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1A - Environmental analytical methods (MOP/13) Soil microorganisms - carbon transformation test: results with Woesthoff Ultragas and OxiTop Control testsystems. Reuter, Stephan1, Sandra, Siemoneit1, Kubiak, Roland1, 1 State Education and Research Center, Neustadt, Germany ABSTRACT- The testing of chemicals according to the OECD guideline 217 "Soil Microorganisms: Carbon Transformation Test" includes the measurement of glucose-induced respiration rate (SIR) of soil samples after treatment with a test substance. To ensure the validity of the testsystem, a test was performed with the active substance Dinoterb as reference substance, applied in concentrations of 1.83 and 9.17 mg/kg dry soil. Two testsystems were compared: the Woesthoff Ultragas U4S-CO2 apparatus, which is well established for the carbon transformation test, and the OxiTop Control as a new testsystem. The technical principals of the two systems are different. With the Woesthoff apparatus a 40 g soil sample (dry soil equivalent) was continuously aerated and CO2-concentration was measured by electrolytic conductivity. With the OxiTop Control a 200 g soil sample (dry soil equivalent) was incubated in a 1.5 L tightly closed glass jar with a CO2-trap inside. The low pressure as a result of the removal of the CO2 from the system was recorded and is proportional to the CO2-production from the SIR. The SIR was measured after 0, 7, 14, and 28 days incubation of the soil samples. For both systems the respiration rates, expressed as mg CO2/kg/h were calculated by means of the linear phase of CO2-production. The respiration rates were on an average 30 % higher with the Woesthoff apparatus, presumably due to better aeration conditions. Expressed as deviation from the untreated control the results showed the same sequence of effects during the incubation period with 56 % and 43 % reduction after 28 days at the highest concentration for the Woesthoff and OxiTop Control system, respectively. Key words: respiration, soil, testsystem, validity |
