Contribution of cadmium isotopes to the understanding of
its natural and anthropic biogeochemical cycle in the Critical Zone
Geochemical tracers, heavy metals, speciation, weathering, Cd isotopes
Biogeochemical processes and metal dynamics in the so-called "Critical Zone" are accompanied by changes in metal speciation and their redistribution among different organic and/or inorganic phases. These changes are commonly associated with isotopic fractionation. The so-called "Non-Traditional Stable Isotopes" have been successfully applied in Geosciences and, particularly, in Environmental Geochemistry due to their potential as tracers of sources and processes. Transformation reactions occurring in the Critical Zone led to the separation of isotopes into different chemical or physical compartments through mechanisms of mass-dependent or mass-independent fractionation. In this research project, particular focus is given to cadmium isotopes, a potentially toxic trace metal whose natural cycle has been significantly altered in recent decades due to emissions from anthropogenic activities such as mining, coal combustion for energy production, and urbanization. Pioneering studies have shown that Cd isotopes can be used as a promising tool, primarily in tracing sources in environmental samples. Literature data indicate that these isotopes can be highly fractionated when the metal is industrially processed, but natural processes such as adsorption, precipitation, and interactions with living organisms also generate relatively significant fractionations. A systematic literature review was conducted, highlighting the need to expand the number of studies on this topic in order to establish Cd isotopes as a relevant tracer of pollution sources and as an important tool in the process of mitigating impacts caused by anthropogenic activities. The dynamics of Cd are being studied at the soil-plant interface, specifically in soil profiles and in the Theobroma grandiflorum species, as well as in sediments potentially contaminated by anthropogenic sources. The expected results will generate new data for the literature and contribute to understanding the dynamics of Cd throughout environmental changes.