Metal species distribution in top- and sub-soil in an area affected by copper smelter emissions

Geochemistry, Vol. 11,pp. 35-42, 1996 Copyright fQ 1996ElsevierScienceLtd Printed in Great Britain. All rights reserved 0883-2927/96$15.00+0.00

Applied

Pergamon

088s2927(95)0006W

Metal species distribution in top- and sub-soil in an area affected by copper smelter emissions Anna Karczewska Institute of Soil Science and Agricultural Environment Protection, Agricultural University of Wroclaw, ul. Grunwaldzka 53,50-357 Wroclaw, Poland Abstract-The

major objective of this study was to investigate the chemical forms in which selected metals occur in soils polluted with metallurgical dusts as well as to estimate potential mobility and bioavailability of these metals. Six soil profiles situated at different distances from Cu smelters were chosen and soil samples were taken from top- and sub-surface layers. The soils differed in their textures but all of them showed high contents of sand fraction and were neutral or slightly alkaline in reaction, due to liming. Ale research involved the analysis of the total contents of 8 metals (Al, Fe, Mu, Zn, Cr, Ni, Cu and Pb) and their speciation according to the Zeien and Bruemmer method. Total concentrations of metals varied in the following ranges (mg/kg): Al, 1420-l 1,400; Fe, 1710-19,700; Mn, 55-470; Zn, 6.4153; Cr, 2.15-16.9; Ni, 1.18-13.8; Cu, 7.4-1710; Pb, 1l460. The metal fractions determined were: mobile, exchangeable, occluded in MnO,, organically bound, occluded in amorphous and crystalline FeO, and residual. The metals’ behaviour in soils depended both on the soil properties and the metals’ origin. Typically lithogenic metals (Al, Fe, Cr, Ni) occured in the soils

predominantly in stable fractions (bound to FeO, and silicates), whereas metals of anthropogenic origin (Cu, Pb) showed considerably higher percentages of mobile and exchangeable fractions, which together made up 17.0-59.7% of Cu and 2.5-38.8% of Pb. The highest contributions of those fractions occured in the top layers of sandy soils. Therefore, it is concluded that anthropogenic metals are likely to be leached from the polluted soils, especially the sandy ones. Copyright 0 1996 Elsevier Science Ltd

INTRODUCTION

occur in the polluted soils. Several sequential extraction methods have recently been developed to estimate the “chemical forms” of heavy metals in soils and to assess the risk of metal mobilization. Although such procedures, being only operationally defined, apportion metals only to certain mineral phases without defining their chemical species, the term “metal speciation” is generally used for this kind of assessment (Quevauviller et al., 1993) and is also used in this paper. None of the speciation methods has until now been commonly accepted as a standard procedure (Hirner, 1992; Quevauveller et al., 1993). In this work, a method developed by Zeien and Bruemmer (1989, 1991) was applied to determine the “forms” of metals in the surface and sub-surface layers of the polluted soils. Some conclusions obtained from this work are believed to be important for better understanding the mechanisms of metal transformations under real, non-artificial field circumstances. Furthermore, such conclusions should be helpful in predicting the fate of heavy metals in the examined soils.

Since the 1980s there has been growing concern over environmental pollution in the areas affected by Cu metallurgy in the SW part of Poland (LGOM). Two Cu smelters “Legnica” and “Glogbw” have emitted into the atmospheare large amounts of metallurgical dusts containing heavy metals, in particular Cu and Pb. A yearly emission of these 2 metals in the early 1980s was as high as 2900 tons Cu and 3100 tons Pb (see Table 1). Dust precipitation has resulted in strong soil pollution in the vicinity of the smelters. Although the dust emissions from the smelters have been dramatically reduced in recent years. by over 10 times, the environmental problems arising from soil pollution are still of great importance. Total metal concentrations in the surface layers of the polluted soils have been measured and monitored for about 20 a (Kowaliriski et al., 1979; Szerszeti et al., 1991, Szersze6 et al., 1993), but there are still some unanswered questions concerning the processes of metal transformation, mobility and bioavailability as well as the long-term risk assessment. As it is the chemical forms of pollutants rather than their total concentrations in the soil that determines the potential risk of metal mobilization and transfer to other compartments of the environment (such as plants or underground water), the data on metal speciation would seem to be essential for any general conclusions. The main objective of this work was to investigate the chemical forms in which different metals, both of lithogenic and anthropogenic origin,

