Polycyclic aromatic hydrocarbons in Norwegian forest soils: Impact of long range atmospheric transport

EnvironmentalPollution,Vol. 92, No.

3, pp. 275-280, 1996 Copyright © 1996 Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0269-7491/96 $15.00 + 0.00

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0269-7491(95)00114-X

POLYCYCLIC AROMATIC H Y D R O C A R B O N S IN N O R W E G I A N FOREST SOILS: IMPACT OF LONG R A N G E ATMOSPHERIC TRANSPORT Eli Aamot,* Eiliv Steinnes & Rudolf Schmid Department of Chemistry, University of Trondheim, A VH, N-7055 Dragvoll, Norway

(Received 8 August 1994; accepted 20 November 1995)

Abstract Levels of nine selected polycyclic aromatic hydrocarbons, PAHs, in surface soils from areas in southern and central Norway are presented. Levels in central Norway are generally low, while the southern Norway soils are about ten-fold higher with respect to 4 and 5 ring PAHs. Comparison with air quality data indicates long-range atmospheric transport to be the major source of the excess 4 and 5 ring PAHs in the south. Analyses of peat cores from ombrotrophic bogs support this assumption, and these provide a potentially useful approach for temporal studies of atmospheric P A H deposition. Analytical data .['or naphthalene in soils depend very much on the sampling and storage of the samples before analysis. Copyright © 1996 Published by Elsevier Science Ltd

range atmospheric transport. In a previous work mainly aimed at studying soil contamination with PAHs near local industrial pollution sources, some data indicated that long-range transport might be a significant source also for PAHs in natural soils of southern Norway (Vogt et al., 1987). The purpose of the present work was to study background levels of PAHs in Norwegian forest soils and attempt to identify possible contributions from long-range transport.

MATERIALS AND METHODS Samples Surface soils were collected in forested areas of southern and central Norway, the locations of which are shown in Fig. 1. In addition peat samples from two ombrotrophic bogs in southern Norway were collected at different depths to study possible temporal trends. The sampling sites were selected in a way to avoid significant interference from local sources (main roads, industries, urban areas). The sampling procedure for the forest soils depended on the soil type concerned. For podsols the samples were taken at about 2-5 cm depth in the A0 horizon. In one of the areas (Birkenes) a second sample at 5-10 cm depth was collected if the humus layer was sufficiently thick. In the case of brown earth soils, samples were collected in the upper 1-2 cm of the soil profile. In the subsequent text the surface soils will be denoted 0-5 cm. The samples were transported to the laboratory in polyethylene bags, dried at 25°C and repacked in cotton bags. Prior to extraction, the soils were disaggregated with a wood club while still in the closed bag, and sieved through a 2 mm mesh sieve. For each area, ten individual samples were collected. However, at the locations along the valley Setesdalen, only three samples from each location were collected.

INTRODUCTION When polycyclic aromatic hydrocarbons, PAHs, were first identified in surface soils from rural areas (Blumer, 1961), they were thought to be the result of natural processes in the soil. More recently it has become evident that fossil fuel burning is a very significant source of PAHs in soils. Most of the numerous studies (Edwards, 1983) of PAH concentrations in soils, however, deal with agricultural soils, or with forest soils near local sources. Investigations of natural sources located far from regions of major source of air pollutants have been scarce, and in boreal forest almost nonexistent. The southern part of Norway is considerably exposed to air pollutants derived from other parts of Europe, as documented for acidic compounds (Overrein et al., 1980), heavy metals (Hanssen et al., 1980) and PAHs (Lunde & Bjorseth, 1977). In the case of heavy metals this has led to a substantial contamination of natural surface soils in southern Norway (Allen & Steinnes, 1980; Steinnes et al., 1989), e.g. for Pb the present background level in surface soils in southernmost Norway is ten-fold higher than in more northerly parts of the country that receive only small contributions from long-

Analysis The procedures used for extraction, clean-up and determinations of PAHs in the soils are described in detail elsewhere (Aamot et aL, 1987), and are dealt with only very briefly here. About 20 g of soil was extracted twice by ultrasonic extraction for 30min in 150ml of

