ASTM D6139 Aerobic Aquatic Biodegradation of Lubricants or Their Components
ASTM D6139 Standard Test Method for Determining the Aerobic Aquatic Biodegradation of Lubricants or Their Components Using the Gledhill Shake Flask
4. Summary of Test Method
4.1 Biodegradation of a lubricant or the component(s) of a lubricant is estimated by collecting and measuring the CO2 produced when the lubricant or component is exposed to microorganisms under controlled aerobic aquatic conditions. This value is then compared to the theoretical amount of CO2 which could be generated if all of the carbon in the test material were converted to CO2. Carbon dioxide is a product of aerobic microbial metabolism of carbon-containing materials and so is a direct measure of the test material's ultimate biodegradation. The evolved CO2 is trapped in a Ba(OH)2 or other alkaline solution and the amount of CO2 absorbed is determined by titrating the remaining hydroxide in solution.
4.2 The carbon content of the test material is determined by Test Method D5291 or another appropriate method and the theoretical CO2 is calculated from that measurement. It is necessary to directly measure the carbon content of the test material instead of calculating this number, because of the complexity of the mixture of compounds present in lubricants.
4.3 Biodegradability is expressed as a percentage of theoretical CO2 production.
5. Significance and Use
5.1 Results from this CO2 evolution test method suggest, within the confines of a controlled laboratory setting, the degree of ultimate aerobic aquatic biodegradability of a lubricant or components of a lubricant. Test materials which achieve a high degree of biodegradation in this test method may be assumed to easily biodegrade in many aerobic aquatic environments.
5.2 Because of the stringency of this test method, a low yield of CO2 does not necessarily mean that the test material is not biodegradable under environmental conditions, but indicates that further testing needs to be carried out in order to establish biodegradability.
5.3 Information on the toxicity of the test material to the inoculum may be useful in the interpretation of low biodegradation results.
5.4 Activated sewage-sludge from a sewage treatment plant that principally treats domestic waste may be used as an aerobic inoculum. An inoculum derived from soil or natural surface waters, or any combination of the three sources, may also be used in this test method.
NOTE 1 - Allowance for various and multiple inoculum sources provides access to a greater diversity of biochemical competency and potentially represents more accurately the capacity for biodegradation.
5.5 A reference or control material known to biodegrade under the conditions of this test method is necessary in order to verify the activity of the inoculum. The test method must be regarded as invalid and should be repeated using a fresh inoculum if the reference does not demonstrate biodegradation to the extent of >60 % of the theoretical CO2 within 28 days.
5.6 The water solubility or dispersibility of the lubricant or components may influence the results obtained and hence the procedure may be limited to comparing lubricants or components with similar solubilities.
5.7 The ratio of carbon incorporated into cellular material to carbon metabolized to CO2 will vary depending on the organic substrate, on the particular microorganisms carrying out the conversion, and on the environmental conditions under which the conversion takes place. In principle, this variability complicates the interpretation of the results from this test method.
5.8 The behavior of complex mixtures may not always be consistent with the individual properties of the components. The biodegradability of the components may be suggestive of whether a mixture containing these components (that is, a fully formulated lubricant) is biodegradable but such information should be used judiciously.
