arsenic in contaminated soil and river sediment

Fresenius J Anal Chem (1994) 350:49-53 Fresenius' Joumal of

© Springer-Verlag 1994

Arsenic in contaminated soil and river sediment

G. Bombach, A. Pierra, W. Klemm

Freiberg University of Mining and Technology, Institute of Mineralogy, Geochemistry and Ore Deposits, Brennhausgasse 14, D-09596 Freiberg, Germany

Received: 5 June 1993/Accepted: 17 January 1994

Abstract. Different areas in the Erzgebirge mountains are contaminated by high arsenic concentration which is caused by the occurrence of ore and industrial sources. The study showed clearly a high concentration of arsenic in the surface and under soil (A and B horizons) in the Freiberg district. The distribution of the arsenic concentration in the area, the content of water soluble arsenic, the several oxidation states (As 3+, As 5+) and the bond- ing types have been analyzed.

Introduction

For over 800 years, various ores have been mined in the Freiberg and similar ore districts in the Erzgebirge Moun- tains. Different metallurgical processes have produced sil- ver, tin, zinc, lead and uranium. The association of minerals of arsenic with (or the high concentration of arsenic in) the ore minerals caused both natural and industrial contamination of soils and river sediments in different districts of the Erzgebirge; metallurgical processes have been carried out for a long period. The area around Freiberg is one of the main districts with a particularly in- tensive contamination. Attempts were made to character- ize the situation of arsenic contamination by an analysis of the total arsenic content in soil distributed over the area, by determination of the water soluble part of the arsenic concentration and by speciation.

Experimental

Analytical determination of the arsenic concentration was performed after dissolving the samples in a mixture of hydrochloric and nitric acid (DIN 38414) using atomic absorption spectrometry and the hydride technique. In the first stage, a AAS-1 (Carl Zeiss Jena) with self-made hydride equipment [1] was used. Later a ZL 4100 (Perkin Elmer) with FIAS 200 was employed.

Correspondence to: W. Klemm

Determination of the total arsenic concentration

The formation of AsH3 was performed in a solution with pH 6 (addition of corresponding volume of HC1 to the sample solution) with a solution of NaBH 4 (2%) in a nitrogen gas stream. The temperature of the quartz absorption tube was 1000°C. In the second variant, 3 ml HCI (conc.) and 1 m lK J solution (5%) were added for prereduction [2]. After 2 h, hydride formation was carried out with NaBH 4 solution [0,2%).

The absorption was measured at 193.7 nm. The practical detection limit was 1 ~tg/1 for both procedures.

Determination of A J +

The determination of As 3+ was performed after addition of a buffer solution (Na acetate/acetic acid, pH 5) with NaBH4 solution (2%) in the same way as the determination of the total arsenic concentration. For the application of the flow injection system, the reduction was carried out with ascorbic acid (10 g/l) and NaBH4 solution.

Practical detection limits were 1 mg/1 and 10 ~tg/1 re- spectively.

Speciation using a sequential leaching procedure

The speciation of arsenic in soils and sediments was carried out during investigations on mobilization using the following sequential leaching procedure [2]:

arsenic fraction solution, procedure conditions

1. water soluble HzO bidistilled; 2. exchangeable 1 mol/1 NH 4 acetate, pH 7,

1 : 20 (sample : solution), 20°C, 5 h shaking;

3. carbonate 1 mol/1 Na acetate, pH 5, 1:20, 20°C, 5h;

4. easily reducible 0.1 tool/1, hydroxylamine hy- drochloride, 0.1 mol/1 HNO3, pH2 , 1 : 100, 12h;

5. moderately reducible 0.2 mol/1 NH 4 oxalate,

50 '\

6. organic matter and sulfide

7. residual mineral

0.2 mol/1 oxalic acid, pH 3, 1 : 100, 24 h; H202 (0.30 g/g), HNO3, pH 2, 85 °C, NH 4 acetate (1 mol/1), 24 h; HF/HC10+.

Analyses of water soluble fraction

The sample (5 g) was shaken with 50 ml H20 at 20 °C for a definite time. In the supernatant solution pH, Eh (--redox potential), As(total) and As 3+ were analyzed after filtration through a 0.45 gm filter.

Resul t s

Table 1 lists the results of analysis of arsenic in the A and B horizons in the Freiberg district. The results differenti-

Table 1. Arsenic content in soil of A and B horizon depending on agriculture

Forest Field Meadow Average

A horizon ,R (mg/kg) 116 71.7 54.8 70.6 n 24 62 95 181

B horizon (mg/kg) 47.8 27 35.4 36.5

n 24 62 95 181

ate between several areas with different cultivation. The dominance of industrial contamination by air transport is documented by the significantly higher concentration

o f arsenic in the samples of the A horizon in all sample types. Figure 1 illustrates the distribution of the concen-

5 6 5 2 -

\

5644 k

J

5640

5636 4584

@

_ _ £ L i L I l i _ _ ' . . . . . 4588 4592 4596 4600 4604

Fig. 1. Distribution of arsenic in soil (A horizon) in the district of Freiberg, data in mg/kg. Sampling was per~rmed in a screening distance of 2×2km

tration of arsenic in the A horizon of the area. Higher concentrations of arsenic were detected in the direction nor th /nor th east. This is the dominant direction of the wind.

The highest concentration was found north of the tin and lead plant. Figure 2 shows an east-west traverse and documents the influence of the tin and lead plant. The concentration of arsenic in the sediments of the Freiberger Mulde river also reflects the high concentration of arsenic in this area (Fig. 3), which reaches a geoindex (after Mil ler [41) between 6 and 7. This means extreme contamination.

