ENRICHMENT OF Cu, Ni, Zn, Pb AND As IN AN OMBROTROPHIC PEAT BOG NEAR A Cu-Ni SMELTER IN SW FINLAND

 

Nieminen, T.M. 1 and Shotyk W.2

1Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, e-mail tiina.nieminen@metla.fi

2Geological Institute, University of Berne, Balzerstrasse 1, CH-3012, Berne, Switzerland

 

 

 

ABSTRACT

 

The accumulation of selected trace metals in the surface peat layer  of an ombrotrophic bog  2.4 km from a Cu-Ni smelter at Harjavalta, Finland was studied using a peat core. A reference core was taken from an unpolluted ombrotrophic bog at Hietajärvi in Finland. Element concentrations were analysed  using EMMA from 1 cm slices, and enrichment factors (EF) were calculated. The accumulated amounts of both Cu and Ni in Harjavalta peat bog are extremely high compared to the Hietajärvi site. Somewhat surprisingly only the 6 cm-surface-peat Pb EF values were higher in Harjavalta compared to Hietajärvi. The variation in EF of the Harjavalta peat core with respect to depth shows two patterns: Cu and Pb are rather similar, as are Ni, Zn, and As. The vertical gradient in  Harjavalta Cu EF  suggests that Cu supplied to the peat by atmospheric deposition is very well preserved by the bog.

 

 

 

INTRODUCTION

 

Text Box: Table 1. Estimated particulate emissions from Harjavalta smelter in tonnes per 5-year-period. Period dust from Cu production dust from Ni production 1945-1949 2388 0 1950-1954 2671 0 1955-1959 3908 10 1960-1964 5105 870 1965-1969 2379 780 1970-1974 951 1787 1975-1979 1182 2708 1980-1984 1452 3064

Heavy metals derived from anthropogenic sources have major impacts on the global and regional cycles of most trace elements (Nriagu and Pacyna, 1988). The capacity of ecosystems to bind deposited elements varies according to the type of ecosystem and the element in concern. The gradual movement of  toxic metals vertically downward in soil profiles pose a potential threat to groundwater quality. Peat cores taken from ombrotrophic bogs have been succesfully used to reconstruct historical record of atmospheric metal deposition, especially for Pb (e.g. Shotyk, 1995; Shotyk et al., 1997 and Shotyk et al., 1998).  However, peat cores can also serve as an excellent tool in studying the mobility of different trace elements in organic soil. In this study  trace element concentrations of a peat core taken from  a polluted ombrotrophic  bog near a Cu-Ni smelter were compared with smelters emission records and with element concentrations of a reference peat core taken from an unpolluted background site.

The Harjavalta copper smelter started operating in 1945 and the nickel smelter in 1959. Heavy metals and arsenic are emitted as components of  dust emissions.  Particulate emissions during 1945-1984 were estimated on the basis of dust emitted  per tonne of metal produced from figures supplied by the smelter company (Table 1). Monitoring of emissions was started in 1985 by the smelter company (Table 2.)

 

Text Box: Table 2. Emissions from Harjavalta smelter in tonnes per year during 1985-1999 (As monitoring started in 1993). Year Dust Cu Ni Zn Pb As 1985 1100 98 47 216 55 1986 1200 126 46 232 60 1987 1800 140 96 162 94 1988 1000 104 45 103 48 1989 1000 80 33 190 70 1990 960 80 31 160 80 1991 640 80 14 90 45 1992 280 60 10 12 9 1993 250 50 7 13 6 11.0 1994 190 40 6 6 3 5.0 1995 70 17 1.4 1.7 0.5 0.2 1996 195 49 1.2 5.3 1.9 4.2 1997 360 70 3 14 4 10.0 1998 132 23 1.7 6.1 2.4 10.1 1999 48 6 0.8 4.2 1.0 1.8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

METHODS


A peat core (15 cm depth x 5 cm x 5 cm) was taken from the surface layer of an ombrotrophic bog 2.4 km SW-W from a Cu-Ni smelter at Harjavalta,  southwestern Finland. A reference core was taken from an unpolluted ombrotrophic bog at Hietajärvi in eastern Finland where there are no local emission sources. The cores were frozen and cut into 1 cm slices using stainless steel band saw at the University of Berne. All peat samples were dried at 105 oC in acid-washed Teflon bowls, and macerated in a centrifugal mill equipped with a Ti rotor and 0.25 mm Ti sieve. The milling was carried out in a Class 100 laminar flow clean air cabinet to prevent possible contamination of the peat samples by lab dust. Selected trace elements were measured using the Energy-dispersive Miniprobe Multielement Analyzer (EMMA) at EMMA Analytical Inc., Elmvale, Ontario, Canada. The instrument was calibrated using certified standard reference plant materials.

 

In order to separate the natural variations in element concentrations with depth from changes due to smelter derived inputs, M/Ti ratios were calculated for individual samples and then normalized to the metal/Ti ratio for the Earth`s crust using the data of Wedepohl (1995). The calculated enrichment factors (EF) show the extent of the changes in element abundances in the profile relative to crustal values.

