Fs in lake sediments of Großer Arbersee, Bavarian Forest, South Germany

Environmental Pollution, Vol. 95, No. 1, pp. 19-25, 1997 Pll:

S0269-7491(96)00118-2

© 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0269-7491/97 $17.00+0.00

ELSEVIER

PCBs AND PCDD/Fs IN LAKE SEDIMENTS OF GROBER ARBERSEE, BAVARIAN FOREST, SOUTH GERMANY Bernhard F. A. Bruckmeier, a* Ingrid Jtittner, ab Karl-Werner Schramm, ~ R a i m u n d Winkler, c Christian E. W. Steinberg ~a & Antonius Kettrup a ~GSF-National Research Centerfor Environment and Health, Institute of Ecological Chemistry, D-85764, Oberschleiflheim, Germany hCatchment Research Group, School of Pure and Applied Biology, University of Wales, Cardiff, PO Box 915, Cardiff, UK, CF1 3TL 'GSF-National Research Centerfor Environment and Health, Institute of Radiation Protection, D-85764, Oberschleiflheim, Germany dlnstitute for Freshwaterand Fish Ecology, Mfiggelseedamm 310, D-12587, Berlin, Germany

(Received 17 July 1996; accepted 1 October 1996)

Abstract Despite their environmental importance, there are still relatively few historical studies of the environmental occurrence of polychlorinated biphenyls ( PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), especially in middle Europe. Trends in PCBs and PCDD/Fs were, therefore, assessed in lake sediments of the Grofler Arbersee over the past 130 years (1860-1990). Ballschmiter-PCB concentrations (congeners # 28, 52, 101,138, 153, 180) increased between 1946 and 1972 from 4.2 to 32.0 I.tgkg -1 dry Wt, but have since decreased to 25.6 Izg kg -1 dry wt. High chlorinated PCB congeners reached their maxima earlier (1968-1972) than low chlorinated congeners (1985-1991). These trends were consistent with patterns expected from the production and use of PCBs and their precursors. PCDD/F concentrations increased between 1950from 0.6 tzg kg -1 dry wt to 2.3 #g kg - / d r y wt in 1977,falling to 1.7 lzg kg -1 dry wt by 1993. PCDF concentrations exceeded those of PCDD until 1968, but afterwards PCDDs (especially OCDD) were predominant. These patterns suggest that domestic heating and waste combustion were the most likely sources, but pollution from local industries, such as metal smelting and glass production, might also have been involved. The data provide a valuable case study from central Europe which confirms the overall declining trends of PCB and PCDD/F contamination shown elsewhere. © 1997 Elsevier Science Ltd. All rights reserved

old equipment, but large quantities are also in environmental circulation (Lorenz & Neumeier, 1983). PCDD/Fs are formed during combustion processes from waste incinerators, power plants, private heating and automobile exhausts, and in industrial processes, such as the production of chloro-organics, pulp bleaching and metal refining/melting (Hutzinger & Fiedler, 1989). Atmospheric transport over long distances occurs via dust particles (e.g. Bumb et al., 1980; Ballschmiter, 1984; Broman et al., 1989), leading ultimately to accumulation in sink areas such as lake sediments. Here, past deposition patterns can be reconstructed and sources identified from homologue profiles (Czuczwa & Hites, 1984; Hutzinger & Fiedler, 1989; Oliver et al., 1989; Hites, 1990; Fletcher & McKay, 1993; Hagenmaier et al., 1994; Schramm et al., 1994, 1995; Kjeller & Rappe, 1995; Sanders et al., 1995; Jiittner et al., in press). So far, however, there have been few paleolimnological reconstructions of past trends in PCBs and PCDD/Fs particularly in central Europe. Here we present a sediment record of PCB and PCDD/F concentrations and homologue pattern in a remote lake in south east Germany.

MATERIAL AND METHODS Study site The GroBer Arbersee is a glacial cirque (max. depth 16 m, surface area 0.75 km, 935 m a.s.1.) near Bayerisch-Eisenstein in the Bavarian Forest, south east Germany (Fig. 1). Since the Middle Ages, mining and smelting of iron-ores, and glass production, were important sources of gaseous emissions in this region (Winkler, 1981; Rutte, 1992). At present glass manufacturing and the wood industry are the major economies. The GroBer Arbersee has been acidified due to acid atmospheric deposition from local sources before industrialisation, and from an increase in transboundary acidifying pollutants in the 20th century (Melzer & Rothmeyer, 1983; Steinberg et al., 1984; Arzet et al., 1986; Arzet, 1987; Bruckmeier, 1994). There

Keywords: PCB, PCDD/F, lake sediments, homologue pattern, historical trends.

