Preliminary data on enviornmental distribution of mercury in northern Victoria Land, Antarctica

Antarctic Science 5 (1): 3-8 (1993)

Preliminary data on environmental distribution of mercury in northern Victoria Land, Antarctica R. BARGAGLI, E. BATTISTI, S. FOCARDI and P. FORMICHI Department of Environmental Biology, University of Siena, Via delle Cerchia 3, 53100 Siena, Italy

Abstract: Concentrations of mercury were measured in soil and two species of epilithic macrolichens (Umbilicaria decussata and Usnea antarctica) collected along of the coast of northern Victoria Land coast. Most of the soil samples had a very low mercury content, whereas lichens had levels higher than in other remote areas. Although a possible contamination of samples cannot be completely excluded, the relevance to bioaccumulation of the very slow growth rate of lichens and of volcanic activity are discussed. Received 4 February 1992,accepted 10 August 1992

Key words: mercury, soil, macrolichens, growth rate, volcanic emissions

Lichens readily take up and retain elements, which enter the thallus (either dissolved or as atmospheric dryfall) by processes of particle trapping, passive adsorption of cations and active uptake of anions (Nieboer & Richardson 1981). The use of lichens has been found to be an effective method of monitoringlevels of airborneheavy metals and particularly of Hg (Bargagli 1990, Bargagli & Barghigiani 1991). It seems well suited to studies in continental Antarctica where it is rather difficult to perform accurate direct measurements. Owing to the inconsistency of the little data available, the aim of this study was to establish present levels of mercury in the coastal environment of northern Victoria Land and to obtain some indication of the relative content in the atmosphere. Moreover, the macrolichens used in the present study are common throughout continental, maritime and subantarctic regions and can also be found in the northern hemisphere. This could allow mercury biomonitoring in almost all remote zones of the southern hemisphere and comparisons with data from the northern hemisphere.

Introduction In the context of global cycles of metals, mercury is unique as it is emitted mainly as vapour by natural or anthropogenic sources and it is the only metal that biomagnifies through food chains. The relatively long residence time in the atmosphere (c. 1y, Slemr et al. 1985) and consequent long range transport, together with natural transformation into methylmercury, make exposure of target organisms to mercury potentially serious, even in remote areas. Quantitative estimates of the global fluxes and reservoir contents of mercury are still widely divergent owing to the lack of sufficient and reliable data on natural emission and deposition. These data are lacking especially for the remote regions of the southern hemisphere (Fitzgerald 1986). Research performed in the last decade (Brosset 1982, Fitzgerald et al. 1983, Slemr et al. 1985) has shown that oceans are sources of mercury to the atmosphere even if continental emissions (anthropogenic, crustal degassing, volcanoes and forest fires) are decidedly higher. Moreover, average concentration of atmospheric mercury seems to increase with time in both hemispheres (Slemr et al. 1985). One way to reconstruct the past and present natural tropospheric fluxes of mercury is the analysis of wellpreserved dated snow and ice layers deposited in the central Antarctic and Greenland ice sheets. Unfortunately, studies on long-term trends of mercury deposition using dated ice cores have been rather inconclusive (Appelquist et al. 1978, Wolff 1990). Techniques for sampling and determining ultra-trace elements are continuously improving, However, in areas like VictoriaLand, the mercury concentrations in air and snow samples are affected by the relative activity of volcanoes and fumaroles and by meteorological conditions. Consequently the concentrations are rather variable and to obtain significant data measurements need to be made over long periods of time.

