Ph.D. thesis in mineral ressources under the supervision of Dr. Jayanta Guha.
This study focuses on natural accumulation of thallium associated with Hg-Tl-(Au) mineralization in the Lanmuchang area in southwest Guizhou Province, China, as a case study for thallium hazard in a geo-environmental perspective. It aims at understanding of the occurrence, the transfer processes and the environmental impacts of thallium related to natural processes and human activity. The distribution and dispersion of thallium together with mercury and arsenic in bedrock, sulfide ore, coals, soil, sediment, ground and surface waters, crops and vegetation have been examined. Tl, Hg and As accumulations are characterized by their high concentrations in rocks/ores, soils, sediments, (sub)surface waters and various crops. The dispersion of thallium together with mercury and arsenic in the specific ecosystem of Lanmuchang is constrained by the original Tl-Hg-As sulfide mineralization, the specific topography and hydro-geomorphology, and by the disturbance of human activity. The recognition of natural sources and the definition of specific geochemical baselines for toxic metals have been used to help discriminate the relative contributions of thallium due to past and present mining versus natural processes. The uptake of thallium in arable soils is species-dependent. The pathways of T1 into the human body are mainly through the food chain, and dermal and inhalation exposures which are less pronounced. Due to high uptake of Tl by crops, the principal pathway of thallium into the food chain is through the consumption of crops grown in contaminated soils. The daily uptake content of T1 through consumption of locally planted T1 rich crops is estimated to be around 2.7 mg, which is 60 times more than the daily ingestion in thallium-free background areas. T1 levels in drinking water is below the safe drinking limit, and poses no risk to human health under current conditions. Hg and As play an insignificant role in the health problems of the Lanmuchang area.
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