The Role of Thorium in Agroecosystems: Sources of Input, Migration in the Soil–Water System, and Sorption-Based Approaches to Risk Reduction

Abstract

Background andAim. Thorium (Th), although considered a strategic element associated with Th-232-based fuel cycles, can pose long-term environmental and sanitary risks to agroecosystems when introduced into soil and water through technogenic sources. The aim of this review is to systematize the pathways of thorium input into agrolandscapes and the factors controlling its migration in the “soil–water” system, as well as to summarize sorption based and integrated remediation approaches for risk reduction.

Materials and Methods. The study was conducted as a structured analytical review. Literature sources were selected from Scopus, Web of Science, ScienceDirect, and Google Scholar databases, covering publications from 1990 to 2025. The search was performed using keywords related to Th (IV), thorium geochemistry, migration in the “soil–water” system, complexation, and sorption/remediation. Only peer-reviewed sources with an environmental focus were included, while purely energy-engineering studies were excluded.

Results. In aquatic environments, thorium is predominantly associated with particulate and colloidal fractions, and its mobility depends on pH, dissolved organic matter (DOC), and carbonate content. DOC and carbonates enhance the formation of soluble complexes and stabilize colloids, thereby facilitating thorium transport into drainage and groundwater systems. In agrolandscapes, mobilization is associated with the combined effects of acidity, organic matter, suspended particles, and seasonal hydrochemical fluctuations. Risk mitigation approaches include coagulation, membrane processes, ion exchange, and
adsorption. From an applied perspective, diatomite, bentonite, biosorbents, and composite materials are considered promising. Sorbents are conventionally classified into mineral/natural materials, biocharbased sorbents, and highly selective functional materials.

Conclusion. Risk reduction of thorium in agroecosystems is based on the integrating environmental monitoring (pH, DOC, salinity, suspended particles) with sorption and immobilization strategies. For water treatment, an effective approach involves preliminary coagulation/sedimentation followed by sorption-based polishing (with optional ion exchange or membrane processes). In soils, the priority is the immobilization of thorium in the top layer using barrier amendments (natural sorbents, biochar, iron oxides, phosphates). The safe management of secondary wastes is also essential.