Test No. 209: Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation)
The OECD 209 test, also known as the Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation), is a standardized laboratory procedure used to assess the potential negative effects of a substance on the microorganisms in activated sludge from wastewater treatment plants.
Activated sludge in a wastewater treatment plant.
The test measures the respiration rate of the microorganisms, which is an indicator of their metabolic activity. A decrease in respiration rate indicates that the substance is inhibiting the microorganisms and could potentially interfere with the effectiveness of the wastewater treatment process.
The OECD 209 test is a relatively simple and inexpensive test that can be used to screen a wide range of substances for potential toxicity to wastewater treatment microorganisms. It is also a flexible test that can be modified to meet the specific needs of a particular study.
Interpreting the Results: From Data to Decisions
Water testing alone isn’t enough. The key lies in deciphering the data and acting upon it. Water quality standards established by organizations like the EPA or WHO set acceptable levels for various contaminants. Comparing test results to these standards helps determine if the water is safe for drinking, recreation, or other intended uses.
Here are some of the key features of the OECD 209 test:
- It is a short-term test, typically lasting for 3 hours.
- It is conducted at a neutral pH (7.0-7.5) and a temperature of 20°C.
- It uses a mixed culture of microorganisms from activated sludge.
- The test substance is added to the activated sludge at a range of concentrations.
- The oxygen consumption of the microorganisms is measured over time.
- The results of the test are expressed as the ECx value, which is the concentration of the test substance that causes a 50% reduction in oxygen consumption.
The results of the test can also be expressed as the NOEC (no observed effect concentration), which is the highest concentration of the test substance that does not cause a statistically significant reduction in oxygen consumption.
