EXTENDED STUDY OF ATMOSPHERIC HEAVY METAL DEPOSITION IN LITHUANIA BASED ON MOSS ANALYSIS. 1. Introduction

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1 EXTENDED STUDY OF ATMOSPHERIC HEAVY METAL DEPOSITION IN LITHUANIA BASED ON MOSS ANALYSIS D. CEBURNIS 1,Å.RÜHLING 2 and K. KVIETKUS 1 1 Ecological spectroscopy laboratory, Institute of Physics, A. Gostauto 12, 2600 Vilnius, Lithuania; 2 Institute of Ecology, Ecology Building, S Lund, Sweden (Received 14 July 1995; accepted in final form 26 July 1996) Abstract. The use of different moss species Hylocomium splendens, Pleurozium schreberi, Eurhynchium angustirete, Sphagnum and Rhytidiadelphus was tested for the investigation of atmospheric heavy metal deposition. Maps representing heavy metal deposition pattern in Lithuania are presented for Cd, Cr, Cu, Fe, Ni, Pb and V. The most suitable species for heavy metal deposition studies was Hylocomium splendens in which the concentrations of metals were found to be up to 25% higher than in other species. Interspecies and interelemental comparison was also performed. Several well defined local pollution sources were identified. Key words: bioindicator, heavy metals, moss 1. Introduction The use of mosses as indicators of atmospheric pollution by heavy metals was developed in Sweden (Rühling and Tyler, 1968, 1969) and is now well established. Apart from the monitoring of emissions from local hot spots such as industrial plants, smelters (Burkit et al., 1972; Ellison et al., 1976; Tyler, 1984), mosses have also been used for extensive regional surveys in various parts of the world. These include studies in the north-eastern USA (Groet, 1976), New Zealand (Ward et al., 1977), Maritime provinces of Canada (Percy, 1983), Nigeria (Onianwa et al., 1986), periodically in Northern Europe (Rühling et al., 1983, 1987, 1992) and extensive survey in Europe (Rühling, 1994). The stability of metal organic complexes and chelates and the great cation exchange capacity of the tissues are primarily conditions for the sorption of heavy metals by mosses (Tyler, 1970). The degree of retention proved to decrease in the order Cu > Pb > Ni > Co > Cd > Zn, Mn (Rühling and Tyler, 1969). There are many secondary processes other than atmospheric deposition that could influence heavy metal content in the mosses (Ross, 1990; Steinnes, 1992, 1995). As the magnitude of the secondary processes tends to vary significantly depending on the different environmental conditions, more detailed and extensive studies from different regions are required to elucidate these processes (Ceburnis, 1994). This study includes results from a previous survey in 1990 (Rühling et al., 1992) and a recent study in The main purposes of the latter study were: (1) to compare heavy metal distribution pattern in Lithuania in 1990 and 1993; (2) to prove the efficiency of improved analytical technique and the repeatability of results Environmental Monitoring and Assessment 47: , c 1997 Kluwer Academic Publishers. Printed in the Netherlands.

2 136 D. CEBURNIS ET AL. Table I The number of samples of different moss species collected Genera/species Number Hylocomium splendens 79 Pleurozium schreberi 43 Eurhynchium angustirete 38 Rhytidiadelphus 9 Sphagnum (in duplicate 22 with Hylocomium) Total 191 (169 without Sphagnum) Density of samples 2.6/1000 km 2 (data from the previous survey in 1990 contained some uncertainties concerning Cd, Fe and Zn); (3) to make interspecies comparison for further monitoring surveys. This study is the first extensive national survey on the atmospheric heavy metal deposition in Lithuania based on moss analysis. 2. Materials and Methods Samples of five different moss species: Hylocomium splendens, Pleurozium schreberi, Eurhynchium angustirete, Sphagnum spp. andrhytidiadelphus spp. were collected by the workers of the Forest Research Institute in Kaunas during August September 1993 as shown in Table I and Figure 1. Samples of the Sphagnum genera were duplicated with Hylocomium splendens. The territory of Lithuania was divided into 44 km plots. In the center of each plot the most abundant species was collected if sampling of moss was possible at all. Sampling sites were located at least 300 m from the main roads, at least 100 m from any road or single house. On each sampling site on average 5 subsamples were taken within an area of 5050 m. At each location the most abundant species was collected, thus providing an information about natural distribution of species. The three youngest fully developed segments of each Hylocomium plant and corresponding green parts of other species were removed with clean hands and the unwashed samples were dried at 40 C. For the wet digestion 1.5 g of moss was decomposed in hot nitric acid (max. temperature around 95 C). Chemical analysis was performed by atomic absorption spectrophotometry, using a Perkin Elmer, Zeeman/3030 instrument. Moss samples were analyzed for cadmium, chromium, copper, iron, lead, nickel and vanadium. Only clear solution of moss extract was used for analysis. All concentrations were expressed in g/g (micrograms per gramme) dry weight at 40 C. All preparations and analysis was performed at the authors laboratory.

