Test No. 306: Biodegradability in Seawater
The OECD 306 Guideline describes two methods for assessing the biodegradability of organic materials in seawater:
Importance of Seawater Biodegradability Testing:
Understanding how chemicals break down in marine environments is crucial for protecting the health of our oceans and the organisms that live there. This test helps predict the fate and potential impact of chemicals released into seawater, such as:
- Industrial wastewaters
- Pesticides and herbicides
- Personal care products
- Oil spills
Test Methods
- Shake Flask Method:
- The test substance is dissolved in seawater and added to flasks containing microorganisms naturally present in seawater.
- The flasks are incubated at a constant temperature for 28 days, with shaking to ensure oxygen availability.
- The biodegradation is measured by monitoring the dissolved organic carbon (DOC) removal or oxygen consumption over time.
- Closed Bottle Method:
- The test substance is similarly added to seawater in sealed bottles containing microorganisms.
- The bottles are incubated at a constant temperature in the dark for 28 days.
- Biodegradation is measured by analyzing the oxygen consumption within the closed system.
Evaluation:
Based on the test results, the biodegradability of the test substance in seawater is classified as:
- Readily biodegradable: If 60% or more of the DOC is removed or oxygen is consumed within 28 days.
- Ultimately biodegradable: If the DOC removal or oxygen consumption reaches 70% within an extended period (up to 60 days).
- Not readily biodegradable: If the biodegradation criteria are not met within the test period.
Benefits of OECD 306:
- Standardized protocol: Ensures consistent and reliable results.
- Environmentally relevant: Uses natural seawater and microorganisms, providing realistic data for marine environments.
- Flexible: Can be adapted for different types of test substances and study objectives.
Limitations:
Time-consuming, typically requiring 28 days or more.
- May not account for all environmental factors influencing biodegradation in real-world scenarios.
- Requires specialized equipment and expertise.
- May not be suitable for all types of chemicals, especially volatile or poorly water-soluble substances.
- Does not provide information on the specific biodegradation pathways or the organisms involved.
- Cannot predict the long-term fate and effects of chemicals in complex marine environments.
Overall, OECD 306 is a valuable tool for assessing the biodegradability of chemicals in seawater and informing environmental risk assessments and regulations. Understanding how quickly and easily substances break down in marine environments is critical for protecting the health and sustainability of our oceans.
