atmospheric transport of chlorinated hydrocarbons to sweden in 1985 compared to 1973

Atmospheric Enuironment Vol. 23, No. 8, pp. 1699-1711, 1989. 0@%6981/89 $3.W+O.W

Printed in Great Britain. 8 1989 Pergamon Press plc

ATMOSPHERIC TRANSPORT OF CHLORINATED HYDROCARBONS TO SWEDEN IN 1985 COMPARED TO

1973

PER LARSSON and LENNART OKLA Limnology, Department of Ecology, University of Lund, Box 65, S-221 00 Lund, Sweden

(First received 17 October 1988 and received for publication 1 February 1989)

Abstract-The atmospheric fallout of DDT and DDE (ZDDT) over Sweden has decreased during the last decade. Today long-range transport from southern sources outside the country dominates the inflow. This was reflected in a decreasing south-to-north gradient of the compounds in atmospheric deposition and in the lower atomosphere. The fallout of PCBs was similar in 1984-1985 and 1972-1973, and today local contamination by combustion is more prominent than it was 10 years ago, even though PCB restrictions have been in force during the interim. Since PCB deposition is higher in the coastal areas than in the inland regions, other sources, such as volatilization from the seas and long-range transport also contribute to PCBs in fallout.

The levels of PCB and ZDDT in the lower atmosphere were positively correlated with temperature. Consequently, the compounds tended to be in the gas phase during the warmer summer period whereas during winter they were more liable to be adsorbed to particles, partition to airborne water and contribute in fallout.

From each sampling station a chromatographic ‘fingerprint’ of pollutants in airborne fallout and in the lower atmosphere was obtained. The fingerprint was the combined result of the station’s location and climate.

The results show that considerable amounts of chlorinated pollutants are being transported to and within Sweden via the atmosphere.

Key word index: Atmospheric fallout, atmospheric contamination, transport processes, PCB, DDT, chlorinated hydrocarbon, Sweden.

1. INTRODUCTION

A study of the atmospheric fallout (wet plus dry deposition) of persistent chlorinated hydrocarbons including polychlorinated biphenyls (PCBs), l,l,l- trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and l,l-dichloro-2,2-bis(p-chlorophenyl)ethane (DDE) over Sweden was carried out in 1972-1973 (Sodergren, 1975). The fallout was examined at 11 stations starting in the south and extending 1600 km to the north. Sampling was performed for periods of 3 months. The highest deposition of pollutants was recorded in the southern and western parts of Sweden, while the fallout was lower in the northern part.

In 1984-1985 a similar fallout study was performed with the same sampling equipment and stations. The study was supplemented with measurements from three additional stations, two in the coastal area of the Baltic and one in the Subarctic area of northern Sweden. The 14 stations thus cover a wide range of climatic conditions, from a warm-temperate, humid climate in the south to a very cold-temperate, high- altitude climate in the north (Fig. 1). Chlorinated hydrocarbons (HCs) in airborne fallout were trapped on a nylon net impregnated with a silicone oil. Lipo- philic, chlorinated compounds in dry deposition as well as in rainwater are retained by the lipophilic oil. At each sampling site levels of persistent pollutants in

the lower atmosphere were determined by filter technique.

Chlorinated hydrocarbons reaching the atmosphere mainly originate from the combustion of municipal and industrial wastes. When incinerated, pollutant-containing material releases its load to the air. The incineration of common precursors like phenol and HCI results in the formation of a large number of chlorinated aromatics, such as polychlorinated biphenyls, chlorinated dioxins and dibenzofurans (Eklund et al., 1986). Persistent organic pollutants in the atmosphere are present mainly in the gas phase (Doskey and Andren, 1981). In air, organic compounds with a saturation vapor pressure > 10m4 mm Hg should exist exclusively in the vapor phase, whereas compounds with vapor pressures < lo-’ mm Hg are adsorbed to particles (Eisenreich et al., 1981). Persistent pollutants have vapor pressures somewhere between these extremes. The density of particles in the air determines the phase distribution of chlorinated aromatics; thus as the density of particles increases close to industrial areas the proportion of particle-associated pollutants also increases (Rodhe et al., 1980). The atmospheric deposition of particles (and pollutants associated to particles) is difficult to measure, and the aerodynamics of the sampler affect sampling. Therefore, measured values of atmospheric fallout depend on the sampling method employed.

1699

PER LARSSON and LENNART OKLA

1 3. 56’12’N. 15’4O’E

4. WSO’N. 16’37’E

5. 57’41’N. 14’43’E

6. 57’47’N. 13’24’E

7. 58’16’N, 11’26’E

8. 58’38’N. 12’26’E

9. 59’39’N. 17’04’E

1

3 1

% 1

2 3

10. 60’3!?N, 17’1O’E

1

Fig. 1. Average monthly levels of PCBs and ZDDT (p,p’-DDT + p,p’-DDE) in airborne fallout in Sweden during 1972-1973 and 1984-1985. Sampling at 8tatiOnS 3,10 and 13 was not performed in the earlier study. The fallout was trapped on a nylon net impregnated with silicon oil and exposed in periods for 3 months. Period 1. includes October-December; period 2,

January-March; period 3, April-June, period 4, July-September.