3 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 137 Figure 1. Map of Lithuania showing moss sampling sites. Quality assurance samples (QAS) were obtained from intercalibration exercise which preceded the project Atmospheric heavy metal deposition in Northern Europe 1990 (intercalibration samples were moss samples made in a special way for intercalibration purposes). Every 30 samples included 2 QAS. Results were recorded when QAS concentrations were within the acceptable limits which are listed in Table VI, otherwise calibration of the instrument was repeated. Acceptable limits were established after examination of intercalibration results. 3. Results and Discussion 3.1. ATMOSPHERIC HEAVY METAL DEPOSITION PATTERN The most abundant of the moss species considered in Lithuania appeared to be Hylocomium splendens (found in 50% of the sites), Pleurozium schreberi (found in 25% of the sites), Eurhynchium angustirete (found in 20% of the sites) and several species of Rhytidiadelphus genera (found in 5% of the sites). The first three species could be found almost all over the territory. Hylocomium splendens and Pleurozium schreberi were more common in coniferous forests while Eurhynchium angustirete

4 138 D. CEBURNIS ET AL. Figure 2. Point sources of heavy metal pollution mentioned in the text. was more abundant in deciduous and mixed forests. Since these three species are distributed homogeneously all over the territory, interspecies comparison and subsequent species calibration could be performed. The interspecies comparison is also possible because any expressed concentration gradient in any direction was neither found in 1990 non 1993, however mainly because the territory of Lithuania is rather small. Mosses of several species of the Sphagnum genera were duplicated in 22 sites with samples of Hylocomium splendens. No further identification of particular species was done concerning Sphagnum. Several studies indicated significant difference between heavy metal concentrations (Pakarinen, 1978) and metal accumulation capacity (Aulio, 1985) in different Sphagnum species. No single Sphagnum species was abundant all over Lithuania, so it was decided to check if there is any principal difference between metal concentrations in Hylocomium splendens and Sphagnum spp. Maps with the pattern of the different concentrations classes are presented in Figures 3 9 for different metals Lead Concentrations of lead were found in the range of 5 15 g/g (Figure 3). In general

5 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 139 Figure 3. Map with distribution pattern of lead concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend). variation of lead concentrations in the mosses in Lithuania is quite small. Only at the sites representing local anthropogenic pollution the concentration of lead was much higher-up to 83 g/g in the Naujoji Akmene (Figures 2, 3) with a very big factory of building materials (mainly cement). All the three sites with elevated concentrations (83, 40 and 24 g/g) surround the factory in 3.5, 5.5 and 7.5 km respectively towards the east and northeast following the direction of prevailing winds. It is rather evident that elevated concentrations near the hot spot return to background concentrations (here and further background concentration means the concentration found in moss from unpolluted sites of Lithuania) within as much as approximately km from the source. There are some other single sites with elevated concentrations of lead which could be explained by very specific contamination of those sites Nickel Concentrations of nickel in the moss usually do not exceed 4 g/g (Figure 4). A remarkably higher concentration was observed in the vicinity of the factory of building materials (Naujoji Akmene) 13 g/g. This factory burns large amounts of oil, which explains the increased nickel deposition.

