PLANT-AVAILABLE CADMIUM IN SOIL AS INFLUENCED BY AN ADDITION OF SEWAGE SLUDGE

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1 PLANT-AVAILABLE CADMIUM IN SOIL AS INFLUENCED BY AN ADDITION OF SEWAGE SLUDGE SZÁKOVÁ. J.,TLUSTOŠ P.,BALÍK J.,PAVLÍKOVÁ D.,BALÍKOVÁ M. Department of Agrochemistry and Plant Nutrition, Czech University of Agriculture, CZ Prague 6 - Suchdol, Introduction The application of sewage sludge into the agricultural soil can improve nutrient status of the soils as well as their physical - chemical properties. However, excess of organic and/or inorganic pollutants in sewage sludge brings the environmental risk. Among potentially risk elements contained in sewage sludge, cadmium belongs to the most hazardous ones. The mobility of cadmium in sewage sludge depends on source of sludge, ph, redox conditions, moisture, and decomposition processes during storage of this material [1,2]. In our experiment, the influence of both and stored sewage sludge on plant-available portions of soil cadmium were evaluated. Material and methods Three soils differing in physical - chemical properties (Table 1) were used in model pot experiment. Sewage sludge was applied to the soil in the rate equivalent to tons of dry matter per ha. The sludge was added either or processed by 8 months incubation under and an environment. The main properties of sludge and their changes after and an storage are summarized in Table 2. The application of the sludge increased total cadmium content in the pots by - 23 regarding to total cadmium content in individual soils. Location Soil type ph C ox CEC mval.kg -1 Total Cd mg.kg -1 Suchdol Červený Újezd Přerov Fluvisols Tab. 1. The main characteristics of experimental soils. Sludge treatment ph C ox N Total Cd mg.kg an Tab. 2. The main characteristics of and processed sewage sludge. At, both direct and subsequent effect of sludge addition was studied in two growing seasons. Spinach and oat were planted in the pots in the first growing season and maize in the second one. The soils were sampled after harvest, air-dried, homogenized, and extracted by three extracting agents as follows: 0.43 mol.l -1 CH 3 COOH (1 : w/v) [3], 0.0 mol.l -1 EDTA (1 : 5 w/v, ph = 4.6) [4], 0.01 mol.l -1 CaCl 2 (1 : w/v) [5]. The cadmium concentrations in extracts were determined by flameless atomic absorption spectrometry (Varian SpectrAA-0) using standard addition measurement mode for evaluation of cadmium signal. Results and discussion In previous experiment, cadmium fractions associated with individual sludge components leading to a better characterization of plant-availability of cadmium and to an understanding of the behavior of this element in sewage sludge were identified and quantified [6]. Significant influence of sludge processing on cadmium distribution among individual sludge fractions was found (Table 3). In sludge, majority of cadmium was bound into organic and residual fractions while destruction of organic matter during the process of storage of the sludge under environment led to the higher mobility of organically and residually bound cadmium. In the case of an sludge storage, the release of cadmium was less affected as compared to one. The loss of sludge organic matter led to change in total cadmium contents in processed sludge (Table 2). IUAPPA Praha Section: B

2 Sludge treatment Fraction 1 Fraction 2 Fraction 3 Fraction 4 Fraction an Fraction 1: water soluble, Fraction 2: exchangeable, Fraction 3: bound on Fe/Mn oxides, Fraction 4: organically bound, Fraction 5: residual Tab. 3. Percentage of cadmium in individual fractions of and processed sewage sludge determined by sequential extraction procedure [3]. While calcium chloride is able to extract the element fraction corresponding to plant-available portion of element [5,7], the next two extractants partially release also less mobile fractions of elements. Diluted acetic acid is characterized as the extractant releasing element fractions specifically adsorbed on soil oxides [8]. Chelating agents are able to create tight complexes with metal cations bound in surface layer of oxides [9] and by organic bounds []. These Cd fractions are potentially mobilizable under changes of soil properties. The addition of sewage sludge into the soil led to a change in extractable portions of cadmium by individual extractants, as well. The results were calculated as percentage of extractable portion of cadmium from total cadmium in soil, and are presented in Figures 1-4. The cadmium extractability was affected predominantly by physical-chemical properties of individual soils. The cadmium concentrations in extracts of soils amended by differently treated sewage sludge did not correspond to different portion of the most mobile fractions in individual sludge treatments (Table 3). The mildest extractant, CaCl 2, representing the plant - available portion of cadmium, released of total cadmium from light sandy Fluvisols while from was extracted only 2-3 and the extractability of cadmium from did not exceed 0.5 of total cadmium in this soil (Figure 1). Soil ph was the factor determining the cadmium extractability by this agent [7]. The addition of sludge did not affect the final ph of sludge amended soil. In Fluvisols and the plant-available cadmium fraction slightly increased after addition of sludge. In were the plant-available concentrations of cadmium very low and the values were very close to detection limit of atomic absorption determination. From this reason, the evaluation of such results is very limited Fluvisols Fig. 1. Mean relative cadmium concentrations extractable by 0.01 mol.l -1 CaCl 2 from individual soils treated by and processed sewage sludge The more significant changes occurred in the case of acetic acid (Figure 2) and EDTA (Figure 3) extractable Cd concentrations in sludge amended soils. Similarly as for CaCl 2 extracts, the cadmium extractability by acetic acid decreased in order Fluvisols > >. However, the extractable concentrations were significantly higher, and varied in range - 42 of total cadmium content. Decreasing Cd concentrations in acetic acid extracts after addition of sludge to and suggested improved sorption capacity and better possibility of incorporation of Cd into organic matrix in treated soil. In the opposite, lack of sorption sites in light sandy Fluvisols caused higher mobility of acetic acid extractable cadmium in IUAPPA Section:.B