RESULTS AND DISCUSSION

 

The variation in EF of the Harjavalta peat core with respect to depth shows two patterns: Cu and Pb are rather similar, as are Ni, Zn, and As (Table 3). The vertical gradient in  Harjavalta Cu EF (from 4420 x to 45 x over a distance of only 9 cm) suggests that Cu supplied to the peat by atmospheric deposition is very well preserved by the bog. The relatively high Ni values compared to Cu  in depths more than 7-8 cm indicates post-depositional migration, since the emissions of Ni from the smelter started 15 years later than those of Cu (Table 1). In addition, the fact that the peat Ni values are consistently much lower than the Cu values, although  Ni production induced dust emissions during 1970-1985 were superior to Cu emissions, gives further evidence of greater Ni mobility. However, the transportation distance of Ni containing particles may be larger than that of Cu containing particles, and hence lead to relatively lower Ni deposition in the immediate vicinity of the smelter.

 

The accumulated amounts of both Cu and Ni in Harjavalta peat bog are extremely high. The Harjavalta Cu EF values are hundreds of  times  greater than those of Hietajärvi background site, and Ni values correspondingly tens of  times higher. Derome (2000) reported quite comparable enrichment for  the organic layer of forest soil in the vicinity of the same Harjavalta smelter. The Cu concentrations of polluted forest humus were 200-800 times higher than the average Cu value for the same forest type. Ni concentrations were correspondingly 40-90 times higher than the average value. 

 

Text Box: Table 3. The metal enrichment factors (EF) and concentrations (ppm) of a peat core from an ombrotrophic bog near a Cu-Ni smelter in Harjavalta, SW Finland. depth, cm Cu EF Cu ppm Ni EF Ni ppm Zn EF Zn ppm Pb EF Pb ppm As EF As ppm 1 604 3528 69 913 33 500 59 204 153 58 2 971 4384 85 865 47 559 49 131 138 40 3 3056 4524 195 652 139 537 93 82 259 25 4 3697 4497 197 540 162 515 94 68 242 19 5 4420 4659 243 578 216 594 100 63 248 17 6 3036 3233 248 595 247 688 68 43 243 17 7 1309 1092 301 567 311 678 42 21 298 16 8 311 349 209 529 231 677 25 17 209 15 9 135 158 173 459 203 624 21 15 213 16 10 102 136 160 482 203 707 28 23 192 17 11 145 107 218 365 324 626 40 18 313 15 12 131 100 187 321 290 575 52 24 305 15 13 62 61 127 286 210 545 31 19 218 14 14 45 46 112 260 213 574 35 22 222 15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are no clear gradients in the vertical distribution of  EF for Zn and As, but the clearly higher  values in Harjavalta peat compared to Hietajärvi peat indicate accumulation of smelter induced Zn and As. However, the Zn values of Harjavalta peat are surprisingly low when compared to quite high Zn emissions (Table 2), which suggests Zn mobility in the peat.

Veijalainen (1998) has reported interesting results from an old ore-prospecting experiment in Alkkia, SW Finland.  Very high doses of Cu, Ni and Zn were applied on an ombrotrophic peat  bog in July 1962.  In 1990 the surface peat (0-20 cm) still contained 93% of the applied  Cu dose (400 kg/ha), but in Ni plots the surface peat contained only 63%  of the applied Ni dose (400 kg/ha). The corresponding Zn retention rate was even lower, only 47%.

 

The vertical gradient of Harjavalta peat Pb EF follows quite closely the same pattern as Cu, although the EF –values are considerably smaller. In fact only the 6 cm-surface- peat Pb EF values were higher than those of the background peat core from Hietajärvi. The Pb enrichment of forest humus in the vicinity of the smelter varied from 3 to 8 according to Derome (2000). 

 

Text Box: Table 4. The metal enrichment factors (EF) and concentrations of a peat core from an unpolluted ombrotrophic bog in Hietajärvi, eastern Finland. depth, cm Cu EF Cu ppm Ni EF Ni ppm Zn EF Zn ppm Pb EF Pb ppm As EF As ppm 1 14 8 3 4 33 50 12 4 0 0 2 7 6 2 3 25 53 14 7 0 0 3 7 6 2 5 24 53 13 6 0 0 4 10 7 4 6 35 63 20 8 32 1.4 5 13 6 4 5 65 80 46 13 117 3.5 6 10 6 5 6 53 76 50 16 55 1.9 7 13 6 0 0 66 78 62 17 74 2.2 8 5 3 4 5 54 78 52 17 74 2.6 9 6 3 8 9 67 84 50 14 79 2.5 10 9 5 12 14 56 78 54 18 108 3.8 11 8 8 5 10 29 71 32 18 63 3.9 12 11 6 7 9 46 70 53 19 49 1.9 13 10 8 0 0 33 69 38 18 88 4.6 14 9 5 5 7 41 60 55 19 96 3.5 15 10 7 5 8 38 68 52 21 73 3.2 16 8 4 6 7 43 61 64 20 150 5.2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES:

 

Derome, J. (2000), Finnish Forest Research Institute, Research Papers 769. Helsinki. Hakapaino.

Nriagu, J.O., Pacyna, J.M. (1988), Nature 333:134-139.

Shotyk, W. (1995), Water, Air, and soil Pollution 90:375-405

Shotyk, W., Appleby, P.G., Cheburkin, A.K., Frankhauser, A., Kramers, J-D. (1997), Water, Air, and soil Pollution 100:297-310.

Shotyk, W., Weiss, D., Appleby, P.G., Cheburkin, A.K. Frei, R., Gloor, M. Kramers, J.D., Reese, S., van der Knaap, W.O. (1998), Science 281:1635-1640.

Veijalainen, H. (1998), Water, Air, and soil Pollution 107:367-391.

Wedepohl, K.H. (1995), The composition of the continental crust. Geochim.

Cosmochim. Acta 59:1217-1232.