Materials and methods Two species of epilithic macrolichens were collected: the foliose Umbilicaria decussata pill.) Zahlbr. and the fruticose Usnea antarctica Du Rietz. Whereas the latter species has an Antarctic circumpolar distribution (continental and subantarctic regions, New Zealand and Tierra del Fuego; Walker 1985), U.decussata is cosmopolitan (Golubkova et al. 1978). As in other areas of continental Antarctica (Llano 1965, Nakanishi 1977, Longton 1979), in coastal Victoria Land these species are frequently associated and may become dominant on cliffs, scree slopes and other rocky habitats. Lichen thalli were collected during the 1989/90 Antarctic summer. Whenever possible, in each site a composite of several thalli of each species and a sample of ‘soil’ (fine

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particles carried by meltwater at the base of rocks or stones bearing lichens), were collected. Directly after returning to the laboratory of Baia Terra Nova Station, the samples were dried at 40°C for 36 h, and then sorted to remove as much extraneous material as possible and dead or senescent tissues. Soils were sorted for gravel and larger organic debris and then homogenized and passed through a stainless steel 250pm mesh sieve. This is necessary as the large variations in the grain-size could exercise a determining influence on metal concentrations. Although in previous quantitative biomonitoring with lichens, the different age of different parts of the thallus has hardly ever been considered, it cannotbe neglected (Bargagli 1989), especially in Antarctic ecosystems. In order to obtain relatively comparable data, the same portion of the thallus in eachsample was excised and analysed: the outermost 2-3 mm of Urnbilicaria and the terminal 8-10 mm of Usnea were used for analysis. About 150 mg of plant material and soil were used for digestions with concentrated HNO, (Merck Nr. 441 Suprapur) in apressurized digestion system at 120°C for 8 h. Concentrations of total Hg were determined by flameless atomic absorption spectrophotometry andAl content was also determined in thesame solution by graphite furnace. Since this element is widespread in the lithosphere and has limited or no metabolic significance in lichens, it provides useful information on the presence of rock dust particles in lichen thalli. The straight-line response was calibration obtained with different dilutions of a standard Hg solution (lg 1.’ Spectrosil, BDH) prepared in the same manner as the unknown samples. Both equipment and procedure blanks usually were below the minimum level of detection. The coefficient of variation calculated from replicate analysis of soil and lichen samples ranged from 5 . 2 4 4 % for Hg and from 12.4-16.9% for Al. Data quality was controlled and corroborated through the analysis of Standard Reference Materials(NBS 1572 ‘citrusleaves’ andNBS 1646 ‘estuarine sediments’, Table I). Moreover, in soil samples the total organic carbon content was determined according to the procedure outlined by Gaudette et al. (1974). The Hg content in lichens collected in northern Victoria Land during the 1989/90 Antarctic summer proved surprisingly high and the results were considered unreliable. During the 1990/91 expedition the sampling was repeated from Football Saddle (72’31’s) to Cape Ross (76’44’s)

adopting all possible precautions to prevent sample contamination: sampling places were positioned 2 km from manned stations of Baia Terra Nova (Italy) and Gondwana (Germany) and over 500 m from helicopter landing places. a new pair of disposable plastic gloves and very clean stainless steel forceps were used each time a sample was collected and placed in paper bags (Hg content 8 2 3 ng g-l d.w.). preparation and storage of samples took place immediately after returning to the Baia Terra Nova Station, in a laminar flow chamber. in Italy, samples were unsealed in a chamber under an N, flow and about 150mg was immediatelyplaced inTeflon vessels, previously washed with Merck Suprapur HNO,. All analytical determinations werecompletedwithin two weeks of the arrival of samples. In spite of all precautions against contamination and the care taken for accuracy and precision of measurements, the 1990J91data corresponded to those of the previous expedition (Table I) and all data were therefore averaged. The stability of Hg values in lichens one and two years after their arrival in Italy, has also been evaluated in five samples of the two species and an average Hg increase of 5.6 5 2.4 % has been recorded. Samples of U.antarctica from the Antarctic Peninsula, King George Island and Deception Island and one of U-decussatafrom Kongsfjorden (Svalbard) have also been considered. Results and discussion Mercury distribution in surface soil

The fine fraction of surface soils from coastal northern Victoria Land had a rather low content of total Hg (range 0.007-0.096 g” d.w.; X = 0.034_+0.023). Although differences in ecology and in pretreatment of samples do not allow accurate comparison, these data are among the lowest reported for rocks (NRCC 1979) and soils of remote regions (Shacklette & Boerngen, 1984). This was rather unexpected as samples had an average organic matter content of 6% and very few can be defined as frigic (Campbell & Claridge

Table I. Quality control results and comparison betwen Hg concentration in lichens collected twice in the same station. Data as pg g l , n

U.antarctica

n

U.decussata

1989/90

range i? s.d.