One of the dominant mechanisms by which persistent organics are deposited in the ecosystems is wash-out by rain (Ligocki et al., 1985; Thomas et al.,

1986). The extent to which this process occurs is determined by Henry’s Law, where the partial pressures and water solubilities of the compounds together determine the value of Henry’s constant (H, Ligocki et

al., 1985) and, consequently, regulate the equilibrium reactions with airborne water. H is strongly influenced by temperature and increases for organic compounds

by about a factor of 2 for each 10°C rise in temperature. In their gas-phase, non-reactive organ- its, like chlorinated aromatics, present in gas phase have been estimated to reach equilibrium with a rain droplet after falling a few tens of meters (Slinn et al.,

1978). Another dominating transport mechanism leading

to the removal of pollutants from the atmosphere is dry deposition. Chlorinated hydrocarbons may either be deposited directly from the vapor phase, or they

Atmospheric transport of chlorinated HC to Sweden 1701

may be deposited along with the particles to which the compounds are adsorbed. The deposition of particle- associated residues (particles > 5 pm) from the atmosphere is roughly determined by the sedimentation rate of a given particle (which in turn is a function of particle size, its reactivity characteristics, charge etc.) and its content of pollutants. The deposition velocity is generally approximated as (e.g. Bidleman and Chris- tensen, 1979):

Vd= F/C= ems-’

where Vis the deposition velocity, F represents the dry deposition fluxes of organochlorines and C is the concentration of the compound in the air. Wind is important in this context, and the deposition velocities of PCBs and DDT are positively correlated to wind speed (Bidleman and Christensen, 1979).

There is no question that atmospheric transport is an essential and probably the major route by which many chlorinated HCs enter northern terrestrial and aquatic ecosystems. PCBs, DDT, BHC-isomers and chlorinated camphenes (toxaphene) are among the pollutants that have been detected in air and precipitation from Sweden (Sodergren, 1972,1975; Ekstedt and Oden, 1973-1974; Sundstriim, 1981; Bidleman et al., 1987). Deposition of other pollutants, like phthalic esters, decreases along a gradient from urban to rural locations, found in Norway by Lunde et al., (1977). The global contamination of the atmosphere can be illustrated by the various chlorinated HCs detected in air from Arctic (Oehme and Stray, 1982; Oehme and Man& 1984) and Antarctic regions (Tanabe et al., 1982, 1983).

The aims of the present study can be summarized as follows.

(1) To qualitatively and quantitatively compare the fallout of chlorinated HCs deposited over Sweden in 1972-1973 to that deposited during 1984-1985. (2) To determine the composition and levels of chlorinated HCs in the lower atmosphere (within 5 m from the ground) at the different sampling stations and to investigate the factors responsible for the distribution of the compounds between gas and particulate phases. (3) To determine if a relationship exists between levels of chlorinated residues in air and those present in airborne fallout and to examine the import- ance of climatic variables, such as latitude, amount of precipitation, mean temperature and mean wind direction.

2. MATERIALS AND METHODS

2.1. Sampling

Chlorinated HCs in airborne fallout were sampled with a nylon net (mesh-size 200 pm) impregnated with a silicone oil. The samplers were located 2.5 m above the ground, in an area free of buildings and trees. The

method was identical to that used by Sodergren (I 972, 1975). The lipophilic pollutants as well as airborne particles are collected and retained in the lipophilic oil. Lipophilic pollutants present in rainwater are extracted by the oil as the water percolates through the net. The screens thus sample chlorinated residues resulting from both dry and wet deposition. Sampling was carried out for 3-month periods during 1 year (period I: October-January, period II: January-April, period III: April-July, period IV: July-October). These periods corresponded to those used in the previous study.

While fallout was being sampled, levels of chlorinated HCs in air were also being determined by means of filter technique (Billings and Bidleman, 1980; Giam et

al., 1980, Larsson, 1985a,b). About 30@400m3 of air was passed through particle filters (Whatman GF/F) and one or two polyurethane foam-plugs (PPF) connected in series by a suction pump (pump rate 4.5 m3 air day- ‘). Sampling lasted for 3 months, and the efficiency of the pumps was tested at the beginning and end of the sampling periods.

The estimates from each method resulted, consequently, in an integrated value of persistant pollutants in fallout and air over the 3 month periods. The sampling did not allow trajectory calculations to determine the compound origins, however, owing to the long sampling time.

2.2. Extraction and sampling efficiency

Chlorinated HCs from the fallout nets were extracted with hexane in a Soxhlet apparatus according to Sodergren (1972). The extracts were cleaned-up (impurities disturbing later analyzed, oxidized and separated) with fuming H,SO, and evaporated to 0.5 ml before the compounds were analyzed by gas chromatography/ECD.

