Methods to ensure the quality of excavated soil material from geogenically metalliferous sites

1. Methods to ensure the quality of excavated soil material from geogenically metalliferous sites Peter Liebhard and Manfred Sager Institut für Pflanzenbau Universität für Bodenkultur 1180 Wien E-mail: peter.liebhard@boku.ac.at Bioforschung Austria 1220 Wien E-mail: m.sager@bioforschung.at

2. Occurrence of metals in higher concentrations than mean crustal abundance: Geogenic: Metalliferous ore veins and adjacent soils Antropogenic: Input from atmospheric deposition smelter, coal burning, traffic Waste dumps Fertilizers from agriculture mineral fertilizers composts, manures, dungs Lost bullets from hunting Legal threshold values based upon impact upon mankind: direct soil ingestion by babies and small children at playgrounds inhalation of soil dust solubilities during groundwater/ potable water formation transfer to edible parts of green plants lowering of crop yields

3. In the Alps, within a zone between limestones and igneous rocks, • polymetallic mineralization veins migh occur • e.g. pyrite-based Pb-Zn-Cu-Ag-As-Sb sulfides • Magnetite, hematite, baryte • No enrichment expected: Cr, Co, Ni, Mo, Sn • Mine dumps, slag heaps from historic mining • Adjacent natural soils with high metal levels of geogenic origin Problem: soils used for agriculture for about 1000 years (mainly greenland) may exceed legal thresholds for As, Cd, Cu, Pb etc. (aqua regia or total) nutrients N, P, K, as well as org.C and pH indicate normal soil life when excavated  have to be dumped at special sites

4. mg/kg in aqua regia 11 sites sampled

5. In Austria, 10ha of soil are sealed every day • Sealed soil loses its biological functions: substrate for plant production • storage and filter for groundwater formation • In Austria, annual excavation of soil makes 33 mio. tons due to construction works • Excavated soil is termed as waste, and gets deposited – no agricultural use • minimize waste volume by establishing legal criteria to permit agricultural use of excavated soil of high geogenic metal load At 11 sites in Styria (Austria), upper and lower soil horizons have been analyzed for nutrients: P-CAL, K-CAL, pH, %N, C-org and total and aqua regia soluble contents of As, Cd, Cr, Cu, Hg, Ni, Pb Upper and lower horizons Sieved and unsieved Oxidation of sulphides in mine dumps can lead to acid and highly metalliferous groundwater contaminations

6. Goal: Find criteria to obtain permission from authorities for the use of excavated soil material from metalliferous areas in spite of exceeding threshold levels Methods: discrimination of geogenic loads from other sources by selective resp. sequential leaching Pot experiments with test crops in the greenhouse to correlate soil to plant transfer with mobile soil fractions Italian raygrass (Lolium multiflorum) - typically greenland Green salad (Lactuca sativa) – leafy food Oats (Avena sativa) – cereal food enriched in inorganics Maize (Zea mais) – food low in inorganics

7. Estimation of environmental mobility and availablity by sequential leaching Modified after Tessier 1g + 50 ml I ammonium acetate pH 7  exchangeables, living cells II ammonium acetate pH 5  carbonates, acid-exchangeables III 0,1M NH2OH in 25% acetic acid Mn-oxides IV oxalate buffer pH 3 Fe-oxides V oxidation with H2O2 humics, sulfides VI boiling HNO3 residual More speciations than fractions are possible; fractions operationally defined Ideal: main and trace elements dissolve from the same solid Uncertainties: desorptions and resorptions Leaching patterns depend on: presence of minority phases individual properties – solubilities of the hydroxide, affinities occurrence of main sorbing phases level of load of sorbing phases

8. Affinity of trace elements to main solid phases in oxic soils (no sulphides) Fe-Mn-Oxides Cr, Mo, Sn, V Al As, Co, Ni, Zn, Se, P B Cu Humics Clay minerals K, Li, Tl Mg Sr, Pb Carbonates

9. Fe - Mn - Oxides Selective le aching methods Hydroxylamine, oxalate, dithionite Complexing agents Salts Bases Org.C, CEC, XRD, Clay minerals Humics Wet oxidation < 2 µ Fraktion A cids XRD, Scheibler Carbonates Determination of main phases in oxic soils

10. Sequential leaching yields environmental mobilities under changing conditions (acidification, oxidation, reduction etc.) Proof of the applied sequential leaching sequence: Which leaching patterns result from pure test substances e.g. defined minerals, earthworms, humics Adsorption of solutes upon test soils in which fractions these additions are recovered Input from metal emitting smelters mobilities different to non-contamianted soils? Assignment of selective fractions to uptake into green and crop plants Why Tessier sequence? Many data available low cross contaminations from reagents ascending stability of phases developed for cations applicable for some anions also

11. In addition to total contents and mineral composition, sequential leaching tells you: Primary minerals enriched in large grains Primary minerals are largely immobile – Weathering leads to increasing mobility: formation of hydroxides and clays sorption of trace elements upon hydroxides and clays precipitation of secondary minerals, e.g. Pb5(PO4)3Cl pyromorphite Pb5(AsO4)3Cl mimetite Soils close to the root zone: decrease of exchangeables (uptake) decrease of residuals (weathering) Proportion of poorly crystalline Fe-hydroxides over total iron increases with soil age Recrystallization of ferrihydrite to goethite (wet dry-cycles) decreases mobility of traces Atmospheric input might be of low mobility: In Mežica and Celje (SLO): Pb input mainly oxidizable Zn input mainly residual In Brixlegg: more increase of mobile phases  Indication via soil profile and grain size

12. Growing green salad seedlings in mine tailings:

13. End of the show Thanks for attention