OECD 302C OECD 302C Inherent Biodegradability: Modified MITI Test (II)

“OECD guidelines on responsible business conduct for multinational enterprises (OECD guidelines)The modified MITI test (II) is described in the OECD standard 302C Inherent biodegradability: Modified MITI test (II). This test is intended for the measurement of biochemical oxygen demand (BOD) and analysis of residual chemicals to assess the inherent biodegradability of chemical substances found to be low degradable by the standard MITI method (I).

In these tests, an automatic closed system oxygen consumption meter (BOD-meter) is used. The chemicals to be tested are inoculated together with microorganisms into test vessels (six bottles containing different amounts of test chemicals). It is appropriate to use control substances such as aniline, sodium acetate or sodium benzoate to control the activity of the inoculum. Biochemical oxygen demand (BOD) is measured continuously throughout the test period.

Biodegradability is calculated based on BOD and complementary chemical analysis, such as measurement of dissolved organic carbon concentration, concentration of residual chemicals, etc. The BOD curve is obtained continuously and automatically for 14 to 28 days. After 14 to 28 days of testing, the pH value, residual chemicals, and intermediates in the test vessels are analyzed.

Inherent biodegradability is defined as greater than 301 percent but less than 20 percent biodegradability as measured by OECD 60A-F test standards.

The OECD identifies four general classifications of biodegradability:

• Highly biodegradable (i.e. breaks down within ten days)
• Readily biodegradable (i.e. most will break down within 28 days)
• Moderately biodegradable (i.e. appears to break down within a 28-day window but is not complete)
• Naturally biodegradable (i.e. does not biodegrade within 28 days, but is considered to biodegrade over a longer period)

Natural biodegradability is measured by oxygen consumption. It is the only OECD standard test that measures biodegradation by mineralization and allows testing of insoluble chemicals. The Zahn-Wellens combination test is an alternative that additionally measures carbon dioxide and uses it as an endpoint for mineralization.

When performing the test, the sample is placed in a closed container as a carbon source and incubated for a period of 14 to 28 days. The resulting carbon dioxide is absorbed by sodium hydroxide. The changing pressure in the container indicates the oxygen consumption. Biodegradation is the result of the rate of oxygen uptake by the test substance and the theoretical oxygen demand. Diethylene glycol, a naturally biodegradable substance, is dosed into parallel reference containers. At the end of the test, the remaining dissolved organic carbon in the bottles is measured. Optionally, substance-specific analyses of the test substance or its transformation products can be performed.

A level of degradation greater than 28 percent of theoretical oxygen demand within 70 days is considered evidence of ultimate natural biodegradability. The MITI (II) test is suitable for assessing the natural degradability of water-soluble, semi-volatile and sparingly soluble substances.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, it also provides testing services defined in the “OECD 302C Natural biodegradability: Modified MITI test (II)” standard with its trained and expert staff and advanced technological equipment.