6 140 D. CEBURNIS ET AL. Figure 4. Map with distribution pattern of nickel concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend) Copper The distribution pattern of copper is the most homogeneous among all the metals studied, mainly ranging from 4 to 8 g/g (Figure 5). Elevated concentrations were found only close to the factory in Naujoji Akmene 16 g/g. During the investigation in 1990 elevated concentrations found in the western region of Lithuania were explained by the higher precipitation amount in this region (Rühling et al., 1992). As the survey in 1993 took place after two very dry summers with significantly lower precipitation amount the pattern observed in 1990 might be masked in Chromium Rather low chromium concentrations were found in the mosses 1 2 g/g (Figure 6). It was found during the subsequent analysis of samples that it is not enough to run sample decomposition at the temperature below 100 C to make it complete. The surface of mosses is always covered with mineral particles of different origin and some of the heavy metals (considered Cr, V, Ni) present in the form of oxides, etc. which are usually chemically and thermally resistant. Decomposition of samples at less than 100 C could not be complete as the decomposed sample very often contains appreciable amount of deposits or sediments, where a part of metals considered could be accumulated. This was proved by further investigations in the

7 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 141 Figure 5. Map with distribution pattern of copper concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend). laboratory. For example the loss of chromium from the moss extract sometimes amounts up to 40% (V 20%). According to our knowledge decomposition of mosses in nitric acid should be run at the temperature not less than approximately 120 C. The highest chromium concentration was found close to the building material factory 18 g/g and exceeded the average concentration more than ten fold. Chromium was the only element where the relative difference between average and maximum concentration was so high Cadmium Concentrations of cadmium are the least evenly distributed in the Lithuanian territory (Figure 7). They vary in the range g/g without any clear pattern. Similar distribution was observed in other countries also (Rühling (ed.), 1994). Such specific pattern could be attributed to the use of a mineral fertilizers in agriculture which were used in Lithuania very extensively until The influence of phosphorous fertilizers to the content of Cd to the higher plants was observed in agricultural areas (Bærug et al., 1989). Much higher cadmium concentrations were found close to the factory of building materials (Naujoji Akmene) 1.43 g/g.

8 142 D. CEBURNIS ET AL. Figure 6. Map with distribution pattern of chromium concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend) Vanadium The main emission sources of vanadium are oil refineries and burning of fuels. Elevated concentrations are usually found close to thermal power stations and other industries which use such fuel. In the map (Figure 8) elevated concentrations are clearly visible near the Elektrenai thermal power station (21 g/g), Alytus thermal power station (16 g/g) and close to the mentioned factory of building materials(14 g/g). Pollution with vanadium was more expressed the closer the samples were collected to the source. Average concentration of vanadium in the moss was around 5 g/g Iron Iron is usually considered mainly as an element of soil origin and its content in the moss is caused not only by an atmospheric deposition. Average concentration of iron was found to be about 850g/g (Figure 9). Near the identified pollution sources concentrations of iron were also elevated 4200 g/g close to the mentioned building material factory. Due to the composite origin of iron in the moss only highly elevated concentrations could indicate elevated atmospheric deposition. Owing to the similar heavy metal survey in 1990 it was possible to compare heavy metal concentrations found in 1990 and 1993 (Table II). As might be expected

9 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 143 Figure 7. Map with distribution pattern of cadmium concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend). Table II Heavy metal concentrations in moss in Lithuania (1990 and 1993, mean conc., g/g d.w.) and similar studies from other regions at the same latitude Year Pb Ni Cu Cr Cd V Fe Lithuania Lithuania Southern Sweden a Canada b nd 353 North-western Poland c nd=nodataavailable; According to the uncertainties concerning Cd and Fe in 1990 calibrated concentrations are presented (Rühling et al. 1992); a Rühling (ed.) (1994); b Percy (1983); c Grodzinska et al. (1994). there are no remarkable differences in heavy metal concentrations between 1990 and 1993, which is not surprising considering the short time period between these two surveys. Comparison of the data from similar studies at the same latitude (Table II) clearly shows findings of this study are in good agreement with the data

