Tracing anthropogenic thallium in soil using stable isotope compositions

Area of Science:

• Environmental Geochemistry
• Isotope Geochemistry
• Trace Metal Analysis

Background:

• Cement production can release thallium (Tl) into the environment.
• Understanding the source of Tl contamination in soils is crucial for environmental risk assessment.

Purpose of the Study:

• To utilize stable thallium isotope data for the first time to apportion Tl contamination sources in soils.
• To distinguish between geogenic Tl background and anthropogenic Tl emissions.

Main Methods:

• Analysis of thallium (Tl) stable isotope compositions (ε(205)Tl) in soil profiles and cement kiln dust (CKD).
• Application of binary mixing models using Tl isotope data and Tl concentrations.
• Comparison of Tl isotope signatures in soils, CKD, pyrite, and a biological sample (green cabbage).

Main Results:

• Soil Tl isotope data exhibited a binary mixing relationship between geogenic background (ε(205)Tl ≈ -4) and Tl emissions (ε(205)Tl ≈ ±0).
• Cement kiln dust (CKD) and associated pyrite showed similar Tl isotope compositions (ε(205)Tl ≈ ±0) to the contaminated topsoils.
• Significant biological isotope fractionation of Tl was observed in green cabbage (ε(205)Tl -2.5 to -5.4), distinct from the Lengerich topsoil signature.

Conclusions:

• Stable thallium isotope analysis is a powerful tool for apportioning Tl contamination sources in soils.
• Anthropogenic Tl emissions from cement processing were confirmed as the source of heavy Tl in Lengerich topsoils.
• Isotope data effectively complements receptor modeling for toxic trace metals like thallium.