Heavy metals in Swiss forest soils

Fig. 1: "Totalp" near Davos; here the soil has a very high lithogenic, i.e. natural content of chromium and nickel. Picture: Marco Walser, WSL.

Fig. 2: Overview of the investigated forest soils (from Luster et al. 2006b).

Fig. 3: Forming a cast from a mixture of soil and matrix material as preparation for total metal analysis. Picture: Christoph Zwicky, EMPA.

The aim of this project is to obtain an overview of contents, effective mobility and potential ecotoxicity of heavy metals in Swiss forest soils.

Collaboration and Framework

In this project, the WSL research unit “Soil Sciences” collaborates with the Group of “Solid Materials Analytics” at “EMPA Materials Science and Technology” (Peter Lienemann, Christoph Zwicky), the "Dept. of Applied Environmental Science" of the Stockholm University (Markus Meili), and Alterra, Wageningen (Bert-Jan Groenenberg).

The investigations on mercury and lead are carried out in the framework of the UN-ECE "Convention on Long-range Transboundary Air Pollution" (LRTAP). The metal specific background can be found in chapter 5.5. of the current "Mapping Manual".

Mobility of Chromium, Nickel, Copper, Zinc and Lead

Heavy metal contents at various soil depths were determined for soils at 96 forest sites in Switzerland. The physical and chemical properties of these soils are described in great detail in the three volumes “Waldböden der Schweiz”. The calculation of enrichment factors relative to Zirconium allowed to estimate relative mobilities of the metals and to detect atmospheric input. Potential ecotoxicity was estimated by comparison with the guide levels set by the Swiss Ordinance Relating to Impacts on the Soil (VBBo) and with lowest observation effect concentrations for effects on microorganisms in topsoils recommended by the UN-ECE.
Most important results:

• Chromium, nickel, copper and zinc were mainly lithogenic, with a wide range of contents reflecting the diverse geology of Switzerland.
• Lead was enriched in the topsoil of almost all soils which was interpreted as result of long-range input of anthropogenic origin.
• Pedogenetic processes exerted a strong influence on the translocation or leaching of the heavy metals. In acidic soils nickel, copper and lead were more mobile than chromium and zinc. We relate this behaviour to the strong affinity of the former metals to dissolved or colloidal organic matter. On the other hand, nutrient cycling by the vegetation probably led to an apparent reduction of zinc downward mobility.
• In many soils, the above-mentioned guide levels and / or threshold values were exceeded. As a consequence of translocation, guide levels for chromium, nickel and copper were exceeded more often in subsoils than in topsoils.
  In conclusion, while the widespread exceedance of guide levels and effect-based threshold values indicate a potential risk for long-term soil fertility, it is not clear to what extent drinking water quality is affected by the leaching of metals from acid soils into aquifers in acid bedrock.

(Lit.: Luster et al. 2006b, c)

Mobility of Mercury

Currently, the relative mobility of mercury is determined in a representative subset of the soils. These investigations complement the determination of critical mercury limits for effects on soil organisms.

Transferfunctions for Cadmium, Copper, Nickel, Lead and Zinc

The relations between water soluble and reactive metal pools were expressed as so-called transferfunctions. The data on a representative set of Swiss forest soils from all regions served to validate transferfunctions derived from Dutch and UK data sets. In particular, the Swiss data set included carbonate containing soils not available in the latter data sets.
(Lit.: Groenenberg et al. 2009)

Publications

• Groenenberg, J.E.; Römkens, P.F.A.M.; Comans, R.N.J.; Luster, J.; Pampura, T.; Shotbolt, L.; Tipping, E.; De Vries, W. 2009. Transferfunctions for solid solution partitioning of cadmium, copper, nickel, lead and zinc in soils: Derivation of Relations for free metal ion activities and validation on independent data. Eur. J. Soil Sci., submitted
• Luster, J.; Zimmermann, S.; Lüscher, P.; Walthert, L.; Zwicky, C.; Lienemann, P.; Blaser, P. 2006c. Tiefenverteilung von Chrom, Nickel, Kupfer, Zink und Blei in Schweizer Waldböden und Implikationen für die Mobilität dieser Schwermetalle. - Bull. Bodenkd. Ges. Schweiz 29: 31-34.
• Luster, J.; Zimmermann, S.; Zwicky, C.N.; Lienemann, P.; Blaser, P. 2006b. Heavy metals in Swiss forest soils: modification of lithogenic and anthropogenic contents by pedogenetic processes and implications for ecological risk assessment. In: Frossard, E.; Blum, W.E.H.; Warkentin, B. (Eds.). Function of soils for human societies and the environment. Geological Society, London, Special Publications 266: 63-78. (Invited)
• Luster, J.; Zimmermann, S.; Frey, B.; Brunner, I.: Lüscher, P.; Walthert, L.; Blaser, P. 2006a. Schwermetalle in Schweizer Waldböden. Wald und Holz 4/06: 35-36
• Zimmermann, S.; Blaser, P.; Luster, J.; Waltert, L; Lüscher, P. 2006. Waldböden der Schweiz. Band 3. Region Mittelland und Voralpen. - Birmensdorf, Eidg. Forschungsanstalt WSL, Bern, Hep Verlag., 847 pp.
• Blaser, P.; Zimmermann, S.; Luster, J.; Walthert, L.; Lüscher, P. 2005. Waldböden der Schweiz. Band 2. Region Alpen und Alpensüdseite. - Birmensdorf, Eidg. Forschungsanstalt WSL, Bern, Hep Verlag. 920 pp.
• Walthert, L.; Zimmermann, S.; Blaser, P.; Luster, J.; Lüscher, P. 2004. Waldböden der Schweiz. Band 1. Grundlagen und Region Jura. - Birmensdorf, Eidg. Forschungsanstalt WSL, Bern, Hep Verlag. 768 pp.
• Blaser, P.; Zimmermann, S.; Luster, J.; Shotyk, W. 2000. Critical examination of trace element enrichments and depletions in soils: As, Cr, Cu, Ni, Pb, and Zn in Swiss forest soils. - Sci. Total Environ. 249: 257-280.