*To whom correspondence should be addressed. Present address: Statoil, Postuttak, N-7004 Trondheim, Norway. 275

276

E. A a m o t et al.

~

Kl~ebu Holonda

x : Ombrotrophic bog O: Soil sampling areas Setesdal Gyl ~kenes~ Lyngdal Fig. 1. Sampling locations for the present work.

dichloromethane. Internal standards, 3,6-dimethylphenanthrene and 1,1-binaphthyl, were added to the solvent prior to extraction. The extracts were filtered and the volumes reduced to about 10ml using a Biichi rotavapor and further to 1 ml under a gentle stream of nitrogen. The extracts were then diluted with hexane and an initial clean-up by liquid-liquid partitioning with dimethylformamide, hexane and water was performed. A further clean-up of the extracts on a silica high performance column (Supelcosil LC-SI 5m, 250x4.6mm) was performed where the PAH fraction was eluted with hexane. The quantitative analyses were performed by combined gas chromatography-mass spectrometry (GC/MS) in the Selected Ion Monitoring (SIM) mode using a DB5 column (0.25mm i.d., length 25m, film thickness 0.25#m). The molecular ions of each PAH were monitored and used for quantification. The recovery of PAHs for the clean-up steps were in the range 79-90%, determined by spiking a portion of DCM with a solution of an individual PAH. The recovery of PAHs from soil obtained using ultrasonic extraction was comparable to the recovery obtained with soxhlet extraction (Aamot et al., 1987). For each soil sample four replicates were analysed unless

otherwise stated. The nine PAHs monitored were naphthalene, biphenyl, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene/triphenylene and benzo(a)pyrene. For each of them a relative response factor was determined and used for quantification.

RESULTS AND DISCUSSION PAH concentrations in soils The complete data set for individual PAHs in 0-5 cm soils from two forest areas in southern Norway (Birkenes and Lyngdal) and one in Central Norway (Kl~ebu/Holonda) is given in Table I. In Table 2 median values for these three areas are presented along with the data for the 5-10cm humus layer at Birkenes. Individual results from peat samples taken at various depths in two ombrotrophic bogs in Southern Norway (cf. Fig. 1) are shown in Table 3. The data exhibited in Table 4 are from a gradient study, where 0-5 cm samples were taken at three sites in four locations along a valley (Setesdal) running in the N-S direction which coincides with the general gradient for pollutants from

P A i l s in Norwegian forest soils

277

Table 1. PAH data from Norwegian forest soils (0-5 cm): ~g kg-I dry weight Site

Naph

Biphenyl

Acena

Fluorene

Phen

A2 A3 A5 A7 A8 A10 A4 A6 A9 All

Fluora

Pyrene

Chrysene

B(a)P

41 29 37 47 38 37 17 7 51 34

24 24 11 31 29 25 13 <5 28 36

10 21 12 5 5 15 9 <5 9 7

18 18 9 17 17 9 6 <5 15 8

86 51 87 120 85 59 28 21 70 65

172 75 181 184 141 89 28 54 113 109

135 59 122 133 102 67 21 46 89 79

403 124 218 187 283 161 52 69 177 106

<5 18 29 20 <5 20 6 11 <5 12

Bl B5 B7 B9 B10 B2 B3 B4 B6 B8

110 29 88 5 47 57 56 40 4 51

65 18 45 35 21 41 28 21 93 34

42 5 12 <5

42 5 !1 5

5

5

14 5 5 62 5

22 5 5 19 5

78 20 72 58 46 83 54 32 64 80

121 51 134 95 97 170 120 114 114 128

99 42 14 88 71 151 107 89 95 107

155 73 174 131 166 358 164 123 179 142

61 25 83 58 39 <5 10 44 71 21

H4 H5 H6 HI H2 H3 Br3 Br4 Brl

72 95 60 13 22 23 31 23 6

5 15 16 5 5 <5 13 9 <5

<5 <5 21 5 <5 <5 <5 <5 <5

5 <5 10 5 <5 <5 14 6 <5

5 14 17 21 5 <5 23 16 <5

5 5 5 28 5 <5 16 13 <5

5 5 5 25 5 <5 15 11 <5

5 5 5 31 <5 5 I! 12 <5

<5 26 12 <5 <5 <5 <5 <5 <5

A2-A11 samples from Birkenes, B1-B10 samples from Lyngdal, H l - H 6 samples from H~londa, Brl-Br4 samples from Kl~ebu, see Fig. 1. Abbreviations: Naph = Naphthalene, Acena = Acenaphthene, Phen = Phenanthrene, Fluora = Fluoranthene.