INTRODUCTION PCBs and PCDD/Fs are widespread and persistent environmental contaminants. PCBs were commercially produced for use in lubricants, softening agents, transformers, capacitors and many other electrical appliances. Much is still stored, landstocked or contained in *To whom correspondence should be addressed. 19

B . F . A . Bruckmeier et al.

20

are no direct discharges into the lake, which is fed by a catchment of 2.58 km 2.

Coring, sample processing and sediment dating Four cores (30 cm length, 6 cm diameter) were taken from the deepest part of the lake in October 1993 using a gravity corer (Core-Stecher, System Niederreiter, Austria). The cores were cut into l-cm slices, with equivalent slices then combined across cores. The resulting individual samples were freeze-dried in a Virtis Sentry 5 L (The Virtis Co., N.Y.) for three days and then homogenised. The samples had dry weights of 2 4 g. Samples were dated using 2~°Pb and the c.r.s, and c.f.c.s. models of Oldfield and Appleby (1984). Additionally, peak concentrations of 137Cs indicated the years 1986 (Chernobyl fallout) and 1963 (nuclear weapon tests; Jaakkola et al., 1983).

oaom

PCB analysis The major PCB congeners Nos 28, 52, 101, 138, 153, 180 (Ballschmiter-PCBs) were used for setting threshold

Fig. 1. Location of study site.

Table 1. PCB concentrations in sediments of Grofler Arbersee PCB

#28 #52 #101 #138 #153 #180 Ballschmi~r(sum)

1884-1990 20-19 cm

1940--1946 ll-10cm

1946-1951 10-9 cm

Time/layer 1951-1957 9-8 cm (ng kg -1 dry wt)

1957-1963 8-7 cm

1963-1968 7-6 cm

1968-1972 6-5 cm

n.d. n.d. 370 457 669 239 1734

n.d. n.d. 652 1229 1545 774 4200

1563 961 2112 3878 4909 2360 15784

1250 974 2496 4840 6307 3191 19058

1308 1107 2892 6417 8225 4226 24174

1919 1140 2884 6789 8620 5339 26692

1608 1205 3396 8475 10475 6880 32029

#77 #126 #169

n.d. n.d. n.d.

47 2 n.d.

31 2 n.d.

55 12 7

76 21 4

105 51 17

126 60 16

#105 #114 #156

n.d. n.d. n.d.

106 n.d. n.d.

211 n.d. 511

281 n.d. 692

365 n.d. 998

496 n.d. 1102

622 n.d. 1362

I-TEQ(WHO) I-TEQ (Sa~)

0.00 0.00

0.25 0.79

0.52 1.26

1.72 2.80

2.74 4.27

5.92 7,83

6.97 9.32

PCB

1972-1977 5-4 cm

1977-1981 4-3 cm

Time/layer 1981-1985 1985-1991 3-2 cm 2-1 cm (ng kg-I dry wt)

1991-1993 14) cm

1.Blank

#28 #52 #101 # 138 #153 #180 Ballschmiter (sum)

1946 1162 2837 7307 8707 5596 27 554

2416 825 2506 6479 8336 4833 25 395

4781 1106 2096 5602 7642 3796 25 023

5204 2012 2616 5912 7425 4172 27 341

3582 1089 2483 6015 8400 3984 25 553

842 237 316 248 412 n.d. 2055

311 436 598 220 1565

#77 # 126 #169

126 52 13

111 50 63

100 45 14

118 44 36

103 44 14

14 1 n.d.

n.d. n.d. n.d.

#105 #114 #156

562 n.d. 1044

432 n.d. 1051

552 n.d. 938

478 n.d. 898

538 n.d. i 133

n.d. n.d. n.d.

n.d.

