Specific strategies for ensuring data quality in the quantitative determination of REE in sediments

Abstract

Rare Earth Elements (REE) are increasingly studied as biogeochemical tracers due to their distinctive properties and wide applicability across various scientific disciplines. However, their extensive use in recent years in high-tech applications has resulted in significant anthropogenic discharges into the environment, leading to their classification as emerging contaminants (Hanana et al., 2022). In addition to natural processes, human activities have become a major source of REE inputs into marine systems. Considering the gradual enrichment of REE in natural systems and their potential ecotoxicological risks, studying their interactions at the ecosystem level under natural conditions is essential. The common methods for evaluating fractionation processes from abiotic compartments to biota, and within biota from prey to predator, typically involve the biota-sediment accumulation factor (BSAF) and the bioaccumulation factor (BAF). Although REE quantification in sediments is critical for assessing fractionation along the trophic chain, the methodologies used lack standardisation, particularly in the choice of mineralisation procedure. Some studies apply total mineralisation, which also determines the fraction of REE associated with silicates, reflecting the lithological background. Other studies focus on pseudo-total mineralisation, which targets REE content in carbonates, sulfates, oxides, and other less stable phases, thereby corresponding to the bioavailable (pseudo-total) fraction. These different approaches yield non-comparable data. Since REE concentrations in the labile fraction can vary significantly, even when the underlying lithological origin is similar, we argue that studies on REE biogeochemical behaviour should prioritise the labile fraction, which provides a more realistic representation of their availability for bioaccumulation (Zhang and Shan, 2001; Censi et al., 2014). Nonetheless, the analytical validation of REE quantification for the labile fraction is challenging due to the absence of certified reference materials (SRMs) for the pseudo-total fraction and the lack of standardised validation protocols in the literature. To address these gaps, we validated the analytical process for REE quantification in sediments by assessing accuracy through recovery experiments using certified SRM for the total fraction. Specifically, we estimated the REE concentrations using pseudo-total mineralisation and then calculated the amount of REE to be added to obtain a reference value. We then re-analysed the spiked sample and calculated the recovery. Recovery rates ranged between 84% and 103%, demonstrating that the extraction method effectively quantifies REE concentrations without significant interference. In conclusion, we propose a standardised methodology for validating the labile REE frac-tion in sediments. This approach ensures data reliability, enhances the comparability of results across studies, and contributes to a broader understanding of REE as bioge-ochemical tracers.