A CHRONOLOGY OF ATMOSPHERIC SILVER IN THE SEDIMENTS OF THE “HUZENBACHER SEE”, SW GERMANY

German Müller, University of Heidelberg, Institute of Environmental Geochemistry, D-69120 Heidelberg

e-mail gmueller@ugc.uni-heidelberg.de

ABSTRACT

Our knowledge on the historical evolution of silver in the geosphere is still restricted. From studies of particulate matter (“dust”) in urban areas we know, that silver - together with other heavy metals is enriched by a factor 100 - 1000 if related to Al. Dated lake sediments in remote areas with no direct input of anthropogenic materials offer the possibility to study the influence of atmospheric immissions. Lake Huzenbach in a remote area of the Blackforest seems to be an ideal area for such a study. Hilgers (1992) in her master’s thesis had already found the strong correlation between specific heavy metals and polycyclic aromatic hydrocarbons, detected already earlier in Lake Constance sediments (Müller et al.,1977), both groups of pollutants derived from industry, mainly from (incomplete) combustion of coal and other high-temperature processes.

Our studies in Lake Huzenbach, now including silver, mercury and lithium, confirm her conclusions derived from other metals, and also our own results obtained from sediments in Lake Constance (Müller, 1999).

INTRODUCTION

If compared with other heavy metals (p.ex. Cd, Hg, Pb, Cu, Ni, Cr) the study of silver in the geosphere has been somewhat neglected. This is especially the case in Europe.The main reason lies in the fact, that silver is not listed in the “Klärschlammverordnung” (Germany) or in the “Leidraad Bodemsanering” (Netherlands) or in comparable lists of other countries setting limits for the use or disposal of materials containing silver. As a consequence relatively few analyses exist for silver in soils and sediments.

In their article “Sources of Silver in the Environment”, Purcell & Peters (1998) gave a first comprehensive

review of the diverse aspects of silver that is used in industry, the quantities they employ, and the forms and the amounts of silver that may be discharged into the environment. In 1994 the total U.S. industrial demand for silver was 4.2 x10⁶ kg. According to their calculations photographic manufacturing was (with 53.7%) the main silver consumer, followed by electrical contacts and conductors (14.6%) and brazing alloys and solders (7%). The list closes with 3000 kg for cloud seeding.

During the past decades the interest in man’s impact on atmospheric trace metals deposited as dust has increased (Lantzy & Mackenzie 1979, Heinrichs 1993, Heinrichs & Brumsack 1997). The concentrations of Cu, As, Zn, Ag, Hg, Sb, Pb, Se and Cd in urban particulates were found to be enriched by a factor of 100 to 1000 related to Al = 1. Coal-fired power plants have been recognized as major contributors (Klein et al.,1975, Brumsack HJ, Heinrichs H, Lange H,1984) of heavy metals.

LAKE HUZENBACH

The headwater lake “Huzenbacher See” is a small dystrophic mountain lake in SW Germany (state Baden-Württemberg) within the coniferous northern Black Forest, at 747 m a.s.ll (Fig 1).

The bedrock is an extremely low buffered triassic Bunter sandstone with SiO₂ concentrations up to 95%.

The main vegetation of the 67 ha watershed consists of Norway spruce (Picea abies) and fir (Abies alba) which both show severe damages induced by acidic deposition.

The cirque lake was formed during the Würm (=Wisconsin) glaciation and has a maximum depth of 8 m, a volume of 65.000 m³, an open water surface area of 2 ha and an estimatedd theoretical mean water retention time of one month. The original shore line of the lake is formed by a floating Sphagnum peat mat.

During the last century there has been no major anthropogenic interference within the watershed of this lake except for very limited logging activities.

The lake has been intensively studied in the 90s (Hilgers 1992, Hilgers et al..1993, Thies 1994, 1995, 1997, Sommer et al.,1997).

Fig. 1 Location of Lake Huzenbach in Baden- Württemberg in the Blackforest area.

Earlier sediment studies

In 1992 Hilgers completed her Diplomarbeit (master thesis) on the distribution of heavy metals, polycyclic aromatic hydrocarbons, soot particles and sulfur in dated sediment cores of Lake Huzenbach. One year later the data were published by Hilgers et al., 1993.