10 144 D. CEBURNIS ET AL. Figure 8. Map with distribution pattern of vanadium concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend). from other studies. The remarkably lower lead concentrations in Lithuania than in Southern Sweden and North-Western Poland could be simply explained by a less intensive traffic in Lithuania and no concentrated industry in one particular region as in some parts of Western Europe. Long-range transport also affects the less polluted areas as it is observed in Southern Scandinavia. Correlation matrices were calculated for different species. Only correlations which were significant at the P<0.05 level are presented in Table IV. As the number of Sphagnum and Rhytidiadelphus samples was rather small (22 and 9 samples respectively) correlation matrices are not presented for these species. The largest number of significant correlations was found for Hylocomium splendens and a little less for Pleurozium schreberi. All species showhigh Ni V correlation, even Sphagnum spp. It seems that the main emission sources or processes for these metals are the same, predominantly burning of fuel oils. High correlations were observed between lead and other elements in Hylocomium splendens and Pleurozium schreberi. This also confirms the applicability of these species for reliable identification of polluted areas. In spite of the fact that the highest elemental concentrations were observed in Eurhynchium angustirete (Table III, Figure 9), it is likely that much of the metals observed in this species originate from other sources than atmosphere, since the correlations between the typical air pollution elements

11 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 145 Figure 9. Map with distribution pattern of iron concentrations (g/g). (circles with different radius represent different concentration classes as showed in the legend). are much weaker than in Hylocomium splendens or Pleurozium schreberi. Itis also supported by the fact that in samples of Eurhynchium angustirete the moss was strongly mixed with extraneous material, especially with different grasses. The results of this study support the opinion that the most suitable species for assessing atmospheric deposition by means of moss analysis in northern Europe are Hylocomium splendens and Pleurozium schreberi. Separate correlation analysis was performed for elevated concentrations of all the metals (Table V). Elevated concentrations were assumed to be higher than double median concentration. For that purpose sites with elevated concentration of at least one element were selected from the data set. It is evident from the Table V that at sites with elevated metal concentrations significant positive correlations were observed between all elements except Ni and V. Especially high correlations were calculated for Pb and Cd, even not only between these and other elements, but also between almost all the metals. Thus it could be concluded that at the sites with elevated concentrations the pollution pattern is rather unique, i.e. the pollution is multielemental. Absence of correlation for Ni and V can be explained by single element pollution sources and processes for these elements. Besides this, pollution with Ni is always accompanied by pollution with V but not opposite (Figures 4, 8).

12 146 D. CEBURNIS ET AL. Table III Survey of metal concentrations (g/g) in different species Statistics Pb Ni Cu Cr Cd V Fe Hylocomium splendens min max arithmetic mean median (concentration) Pleurozium schreberi min max arithmetic mean median (concentration) Eurhynchium angustirete min max arithmetic mean median (concentration) Sphagnum min max arithmetic mean median (concentration) Rhytidiadelphus min max arithmetic mean median (concentration) INTERSPECIES COMPARISON In accordance with the considerations made above it is possible to make interspecies comparison (Figure 10). According to Table III and Figure 10 the concentrations of heavy metals in different moss species can generally be expressed in the following order: Eurhynchium angustirete > Hylocomium splendens > Pleurozium schreberi > Rhytidiadelphus (Sphagnum). Due to the feature of Eurhynchium angustirete to be mixed with surrounding vegetation it is unlikely that higher concentrations in this species represent higher metal accumulation capacity. Comparison of moss

13 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 147 Table IV Correlation matrices for metal concentrations in different species (correlations are significant at the P <0.05) Pb Ni Cu Cr Cd V Hylocomium splendens (n=76) Ni Cu Cr Cd V Fe Pleurozium schreberi (n=43) Ni Cu Cr Cd V Fe Eurhynchium angustirete (n=38) Ni Cu Cr Cd V Fe concentrations with deposition amounts calculated from the precipitation analysis also suggests the latter (Ceburnis, in preparation). Sphagnum spp. were collected in duplicate with Hylocomium splendens at 22 sites. Several more exact comments could be made from that data. Correlation between the average elemental concentrations (all elements together) in these two species was significant at the P<<0.01 level (r = ). In linear terms this can be expressed as follows: Conc. (g/g) in Sphagnum spp. = 0.87conc. (g/g) in Hylo spl. For some of the metals (V, Ni, Cr) even single element significant correlation was observed, similar as presented for vanadium (Figure 11). Figure 12 shows the actual difference between the concentrations in Sphagnum spp. andhylocomium splendens for different elements. The greatest differences were observed for V, Ni and Cu. Only for Cd the concentrations in Hylocomium splendens were a little lower than in Sphagnum spp. The lower concentrations in

