What is the redox speciation of contaminants at the surface of heterogeneous colloids in aquatic and urban environments?

Trace elements (TEs) have become an increasing concern for human health, aquatic life, and the environment. Therefore, accurately predicting their biogeochemical behaviour in natural systems is crucial. The speciation of TEs governs their environmental transport, bioavailability, and toxicity. However, determining TE speciation is complicated by the presence of colloids—heterogeneous environmental nanoparticles that are highly reactive toward TEs. Redox-sensitive TEs pose additional challenges, as their behaviour and toxicity strongly depend on their oxidation state. This research aims to elucidate how redox-sensitive TEs interact with heterogeneous colloids composed of natural organic matter, metal oxides (iron or manganese oxides), and clays. Specifically, this study seeks to answer the following questions:

1. How and where do redox reactions occur on the surface of heterogeneous colloids?
2. To which constitutive phase of the colloids do TEs bind in their final oxidation state?