain 
27 9.02 2.95 2.39 1.40 51.82 5.95 49.13 2.80 
in unpolluted plants, mg kg-1 0.1 - 5.0 25 - 150  
There was not significant difference among treatments, according to the Tukey’s test (p>0.05) 
Maize (Zea mays) 
In Figure 1 presents Zn content in maize in the sewage 
sludge compost experiment. Zn concentration was under 30 
mg kg-1 in the test plant. The quantity of Zn measured in 
maize was higher in the 9 t ha-1 dose of compost treated 
plots in 2008. 
In 2008 we did not find significant differences between 
the three treatments, as it is showed in Figure 2. Other 
researchers found significantly increased Ni concentration in 
the roots of the lettuce plants after compost application. The 
Ni concentration was particularly higher in the leaves of the 
control sample13. Quantity of Ni in the maize crop was 
lower than detection limit in 2009.  
Triticale (x Triticosecale Wittmack) 
Figure 3 shows Zn content of triticale crop in the sewage 
sludge compost experiment in 2008 and 2009. We can see 
that amount of Zn was increased in the treatments in 2008. 
Measurements by Chaney15 demonstrated that in plant tissue, 
the concentration of Zn was the highest in the compost 
treatment which reflect the high Zn concentrations in the 
compost material. 
In the year 2009 the amount of Zn increased only in the 9 t 
ha-1 treatment in comparison with the control plot, while the 
measured Zn concentrations of the other two treatments 
were similar to the concentrations of control samples. Figure 
4 presents the Ni concentration in triticale in the sewage 
sludge compost treatment. Effect of compost treatment did 
not increase the amount of Ni in 2008. 
Figure 1. Zinc (Zn) content of maize in the sewage sludge compost 
experiment  
Figure 2. Nickel (Ni) content of maize in the sewage sludge 
compost experiment in 2008 
Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 484
Zn content in triticale
in unpolluted plants: 25-150 mg kg-1
0,0
10,0
20,0
30,0
40,0
control 9 18 27
Dose of compost (t ha-1)
m
g 
kg
-1 2008
2009
Ni content in triticale
in unpolluted plants: 0.1-5  mg kg-1
0,0
0,5
1,0
1,5
control 9 18 27
Dose of compost (t ha-1)
m
g 
kg
-1
Figure 3. Zinc (Zn) content of triticale seed in the sewage sludge 
compost experiment  
Figure 4. Nickel (Ni) content in triticale seed in the sewage sludge 
compost treatment in 2008 
Similar to the Ni content of the corn, Ni content of 
triticale samples could not be measured in 2009. 
Conclusion 
Our results proved that the repeated use of composted 
sewage sludge for crop production did not cause any danger 
for agriculture and feed/food safety. We have not found 
toxic elements accumulation in the measured layers of the 
soil. The green pea accumulated Ni primarily in its root , 
which is important from food safety aspect, because it is not 
edible part of the plant. The other two test plants (triticale 
and maize) contain similar quantity of Zn in the grain while 
green pea concentrated this element in its grain with a 
higher quantity. The content of Zn and Ni were the lowest  
in the grain of maize.  
 
 
 
 
 
 
 
 
Both measured elements were in the soil and plants, but 
these Zn and Ni did not accumulate hazardous in soil-plant 
chain. In conclusion it can be stated that the good quality 
and the circumspect application of the sewage sludge 
compost could guarantee its safe utilization. 
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Science & Utilization. 2000, 8, 3, 224-235.  
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Received: 31.10.2012. 
Accepted:20.11.2012. 
 
Toxic elements in the sewage sludge-soil-plant chain         Section B – Research Paper 
Eur. Chem. Bull. 2012, 1(11), 480-484 485
 


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