Table 2. Median values for PAHs in natural surface soils in different areas and at different depths (~tg kg -j dry weight) Area/Site

Naph

Biphenyl

S. Norway Birkenes0-5cm Lyngdal0-5cm Birkenes 5-10cm

37 49 119

25 35 19

8 10 5

13 10 <5

68 62 13

111 117 45

C. Norway Holonda/Kl~ebu

23

5

<5

5

11

<5

<5

<5

22

Wales Jones et al., 1989: 0-5 cm

2.40

Acena

Fluorene

Phen

Fluora

Pyrene

Chrysene

B(a)P

84 97 40

169 160 41

12 51 <5

5

5

5

<5

42

29

36

13

Abbreviations: see Table 1.

Table 3. PAH concentrations in peat samples from two ombrotrophie bogs (~tg kg i dry weight) Depth (cm)

Naph

Biphenyl

Acena

Fluorene

Birkenes 5cm 10cm 20cm 30cm

77 71 81 48

31 20 32 29

10 <5 <5 <5

<5 <5 <5 <5

49 20 <5 <5

Ill 53 <5 <5

116 62 <5 <5

115 82 <5 <5

15 17 <5 <5

Gyland 5 cm 20cm

55 25

20 12

<5 <5

<5 <5

40 <5

84 <5

77 <5

96 <5

19 <5

Abbreviations: see Table 1.

Phen

Fluora

Pyrene

Chrysene

B(a)P

278

E. Aamot et al.

Table 4. PAH concentrations in forest soils (0-10cm) from 4 areas along a N - S gradient in southern Norway (Setesdai Valley) associated with long range atmospheric transport (~tg kg -~ dry weight)

Site

Pb, #g g-I

Naph

Biphenyl

Acena

Fluorene

Phen

Fluora

Pyrene

Chrysene

B(a)P

1

120 100 80 60

35 57 7 83

14 15 <5 14

<5

<5

<5 <5 <5

<5 <5 <5

35 <5 <5 <5

71 53 36 39

67 54 30 35

57 31 37 123

<5 <5 <5

2 3 4

13

Abbreviations: see Table 1.

long-range atmospheric transport to this region. The extent of this N-S gradient corresponds to a decline of surface soil Pb, which is mainly derived from long-range atmospheric transport to this region, from about 60 #g- 1g to approximately 12 #g- 1g (Table 4). The relative standard deviation of the mean for each sampling site was less than 20%, while the relative standard deviation of the mean for each region was in the range 10-60%. The detection limits were 5 #g lkg for each PAH, determined by a signal to noise ratio of 3. Statistical analysis

Multivariate statistical analysis was performed using SIMCA (Soft Independent Modelling of Class Analogy) principal component analysis (Simca-R 4.4, 1992). The underlying principle is that data in multidimensional space are projected into a space of fewer dimensions (preferably two dimensional space) preserving as much as possible of the systematic variation in the data set. The data from Table 1 were analysed by SIMCA and two significant principal components were calculated accounting for 51.9 and 15.4% of the total variance. The score plot of the samples in this two dimensional space is shown in Fig. 2. It is seen from this plot that the samples from central Norway are clustered, forming a separate subgroup or class, while the samples from southern Norway are scattered. The scattering of the samples from southern Norway reflects the varying

