OECD 306 Seawater Biodegradability Test

The “OECD 306 Seawater biodegradability test” standard, published under the OECD guidelines on responsible business conduct for multinational enterprises (OECD guidelines), describes two methods for biodegradability in seawater:

• The shake flask method is used to dissolve a predetermined amount of the test substance in the test medium at 5-40 mg/l. organic carbon It consists of dissolving the test substance to obtain the concentration. A minimum of five vials should be used in these tests. Two for the test suspension, two for the blank and one for the procedural control. The solution of the test substance in the test medium is incubated at a constant temperature, normally in the range of 15-20 degrees, in the dark or under aerobic conditions with scattered light under shaking. The maximum recommended test period is approximately 60 days. Degradation is followed by measurements of dissolved organic carbon (final degradation) and in some cases by specific analysis (primary degradation).
• The closed bottle method consists of dissolving a predetermined amount of the test substance, usually at a concentration of 2-10 mg/l (one or more concentrations may be used), in the test medium. The solution is kept in a closed bottle filled in the dark in a constant temperature bath or enclosure controlled within the range of 15-20 degrees. Degradation is followed by oxygen analyses for a period of 28 days, but the test can be extended if the empty biological oxygen demand value remains within the 30 percent limit. A minimum of twenty-four bottles are used in these tests (8 bottles for the test substance, 8 bottles for the reference compound and 8 bottles for the sweater plus food). All analyses are carried out in duplicate bottles. At least four dissolved oxygen determinations (days 0, 5, 15 and 28) are carried out using a chemical or electrochemical method.

While many relevant OECD guidelines for aqueous aerobic biodegradability tests are for freshwater environments only, the OECD 306 standard was designed due to the increasing recognition of the need to protect the marine environment. Although the methods described are similar to the OECD 301 methods in terms of system setup and parameter analysis, OECD 306 is not a test for ready biodegradability as no inoculant is added in addition to microorganisms already present in seawater. Furthermore, the tests do not simulate the marine environment as nutrients (mineral media) are added and the concentration of the test substance is much higher than would be found in the sea.

In short, the shake bottle method allows a maximum of 60 days, while the closed bottle method recommends a maximum of 28 days. The shake bottle method measures the removal of dissolved organic carbon during aerobic biodegradation in a shake bottle setup. Percentage of degradation is calculated as the ratio of the dissolved organic carbon removal to the initial dissolved organic carbon dosed into the test medium. A 70 percent dissolved organic carbon removal indicates that the sample has the potential to biodegrade in the marine environment.

The closed bottle method measures the consumption of dissolved oxygen during aerobic biodegradation in a closed bottle setup with no headspace. Percent degradation is calculated as the ratio of dissolved carbon consumption to theoretical oxygen demand. If the ratio of theoretical oxygen demand to carbon is not obtained, the chemical oxygen demand can be determined experimentally and used as a less satisfactory alternative. A 60 percent dissolved oxygen consumption indicates that the sample has the potential to biodegrade in the marine environment.

The shake flask method can test samples that are highly soluble, non-volatile, and non-adsorbing. The closed flask method allows testing of samples that are highly soluble, volatile, and adsorbing.

Biodegradation is an important but poorly understood process that can result in the loss or transformation of a chemical in the environment. Prediction of biodegradation is critical in determining the persistence of chemicals in biota, including humans, their ultimate environmental concentrations, potential exposure, and ultimately the risk of long-term adverse effects. A number of international standard biodegradation screening tests and simulation tests, including ready-made biodegradation tests (OECD 301 and 310), marine biodegradation tests (OECD 306), and natural biodegradation tests (OECD 302), have been developed and validated by the Organisation for Economic Co-operation and Development (OECD) to measure the relative biodegradability of substances.

Biodegradability screening tests are among the more conservative regulatory tests that have historically formed the basis for measuring the biodegradability of chemicals in regulatory frameworks for hazard and environmental risk assessments.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "OECD 306 Seawater biodegradability test" standard are also provided to businesses.