Compounds adsorbed to the particle and PPF filters were extracted with acetone/hexane in an ultra- sonic bath (Larsson, 1985b) and cleaned-up, concen- trated and analyzed as described above.

The extraction efficiencies of the PPF filters were determined for PCBs (Clophen A 60) DDE and toxaphene. Known amounts of the compounds were mixed in 1 ml of ethanol. The mixture was then injected into the PPF filters, and the solvent was evaporated by passing about 10 m3 of clean air through the filters (the pumps were the same as those used in the later field sampling). After extraction (Larsson, 1985b) and pre- separation of the compounds on an activated silica column (the silica, mesh-size 70-230 was activated at 200°C and eluted with 6 + 9 ml of hexane followed by 4 ml hexane/diethylether 3: 1) recoveries were 89% for PCB(SD= 13%,n=6)49%forDDE(SD=7%,n=6) and 108% for toxaphene (SD= 12%, n=6). The results were considered to be satisfactory.

In the field sampling, escape of PCBs through the PPF filters was examined for the first sampling series by attaching two PPF filters, connected in series,

1102 PER LARSON and LENNART OKLA

behind the particle filter. The first filter contained 3-3273 ng PCBs, while no PCB was detected on the second filter (n= 14).

2.3. Comparison between the analytical methods 1972-1973 and 1984-1985

While the same method was used for sampling airborne fallout in 1972-1973 and 1984-1985, the gas chromatographic separation/detection method differed between studies. Sddergren (1972, 1975) used a packed column for separation of the chlorinated pollutants and 3H-ECD for detection. As a standard for PCBs Clophen A 50 was used, and confirmation of DDT was carried out by chemical degradation to DDE. In 1985, the compounds were separated by a cross-linked, fused silica capillary column and detected by 63 Ni-ECD (Okla and We&, 1984). The analytical method was optimized for PCBs and CDDT (p,p-DDT and p,p-DDE) which means that 28PCB congeners were quantified (and numbered according to IUPAC after Ballschmiter and Zell, 1980; Duinker and Hillebrand, 1983). The limit of detection for PCBs was 0.5 ng for PPF-filters and 1 ng for the fallout nets.

column was poor compared with that on the capillary column, resulting in a more uncertain quantification using the former. CDDT was probably underestima- ted because of the XDDT in the reference material (unexposed screens) was overestimated (confirmed when reanalyzed 1985), that a chemical conversion to DDE was used for confirmation of p,p DDT and by using a different standard composition of XDDT for quantification.

Blank values for PCBs were < 1 ng (n= 10) for unexposed PPF plugs and 49.6ng for unexposed fallout nets (n = 5). All other investigated chlorinated hydrocarbons were absent from the unexposed PPF- filters and fallout nets. Field fallout values were cor- rected by subtracting the blank value.

3. RESULTS AND DISCUSSION

3.1. CDDT in airborne fallout

As the analytical methods differed a calibration was performed. Samples (stored in sealed glass ampoules) from the 197221973 study were analyzed with modern techniques. The results were compared with the previous data and evaluated by linear regression (Fig. 2). The slope of the equation represents the calibration factor. It was found that the result from the earlier study had to be multiplied by a factor 2.3 for PCBs and by a factor 4.8 for XDDT. The reasons for the earlier underestimation of PCBs in fallout were as follows: (1) Clophen A 50 was used as a standard in the first study whereas Clophen A60 was used in the second-the latter standard providing a far better match for fallout samples in both investigations. Using Clophen A50 resulted in the exclusion of several congeners (peaks) from the gas chromatographic quantification.(2) Separation of PCBs on the packed

The overall fallout of XDDT significantly decreased from 1972-1973 to 1984-1985 (p<O.OOOl, Wilcoxon matched-pairs signed-rank test, Fig. 1). This means that the DDT restrictions introduced in 1971 have been effective and that sources within the country have ceased. The conclusion was supported by the fact that the proportion of DDT to DDE was significantly higher 12 years ago than it was in 19841985 (p < 0.0002, Mann-Whitney U-test, one-tailed). The DDT/DDE quotient was 4.10 (n= 17) in 1972-1973 while by 1984-1985 it had decreased to 2.64 (n=52). The commercial DDT product contains < 1% DDE (Ekstedt and Oden, 1974), which implies that the influence of the fresh commercial product on the atmospheric pool of pollutants was higher a decade ago than it is today. DDT is broken down to DDE by u.v.-light in the atmosphere and by the metabolism of organisms. The XDDT that reaches Sweden has ‘aged’ during long-range transport from distant sources.

0 1 2 3

[PCB] 1973 (~&&nonth))

1

XDDT 1973 (&(m2*month))

Fig. 2. Calibration of the gas chromatographic methods performed in 1972-1973 compared to 1984-1985. Field samples from the earlier study were analyzed by capillary gas chromatography and evaluated against results obtained in 1972-1973. The

slopes obtained were used as calibration factors.


