Critical Limits and Effect Based Approaches for Heavy Metals

Fungi and bacteria in soils are responsive to environmental impacts such as heavy metals, nitrogen and acids. Foto: Beat Frey (WSL)

Heavy metals are emitted in the atmosphere by industrial activities, transported through long distances, they deposit and accumulate in terrestrial ecosystems. The problem of Long-Range Transboundary Air Pollution of Terrestrial Ecosystems (LRTAP) includes cadmium (Cd), mercury (Hg) and lead (Pb) and are priority metals in the United Nations / Economic Commission for Europe (UN/ECE) Convention from 1998. Increased accumulation of Cd, Hg and Pb from anthropogenic and geogenic sources in soils especially of forest soils has led to exceedances of the current guide values defined by the environmental legislation. Especially, Hg as a global pollutant is of high ecotoxicological concern. However, little information is available on rates of atmospheric deposition, distribution, mobility of Hg compounds (methylmercury) in soils and their transfer functions in the biosphere (bioaccumulation). An impact of current Hg (Cd and Pb) concentrations on the soil ecosystem is possible but still unknown.

Aims

This study is part of a comprehensive investigation to determine Hg (Cd and Pb) levels in the soil matrix, soil solution, fungi, earthworms and their food sources (soil, leaf and root litter) and to evaluate the ecotoxicological effects of Hg on the soil microbial communities.

1. What is the current situation of Cd, Hg and Pb in Swiss forest soils?
2. What are the transfer functions of Cd, Hg and Pb from soil to earthworms and mushrooms?
3. Which microbial parameters (microbial activities and/or bacterial community structures) are most suitable to reveal effects of Cd, Hg and Pb on forest soils?
4. Which heavy metal species in soil can be considered as appropriate predictors of Cd, Hg and Pb bioavailability to microbial communities in soils?
5. Which soil bacterial groups are affected by Cd, Hg and Pb?
6. Are the current critical limits for the total dissolved Cd, Hg and Pb, suggested by the UN/ECE, in accordance with the values estimated for Swiss forest soils?

Methods

Determination of "reactive" heavy metal pool in soil

• Water-extractable HM
• Heavy metal specific bacterial biosensors (quantification of lux-gene)
• Modeling of free ions (WHAM 6)

Determination of microbial activity

• Soil respiration
• Nitrification
• Phosphatase, beta-Glycosidase

Changes of total bacterial communities

• T-RFLP and DGGE fingerprinting of 16S rRNA gene
• Cloning and sequencing
• Design of specific primers for detecting HM tolerant bacterial groups

Publications

• Brunner I, Luster J, Günthardt-Goerg MS, Frey B. 2007. Heavy metal accumulation and phytostabilisation potential of tree fine roots in a contaminated soil. Environmental Pollution (in press).
• Ernst G., Frey B. (2007) The effect of feeding behaviour on Hg accumulation in the ecophysiologically different earthworms Lumbricus terrestris and Octolaseon cyaneum: a microcosm experiment. Soil Biology and Biochemistry 39: 386-390.
• Lazzaro A., Schulin R., Widmer F., Frey B. (2006) Changes in lead availability affect bacterial community structure but not basal respiration. Science of Total Environment 371: 110-124.
• Frey B., Stemmer M., Widmer F., Luster J., Sperisen C. (2006) Microbial characterization of a heavy metal-contaminated soil in a model forest ecosystem. Soil Biology and Biochemistry 38: 1745-1756.
• Lazzaro A., Hartmann M., Blaser P., Widmer F., Schulin R., Frey B. (2006) Bacterial community structure and activity in different Cd-treated forest soils. FEMS Microbiology Ecology 58: 278-292.
• Rigling D., Günthardt-Goerg M., Blauenstein H., Frey B. (2006). Absorption of heavy metals into Armillaria rhizomorphs from contaminated soils. For. Snow Landsc. Res. 80: 213–220.
• Novak B., Rais D., Frey B., Menon M., Schulin R., Günthardt-Goerg M., Luster J. (2006). Influence of heavy metal contamination on soil parameters in a lysimeter experiment designed to evaluate phytostabilization by afforestation. For. Snow Landsc. Res. 80: 201–211.
• Hartmann M., Frey B., Kölliker R., Widmer F. (2005) Semi-automated genetic analyses of soil microbial communities: comparison of T-RFLP and RISA based on descriptive and discriminative statistical spproaches. Journal of Microbiological Methods 61: 349-360.