Establishing Agarose as a Diffusive Gel for In Situ Measurement of Rare Earth Elements in the Environment via the Diffusive Gradients in Thin Films (DGT) Technique

• Grant number: 24/18362-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: January 01, 2025
• End date: December 31, 2025
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Analytical Chemistry
• Principal Investigator: Amauri Antonio Menegário
• Grantee: Fernando Paes de Barros Machado Filho
• Host Institution: Centro de Estudos Ambientais (CEA). Universidade Estadual Paulista (UNESP). Campus de Rio Claro. Rio Claro , SP, Brazil

Abstract

Diffusive gradients in thin films (DGT) is a passive sampling technique that has gained relevance in the context of chemical speciation and metal fractioning in the environment due to its several features, such as the possibility of in situ measurement of labile species. Since the DGT depends on the diffusion of chemical elements through a diffusive gel towards a binding resin, deep knowledge on the diffusion of elements through the gel under several conditions is essential. The use of agarose as the diffusive medium in DGT probes has achieved significance due to the high costs involved in the acquisition of conventional polyacrylamide gel crosslinked with an agarose derivative (APA), and the toxicity of acrylamide itself. In fact, diffusion coefficients of several elements in agarose have been determined, which expanded its application, although still limited. This is not the case, however, for rare earth elements (REEs), which constitute a class of emerging contaminants due to their relatively new anthropogenic discharge into the environment. Thus, determining reliable diffusion coefficients for REEs in agarose is essential for establishing this gel as a suitable diffusive medium for DGT applications. Another limitation of agarose in the context of DGT is its fragile nature. Usually, the conventional 1.5% w v-1 agarose concentration constitutes a practical constraint in making gels for DGT flat sediment probes (18 mm ¿ 150 mm) due to the frequent cracking and limited strength when put in contact with the sediment. The hypothesis of this project is that increasing the concentration of agarose gels will make them more resistant to handling, allowing their use in flat DGT sediment probes. Yet, this will provoke significant changes in the inner structure of the gel, affecting the diffusion coefficients of REEs. The thorough assessment of these effects as well as developing correction factors for unconventional agarose concentrations constitute the core of this research project. Experiments covering a wide range of agarose concentrations, ionic strengths, pH and considering the effects of filter membranes will be performed in a diffusion chamber and ICP-MS will be used for all elemental determinations. This work will produce original results that are considered of importance for the development of the DGT technique for REE measurements.