I-TEQ(WHO) I-TEQ (Safe)

5.95 8.10

6.27 7.93

5.21 7.06

5.33 7.15

5.16 7.13

0.11 0.20

2.Blank

n.d.

n.d.

n.d. n.d. 0.00 0.00

21

PCBs and PCDD/Fs in lake sediments

limits and for marking the distribution pattern of PCBs in the environment (Ballschmiter et al., 1992; Beck & Mathar, 1985). Additionally, the toxic non-ortho and selected mono-ortho PCBs (PCB Nos 77, 126, 169, 105, 114, 156) were determined, and toxic equivalents (I-TEQ) calculated (UBA, 1985; Safe, 1990). The TEF schemes of Safe (1990), the WHO-European Centre for Environment and Health (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) were applied (Ahlborg et al., 1994). The Ballschmiter-PCBs, the non-ortho and mono-ortho PCBs were measured from 1-11 cm, where concentrations strongly decreased, whereas the sample from 20 cm depth was analysed to assess background concentrations. After the addition of labelled standards, quantitative extraction of 1.5 to 2.5 g of the sample was carried out by the Soxhlet method for 4-6 h (80-100 cycles, Kl/irschlammverordnung, 1992). The clean-up procedure followed Schramm et al. (1995) with the following modifications: samples were processed using 965 mbar (14 PSI) head pressure and 250°C injection and transferline temperature. The GC/MS temperature programme was: 90°C 170°C 280°C 1 min 20°C/min 7.5 mi-------n3°C/min 2 min"

PCB overall trends PCB concentrations (sum of Ballschmiter-PCBs) increased between 1946 and 1972 (Fig. 3, Table 1) with a corresponding increase of I-TEQ between 1951-1972. Their peak concentrations in 1968-1972 were 19 times background in 1884-1890. PCB concentrations have decreased since but, even in 1991-1993, they were still 15 times higher than background. Although PCB were detected in deep slices (18841990) they do not exceed blank levels (Table 1). Therefore contaminations during extraction and clean-up procedure are responsible.

PCB congener-specific trends Trends varied between congeners: the low chlorinated PCB No. 28 and PCB No. 52 peaked in 1985-1991, whereas the high chlorinated congeners PCB No.101, No. 138, No. 153 and No. 180 reached their maxima earlier in 1968-1972 (Table 1). Among the toxic non-ortho substituted PCBs, the highest concentrations were found around 1968-1972 (PCB Nos 77 and 126) or 1977-1981 (PCB No. 169). The mono-ortho PCBs (Nos 105 and 156) also peaked in 1968-1972.

PCDD/F overall trends Two blanks were processed parallel to the samples (Table 1). Pure solvent without sample material was taken for extraction and clean-up procedure.

PCDD/F analysis PCDD/Fs were measured from 1-9 cm, where concentrations strongly decreased, and from 16, 21 and 23 cm. The concentration measured at 23 cm depth was defined as background. The analysis of PCDD/Fs was carried out according to Schramm et al. (1995).

PCDD/Fs increased slightly in the late 19th century and by 1911-1918 concentrations were 14 times higher than background in 1865-1872 (Fig. 4, Tables 2 and 3). I-TEQ increased in the early 20th century prior to a strong increase in PCDD/F concentration which occurred after 1950. Peak concentrations in 1977-1981 reached 266 times background, but have since declined by 33% in PCDDs and 19% in PCDFs. In contrast, I-TEQ peaked later in 1981-1985, reflecting variable patterns among the homologues.

PCDD/F homologue trends RESULTS

Dating The 2~°Pb dating results for the two different models (c.f.c.s. and c.r.s.) were very similar and were confirmed by the 137Cs maxima providing confidence that the sediments could be dated accurately (Fig. 2).

2010

0,7 o~ "O ¢D

-Peak 1963

1990 ~

:0,6 9

1970t~

1930 ! E

k~

137Cs-Peak 1986

t950~ •

•

A

L •

1910 ~

•

A •

A

A

•

18901870 ~

-0,5

" ' ,~-'i'--,-,.~= • •

A

•

c.f.c.s.model • sedimentation rate

::1

;0,4

•

..... c.r.s.model

1850

o,3 ;0,2 ;O,I o

0

e-i

,,7

Homologue patterns changed several times in the sedimentary record. In the 19th century OCDD was the dominating compound. In 1911-1918 concentrations of low chlorinated furans (TCDFs, PeCDFs) also

0 0-1cm, 1-2cm, 2-3cm, 3-4cm, 4-5cm, 5-6cm, 6-7cm, 7-8cm, 8-9cm, 9-10cm, 10-1 lcm, 19-20cm,

Fig. 2. Sediment dating of Grol3er Arbersee.