100

90

80

70 w60 @ 50 2 40

e 30

20

10

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Station

Fig. 3. The ratio of p,p-DDE/p,p-DDT in atmospheric fallout in 19841985. The bars represent the mean of the four sampling stations during the year. Station 0 represents

Berlin, F.R.G., where one sampling was carried out.

During transport from southern to northern Swe- den, a distance of 16OOkm, EDDT ‘aged’, and the proportion of DDE toDDT increased (Fig. 3). The proportion of DDT was highest in Berlin, F.R.G., indicating that this station was closest to the source. Thus, the source for CDDT presumably was to the south and the reduction in fallout compared with 12 years ago confirmed that the compounds originate from long-range sources outside of Sweden.

The fallout of EDDT decreased along a north-south gradient (R. = 0.51, 0.0005 < p < 0.005, Spearman rank correlation). This was also the case for levels of ZDDT in the lower atmosphere (R,=OS, p < 0.0005, Fig. 4). The results supported the conclusion that the CDDT compounds may originate from southern sources.

In 1984-1985 the fallout of EDDT was highest in periods I and IV (October-January, July-October, p < 0.0001, Friedman two-way analysis of variance by ranks, Fig. 1) during the transition from warm to cold weather. One of the reasons for the high ZDDT fallout during these periods could be that the volatilized

compounds in the atmosphere are converted from the gas phase to the particle phase during periods of decreasing temperatures (Eisenreich et al., 1981; Dos- key and Andren, 1981), and, subsequently, that the particles more easily are washed-out by rain. The compounds may also partition directly into the liquid phase and fall to the ground as rain.

It has also been shown that airborne pollutants from mid-latitudinal emissions are transported to the north (to the Arctic) in the winter along with Arctic air masses which cover much of Eurasia and North America (Barrie, 1986). This south-north transport includes chlorinated HCs, thereby increasing the rate of fallout and levels of organochlorine pollutants in the lower atmosphere during the winter in Sweden.

The impact of the processes of adsorption and/or partitioning to liquid phase on atmospheric fallout of chlorinated hydrocarbons is greater during a seasonal changeover from warmer to colder weather than during a period of increasing temperatures. The pesti- cide pool in the atmosphere is built up during warm periods owing to volatilization from the areas of use and dumping sites. At the same time pollutants adsorbed to particles are converted to the gas phase. Pollutants present in the gas phase are more easily transported over long distances than are particle- associated ones (Rodhe et al., 1980). When the pollutants hit the northern, colder climate they contribute to the fallout. In Sweden the ‘fallout-point’, at which the chlorinated HCs converts from gas phase to particle phase and/or partition to rain droplets owing to decreasing temperature, forms a gliding scale from south to north. This trend is due to the higher mean temperatures in the south, which gradually decrease to the north.

Wash-out by rain will have a greater impact in period IV since mean precipitation is highest during this period (283 mm being the mean for the 14 stations compared with 126-155mm during the remaining

. Rs = 0.55 p < 0.001 cc 0.08 - q Jp

q

E % .E. 0.06 - q

i 0.04:

s q

J

0.02 -

0.00 fl!l 0

q - O8 q q q I; +ir

I 1000 Distance (km) 2000

North South

Fig. 4. Correlation of the distance from Sweden’s most northern point to the south with the levels of DDT + DDE in the lower atmosphere. One data point was deleted from the figure for reasons of overview, however not from

the correlation.

1704 PER LARSSON and LENNART OKLA

periods). During period II (winter) in 1984-1985 precipitation was in the form of snow at all stations and the fallout of XDDT was low.

3.2. Fallout of PCBs

The fallout of PCBs has not decreased from 1972-1973 to 1984-1985 (p=O.45, Wilcoxon signed rank, Fig. 1). Instead the deposition has decreased in the south of Sweden, increased in the western and central parts and decreased slightly in the northern parts. It is surprising that the PCB flow from the atmosphere to the ecosystems has not diminished since the restrictions against open use were introduced in 1971, especially when considering the trend for XDDT. The similar fallout of PCBs over the last decade can be explained by the fact that PCB-containing material and oils used in the 1960s and 1970s are now burned or stored in an inappropriate manner. Such local combustion or storage occurred close to stations 7 and 8 near the Swedish west coast and station 9 situated inland in eastern Sweden. Such combustion apparently contributes substantially to PCB fallout and PCB levels in the lower atmosphere. This conclusion is supported by several arguments. (1) The PCB-pattern resulting from the gas chromatographic analysis of fallout from all investigated period- s was identical to that produced by an industrial PCB oil, Clophen A60 (see section 3.3). This identical pattern (i.e. identical composition of PCB congeners) was demonstrated in samples collected in the vicinity of the source(s); a long residence time in the atmosphere would have resulted in dissimilar breakdown rates of the different PCB congeners by u.v.-light and thus a changed PCB pattern (Bunce et al., 1978). (2) PCBs in air (measured by filter technique) at the three stations showed a higher degree of particle-associ- ation, 0.4-7.3% (adsorbed to Whatman filter) than PCBs collected at other stations, where particle associated PCB levels were below the detection limit. The higher proportion of particle-associated PCBs reflected a closer proximity to the source (Rodhe et al., 1980), since particles have a shorter residence time in the atmosphere compared with volatilized compounds. (3) PCB fallout and PCB levels in air were simultaneously high. Consequently, the discharge to the atmosphere was continuous and high throughout the year. If the source had been discontinuous, lower levels of PCBs would have been recorded by the filter technique. The method resulted in an integrated PCB value for the 3-month period owing to the continuous, low pumping rate. (4) The PCB fallout and levels of PCBs in air were considerably higher at the three stations than at any of the other stations (excepting for fallout at station 13).

