Tellurium and selenium sorption kinetics and solid fractionation under contrasting estuarine salinity and turbidity conditions

Abstract

Tellurium (Te) is a Technology Critical Element (TCE) and a relevant product of nuclear fission. It has an unknown environmental biogeochemical cycle, mostly related to current analytical challenges in measuring its ultra-trace dissolved concentrations in complex environmental matrices. It is therefore generally compared to its geochemical pair selenium (Se), which shows a narrow range between diet essentiality and toxicity properties. Batch experiments using isotopically-labelled stable Te and Se were performed with fresh suspended particulate matter (SPM) from the fluvial part of the Gironde Estuary, simulating both estuarine salinity (S = 0 vs S = 32) and turbidity (100 mg L−1 vs 1000 mg L−1) gradients to understand the importance of the particulate phases in Te reactivity under estuarine conditions and verify the resemblance to Se behaviour. These experiments addressed sorption kinetics, sorption isotherms and fractionation from selective extractions of final equilibrated SPM. Results showed a strong, salinity-independent affinity of Te for the particulate phases (log10 Kd ~ 4.9 L kg−1), following a Langmuir-type isotherm. Contrastingly, Se adsorbs clearly less to estuarine SPM (log10 Kd ~ 2.5 L kg−1), following a Freundlich-type isotherm. Both isotherms and selective extractions highlighted differences between Te and Se sequestration. Selective extractions suggested higher mobility of particulate Se in contrast to Te. Based on these results the paper sets a first dispersion scenario on the environmental fate of radioactive Te and Se after hypothetical nuclear power plant accidental releases in coastal aquatic systems such as the Garonne-Gironde fluvial-estuarine system.