14 148 D. CEBURNIS ET AL. Table V Correlation matrices for elevated concentrations of Pb, Ni, Cr, Cr, Cd and Fe (elevated concentrations were assumed as higher than double median concentration; sites with elevated concentration of at least one element were selected from the main data set) Pb Pb Ni Cu Cr Cd V Fe Ni Cu Cr Cd V Fe Ni Ni Cr Cr Cd Ni Cu Cr Cd V Fe Fe Fe For Cu only two sites with elevated concentrations were selected, so correlations were not calculated; For V no significant correlation was found. Table VI Acceptable limits for quality assuarance samples Sample code Pb Ni Cu Cr Cd V Fe DK N

15 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 149 Figure 10. Concentrations (g/g) of heavy metals in different species. (Cr and Cd are expressed 10 times higher, Fe 100 times lower). Figure 11. Plot of vanadium concentration in Hylocomium splendens versus concentration in Sphagnum spp. Sphagnum spp. compared to Hylocomium splendens could possibly be explained by lower metal accumulation rate or by different mass production rate, but this needs more careful calibration work. Leaching of metals from the Sphagnum tissues was not suggested (Pakarinen, 1978). At the same time it is not impossible that some species among the Sphagnum genera could have the same or very similar metal accumulation capacity as Hylocomium splendens, but as no one species of Sphagnum genera was found to be present in the whole territory, the use of Sphagnum for monitoring purposes at least in Lithuania is thought to be rather complicated.

16 150 D. CEBURNIS ET AL. Figure 12. Concentrations in Hylocomium splendens relative to Sphagnum spp. 4. Conclusions This study was performed as part of the project for estimation of the ecological sustainability of Lithuania (ECOSLIT) and was a good exercise during preparation for atmospheric heavy metal deposition monitoring survey in Europe in Several conclusions on the use of mosses in general and especially concerning the use of different species for monitoring purposes could be made. 1. The most suitable species for investigation of atmospheric heavy metal deposition in Lithuania appears to be Hylocomium splendens considering its abundance and interelemental correlations. 2. Significant interelemental correlations showed that pollution sources which are responsible for higher levels of Pb and Cd in the moss likely have unique origin, being sources of multielemental pollution and mainly represent local sources. 3. Interspecies comparisons show a general order of the metal concentrations in different species as follows: Eurhynchium angustirete > Hylocomium splendens > Pleurozium schreberi > Rhytidiadelphus (Sphagnum. However,itis quite unlikely that higher concentrations of metals in Eurhynchium angustirete represent a higher accumulation rate. 4. Concentrations of metals in Sphagnum spp. were about 25% lower than the corresponding values in Hylocomium splendens. The main achievement of this study is an extensive survey of atmospheric heavy metal deposition in Lithuania and evaluation of possible use of some of the most abundant species for monitoring surveys as well as for scientific studies.