The high local PCB contamination from the atmosphere in the western part of Sweden was reflected in the vegetation and biota. The PCB content of mosses and lichens in this area was elevated compared with ‘background’ samples, and the PCB composition re-

sembled a Clophen A 60 pattern (Thomas et al., 1984). Mosses are used as monitoring organisms for airborne pollutants since they obtain nutrients directly from rainwater and through the impaction and sedimentation of airborne particulates (and thus also receive atmospheric pollutants, Larsen et al., 1985). The PCB content of unhatched osprey eggs (Pan&on halietus) was higher in the western parts of Sweden than in southern Swedish localities (Ahlgren and Eriksson, 1984). The results indicate that previously airborne pollutants are directly bioavailable for plants and may be transferred in the food webs to predators.

The composition of PCB congeners in all fallout samples resembled the Clophen A 60 standard (Fig. 5). Generally, all 28 congeners were identified in the fallout samples. The same phenomenon has been observed for PCBs taken up from air by vegetation, for instance, in pine needles (Gaggi and Bacci, 1985). In the needles airborne PCBs are enriched in the wax layer that surrounds the needle surface. This wax layer, similar in lipophilicity to the silicone oil on the fallout screens, may selectively capture highly chlorinated PCBs. Airborne, highly chlorinated, more lipophilic PCB congeners might be partitioned to the lipophilic waxes or the oil, to a larger extent than are the less lipophilic, less chlorinated PCB compounds. Another explanation could be that the more adsorptive, less volatile, highly chlorinated PCBs adhered to a higher degree to particles in the atmosphere and therefore contributed more to the fallout than did the less chlorinated, less adsorptive PCB congeners.

PCB fallout did not differ significantly between sampling periods (0.05 < p < 0.10, Friedman analysis) in contrast to ZDDT, probably because at least three of the sampling stations were influenced by local, seasonally independent sources. The other stations influenced by long-range seasonally dependent transport received less PCB fallout. The two processes resulted in fallout over the sampling periods being similar for the stations. This was not the case in 1972-1973 when higher fallout of PCBs were recorded during the colder winter season (p < 0.001, Friedman analysis). The conclusion drawn from the results was that the impact of local atmospheric PCB contamination on ecosystems in Sweden is greater today than it was over a decade ago when the PCB restrictions were first introduced.

The ‘background’ fallout of PCBs over Sweden in 1984-1985 was 0.75 pgm-2 month-’ as defined by that 82% of the fallout values were below this value. 18% of the values were considerably higher than this value and probably resulting from local contamination. The fallout was thus a result of contamination from sources within the country as well as long-range transport. The mean value of the fallout was higher, being 13.4 pg m -2month-1. The extent of the PCB- fallout is sufficient to explain the estimated mass of PCBs within the biota of holarctic ecosystems (the total biomass of the Baltic Sea was estimated as containing 2-3 t (Kihlstriim and Berglund, 1978).


STATION 1

STATION 7

STATION 13

Fig 5. Capillary gas chromatograms of chlorinated, persistent pollutants in atmospheric fallout in 1984-1985 (period 1) from stations 1, 7 and 13. At the bottom a chromatogram of Clophen A 60, a commercial PCB mixture, is shown. The chromatograms can be seen as a ‘fingerprint’ unique for each

sampling station.

3.3. Gas chromatographic ‘jingerprints’ of persistent pollutants in fallout and in the lower atmosphere

The persistent pollutants in atmospheric fallout and in the lower atmosphere resulted in a gas chromatographic ‘fingerprint’ unique for each station (Fig. 5). Each fingerprint is defined by the relative amounts of the 28 dominant PCB congeners included in Clophen A60, p,p-DDT, o,p-DDT, p,p-DDE, a- and b-HCH, phthalic ester acids (mainly diethylhexylphthalate and dibutylphthalate) and several unknown H,SO,- persistent chlorinated organic chemicals. Each station-specific fingerprint is probably the cumulative result of the effects of several factors, including vicinity to the source (which, among other variables, affects the residence and transport time in the atmosphere, thereby influencing the degree of degradation by u.v.-light and atmospheric chemical processes), climatic vari-

ables like temperature and predominant wind direc-

tion, amount and type of precipitation, and geographi- cal location*.g. distance to the sea, altitude.