<

degree of contamination in this area. A separate PCA model was calculated for the samples from central Norway and a tolerance level was calculated. In a three dimensional space this tolerance level will be a cylinder. Objects (samples) similar to the samples from central Norway will be located inside the tolerance level (cylinder). The remaining samples (samples from southern Norway and bog-samples) were fitted into this model and the distance to the class was calculated for each sample. All samples from southern Norway including the bog samples, were classified as nonmembers to the class, e.g. a probability of being equal to samples from central Norway of <0.5%. Thus, the assumption of long-range atmospheric transport of PAH to southern Norway is supported. The loading plot shown in Fig. 3 shows the influence of the variables. The concentrations of phenanthrene, fluoranthene, pyrene and chrysene are the most important variables in describing the variance along the first PCA which explains most of the total variance in the data set. These variables are the most important in differentiating between polluted and nonpolluted samples. The results from the analyses of samples from Setesdal were not analysed by this technique because of the relatively few samples from each location. The PAH levels in central Norway appear to be lower than any other published data for PAH in soils that the authors are aware of. It is interesting to note that the

0 _n n u

0

0

0

-1

-2 T - 0

PCA 1

2

I

4

Fig. 2. Score plot showing samples from central Norway ((3) and southern Norway (*) in the two dimensional space created by the two first principal components.

P A H s in Norwegian forest soils

279

0.4

Bipl~onyl

Np

0.2

Fiuorene

0.0-

-0.2

Chryscnc Ru~,l~ne oe Pyl-en¢

oi~

0.0

~

o12

o13

0.4

PCA I

Fig. 3. Loading plot showing the influence of each variable (PAH).

Kl~ebu site is located only 20 km from the city of Trondheim, with a population of 140000. The 0 - 5 c m soils from southern Norway have similar levels for naphthalene and only slightly higher concentrations of the 2 ring PAHs. Considering PAHs with three or more rings (phenanthrene-benzo(a)pyrene). However, there is a difference of the order of a factor of 10 between the two regions, which is very similar to the trend previously shown for metals associated with long-range atmospheric transport, such as Pb, Cd, As and Sb (Allen & Steinnes, 1980). In comparison with a somewhat similar material from Wales (Jones et al., 1989), most members of this PAH fraction show over twice as high median values in the 0-5 cm soil in southern Norway, whereas the corresponding level in central Norway is below any individual sample analyzed from Wales. Compared to PAH values reported from forest areas in central Europe (Matzner et al., 1981; Berteigne et al., 1988), however, the southern Norway data appear lOW.

The possible association of surface soil PAHs in southern Norway with long-range atmospheric transport may be further tested by comparison with air concentration data. Bjerseth et al. (1979), in a study of PAHs in air under winter conditions at a sampling

station at Birkenes, southern Norway, were able to identify a number of episodes with air transport from southerly directions with particularly high PAH levels. In Table 5 their values for the particular 3-5 ring PAH compounds studied in the present work are normalized to pyrene. It appears that the relative proportions are fairly constant. When the southern Norway 0-5 cm soil data and the surface peat values from the present work are normalized in the same manner (Table 5), the resulting ratios are fairly similar to those observed in air. This may be considered as a further indication of long-range atmospheric transport from areas outside of Norway as being the major source of these PAHs in natural surface soils of southern Norway. Other data from the present work point in the same direction. The results shown in Table 4 exhibit a similar decreasing trend for the 4 and 5 ring PAHs as for Pb along a S-N gradient, with the exception of one anomalous value for chrysene/triphenylene at site 4. However, the observed differences are not significant at the 95% level. The results from analyses of peat profiles in Table 3 may be interpreted as follows: naphthalene and biphenyl, presumably originating from natural processes, show constant levels at different depths. The other PAHs, derived mainly from recent anthropogenic

Table 5. Relative levels of some PAHs in air, surface soil and surface peat in southern Norway, pyrene as the reference compound

Phen

Fluora

Pyrene

Chrysene

B(a)P

Episodes of polluted air (Bjorseth et al., 1979) 1 0.66 3 0.47 4 0.73 6 1.04 mean 0.73 s.d 0.24

1.20 1.12 1.20 1.28 1.20 0.07

1.00 1.00 1.00 1.00 1.00

0.69 0.75 0.59 1.26 0.82 0.30

0.23 0.67 0.16 0.48 0.38 0.23

Soils (Table 2) Birkenes Lyngdal

0-5 cm 0-5 cm

0.81 0.64

1.32 1.21

1.00 1.00

2.01 1.65

0.14 0.53

Peat (Table 3) Birkenes Gyland

0-5 cm 0-5 cm

0.42 0.52

0.96 1.09

1.00 1.00

0.99 1.24

0.13 0.25

Abbreviations: see Table 1.