The pH-reaction of soil suspensions varies between 5.5 and 7; only in some stretches of forest does the pH change to 4.5.

The portion of the total arsenic concentration which can be dissolved in water is low and amounts to 0.2% in areas without contamination and is between 1.5% and 5.9% in highly contaminated areas. The arsenic concentration in the soil water can reach more than 1 mg/1 as detected by model tests. The proportion of As 3+ in the total water soluble arsenic content amounts to roughly 10%. Figure 4 shows the changes of the parameters, arsenic concentration, arsenic 3 +, pH, and Eh during tests of solubility with a highly contaminated soil sample (650 mg/kg As). As demonstrated by Fig. 5, the solubility

51

of the arsenic content in the soil increases at pH conditions <2. In highly contaminated samples, the proportion of dissolved arsenic can reach more than 50%. This fact can be explained by the speciation of arsenic. Studies of speciation using sequential leaching procedures [3] in- dicate that the main proportion of arsenic is associated with the easily or moderately reducible metal fraction in soils and sediments (Fig. 6). This fraction is obviously dissolved at pH < 2. Other elements which are also associated with this fraction can also be detected in these solutions.

Conclusion

The very high contamination of soil and river sediment with arsenic in the Freiberg district has mainly been caused by several metallurgical plants for long periods. Over large highly contaminated areas, the concentration of arsenic exceeds 100 mg/kg and reaches a maximum of 1200mg/kg. The water soluble fraction of arsenic amounts to 0.2% of the total content in areas without contamination and 1.5 to 5.9% in contaminated samples. The sediment in the Freiberger Mulde river also contains a very high concentration of arsenic. The geoindex is 7 (i.e. extreme contamination). The soil solutions can con-

1400 'l

1200 -I

As[mg/kg ]

Hilbersdoff

800

600

400 Freiberg Conradsdoff

Ol~rihOnau / S ~ ~

0 . . . . i" I ' i I

XVll XXVll XX XXl XXX XXXl II X Xl Xll

Fig. 2. Concentration of arsenic (mg/kg) in soil in a west - east traverse; [] A horizon, + B horizon; further positions: XVII - Franken- stein, XXVII - Wegefarth (railway station), XXI - Kleinschirma; XXX - Freiberg (Wasserberg), XXXI - Freiberg (metallurgical plant), X - Niederbobritsch, XI - between Niederbobritsch and Colmnitz

52

re/- ~

.L 1. + 1 + % - ~ . ~ + ~

~ o

t ,~ -~ l

L----J 2

nTrr~ 3

F-Y~4

~ 5

~ 6

m 7

s ,

C,~emnitz

I

~ / ) ,, h

\ N_ \

~+ +~

'i

i /

i

/

/

Frelberg

l / \

. . f

Fig. 3. Geo- index for arsenic in sed iments of the Freiberger M u l d e river;

Igeo = log 2 Csample/1.5XCstandard, 0 -- no con tamina t ion ; 1 , no to modera te con tamina t ion ; 2 - modera te con tamina t ion ; 3 - modera te

to high con tamina t ion ; 4 - high con tamina t ion ; 5 - high to excessive

con tamina tu ion , 6 - excessive con tamina t ion , 7 - extreme con t amina - tion, - - - no da ta

[pg/I) 1600

E h [V]

1400

1200

1000

900

600

400

200

~ / / ~ 2 6

/~ ,,

f / /

! /

.g 7 ~.,..." 0.17

pH 8.5

8

7,5

7

8.5

S.S

0 f I I I I I I I ' I 4 . 5

o 20 40 60 so 100 120 140 160 100 200

t ime [hi

[ m ~ A S ' o ~ 1 - - I . - A s ( I l l ) x p H E h J 1 10

Fig. 4. Results o f solubility studies in contaminated sample; change of concentration As (total), As (III), Eh, and pH

As (%-total) 60

50

4O

30 [ ~ sample Ilia i • +" sarnpe XX/a

20

10

0 I - l . . . . ~ . . . . I . . . . t . . . . . . . . . . . . . . . . .

0,5 1 2 3 4 5 6 pH

Fig. 5. Solubility of arsenic in dependence on pH in the solution for a soil sample with ( I ) and without contamination (+)

53

100%

80%

60%

40%

20%

0%

m

m , IIIIIIIIIIIII1!"

I II

E 7

I s

D5

I 3

III Fig. 6. Speciation of arsenic using sequential leaching procedure, I - braunerde; II - riverside soil; I I I - river sediment; numbers on the symbols correspond with the leaching scheme in the text: 3 - carbonate-associated metal fraction; 4 - easily reducible iron oxyhydrate-associated metal fraction; 5 - moderately reducible iron and manganese oxyhydrate-associated metal fraction; 6 - organic matter- and sulfide- associated metal fraction; 7 - residual mineral associated

ta in m o r e t h a n 1 rag/1 arsenic as was d e m o n s t r a t e d by test s tudies . T h e m a i n p r o p o r t i o n o f arsenic is a s soc ia ted w i t h the eas i ly or m o d e r a t e l y reduc ib le m e t a l fract ion in soi ls a n d s ed iment s .

References

1. Bombach H, Luft B, Mohr E (1984) Neue Htitte 29:233-236 2. Guo T, Erler W, Schulze H, Application paper, Nr. 5.2 D, Perkin

Elmer 3. Salomons S, F6rstner U (1984) Metals in hydrocycle, Springer, Berlin

Heidelberg New York 4. Mtiller G (1981) Chemiker Ztg 105:157-164

arsenic in contaminated soil and river sediment

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