The spatial distribution of a variety of organic and

inorganic compounds contained in rain samples and their source characterization have been determined by various methods. In urban aerosols, Hopke et al. (1976) applied factor and cluster analysis for several elements. Thomas (1986) applied multivariate principal component analysis for chlorinated and polyaro- matic HCs for which several differences in emission were registered.

We applied cluster analysis to distinguish different sources of PCBs. For the calculation, the industrial PCB oil Clophen A 60 was defined as the basis for two reasons. First, when analyzing the different compo- nents of PCBs in fallout and in the lower atmosphere for all stations, Clophen A60 gave, by far, the best


‘match’ of PCBs (when comparing five European, industrial PCB oils with the Clophen A trademark and with increasing chlorination, and four American PCB oils with the Aroclor trademark). Secondly, we assumed that industrial combustion of PCBs would not change the composition of PCBs in fallout or that in the lower atmosphere since PCBs are not normally degraded by such combustion processes. As industrial PCB oils have a specific and constant composition of congeners (Ballschmiter and Zell, 1980; Duinker and Hillebrand, 1983), a gas chromatographic analysis of the compounds will result in a reproducible pattern of PCBs. Differences in the pattern between field samples should therefore be a cumulative result of the above- mentioned environmental processes.

Clophen A 60 (as exemplified by Fig. 6). The cluster clearly pointed out that the compounds originated from local sources of combustion. Cluster analysis of PCBs in the lower atmosphere yielded the same results for the stations (however, not for Berlin because the filter technique was not applied there). These results were further supported by regression analysis relating the composition of the industrial PCB oil to that of the fallout samples from these stations (Fig. 7).

The composition of PCBs in fallout and in air samples was compared with that of Clophen A 60. The amounts of the various congeners found in the samples were each divided by the amounts of the identical congeners in the commercial PCB mixture. There is a significant advantage in using such a comparison of PCB fingerprints. If only a few PCB congeners were detected in the sample (which occurred occasionally at certain stations with low fallout and low PCB levels in the lower atmosphere, e.g. stations 5,.6, 10 and 14) the PCB basis did not change owing to the apparent domination of these congeners.

The cluster analysis further revealed a similarity in the fallout of PCBs among a majority of the eastern coastal stations along the border of the Baltic Sea as well as at a northern station influenced by precipitation contaminated by southerly to easterly sources (see 3.5). These stations were probably dominated by LRT from easterly to southeasterly sources or by transport of volatilized compounds from the Baltic (Larsson, 1985a), which is highly contaminated with PCBs (Kihlstrom and Berglund, 1978).

Inland stations situated in sparsely populated, woodland areas (stations 6, 12) and the northern station 14, influenced by air masses from the northern Atlantic, did not show any specific clusters but tem- poral. These stations were exposed to low amounts of chlorinated HCs in atmospheric fallout and represen- ted the environments least influenced by LRT and thus contamination.

The cluster analysis revealed a similarity in the PCB The regression analysis relating the PCB composi- fingerprint between the fallout of stations 7, 8 and 9, tion of the industrial PCB oil to that of fallout for the and at the station in Berlin, and the industrial PCB oil stations (exemplified in Fig. 7) confirmed the results of

Station NQ

h I

2z”%%:ltr?fiR rrr-_-_rrr

IUPAC numbers I I I I I I

0 0.1 0.2 03 04 0.5

Distance

Fig 6. Cluster analysis (single linkage cluster, distances are Pearson correlation coefficients) of PCBs in the airborne fallout during July-October 1985 (period 4). Stations connected at or near distance 0 have a PCB composition, identical or similar to the reference (Clophen A 60). In general, the longer the distance of a station from 0 to connection, the greater is the degree of deviation between its composition and that of the other stations and the reference. The pattern and intensities of the major peaks in the gas chromatograms exemplify sea (station 4), local (station 7) and long range influences (station 12). For location of the stations, see Fig. 1. Station B was located in

Berlin, F.R.G.


I Station nr 2 I

Station nr 7 I

d I- Clophcn A 60

Fig 7. Composition of PCBs in airborne fallout and in the industrial PCB-mixture Clophen A60. To the left the PCB composition in atmospheric fallout of stations 2 and 7 is shown. To the lower right the PCB composition in Clophen A 60 is shown. To the upper right the relation between proportion of PCB congeners in Clophen A60 and the proportion of congeners in atmospheric fallout for two sampling stations. The proportions were different for station 2 resulting in a low r*, while they were similar for station 7 resulting in a high r2. A high r* indicates that the station was influenced by local

contamination.

cluster analysis. There was a linear relationship between fallout from stations influenced by local combustion Clophen A 60, while fallout from stations exposed to LRT showed no such relationship.

When comparing the composition of all the analyzed persistent pollutants in atmospheric fallout and in the lower atmosphere between stations, two revealed marked divergences. Samples from station 4 consistently contained a high proportion of 2,2’,3,5’,6- pentachlorobiphenyl (IUPAC 95 Fig. 6). This is one of the least chlorinated congeners dominant in Clophen A60. It has been shown that low-chlorinated PCBs more easily volatilize from water to air than do more highly chlorinated ones (Larsson, 1985a,b; Larsson and Okla, 1987). Consequently, this station was most likely exposed to volatilization originating in the southern Baltic. In fact, the station was situated on an

island and thus exposed to transport from the sea regardless of wind direction. Samples from station 11, situated on the shoreline of the northern Baltic, always contained several specific, H,SO, resistent compounds that have yet to be identified.

