Rare earth elements as tracers of active colloidal organic matter composition

Abstract

Environmental contextThe origin of organic matter at Earth’s continental surface can be either terrestrial or microbial, and its precise composition can influence its reactivity towards metals. We investigated the potential of rare earth elements to fingerprint the origin of various organic matters through their reactivity and composition. The rare earth element patterns can be useful tools to determine the reactivity and also pristine source of natural organic matter. AbstractRare earth elements (REEs) have been shown to be efficient tracers of the functional sites and/or complexes formed on humic molecules. In the present study, we test the potential of REEs to be used as tracers of the sources of humic substances (HSs). Three types of organic matter (OM) of terrestrial and microbiological origin were tested. The experiments of REEs binding to the HSs were combined with size-fractionation experiments. The REE patterns were the most fractionated in the <10kDa fraction. For Leonardite humic acid (LHA) and Aldrich humic acid (AHA), the REE patterns were consistent with the REEs binding to strong but low density sites for a low REE/C loading. By contrast, for Pony Lake fulvic acid (PLFA), the REE pattern was similar to the REE pattern developed onto a bacteria cell surface and was attributed to the REEs binding to phosphate surface sites. Fluorescence and elemental analysis of PLFA showed that the <10kDa fraction was the fraction with the stronger microbiological character, which suggested the REEs were probably bound to PLFA through REE-phosphate complexes. Such results therefore provide a new possibility for the use of REEs to assess an OM source without the need to perform numerous or complex analytical methodologies.

Modeling rare earth elements binding to humic acids with model VII

“…However, if the present study provides a valuable predictive tool of REE speciation and REE patterns in organic-rich waters, the impact of NOM quality requires further work. For instance, NOM of bacterial origin might produce different REE binding patterns than the humic fractions presently evaluated (Catrouillet et al, 2019). In environmental systems J o u r n a l P r e -p r o o f characterized by high physico-chemical gradients and under the influence of various biogeochemical factors, such as flooded soils (Davranche et al, 2011) or estuaries (Dulaquais et al, 2018), large spatial and temporal variability in NOM composition occurs.…”

A review of tracer testing techniques in porous media specially attributed to the oil and gas industry

“…The humic substances play an important role in controlling metal speciation, as well as the trace element mobility in water and soil (Pédrot et al 2010). For colloidal organic matter composition, they have resulted to be very efficient on the functional sites and quite complexes formed on the humic molecules (Catrouillet et al 2019).…”

Rare earth element behaviour in seawater under the influence of organic matter cycling during a phytoplankton spring bloom – A mesocosm study

“…Many studies have modelled the organic complexation of dREEs with terrestrial humic and fulvic acids (HFAs) (Tang and Johannesson, 2003;Sonke and Salters, 2006;Pourret et al, 2007). Catrouillet et al (2020) showed that microbiologically produced HFAs, in contrast to those of terrestrial origin, preferentially complex HREEs and thus show different complexation patterns with dREEs. Since the existence of terrestrial HFAs can be excluded in our mesocosm approach and the DOC pool in general is probably less complex than in natural coastal waters due to the absence of large algae and a refractory DOC pool, we decided to use only one well described microbially produced organic ligand, DFOB, in our model.…”

“…Studies on natural groundwaters observed a correlation between dissolved organic carbon (DOC) and REEs that increases with atomic number, suggesting that the process of organic complexation is most relevant for HREEs (Johannesson et al, 2004). Due to the different structures and therefore possible binding sites of terrestrial humic acids and bacterially produced dissolved OM (DOM) in the ocean (Catrouillet et al, 2020), their effects on REE complexation can be expected to differ. Experiments conducted to determine the stability constants of organic REE complexes and to model their relevance in the marine environment showed that bacterially produced DOM is able to strongly complex REEs (Christenson and Schijf, 2011).…”