17 MOSS ANALYSIS OF ATMOSPHERIC HEAVY METAL DEPOSITION 151 Acknowledgments The Lithuanian Forest Research Institute collected all the moss samples. We thank the workers of this Institute for valuable comments on the sampling procedure. The Swedish Institute is gratefully acknowledged for a scholarship fund to D. Ceburnis during preparation of this article and for literature search. Sincere thanks are given to Prof. E. Steinnes for valuable comments and improved language of the manuscript. Colleague D. Valiulis is thanked for the assistance in laboratory analysis. References Aulio, K.: 1985, Metal accumulation capacity of five species of Sphagnum moss, Bull. Environ. Contam. Toxicol. 35, Burkit, A., Lester, P. and Nickless, G.: 1972, Distribution of heavy metals in the vicinity of an industrial complex, Nature 238, Bærug, R., Singh, B. R., Selmer-Olsen, A. R., Håland, A., Myhr, K. and Steinnes, E.: 1989, Effect of phosphorous fertilizers on the Cd content of soils and plants from southern and central parts of Norway, Proceedings of the International Conference Heavy Metals in the Environment, Geneva, 2, Ceburnis, D.: 1994, Heavy metals in the interaction atmosphere Earth s surface, Proceedings of the Third Nordic Symposium on Atmospheric Chemistry NORSAC 93, Geilo, Norway, Ceburnis, D., Steinnes, E. and Kvietkus, K.: Estimation of metal uptake efficiencies from precipitation in mosses in Lithuania, submitted to Environ. Monit. and Asses. Ellison, G., Newham, J., Pinchin, M. J. and Thompson, I.: 1976, Heavy metal content of moss in the region of Consett (North East England), Environ. Pollut. 11, Groet, G. S.: 1976, Regional and local variation in heavy metal conc. of bryophytes in the north eastern United States, Oikos 27, Grodzinska, K., Szarek, G., Godzik, B., Braniewski, S. and Chrzanowska, E.: 1994, Mapping air pollution in Poland by measuring heavy metal concentration in mosses, Proceedings of the conference Climate and atmospheric deposition studies in forests 19, Gydesen, H., Pilegaard, K., Rasmusen, L. and Rühling, Å.: 1983, Moss analyses used as a means of surveying of atmospheric heavy metal deposition in Sweden, Denmark and Greenland in 1980, Bulletin SNV PM 1670, Nordic Council of Ministers. Onianwa, P. C., Ajayi, S. O., Osibanjo, O. and Egunyomi, A.: 1986, Accumulation patterns of heavy metals in forest mosses from the southwest region of Nigeria, Environ. Pollut. Ser. B. Chem. Phys. 11, 1, Pakarinen, P.: 1978, Distribution of heavy metals in the Sphagnum layer of bog hummocks and hollows, Ann. Bot. Fennici 15, Percy K. E.: 1983, Heavy metal and sulfur concentration in Sphagnum magellanicum in the Maritime provinces of Canada, Water, Air, and Soil Pollut. 19, Ross, H.: 1990, On the use of mosses (Hylocomium splendens and Pleurozium schreberi) for estimating atmospheric trace metal deposition, Water, Air, and Soil Pollut. 50, Rühling, Å., Rasmusen, L., Pilegaard, K., Mäkinen, A. and Steinnes, E.: 1987, Survey of atmospheric heavy metal deposition in the Nordic countries in 1985 monitored by moss analysis, NORD 1987:21, Nordic Council of Ministers. Rühling, Å., Brumelis, G., Goltsova, N., Kvietkus, K., Kubin, E., Liiv, S., Magnusson, S., Mäkinen, A., Pilegaard, K., Rasmusen, L., Sander, E. and Steinnes, E.: 1992, Atmospheric heavy metal deposition in Northern Europe, NORD 1992:12, Nordic Council of Ministers. Rühling, Å. (ed.): 1994, Atmospheric heavy metal deposition in Europe estimation based on moss analysis, NORD 1994:9, Nordic Council of Ministers.

18 152 D. CEBURNIS ET AL. Rühling, Å. and Tyler, G.: 1968, An ecological approach to the lead problem, Botaniska Notiser 121, Rühling, Å. and Tyler, G.: 1969, Ecology of heavy metals a regional and historical study, Botaniska Notiser 122, Rühling, Å. and Tyler, G.: 1970, Sorption and retention of heavy metals in the woodland moss Hylocomium splendens (Hedw.) Br. et Sch., Oikos 21, Steinnes, E., Rambaek, J. P. and Hanssen, J. E.: 1992, Large scale multi element survey of atmospheric deposition using naturally growing moss as biomonitor, Chemosphere 25, Steinnes E.: 1995, A critical evaluation of the use of naturally growing moss to monitor the deposition of atmospheric metals, Sci. Tot. Environ. 160/161, Tyler, G.: 1970, Moss Analysis A Method for Surveying Heavy Metal Deposition, in: Englund, H. M. and Berry, W. T. (eds.), Proc. Sec. Int. Clean Air Congress, Academic Press, New York. Tyler, G.: 1984, The impact of heavy metal pollution on forests: a case study of Gusum, Sweden, Ambio 13, 1, Ward, N. I., Brooks, R. R. and Roberts, E.: 1977, Heavy metals in some New Zealand bryophytes, Bryologist 80,