Application of an "O2/CO2 headspace test with GC-TCD" for biodegradability testing of synthetic ester lubricants in water and soil

A ready biodegradability test system is established which is based on the quantification of oxygen and carbon dioxide in the head space of batch vessels using gaschromatography with thermal conductivity detector. The test system is in accordance with the standard procedures ISO 10708 (BODIS-Test), ISO 11266 and ISO 14593 (ISO CO2 Headspace Test) with slight modifications. It is applicable for the assessment of ready biodegradability in water and soil. In this study the "O2/CO2 Headspace Test with GC-TCD" is used for the assessment of synthetic ester lubricants. The effects on biodegradability in water and soil of both additives and usage are examined and discussed. Ester based cutting fluids, gear fluids and hydraulic fluids with and without additives are used under defined conditions in machine tools and hydraulic and plain bearing test benches. The lubricants are characterised additionally with respect to kinematic viscosity, acidity and elemental composition. Furthermore, a formulated mineral oil is characterised before and after usage in the hydraulic test bench. Early results clearly show that the mineral oil is far less biodegradable than the ester oils and that their biodegradability is not affected by usage. The biodegradability of the ester oils mainly depends on the characteristics of the base fluids and is not affected by the additives. Antioxidants influence stability and biodegradability indirectly, since they prevent oxopolymerisation effects. Other effects of usage on biodegradation of lubricants are not detected. In this context, the antioxidants ensure ready biodegradability and have a positive effect on the environmental fate of synthetic ester lubricants. These statements could be affirmed in advanced studies with the results on biodegradability in soil.. Furthermore, the fluids show a lower biodegradability in soil within 32 days than in water.