SAMPLING

AREA

Top- and sub-surface soil samples (depth: 5-15 cm and 3040 cm) were collected at 6 points situated in the area of the sanitary protection zone, at different distances from the Cu smelters “Legnica” and “Glogbw” (Fig. 1). The whole area around the smelters from where the soil samples were taken had been used as arable land until the late 1970s when the fields located close to the smelters were afforested. Conse35

A. Karc:zewska

36 Table

1. Selected data on the emissions from the Cu smelters, Mg/a

Smelter

Year

SOz

CO

Legnica

1980 1990 1994 1980 1990 1994

26,300 13,380 10,950 125,600 34,200 19,300

76,100 17,760 2800 238,800 102,700 2400

Glogow

Dust

Cu

Pb

14,460 962 1720 6070 32 17 145 5 12 14,400 1900 1390 2000 131 101 1230 73 51

quently, the soils have not been ploughed for many years, though, they have been limed in order to keep soil pH at a level high enough to avoid metal mobilization.

ANALYTICAL METHODS

The collected soil samples were air-dried, disaggregated in a porcelain mortar and sieved with a 2-mm stainless steel screen. The granulometric composition of the soils was determined using the Kohn pipette method. The soil pH was measured in 1 M KC1 at a soil:solution ratio of 1:2.5. Organic matter content was determined by a modified oxidometric Tiurin’s method involving the oxidation of soil organic C with a mixture of KzCrz07 and concentrated H2S04 followed by the titration of excess oxidant with Mohr’s salt in the presence of ortho-phenanthroline.

Cation exchange capacity (CEC) and exchangeable bases were determined in the NHdOAc extract (pH 7.0). Pseudo-total contents of 8 metals in soils were determined after aqua regia digestion (1 g soil was treated with 7.5 ml cont. HCl + 2.5 ml cont. HN03 overnight at room temperature and then boiled under reflux for 2-3 h). The following metals were examined: Fe, Al, Cr, Ni, Mn, Zn, Cu and Pb. Metal fractionation was carried out according to the Zeien and Bruemmer (1989, 1991) method, this being reported as the one which avoids the main analytical problems inherent to the other procedures (Zeien and Bruemmer, 1989; Karczewska et al.. 1994). The following fractions were separated and determined using DCP and GF-AAS techniques: (1) mobile; (2) exchangeable; (3) occluded in Mn oxides; (4) organically bound; (5) occluded in amorphous Fe oxides; (6) occluded in crystalline Fe oxides; (7) residual. The extractants used in the speciation, their concentrations and other methodological details are listed in the Table 2. The residual fraction was obtained with aqua regia. The sequential extraction was carried out in 2 replicates. The analytical precision of the total and sequential extraction was estimated by the standard error of analysis and was very good (SD
Fig. 1. Location of sampling points in the sanitary protection zones of Cu smelters: G, Glogow; L, Legnica.

37

Metal species distribution in top- and sub-soil

Table 2. Extractants used in sequential extraction according to Zeien and Bruemmer (1989) Extractant

Fraction

PH

1 M NH4NOs

1. Mobile (unspecifically adsorbed) 2. Exchangeable (specifically adsorbed) 3. Occluded in MnO, 4. Organically bound 5. Occluded in amorphous FeO, 6. Occluded in crystalline FeO, 7. Residual (structurally bound in some silicates)

The recovery rates, defined as the sum of the 7 fractions compared to a single digestion by aqua regia, were satisfactory for all elements (P>O.90) according to the Wilcoxon test.

RESULTS AND DISCUSSION General soil characteristics

The investigated soils differed in their types and properties and showed the granulometric compositions of sands and loams containing l-10% clay fraction. Reflecting the soil textures also soil sorption properties varied considerably. The CEC values ranged from 2.8 to 12.3 meq/lOO g in the surface layer (A) and from 1.0 to 12.2 meq/lOO g in the subsurface layer (B). All soils showed a neutral or slightly alkaline reaction due to the liming. The soil pH varied from 6.82 to 8.02. Selected typological, physical and chemical characteristics of the soils are shown in Table 3.