3.4. Fallout of PCBs at inland us coastal stations

The fallout of PCBs was significantly higher at the coastal stations than at the corresponding inland ones (p =0.0056, Wilcoxon signed rank, Table 1). This was also the case in 1972-1973. The higher rates of coastal deposition might have been due to the seas surrounding Scandinavia acting as sources for the compounds. Through volatilization (Larsson, 1985a.b; Larsson and Okla, 1987) and via seaspray (McIntyre, 1974) the lipophilic pollutants can be transported from water to air and hit coastal areas as fallout, decreasing along a


Table 1. The atmospheric fallout of PCBs @m-a month-‘) for stations located at the Swedish coast and for corresponding stations situated inland. Figures within brackets indicate that the sea outside the station was covered

with ice during sampling. ND = not detected

Period

Station no.

2 3

4

7 10

11

Coastal stations Fallout Inland stations Fallout I II III IV Period I II III IV

Station no.

(0.19) 0.42 0.07 1.60 1 (0.42) 0.24 ND 0.07 (1.24) 0.79 4.59 10.1

(1.92) 0.18 0.05 0.81 5 (0.59) 0.77 0.02 0.22

6.23 2.31 2.26 30.63 6 0.42 0.26 0.13 ND (1.47) (0.35) 1.48 0.21 9 (1.73) (1.17) 0.79 2.21

(0.95) 0.62 0.29 1.50 11 (0.57) (0.20) 0.26 0.21

gradient from the shore towards the inland regions. The higher deposition near the sea could also have been the result of long-range transport from sources outside Sweden, which decreased as the distance from the sources increased.

3.5. Fallout of PCBs at the northern stations Abisko and Katterjiikk

The fallout of PCBs in Abisko (station 13) was among the highest in Sweden while Katterjakk (station 14) had the lowest. Additionally, levels of PCBs in the lower atmosphere were considerably higher for station 13 than for station 14. The stations are situated in a mountainous area in the northern part of Sweden, far from industrial regions and with a very cold, Subarctic climate (the annual mean temperature was -4°C). The distance between the stations is only 40 km, but they are separated by a mountain, with station 13 situated on the eastern side and station 14 on the western side. The stark difference in contamination situation between the two stations can be attributed to differences in local climate. Station 13 is situated in a rainshadow; thus 74% of its sparse precipitation (on average 298 mm a- ‘) is brought by eastern and southern winds whereas only 2% comes in from the North Atlantic to the west. This precipitation seems to be highly contaminated with PCBs, the contamination occurring directly and/or by wash-out of contaminated eastern to southern air packages. Station 14, on the other hand, receives abundant (on average 807 mm a- ‘) clean precipitation via westerly winds (47% of the total precipitation) from the North Atlantic.

The local climate hypothesis is supported by another two arguments. Station 13 was dominated by southern winds during periods I, II and IV. The fallout of PCBs during these periods was high. During Period III, fallout of PCBs was considerably lower. During this period northern winds dominated, and the northern air masses, probably originating from the Arctic, seemed to be only lightly contaminated. Additionally, a high amount of several H,SO,-persistent compounds, mainly resembling chlorinated terphenyls, were found in fallout from station 13 during period IV.

This compound group was not found in fallout from any other station.

The results show that even wilderness area far from human domain may receive a large inflow of persistent pollutants via the atmosphere.

3.6. Levels of PCBs and ZDDTin the lower atmosphere

The distribution of chlorinated HCs was heavily skewed towards the gas phase. In all but a few samples, only just detectable traces of CDDT (mainly p,p- DDT) and PCBs were found adsorbed to the particle filters. However, the results may be an artifact resulting from the volatilization of these compounds from the particle filters and their subsequent capture by the adsorbent during sampling (Doskey and And&, 1981). In the lower atmosphere of stations 7, 8 and 9, 0.4-7.3% of the PCBs was found in the particulate state. This strongly suggested that the sampling was performed close to the sources (see 3.2).

The levels of ZDDT in the lower atmosphere decreased along a south-north gradient (Fig. 4). The reasons for this gradient have been explained earlier

-10 -5 0 5 10 15 Average temperature (“C)

Fig 8. Concentration (log scale) of PCBs in the air over Sweden in 19841985 as a function of the average ambient temperature. The slope of the lines con- necting each station show that the concentration of PCBs in the air is positively related to temperature (see the text for statistical examination). n = 4 for each

station. For location of the stations, see Fig. 1.

Atmospheric transport of chlorinated HC to Sweden

[XPCBI (ng/mlf) - _ 0.4

8.25

1709

lZDDT1 (r&n31 U.“..“..