2

I-TEQ (rig kg"1 dry wt) 3 4 5 6 7

1993-91i ...... . . . .L....L=..~! . . . . . . . ' " ' ........... " I~, 'J' i" 1991-851 . . . . . . . . . . . . . . . . . . . . . . . . . . ~. ,~ 1985-81-1 r "Ff,i

198177] •.,, I

I

"

I_1

1977-721 . . . . . . ~ I 71 1972-68] . . . . . . . m,-~ ,t 1968-631 .....J-=--~L- -~L--. -.~-[~or- It 1963-57~ 1957-511 . . . . ~. . . . . . 1951-463~ ' [ ] I-TEQ (WHO) 1946-40~m= i • Ballschmiter-PCB 1890"84 ~= Ii , 0

depth of sediments (cm)

1

5

10

I

J

I

I

15

20

25

30

I

35

40

Ballschmiter-PCB (ng kg"1 dr'/wt)

Fig.

3. C o n c e n t r a t i o n s in s e d i m e n t s o f G r o B e r A r b e r s e e .

22

B.F.A.

Bruckmeier et al.

increased. In 1951-1968 the profiles were still dominated by PCDFs, but the pattern had changed due to an increase in high chlorinated homologues. PCDDs, especially HpCDDs and OCDD, had also increased. By 1968-1993 O C D D was by far the most important compound (Fig. 5). I-TEO (ng kg-1 dry ~) 10 15 20 25

5 I

,

0-1cm, 1993-91

.... - .........

2-3cm, 1 9 8 5 - 8 1

,. . . . . . . . . . . . . . .

I

,

~'id

3-~rn, 1981-77 4-5cm, 1977-72 5-6cm, 1972-68 _m

I

I

,

,

DISCUSSION PCBs The world-wide commercial production of PCBs started in 1929, peaking in Germany in 1974 (11 000 t; Schenkel & Bayer, 1980), where PCBs were openly used until 1972 (Lorenz & Neumeier, 1983). Between 1950-1980 an estimated 30 000 t PCBs were used in closed systems (transformers, capacitors) and in underground mining (hydraulic fluids), of which 10 000 t were released (Lorenz & Neumeier, 1983). Between 1974-1980, PCB consumption decreased to 2-3000 t a -=, and a shift towards the production of lower chlorinated PCBs in production occurred. From 1981, Bayer A G produced only lower chlorinated PCBs (Clophen A30) with production finally ceasing in 1983 (DFG, 1988). Trends in lake sediments reflect these changes in commercial production and use: similar to the Grol3er Arbersee, where peak concentrations were found between 1968-1972, PCBs increased in Lake Ontario 1935-1950 and peaked in 1962-1971 (Oliver et al., 1989). In the UK, PCB concentrations in sediment cores peaked in the early to mid-1960s and declined in the 1970s following restricted use (Harrad et al., 1994). Sanders et aL (1995) found PCB fluxes in a dated UK peat core to increase in 1932-1945 with maximum fluxes in 1964.

30

I

'

r

I

I

,

I

6-7cm, 1968-63

7-8cm, 1963-57 8-9cm, 1957-51 ~ 15-16cm, 1 9 1 8 - 1 1 ~ 20-21cm, 1884-78~ ,,

', i

1PCDD [ ] PCDF NATO/CCMS) i I-TEQ (NATO, 22"23cm' 1872"65 I ; i. I t Jr I 0 200 400 600 800 1000120014001600 PCDD/F (ng kg"1 dry ~)

Fig. 4. PCDD/F concentrations in sediments of Grol3er Arbersee.

Table 2. PCDD/F concentrations in sediments of Grofler Arbersee deposited 1865-1963

1865--1872 23-22 cm

1878-1884 21-20 cm

Time/layer 191 i-1918 16-15 cm (ng kg-I dry wt)