The distribution patterns of both heavy metals and PAHs in principle resemble the patterns in Lake Constance:

Heavy metals and PAHs rise from about 1850 (in Lake Constance some 20 to 30 years later) onwards significantly towards maxima around the 1970s. As an example for the historical evolution of PAHs in the sediments of Lake Huzenbach Fig. 3 depicts the development of benzo(k)fluoranthene. After the 70s a strong decrease is to be observed in both lakes.The patterns from Lake Huzenbach can be related to contemporary sources of industrial emissions, e.g. steel and chemical industries, oil refineries, waste and sludge incineration situated in the upper Rhine valley (concentrated in the Kehl - Strassburg area) with Lake Huzenbach lying about only 50 km eastward (Fig.1) in the main wind direction.

This study

Table 1. Concentrations of selected heavy metals and lithium in a sediment core from Lake Huzenbach.

Our growing interest in silver in the geosphere was a reason to visit Lake Huzenbach with the hope (and belief!) to find a positive correlation between this metal and other specific heavy metals and PAHs in the sediments if a common source were responsible for the co-occurence.

In addition to silver we also analyzed mercury, not determined by Hilgers (1992).

Lithium was analyzed as an internal standard reflecting a nearly exclusively geogenic concentration representing coarser grained (or humic-rich) sediment layers within the sediment sequence.

Table 1 and Fig.2 represent the results of our analytical data. The lead-210 age determinations could be transfered directly from Hilgers data without any manipulation.

Fig. 2 Concentration of various heavy metals (Hg, Zn, Ag, and Cd) and of Li in a sediment core from Lake

Huzenbach. Chronology after (Hilgers 1992)

Highest concentrations of all four heavy metals were found in the 3.1 - 3.8 mm sediment layer, representing the time span between about 1967 and 1972: Ag 0.74, Cd 1.54, Zn 174, Hg 0.6 mg/kg.

Highly significant positive correlations exist between Ag:Zn (0.9), Ag:Cd (0.8), Ag:Hg (0.8) and Hg : Zn (0.7)

Between Cd:Li and Ag:Li correlations are negative: -0.4 and -0.1, respectively.

The uppermost -1 to 0 cm layer with the highest Cd content of the whole series (and the lowest Li content and very high Hg, Ag and Zn concentrations) belongs to a highly porous accumulation of humus lying on the sediment surface. A detailed study of this humose layer will throw more light into the present day accumulation of heavy metals and PAH from atmospheric immissions.

The high Li concentrations and correspondingly low heavy metal concentrations represent sediments with a high percentage of coarse grained (sandy) material flooded into the lake after strong rainfalls, leading to a dilution of the heavy metals.

Fig. 3 Concentration of benzo(k)fluoranthene in a dated sediment core. From Hilgers (1952)

CONCLUSIONS

Lake Huzenbach may serve as an example for a nearly exclusively atmospheric input of silver and other heavy metals from industrial sources, i.e. coal combustion and other high temperature processes including traffic, ore processing, waste combustion etc.

On a world wide basis, coal combustion was and is a major source of silver, cadmium and mercury emitted into the atmosphere. In countries with a still relatively low technology standard emissions may become a global threat. In China the annual coal consumption has surpassed already the 3.000.000.000 tonnes limit with a still increasing tendency.

LITERATURE

Brumsack HJ, Heinrichs H, Lange H (1984), Environ Technol Letters 5, 7 - 22

Hilgers E (1992), Diplomarbeit Univ. Freiburg, 85 pp.

Hilgers E,Thies H, Kalbfus W (1993), Verh. Internat. Verein. Limnol. 25, 1091 - 1094

Heinrichs H (1993), Habilitationsschrift Univer. Göttingen, 119 pp

Heinrichs H, Brumsack HJ (1997), in Geochemie und Umwelt, Matschullat J, Tobschall HJ, Voigt HJ (editors), Springer Verlag Berlin Heidelberg, 25 - 37

Klein DH, Andren AW, Carter JA, Emery JF, Feldman C, Fulkerson W, Lyon WS, Ogle JC, van Hook RI, Bolton, N (1975), Environm. Sci Technol 9,,,973 - 979

Lantzy R, Mackenzie FT (1979), Geochim. Cosmochim Acta 43, 511 - 525

Müller, G. (1999), Extended abstract, 6 th Internat. Argentum Conference, Madison, USA August 1999

Müller G, Grimmer G, Böhnke H (1977), Naturwissenschaften 64, 427 - 431

Purcell, TW, Peters, JJ (1998), Environ. Toxicol. Chem.12, 539 -546

Sommer M, Thies H,Kolb E, Bächle H, Stahr K(1997), Water Resources Reseasrch 33, 2129 - 2142

Thies H (1994), Hydrobiologia 274 ,, 143 - 154

Thies H (1995), Water Air and Soil Pollution 85, 541 - 546

Thies H (1997), Verh. Internat.Verein.Limnol. 26, 283 -288