3 sludge amended soil. The results of EDTA soil extraction show that the addition of sewage sludge into the soil increased the strenght of cadmium bounds in organic fraction of the soil. The highest effect was evaluated at Fluvisols where the addition of sludge led to significant improvement of total content of organic matter. In and, the lowest effects of sludge amendment occurred if anally incubated sludge was applied into the soil as compared to and ones in most of cases. The addition of sewage sludge to the soil lead to the increase of total cadmium amount in the pot. The increment was from at with the highest cadmium concentration to 23 at with the lowest total cadmium concentrations. The total amounts of extractable cadmium in individual pots differed after soil type and extraction agent used. The amount of EDTA extractable cadmium was lower in sludge amended pots as compared to pot regardless of sludge treatment because of the immobilization of cadmium by sludge organic matter. However, the most mobile cadmium portion, i.e. CaCl 2 extractable one, increased at even by 80-0 compared to the pot if or ally incubated sludge was applied into the soil. This result suggested the possibility of increased cadmium uptake by plants growing in these pots. The comparison of cadmium extractability from sludge amended in two following growing seasons is given in Figure 4. Concerning CaCl 2 extracts, the evaluation of the results is limited similarly as in the Figure 1 because of low cadmium level resulting in variability of the analytical data. In the acetic acid and EDTA extracts decreased cadmium concentrations in all the treatments including sample. We can assume that cadmium was immobilized during storage of air-dried soil samples between first and second vegetation period. 35 Fluvisols Fig. 2. Mean relative cadmium concentrations extractable by 0.43 mol.l -1 acetic acid from individual soils treated by and processed sewage sludge. 4. Conclusion The addition of and processed sewage sludge into the soil led to the change of both plant-available and potentially mobilizable portions of cadmium. However, complex of soil physical - chemical properties seemed to be the predominant factor determining the behavior of individual treatments of sewage sludge in soil. Especially, soil sorption complex, and soil organic matter will play an important role in this case. From this reason, more detailed information concerning the composition of organic matter (as determination of humic and fulvic acids) and the fractionation of individual types of oxides in both soil and sewage sludge will be necessary in further research. The increment of the total cadmium amount in the pot due to sewage sludge amendment can lead to increase of total amount of available cadmium in pot. Especially at the soils with low level of total cadmium in soil it can cause the future environmental risk if multiply sludge application is used. Because of changes in cadmium extractability after the subsequent growing season, the evaluation of the long - term effect of sewage sludge must be included to the further research, as well. IUAPPA Section:.B

4 80 70 Fluvisols Fig. 3. Mean relative cadmium concentrations extractable by 0.0 mol.l -1 EDTA from individual soils treated by and processed sewage sludge. 0.5 CaCl 2 Acetic acid 70 EDTA an an an Fig. 4. Comparison of relative cadmium concentrations extractable by individual extracting agents from treated by and processed sewage sludge in first ( ) and second ( ) growing season. Acknowledgements Financial support for these investigations was provided by Grant Agency of Czech Republic Project No. 526/97/0845. References [1] G. L.Mullins, L. E Sommers, J. Environ. Qual.,, 1986, 382. IUAPPA Section:.B

5 [2] R. Canet, F.Pomares, F.Tarazona, Soil Use and Management, 13, 1997, 117. [3] A. Ure, P. Quevauviller, H. Muntau, B. Griepink, BCR information EUR EN, Community Bureau of Science,1993 [4] H. Zeien, Chemische Extraktionen zur Bestimmung der Bindungsformen von Schwermetallen in Böden. Universität Bonn, 1995, pp.284. [5] J. Novozamsky, T. M.Lexmond, V. J. G. Houba, Intern. J. Environ. Anal. Chem. 51,1993, 47 [6] S. Kaewrahun, Uptake of heavy metals by plant from soils treated by sewage sludge. Doctoral thesis. Czech University of Agriculture, Prague, 1999, pp. 9 [7] J. Száková, P.Tlustoš, J. Balík, D. Pavlíková, M. Balíková, Proc. Biogeochemistry of trace elements, Wienna, 1999, 594 [8] W. P. Miller, D. C. Martens, L. W. Zelazny, E. T. Kornegay, J. Environ. Qual., 1986, 69 [9] W. P. Miller, W. W. McFee, J. Environ. Qual. 12, 1983, 29 [] M. G. Hickey, J. A. Kittrick, J. Environ. Qual. 13, 1984, 372 IUAPPA Section:.B