title: Carbon dioxide recovery in ready biodegradation tests: mass transfer and kinetic considerations.
abstract: The kinetics and efficiency of carbon dioxide recovery in modern versions of the Sturm Ready Biodegradation Test were examined to determine the ability of CO2 evolution measurements to accurately estimate the rate and extent of ultimate biodegradation (mineralization). Kinetic data were analyzed by nonlinear regression techniques using an automated curve-fitting package available from commercial sources. The kinetics of CO2 recovery in standard 3.8 L glass carboys containing 2 L of medium were rapid when headspace aeration (approximately 6 ml/min) and moderate agitation (140 rev/min) on a rotary platform shaker were used to ensure adequate aeration and mixing. The time (half-life) for 50% CO2 recovery in external base traps was 4-5 hours, and stoichiometric recoveries of CO2 equivalents added as bicarbonate were obtained within 24 hours. The kinetics of CO2 evolution during biodegradation of several test compounds were significantly slower than the kinetics of CO2 recovery, with half-lives between 65 and 191 hours. Our results indicate that mass transfer limitations do not impact CO2 recoveries or biodegradation kinetic measurements in modern versions of the Sturm Test, even in test vessels with relatively low surface area to volume ratios (1:1). The use of headspace aeration and mixing generates reliable kinetic data, which can be analyzed by commercially-available nonlinear regression packages to provide rate information for the classification of chemicals with different biodegradation profiles.
authors.affiliation: Environmental Science Department, Procter & Gamble Company, Ivorydale Technical Center, Cincinnati, Ohio 45217-1087, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Larson
authors.forename: M A
authors.initials: MA
authors.lastname: Hansmann
authors.forename: E A
authors.initials: EA
authors.lastname: Bookland
mesh_terms: D001673:Biodegradation, Environmental; D002245:Carbon Dioxide / Q000378:metabolism*; D004785:Environmental Pollutants / Q000378:metabolism; D006207:Half-Life; D006838:Hydrocarbons / Q000378:metabolism*; D007700:Kinetics; D012044:Regression Analysis; D013223:Statistics as Topic
chemical_list: D004785:Environmental Pollutants; D006838:Hydrocarbons; D002245:Carbon Dioxide