TCDD PeCDD HxCDD HpCDD OCDD sum of PCDD

0.55 0.12 0.38 0.43 3.79 5.27

2.00 0.21 0.48 0.65 17.91 21.25

1.96 0.51 0.94 2.08 24.07 29.56

7.75 7.24 20.04 35.69 60.64 131.37

10.77 11.55 26.60 49.68 86.50 i 85.10

2,3,7,8 TCDD 1,2,3,7,8 PeCDD 1,2,3,4,7,8 HxCDD 1,2,3,6,7,8 HxCDD 1,2,3,7,8,9 HxCDD 1,2,3,4,6,7,8 HpCDD

n.d. 0.04 n.d. n.d. n.d. 0.20

1.00 n.d. n.d. n.d. n.d. 0.25

0.68 0.08 n.d. n.d. n.d. 1.05

n.d. 0.61 n.d. 0.89 0.54 17.62

0.14 0.58 n.d. 1.07 0.53 25.79

I] TCDF E PeCDF I~ HxCDF E HpCDF OCDF sum of PCDF

1.75 0.45 0.72 0.40 0.06 3.37

5.71 0.65 0.34 1.13 1.32 9.15

49.18 35.90 2.21 3.47 0.83 91.59

119.79 103.46 74.91 53.08 77.32 428.56

155.52 133.97 107.63 64.64 100.67 562.43

2,3,7,8 TCDF 1,2,3,7,8/1.2.3.4.8 PeCDF 2,3,4,7,8 PeCDF 1,2,3,4,7,8/1,2,3,4,7,9 HxCDF 1,2,3,6,7,8 HxCDF 1,2,3,7,8,9 HxCDF 2,3,4,6,7,8 HxCDF 1,2,3,4,6,7,8 HpCDF 1,2,3,4,7,8,9 HpCDF

0.15 0.07 n.d. n.d. n.d. n.d. n.d. 0.40 n.d.

0.21 0.06 0.07 0.07 n.d. n.d. n.d. 1.03 n.d.

9.92 2.17 5.99 0.56 0.26 n.d. 0.13 3.47 n.d.

7.62 12.03 8.45 14.32 9.74 n.d. 5.44 40.29 2.14

9.82 16.35 10.29 17.36 12.59 n.d. 8.01 50.35 2.37

sum of PCDD/F (tetra through octa) I-TEQ (NATO/CCMS)

8.64 0.05

30.40 1.10

121.16 4.98

559.93 9.73

747.53 12.30

PCDD/F

1951-1957 9-8 cm

1957-1963 8-7 cm

23

PCBs and PCDD/Fs in lake sediments Table 3. PCDD/F concentrations in sediments of Gro6er Arbersee deposited 1963--1993

PCDD/F

E TCDD E PeCDD E HxCDD E HpCDD OCDD sum of PCDD 2,3,7,8TCDD 1,2,3,7,8 PeCDD 1,2,3,4,7,8 HxCDD 1,2,3,6,7,8 HxCDD 1,2,3,7,8,9 HxCDD 1,2,3,4,6,7,8 HpCDD E TCDF E PeCDF E HxCDF E HpCDF OCDF sum of PCDF 2,3,7,8 TCDF 1,2,3,7,8/1.2.3.4.8 PeCDF 2,3,4,7,8 PeCDF 1,2,3,4,7,8/1,2,3,4,7,9 HxCDF 1,2,3,6,7,8 HxCDF 1,2,3,7,8,9 HxCDF 2,3,4,6,7,8 HxCDF 1,2,3,4,6,7,8 HpCDF 1,2,3,4,7,8,9 HpCDF sum of PCDD/F (tetra through octa) I-TEQ (NATO/CCMS)

Time/layer 1972-1977 1977-1981 5-4 cm 4-3 cm (ng kg-I dry wt)