1M NH40Ac

6.00

1 M NHaOH-HCl + 1 M NH40Ac 0.025 M NH4-EDTA 0.2 M NH4-oxalate 0.2 M NH4-oxalate + 0.1 M ascorbic acid aqua regia

6.00 4.60 3.25 3.25

TOTAL METAL CONTENT Total metal concentrations differed strongly in both top- and sub-surface samples, depending apparently on the metal origin. This can be seen in the Fig. 2, which shows the total metal concentrations in 3 of the examined soils, differing significantly in clay contents (sandy, sandy loam and silty loam). Total contents of typically lithogenic metals (Al, Fe, Mn as well as Ni and Cr) appear to depend primarily on soil type and texture, particularly on the clay content of the soil, these metals were very low in sandy soils and much higher in soils rich in clay. Differences in concentration of these metals in top- and subsurface samples were small and were more evident only in the sandy soil which was characterized by a very low sorption capacity. However, the top-soil concentrations of metals originating from metallurgical sources (Cu, Pb and partly Zn) did not show any significant dependence on soil properties (such as texture) and reflected primarily the distance from the source and the direction related to the prevailing wind.

Table 3. General soil characteristics P

CEC

layer

sand

silt

clay

PH lMKC1

Corg

Location

Distance (km) Direction

(%)

(mval/l 00 g)

1 Zukowice 2 Bogomice 3 Legnica 4 Glogow 5 Bogomice 6 Legnica

2 SW 2.5 NE 2.5 W 0.5 5 2.5 NE 1.5 W

A B A B A B A B A B A B

59 83 93 97 30 28 63 92 88 96 42 40

34 13 5 2 64 62 31 5 6 2 48 51

7 4 2 1 6 10 6 3 6 2 10 91

7.36 6.83 8.02 7.93 6.97 7.01 6.42 6.70 7.82 7.76 6.48 6.51

1.05 0.34 0.37 0.05 1.04 0.49 1.31 0.26 0.53 0.11 1.17 0.52

8.41 4.55 2.86 1.oo 10.26 12.20 4.81 2.37 3.86 1.38 9.36 8.32

Soil texture (%)

Soil

38

A. Karczewska

Location: 2

B

A

1

A

0

A

0

A

AB

AB

AB

1

Location: 2

1

B

3

, A

B

, A

A6

AB

AB

AB

AB

AB

I B

80 70 @.Y 50 40 30 20 10 0 1

AB

AB

ABI/ I

I

,

500 40 303 a0 100 0

A

B

A

B

A

B

A

B

A

B

A

B

Fig. 2. Total amounts of metals in top- (A) and sub-surface (B) soil samples in soils differing in their textures: sand (Bogomice 2), sandy loam (Zukowice 1) and silty loam (Legnica 3).

The highest concentrations of Cu, Pb and Zn were found in the top-soil sample taken from point 4 (Glogow), situated at a distance of 0.5 km from the emission source. These concentrations were as follows: 1710 mg/kg Cu, 460 mg/kg Pb and 98 mg/kg Zn. In all profiles, metals of anthropogenic (metallurgical) origin showed high accumulation in the top-soil, while their concentrations in the sub-surface layers were much lower and differed from one point to another which seemed to depend vitally on the soil texture and clay content. The proportions between Cu, Pb (and Zn) concentrations in sub- and top-soil samples were

lowest in the sandy soil (Bogomice 2) and highest in the silty loam (Legnica 3). Cu and Pb concentrations in sub-surface layers of silty and loamy soils were significantly higher than the background concentrations in similar, unpolluted soils (Dudka, 1992; Kabata-Pendias and Pendias, 1993), whereas there was no evidence of Cu or Pb accumulation in sub-surface layers of the sandy soils (e.g. Bogomice 2). It seems likely that metal translocation from the surface layer to the deeper parts of soil or into the underground waters occured in the sandy soils due to the very poor sorption properties of their

Metal species distribution in top- and sub-soil

sub-surface layers. However, this result is not consistent with the commonly accepted thesis that liming should protect soils effectively against metal mobilization (Szerszen et al., 1991)

39

sub-surface samples. This probably results from the different degrees of weathering in the different soil horizons. The predominating fractions of lithogenic metals in the examined top- and sub-surface samples were residual and occluded in iron oxides, as shown below (average percentages of fractions are given in brackets): (1) Al fractions: 7 (78.5%) > 6 (13.3%) > 5 (5.6%) (2) Fe fractions: 6 (38.7%) and 7 (36.5%) > 5 (20.4%) (3) Cr fractions: 7 (56.8%) ~6 (25.2%) > 5 (13.9%) (4) Ni fractions: 6 (32.7%), 7 (30.1%) and 5 (24.2%) >4 (4.8%)

