TCEs stands for technology-critical elements, a group of chemical elements for which imbalances between supply and demand exist or are considered likely to exist. The concept is economic and geopolitical and is not based on any scientific consideration. The term TCE is linked to competition for natural resources, now dramatically intensified by geopolitical instability and the green-energy transition.

Since it is a geopolitical concept, the elements that are considered as TCEs depend on the country and change over time; basically, they depend on the "eye of the beholder". For example, in the EU list of 2023, compared to the 30 Critical Raw Materials (CRMs) of 2020, there are six new CRMs (arsenic, feldspar, helium and manganese, plus copper and nickel as Strategic Raw Materials) and two have disappeared (indium and natural rubber).

Currently, the European Union considers a large number of materials to be technologically critical (mostly, but not all, chemical elements): 51. Given that the total number of elements in the periodic table is 118, of which 94 occur naturally on Earth and the remaining 24 are synthetic, this means that we are talking about ≈50% of all naturally occurring chemical elements!

In this context, what are the reasons for studying the environmental and (eco)toxicological effects of TCEs? Obviously, they will be different in the European Union than in the producer countries. In this communication, the reasons and research needs on both sides of the so-called supply chain (producers and end-users) will be analysed.

Technology-critical elements (TCEs) show a dramatic increase in industrial applications in recent years and decades. Technological applications in our everyday life have come a long way in the number of used elements, with almost every element of the periodic table today. Based on the fact that many TCEs are recycled only to a very small extent or not at all, TCEs may become contaminants of high concern in the future.

Yet, important knowledge gaps remain about the environmental behavior of TCEs and their uptake into the food chain. Therefore, tools are needed that enable a sound and reliable determination of TCEs in order to further understand their impact on the environment. We present the advantages of N₂O as a reaction gas for inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) for the multi elemental analysis of the majority of TCEs (e.g.: Ga, Ge, In and Ta). Thus, allowing the determination with LODs between 0.00023 µg L^-1 (Eu) and 0.13 µg L^-1 (Te). In addition, we used a microwave assisted closed vessel digestion to determine non-certified TCE mass fractions within four commonly used reference materials in the field of environmental marine chemistry: NIST 2976 (mussel tissue), NIST 1566a (oyster tissue), BCR 668 (mussel tissue) and NCS ZC73034 (prawn). Presenting mass fractions for Ga (11 µg kg^-1 ± 9 µg kg^-1 - 63 µg kg^-1 ± 8 µg kg^-1) and In (0.39 µg kg^-1 ± 0.29 µg kg^-1 – 0.7 µg kg^-1 ± 0.7 µg kg^-1) as non-certified elements within all of these CRMs.

TCEs have a wide-spread range of applications and are released into the aquatic environment in various ways. For their sound determination in natural waters not only new analytical methods are needed but also reference materials for method validation. Even though a wide variety of certified reference materials (CRMs) of different water matrices are available, certified values of many elements, especially TCEs, do not exist. In this study, an online preconcentration method coupled with ICP-MS/MS was used for the quantification of 34 elements among which are 21 TCEs. The method was applied to 17 water CRMs and measured data is combined with a comprehensive literature review on non-certified values in the CRMs resulting in the suggestion of consensus values for various TCEs.

The method is applied to a set field samples from German rivers and from the North Sea in order to trace different inputs of TCEs into the aquatic environment: In and Ga ware analyzed as tracers for offshore wind farms where they are applied in corrosion protection systems. The Gd anomaly was used as a proxy of coastal and riverine inputs into the North Sea in an attempt to differentiate anthropogenic from geogenic signal. The concentrations in seawater ranged between 0.011 ng L^-1 ± 0.001 ng L^-1 and 0.27 ng L^-1 ± 0.15 ng L^-1 for In and between 1.37 ng L^-1 ± 0.05 ng L^-1 and 4.9 ng L^-1 ± 0.5 ng L^-1 for Ga and Gd anomalies of up to 4 were found in the North Sea.

The picturesque fjords along Norway’s coastline play an important role for the country’s tourism and aquaculture industry. Despite their economic importance for the country, surprisingly little is known about the occurrence and behaviour of rare earths and yttrium (REY) in Norwegian fjords. We will present dissolved (0.2 µm-filtered) REY data for different sites and depths from several Norwegian fjords with focus on the Seaward Basin in the Trondheimfjord. Our sample set is complemented by data for rivers feeding into the fjord (Orkla, Gaula, Nidelva, Stjørdalselva) and for two waste water treatment plants (WWTPs) releasing their effluents into the Seaward Basin.

All fjordwaters show REY concentrations in a similar range with decreasing concentrations with increasing water depth. Their shale-normalised (_SN) REY patterns share common features with typical seawater patterns, however, light and middle REY are less fractionated compared to open-ocean water. Samples taken close to river mouths have notably higher REY concentrations in surface layers with very flat REY_SN patterns, similar to the rivers investigated and characteristic of boreal rivers with a high nanoparticle and colloid load. In contrast, the truly dissolved (< 1 kDa) REY in river water of the Nidelva show patterns similar to those of seawater.

The effluents of the WWTPs carry a strong anthropogenic Gd signal into the Trondheimfjord, which results from the application of Gd-based contrast agents in magnetic resonance imaging. However, no anomalous enrichment of Gd is detected in the Seaward Basin itself because the large water volume immediately dilutes and obliterates the anthropogenic signal.

Contrasting sediments behave radically differently in aquatic systems, releasing elements of concern. Their behavior is a function of mineralogy, geochemical composition, and the conditions of the medium (e.g., ionic composition, pH). One way of understanding the reactivity of contrasting sediments, but also the operationally defined fraction of the associated elements is to use selective extraction protocols. Nevertheless, these are generally used without verifying the adequacy of the extraction times, in accordance with the sediment characteristics, nor the potential impact of element-specific behavior to the extracting reagents, biasing the final interpretation. This study aims at providing such understanding for the rare earth elements (including lanthanides, yttrium, and scandium). The sediments used originate from modern aquatic sedimentary environments of both terrestrial and marine-transitional origin, associated to either natural (beach and riverbank sediments) or anthropogenic (mine tailings) sources. A qualitative mineralogical determination of the sediments was performed via XRD. Element mobility was studied via selective extraction protocols applied in parallel, with a kinetic approach, and sequentially. Quantitative analysis of the total concentrations of major and trace elements was determined via XRF-EDX, ICP-OES and ICP-MS, to obtain elemental correlations and total REY+Sc sediment content for mass balance purposes. For each extraction solution, the elemental concentrations were quantified via ICP-MS. The information gained in this study provides further experimental results on the unknown aquatic behavior of REY+Sc elements, for which there is currently an increasing demand for major technological applications.

Acknowledgements:

Funded as part of the Excellence Strategy of the German Federal and State Governments.