Mercury speciation in soils from a long-term contaminated area

Justin Brieno

Master's thesis

Abstract:

Mercury contamination in the environment is characterized by high toxicity and bioaccumulation potential. The main objective of this thesis is to determine the concentration of some mercury species present in soils from two mining sites in the Czech Republic, and observe how they interact with some soil properties (particularly organic matter) based on the Hg origin in order to determine the fate of Hg in these soils, and assess the threat it poses. Upon the completion of this thesis, there should be a better understanding of 1) concentration of some Hg species in the soil, especially in comparison to the organic matter present, 2) how these different Hg species behave physically and chemically in the environment (and how toxic they can become), and 3) to use this information to ultimately find solutions to remediate these areas. This objective is being fulfilled by the comparison of two sites in the Czech Republic with different origins of mercur􀁜; Lib􀃾ice (with anthropogenic Hg sources from gold mining) and Horní Luby (with anthropogenic and geogenic Hg sources following abandoned cinnabar mining). The two sites also have similar soil types, vegetation, and climate, so most environmental conditions are quite similar between the two locations. Soil samples were taken from both locations and analysed in the lab for specific soil properties such as pH, cationexchange capacity, carbon species, carbon-nitrogen ratio, and sulfur. Hg was extracted and speciation was performed using mass spectrometry. All observed Hg species observed were compared and evaluated for correlation with the specific soil properties mentioned. Statistical analyses were done on all parameters using such methods as the Shapiro-Wilk test for normality and the Spearmen correlation, in addition to general descriptive statistics for all soil and Hg parameters Despite most environmental conditions being comparable between the sites, it was found that conditions such as higher pH, higher cation-exchange capacity, and higher carbon species content found in Lib􀃾ice did not favour high Hg meth􀁜lation. However, meth􀁜lated and mobile forms of Hg were observed almost equally observed between the sites. This poses some questions regarding the origins of the Hg contamination, and why it could be behaving differently based on that origin. These results suggest that despite the overall indicators of higher organic matter which should immobilize mercury in soils, mercury from the gold mining is not immobilizing as expected; more research would need to be done to explore best remediation techniques for situations such as this.

Keywords

mercury, soils, pollution, contamination, speciation, toxicity, mobility, risk assessment, extraction, remediation

Language used: English

Date on which the thesis was submitted / produced: 26. 4. 2023

Thesis defence

• Date of defence: 15. 5. 2023
• Supervisor: prof. Ing. Jiřina Száková, CSc.
• Reader: Manhattan Lebrun, Ph.D.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme:
Natural Resources Management and Ecological Engineering