METAL SPECIATION Determining of the metal forms (species) in the topand sub-surface soil samples would seem to be of great significance when interpreting heavy metal fate and mobility in the soil profiles. The “mobile” fraction (1) is likely to reflect the actual concentration of metals in the soil solution. The exchangeable (2), occluded in MnO, (3) and organically bound (4) fractions might be mobilized in the short and medium term by changes in soil chemistry. The occluded in FeO, (5 and 6) and residual (7) fractions are expected to be relatively stable in well aerated soils due to the low solubility products of Fe oxides and silicates (McBride, 1989; Karczewska et al., 1994). The sequential extraction results showed significant differences between the groups of “lithogenic” and “anthropogenic” metals. The average contributions of all fractions, calculated separately for top- and subsoils, are presented in Table 4.

METALS OF METALLURGICAL ORIGIN: Cu AND Pb

The results for Cu and Pb fractionation were quite different from those of the lithogenic metals. Vital differences between top- and sub-surface soil layers were observed not only in the total concentrations of these metals but also in their fractional distribution. This was particularly apparent in the case of sandy soils (Bogomice 2 and 5, Glogow 4). It should be pointed out that potentially available and mobilizable Cu and Pb (“mobile” and “exchangeable” fractions) were high in top soils from these sites varying in the following ranges: (1) mobile Cu: 2.6-25.3% (average: 10.5%); (2) exchangeable Cu: 17.1-38.4% (average: 28.7%); and (1) mobile Pb: 0.2-6.4% (average: 1.3%); (2) exchangeable Pb: lO.l-38.4% (average: 24.7%). The highest amounts of mobile and exchangeable

TYPICAL LITI-IOGENIC METALS: Fe, Al, Cr, Ni In the case of the typical lithogenic metals similar speciation results were obtained for top- and subsurface samples. The small diference consisted only in slightly higher contributions of fraction 5 (metals occluded in the amorphous Fe oxides) and lower

contributions of fractions 6 and 7 (metals occluded in the crystalline Fe oxides and bound in silicate lattices) found in top-soil samples when compared with the

Table 4. Metal fractionation results: average fraction contributions calculated separately for topsurface (A) and sub-surface (B) soil samples

Metal Al Fe Cr Ni Mn Zn cu Pb

Horizon

Average total content @g/kg)

A B A B A B A B A B A B A B A B

6422 6780 8650 6840 9.39 9.35 7.03 8.09 313 294 75.8 30.5 596 45.8 198.5 28.7

Distribution among the fractions (%) I

2

3

4

5

6

7

0.0 0.0

0.0

0.0

0.1

0.0

0.0

0.1 0.8 1.3 2.7 4.3 7.6 5.2 10.0 2.4 10.5 1.6 1.3 0.3

0.1 0.6 0.0 2.7 2.0 6.3 3.0 20.2 6.0 28.7 27.1 24.7 3.4

0.2 0.8 A’:

2.5 2.1 3.8 26 3’0 2:4 4.9 4.6 4.3 3.8 5.4 5.8 26.5 25.8 29.4 28.9

6.2 4.7 22.7 15.8 17.8 7.5 29.0 16.3 27.3 13.8 10.6 12.7 10.3 8.8 13.1 30.8

13.5 13.1 37.0 42.1 24.9 25.1 28.6 39.4 8.1 8.1 21.6 23.2 5.81 14.9 3.5 10.0

77.7 79.8 35.7 38.1 52.8 63.7 30.3 29.7 9.0 9.7 24.7 39.9 2.0 13.7 3.0 8.1

0:l 1.9 3.6 37.4 56.4 7.6 10.0 11.1 17.3 25.1 18.5

A. Karczewska

40

Cu and Pb were found in strongly polluted sandy soils (locations 2, 4 and 5) in which fractions 1 and 2 together contributed more than 50% of total Cu and nearly 40% of total Pb. Table 5 illustrates the detailed results of Cu and Pb fractionation in selected top soils containing similar total amounts of Cu and Pb and varying considerably in clay content and CEC values. The dependence of fractionation results on soil texture can be easily seen from the table. Considerably higher amounts of mobile and exchangeable Cu and Pb are found in sandy soils showing that a risk of heavy metal mobilization from these soils still exists in spite of protective measures such as liming. High percentages of mobile Cu and Pb in polluted soils have already been reported in some studies confirming that anthropogenic metal input contributes to the potentially available metal pool (Ure et al., 1993; McBride, 1989) and is likely to move downward through the soil profile (Stokes, 1988). On the other hand, it has also been indicated in many works that metals of metallurgical origin, and particularly Pb, accumulate in the top-soil layer and cannot be mobilized if soil reaction remains neutral or slightly alkaline (Szerszen et al., 199 1) The contributions of mobile Cu and Pb in subsurface samples were much lower than those of the top soils (Table 6). Also exchangeable Pb in the subsurface samples was much lower than in the top layers. Relative stability and immobilization of Cu and Pb in soils might account for such results. However, the author of this study would suggest that Cu and Pb mobilization and translocation downward could take place in sandy soils but due to the poor CEC the leached metals will not accumulate in the sub-surface layer and migrate to the deeper soil horizons and underground water. This hypothesis seems to be supported by the fact that total Cu and Pb concentrations in the top layers of sandy soils were lower than in the surrounding more clay-rich soils, at lesser and greater distances from the smelter (Szerszen et al., 1993). The problem of metal mobility in such polluted

soils requires further research and the hypothesis of metal mobilization should be examined thoroughly. Comprehensive laboratory and pot experiments dealing with this problem are on going but at this stage no further insight into the processes of metal transformation is available.

OTHER METALS: Zn AND Mn

Total analysis and fractionation of Zn and Mn showed that their behaviour in soils was between those of the 2 groups described above. Manganese seems to be more alike the other lithogenic metals and this similarity shows particularly in the small difference of total Mn content and its speciation between top- and sub-surface soils. However, the amounts of Mn in the mobile and exchangeable fractions were quite high, especially in sandy soils, and this feature was not typical of other lithogenic metals. The results obtained for Zn showed the greater similarity of this metal to the ones of metallurgic origin: Cu and Pb; although total Zn concentrations in the examined samples were only slightly higher than background concentrations in similar unpolluted soils (Dudka, 1992; Kabata-Pendias and Pendias, 1993). Contributions of the mobile and exchangeable fractions of Zn in top soils were high (average values were: 9.9% and 20.2%, respectively). The highest relative amounts of these 2 fractions occured in sandy soils. Contributions of mobile and exchangeable fractions of Zn in sub-surface soils were much lower than in top soils (with average values of 2.4% and 6.0%). In sandy soils these 2 fractions were practically absent. This could be easily explained by the relatively high mobility of Zn in the soil environment (McBride, 1989; Hornburg and Bruemmer, 1993) which can result in this metal being leached into underground waters and not being concentrated in the sub-surface soil layer.

Table 5. Cu and Pb fractionation in top-soil samples (A layer) in selected soils Sampling point

@j2Cu 4 6 3

Soil texture

Total content (mgkg)

Distribution among the fractions (%)

1

2

3

4

5

6

7

Sand Sandy loam Silty loam Loam

426 1710 519 240

14.0 25.3 2.6 3.3

38.4 34.4 20.4 17.1

10.3 7.7 15.2 9.5

18.2 13.2 30.0 40.5

9.3 8.5 14.8 12.2

4.7 3.4 8.1 8.8

5.1 7.5 18.9 8.6

Sand Sandy loam Silty loam Loam

149 460 233 128

0.5 8::

38.4 36.8 16.4 10.1

24.3 19.5 35.3 21.4

23.0 22.4 30.6 39.2

9.8 9.0 9.8 20.5

1.2 3.3 3.8 5.2

2.8 2.6 3.8 13.4

(b) Pb 2 4 6 3

0.2

Metal species distribution in top- and sub-soil

41

Table 6. Cu and Pb fractionation in subsurface samples (B layer) in selected soils Sampling point

Soil texture

Total content (mg/kg)

Distribution among the fractions (%) -

1

(a) Cu 2 3

Sand Loam

1.4 65

0.0 2.5

(b) Pb 2 3

Sand Loam

11 42

0.61 0.6

OTHER COMMENTS

The limitations in the interpretation of the sequential extraction results are still open to question. High contributions of “mobile” Cu and Pb fractions seem to be overestimated, especially at neutral or alkali pH, when heavy metals are believed to be immobile. On the other hand, the fate of metals in soils depends strongly on the soil moisture conditions and soil to soil solution equilibrium, so the actual amount of metals mobilized might be far below their potential mobility determined in fraction 1, i.e. in 1 M NHdNOs at low soil to soil solution ratio (1:25 w/v). Undoubtedly, this problem requires further examination.

