Thesis
Formation of Chromium (VI) in Surface Soils During Simulated Bushfire Temperatures
Southern Cross University
Master of Science (MSc), Southern Cross University
2022
DOI:
https://doi.org/10.25918/thesis.282
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Abstract
Hexavalent chromium has emerged in recent research as a potential environmental contaminant of concern in soil systems impacted by bushfire. Limited publications to date have offered evidence supporting high temperature aerobic oxidation of Cr(III) as an avenue for toxic Cr(VI) genesis in fire-impacted surface soils. In this study, heating -induced alteration of native Cr species in surface soils is investigated. Five different A horizon soils from northeastern NSW, Australia were analyzed for chromium speciation in response to temperature ramp analysis at 2-hour 100°C increments (100-900°C), and time series temperature duration at 500°C to investigate the kinetics of chromium (VI) genesis (according to UV-Vis colorimetry and aqua regia ICP-MS quantification). Total Cr(VI) concentrations were observed to increase up to 78% of total native Cr at temperatures of 300-500°C after 2hrs duration. Positive linear relationship between Cr(VI) and Cr(T) concentrations were established. Kinetics investigations into Cr(III) oxidation showed increases in Cr(VI) concentrations of up to 8 times native Cr(VI) within 15 minutes, reaching maximum conversion of up to 22 times within 1-2hr exposure at 500°C. Native leachable Cr(VI) concentrations increased up to 100% of leachable Cr(T) (47% of total Cr) dependent on soil type, after 2hr 500°C exposure expected during medium intensity fire events. Increased pH of 3 unit points at temperatures of over 400°C coupled with complete organic carbon loss on ignition at 400-500°C created a stabilizing environment for Cr(VI). Overall, results show rapid Cr(VI) formation in surface soils exposed to temperatures expected during medium intensity bushfire events. Given the large global land area affected by fire annually, and the expected increase in bushfire frequency due to climate change, aerobic oxidation of Cr(III) to Cr(VI) may represent an unaccounted for pathway for Cr(VI) formation and environmental release.
Details
- Title
- Formation of Chromium (VI) in Surface Soils During Simulated Bushfire Temperatures
- Creators
- Jane Carroll
- Contributors
- Edward D Burton (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Master of Science (MSc)
- Theses
- Master of Science (MSc), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- 88
- Identifiers
- 991013127013702368
- Copyright
- © J Carroll 2022
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis