SETAC Presentation: An Inherent Biodegradation Test using a modified OECD 301B Ready Biodegradation
SETAC Presentation: An Inherent Biodegradation Test using a modified OECD 301B Ready Biodegradation Test Design Presenting Additional Extended Results
The OECD Ready Biodegradation and the Inherent Biodegradation Test Methods have provided years of guidance for assessing the persistence of organic chemicals. If a test substance exposed to a dilute inoculum generally comprised of activated sludge achieves 60% biodegradation equivalent to 60% of its organic carbon being converted to CO2 within a 10-day window (once reaching 10% CO2 evolution) during the 28-day test, the test substance can be labeled ‘readily biodegradable’. If the test substance does not pass this criteria, it can then still be tested for persistence using Inherent Biodegradability Tests described in the OECD 302 Series. However, for chemicals that are insoluble, many of the current 302 test methods provide limited testing options when trying to evaluate mineralization of the test chemical to CO2.
An OECD 301B test design was conducted with one of the standard reference substances, sodium benzoate which demonstrated that the optimum amount of the activated sludge inoculum was 100 mg/L (based on dry weight). This sludge concentration was determined to be the maximum amount of local sludge that could be used in a test system designed to monitor CO2 evolution from the biodegradation of the test chemical while keeping endogenous CO2 from the blank inoculum to a minimum in order to calculate the percent biodegradation of the test chemical. The results demonstrate that the method is appropriate at concentrations of sludge up to 3 times higher than what is allowed in the Ready Biodegradation Tests. For this presentation, additional test compounds namely cellulose and metformin were selected to implement the method and new data beyond day 28 is presented to show improved biodegradation in the solutions with an inoculum concentration of 100 mg/L dry sludge solids versus the standard OECD 301B test inoculum of 30 mg/L dry sludge solids.
Sean McLaughlin will present the research at the SETAC North America 42nd Annual Meeting, November 14-18, 2021.