0.08

0.06

0 1 2 3 4 5 6 7 9 10 11 12 13 14

Station

Fig 9. Levels of PCBs and ZDDT in the lower atmosphere in 1984-1985 (for four sampling periods each lasting 3 months) for the sampling stations.

(see 3.1). However, there was one notable exception to this trend. In the warmer summer periods high levels of CDDT were recorded in air at station 12 (Fig. 9). This station is situated in a woodland area subject to intensive forestry. Even after the main restrictions were placed on DDT in Sweden, some DDT was still used to protect young spruce from insects. Conse- quently, it is possible that some of this DDT was inappropriately stored or used illegally and thereby volatilized, causing the present atmospheric contamination in this region.

The levels of PCBs and ZDDT in the lower atmosphere were positively related to the mean temperatures of the sampling stations (Fig. 8, for PCBs: t,, = 5.56, significance of average regression coefficient; p = 0.0001. For DDT: t,, = 4.19, significance of average regression coefficient; p = 0.0003). Consequently, the levels of persistent pollutants were higher during the warmer summer periods and lower during winter. The results showed that the chlorinated HCs volatilize from airborne particles, from the ground and from contaminated water bodies (Larsson, 1985a) at higher temperatures. They are then present in the gas phase. At lower temperatures the pollutants are adsorbed to particles or partitioned to the liquid phase and are washed out by rain or become a part of dry deposition. Thus, a negative correlation should be expected between the levels of the persistent pollutants in air and

those in fallout. No such statistically significant correlation could be established in this investigation, probably owing to local contamination by combustion near several sampling stations (that should have resulted in the simultaneous presence of high amounts of chlorinated HCs in air and in fallout).

Levels of persistent pollutants in the lower atmosphere were highest during the vegetation season (periods III, IV, Fig. 9). This means that the pollutants were available for direct uptake in plants (e.g. Buckley, 1982; Thomas et al., 1984) that are exploited by herbivores. Thus, the compounds are transferred within the food webs. Additionally, the pollutants are available for uptake via the breathing apparatus of organisms during the period when Holarctic animal populations are in their most intense growing phase.

In contrast to the PCB composition of airborne fallout, lower chlorinated congeners of Clophen A 60 dominated in air samples from the lower atmosphere, e.g. 2,2’,3,5’,6pentachlorobiphenyl, 2,2’,3,5,5’-pentachlorobiphenyl and 2,2’,4,5,5’-pentachlorobiphenyl (Fig. 10). The phenomenon has been reported previously by Doskey and Andrtn (1981) and by Larsson (1985a). Compared with more chlorinated biphenyls, these compounds have a higher tendency to volatilize. The results obtained using filter technique probably qualitatively reflect the presence of chlorinated hydrocarbons in a better way than do the results using


0 PCBsinair PCBs in fallout

16

PCB congeners

Fig 10. Composition of PCB congeners (%) in atmospheric fallout and in the lower atmosphere (%) for station 9. The pattern was representative for a majority of the sampling stations and periods.

fallout screens, since no selection of the compounds occurs using the former method. However, when sampling large amounts of air at high pumping rates (>1000m3h-*, not the case in this study) break- through of certain low-chlorinated PCBs may occur

(5)

(6) (Simon and Bidleman, 1979).

4. CONCLUSIONS

(1) Whereas the airborne fallout of ZDDT over Sweden significantly decreased from 1972-1973 to 19841985, the fallout of PCBs was similar during the two periods.

(7)

(2) From each sampling station the composition of persistent pollutants in fallout and in the lower atmosphere was specific, The composition of pollutants was determined by the location of the station and climatic factors.

(3) Fallout of PCBs was higher at coastal stations than at corresponding inland ones. The reasons “^,.__

~Lnr~~wledgements-We thank A. Siidergren for all his help. We also thank P. Capel, W. Giger, G. Carlberg and J.-E. Kihlstrijm for constructive criticism of the early drafts of this manuscript. The project was financed by the Swedish En- vironmental Protection Board.

(4)

for the difference could be that the compounds volatilize from the seas surrounding Scandin- avia, which act as large reservoirs and/or that long range-transport from sources outside Swe- den resulted in gradient deposition. The atmospheric deposition of PCBs was highest in the western parts of the country, owing to local combustion. High fallout was also recorded in one of two closely situated stations in the northern mountain area of Sweden, while low deposition was recorded at the other. The difference can be explained in terms of local dissimilarities in climate.

The fallout of ZDDT decreased in along a gradient from the south to the north of the country, indicating that LRT from southern sources was responsible for the deposition. Levels of PCBs and EDDT in the lower atmosphere were positively correlated with temperature. Levels of PCBs were highest in the western part of Sweden, owing to local contamination, while levels of XDDT showed a similar decreasing gradient from the south to north as fallout of the compounds. The results show that considerable atmospheric transport of persistent pollutants to and within Sweden is now occurring. Atmospheric deposition of chlorinated HCs seems to dominate the inflow to northern ecosystems, and this process alone could explain the contamination levels found in organisms inhabiting these environments.

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