14

0.12-0.70 0.40 2 0.22

15

0.11-1.14 0.372 0.26

1990/91

range s.d.

14

0.11-0.93 0.382 0.25

15

0.11-0.87 0.34 2 0.21

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NBS 1572 Citrus Leaves certified value measured value

Al = 92 f 15 Hg ~ 0 . 0 82 0.02

95.2 ?I 13.8 0.085 ? 0.015 97.3 f 14.6 0.077 f 0.010

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MERCURY DISTRIBUTION IN VICTORIA LAND

1969) or ahumic (Tedrow & Ugolini 1966). It is well known that organic materials in the soil act as a very effective sorbent for Hg, but, contrary to previous reports (Anderson 1979, Adriano 1986), a significant relationship between the metal content and that of organic carbon was not found (Fig. 1). This could be due to the very low moisture content and to the paucity of biological activity, which makes soil development very slow. However, the relationship in Fig. 1 would be very significant (n = 24, r = 0.603, P

5

1

7

9

c erg(%)

Fig. 1. Relationship between Hg and organic C content of surface soils, divided according to parent rock type.

epiphytic species of urban and industrial areas of the northern hemisphere (Table 11). The very low Hg concentration in Victoria Land soils and in lichens from the Antarctic Peninsula (which were prepared in Italy) seems to exclude a systematic contamination of samples. Moreover, the lichen Hg enrichment in Italy seems unimportant, even two years after their arrival. Thus, although contamination of samples cannot be completely excluded, other factors such as the very slow growth rate of lichens and volcanic emissions could be involved in the Hg accumulation. Studies on the growth of Usnea antarctica on Signy Island South Orkney Islands; (Hooker 1980) showed a net annual production of about 40 mgg’ldryweight inmature thalli. The productivity decreasedprogressivelyinvery old thalli. Taking into account that ecological conditions in Victoria Land are much more severe than those at Signy Island and that, in general, during sampling, the largest thalli were used, it seems reasonable to assume a very low growth rate for our samples. Thismight contributeto the higherHgconcentrations in Usnea from North Victoria Land compared to those from the Antarctic Peninsula. The potential contribution of active volcanoes and fumaroles should not be underestimated. The significance of volcanic emissions as primary sources of Hg has been well documented (Siegel & Siegel 1984, Varekamp & Buseck 1986). At Mount Erebus for instance, an active volcano with a permanent lava lake in its summit crater, situated c. 300 km to the south of the study area, an average concentration of gaseous Hg of 11.3 2 6.4 pg m-3was measured (Siegel etat. 1980). This value is about 5 000 times higher than “normal” baseline values and is of the same order of magnitude as those from Hawaiian or Icelandic volcanoes. Moreover, in the moss Campylopluspyr$ormis, growing in the warm soil at the southern rim of the main crater of Mount Melbourne, we

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Hg Umbilicaria

I

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MERCURY DISTRIBUTION IN VICTORIA LAND

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Table 11. Average and range of Hg and Al concentrations(ug g' d.w f s.d.) in macrolichens in Antarctica and in some foliose species from urban and industrial areas of the northern hemisphere Collection site

species

samples

n

Hg

A1

Northern Victoria Land

Usnea antarctica

(22sites)

34

Umbilicaria decussata

(25 sites)

45

0.386 5 0.190 (0.112-0.927) 0.344 t 0.204 (0.114-1.140) 0.068 2 0.013 (0.05C-0.080) 0.043 t 0.015 (0.0260.061) 0.213 5 0.028 (0.190-0.253) 0.366

420 c 214 (1 31-1 042) 455 f 243 (115-1370) 110 -+ 28 (83-149) 187 f 30 (146-215) 454 c 113 (312-590) 410

