Germanium in the environment: Current knowledge and gap identification

Abstract

Trace element germanium (Ge) plays a key role in some modern technologies including fibre optics, infrared optics, and semiconductors, but remains under-researched in environmental contexts. Naturally occurring in low concentrations, Ge behaves similarly to Si and is often found in mineral particles rather than in dissolved form in soils and freshwaters. Its distribution in the environment is largely driven by weathering processes, where it replaces Si in silicate minerals, making it a valuable indicator of weathering intensity through Ge/Si ratios. In oceans, estuaries and lakes, Ge follows the Si cycle, especially in diatom-dominated systems. However, the emphasis on Ge/Si ratios has somewhat overshadowed direct studies on its independent geochemical cycling, mobility and potential ecological impacts. This has left gaps in understanding the unique aspects of Ge's behaviours in natural and polluted systems, both at the level of understanding laboratory-scale interactions (e.g., binding by natural organic matter, and iron oxyhydroxides) and data collection in environmental compartments (e.g., lack of data on methylated species). The measurement of Ge in the environment is technically challenging due to its low concentrations and the complexity of its chemical forms, which partially explains the lack of data and/or their poor quality. This review is the first comprehensive effort to compile the published data, assessing their reliability and identifying the main processes and gaps in our knowledge. The collected data on environmental compartments are provided ready for use, which will facilitate the completion of the collection and integration of new data.