Determination of an environmentally safe concentration of germanium in ordinary chernozem

Introduction. Germanium (Ge) is a valuable chemical element for the technological sphere. In recent years, Ge has been increasingly used in various branches of high-tech industry: in the creation of fiber and infrared optics, as well as as polymerization catalysts in the production of polyethylene terephthalate (PET).
In soils contaminated with mining waste, the Ge content ranges from 1.45 to 7.91 mg/kg. The maximum permissible concentrations (MPC) of Ge in the soil have not been developed, accordingly, it seems relevant to conduct a comprehensive assessment of the effect of Ge on biological indicators of soil condition and establish an environmentally safe concentration of Ge in the soil.
Materials and methods. In a laboratory experiment, the ecotoxicity of 3, 30, and 300 Ge background concentrations (BC) on 10th, 30th, and 90th day was evaluated using biodiagnostic methods. All the studied indicators were included in the calculation of the integral indicator of the biological state (IIBS) of the soil. In case of contamination with Ge there was diagnosed the sequence of violations of the ecosystem functions of the soil according to the degree of decrease in IIBS. The dose of the element, under the influence of which there is a violation of the integral functions of the soil, characterizing the degree of the soil fertility, is defined as an environmentally safe concentration of Ge in this soil.
Results. With an increase in the Ge dose in the soil, the ecotoxic effect of the impact of the mineral on catalase and dehydrogenases activity, the abundance of bacteria of the genus Azotobacter, cellulolytic activity, germination and length of radish roots increased. After Ge contamination of the soil, the maximum toxicity was revealed for the indicators studied on the 10th and 30th das. The radish root length index showed the greatest sensitivity to Ge soil contamination compared with the indicator of dehydrogenases activity. The strongest correlation was noted between the Ge content in the soil and catalase activity. An environmentally safe concentration of Ge in the soil has been established – 6.5 mg/kg. The obtained results on the assessment of ecotoxicity of soils contaminated with Ge can be used to diagnose the ecological state of soils.
Limitations. The proposed environmentally safe concentrations in Ge soils are applicable, first, for ordinary chernozem.
Conclusion. An increase in background concentrations of Ge in the soil inhibited the biological parameters of ordinary chernozem. The maximum ecotoxic effect of Ge on the studied parameters was demonstrated on 10th and 30th days. The length of radish roots is most sensitive to Ge soil contamination compared to the indicator of dehydrogenase activity. The strongest correlation was noted between the Ge content in the soil and catalase activity. An environmentally safe Ge concentration in the soil has been established – 6.5 mg/kg. The obtained results on the assessment of ecotoxicity of soils contaminated with Ge can be used for diagnostics and as an indicator of the ecological state of soils.

chernozem, germanium, biological indicators, environmentally safe concentration, rationing, biotesting, ecotoxicity