Germanium speciation analysis of soil polluted by an electronic waste processing plant

Germanium (Ge) is widely used in electronic and industrial products and therefore is considered to be a Technology Critical Element (TCE). Ge is widespread in the Earth's crust, and is the 54th most abundant element, with an estimated abundance of 1.3-1.6 µg/g. Ge shows remarkable geochemical similarities to silicon (Si), and has often been considered as its "pseudoisotope". However, Ge has a larger atomic radius than Si, allowing for longer bonds with oxygen and sulphur, indicating that the biogeochemical cycling of Ge is likely not to be as simple as that of silica. In order to study the transfer of Ge into the environment, information about its mobility, reactivity, and chemical transformations has to be collected. In the environment, Germanium occurs as Ge(II), Ge(IV), monomethylgermanium (MMGe), dimethylgermanium (DMGe), and trimethylgermanium (TMGe). Anyhow, information about the speciation of Ge in soil is very limited.

Researchers from Poland have investigated the Ge pollution of soil through an electronic waste processing plant. Thirty soil cores (each 30 cm long) were collected from an area around a WEEE plant situated near Katowice in Poland. Before speciation analysis, soil samples were characterized by basic physicochemical analysis with respect to pH, Eh, and total element concentrations. 

Further characterization was performed by soil magnetometry methods. For speciation analysis, 2 g portions of soil samples were extracted with 10 ml of extractant assisted by ultrasonic agitation. The highest extraction efficiency was achieved by using 100 mM NH₄NO₃ with 1 mM potassium sodium tartrate as an extractant, that washes out Ge from soils within 4 h. After centrifugation, the sample solution was then subjected to HPLC-ICP-MS analysis. The Ge species (Ge(IV), monomethylgermanium (MMGe), and dimethylgermanium (DMGe)) were successfully separated after 12 min on a Dionex IonPac AS9-HC column with ammonium nitrate and potassium sodium tartrate under optimized conditions.  For interference free detection, an ICP-MS with a reaction cell using CH₄ as cell gas was used. The limit of quantification was below 1.2 µg/kg for all three species.

  

Fig. 1: Chromatographic separation of DMGe, MMGe and Ge(OH)₄ under optimized conditions

The results of the speciation analysis showed that, in the soils around the electronic waste processing plant, germanium was mainly present in Ge(VI) form. Methyl germanium derivatives were only found in a few soil samples. The highest total Ge concentration reached nearly 7.6 mg/kg and clearly indicate the pollution by the plant. Unfortunately, the extraction efficiency was on average only about 30 % of the total Ge.

The authors concluded, that their study could show that soil samples were indeed polluted by the waste processing plant. They also confirmed that the highest pollution was found in samples with very high magnetic susceptibility.

The original publication

A.V. Hirner, U.M. Grüter, J. Kresimon,  Metal(loid)organic compounds in contaminated soil, Fresenius' J. Anal. Chem., 368 (2000) 263–267. DOI: 10.1007/s002160000451

Brief summary: Trace element speciation analysis for environmental sciences
Brief Summary: LC-ICP-MS: The most often used hyphenated system for speciation analysis