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A study of Clemente et al (2004) indicated that naphtenic acids are readily biodegradable.

Additional information

Because naphthenic acid is a mixture of many different isomers of cycloalkyl carboxylic acids the rate of biodegradation strongly varies depending upon the composition of the complex mixture. Available data on both model and commercially available naphthenic acids however show that biodegradation occurs. Furthermore the data suggest that the microbial degradation is the predominant factor in the reduction of aquatic acute toxicity of naphthenic acids. A number of relevant scientific journal articles show that naphthenic acid is inherently biodegradable. QSAR results for the acidic fraction support the ready (for some components) and inherent biodegradation that was shown in these biodegradation studies. The hydrocarbon fraction (non-acidic) can be characterized as a kerosene or diesel, which have a very similar composition. Read across from kerosene to diesel seems therefore appropriate (Concawe, 2010*). Based on compositional information available and measured or predicted data on key constituents, kerosenes are not expected to meet the criteria for ready degradability but are inherently biodegradable (Concawe, 2010). Hence the non-acidic fraction of naphthenic acids can be considered to be inherently biodegradable.

* CONCAWE. Hazard classification and labelling of petroleum substances in the European Economic Area – 2010