1981-1985 3-2 cm

1991-1993 1-0 cm

13.92 36.43 104.75 198.09 1048.56 1401.74

31.30 56.11 122.31 216.32 591.11 1017.14

22.34 34.34 108.86 217.34 560.18 943.06

n.d. 1.13 1.04 4.57 3.75 67.77

n.d. 1.57 0.97 4.40 5.59 99.73

n.d. 4.52 6.04 9.63 11.06 111.99

n.d. 2.46 1.49 7.61 6.68 108.93

159.63 168.05 132.78 94.21 264.23 818.91

173.22 206.02 158.71 112.68 189.26 839.89

200.35 221.08 188.34 123.67 162.60 896.04

185.31 197.83 168.53 126.28 169.67 847.62

186.97 171.75 142.38 99.82 125.80 726.72

11.73 18.80 12.59 20.71 14.60 0.77 10.95 60.39 8.95

11.18 18.07 13.62 21.14 16.60 n.d. 14.04 68.01 5.25

13.06 21.05 16.38 24.33 18.96 n.d, 15.90 77.04 7.53

14.67 23.61 18.71 28.42 22.65 n.d. 19.70 91.69 5.86

15.45 20.33 18.43 24.29 20.32 2.72 18.36 83.81 13.24

14.47 18.99 15.45 21.76 17.68 n.d. 17.88 70.03 6.13

995.64 15.57

1435.18 16.81

2048.78 20.64

2297.78 24.14

1864.76 26.13

1669.79 21.20

1963-1968 7 4 cm

1968-1972 6-5 cm

19.68 23.42 42.30 78.50 128.02 291.93

8.13 20.82 55.00 84.82 447.49 616.27

10.91 30.33 75.58 132.84 959.23 1208.89

n.d. 1.15 0.88 2.11 2.64 38.26

n.d. 0.93 0.70 1.88 1.93 43.90

193.00 174.30 123.25 91.77 121.39 703.71

Also, PCB pattern in the GroBer Arbersee changed through time, as reflected by the shift in individual Ballschmiter congeners. Oliver et al. (1989) found a shift to less chlorinated congeners for cores in Lake Ontario as a result of a change in production to low chlorinated PCBs (Arochlor 1016). Differential degradation of PCBs (Farley et al., 1994) is unlikely to account for the changes in congener pattern in our lake as we found no decrease in high chlorinated PCBs with depth which would be required if dehalogination was important. Post-depositional re-mobilisation cannot explain the profiles found in the Groger Arbersee. Enrichment of low chlorinated congeners would have been expected in the upper sediment layers because they volatilize more easily than high chlorinated congeners. In reality the top horizon (1991-1993) contained less PCB No. 28 and No. 52 than the sediment layers deposited in 1985-1991 and 1981-1985, suggesting that the profile reflects the true deposition pattern.

PCDD/Fs A marked increase in PCDD/F concentrations in the 1950s has also been found elsewhere (Hagenmeier et al., 1986) but a prior increase in I-TEQ suggests that other sources were important for the release of dioxins into the environment before the production of chlororganics; the most likely is the burning of fossil fuels

60

,oo.

zoo

200 -

200

iR _ a

O"

ll'"'

t'6°] '''3 Hn

. . . . .

)1oool

80

I

---

I

"~ lO

"

~0~t

i'.

100"

0

4oo f

15-16~u

50 ' t g t e 40 i19zz 30 . . .

200-

. ~

100

.

g ;"~;; 116°1'-0~= 1204::::-

It

80

2

nH~

....

0 122-23Cm 1872-

43

....

2

i X865 I

4

ooo1 " i] :_-_5=' 1 2o- o-,=, 6°°1

II ;;;;- I 1°°'''''6o:t ""

:°°:°t::::ll

......

0~

60 40

20

o i_n .

.

.

.

.

" : :1 illl:

. . . . . ....

0 ,,~.,,..,ci .,-,t.,,.,~t.k u. kk t.t.u.

I-"~ "~x"t"-- I" ~- -t- 2[ -

ID D e.~e-~t-=U..t.t. U=.k~ U.

=a.'t =

gk .L

Fig. 5. Sediment pattern of PCDD/F-homologues in GroBer Arbersee.

24

B . F . A . Bruckmeier et al.

(Kjeller et al., 1991; Kjeller & Rappe, 1995). This was also indicated by the homologue profiles in 1911-1918 which were dominated by low chlorinated furans similar to those of soot derived from coal and wood burning (Thoma, 1988). Additionally, high proportions of O C D D suggest that other sources, such as local glass production and metal smelting industries, might have been involved. They operated in the area until 1907 (glass production) and 1962 (smelting industry; Winkler, 1981; Rutte, 1992). By 1957-1968, the homologue profiles in the Grol3er Arbersee were still dominated by PCDFs with an increasing proportion of high chlorinated compounds, but PCDDs had also increased, suggesting different sources of pollution. From the 1970s, homologue profiles were similar to those of waste incineration plants, indicating long distance transport of pollutants. Similar patterns were also found in recent sediments (19761981) in Lake Constance (Hagenmaier, 1987) and in lakes in the Black Forest (Jiittner et al., in press). P C D D / F concentrations have decreased since the 1980s, as have those in some lakes in the Black Forest (Jiittner et al., in press). PCDD/Fs have also declined since the 1980s in archived herbage samples from rural parts of the U K (Kjeller et al., 1996) suggesting a decline in atmospheric emissions.

ACKNOWLEDGEMENTS We are grateful to B. Henkelmann, C. Klimm and T. Wottgen for analytical help and advice. The authors thank S. J. Ormerod for his valuable comments on the manuscript.

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