A review of the biogeochemistry of germanium in natural waters

Abstract

Three germanium species, inorganic germanium (Ge i), monomethylgermanium (MMGe) and dimethylgermanium (DMGe) have been identified in natural waters. Ge i in solution varies as a coherent pair with silicon, reflecting uptake into the release from the tests of siliceous organisms. MMGe and DMGe display conservative (non-reactive) behavior in estuaries and oceans, varying only with salinity. This conservative behavior implies that methylgermanium species are not incorporated into the silicon biogeochemical cycle. The residence time of methyl-Ge in the ocean is estimated to be on the order of a few million years. We have observed production of MMGe, DMGe and trimethylgermanium (TMGe) in an anaerobic sewage digester, suggesting that methyl-Ge in the environment may be produced by microbial biomethylation of Ge i during methanogenesis. Algal cultures grown in Ge i-enriched media were not observed to produce methylgermanium, nor was Ge i methylated by reaction with methylcobalamin, a methylated vitamin B 12 derivative.