2

3

4

5

6

7

44.2 22.4

28.4 11.7

2.1 31.3

3.1 10.6

22.2 14.9

27.6 6.6

12.6 24.0

23.1 33.4

31.6 21.3

12.6 10.0

15.7 2.8

3.21 2.3

Acknou~ledgements-Chemical analyses involved in this work were partly carried out during my stay at the Institute of Soil Science at Vienna Agricultural University and were financially supported within the Project BU16. I am grateful to the Institute staff for their kind help as well as for technical and financial assistance. In particular I should like to thank Dr W. Wenzel for most helpful discussion and comments, and to MS R. Mavrodieva for analytical cooperation. Editorial handling: Dr Ron Fuge.

REFERENCES Dudka S. (1992) Factor analysis of total element concentrations in surface soils of Poland. Sci. Total Environ. 121, 39-52.

CONCLUSIONS

(1) Eight metals involved in this research differed in their origin, total concentrations and behaviour in soils, which was reflected by their chemical forms determined by sequential extraction. (2) Metal speciation was found to depend strongly both on metal origin and soil properties (in particular on clay and organic matter content). The dependence of metal behaviour on pH could not be seen in this research for all soils were neutral or slightly alkaline. (3) The examined metals could be divided into 3 groups: typically anthropogenic (Al, Fe, Cr, Ni), typically anthropogenic (Cu, Pb) and other metals of mixed character (Zn, Mn). (4) The chemical forms of metals were quite different for each group. Lithogenic metals occured primarily in relatively stable fractions: residual and occluded in Fe oxides (both crystalline and amorphous), whereas metals originating from metallurgical dusts showed very high contributions of mobile and exchangeable fractions. Total amounts of these metals were much higher in top-soil than in sub-soil. (5) According to the results of this research, heavy metals of anthropogenic origin can be expected to be easily leached from the surface layer of polluted soils, especially sandy ones, even if soil liming is performed. However, this hypothesis should be verified in further research.

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,A. and Pendias H. (1993) Biogeochemia Pierwiastkdw Sladowych (in Polish). PWN, Warsaw.

Kabata-Pendias

Karczewska A., Wenzel W. W. and Mavrodieva R. (1994) Effect of metal sources and indigenous soil pH on metal fractions in soil. Environ. Geochem. Health, in press. Kowalinski S., Drozd J. and Licznar M. (1979) The influence of the distance of a copper smelter on the physico-chemical properties of soils. Polish Soil Sci. 12, 1. McBride M. B. (1989): Reaction controlling heavy metal solubility in soils. In Advances in Soil Science, Vol. 10, pp. l-56. Springer, New York. Quevauviller. Ph., Rauret G. and Griepink B. (1993) Single and sequential extraction in sediments and soils. Conclusions of the Workshop. In Workshop on Sequential Extraction in Sediments and Soils (ed. G. Rauret), Selected Papers. Int. J. Environ. Anal. Chem. (special issue) 51, 231-235. Stokes P. (1988) Lead in soils: Canada case studies and perspectives. In Lead in Soil (B.E. Davies), 3 15 pp. Wixon B.G., Northwood. Szerszen L., Chodak T. and Karczewska A. (1993) Areal, profile and time differentiation of heavy metal content in soils in the vicinity of copper smelters in LGOM, Poland. In Integrated Soil and Sediment Research. A Basis for Proper Protection (eds H. J. P. Eijsackers and T. Hamers), pp. 279-281. Kluwer, Dordrecht. Szerszen L., Karczewska A., Roszyk E. and Chodak T. (1991) Distribution of Cu, Pb and Zn in profiles of soils adjoining copper metallurgic plants (in Polish). Rocz. Glrbom. 42(3/4), 199-206

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tionen zur Bestimmung von Schwermetallbindungsformen in Boeden. Mitt. Dtsch. Bodetikundl. Gesellsch. 5911, 505-510 Zeien H. and Bruemmer G. W. (1991) Ermitthmg der Mobilitaet und Bindungsformen von Schwermetallen in Boeden mittels sequentieller Extraktionen. Mirr. Drsch. Bodenkundl. Gesellsch. 66/l, 43942