280

E. Aamot et al.

action, decrease to levels below the detection limits of the analytical technique below 10cm depth. It seems likely that the decomposition rate of P A H s due to biological activity in these peat cores is very low. I f so, the ombrotrophic peat bog forms an excellent medium for temporal trend studies of atmospheric deposition of PAHs. The results from the 5 - 1 0 c m humus at Birkenes compared to the 0-5 cm results (Table 2) are more difficult to explain. It is possible that the differences observed in the profiles of 4 and 5 ring P A H s may be associated with different leaching of individual P A H s according to their different solubility in water, or differences in decomposition rate. In the humus layer, as distinct from the peat, the activity of biological decomposition (bacteria, fungi) is likely to be significant. The differences observed in naphthalene content seem to warrant a comment. The values observed in the present work are consistently about 10 times higher than the median values reported by Jones et al. (1989) from the Welsh soils, as well as other data reported by the same group (Wild et al., 1990, 1991). Apparently the results obtained for the relatively volatile compound naphthalene in soils depend critically on the sampling and storage conditions employed.

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des sols. R61ations possibles avec le d6p6rissement des forets. Eur. J. For. Path., 18, 310-18. Bjorseth, A., Lunde, G. & Lindskog, A. (1979). Long-range transport of polycyclic aromatic hydrocarbons. Atmos. Environ., 13, 45-53. Blumer, M. (1961 ). Benzpyrenes in soil. Science, 44, 474-5. Edwards, N. T. J. (1983). Polycyclic aromatic hydrocarbons (PAHs) in the terrestrial environment i a review. J. Environ. Qual., 12, 427-41. Hanssen, J. E., Rambaek, J. P., Semb, A. & Steinnes, E. (1980). Atmospheric deposition of trace elements in Norway. In Ecological Impact of Acid Precipitation, ed. D. Drablcs & A. Tollan. SNSF Project, Oslo-As, pp. 116-17. Jones, K. C., Stratford, J. A., Waterhouse, K. S. & Vogt, N, B. (1989). Organic contaminants in Welsh soils: Polynuclear aromatic hydrocarbons. Environ. Sci. Teehnol., 23, 540-50. Lunde, G. & Bj0rseth, A. (1977). Polycyclic aromatic hydrocarbons in long-range transported aerosols. Nature, 268, 518-19. Matzner, E., Hubner, D. & Thomas, W. (1981). Content and storage of polycyclic aromatic hydrocarbons in two forested ecosystems in northern Germany. Z. Planzenernaehr. Bodenk., 144, 233-58. Overrein, L., Seip, H. M. & Tollan, A., (1980). Acid precipitation - - e ectson forest and fish. Final report on the SNSF, project 1972-1980. ISBN 82-90376-16-2, Oslo-~,s. SIMCA-R version 4.4 Multivariate Modelling and Analysis (1992). UMETRI AB. Steinnes, E., Solberg, W., Petersen, H. M. & Wren, C. D. (1989). Heavy metal pollution by long range atmospheric transport in natural soils of southern Norway. Water Air Soil Pollut., 45, 207-18. Vogt, N. B., Brakstad, F., Thrane, K., Nordenson, S., Krane, J., Aamot, E., Kolset, K., Esbensen, K. & Steinnes, E. (1987). Polycyclic aromatic hydrocarbons in soil and air: Statistical analysis and classification by the SIMCA method. Environ. Sci. Technol., 21, 35-44. Wild, S. R., Waterhouse, K. S., McGrath, S. P. & Jones, K. C. (1990). Organic Contaminants in an agricultural soil with a known history of sewage sludge amendments: Polynuclear aromatic hydrocarbons. Environ. Sci. Technol., 24, 1706-11. Wild, S. R., Obard, J. P., Munn, C. I., Berrow, M. L. & Jones, K. C. ( 1991). The long-term persistence of polynuclear aromatic hydrocarbons (PAHs) in an agricultural soil amended with metal-contaminated sewage sludges. Sci. Total Environ., 101,235-53.