Isotopic fractionation of Cd and Zn in contaminated soils

Bc. Šárka Lewandowská

Master's thesis

Abstract:

This diploma thesis deals with the mobility and bioavailability of trace elements in contaminated soils and isotopic fractionation of Cd and Zn, which may provide insight into their biogeochemical cycling. The theoretical part summarizes information about soil contamination, isotopic and extraction analyses, and target metal contaminants, Cd and Zn, including their isotope fractionation. The study investigated 5 soil samples collected in the vicinity of Czech town Příbram, known for its historical mining, processing, and smelting of polymetallic ores, resulting in pollution of surrounding soils and streams. The total metal(loid) concentrations and the potential mobility of selected elements (As, Cd, Cu, Pb, Zn) were determined using different extracting procedures (DGT technique, single extractions with 1 M KNO3, 1 M CH3COONa, and 0.005 M DTPA + 0.01 M CaCl2). Moreover, the isotopic compositions of Zn and Cd in bulk soil and extracted solutions were investigated using multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS) and thermal ionisation mass spectrometry (TIMS), respectively. Based on the total metal concentrations, the soils were particularly enriched with Pb (up to 16 907 ± 1 963 mg/kg), followed by (in order of decreasing concentration) the Zn, As, Cu, and Cd. Relatively the most mobile element was Cd, and the least mobile element was As. The highest extraction efficiency was obtained using a mixture of DTPA with CaCl2. The DGT technique was able to extract just the most exchangeable metal pool. Isotopic data revealed that the Cd isotopes in the extracts were heavier (δ114/110Cd of up to 0.11 ± 0.06‰) than those in the bulk soil (δ114/110Cd of 0.24 ± 0.05‰ to -0.34 ± 0.03‰), suggesting that the heavier Cd isotopes are preferentially partitioned into the soil solution, thereby being available to plants. Similar results were obtained for Zn isotopes. However, forest samples showed the opposite results, with lighter Zn isotopes favourably distributed into the soil solution (e.g., soil δ66/64Zn = 0.22 ± 0.03‰ vs DTPA-extract δ66/64Zn = -0.39 ± 0.00‰). Interestingly, the δ66/64Zn values obtained after DGT extraction (e.g., 0.29 ± 0.01‰) were mostly depleted in heavy isotopes in comparison to single extractions (e.g., δ66/64Zn = -0.06 ± 0.01‰ for CH3COONa extract) and bulk soil (e.g., δ66/64Zn = -0.20 ± 0.01‰), suggesting that lighter Zn isotopes are more available to plants.

Keywords

soil contamination, isotopic fractionation, mass spectrometry, cadmium, zinc

Language used: English

Date on which the thesis was submitted / produced: 29. 3. 2021

Thesis defence

• Supervisor: Ing. Zuzana Vaňková, Ph.D.

Czech University of Life Sciences Prague

Faculty of Environmental Sciences

Master programme:
Environmental Geosciences