ASTM D6731-18

5.1 Results from this test method suggest the degree of aerobic, aquatic biodegradation of a lubricant or lubricant component. The rate and extent of oxygen consumption is measured upon exposure of the test material to an inoculum within the confines of a controlled laboratory setting. Test materials which achieve a high degree of biodegradation in this test may be assumed to easily biodegrade in many aerobic aquatic environments.

5.2 Because of the stringency of this test method, low results do not necessarily mean that the test material is not biodegradable under environmental conditions, but indicate that further testing is necessary to establish biodegradability.

5.3 If the pH value at the end of the test is outside the range from 6 to 8 and if the percentage degradation of the test material is less than 50 %, it is advisable to repeat the test with a lower concentration of the test material or a higher concentration of the buffer solution, or both.

5.4 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 must be regarded as invalid and shall be repeated using a fresh inoculum if the reference material does not demonstrate biodegradation to the extent of >60 % of the ThO₂ within 28 days.

5.5 Information on the toxicity of the test material to the inoculum may be useful in the interpretation of low biodegradation results. Toxicity of the test material to the inoculum may be evaluated by testing the test material in combination with the reference material in inhibition control systems. If an inhibition control is included, the test material is assumed to be inhibiting if the degradation percentage of the reference material is lower than 40 % (ISO 8192). In this case, it is advisable to repeat the test with lower concentrations of the test material.

5.6 Total oxygen utilization in the blank at the end of the test exceeding 60 mg O₂/L invalidates the test.

5.7 The water solubility or dispersibility of the lubricant or component may influence the results obtained and hence comparison of test results may be limited to lubricants or components with similar solubilities.

5.8 The behaviors of complex mixtures are not always consistent with the individual properties of the components. Test results for individual lubricant components may be suggestive of whether a mixture containing these components (that is, fully formulated lubricants) is biodegradable, but such information should be used judiciously.

1.1 This test method covers a procedure for determining the degree of biodegradability of lubricants or their components in an aerobic aqueous medium on exposure to an inoculum under controlled laboratory conditions. This test method is an ultimate biodegradation test that measures oxygen demand in a closed respirometer.

1.2 This test method is suitable for evaluating the biodegradation of volatile as well as nonvolatile lubricants or lubricant components.

1.3 This test method is applicable to lubricants and lubricant components which are not toxic and not inhibitory to the test microorganisms at the test concentration.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.