0.35 t 0.08 0.33 f 0.06 0.29 f 0.11 (0.13-0.87) 0.26 f 0.08 (0.14-0.43) 0.32 f 0.15 (0.16-0.57)

5140 -+ 2070 7850 f 4680

Graham Land

Usnea antarctica

3

King George Island

Usnea antarctica

3

Deception Island

Usnea antarctica

3

Svalbard

Umbilicaria decussata

1

Town of Sendai (Japan)

Parmelia caperata Parmelia conspersa Hypogymnia physodes

6 18 63

Parmelia tinctorum

16

Xanihoria parietina

13

Around a chlor-alkali plant (Finland) Around a steelworks Eastern Harima (Japan) Geothermal power plant Larderello (Italy) ~~

~

__

ref.

(4 (b)

854 k 482 (212-3430)

(4

(a) Saeki et al. 1977;@) Lodenius & Laaksovirta 1979;(c) Kobayashi et al. 1986; (d) Bargagli & Barghigiani 1991.

measured an Hg concentration of 1.520 pg g-'. During the 1990/91 expedition another area with hot ground, fumaroles and ice-towers was located at 73"28'S/165"37'E. Deception Island is the other active volcano in Antarctica, with many hot springs and fumaroles, which erupted at several places between 1967 and 1970. Samples of Usnea from Deception Island had a three times higher Hg content than those from Graham Land or King George Island.

Conclusions Although four-fifths of the Pb increase in the Antarctic troposphere has been attributed to local anthropogenic emission (Boutron & Patterson 1987), this seems unlikely source for Hg in a coastal northern Victoria Land, a very remote area. Except for a few samples from ice-free areas around the Nansen ice sheet, surface soils have an average Hg content that is among the lowest ever reported. Likewise the more recent data on the Hg content of ice and snow in southern Victoria Land (sampled with ultra-cleantechniques, followed by on-site extraction and analysis; Dick etal. 1990,Sheppard et al. 1991) give very low levels (4pg g").

Fig. 2. The study area (a) and the distribution of total Hg (pg g-l) in surface soils (b), Umbilicaria (c) and Usnea (d).

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These data clearly contrast with the results of lichen biomonitoring. In Victoria Land the two species have a Hg content that is higher than in the Antarctic Peninsula and roughly corresponds to that in epiphytic species in urban and industrial areas of the northern hemisphere. Possible explanations for this are: a) in continental Antarctica, the very slow growth rate of lichens (probably, the lowest up to now, among lichens used as biomonitors) enhances metal accumulationin the thallus. b) available data on gaseous Hg at Mount Erebus, those on mosses from Mount Melbourne, and the occurrence of the highest Hg content in lichens collected in the southern part of the study area (facing Mount Erebus), seems to indicate a contribution of volcanic activities to environmental levels of the metal. c) the very low levels of Hg in Antarctic surface soils are probably due to the low biological activity and the scarce development of soil. Siege1et al. (1980) pointed out an extremely low Hg content even around Mount Erebus and attributed the anomalously low ratio Hg soiVHg air (if compared with those of other volcanic sites) to the paucity of vegetation. d) the extremely low Hg concentrations in ice and snow collected just below (40 km south-west) Mount Erebus and at the edge of the Antarctic Plateau (c. 170 km to the west of the volcano) are not completely in opposition to the lichen data. Only the reactive fraction of total Hg was

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R.BARGAGLi eta/. measured in snow and ice and the sampling places were very slightly or not at all affected by Mount Erebus emissionswhich occur at 3794m and are generally blown towards north Victoria Land. Further work is needed to evaluate the consistency of these hypotheses.

Acknowledgements This work was done within the framework of the Italian National Programme for Antarctic Research (PNRA). We are very grateful to the staff of Baia Terra Nova Station for their support during the 1989/90 and 1990/91 sampling programme andto Prof. H.F. Linskensforthelichen sampling in the Antarctic Peninsula. We also thankDrs Eric Wolff and Dennis Brown for providing constructive criticism of the manuscript.

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