Characterization and chemical availability of contaminants in permafrost soils of Alaska

December 3, 2025

This study investigates the behavior and chemical availability of contaminants in permafrost soils from an old gold mining tunnel, the Vault Creek tunnel, in Fairbanks, Alaska. Soil samples were analyzed to assess the concentration, distribution, and potential mobility of trace elements such as Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb), and Zinc (Zn). Total digestions and sequential extractions were employed alongside ICP-MS analysis to explore the geochemical behavior of these elements across soil layers up to 13 meters deep, a novelty among this type of study. Accelerator mass spectrometry radiocarbon dating was used to determine the ages of samples, with ages exceeding 60,000 years. Total concentration of each trace element ranged from 85.1 − 105 μg/g for Cr, 33.3 − 53.1 μg/g for Ni, 25.3 − 47.2 μg/g for Cu, 66.8 − 98.0 μg/g for Zn, 11.5 − 22.6 μg/g for As, 0.26 − 0.47 μg/g for Cd and 13.0 − 16.4 μg/g for Pb. The sequential extraction results show that the reducible fraction of trace elements is the most mobilized, with Cd and Pb posing environmental risks under thawing and reducing conditions. Enrichment factor analysis indicates minor natural enrichment for most metals, while As and Cd exhibit moderate anthropogenic impacts, likely related to past mining activities. These findings provide a deeper understanding of trace element distribution across different depths in permafrost and an assessment of the risk of their release due to thawing processes.

Authors in the community:

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  T

  Tiago Galhardo Benedito

  ist1100454

Supervisors of this institution:

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  M

  Maria de Fátima Duarte de Araújo

  ist25372

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  J

  João Alfredo Vieira Canário

  ist90799

chemical-engineering - Chemical engineering

por - Portuguese

Instituto Superior Técnico